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Honeywell AUTOMATIC CONTROL Engineering Manual

For commercial buildings
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Table of Contents
ENGINEERING MANUAL OF AUTOMATIC CONTROL
E
NGINEERING
AUTOMATIC
CONTROL
C
OMMERCIAL
i
HONEYWELL
M
ANUAL of
for
B
UILDINGS

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  Summary of Contents for Honeywell AUTOMATIC CONTROL

  • Page 1 HONEYWELL NGINEERING ANUAL of AUTOMATIC CONTROL OMMERCIAL UILDINGS ENGINEERING MANUAL OF AUTOMATIC CONTROL...
  • Page 2 Copyright 1934, 1940, 1953, 1988, 1991 and 1997 by Honeywell Inc. All rights reserved. This manual or portions thereof may not be reporduced in any form without permission of Honeywell Inc. Library of Congress Catalog Card Number: 97-72971 Home and Building Control Home and Building Control Honeywell Asia Pacific Inc.
  • Page 3 Chiller, Boiler, and Distribution System Control Applications Section. This twenty-first edition of the Engineering Manual of Automatic Control is our contribution to ensure that we continue to satisfy our customer’s requirements. The contributions and encouragement received from previous users are gratefully acknowledged.
  • Page 4 ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 5: Preface

    PREFACE The purpose of this manual is to provide the reader with a fundamental understanding of controls and how they are applied to the many parts of heating, ventilating, and air conditioning systems in commercial buildings. Many aspects of control are presented including air handling units, terminal units, chillers, boilers, building airflow, water and steam distribution systems, smoke management, and indoor air quality.
  • Page 6 ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 7: Table Of Contents

    NGINEERING ANUAL of AUTOMATIC CONTROL CONTENTS Foreward ................................Preface ................................Control System Fundamentals .................... Control Fundamentals ............................Introduction ..................Definitions .................... HVAC System Characteristics ............. Control System Characteristics ............Control System Components .............. Characteristics And Attributes Of Control Methods ......Psychrometric Chart Fundamentals ........................
  • Page 8 Electronic Control Fundamentals ........................119 Introduction ..................120 Definitions .................... 120 Typical System ..................122 Components ..................122 Electtonic Controller Fundamentals ............ 129 Typical System Application ..............130 Microprocessor-Based/DDC Fundamentals ....................131 Introduction ..................133 Definitions .................... 133 Background ..................134 Advantages ..................
  • Page 9 Control System Applications ....................Air Handling System Control Applications ...................... 201 Introduction ..................203 Abbreviations ..................203 Requirements For Effective Control ............ 204 Applications-General ................206 Valve and Damper Selection ............... 207 Symbols ....................208 Ventilation Control Processes ............. 209 Fixed Quantity of Outdoor Air Control ..........
  • Page 10 Engineering Information ....................... Valve Selection and Sizing ..........................431 Introduction ..................432 Definitions .................... 432 Valve Selection ..................436 Valve Sizing ..................441 Damper Selection and Sizing ..........................451 Introduction ..................453 Definitions .................... 453 Damper Selection ................454 Damper Sizing ..................463 Damper Pressure Drop ...............

  • Page 11: Control System Fundamentals

    CONTROL FUNDAMENTALS CONTROL SYSTEMS FUNDMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 13: Control Fundamentals

    Control Fundamentals Contents Introduction ......................Definitions ......................HVAC System Characteristics ......................General ....................Heating ....................General ....................Heating Equipment ................Cooling ....................General ....................Cooling Equipment ................Dehumidification .................. Humidification ..................Ventilation .................... Filtration ....................Control System Characteristics ......................Controlled Variables ................Control Loop ..................
  • Page 14 CONTROL FUNDAMENTALS Load ....................Lag ....................General ................... Measurement Lag ................Capacitance ..................Resistance ..................Dead Time ..................Control Application Guidelines ............Control System Components ......................Sensing Elements ................Temperature Sensing Elements ............Pressure Sensing Elements ............Moisture Sensing Elements ............Flow Sensors ..................

  • Page 15: Introduction

    Controlled Variable: The quantity or condition that is measured and controlled. Automatic control system: A system that reacts to a change or imbalance in the variable it controls by adjusting Controller: A device that senses changes in the controlled...
  • Page 16 Manipulated variable: The quantity or condition regulated DDC: Direct Digital Control. See also Digital and Digital by the automatic control system to cause the desired control. change in the controlled variable. Digital: A series of on and off pulses arranged to convey Measured variable: A variable that is measured and may be information.
  • Page 17 CONTROL FUNDAMENTALS Step control: Control method in which a multiple-switch Proportional control: A control algorithm or method in which assembly sequentially switches equipment (e.g., the final control element moves to a position electric heat, multiple chillers) as the controller input proportional to the deviation of the value of the varies through the proportional band.

  • Page 18: Hvac System Characteristics

    CONTROL FUNDAMENTALS HVAC SYSTEM CHARACTERISTICS Figure 2 shows how an HVAC system may be distributed in GENERAL a small commercial building. The system control panel, boilers, motors, pumps, and chillers are often located on the lower level. An HVAC system is designed according to capacity The cooling tower is typically located on the roof.

  • Page 19: Heating

    CONTROL FUNDAMENTALS Table 1. Functions of Central HVAC Control Loops. Control Loop Classification Description Ventilation Basic Coordinates operation of the outdoor, return, and exhaust air dampers to maintain the proper amount of ventilation air. Low-temperature protection is often required. Better Measures and controls the volume of outdoor air to provide the proper mix of outdoor and return air under varying indoor conditions (essential in variable air volume systems).

  • Page 20: Heating Equipment

    CONTROL FUNDAMENTALS Infiltration is the process by which outdoor air enters a STEAM OR HOT WATER building through walls, cracks around doors and windows, and SUPPLY open doors due to the difference between indoor and outdoor air pressures. The pressure differential is the result of temperature difference and air intake or exhaust caused by fan operation.

  • Page 21: Cooling

    CONTROL FUNDAMENTALS FINNED TUBE in the warm exhaust air, and the vapor rises toward the higher end in the cool outdoor air, where it gives up the heat of WARM AIR vaporization and condenses. A wick carries the liquid refrigerant back to the warm end, where the cycle repeats. A RETURN AIR heat pipe requires no energy input.

  • Page 22: Cooling Equipment

    CONTROL FUNDAMENTALS COOLING EQUIPMENT Compressors for chilled water systems are usually centrifugal, reciprocating, or screw type. The capacities of centrifugal and screw-type compressors can be controlled by An air handling system cools by moving air across a coil varying the volume of refrigerant or controlling the compressor containing a cooling medium (e.g., chilled water or a speed.

  • Page 23: Humidification

    CONTROL FUNDAMENTALS HUMID VENTILATION HUMID AIR ROTATING EXHAUST GRANULAR Ventilation introduces outdoor air to replenish the oxygen supply and rid building spaces of odors and toxic gases. Ventilation can also be used to pressurize a building to reduce infiltration. While ventilation is required in nearly all buildings, HEATING COIL the design of a ventilation system must consider the cost of...

  • Page 24: Filtration

    CONTROL FUNDAMENTALS losses. The exhaust-air system may be incorporated into the air conditioning unit, or it may be a separate remote exhaust. Supply air is heated or cooled, humidified or dehumidified, and discharged into the space. DAMPER RETURN FAN EXHAUST RETURN FILTER COIL...

  • Page 25: Control System Characteristics

    A control loop consists air in a duct determining the flow of hot water to the heating of an input sensing element, such as a temperature sensor;...

  • Page 26: Control Methods

    If the sampling interval for the digital controller is chosen properly, An automatic control system is classified by the type of discrete output changes provide even and uninterrupted control energy transmission and the type of control signal (analog or performance.

  • Page 27: Control Modes

    CONTROL FUNDAMENTALS An example of differential gap would be in a cooling system ANALOG CONTROL SIGNAL in which the controller is set to open a cooling valve when the OPEN space temperature reaches 78F, and to close the valve when the temperature drops to 76F.

  • Page 28: Timed Two-Position Control

    CONTROL FUNDAMENTALS Figure 22 shows a sample control loop for basic two-position BASIC TWO-POSITION CONTROL control: a thermostat turning a furnace burner on or off in OVERSHOOT CONDITION response to space temperature. Because the thermostat cannot catch up with fluctuations in temperature, overshoot and TEMPERATURE (°F) undershoot enable the temperature to vary, sometimes...

  • Page 29: Step Control

    CONTROL FUNDAMENTALS 73-1/4 TIME PROPORTIONING Time proportioning control provides more effective two- 1-1/4 position control than heat anticipation control and is available with some electromechanical thermostats and in electronic and microprocessor-based controllers. Heat is introduced into the 70-3/4 2-1/2 space using on/off cycles based on the actual heat load on the building and programmable time cycle settings.

  • Page 30: Floating Control

    CONTROL FUNDAMENTALS zero, and the sequence repeats until all stages required to meet THROTTLING RANGE the load condition are on. On a decrease in load, the process reverses. DIFFERENTIAL With microprocessor controls, step control is usually done with multiple, digital, on-off outputs since software allows easily adjustable on-to-off per stage and interstage differentials STAGES as well as no-load and time delayed startup and minimum on...

  • Page 31: Proportional Control

    CONTROL FUNDAMENTALS “CLOSE” SWITCH DIFFERENTIAL SETPOINT DEADBAND CONTROLLER “OPEN” SWITCH CONTROL POINT DIFFERENTIAL FULL LOAD LOAD NO LOAD OPEN DAMPER POSITION CLOSED C2094 TIME Fig. 30. Floating Control. In proportional control, the final control element moves to a PROPORTIONAL CONTROL position proportional to the deviation of the value of the controlled variable from the setpoint.

  • Page 32: Compensation Control

    CONTROL FUNDAMENTALS An example of offset would be the proportional control of a Where: chilled water coil used to cool a space. When the cooling load V = output signal is 50 percent, the controller is in the middle of its throttling K = proportionality constant (gain) range, the properly sized coil valve is half-open, and there is E = deviation (control point - setpoint)

  • Page 33: Proportional-Integral (Pi) Control

    CONTROL FUNDAMENTALS OUTDOOR AIR TEMPERATURE TEMPERATURE CONTROLLER In an application requiring negative reset, a change in outdoor SENSOR air temperature at the reset sensor from 0 to 60F resets the hot water supply temperature (primary sensor) setpoint from 200 to 100F. Assuming a throttling range of 15 degrees F, the RETURN required authority is calculated as follows: SENSOR...
  • Page 34 CONTROL FUNDAMENTALS The reset action of the integral component shifts the Reset error correction time is proportional to the deviation proportional band as necessary around the setpoint as the load of the controlled variable. For example, a four-percent deviation on the system changes. The graph in Figure 36 shows the shift from the setpoint causes a continuous shift of the proportional of the proportional band of a PI controller controlling a band at twice the rate of shift for a two-percent deviation.

  • Page 35: Proportional-Integral-Derivative (Pid) Control

    CONTROL FUNDAMENTALS PROPORTIONAL-INTEGRAL-DERIVATIVE (PID) The graphs in Figures 38, 39, and 40 show the effects of all CONTROL three modes on the controlled variable at system start-up. With proportional control (Fig. 38), the output is a function of the deviation of the controlled variable from the setpoint. As the Proportional-integral-derivative (PID) control adds the control point stabilizes, offset occurs.

  • Page 36: Adaptive Control

    CONTROL FUNDAMENTALS Adaptive control is also used in energy management The start value EPID setpoint sets the output to a fixed value programs such as optimum start. The optimum start program at startup. For a VAV air handling system supply fan, a suitable enables an HVAC system to start as late as possible in the value might be twenty percent, a value high enough to get the morning and still reach the comfort range by the time the...

  • Page 37: Lag

    CONTROL FUNDAMENTALS CONTROLLER COLD FLOW (MANIPULATED WATER VARIABLE) TEMPERATURE VALVE (CONTROLLED HEAT LOSS VARIABLE) STEAM (CONTROL AGENT) HOT WATER SUPPLY SPACE (CONTROLLED MEDIUM) LOAD HOT WATER RETURN THERMOSTAT CONVERTER CONDENSATE RETURN VALVE STEAM TRAP C2073 C2074 Fig. 42. Steam-to-Water Converter. Fig.

  • Page 38: Capacitance

    CONTROL FUNDAMENTALS The difference between repeatability and static error is that Figure 45 shows a high-velocity heat exchanger, which repeatability is the ability to return to a specific condition, represents a process with a small thermal capacitance. The whereas static error is a constant deviation from that condition. rate of flow for the liquid in Figure 45 is the same as for the liquid in Figure 44.

  • Page 39: Resistance

    CONTROL FUNDAMENTALS In terms of heating and air conditioning, a large office area DEAD TIME containing desks, file cabinets, and office machinery has more capacitance than the same area without furnishings. When the Dead time, which is also called “transportation lag”, is the temperature is lowered in an office area over a weekend, the delay between two related actions in a continuous process furniture loses heat.

  • Page 40: Control System Components

    CONTROL FUNDAMENTALS mode that is too complicated for the application may result in Each control mode is applicable to processes having certain combinations of the basic characteristics. The simplest mode poor rather than good control. Conversely, using a control of control that meets application requirements is the best mode mode that is too basic for requirements can make adequate to use, both for economy and for best results.

  • Page 41: Pressure Sensing Elements

    CONTROL FUNDAMENTALS The temperature sensor for an electronic controller may be a length of wire or a thin metallic film (called a resistance FLAPPER temperature device or RTD) or a thermistor. Both types of SPRING resistance elements change electrical resistance as temperature SIGNAL PORT changes.

  • Page 42: Moisture Sensing Elements

    CONTROL FUNDAMENTALS MOISTURE SENSING ELEMENTS FLOW SENSORS Elements that sense relative humidity fall generally into two Flow sensors sense the rate of liquid and gas flow in volume classes: mechanical and electronic. Mechanical elements per unit of time. Flow is difficult to sense accurately under all expand and contract as the moisture level changes and are conditions.

  • Page 43: Proof-Of-Operation Sensors

    CONTROL FUNDAMENTALS The impact of the jet on a collector tube a short distance away causes a positive pressure in the collector. An increase in Controllers may be electric/electronic, microprocessor, or velocity of the air stream perpendicular to the jet deflects the pneumatic.

  • Page 44: Auxiliary Equipment

    CONTROL FUNDAMENTALS Electric actuators are inherently positive positioning. Some ACTUATOR pneumatic control applications require accurate positioning CHAMBER DIAPHRAGM of the valve or damper. For pneumatic actuators, a positive positioning relay is connected to the actuator and ensures that the actuator position is proportional to the control signal. The positive positioning relay receives the controller output signal, PRESSURE reads the actuator position, and repositions the actuator...

  • Page 45: Characteristics And Attributes Of Control Methods

    CONTROL FUNDAMENTALS CHARACTERISTICS AND ATTRIBUTES OF CONTROL METHODS Review the columns of Table 4 to determine the characteristics and attributes of pneumatic, electric, electronic, and microprocessor control methods. Table 4. Characteristics and Attributes of Control Methods. Pneumatic Electric Electronic Microprocessor Naturally Most common for Precise control...
  • Page 46 CONTROL FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 47: Psychrometric Chart Fundamentals

    PSYCHROMETRIC CHART FUNDAMENTALS Psychrometric Chart Fundamentals Contents Introduction ......................Definitions ......................Description of the Psychrometric Chart ......................The Abridged Psychrometric Chart ......................Examples of Air Mixing Process ......................Air Conditioning Processes ......................Heating Process .................. Cooling Process .................. Humidifying Process ......................

  • Page 48: Introduction

    PSYCHROMETRIC CHART FUNDAMENTALS INTRODUCTION changes in relation to the performance of automatic HVAC This section provides information on use of the psychrometric chart as applied to air conditioning processes. The chart provides control systems. The chart is also useful in troubleshooting a a graphic representation of the properties of moist air including system.

  • Page 49: Description Of The Psychrometric Chart

    PSYCHROMETRIC CHART FUNDAMENTALS HANDLE WET-BULB THERMOMETER WATER-SOAKED WICK PIVOT DRY-BULB THERMOMETER RELATIVE HUMIDITY SCALE C1828 Fig. 1. Sling Psychrometer. Although commonly used, sling psychrometers can Wet-bulb temperature: The temperature read on a thermom- cause inaccurate readings, especially at low relative eter with the sensing element encased in a wet wick humidities, because of factors such as inadequate air (stocking or sock) and with an air flow of 900 feet...

  • Page 50: The Abridged Psychrometric Chart

    PSYCHROMETRIC CHART FUNDAMENTALS THE ABRIDGED PSYCHROMETRIC CHART Figure 2 is an abridged form of Chart No. 1. Some of the The chart also contains a protractor nomograph with the scale lines have been removed to simplify illustrations of the following scales: psychrometric processes.
  • Page 51 PSYCHROMETRIC CHART FUNDAMENTALS heat) line. The protractor nomograph, in the upper left corner, is used to establish the slope of a process line. The mechanics of constructing this line are discussed in more detail in the 60% RH 31.6 BTU/LB STEAM JET HUMIDIFIERS section.

  • Page 52: Examples Of Air Mixing Process

    PSYCHROMETRIC CHART FUNDAMENTALS EXAMPLES OF AIR MIXING PROCESS The following examples illustrate use of the psychrometric covers the –40 to 50F temperature range. This is the temperature chart to plot values and determine conditions in a ventilating range immediately below that of Chart No. 1. Note that there is system.

  • Page 53: Air Conditioning Processes

    PSYCHROMETRIC CHART FUNDAMENTALS 4. Calculate the mixed air moisture content as follows: a. For the return air, project a line from Point A hori- zontally to the moisture content scale on Figure 9. The value is 0.0094 pounds of moisture per pound 28.2 BTU/LB of dry air.

  • Page 54: Humidifying Process

    PSYCHROMETRIC CHART FUNDAMENTALS 1. Draw diagonal lines parallel to the constant enthalpy lines COOLING COIL SUPPLY FAN from Points A and B to the enthalpy scale. 90°F DB 70°F DB 50% RH 95% RH 2. Read the enthalpy on the enthalpy scale. AIRFLOW 3.
  • Page 55 PSYCHROMETRIC CHART FUNDAMENTALS SUPPLY FAN HEATING COIL 10,000 CFM 0°F DB 70°F DB 70°F DB 75% RH 35% RH 4.5% RH 0.0006 LB/LB FROM CHART 2 70°F DB 35% RH C1838 4.5% RH 0.0056 LB/LB Fig. 14. Chart No. 1. 4.5% RH 0.0006 LB/LB FROM CHART 2...
  • Page 56 PSYCHROMETRIC CHART FUNDAMENTALS The air at Points A and B has 0.004 pounds of moisture per If each pound of dry air requires 0.005 pounds of moisture, pound of air. While the moisture content remains the same after then the following moisture must be added: the air is heated to 75F (Point B), the relative humidity drops 736 x 0.005 = 3.68 pounds of moisture per minute from 52 percent to 21 percent.
  • Page 57 PSYCHROMETRIC CHART FUNDAMENTALS REFERENCE POINT THIS LINE IS PARALLEL TO THE SOLID 50% RH 1150 LINE C-B ON THE PSYCH CHART 0.0164 LB/LB 0.0065 LB/LB 55°F DB 92°F DB 90°F DB C1841 CONSTRUCTION LINE Fig. 17. ENGINEERING MANUAL OF AUTOMATIC CONTROL...
  • Page 58 PSYCHROMETRIC CHART FUNDAMENTALS Figure 18 is the same as the chart shown in Figure 17 except The remaining 0.9 Btu is sensible heat. The actual moisture that it graphically displays the amount of heat added by the added per pound of dry air is 0.0099 pounds. The specific process.
  • Page 59 PSYCHROMETRIC CHART FUNDAMENTALS This converts to: 0.848 x 60 minutes = 50.9 gallons per hour Recalling that the steam added 11.6 Btu per pound of dry air, the total heat added is: 714.3 x 11.6 = 8286 Btu per minute This converts to: CONSTANT ENTHALPY...

  • Page 60: Vaporizing Humidifier

    PSYCHROMETRIC CHART FUNDAMENTALS washer is always located on the saturation curve. Note that the dry-bulb temperature of the air is reduced as it passes through the washer. This happens because some of its heat is used to evaporate the water; however, the humidity of the air rises SATURATION CURVE considerably.

  • Page 61: Cooling And Dehumidification

    PSYCHROMETRIC CHART FUNDAMENTALS COOLING AND DEHUMIDIFICATION To remove moisture, some air must be cooled below its dew point. By determining the wet-bulb and the dry-bulb temperatures of the leaving air, the total moisture removed per BASIC PROCESS pound of dry air can be read on the humidity ratio scale and is determined as follows: Cooling and dehumidification can be accomplished in a single 1.

  • Page 62: Dehumidification And Reheat

    PSYCHROMETRIC CHART FUNDAMENTALS the wet-bulb temperature of the air as the process line extends. SUPPLY FAN Note that whenever the washer water temperature is between the dew point (Point B) and the dry-bulb (Point D) temperature 58°F DB 90°F DB 85% RH 52% RH of the air, moisture is added and the dry-bulb temperature of...

  • Page 63: Ashrae Psychrometric Chart

    PSYCHROMETRIC CHART FUNDAMENTALS — Enthalpy and humidity ratio, or moisture content, are COOLING HEATING SUPPLY FAN COIL COIL based on a pound of dry air. Zero moisture is the bottom 90°F DB 48°F DB 60°F DB line of the chart. 71.3°F WB 46°F WB 51.2°F WB...
  • Page 64 PSYCHROMETRIC CHART FUNDAMENTALS Fig. 33. ASHRAE Psychrometric Chart No. 1. ENGINEERING MANUAL OF AUTOMATIC CONTROL...
  • Page 65 PSYCHROMETRIC CHART FUNDAMENTALS Fig. 34. ASHRAE Psychrometric Chart No. 2. ENGINEERING MANUAL OF AUTOMATIC CONTROL...
  • Page 66 PSYCHROMETRIC CHART FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 67: Pneumatic Control Fundamentals

    PNEUMATIC CONTROL FUNDAMENTALS Pneumatic Control Fundamentals Contents Introduction ......................Definitions ......................Abbreviations ......................Symbols ......................Basic Pneumatic Control System ......................General ....................Air Supply and Operation ..............Restrictor ..................... Nozzle-Flapper Assembly ..............Pilot Bleed System ................Signal Amplifier ..................Feed and Bleed System ..............Sensing Elements ................
  • Page 68 PNEUMATIC CONTROL FUNDAMENTALS Controllers ......................General ....................Temperature Controllers ..............Humidity Controllers ................Pressure Controllers ................Sensor-Controller Systems ..............Pneumatic Controllers ................. Proportional-Integral (PI) Controllers ..........Controller Adjustments ..............Pneumatic Sensors ................Velocity Sensor-Controller ..............Actuators and Final Control Elements ......................

  • Page 69: Introduction

    PNEUMATIC CONTROL FUNDAMENTALS INTRODUCTION with relatively simple equipment. This section provides basic information on pneumatic control systems and components commonly used to control equipment — Pneumatic equipment is suitable where explosion in commercial heating and air conditioning applications. The hazards exist. information in this section is of a general nature in order to —...

  • Page 70: Abbreviations

    PNEUMATIC CONTROL FUNDAMENTALS Main line: The air line from the air supply system to controllers Reverse acting (RA): A reverse-acting thermostat or controller and other devices. Usually plastic or copper tubing. decreases the branchline pressure on an increase in the measured variable and increases the branchline Manipulated variable: Media or energy controlled to achieve pressure on a decrease in the variable.

  • Page 71: Symbols

    PNEUMATIC CONTROL FUNDAMENTALS SYMBOLS FIXED POINT MAIN AIR SUPPLY FULCRUM RESTRICTOR NOZZLE PIVOT POINT C1082 BASIC PNEUMATIC CONTROL SYSTEM In a typical control system, the final control element (a valve GENERAL or a damper) is selected first because it must produce the desired control results.

  • Page 72: Pilot Bleed System

    PNEUMATIC CONTROL FUNDAMENTALS From the PRV, the air flows through the main line to the To create a branchline pressure, a restrictor (Fig. 3) is controller (in Figure 1, a thermostat) and to other controllers required. The restrictor and nozzle are sized so that the nozzle or relays in other parts of the system.

  • Page 73: Signal Amplifier

    PNEUMATIC CONTROL FUNDAMENTALS the feed valve. If the pilot chamber diaphragm rises enough, it SETPOINT SENSING ADJUSTMENT lifts the bleed valve off the feed valve disc, allowing air to FORCE escape from the branch chamber through the vent, thus decreasing the branchline pressure. Main air is used only when branchline pressure must be increased and to supply the very small amount exhausted through the nozzle.

  • Page 74: Throttling Range Adjustment

    PNEUMATIC CONTROL FUNDAMENTALS A temperature controller consists of a bimetal element linked diaphragm chamber. The expansion causes the diaphragm pad to a flapper so that a change in temperature changes the position to push the pin toward the lever, which moves the flapper to of the flapper.

  • Page 75: Air Supply Equipment

    PNEUMATIC CONTROL FUNDAMENTALS construction (Fig. 10) and are used to amplify, reverse, average, The controlling pressure is connected at the pilot port (P), select, and switch controller outputs before being sent to valve and pressures to be switched are connected at the normally and damper actuators.

  • Page 76: Air Drying Techniques

    PNEUMATIC CONTROL FUNDAMENTALS alternately, so wear is spread over both machines, each capable is the temperature at which moisture starts to condense out of supplying the average requirements of the system without of the air. operating more than half the time. In the event of failure of one compressor, the other assumes the full load.
  • Page 77 PNEUMATIC CONTROL FUNDAMENTALS The heat exchanger reduces the temperature of the com- CONDENSING DRYING pressed air passing through it. A separator/filter condenses both water and oil from the air and ejects the condensate The two methods of condensing drying are high-pressure through a drain.

  • Page 78: Pressure Reducing Valve Station

    PNEUMATIC CONTROL FUNDAMENTALS PRESSURE REDUCING VALVE STATION DESICCANT CHAMBERS The pressure reducing valve station is typically furnished with an air filter. The filter, high-pressure gage, high pressure relief valve, pressure reducing valve (PRV), and low-pressure gage are usually located together at one point in the system and may be mounted directly on the compressor.

  • Page 79: Thermostats

    PNEUMATIC CONTROL FUNDAMENTALS in pressure drop across the filter (to approximately 10 psi) indicates that the filter element needs replacement. For very Two-Pressure Reducing Valve dirty air, a 5-micron prefilter filters out large particles and increases the life of the final filter element. A two-pressure reducing valve is typically set to pass 13 or 18 psi to the control system, as switched by a pilot pressure.

  • Page 80: Controllers

    PNEUMATIC CONTROL FUNDAMENTALS open. Heat enters the space until the temperature at the thermostat increases and the force of the bimetal is again in equilibrium with the opposing force of the pressure at the nozzle. Decreasing the setpoint causes the reverse to occur. The throttling range adjustment provides the means for changing the effective length of the cantilever bimetal in the lever system.

  • Page 81: Temperature Controllers

    PNEUMATIC CONTROL FUNDAMENTALS Controllers may also be classified as single-pressure or two- in respect to atmospheric pressure or another pressure source. pressure controllers. Single-pressure controllers use a constant The low-pressure controller is available in both bleed-type and main air pressure. Two-pressure controllers use a main air pilot-bleed designs.

  • Page 82: Sensor-Controller Systems

    PNEUMATIC CONTROL FUNDAMENTALS SENSOR-CONTROLLER SYSTEMS A sensor-controller system is made up of a pneumatic PRIMARY SENSOR controller, remote pneumatic sensors, and a final control MAIN AIR element. The controller provides proportional or proportional- (18 PSI) integral control of temperature, humidity, dew point, or pressure RESET SENSOR in HVAC systems.

  • Page 83: Pneumatic Sensors

    PNEUMATIC CONTROL FUNDAMENTALS Reset authority, also called “reset ratio”, is the ratio of the VELOCITY SENSOR-CONTROLLER effect of the reset sensor compared to the primary sensor. Figure 23 shows the effect of authority on a typical reset The velocity sensor-controller combines a highly sensitive schedule.

  • Page 84: Actuators And Final Control Elements

    PNEUMATIC CONTROL FUNDAMENTALS Figure 25 shows a typical application of a thermostat and velocity controller on a Variable Air Volume (VAV) terminal unit with hot water reheat. The thermostat senses a change in room temperature and resets the velocity setpoint of the velocity controller.

  • Page 85: Control Valves

    PNEUMATIC CONTROL FUNDAMENTALS provide a simple form of sequence control (e.g., operating The position maintained by the valve stem depends on the heating and cooling valves from a single thermostat). Typical balance of forces acting on it: spring pressure ranges are 2-7 psi, 8-12 psi, and 3-13 psi. —...

  • Page 86: Dampers

    PNEUMATIC CONTROL FUNDAMENTALS Two- and three-way butterfly valves can be operated by long BRANCH LINE stroke pneumatic actuators and appropriate linkage (Fig. 31). One or two low pressure actuators powered directly by branchline pressure can operate butterfly valves up to about 12 inches, depending on the differential close-off rating of the valve.

  • Page 87: Relays And Switches

    PNEUMATIC CONTROL FUNDAMENTALS Figure 33 shows normally open and normally closed paral- lel-blade dampers. A normally open damper returns to the open position with low air pressure in the actuator diaphragm chamber. An increase in branchline pressure forces the rolling BRANCH LINE BRANCH LINE diaphragm piston to move against the spring, and a decrease...

  • Page 88: Snap Acting Relay

    PNEUMATIC CONTROL FUNDAMENTALS ROOM DA OUTDOOR AIR THERMOSTAT THERMOSTAT DA ROOM THERMOSTAT DA WINTER RA SUMMER RESTRICTOR SWITCHING RELAY SNAP ACTING VAV TERMINAL UNIT RELAY DAMPER ACTUATOR N.O. HEATING C2360 VALVE LIMIT VALVE CONTROLLER Fig. 36. Typical Application for Snap Acting Relay. DISCHARGE LOCKOUT RELAY COIL...

  • Page 89: High-Pressure Selector Relay

    PNEUMATIC CONTROL FUNDAMENTALS HIGH-PRESSURE SELECTOR RELAY DA ZONE THERMOSTAT DA ZONE THERMOSTAT The high-pressure selector relay is a three-port relay that transmits the higher of two input signals to the output branch. The high sensitivity of the relay allows it to be used in sensor N.O.

  • Page 90: Capacity Relay

    PNEUMATIC CONTROL FUNDAMENTALS CAPACITY RELAY POSITIVE-POSITIONING RELAY The capacity relay is a direct-acting relay that isolates an The positive-positioning relay (Fig. 44) mounts directly on input and repeats the input pressure with a higher capacity a valve or damper actuator. The relay positions the valve or output.

  • Page 91: Ratio Relay

    PNEUMATIC CONTROL FUNDAMENTALS Figure 45 shows an averaging relay in a typical application PNEUMATIC POTENTIOMETER with two thermostat signals as inputs. The average of the thermostat signals controls a valve or damper actuator. The pneumatic potentiometer is a three-port, adjustable linear restrictor used in control systems to sum two input signal values, average two input pressures, or as an adjustable flow THERMOSTAT 2...

  • Page 92: Hesitation Relay

    PNEUMATIC CONTROL FUNDAMENTALS HESITATION RELAY ELECTRICAL INTERLOCKING RELAYS The hesitation relay is used with a pneumatic actuator in Electrical interlocking relays bridge electric and pneumatic unit ventilator applications. The output pressure goes to circuits. The electric-pneumatic relay uses electric power to minimum whenever the input pressure is below the minimum actuate an air valve in an associated pneumatic circuit.

  • Page 93: Electronic-Pneumatic Transducer

    PNEUMATIC CONTROL FUNDAMENTALS A resistance-type temperature sensor in the discharge air TEMPERATURE CONTROLLER duct is the input to the controller, which provides all of the system adjustments and logic requirements for control. The controller output of 2 to 10 volts dc is input to the electronic- pneumatic transducer, which converts the signal to a 3 to 15 psi output to position the heating valve.

  • Page 94: Pneumatic Control Combinations

    PNEUMATIC CONTROL FUNDAMENTALS Figure 56 shows the switch functioning as a minimum THERMOSTAT positioning switch. The damper will not close beyond the minimum setting of the positioning switch. As the controller signal increases above the switch setting, the switch positions the damper according to the controller signal.

  • Page 95: Sequence Control

    PNEUMATIC CONTROL FUNDAMENTALS — The controller must be located where the condition it valve is closed. As the temperature rises, the branchline measures is uniformly affected by changes in position pressure increases and the heating valve starts to close. At of the multiple valves.

  • Page 96: Manual Switch Control

    Common applications for a diverting switch include on/off/ pressure regardless of the demands of the room controller, thus automatic control for a heating or a cooling valve, open/closed opening the valve to prevent the discharge air temperature from control for a damper, and changeover control for a two-pressure dropping below the limit controller setpoint.

  • Page 97: Changeover Control For Two-Pressure Supply System

    PNEUMATIC CONTROL FUNDAMENTALS according to a preset schedule. The system then provides the CHANGEOVER CONTROL FOR TWO- scheduled water temperature to the convectors, fan-coil units, PRESSURE SUPPLY SYSTEM or other heat exchangers in the system. Figure 65 shows a manual switch used for changeover from HOT WATER SUPPLY 13 to 18 psi in the mains.

  • Page 98: Pneumatic-Electric Relay Control

    PNEUMATIC CONTROL FUNDAMENTALS branchline pressure to 14 psi, Relay 2 breaks the normally PNEUMATIC-ELECTRIC RELAY CONTROL closed circuit and makes the normally open circuit, removing voltage from Relay 1, shutting down the low speed, and A P/E relay provides the interlock when a pneumatic energizing the high speed.

  • Page 99: Pneumatic Centeralization

    PNEUMATIC CONTROL FUNDAMENTALS The Discharge Air Temperature Indicator is fed from the PNEUMATIC CENTRALIZATION pneumatic discharge air temperature sensor and the Three-Way Valve Gauge is fed from the valve control line. Building environmental systems may be pneumatically automated to any degree desired. Figure 73 provides an When pneumatic automation panels are located local to the example of the front of a pneumatic automation panel.

  • Page 100: Pneumatic Control System Example

    PNEUMATIC CONTROL FUNDAMENTALS PNEUMATIC CONTROL SYSTEM EXAMPLE The following is an example of a typical air handling system Control Requirements: (Fig. 74) with a pneumatic control system. The control system — Maintain design outside air airflow during all levels of is presented in the following seven control sequences (Fig.
  • Page 101 PNEUMATIC CONTROL FUNDAMENTALS Any time the Supply Fan 1M runs, the Return Fan 2M runs. Interval Timer or by the Occupancy Schedule Time Clock 2TC set for 0750. Any time the Return Fan 2M runs, the Exhaust Fan 3M and the ventilation controls are energized by the After-Hours Both Clocks 1TC and 2TC are set to shut the system down at 1700.

  • Page 102: Supply Fan Control Sequence

    PNEUMATIC CONTROL FUNDAMENTALS NOTE: 1. Because of varying exhaust between occupied and SUPPLY FAN CONTROL SEQUENCE warm-up modes, space static pressure control of the return fan is selected. Return fan tracking from Any time the Supply Fan (Fig. 76) runs, the pressure supply fan airflow is acceptable but is complex if controller with the greatest demand, Static Pressure Controller varying exhaust is worked into the control scheme.

  • Page 103: Mixing Damper Control Sequence

    PNEUMATIC CONTROL FUNDAMENTALS RETURN FAN RETURN SA-1 B S M SNAP TC-1 ACTING RELAY C-X < 69 C-O >71 AIR DURING COLD RETURN AIR (WARM-UP) SUPPLY FAN OUTSIDE FROM TO COOLING TS-1 COOLING CONTROLS CONTROLS SR-1 3-8 PSI N.O. SR-3 B S M TC-2 SR-2...

  • Page 104: Discharge Air Temperature Control Sequence

    PNEUMATIC CONTROL FUNDAMENTALS DISCHARGE AIR TEMPERATURE OFF/FAILURE MODE CONTROL CONTROL SEQUENCE SEQUENCE Any time the AHU (Fig. 79) operates in the non-warm-up If compressed air fails, both control valves open, the outside mode, Switching Relay SR-4 operates to allow the normal air damper closes, and the return air damper opens.

  • Page 105: Electric Control Fundamentals

    ELECTRIC CONTROL FUNDAMENTALS Electric Control Fundamentals Contents Introduction ......................Definitions ......................How Electric Control Circuits are Classified ....................Series 40 Control Circuits ......................100 Application ................... 100 Equipment ................... 100 Controllers ..................100 Relays ..................... 100 Actuators ..................100 Operation ..................... 101 Control Combinations ................
  • Page 106 ELECTRIC CONTROL FUNDAMENTALS Series 60 Floating Control Circuits ......................106 Application ................... 106 Equipment ................... 106 Controllers ..................106 Actuators ..................106 Operation ..................... 106 Control Combinations ................106 Series 90 Control Circuits ......................107 Application ................... 107 Equipment ................... 107 Controllers ..................

  • Page 107: Introduction

    There are – The signals received from sensing elements can be used places where Honeywell nomenclature is used, such as R, to produce one or a combination of electro-mechanical W, B, for wiring terminals and Series 40 through 90 for outputs.
  • Page 108 ELECTRIC CONTROL FUNDAMENTALS N.O./N.C. contact arrangement but provide a LOW-VOLTAGE CONTROL CIRCUIT switching action dependent on the condition of the controlled variable. Floating controllers (Fig. 3D) are spdt devices with a center-off position. Refer to MOTOR COILS SERIES 60 FLOATING CONTROL CIRCUITS for a discussion of floating control operation.

  • Page 109: How Electric Control Circuits Classified

    (Table 1). Series 10 and 20 are no longer used. Series 70 is controls of different series in the same control circuit. electronic control and is covered in the Electronic Control Fundamentals section. Table 1. Honeywell Electric Control Circuits. Series Controller Signal Circuit...

  • Page 110: Series 40 Control Circuits

    ELECTRIC CONTROL FUNDAMENTALS SERIES 40 CONTROL CIRCUITS RELAYS APPLICATION A Series 40 relay consists of a line-voltage coil which operates A Series 40 circuit is a line-voltage control circuit which is an armature to control one or more normally open or normally switched directly by the single-pole, single-throw switching closed, or single-pole, double-throw contacts.

  • Page 111: Operation

    ELECTRIC CONTROL FUNDAMENTALS CONTROL COMBINATIONS CONTROLLER UNIT HEATER CONTROL LINE VOLTAGE In unit heater control (Fig. 7) it is usually necessary to keep the heater fan from running to prevent circulation of cold air when heat is not being supplied to the heater coils. DRIVE LOW-LIMIT SHAFT...

  • Page 112: Series 80 Control Circuits

    ELECTRIC CONTROL FUNDAMENTALS LOW-LIMIT CONTROL LOW-LIMIT CONTROLLER THERMOSTAT ACTUATOR A low-limit controller is connected in parallel with the thermostat as shown in Figure 9. The low-limit controller can complete the circuit to the valve actuator even though the thermostat has opened the circuit. The actuator remains LINE VOLTAGE HOT WATER energized when the contacts on either controller are closed.

  • Page 113: Series 60 Two-Position Control Circuits

    ELECTRIC CONTROL FUNDAMENTALS CONTROL COMBINATIONS HIGH-LIMIT THERMOSTAT CONTROLLER ACTUATOR Series 80 control combinations are similar to those of Series 40. The following applies: 1. Series 80 circuits require an external, low-voltage transformer. TRANSFORMER HOT WATER 2. Series 80 equipment can be controlled by Series 40 or SUPPLY COIL 80 controllers.

  • Page 114: Operation

    (CLOSE) (OPEN) the CLOSE limit switch. NOTE: Most Honeywell Series 60 controllers close R to B on a fall in the controlled variable and R to W on a rise. TRANSFORMER LINE VOLTAGE C2515 Fig.

  • Page 115: Control Combinations

    ELECTRIC CONTROL FUNDAMENTALS CONTROL COMBINATIONS OUTDOOR CONTROLLER The following are representative Series 60 two-position control circuits. Notice that many of these functions can be done with Series 40 or 80 systems. If spring-return action is required when power fails, use Series 40 or 80. LOW-LIMIT HIGH-LIMIT CONTROLLER...

  • Page 116: Series 60 Floating Control Circuits

    ELECTRIC CONTROL FUNDAMENTALS SERIES 60 FLOATING CONTROL CIRCUITS APPLICATION OPERATION A Series 60 floating control circuit is a line- or low-voltage Operation of the Series 60 floating control circuit is similar control circuit comprising a spdt controller with a center-off to that discussed in SERIES 60 TWO-POSITION CONTROL (floating) position and a reversible actuator.

  • Page 117: Series 90 Control Circuits

    ELECTRIC CONTROL FUNDAMENTALS SERIES 90 CONTROL CIRCUITS ACTUATORS APPLICATION A Series 90 actuator (Fig. 19) consists of the following: The Series 90 low-voltage control circuit provides modulating – Reversible drive motor. or proportional control and can be applied to: – Electronic relay. –...

  • Page 118: Operation

    BRIDGE CIRCUIT ON INCREASE IN CONTROLLED VARIABLE NOTE: Most Honeywell Series 90 controllers move the po- tentiometer wiper toward B on a fall in the controlled Figure 21 illustrates the bridge circuit in an unbalanced variable and toward W on a rise.

  • Page 119: Bridge Circuit On Decrease In Controlled Variable

    ELECTRIC CONTROL FUNDAMENTALS CONTROLLER CONTROLLER POTENTIOMETER POTENTIOMETER SENSING SENSING ELEMENT ELEMENT ELECTRONIC ELECTRONIC RELAY RELAY DRIVE DRIVE SHAFT SHAFT OPEN CLOSE CLOSE OPEN FEEDBACK FEEDBACK POTENTIOMETER C2522 POTENTIOMETER C2523 Fig. 21. Bridge Circuit on Increase Fig. 22. Bridge Circuit on Decrease in Controlled Variable.

  • Page 120: Bridge Circuit With Low-Limit Control

    ELECTRIC CONTROL FUNDAMENTALS has to go on each side of the bridge to rebalance the circuit, the BRIDGE CIRCUIT WITH LOW-LIMIT CONTROL feedback potentiometer moves 35 ohms to the left. The table In a heating application, a low-limit controller moves a valve then appears as follows: actuator toward open when the low-limit setting is reached.

  • Page 121: Control Combinations

    ELECTRIC CONTROL FUNDAMENTALS When the high-limit controller calls for less heat, the poten- DISCHARGE AIR LOW LIMIT ROOM tiometer wiper R (shown dotted) moves halfway from B to W. CONTROLLER CONTROLLER This causes an unbalance of 70 ohms (210 – 140) in the right leg of the bridge as shown in the following table: Left Leg Right Leg...

  • Page 122: Two-Position Limit Control

    ELECTRIC CONTROL FUNDAMENTALS the controller and shorts R to W at the actuator. The actuator TWO-POSITION LIMIT CONTROL drives to the closed position. Such a hookup is often used in fan heating systems to manually close a valve or damper when Two-position limit controllers can be used in Series 90 operation is unnecessary.

  • Page 123: Transferring Controller From One Actuator To Another

    ELECTRIC CONTROL FUNDAMENTALS UNISON CONTROL THERMOSTAT Figure 32 illustrates a circuit for controlling up to six DPDT Series 90 actuators in unison from one Series 90 controller. SWITCH, RELAY, OR The B to W terminals of the controller are shunted with the THERMOSTAT appropriate value resistor, depending on the number of HEATING...

  • Page 124: Motor Control Circuits

    ELECTRIC CONTROL FUNDAMENTALS A 135-ohm manual potentiometer provides up to a 50 percent THERMOSTAT minimum-position opening, and a 270-ohm manual potentiom- eter provides up to a 100 percent minimum-position opening. CAM OPERATED SWITCHES SPRING-RETURN ACTUATOR STEP STEP CONTROLLERS CONTROLLER A step controller consists of a series of switches operated LINKAGE sequentially by cams on a crankshaft.

  • Page 125: Operation

    ELECTRIC CONTROL FUNDAMENTALS OPERATION HAND-OFF-AUTO START-STOP CIRCUIT The starter switch in Figure 36 has three positions: HAND, Three basic types of motor control circuits are discussed in OFF, and AUTO. The HAND position energizes starter solenoid the following. This topic is only intended to illustrate general M and starts the motor.

  • Page 126: Momentary Fast-Slow-Off Start-Stop Circuit

    ELECTRIC CONTROL FUNDAMENTALS windings at the same time. Pressing the STOP button opens MOMENTARY FAST-SLOW-OFF START-STOP both holding circuits and stops the motor. CIRCUIT Where a mechanical interlock does not exist between the Figure 37 illustrates a momentary, two-speed, start-stop holding circuits and push-button contacts, the fast speed start circuit with separate windings for fast and slow motor speeds.

  • Page 127: Control Combinations

    ELECTRIC CONTROL FUNDAMENTALS CONTROL COMBINATIONS There are many different control combinations for motor The return fan will not start until supply airflow is proven. A control circuits. Figure 38 illustrates a return fan interlocked relay can be added to interlock to the temperature control with the supply fan.
  • Page 128 ELECTRIC CONTROL FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATION CONTROL...

  • Page 129: Electronic Control Fundamentals

    ELECTRONIC CONTROL FUNDAMENTALS Electronic Control Fundamentals Contents Introduction ......................120 Definitions ......................120 Typical System ......................122 C o m p o n e n t s ......................122 Sensors ....................122 Temperature Sensors ..............122 Resistance Temperature Devices ..........122 Solid-State Resistance Temperature Devices ......

  • Page 130: Introduction

    ELECTRONIC CONTROL FUNDAMENTALS INTRODUCTION The sensor s and output de vices (e.g., actua tor s, relays) used This section pr ovides infor mation a bout electr onic contr ol for electronic control systems are usually the same ones used systems used to contr ol HVAC equipment. An electr onic contr ol on micr opr ocessor-based systems.
  • Page 131 ELECTRONIC CONTROL FUNDAMENTALS Electronic controller: A solid-sta te device usuall y consisting Proportional control (P): A contr ol algor ithm or method in of a po wer suppl y, a sensor amplif ication cir cuit, a which the f inal contr ol element mo ves to a position pr ocess/compar ing cir cuit, an output dr iver section, pr opor tional to the de viation of the v alue of the and v ar ious components tha t sense c hang es in the...

  • Page 132: Typical System

    ELECTRONIC CONTROL FUNDAMENTALS TYPICAL SYSTEM Figur e 1 shows a simple electr onic contr ol system with a ELECTRONIC FINAL CONTROL CONTROLLER DEVICE INPUTS contr oller tha t r egulates suppl y water temper atur e by mixing retur n water with w ater fr om the boiler . The main temper atur e MAIN SENSOR (HOT WATER SUPPLY) sensor is loca ted in the hot w ater suppl y from the v alve.

  • Page 133: Electronic Control Fundamentals

    ELECTRONIC CONTROL FUNDAMENTALS INDICATING ACCESSORY INTERFACING OUTPUT FINAL CONTROL INDICATING SENSORS/TRANSMITTERS CONTROLLERS DEVICES DEVICES DEVICES DEVICES ELEMENTS DEVICES DIGITAL SENSOR CONTACTOR FAN/PUMP TEMPERATURE LED PANEL SPST/SPDT OR RELAY CONTROLLER LED PANEL ANALOG TEMPERATURE SENSOR GAUGE ANALOG GAUGE POSITIVE RTD, OHMS THERMISTOR, OR DIGITAL TWO-POSITION...
  • Page 134 ELECTRONIC CONTROL FUNDAMENTALS Another material used in RTD sensors is platinum. It is or small tr ansistor) and pr ovide quic k r esponse . As the linear in response and stable over time. In some applications temperature increases, the resistance of a thermistor decreases a short length of wire is used to provide a nominal resistance (Fig.
  • Page 135 ELECTRONIC CONTROL FUNDAMENTALS Transmitters measure various conditions such as Thermocouples temperature, relative humidity, airflow, water flow, power consumption, air velocity, and light intensity. An example of a A thermocouple, consists of two dissimilar metals, such as transmitter would be a sensor that measures the level of carbon iron and constantan, welded together to form a two thermocouple dioxide (CO ) in the return air of an air handling unit.
  • Page 136 ELECTRONIC CONTROL FUNDAMENTALS WIRES TO CONTROLLER PROTECTIVE POLYMER OR SENSING CIRCUIT MOISTURE SENSITIVE POROUS POLYMER PLATINUM DIELECTRIC POLYMER CERAMIC GOLD FOIL OR OTHER SUBSTRATE TYPE OF ELECTRODE PLATES A. MOISTURE SENSITIVE MATERIAL BETWEEN ELECTRODE PLATES. ELECTRODE 1000 OHM FINGERS PLATINUM RTD M10685 ULTRA THIN LAYER OF CONDUCTIVE MATERIAL...

  • Page 137: Pressure Sensors

    ELECTRONIC CONTROL FUNDAMENTALS POLYMER COATING PRESSURE INLET (E.G., AIR, WATER) FLEXIBLE DIAPHRAGM OSCILLATING FREQUENCY CIRCUIT MEASURING TO CONTROLLER CIRCUIT FLEXIBLE PLATE QUARTZ CRYSTAL (TOP PORTION OF (ENLARGED VIEW) C3088 CAPACITOR) Fig. 13. Quartz Crystal Relative Humidity Sensor. AMPLIFIER FIXED PLATE (BOTTOM PORTION PRESSURE SENSORS OF CAPACITOR)

  • Page 138: Output Devices

    ELECTRONIC CONTROL FUNDAMENTALS Temperature Controllers OUTPUT CONTROL Temperature controllers typically require a specific type or Electronic controllers provide outputs to a relay or actuator category of input sensors. Some have input circuits to accept for the final control element. The output is not dependent on RTD sensors such as BALCO or platinum elements, while the input types or control method.

  • Page 139: Electtonic Controller Fundamentals

    ELECTRONIC CONTROL FUNDAMENTALS ELECTRONIC CONTROLLER INDICATING DEVICE OUTPUT MODULATING An electronic control system can be enhanced with visual VALVE ACTUATOR displays that show system status and operation. Many electronic POWER controllers have built-in indicators that show power, input signal, CHILLED WATER SUPPLY TO COIL deviation signal, and output signal.

  • Page 140: Typical System Application

    ELECTRONIC CONTROL FUNDAMENTALS TYPICAL SYSTEM APPLICATION Figure 22 shows a typical air handling system controlled by limit setpoint. A minimum discharge air temperature two electronic controllers, C1 and C2; sequencer S; is maintained regardless of space temperature. multicompensator M; temperature sensors T1 through T4; modulating hot and chilled water valves V1 and V2;...

  • Page 141: Microprocessor-Based/Ddc Fundamentals

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS Microprocessor-Based/ DDC Fundamentals Contents Introduction ......................133 Definitions ......................133 Background ......................134 Computer Based Control ..............134 Direct Digital Control ................134 Advantages ......................134 Lower Cost per Function ..............134 Application Flexibility ................135 Coordinated Multifunction Capability ........... 135 Precise and Accurate Control ..............
  • Page 142 MICROPROCESSOR-BASED/DDC FUNDAMENTALS Controller Programming ......................142 General ....................142 Programming Categories ..............143 Configuration Programming ............143 System Initialization Programming ..........143 Data File Programming ..............143 Custom Control Programming ............143 Analyze Control Application ............144 Partition Into Control Loops ............144 Determine Inputs and Outputs ............

  • Page 143: Introduction

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS INTRODUCTION functions. A stand-alone controller can take several forms. The This section discusses the types of microprocessor-based simplest generally controls only one control loop while larger controllers used in commercial buildings. These controllers versions can control from eight to 40 control loops. As the measure signals from sensors, perform control routines in systems get larger, they generally incorporate more software programs, and take corrective action in the form of...

  • Page 144: Background

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS BACKGROUND A more detailed definition is provided in the ASHRAE 1995 COMPUTER BASED CONTROL HVAC Applications Handbook. “A digital controller can be either single- or multiloop. Interface hardware allows the digital Computer based control systems have been available as an computer to process signals from various input devices, such alternative to conventional pneumatic and electronic systems as the electronic temperature, humidity, and pressure sensors...

  • Page 145: Controller Configuration

    ACTUATORS purpose device. Dedicated purpose configurable controllers C2421 normally have standard programs and are furnished with read Fig. 3. Microprocessor Controller Configuration for only memory (ROM) or programmable read only memory Automatic Control Applications. ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 146: Types Of Controllers

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS All input signals, whether analog or digital, undergo verter provides a resolution of one count in 256. A 12-bit A/D conditioning (Fig. 3) to eliminate the adverse affects of contact converter provides a resolution of one count in 4096. If the A/D bounce, induced voltage, or electrical transients.

  • Page 147: Controller Software

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS Zone- and system-level controllers should be equipped with values to be shared and interaction between zone-level a communications port. This allows dynamic data, setpoints, programs and system-level programs to be coordinated. For and parameters to be passed between a local operator terminal, example, night setback and morning warmup can be a central building management system, and/or other implemented at the zone-level controller based on operational...

  • Page 148: Energy Management Software

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS Table 1. Typical DDC Operators. VAV AHU at reduced capacity. Unless required by IAQ, outdoor air dampers and ventilation fans should be inactive Operator Description during preoccupancy warmup periods. For weekend shutdown Sequence Allows several controller outputs to be periods, the program automatically adjusts to provide longer sequenced, each one operating over a full lead times.

  • Page 149: Night Cycle

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS Night Cycle OADB The night cycle program (Fig. 7) maintains a low temperature > OAh > RAh RADB limit (heating season) or high temperature limit (cooling season) during unoccupied periods by cycling the air handling unit while the outdoor air damper is closed. Digital control systems often reduce fan capacity of VAV AHU systems to SELECT SELECT...
  • Page 150 MICROPROCESSOR-BASED/DDC FUNDAMENTALS Without knowledge of the actual instantaneous demands of d. As the chilled water temperature increases, the the loads that load reset controls, systems must run at the discharge air temperature increases. theoretical worst-case setpoints for temperature and pressure. e.

  • Page 151: Zero Energy Band

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS CHILLED WATER TEMPERATURE SETPOINT CONTROL MANUAL SETPOINT AUTO-MANUAL SELECTOR AUTO CURRENT VALUE CHILLED WATER CURRENT LEAVING WATER TEMPERATURE VALVES CURRENT CHILLER LOAD (% AMPS) OPEN AUTOMATIC MODE SEQUENCE OF CONTROL ANYTIME ANY AHU CHW VALVE IS % OPEN, THE CHW TEMPERATURE SETPOINT WILL BE DECREMENTED DEGREES, BUT TO NO LESS THAN...

  • Page 152: Controller Programming

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS Distributed Power Demand BUILDING MANAGEMENT SOFTWARE The distributed power demand program (Fig. 12) is only applicable Microprocessor-based controllers are used extensively as to microprocessor controllers with intercommunications capability. data gathering panels (DGP) for building management The demand program is resident in a single controller which monitors systems.

  • Page 153: Programming Categories

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS PROGRAMMING CATEGORIES System-level controllers are variable-function and are more universal in application. These controllers must be able to perform a wide variety of control sequences with a broad range Programming of microcomputer-based controllers can be of sensor input types and control output signals. System-level subdivided into four discrete categories: controllers require more extensive data file programming.

  • Page 154: Analyze Control Application

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS Partition Into Control Loops START The next step is to partition the entire process into individual control loops. The Control Fundamentals section defines a ANALYZE CONTROL control loop as a process in which a controller compares the STEP 1 APPLICATION measured value of a controlled variable to a desired value or REQUIREMENTS...

  • Page 155: Typical Applications

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS Design, Write, and Compile Program and linking them with other control blocks. Although this process requires little or no knowledge of programming, it does The actual process of designing and writing the control loop require in-depth knowledge of the control blocks and the programs can be a very complex or a relatively straightforward specific HVAC process.

  • Page 156: System-Level Controller

    MICROPROCESSOR-BASED/DDC FUNDAMENTALS staged by a PI algorithm with software heat anticipation. See An example of this approach follows for control of a hot Figure 15. During reheat, the control mode changes to constant water converter: volume, variable discharge temperature. Step 1—Develop flow schematic of the process to be controlled (Fig.
  • Page 157 MICROPROCESSOR-BASED/DDC FUNDAMENTALS Step 3—Write a detailed sequence of operation for the process. START The hot water pump starts anytime the outside air temperature drops to 52F, subject to a software on-off-auto O.A. TEMP function. EQUAL TO OR BELOW 11°C When hot water pumping is proven by a current sensing relay, converter controls are energized.
  • Page 158 MICROPROCESSOR-BASED/DDC FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 159: Indoor Air Quality Fundamentals

    INDOOR AIR QUALITY FUNDAMENTALS Indoor Air Quality Fundamentals Contents Introduction ......................151 Definitions ......................151 Abbreviations ......................153 Indoor Air Quality Concerns ......................154 Air Contaminants ................. 154 Contaminant Sources ..............154 Outdoor Contaminant Sources ........... 154 Indoor Contaminant Sources ............155 General ...................
  • Page 160 INDOOR AIR QUALITY FUNDAMENTALS Codes and Standards ................162 Acceptance Testing ................163 General ................... 163 ASHRAE Guideline 1-1989 ............. 164 Indoor Air Quality Control Applications ......................164 General ....................164 Flow Tracking Control System ............. 165 Flow Tracking System With Mixing Box Static Pressure Control ..166 Rooftop Unit Control System ...............

  • Page 161: Introduction

    INDOOR AIR QUALITY FUNDAMENTALS INTRODUCTION Measures taken to offset increasing energy costs since the 1970s, This section provides basic information on Indoor Air Quality increasing use of synthetic materials in building construction (IAQ) and suggested control solutions. The causes and effects and maintenance, compressed construction schedules, and of several contaminants are discussed.
  • Page 162 INDOOR AIR QUALITY FUNDAMENTALS Dioctyl phthalate: An oily liquid used in testing filters. Materials Safety Data sheets (MSDSs): OSHA required documents supplied by manufacturers of potentially Dose: The amount of a given agent that actually reaches the hazardous products. MSDSs contain information site in the body where it causes an effect.

  • Page 163: Abbreviations

    INDOOR AIR QUALITY FUNDAMENTALS Radon: A colorless, odorless, radioactive gas emitted during Source control: A preventive strategy for reducing airborne the disintegration of radium. Radon can be a serious contaminant levels through the removal of the material indoor air contaminant in building areas which are in or activity generating the pollutants.

  • Page 164: Indoor Air Quality Concerns

    INDOOR AIR QUALITY FUNDAMENTALS INDOOR AIR QUALITY CONCERNS contaminants such as methane are produced both naturally, by AIR CONTAMINANTS animals and decay, and by man made activity such as landfills. Location near a fossil fuel power plant, refinery, chemical Air contaminants are categorized by location and type. production facility, sewage treatment plant, municipal refuse Location of contaminants is divided between outdoor and dump or incinerator, animal feed lot, or other like facility will...

  • Page 165: Indoor Contaminant Sources

    INDOOR AIR QUALITY FUNDAMENTALS Table 1. Annual Median Concentrations for TSP, NO 2 , O 3 , & CO—1979. a (continued) Concentration µg/m mg/m (1 hr average) CO (1 hr average) Location TSP (annual average) (1 hr average) Pittsburgh 88-162 —...

  • Page 166: Occupancy And Process Related Contaminant Sources

    INDOOR AIR QUALITY FUNDAMENTALS Table 3. Sources, Possible Concentrations, and Indoor to Outdoor Concentration Ratios of some Indoor Pollutants. Sources of Possible Indoor Indoor/Outdoor Pollutant Indoor Pollution Concentrations Concentration Location Ratio <10 6 fiber/ m 3 Asbestos Fireproofing Homes, schools, offices Carbon Dioxide Combustion, humans, pets 3000 ppm...

  • Page 167: Health Care Occupancy

    Microscope common and dangerous materials and requires that materials Size in Microns .001 safety data sheets be completed on each of these substances. HONEYWELL EAC EFFECTIVE RANGE DUST/LINT FILTER The National Institute of Occupational Safety & Health EFFECTIVE RANGE* (NIOSH) also publishes a list which includes additional...

  • Page 168: Gas And Vapor Contaminants

    INDOOR AIR QUALITY FUNDAMENTALS Multiple Chemical Sensitivity is the term applied to an illness Gas And Vapor Contaminants resulting from exposure to multiple chemicals, none of which by itself would cause a problem in most people. The terms gas and vapor are often used to describe a common state of a substance.

  • Page 169: Remediating Contaminant Levels

    INDOOR AIR QUALITY FUNDAMENTALS Passive pathways include vertical elevator and mechanical Gas Contaminant Remediation shafts which permit gravity flow of airborne contaminants, and drop ceilings, tunnels, and partition walls where mold, mildew Gas phase filtration is used to reduce and control gas and and fungus may be growing, spreading, and generating spores.

  • Page 170: Effects Of Humidity

    INDOOR AIR QUALITY FUNDAMENTALS Failing to maintain the temperature will affect the relative of the optimum zone is a compromise. It is informative to note humidity which can have an adverse effect on the growth of the overlap of ozone production and chemical reactions, since viruses, mold, mildew, and bacteria.

  • Page 171: Ventilation Rate Design Procedure

    INDOOR AIR QUALITY FUNDAMENTALS This standard also requires detailed documentation of design These rates are set on the assumption that they will maintain assumptions and intent to permit the operating personnel to CO 2 levels below 1000 ppm and that this is a valid indicator of maintain the system as designed to assure continued IAQ during acceptable IAQ.

  • Page 172: Recirculation Requirements

    INDOOR AIR QUALITY FUNDAMENTALS is located in a local makeup air unit if one is used. The filter Recirculation Requirements shown in the outdoor airstream is utilized when outdoor air cannot meet the requirements of the building code, ASHRAE Recirculation of air in HVAC systems is regulated by recommendations, or flow sensors or coils are located in the buildings codes and other rules as well as ASHRAE 62- outside air.

  • Page 173: Acceptance Testing

    INDOOR AIR QUALITY FUNDAMENTALS Table 5. Air Quality Regulatory Agencies. Agency Federal State Advisory Environmental Protection Agency (EPA) Department of Natural Resources (DNR) Occupational Safety & Health Agency (OSHA) Center for Disease Control (CDC) Public Health Department (PHD) American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) American National Standards Institute (ANSI) National Institute of Occupational Safety &...

  • Page 174: Indoor Air Quality Control Applications

    INDOOR AIR QUALITY FUNDAMENTALS deliver the design. The acceptance phase of the process ASHRAE GUIDELINE 1-1989 demonstrates that the systems work as designed. Documentation requirements of the process ensure that the building operators ASHRAE Guideline 1-1989 for commissioning HVAC know the design intent of the systems and how they are to be systems defines commissioning as “documenting and operated.

  • Page 175: Flow Tracking Control System

    INDOOR AIR QUALITY FUNDAMENTALS are 30 to 70 VAV terminal units per fan system. The sample FLOW TRACKING CONTROL SYSTEM VAV terminal unit shown is a fan powered unit but the units could be non-fan powered. Without an air flow station in the Figure 4 provides a simplified hardware schematic of a outdoor air, this system might not deliver the minimum air flow variable volume supply and return fan system with flow stations...

  • Page 176: Flow Tracking System With Mixing Box Static Pressure Control

    INDOOR AIR QUALITY FUNDAMENTALS at a variable minimum position until the economizer calls for FLOW TRACKING SYSTEM WITH MIXING additional outdoor air. During non-economizer periods the EA/ BOX STATIC PRESSURE CONTROL RA dampers modulate to maintain static pressure constant at the filter inlet.

  • Page 177: Rooftop Unit Control System

    INDOOR AIR QUALITY FUNDAMENTALS well suited to roof top applications which usually do not have ROOFTOP UNIT CONTROL SYSTEM sufficient ductwork for flow station outdoor air measurement. Figure 6 shows a typical packaged rooftop VAV system Without the return fan and with a two position exhaust fan it similar to the pervious system but with humidification and is difficult to ensure air balance in the building.

  • Page 178: Indoor Air Quality Fundamentals

    INDOOR AIR QUALITY FUNDAMENTALS For additional information on system configuration, network Actual values for the temperatures, air flows, and valve and communications, and specifying graphics, refer to the Building damper positions and percent fan loads are all shown for the Management System Fundamentals section.
  • Page 179 INDOOR AIR QUALITY FUNDAMENTALS Figure 8 shows how dynamic data can assist an operator. results in real time. This is one of many operator displays that This display provides the operator/engineer with the actual can be designed to facilitate operator understanding and control operating values, at that instant, embedded in the sequence of of IAQ.

  • Page 180: Bibliography

    INDOOR AIR QUALITY FUNDAMENTALS A graphic such as Figure 9 can be automatically displayed provides the necessary closure of the loop from the designer to as an alarm on a quarterly calendar basis to remind the building the user. Alarm acknowledgment can be logged by the owner operators and owners that the maintenance of IAQ is one of to verify compliance.

  • Page 181: Smoke Management Fundamentals

    SMOKE MANAGEMENT FUNDAMENTALS Smoke Management Fundamentals Contents Introduction ......................172 Definitions ......................172 Objectives ......................173 Design Considerations ......................173 General ....................173 Layout of System ................. 174 Codes And Standards ................. 174 Design Principles ......................175 Causes of Smoke Movement .............. 175 Stack Effect ..................

  • Page 182: Introduction

    SMOKE MANAGEMENT FUNDAMENTALS INTRODUCTION This section describes objectives, design considerations, building fires is carbon monoxide. Other toxic agents include hydrogen cyanide, hydrogen chloride, sulphur dioxide, acrolein, design principles, control applications, and acceptance testing for smoke management systems. A smoke management system aldehydes, carbon dioxide, and a variety of airborne particulates modifies the movement of smoke in ways to provide safety for carrying heavy metals (antimony, zinc, chromium, and lead).

  • Page 183: Objectives

    SMOKE MANAGEMENT FUNDAMENTALS Smoke Management System, Active: A system that uses fans Stack Effect: A movement of air or other gas in a vertical to produce airflows and pressure differences across enclosure induced by a difference in density between smoke barriers to limit and direct smoke movement. the air or other gas in the enclosure and the ambient atmosphere.

  • Page 184: Layout Of System

    SMOKE MANAGEMENT FUNDAMENTALS Any alarm activation of a smoke management system that is — End-of-process verification of each control sequence common to all strategies in the building, such as stairwell — Annunciation of any failure to confirm equipment pressurization, atria, and exhaust, is acceptable. operation —...

  • Page 185: Design Principles

    SMOKE MANAGEMENT FUNDAMENTALS — Underwriters Laboratories (UL) Standards: – UL 555S, Standard for Leakage Rated Dampers – UL 555, Standard for Fire Dampers and for Use In Smoke Control Systems Ceiling Dampers – UL 864, Standard for Control Units for Fire– Protective Signaling Systems (UL Category UUKL) DESIGN PRINCIPLES CAUSES OF SMOKE MOVEMENT...

  • Page 186: Expansion

    SMOKE MANAGEMENT FUNDAMENTALS The buoyancy effect can cause smoke movement through The relationship between volumetric airflow (smoke) and barriers above the fire and through leakage paths in walls. pressure through small openings, such as cracks, is as: However, as smoke moves away from the fire, its temperature ...

  • Page 187: Hvac

    SMOKE MANAGEMENT FUNDAMENTALS control system should be able to maintain these minimum HVAC pressure differences while the building is under typical conditions of stack effect and wind. This table is for gas HVAC systems can provide a means for smoke transport temperatures of 1700F adjacent to the barrier.

  • Page 188: Control Applications

    SMOKE MANAGEMENT FUNDAMENTALS The door widths in Table 2 apply only for doors that are PURGING hinged at one side. For other arrangements, door sizes, or for hardware other than knobs (e.g., panic hardware), refer to Because fires produce large quantities of smoke, purging calculation procedures furnished in Design of Smoke Control cannot ensure breathable air in a space while a fire is in progress.

  • Page 189: Zone Pressurization Control

    SMOKE MANAGEMENT FUNDAMENTALS INITIATING ALARM PANEL PROCESSOR OPERATOR’S ALARM CONSOLE DETECTORS TO ADDITIONAL REMOTE CONTROL PANELS REMOTE CONTROL REMOTE FLOW PANEL 1 CONTROL SWITCH PANEL 2 COMMUNICTIONS DAMPER SWITCH FIREFIGHTERS’ SMOKE DETECTOR SMOKE CONTROL (NFPA SYMBOL) STATION (FSCS) M13026 Fig. 6. Typical Smoke Control System Meeting the Requirements of UL Standard 864 and NFPA 92A. The following discussions cover smoke control applications sandwich.

  • Page 190: Stairwell Pressurization Control

    SMOKE MANAGEMENT FUNDAMENTALS Another consideration in zone pressurization is that bringing complex system to modulate dampers or fans at multiple in outdoor air at low temperatures can cause serious freeze injection points (Fig. 9) in response to differential pressure damage. Provision should be made to prevent damage when measurements at these points.

  • Page 191: Acceptance Testing

    SMOKE MANAGEMENT FUNDAMENTALS 5. Operator verifies operation as appropriate (e.g., action EXHAUST DAMPER of differential pressure switch). 6. Operator cancels smoke control mode as long as initiating SPRINKLER panel is not in alarm and FSCS is not in manual override. CONTROL OF MALLS, ATRIA, AND LARGE AREAS SMOKE...

  • Page 192: Bibliography

    SMOKE MANAGEMENT FUNDAMENTALS BIBLIOGRAPHY REFERENCED PUBLICATIONS 6. Smoke Control in Fire Safety Design, A. G. Butcher and A. C. Parnell, E. & F. N. Spon Ltd, 11 New Fetter Lane, London EC4P 4EE, 1979. 1. Toxicity Effects Resulting from Fires in Buildings, State- of-the Art Report, May 16, 1983, National Institute of 7.

  • Page 193: Building Management System Fundamentals

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Building Management System Fundamentals Contents Introduction ......................185 Definitions ......................185 Background ......................186 Energy Management ................186 Facilities Management Systems ............186 System Configurations ......................187 Hardware Configuration ..............187 Zone-Level Controllers ..............187 System-Level Controllers ..............188 Operations-Level Processors ............

  • Page 194: Introduction

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Operation ..................... 193 Specifying Graphics (I/O Summaries) ..........194 Control Graphics ................. 195 Data Penetration ................. 195 Integration of Other Systems ......................197 General ....................197 Surface Integration ................197 In-Depth Integration ................197 ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 195: Background

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS INTRODUCTION — Improved operating-cost record keeping for allocating This section provides information on the fundamentals of Building Management Systems (BMS). The objective of a BMS to cost centers and/or charging individual occupants is to centralize and simplify the monitoring, operation, and —...

  • Page 196: System Configurations

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Operations-level processor: A PC or other device used Zone-level controller: A microprocessor-based controller that primarily by building operation personnel for everyday controls distributed or unitary HVAC equipment such building operations. This processor can access points as VAV terminal units, fan coil units, and heat pumps. or data in all the lower level controllers.

  • Page 197: System Configurations

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Facilities management system configuration must deal with The development of two-wire transmission systems, PCs for two levels of operation: day-to-day operations and long-range centralized functions, and distributed processors including management and planning. Day-to-day operations require a DDC led to a need to define system configurations.

  • Page 198: System-Level Controllers

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS SYSTEM-LEVEL CONTROLLERS — Standard reports: Provides automatic, scheduled, and by- request reports of alarm and operator activity. Also Microprocessor-based system-level controllers have greater provides a broad range of system and category (points- capacity than zone-level controllers in terms of number of in-alarm, disabled points, etc.) summary reports.

  • Page 199: System Functions

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS PEER COMMUNICATIONS PROTOCOL COMMUNICATIONS Peer communications protocol has the following advantages SYSTEM/ZONE SYSTEM/ZONE SYSTEM/ZONE LEVEL LEVEL LEVEL over poll/response communications protocol: CONTROLLER CONTROLLER CONTROLLER — Communication not dependent on a single device as the master. CENTRAL —...

  • Page 200: System Functions

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS A modem is required for signal compatibility with the phone reduced costs, historical storage of alarm activity can be included line. The BMS dial-up phone line interface provides in the remote phone line interface so that the data is compatibility with transmission rate and protocol of the phone transmitted during periodic dialup by the central system.

  • Page 201: Communications Software

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS as word processors, spread sheets, and data bases to operate If no keyboard or mouse activity occurs for a predetermined concurrently with the BMS. In such cases, a BMS alarm time period, the operator is automatically signed-off. All overwrites the monitor screen until acknowledged and canceled.

  • Page 202: System Text

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Color is used to differentiate shapes and to define point System Text status. Red may be reserved for alarm, green may be reserved for “Normal On”, and yellow may be reserved for “Normal BMS system text includes unique names for all controllers, Off”.

  • Page 203: Controller Support

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Controller Support — AUTO/OFF (10 points) are commandable. Cursor selection of these points, allows commanding points ON A major portion of the BMS Software is the definition and or OFF. maintenance of system-level controller software. The software —...

  • Page 204: Specifying Graphics (I/O Summaries)

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Whereas building control strategies are often established SPECIFYING GRAPHICS (I/O SUMMARIES) independent of who will be “operating” the building, operator graphics should not be. Although the graphic (Fig. 7) presents When writing the control sequence of operation, sketch the an adequate overview of the chiller plant for a building engineer, graphic (Fig.

  • Page 205: Building Management System Fundamentals

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS CONNECTED POINTS APPLICATION SOFTWARE ENERGY MANAGEMENT INPUTS OUTPUTS SOFTWARE ANALOG ANALOG DIGITAL DIGITAL SYSTEM DESCRIPTION CHILLER PLANT COOLING TOWER ISOLATION VALVES LEAVING WATER LEAVING WATER COMMON CHILLER LEAVING COND. WATER CONDENSER PUMP CHILLER CONTROL COMMAND STATUS STATUS % MAX.

  • Page 206: Control Graphics

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS CONTROL GRAPHICS required to monitor certain critical alarm points after hours, design special graphics of only those points, with simplified Many digital control strategies require fine tuning to assure explanations, and specific operator response messages. Use systems are staged and loaded without excessive surging and simplified floor plan graphics with appropriately positioned cycling.

  • Page 207: Integration Of Other Systems

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS INTEGRATION OF OTHER SYSTEMS GENERAL IN-DEPTH INTEGRATION Figure 11 shows a system with in-depth integration. System- Information from other subsystems, such as fire alarm, level controllers communicate over a common bus for each security, access control, or lighting control, may be required subsystem.
  • Page 208 BUILDING MANAGEMENT SYSTEM FUNDAMENTALS The advantages of an in-depth integrated system are: — Third party LonMark™ and BACnet points may be — First costs and ongoing operating costs are usually lower positioned on or added to standard system graphics. — Interdependence between subsystems, such as smoke control, can be easily accommodated since there is only The disadvantage of this type of integration is that care must be taken in configuring the system to be sure that transmission...

  • Page 209: Control System Applications

    BUILDING MANAGEMENT SYSTEM FUNDAMENTALS CONTROL SYSTEMS APPLICATIONS ENGINEERING MANUAL OF AUTOMATIC CONTROL...
  • Page 210 BUILDING MANAGEMENT SYSTEM FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...

  • Page 211: Air Handling System Control Applications

    AIR HANDLING SYSTEM CONTROL APPLICATIONS Air Handling System Control Applications Contents Introduction ......................203 Abbreviations ......................203 Requirements For Effective Control ......................204 Applications-General ......................206 Valve and Damper Selection ......................207 Symbols ......................208 Ventilation Control Processes ......................209 Fan System Start-Stop Control ............
  • Page 212 AIR HANDLING SYSTEM CONTROL APPLICATIONS Humidification Control Process ......................235 Control of Modulating Humidifier ............235 Cooling Control Processes ......................236 Control of Modulating Chilled Water Coil Three-Way Valve ....236 Two-Position Control of Direct Expansion Coil System ....... 237 Two-Position Control of Direct Expansion Coil System—Modulating Face and Bypass Damper..............

  • Page 213: Introduction

    AIR HANDLING SYSTEM CONTROL APPLICATIONS INTRODUCTION Psychrometric aspects are included for most applications. This section describes control applications for air handling They are shown in abbreviated form. Unabridged copies of systems commonly found in commercial buildings. The basic ASHRAE Psychrometric Charts No. 1 and No. 2 are included processes such as heating, cooling, humidification, at the end of this section for reference.

  • Page 214: Requirements For Effective Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS REQUIREMENTS FOR EFFECTIVE CONTROL Effective control system performance requires careful design 2) Providing means of loading and unloading a of the mechanical system and selection of components. compressor under light load. Consideration needs to be given to the following by the 3) Sizing the refrigeration equipment mechanical system designer and the control engineer: accurately.
  • Page 215 AIR HANDLING SYSTEM CONTROL APPLICATIONS e. Locate humidifier leaving air humidity sensors f) Initiating low temperature alarms. no less than eight and no more than thirty feet g) Stopping fan if steam is not present. downstream of the humidifier. 2) Providing failure alarms for pump, coils, and other heating systems components.

  • Page 216: Applications-General

    AIR HANDLING SYSTEM CONTROL APPLICATIONS 17. PLACE CONTROL VALVES ON THE LEAVING SIDE 18. CONSIDER THE ABILITY OF THE HVAC SYSTEM OF WATER COILS. OPERATOR TO UNDERSTAND THE SYSTEM WHEN DESIGNING GRAPHICS FOR THE Control valves on the leaving side of water coils OPERATOR INTERFACE.

  • Page 217: Valve And Damper Selection

    AIR HANDLING SYSTEM CONTROL APPLICATIONS VALVE AND DAMPER SELECTION Pneumatic valve and damper actuators are shown in these outlines general actuator selection. The table indicates examples. If actuators are electric, certain ones need not actuator positioning desired on system shutdown and loss be spring return unless a specific reason exists.

  • Page 218: Symbols

    AIR HANDLING SYSTEM CONTROL APPLICATIONS SYMBOLS The following symbols are used in the system schematics following. These symbols denote the nature of the device, such as a thermometer for temperature sensing. CONTROLLER, TEMPERATURE SENSOR, TEMPERATURE LOW LIMIT PRESSURE CONTROLLER, HIGH LIMIT CUT-OUT, MANUAL RESET HIGH LIMIT MANUAL RESET NOTATION...

  • Page 219: Ventilation Control Processes

    AIR HANDLING SYSTEM CONTROL APPLICATIONS VENTILATION CONTROL PROCESSES The following applications show various ways of controlling ventilation in an air conditioning system. FAN SYSTEM START-STOP CONTROL FUNCTIONAL DESCRIPTION SPACE PROPELLER TEMPERATURE EXHAUST SETPOINT STATUS UNOCCUPIED LOW LIMIT FAN SYSTEM PERCENT SCHEDULE AND LOAD AUTO...
  • Page 220 AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES LIMITATIONS 1. Smoke, low temperature, and high static pressure safety 1. Heating and cooling equipment must be available to shutdown (hard-wired). operate. 2. Optimized start-stop control of supply, return, and exhaust 2. On large 100% OA systems and systems where OA and fans.

  • Page 221: Fixed Quantity Of Outdoor Air Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS FIXED QUANTITY OF OUTDOOR AIR CONTROL Functional Description Example, calculate the mixed air temperature of a 10,000 cfm fan with 25% OA at 5°F. RA is 75°F. 2500 MAT = 75 + (5 - 75) = 57.5°F 10,000 MAT = (75 x 0.75) + (5 x 0.25) = 57.5°F SPECIFICATIONS...

  • Page 222: Outdoor Air Fan Control For Multiple Ahu's

    AIR HANDLING SYSTEM CONTROL APPLICATIONS The OA fan loading shall be under EPID (see Control OUTDOOR AIR FAN CONTROL Fundamentals section) control with a start value of 25% and a FOR MULTIPLE AHU’S ramp duration of 250 seconds. NOTE: EPID was selected (and designed specifically) for this Functional Description type of application because of the start-up nature of VAV fans.

  • Page 223: Mixed Air Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS MIXED AIR CONTROL Functional Description NORMAL CONTROL PROGRAM OA MINIMUM SETPOINT M10447 Item FEATURES Function 1. The proper proportions of OA and RA, above minimum OA setting, are admitted to prevent the MA temperature Control system energizes when fan is turned from dropping below the desired MA temperature.
  • Page 224 AIR HANDLING SYSTEM CONTROL APPLICATIONS SPECIFICATIONS See FAN SYSTEM START-STOP CONTROL. 60°F DB MA Anytime the supply fan runs, the OA, EA, and RA dampers CONTROLLER SETPOINT shall be modulated by an MA PID control loop to satisfy the RA 75°F DB, 59.5°F WB MA temperature setpoint down to a minimum ventilation position.

  • Page 225: Economizer Cycle Decision

    AIR HANDLING SYSTEM CONTROL APPLICATIONS The economizer decision does not enable or disable chiller periods ECONOMIZER CYCLE DECISION of operation. Chillers are generally enabled anytime chilled water valves open. At economizer changeover, the OA (containing less heat than Where 100% outdoor air economizer cycles are included with air the RA) is intended to reduce the load on the cooling coil until no handling systems, the decision of when to switch to the economizer chilled water is required.

  • Page 226: Economizer Cycle Decision-Outdoor Air Enthalpy Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS CONDITIONS FOR SUCCESSFUL OPERATION SPECIFICATIONS Local weather data analysis needed to determine the optimum A global economizer function shall be provided to switch all AHUs changeover setpoint. The analysis need only consider data when the from OA cooling to minimum OA based upon an OA temperature OA is between approximately 60°F and 78°F, and during the occupancy setpoint.
  • Page 227 AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES OA RH sensor is bad), a manual economizer ON command (for use if the chiller plant is not 1. Outdoor air is used for cooling (or to supplement the ready to run for any reason), and a manual chilled water system) anytime the OA enthalpy is below economizer OFF command (for use if the the economizer setpoint.

  • Page 228: Economizer Cycle Decision-Outdoor Air/Return Air Enthalpy Comparison

    AIR HANDLING SYSTEM CONTROL APPLICATIONS ECONOMIZER CYCLE DECISION—OUTDOOR AIR/RETURN AIR ENTHALPY COMPARISON Functional Description ENTHALPY BTU PER POUND 29.0 OTHER INPUTS AND OUTPUTS CONTROL 16.8 PROGRAM ENTHALPY OA MINIMUM SETPOINT BTU PER POUND (NOTE: THE TEST AND BALANCE INITIAL ECONOMIZER MODE SELECTOR VALUE FOR PROPER VENTILATION IS 22) 1 = AUTO BASED UPON OA/RA...

  • Page 229: Economizer Cycle Decision-Outdoor Air/Return Air Dry Bulb Temperature Comparison

    AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES SPECIFICATIONS 1. Outdoor air is used for cooling (or to supplement the An economizer decision function shall be provided to switch chilled water system) anytime the OA enthalpy is less the AHU from OA cooling to minimum OA based upon an than the RA enthalpy.

  • Page 230: Mixed Air Control With Economizer Cycle (Ventilation System Only)

    AIR HANDLING SYSTEM CONTROL APPLICATIONS MIXED AIR CONTROL WITH ECONOMIZER CYCLE (VENTILATION SYSTEM ONLY) Functional Description NORMAL PERCENT OPEN CONTROL PROGRAM ECONOMIZER DECISION. REFER TO PREVIOUS ECONOMIZER OPTIONS OA MINIMUM SETPOINT (NOTE: THE TEST AND BALANCE INITIAL VALUE FOR PROPER VENTILATION IS 22) M10453 Item 2.

  • Page 231: Psychrometric Aspects

    AIR HANDLING SYSTEM CONTROL APPLICATIONS SPECIFICATIONS See FAN SYSTEM START-STOP CONTROL. 80°F DB OA Anytime the supply fan runs, the OA, exhaust, and RA CONTROLLER OA SUMMER dampers shall position to a minimum ventilation position and SETPOINT 100°F DB, 74°F WB shall be further modulated by an MA PID control loop to 55°F DB MA maintain the MA temperature setpoint.

  • Page 232: Economizer Cycle Control Of Space Temperature With Supply Air Temperature Setpoint Reset

    AIR HANDLING SYSTEM CONTROL APPLICATIONS ECONOMIZER CYCLE CONTROL OF SPACE TEMPERATURE WITH SUPPLY AIR TEMPERATURE SETPOINT RESET Functional Description SPACE NORMAL TEMPERATURE MIXED AIR TEMPERATURE RESET SCHEDULE SUPPLY AIR SPACE TEMPERATURE COOLING SETPOINT DEMAND CONTROL PROGRAM ECONOMIZER DECISION. REFER TO PREVIOUS ECONOMIZER OPTIONS OA MINIMUM SETPOINT (NOTE: THE TEST AND BALANCE INITIAL VALUE...

  • Page 233: Heating Control Processes

    AIR HANDLING SYSTEM CONTROL APPLICATIONS 75°F as the space temperature PID loop cooling demand varies SPECIFICATIONS from 100 to 0%. Anytime the economizer program is invoked, the SA temperature control shall be enabled. See FAN SYSTEM START-STOP CONTROL. Anytime the supply fan runs, the OA, exhaust, and RA PSYCHROMETRIC ASPECTS dampers shall position to a minimum ventilation position and shall be further modulated by an SA PID control loop to...

  • Page 234: Control From Space With Supply Temperature Reset

    AIR HANDLING SYSTEM CONTROL APPLICATIONS CONTROL FROM SPACE WITH SUPPLY TEMPERATURE RESET Functional Description SPACE NORMAL TEMPERATURE SUPPLY AIR TEMPERATURE RESET SCHEDULE SUPPLY AIR SPACE TEMPERATURE HEATING SETPOINT DEMAND N.O. CONTROL PROGRAM CURRENT SUPPLY AIR TEMPERATURE SETPOINT M10459 1. Anytime the supply fan runs, the hot water valve shall be Item modulated by an SA PID control loop to maintain the SA Function...

  • Page 235: Outdoor Air Temperature Reset Of Supply Air Temperature

    AIR HANDLING SYSTEM CONTROL APPLICATIONS OUTDOOR AIR TEMPERATURE RESET OF SUPPLY AIR TEMPERATURE Functional Description NORMAL CONTROL PROGRAM RESET SCHEDULE OUTDOOR SUPPLY AIR SETPOINT SETPOINT M10460 Item Function PSYCHROMETRIC ASPECTS Control system energizes when fan is turned on The SA condition depends on the entering air condition and (See FAN SYSTEM START-STOP CONTROL).

  • Page 236: Space Temperature Control Of Zone Mixing Dampers And Reset Of Hot Deck Temperature

    AIR HANDLING SYSTEM CONTROL APPLICATIONS SPACE TEMPERATURE CONTROL OF ZONE MIXING DAMPERS AND RESET OF HOT DECK TEMPERATURE SPACE SETPOINT Functional Description OPEN TEMP. HALL LOBBY EAST CONTROL OFFICE PROGRAM WEST OFFICE SETPOINT NORMAL PERCENT OPEN TO HOT DECK ZONE DECK MIXING DAMPERS...
  • Page 237 AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES SPECIFICATIONS 1. A motorized zone mixing damper and space temperature See FAN SYSTEM START-STOP CONTROL. PID control loop for each zone provides zone control. 2. A single coil or group of coils in the hot deck furnishes Anytime the supply fan runs, heating control shall be enabled.

  • Page 238: Preheat Control Processes

    AIR HANDLING SYSTEM CONTROL APPLICATIONS PREHEAT CONTROL PROCESSES The preheat process heats the air in preparation for subsequent 2. Accurate sizing of preheat coils is important. They should conditioning. Preheat is sometimes necessary when high be sized so it is possible to allow OA for cooling yet not percentages of low temperature OA must be handled by the overheat the space.
  • Page 239 AIR HANDLING SYSTEM CONTROL APPLICATIONS The heating coil valve shall position from 0 to 100% open as FEATURES the OA temperature varies from 50°F to 35°F. The face-and- bypass dampers shall modulate to maintain an average face- 1. Preheat coil conditions large quantities of low temperature and-bypass leaving air temperature of 50°F.

  • Page 240: Control From Preheat Leaving Air

    AIR HANDLING SYSTEM CONTROL APPLICATIONS CONTROL FROM PREHEAT LEAVING AIR Functional Description CONTROL PROGRAM OPEN N.O. N.C. NORMAL M10463 Item LIMITATIONS Function If too high a temperature rise is used, the valve may short cycle or slow down the water in the coil and allow the coil to freeze. Control system energizes when fan is turned on (See FAN SYSTEM START-STOP CONTROL).

  • Page 241: Multiple Coil Control From Outdoor And Supply Air

    AIR HANDLING SYSTEM CONTROL APPLICATIONS The following results are obtained: Item Explanation RA 75°F DB, 62.5°F WB Heating of OA occurs along a line of constant moisture content from 35°F to 70°F. This condition represents the mixing of PREHEAT AIR preheated air and RA supplied to the system.
  • Page 242 AIR HANDLING SYSTEM CONTROL APPLICATIONS The heating Coil 1 valve shall open upon loss of actuator FEATURES motive force, shall close upon fan shutdown if the OA temperature is above 35°F, and shall open upon fan shutdown 1. The multiple inline coil system heats below-freezing air if the OA temperature is below 35°F.

  • Page 243: Year-Round Heat Recovery Preheat System Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS The following results are obtained: Item Explanation Coil No. 1 is providing 100 percent capacity Coil No. 2 valve is closed. raising the entering air from 35°F to 65°F. Coil No. 3 is modulating and provides a 5°F temperature rise to the desired supply temperature.
  • Page 244 AIR HANDLING SYSTEM CONTROL APPLICATIONS In the heating season, the recirculating pump shall run FEATURES anytime the OA temperature is less than three degrees below the supply fan SA temperature setpoint. 1. Use of the heat recovery system makes it energy efficient to use 100 percent OA by transferring heat from RA to A pump inlet mixing valve shall be modulated during heating supply air during heating operation and transferring...

  • Page 245: Humidification Control Process

    AIR HANDLING SYSTEM CONTROL APPLICATIONS HUMIDIFICATION CONTROL PROCESS Humidification is a process of adding moisture to air. The Although steam jet humidifiers are depicted, other modulating most commonly used humidifier type is the steam jet. types control similarly. On-off humidifiers require a differential Humidifier requirements vary;...

  • Page 246: Cooling Control Processes

    AIR HANDLING SYSTEM CONTROL APPLICATIONS Item PSYCHROMETRIC ASPECTS Explanation The steam humidification process is almost isothermal. RA and dry OA mix and enter a heating coil. In the following chart it is assumed that: Heating coil leaving air; air gains sensible heat.

  • Page 247: Two-Position Control Of Direct Expansion Coil System

    AIR HANDLING SYSTEM CONTROL APPLICATIONS CONDITION FOR SUCCESSFUL OPERATION The water must be supplied at a reasonably constant pressure. OA 95°F DB, 75°F WB RA 78°F DB, LIMITATIONS 50% RH SA 55°F DB Modulating water flow through a constant air volume chilled water coil usually causes a rise in space RH because the coil leaving water temperature rises significantly.
  • Page 248 AIR HANDLING SYSTEM CONTROL APPLICATIONS Item On a rise in space temperature to the setpoint, the refrigerant liquid line valve shall open and a relay shall enable the Function compressor to start under it’s controls. Control system energizes when fan is turned When the space temperature drops to a value equal to the on (See FAN SYSTEM START-STOP space temperature setpoint minus a differential, the liquid line...

  • Page 249: Two-Position Control Of Direct Expansion Coil System-Modulating Face And Bypass Damper

    AIR HANDLING SYSTEM CONTROL APPLICATIONS TWO-POSITION CONTROL OF DIRECT EXPANSION COIL SYSTEM— MODULATING FACE AND BYPASS DAMPER Functional Description FACE DAMPER SOLENOID PERCENT OPEN POSITION OPEN TO COMPRESSOR START CIRCUIT CLOSED RELAY COMPRESSOR (MINUTES) CONTROL PROGRAM MINIMUM MINIMUM ON TIME OFF TIME RELAY SUPPLY...
  • Page 250 AIR HANDLING SYSTEM CONTROL APPLICATIONS 3. Air entering the system is from the ECONOMIZER SPECIFICATIONS CYCLE DECISION application. The system operates on 25 percent OA during the cooling cycle. See FAN SYSTEM START-STOP CONTROL. 4. Coil leaving air temperature is 55°F. The DX control system shall be enabled anytime the fan operates.

  • Page 251: Cold Deck System With Zone Damper Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS COLD DECK SYSTEM WITH ZONE DAMPER CONTROL Functional Description AS THE DEMAND FOR COOLING FROM THE ZONE VARIES BETWEEN ZERO AND %, ITS COLD DECK DAMPERS MODULATE BETWEEN CLOSED AND OPEN. AS THE DEMAND FOR COOLING FROM THE ZONE WITH THE GREATEST DEMAND FOR COOLING VARIES BETWEEN AND 100%, THE COLD DECK TEMPERATURE SETPOINT VARIES BETWEEN THE MIXED AIR...
  • Page 252 AIR HANDLING SYSTEM CONTROL APPLICATIONS CONDITIONS FOR SUCCESSFUL OPERATION 1. All zones are connected to load analyzer program to satisfy total load requirements. In larger systems only selected diverse zone loads are connected. Zones that may 95°F DB, 75°F WB be allowed to go out of control (storage rooms, etc.) should not be connected to the load analyzer program.

  • Page 253: Dehumidification Control Processes

    AIR HANDLING SYSTEM CONTROL APPLICATIONS DEHUMIDIFICATION CONTROL PROCESSES The following applications show various methods of CONDITIONS FOR SUCCESSFUL OPERATION controlling dehumidification in air conditioning systems. 1. If a chilled water coil is used, the water supply is cold DIRECT EXPANSION OR WATER enough to produce the lowest required dew point.

  • Page 254: Water Coil Face And Bypass System Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS In the following chart it is assumed that: The following results are obtained: 1. Desired space condition is 76°F DB and a maximum of 50% RH. Item 2. OA condition is 80°F DB and 78°F WB. Explanation 3.
  • Page 255 AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES PSYCHROMETRIC ASPECTS 1. Better dehumidification by having the chilled water flow The space relative humidity is maintained at or below a sequence slightly ahead of the face damper opening to desired value depending on the moisture content of the air keep a low dew point temperature.

  • Page 256: Space Control Of Heating, Free Cooling, And Humidification

    AIR HANDLING SYSTEM CONTROL APPLICATIONS HEATING SYSTEM CONTROL PROCESS SPACE CONTROL OF HEATING, ECONOMIZER (FREE COOLING), AND HUMIDIFICATION Functional Description SPACE COOL CONTROL PROGRAM HEAT N.O. N.C. SUPPLY AIR SPACE TEMPERATURE HEATING SETPOINT DEMAND NORMAL CONTROL PROGRAM SUPPLY AIR SPACE ECONOMIZER DECISION.
  • Page 257 AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES PSYCHROMETRIC ASPECTS 1. The outdoor air quantity is modulated from a minimum In the following charts it is assumed that: to take advantage of free cooling based on space 1. Design outdoor air condition is 0°F DB and 50 percent temperature demand.

  • Page 258: Year-Round System Control Processes

    AIR HANDLING SYSTEM CONTROL APPLICATIONS YEAR-ROUND SYSTEM CONTROL PROCESSES HEATING, COOLING, AND ECONOMIZER Functional Description SPACE TEMPERATURE CHILLED WATER COOLING SETPOINT SETPOINT = FREE COOLING SETPOINT PLUS (1.5 MINIMUM) FREE COOLING SETPOINT HEATING SETPOINT = FREE SETPOINT COOLING SETPOINT MINUS (1.5 MINIMUM) SUPPLY AIR SPACE...
  • Page 259 AIR HANDLING SYSTEM CONTROL APPLICATIONS position for free cooling as required. temperature setpoint. Free cooling demand varies SA temperature The space temperature shall have a free cooling PID loop setpoint. setpoint selected to provide optimum occupant comfort Chilled water cooling demand varies SA temperature.

  • Page 260: Multizone Unit

    AIR HANDLING SYSTEM CONTROL APPLICATIONS MULTIZONE UNIT Functional Description THE ZONE WITH THE GREATEST HEATING DEMAND HALL LOBBY RESETS THE HOT DECK TEMPERATURE FROM DEGREES AS REQUIRED TO EAST OFFICE MAINTAIN ITS SPACE TEMPERATURE DEGREES BELOW SETPOINT. WEST OFFICE THE ZONE WITH THE GREATEST COOLING DEMAND RESETS THE COLD DECK TEMPERATURE FROM PERCENT DEGREES AS REQUIRED TO...
  • Page 261 AIR HANDLING SYSTEM CONTROL APPLICATIONS In the winter, zone space temperature is maintained by mixing FEATURES air from the cold deck with hot deck air (the temperature of which is dictated by the zone with the greatest demand for 1. This application uses zone control of heating and cooling. heating).

  • Page 262: Heating, Cooling, Humidification, And Dehumidification Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS HEATING, COOLING, HUMIDIFICATION, AND DEHUMIDIFICATION CONTROL WITHOUT DEADBANDS Functional Description SPACE N.C. SUPPLY AIR NORMAL TEMPERATURE COOLING SETPOINT DEMAND N.O. REHEAT N.C. SUPPLY PERCENT OPEN COOL COIL LEAVING AIR HUMIDI- CONTROL TEMPERATURE FICATION SETPOINT DEMAND PROGRAM ECONOMIZER DECISION.
  • Page 263 AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES PSYCHROMETRIC ASPECTS 1. The system admits outdoor air for cooling based upon For cooling conditions it is assumed that: the economizer decision. 2. Space relative humidity is maintained by controlling both 1. Design outdoor air condition is 95°F DB and 79°F WB. humidification and dehumidification.
  • Page 264 AIR HANDLING SYSTEM CONTROL APPLICATIONS For heating conditions it is assumed that: The following results are obtained: 1. Design outdoor air condition is 0°F DB and 30 percent Item relative humidity. Explanation 2. RA condition is 76°F DB and 56°F WB. 3.

  • Page 265: Vav Ahu, Water-Side Economizer, Oa Airflow Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS VAV AHU, WATER-SIDE ECONOMIZER, OA AIRFLOW CONTROL Functional Description WARM-UP MODE INVOLVED AT OPTIMUM START TIME IF PERIMETER SPACE TEMPERATURE IS LESS THAN WARM-UP ENDS WHEN RETURN AIR REACHES PROPELLER PERIMETER EXHAUST ZONE WARM-UP MODE SPACE SUPPLY AIR TEMPERATURE SETPOINT...
  • Page 266 AIR HANDLING SYSTEM CONTROL APPLICATIONS SA temperature setpoint switches from cooling CONDITIONS FOR SUCCESSFUL OPERATION to heating value during warm-up modes. 1. Airflow element and transducer must be kept clean and Control program coordinates temperature calibrated. control, ventilation, and fan interlock. 2.
  • Page 267 AIR HANDLING SYSTEM CONTROL APPLICATIONS During unoccupied periods, anytime the top floor west zone building. Reducing the AHU airflow and increasing the OA perimeter space temperature is greater than 77°F and the OA airflow should result in the supply airflow being a significant temperature is less than 72°F and the OA dew point is less than proportion OA.

  • Page 268: Vav Ahu With Return Fan And Flow Tracking Control

    AIR HANDLING SYSTEM CONTROL APPLICATIONS VAV AHU WITH RETURN FAN AND FLOW TRACKING CONTROL Functional Description ZERO CALIBRATION EXHAUST EXHAUST FAN "ON" DIFFERENTIAL SPACE PRESSURIZATION 2700 DIFFERENTIAL 1300 9600 CONTROL PERCENT PROGRAM LOAD 13610 NORMAL NORMAL PERCENT LOAD -0.24 -0.24 CONTROL ECONOMIZER DECISION.
  • Page 269 AIR HANDLING SYSTEM CONTROL APPLICATIONS Mixed air temperature is for operator SPECIFICATIONS information. See FAN SYSTEM START-STOP CONTROL. SA temperature setpoint is reset based upon OA temperature. Anytime the supply fan runs, the return fan shall start and 20-22 Mixing dampers modulate for free cooling. the control system shall be enabled.
  • Page 270 AIR HANDLING SYSTEM CONTROL APPLICATIONS The following results are obtained: PSYCHROMETRIC ASPECTS Item In the following chart it is assumed that: Explanation 1. Outdoor air condition is 95°F DB and 79°F WB. 2. RA condition is 75°F DB and 57.5°F WB. RA mixes with 20 percent (minimum 3.

  • Page 271: Ashrae Psychrometric Charts

    AIR HANDLING SYSTEM CONTROL APPLICATIONS ASHRAE PSYCHROMETRIC CHARTS ASHRAE Psychrometric Chart No. 1. ENGINEERING CMANUAL OF AUTOMATION CONTROL...
  • Page 272 AIR HANDLING SYSTEM CONTROL APPLICATIONS ASHRAE Psychrometric Chart No. 2. ENGINEERING CMANUAL OF AUTOMATION CONTROL...

  • Page 273: Building Airflow System Control Applications

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Building Airflow System Control Applications Contents Introduction ......................265 Definitions ......................265 Airflow Control Fundamentals ......................267 Need For Airflow Control ..............267 What Is Airflow Control ................ 267 Types Of Airflow Systems ..............267 Variable Air Volume .................
  • Page 274 BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Airflow Control Applications ......................281 Central Fan System Control ..............281 Supply Fan Control For VAV Systems ..........281 General ..................281 Duct Static High-Limit Control ............. 282 Return Fan Control For VAV Systems ..........283 Open Loop Control ..............

  • Page 275: Introduction

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS INTRODUCTION This section explains the need for airflow control in a central contaminated air does not migrate to unwanted areas. Basic types of space pressure control are static pressure, airflow air handling system, describes the various means of airflow measurement, provides fan and duct characteristics, and tracking, and constant airflow.
  • Page 276 BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Static pressure: The pressure created by air (whether in motion • Peak Velocity—The greatest air velocity occurring in an or not) confined in an enclosed area such as a duct or increment of a duct cross-section. Peak velocity is building due to its potential energy.

  • Page 277: Airflow Control Fundamentals

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS AIRFLOW CONTROL FUNDAMENTALS NEED FOR AIRFLOW CONTROL Single duct, variable air volume-induction Single duct, variable air volume-fan powered Constant fan, intermittent fan Proper control of airflow is important to physiological principles including thermal and air quality considerations. Air Dual-Path Systems: distribution systems, containment pressurization, exhaust Dual duct, single fan-constant air volume...

  • Page 278: Constant Air Volume

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS are fully open, the outdoor air volume will be 5,000 cfm. To CONSTANT AIR VOLUME increase outdoor air volume, it is necessary to modulate the return air damper. This airflow control provides a slightly positive A Constant Air Volume (CAV) system controls space building static pressure with respect to outdoor air in a properly temperature by altering the supply air temperature while...

  • Page 279: Variable Versus Constant Air Volume

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS The dampers may be set at design load as for a constant air VARIABLE VERSUS CONSTANT AIR VOLUME volume system, and the filter inlet pressure noted. Then the noted filter inlet negative pressure can be maintained by Sizing of central equipment is based on climate conditions modulating the return air damper.

  • Page 280: Pressurization

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS OUTDOOR RETURN RELIEF (OR) AIR FAN 35,000 CFM CONSTANT REMOTE EXHAUST FAN SUPPLY AIR FAN 2,000 CFM 40,000 CFM CONSTANT FILTER COOLING COIL OUTDOOR AIR 5,000 CFM EXFILTRATION MINIMUM 3,000 CFM CAV AIR TERMINAL INTERIOR ZONES UNITS REHEAT COILS...

  • Page 281: Containment Pressurization

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Rearranging the equation to calculate the differential pressure Where: results in the following: Pw = Wind pressure in inches of water column (in. wc) ( F - F DA ) x [2 x (W – D Cw = Dimensionless pressure coefficient ranging ∆p = Kd x W x A...

  • Page 282: Characteristics Of Fans And Fan Laws

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS expelled from the fan housing. Some centrifugal fan NORMAL STACK EFFECT REVERSE STACK EFFECT designs are differentiated by the inclination of the blades. Each blade design has a peculiar advantage: NEUTRAL PLANE NOTE: ARROWS INDICATE DIRECTION OF AIR MOVEMENT C5153 Fig.

  • Page 283: Fan Performance Terms

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Table 1. Fan Laws noise. They work up to a maximum static pressure of 3 in. wc. When When — Vaneaxial fans are basically tubeaxial fans with Speed Changes Density Changes Variable straightening vanes added to avoid spiraling air Varies DIRECT with Does Not Change patterns.

  • Page 284: Duct System Curves

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS DUCT SYSTEM CURVES The fan curves shown are for a fan running at two speeds, 400 rpm and 600 rpm. Also, two system curves, A and B, have been plotted. The intersection of the system curves and the Fan unit duct systems have a certain amount of friction, or fan curves indicate the quantities of air the fan will provide.
  • Page 285 BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS pressure are measured in inches of water column (in. wc). Total In a theoretical duct system without friction losses, the total pressure is the sum of the static and velocity pressure and, pressure is constant along the entire duct (Fig. 9). The static therefore, is also measured in inches of water column.

  • Page 286: Effects Of Fittings

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS The size of a duct required to transport a given quantity of An actual duct system (Fig. 10) encounters a phenomenon air depends on the air pressure available to overcome the friction called pressure loss or friction loss. Pressure loss is caused by loss.

  • Page 287: Effects Of Dampers

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS EFFECTS OF DAMPERS MEASUREMENT OF AIRFLOW IN DUCTS Dampers are often used in ducts for mixing, for face and GENERAL bypass control of a coil, for volume control, or for numerous other air volume controls. Figure 12 shows the velocity profile Total pressure and static pressure can be measured directly;...
  • Page 288 BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS The following are guidelines for using pitot tubes: PITOT TUBE SENSORS 1. A pitot tube can be used to measure either static or total pressure. A pitot tube measures both total pressure and static pressure. 2.

  • Page 289: Pitot Tube Sensors

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS An analysis of the accuracy of the pitot tube at 800 fpm EQUAL CONCENTRIC follows: AREAS Velocity Pressure: VP = (800 ÷ 4005) = 0.0399 in. wc Accuracy: CENTERS High OF AREA OF THE EQUAL 0.0399 in.

  • Page 290: Airflow Measuring Devices

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS AIRFLOW MEASURING DEVICES Various devices for measuring airflow are available. Figure 19 shows a flow measuring station that consists of: — An air straightener section to eliminate swirl type airflow and help normalize the velocity profile —...

  • Page 291: Airflow Control Applications

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Figure 22 illustrates an airflow pickup station typically used VAV BOX in the primary air inlet to a VAV air terminal unit. The pickup INLET station consists of two tubes that measure differential pressure. SLEEVE This measurement can be used in an airflow calculation.

  • Page 292: Duct Static High-Limit Control

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS SUPPLY Duct Static High-Limit Control High-limit control of the supply fan duct static should be used to prevent damage to ducts, dampers, and air terminal DUCT STATIC units (Fig. 25). Damage can occur when fire or smoke dampers PRESSURE SENSOR TERMINAL UNITS in the supply duct close or ducts are blocked, especially during...

  • Page 293: Return Fan Control For Vav Systems

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Direct Building Static Control RETURN FAN CONTROL FOR VAV SYSTEMS In direct building static control, the return fan responds Return fan operation influences building (space) directly to the building space static pressure referenced to the pressurization and minimum outdoor air.

  • Page 294: Airflow Tracking Control

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS the tracking control system for constant building and space RETURN pressurization. If controlling the space returns by space pressurization, building and space pressurization remain constant regardless of exhaust fan operation. FLOW MEASURING RELIEF FAN CONTROL FOR VAV SYSTEMS STATIONS CONTROLLER Relief fans are exhaust fans for the central air handling...

  • Page 295: Return Damper Control For Vav Systems

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS RETURN DAMPER CONTROL FOR VAV SYSTEMS SUPPLY In systems having a return fan, when the mixed air control cycle is not operating, the outdoor air (or maximum outdoor air) and relief dampers are closed and the return damper remains fully open.

  • Page 296: Sequencing Fan Control

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Vaneaxial fan sequencing is also decided by total supply flow, SEQUENCING FAN CONTROL but the operating fan(s) is modulated to minimum output when the next fan is turned on. This sequence is used to avoid a stall VAV systems with multiple fans can use fan sequencing.

  • Page 297: Exhaust System Control

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS OUTDOOR SUPPLY INDOOR RETURN RETURN STATIC STATIC PRESSURE PRESSURE SENSOR SENSORS CONTROLLER CONTROLLERS DUCT STATIC REFERENCE AIRFLOW STATIC SENSOR (2) C2664 C2665 Fig. 41. Control of Return Fan in Zone Airflow Control. Fig. 40. Control of Return Dampers in Zone Airflow Control.

  • Page 298: Multiple Fan Systems

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Essentially, the increase of outdoor air above that required to General exhausts route contaminants into common ducts maintain building pressurization is done the same way as mixed which connect to a common exhaust fan. If the airflow is air control except outdoor air is controlled by flow rather than manually balanced, the exhaust fan runs at a fixed level.
  • Page 299 BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS The bypass hood limits face velocity to about twice the full sash open face velocity which may be acceptable. However, DAMPER AND ACTUATOR OR AIR VALVE conditioned air is always exhausted making energy savings improbable. The auxiliary air hood is a bypass type with a supply air diffuser located in front of and above the sash.

  • Page 300: Laboratory Pressurization

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS If future flexibility and changing lab configurations are LABORATORY PRESSURIZATION important considerations, then flow sensor location, duct size, supply airflow rate, and control system design should all include Constant supply airflow often is not capable of constant space capability to be modified in the future.
  • Page 301 BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Figure 49 shows a similar example of negative space When a door is opened, the space pressure control responds pressurization utilizing direct pressure control. If the airflow by reducing the supply airflow to zero and/or increasing general through the hood is 1000 cfm and the pressure control reduces exhaust flow.

  • Page 302: References

    BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS REFERENCES The following references were useful in preparing this section Engineering Fundamentals of Fans and Roof Ventilators Plant Engineering Library on Building Airflow System Control Applications. Selected material was included from: Technical Publishing* 1301 S. Grove Avenue Design of Smoke Control Systems for Buildings P.

  • Page 303: Chiller, Boiler, And Distribution System Control Applications

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Chiller, Boiler and Distribution System Control Applications Contents Introduction ......................297 Abbreviations ......................297 Definitions ......................297 S y m b o l s ......................298 Chiller System Contr ......................299 Introduction ..................299 Vapor-Compression Refrigeration ............
  • Page 304 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Cooling Tower And Condenser Water Control ........318 Cooling Tower Performance Characteristics ........318 Cooling Tower Capacity Control ............318 On-Off Cooling Tower Fan Control ..........319 Two-Speed Cooling Tower Fan Control ........319 Variable Speed Cooling Tower Fan Control ........
  • Page 305 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Methods Of Controlling Distribution Systems ........350 Three-Way Coil Bypass And Two-Way Valve Control ..... 350 Valve Selection Factors ..............350 Flow And Pressure Control Solutions ..........350 Single Pump, Pressure Bypass, Direct Return ......351 Valve Location and Sizing ............
  • Page 306 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Control Principles For Steam Heating Devices ........374 General ................... 374 Modulating Steam Coil Performance ..........374 Oversized Valve ................374 Correctly Sized Valve ..............375 Supply And Return Main Pressures ..........375 System Design Considerations For Steam Coils ......

  • Page 307: Introduction

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS INTRODUCTION This section provides descriptions of and control information digital controllers or by all digital controller programmers. Many about water chillers, cooling towers, hot water boilers, steam solutions are portrayed as they may be specified to be displayed boilers, and water, steam, and district heating distribution systems.

  • Page 308: Symbols

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS • Refrigerant head–The pressure difference between Secondary - Thermal consumption water elements such as AHU compressor suction and discharge pressures or the coils. Thermal consumption air elements such as VAV temperature difference between condensing and boxes.

  • Page 309: Chiller System Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS CHILLER SYSTEM CONTROL INTRODUCTION Chiller types are classified by type of refrigeration cycle: vapor- compression or absorption. In addition, those using the vapor- compression cycle are referred to by the type of compressor: A chilled water system consists of a refrigeration system (water centrifugal or positive displacement.

  • Page 310: Centrifugal Compressor

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS EXPANSION VALVE CHILLED WATER HOT GAS LINE HEAD (HIGHSIDE) CONDENSER PRESSURE WATER CHILLED WATER EVAPORATOR (HEAT EXCHANGER) CONDENSER COMPRESSOR WATER SUCTION (LOWSIDE) SUCTION LINE SENSING PRESSURE CONDENSER BULB (HEAT EXCHANGER) LIQUID LINE C2685 RECIEVER Fig.

  • Page 311: Reciprocating Compressor

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS IMPELLER Reciprocating chiller capacity is controlled in stages (steps). VOLUTE PREROTATION VANES Methods of capacity control include the following: INLET – Unloading cylinders – On-off cycling of multiple compressors – Hot-gas bypass – Hot-gas through evaporator Cylinder unloading or multiple compressor on-off cycling is sequenced by automatic controls.

  • Page 312: Absorption Chiller

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS In the absorber (Fig. 7) the absorbent, also called strong Figure 8 is a typical water-lithium bromide absorption cycle absorbent at this point, assimilates the refrigerant vapor when chiller. Lithium bromide is the absorbent and water is the sprayed through it.

  • Page 313: Chiller Control Requirements

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Some absorption chillers require the condensing water be temperature to reset the supply setpoint upward at light loads to kept constant at the design temperature. To improve seasonal reduce the supply to return chilled water temperature difference. operating efficiency some designs accept condensing water temperatures below design down to 45F.

  • Page 314: Chilled Water Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS It is desirable for the BMCS to have access to the chiller- 3. Using rejected heat when a heating load exists at the same controller database, but due to the cost and complexity of a custom time as a cooling load.

  • Page 315: Single Centrifugal Chiller Control Application

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS SINGLE CENTRIFUGAL CHILLER CONTROL APPLICATION FUNCTIONAL DESCRIPTION CHILLED WATER SETPOINT TOWER CONTROL CHILLER SYSTEM CONTROL MINIMUM CURRENT MAXIMUM AUTO CHILLER 1 ENABLED AUTO NORMAL BY REMOTE OPERATING STATUS PERCENT LOAD ALARM CONTROLS MODE STATUS CURRENT CONTROL...
  • Page 316 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS CHILLED WATER SYSTEM CHILLED WATER SETPOINT MINIMUM CURRENT MAXIMUM ANYTIME ANY AHU VALVE IS OPEN GREATER THAN % FOR MORE THAN 1545 MINUTES AND THE TIME IS BEFORE THE CHILLED WATER PUMP STARTS AND ENABLES THE CHILLER SYSTEM CONTROLS.
  • Page 317 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Anytime chilled water flow is proven via a chilled water pump The temperature sensor in the common chilled water supply current sensing relay, the chiller controls shall be enabled to is the primary capacity control. The temperature low limit operate under factory controls, subject to a chiller software ON- control prevents the outlet temperature of each chiller from OFF-AUTO function (chilled water flow must still be proven...

  • Page 318: Multiple Chiller System Control Applications

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS When two chillers of equal size and similar characteristics are Curves A and B in Figure 13 illustrate that for the chillers used, the point at which the second chiller is activated is usually operating at design condition with a 43F temperature differential when the first chiller reaches 100 percent load.

  • Page 319: Dual Centrifugal Chillers Control Application

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS DUAL CENTRIFUGAL CHILLERS CONTROL APPLICATION FUNCTIONAL DESCRIPTION CHILLED WATER SETPOINT MORNING LEAD CHILLER SELECTOR FLOW & MAXIMUM MINIMUM CURRENT PRESSURE 1 = CHILLER 1 LEADS CONTROL 2 = CHILLER 2 LEADS 3 = ALTERNATES CHILLER CONTROL CONTROL...
  • Page 320 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS CHILLED WATER SYSTEM CHILLED WATER SETPOINT MINIMUM CURRENT MAXIMUM ANYTIME ANY AHU VALVE IS OPEN GREATER THAN % FOR MORE THAN MINUTES AND THE TIME IS BEFORE , THE LEAD CHILLED WATER PUMP STARTS. 1545 ANYTIME THE LEAD CHILLER HAS RUN LONGER THAN MINUTES, THE CHILLED...

  • Page 321: Similar Multiple Centrifugal Chillers Control Applications

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS 4 minutes, the chilled water pump with the longest “on” duration NOTE: When using two-way AHU valves with this since the last start shall stop and remain off at least 30 minutes. coupled chiller configuration, exercise care in optimizing the chilled water temperature.
  • Page 322 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS SYSTEM DESCRIPTION SOFTWARE PARTITIONING Figure 16 shows a typical “decoupled” multiple chiller From an operational and control perspective, the physical system. Each chiller has a (primary) dedicated constant speed configuration of chiller plant digital controllers is usually pump selected to produce the chiller design flow through the transparent.

  • Page 323: Multiple Centrifugal Chiller Sequencing

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS COMMUNICATION WITH CONDENSER PUMP/ CHILLER FAN AND TOWER ISOLATION CONTROLLERS VALVE CONTROL (TYPICAL) COOLING TOWER STAGING & LOADING CONTROLLER 85.0 M10501 Fig. 18. Digital control of Sequenced Cooling Towers. Multiple Centrifugal Chiller Sequencing FUNCTIONAL DESCRIPTION % SPEED 45.0...
  • Page 324 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS CHILLER SEQUENCING CHILLED WATER PUMP OFF LONGEST IS STARTED UPON SECONDARY SYSTEM DEMAND FOR CHILLED WATER. CHILLED WATER PUMPS ARE SEQUENTIALLY STAGED ON ANYTIME THE DECOUPLER TEMPERATURE EXCEEDS THE PRIMARY SUPPLY WATER TEMPERATURE GREATER THAN DEGREES FOR GREATER THAN MINUTES, BUT WITH NO LESS THAN MINUTES BETWEEN STARTS.

  • Page 325: Dissimilar Multiple Centrifugal Chillers Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS chilled water temperature and the entering condenser water DISSIMILAR MULTIPLE CENTRIFUGAL temperature are frequently optimized and chiller capacity varies CHILLERS CONTROL with changes in either temperature, the per-chiller load expected should be dynamically modified based upon When a multiple chiller system consists of chillers that are manufacturers data regarding these variations.

  • Page 326: Chiller Pump Optimization

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS HIGH PRESSURE STEAM SUPPLY PRV SET APPROX. TO INLET VANE 10 PSI ACTUATOR SENSOR IN CHILLED TURBINE-DRIVEN CENTRIFUGAL WATER BACK CHILLER SUPPLY PRESSURE COMPRESSOR ABSORPTION TURBINE CHILLER RELAY CENTRIFUGAL CHILLER PRESSURE ABSORPTION/ CONTROLLER COMBINATION SELECTOR SWITCH...

  • Page 327: Thermal Storage Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS – Charging Cycle: Valves V D and V I are closed and V C THERMAL STORAGE CONTROL is controlled by T 6 to maintain the flow rate at F 1 . Pump P 2 is off. T 1 controls chiller capacity to maintain 40F GENERAL CHWS temperature.

  • Page 328: Cooling Tower And Condenser Water Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS COOLING TOWER AND CONDENSER TEMPERATURE RANGE, °F WATER CONTROL COOLING TOWER PERFORMANCE SUMMER DESIGN CHARACTERISTICS CONDITIONS: ENTERING WATER, 95F LEAVING WATER, 85F The cooling tower dissipates the heat collected from the OA WET BULB, 78F building by the chiller and chilled water system by cooling the condenser water.

  • Page 329: On-Off Cooling Tower Fan Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS On-Off Cooling Tower Fan Control FANS ON IN SEQUENCE ON TEMPERATURE RISE On-off fan control is satisfactory where the load is always high and where several towers are banked together for multistage control. COOLING TOWER On-off cooling tower control with a single setpoint for a PI...

  • Page 330: Variable Speed Cooling Tower Fan Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Specification: If required, use a valve control method similar to the one Condenser water temperature setpoint shall be equal to the OA used for single speed fan control. WB plus 7F, or the minimum temperature acceptable to the chiller, whichever is higher.
  • Page 331 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS LOW LOAD CONDENSER WATER TEMPERATURE CONTROL: TOWER FAN STOPS, VARIABLE SPEED CONTROL IS DISABLED, AND ON-OFF FAN CONTROL IS ENABLED IF LOAD DROPS AFTER FAN DROPS TO SPEED. ON-OFF CONTROL: FAN RESTARTS IF TEMPERATURE RISES TO SETPOINT PLUS DEGREES.

  • Page 332: Dual Cooling Tower Variable Speed Fan Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS DUAL COOLING TOWER VARIABLE SPEED FAN CONTROL Functional Description TOWER ISOLATION SELECTOR COOLING COOLING 0 = NO TOWERS ISOLATED TOWER 1 TOWER 2 1 = TOWER 1 ISOLATED 2 = TOWER 2 ISOLATED SETPOINTS/ SEQUENCES TOWER FAN CONDENSER WATER...
  • Page 333 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS than 85F. During tower free cooling mode, the setpoint shall be Features determined by the tower free cooling control module. The OA 1. Precise PI condenser water control above minimum load. WB shall be calculated from OA RH (the RH sensor shall be of 2.
  • Page 334 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS minutes. The operating tower valves shall modulate to maintain If both fans are off and the water temperature drops to the valve the above noted valve control setpoint at anytime regardless of control setpoint plus 1 degree F, the valves of Tower 1 shall position fan operation.

  • Page 335: Chiller Heat Recovery System

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS If chilled water reset is used, stop the reset action when the CHILLER HEAT RECOVERY SYSTEM cooling tower is off. This provides recovery system heat to a lower outdoor temperature before it is necessary to use fuel for heating. A chiller heat recovery system uses heat rejected from a chiller to satisfy a simultaneous heating load.
  • Page 336 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS In Figure 34, condenser and chilled water flows are diverted from the chiller to a heat exchanger. COOLING TOWER TOWER HEATER COOLING (OPTIONAL) TOWER NOTE: CONDENSER INDICATES NO FLOW WATER PUMP TOWER HEATER (OPTIONAL) CONDENSER CONDENSER...

  • Page 337: Tower Free Cooling, Dual Chillers

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS TOWER FREE COOLING, DUAL CHILLERS FUNCTIONAL DESCRIPTION FREE COOLING OA WB SETPOINT = CHILLED WATER 10.0 TEMPERATURE SETPOINT MINUS DEGREES OUTSIDE CHILLER/ FREE COOLING SETPOINT DRY BULB CHILLER/ FREE CHILLER/ FREE COOLING COOLING CURRENT MODE CURRENT MODE COOLING...
  • Page 338 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Condenser water: Features During the condenser water temperature pull-down period, 1. Production of chilled water via condenser water and a the condenser entering water temperature shall be prevented HX in lieu of chiller operation. from dropping below the minimum acceptable value by 2.

  • Page 339: Boiler System Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS BOILER SYSTEM CONTROL INTRODUCTION Steel boilers come in a large variety of configurations. They are factory assembled and welded and shipped as a unit. Figure 38 illustrates a firetube boiler. The fire and flue gases are A boiler is a closed vessel intended to heat water and produce substantially surrounded by water.

  • Page 340: Electric Boilers

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Some modular boilers have very small storage capacity and very rapid heat transfer so water flow must be proven before the burner is started. SIDE FLUE GAS OUTLET CLOSE-OFF BLOWER HEAT ASSEMBLY EXCHANGER GENERATING CHAMBER FLUE GAS...

  • Page 341: Combustion In Boilers

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS – Steam or air atomizing burners use high pressure air or COMBUSTION IN BOILERS 25 psig steam to break up the oil into fine droplets. PRINCIPLES OF COMBUSTION For modulating or high/low flame control applications the rotary or steam/air atomizing burners are most common.

  • Page 342: Boiler Controls

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS BOILER CONTROLS PILOT STEAM PILOT VALVE PRESSURE PRESSURE MANUAL REGULATOR SENSOR VALVE BOILER OUTPUT CONTROL SUPPLY TO FLAME There are three ways to control the output of a commercial MODULATING SAFEGUARD VALVE boiler: SYSTEM CONTROL LINKAGE...

  • Page 343: Flame Safeguard Instrumentation

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS OPERATING CONTROLLER HI LIMIT POWER FLOW SHUTOFF PRESSURE MAIN BURNER VALVE REGULATOR VALVE PILOTSTAT THERMO- AUTOMATIC COUPLE VALVE PILOT PILOT BURNER M15050 GAS LINE Fig. 45. Simple Flame Safeguard for a Gas Furnace. APPLICATION OF BOILER CONTROLS Figure 46 shows how flame safeguard controls are integrated with combustion controls on a small oil fired steam boiler.

  • Page 344: Multiple Boiler Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS MULTIPLE BOILER SYSTEMS EXPANSION TANK MAKE-UP GENERAL WATER ZONE MANUAL AIR VENT Basic boiler connections for a three-zone hot water system ZONE are shown in Figure 47. In this system, two boilers are connected in parallel.

  • Page 345: Dual Boiler Plant Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS DUAL BOILER PLANT CONTROL FUNCTIONAL DESCRIPTION- HEATING SYSTEM ON-OFF-AUTO SELECTOR LOW LIMIT SET POINT BOILER LEAD SELECTOR AUTO BOILER BOILER BOILER SYSTEM SYSTEM PUMP P1 BOILER -1 ON-OFF-AUTO OFF-AUTO SELECTOR SELECTOR AUTO AUTO OUTSIDE AIR TEMPERATURE BOILER...
  • Page 346 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Specification Features The heating plant shall operate under automatic control anytime 1. Full flow through operating boilers. the secondary pump ON-OFF-AUTO function is not “OFF”, 2. Minimum temperature limit on boiler entering water.

  • Page 347: Modular Boilers

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS During boiler operation, a three way blending valve shall Boilers that are off have no flow and are allowed to cool. position to place the boiler flow in a recirculating mode until Each boiler that is on operates at or near full capacity. Avoiding the water entering the boiler exceeds a low limit value of 145F, intermittent operation prevents losses up the stack or to the surrounding area when the boiler is off.

  • Page 348: Control Requirements For Water Distribution Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS EXPANSION TANK PUMP MAKE-UP SUPPLY WATER PRESSURE REGULATING VALVE HEAT/ HEAT/ HEAT/ SEPARATION COOL COOL COOL COIL COIL COIL HEAT/ COOL SOURCE RETURN M15053 Fig. 51. Typical Water Distribution System. The expansion tank is charged with compressed air to place CONTROL REQUIREMENTS FOR WATER the system under the minimum pressure required at the inlet to DISTRIBUTION SYSTEMS...

  • Page 349: Pump Performance

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Table 2. Characteristics of Centrifugal Pump Types. Motor Impeller No. of Motor Mounting Type Type Impellers Casing Connection Position Circulator Single Volute Flexible- Horizontal suction coupled Close-coupled, Single One or two Volute Close- Horizontal end suction suction...

  • Page 350: Pump Power Requirements

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Pump Power Requirements Pump Performance Curves The pump curve in Figure 53 is part of a family of curves for Commercial pumps have performance curves showing the a pump. Each curve of the family represents a different size following data for a given pump speed: impeller used with the pump at a specified rpm.

  • Page 351: Pump Affinity Laws

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Figure 55 illustrates a pump fitted with a 6-1/2 inch impeller, Table 3. Pump Affinity Laws. operating at 45 ft of head, and delivering 65 gpm of water. Specific Impeller Gravity Correct Multiply Water hp = 65 gpm x 45 ft x 1.0/3960 Diameter Speed...

  • Page 352: Matching Pumps To Water Distribution Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS MATCHING PUMPS TO WATER DISTRIBUTION SYSTEMS System Curves FLOW AT FULL LOAD The pump curves and affinity laws are used to select a pump or pumps for a particular application. The first step is to establish a system head curve.
  • Page 353 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS 9 1/2" BALANCED OPERATING POINT WITH 9 1/2" IMPELLER DESIGN OPERATING POINT 8 3/4" OPERATION WITH 8 3/4" IMPELLER 8" 7 1/4" 15 HP 12 HP 10 HP SYSTEM CURVE 7 1/2 HP 5 HP C1055-1 CAPACITY IN GALLONS PER MINUTE...

  • Page 354: Variable Speed Pumps

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS VARIABLE SPEED PUMPS TYPICAL RANGE OF PERFORMANCE FOR VARIABLE SPEED PUMP From the pump affinity laws (Table 3), pump horsepower decreases by the cube of the decreased speed, and flow decreases linearly with speed; so at 80 percent flow, the horsepower is down to nearly 50 percent (80 percent cubed).

  • Page 355: Pumps Applied To Open Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Table 4. Variable Speed Pump Relationships Load (percent) Condition Flow (gpm) 0.80 x 500 = 400 0.60 x 500 = 300 0.40 x 500 = 200 Speed (rpm) 1750 0.80 x 1750 = 1400 0.60 x 1750 = 1050 0.40 x 1750 = 700 Total Head (ft)

  • Page 356: Operation

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS the lag pump stop setpoint should have a significant margin of CONTROL VALVE(S) safety incorporated. The lag pump start setpoint should be PIPING controlled by a differential pressure controller and have the software requirement that one control valve be full open for LOAD HEAT four minutes before starting.

  • Page 357: Dual Pump Curves

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS through the system (with the control valves full open) at various CONTROL VALVE(S) flow rates. The pump curve shows the pump output pressure at various flow rates. Flow always follows the pump curve. SERIES PUMPS SUPPLY PIPING...

  • Page 358: Direct Vs Reverse Return Piping Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS As flow through the system is reduced, a new system curve COIL, is established. See the 6 gpm curve in Figure 69. When the PUMP 1750 RPM SUPPLY/ CURVE RETURN flow is reduced, the new head loss in source and supply and SYSTEM CURVE PIPING 0.74FT return piping can be calculated using the formula:...

  • Page 359: Coupled Vs Decoupled Piping Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The Figure 70 supply piping runs out to the coils decreasing Supply piping is the same for a reverse return system (Fig. in size between AHU 1, 2, 3, 4, 5, and 6. The return lines 71) as for the direct return system (Fig.

  • Page 360: Methods Of Controlling Distribution Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS — Piping Cost. Costs are higher for three-way valves than METHODS OF CONTROLLING two-way valves, especially where limited space is DISTRIBUTION SYSTEMS available for piping (such as in room air conditioning units and unit ventilators). In addition, balancing cocks There are several methods for controlling pressure and flow in must be installed and adjusted in the bypass line.

  • Page 361: Single Pump, Pressure Bypass, Direct Return

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The examples in this section on Flow And Pressure Control through the chiller (1080 gpm), the chiller and equipment room Solutions use a distribution system that has six equal loads piping drops are 81 percent of design (90 percent squared). (coils) as shown in Figure 73.

  • Page 362: Single Pump, Pressure Bypass, Reverse Return

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS TOP NUMBERS = FULL FLOW NUMBERS IN CIRCLES = GAUGE PRESSURES BOTTOM NUMBERS = HALF FLOW, EACH COIL (PUMP INLET = ZERO FOR SIMPLICITY) PD = PRESSURE DROP 6' DROP TOTAL 48.5 CHILLER HEAT/ 200 GPM HEAT/...
  • Page 363 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The greatest change at the sensor provides the most tolerant Single Pump, Pressure Bypass, Reverse Return and robust control. For this reason the sensor is located, not across the chiller with a setpoint of 9.6 ft, but across Coil 1 A reverse return system analysis equivalent to the direct return where the greatest differential pressure change exists (28 ft at analysis of Figure 74 would show that at half flow and no...

  • Page 364: Dual Pumps, Dual Chillers, Pressure Bypass

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS With digital controls, the differential pressure setpoint offset Dual Pumps, Dual Chillers, Pressure Bypass, adjustment when only one chiller/pump is operating is handled 90 Percent Chiller Flow, Direct Return by a software routine (dual chiller/pump setpoint plus 4.8 ft.) invoked anytime only one pump and one chiller are operating.

  • Page 365: Variable Speed Pump Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS SUPPLY HEAT/ HEAT/ HEAT/ HEAT/ HEAT/ HEAT/ COOL COOL COOL COOL COOL COOL COIL COIL COIL COIL COIL COIL RETURN M15065 Fig. 78. High AHU Valve Differential Pressure Control In these examples, the design differential pressure across Load operation.
  • Page 366 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS VARIABLE SPEED DRIVE HEAT/ HEAT/ HEAT/ HEAT/ HEAT/ HEAT/ COOL COOL COOL COOL COOL COOL COIL COIL COIL COIL COIL COIL M15066 Fig. 79. Variable Speed Pump Control AHU 1 requires a 28 foot differential pressure (8 feet for the OPERATING POINT @ FULL LOAD 400 GPM &...

  • Page 367: Pump Speed Valve Position Load Reset

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS No pump head control example, so far, takes advantage of FULL LOAD both the variable speed pump and a digital control system. The OPERATING POINT digital control system VSD control algorithm adjusts the PUMP CURVE differential pressure setpoint based on the demands of all the @ 1750 RPM...
  • Page 368 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS MULTI-BUILDING VARIABLE FLOW CONTROL CONCEPTS INSET (ONE PER BUILDING) MANUAL AHU CONTROL PERCENT VALVES V2 OPEN VALUE (TYPICAL) MANUAL AUTO SELECTOR AUTO VALVE V-1 CURRENT PERCENT SETPOINT OPEN BLDG. A CONTROL RETURN RETURN VALVE VI BLDG.

  • Page 369: Balancing Valve Considerations

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Each building is provided with a “choke” valve (V-1), and a 2. Cool-down periods for other than AHUs 1 and 2 will be load reset loop to maintain water pressure within the building, extended.

  • Page 370: Decoupled Variable Speed Pump Control, Reverse Return

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The control objectives for a hot water distribution system Minimum BHP x 0.746 kW/bhp x 3 ,412 Btu/kW providing space heating are: flow (gpm) 8.33 lb/gal x 60 min/hr x ∆T Where: 1. Provide adequate hot water flow to all heating units. 2.

  • Page 371: Hot Water Piping Arrangements

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS LOAD LOAD SINGLE INPUT CONTROL HOT WATER STEAM SENSOR LOAD SUPPLY LOAD FLOW DIVERTING FITTINGS STEAM TO SUPPLY HOT WATER CONDENSATE CONVERTER RETURN RETURN LOAD LOAD C2831 PUMP Fig. 83. Constant Temperature Hot Water Converter Control.

  • Page 372: Primary-Secondary Pumping

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS A converter (heat exchanger) shown in Figure 89 can be used EXPANSION TANK in large or high rise buildings to reduce the zone temperature/ pressure requirements from those of the mains. LOAD LOAD LOAD LOAD LOAD...

  • Page 373: Supply Hot Water Temperature Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS 75% FLOW REDUCTION RATED OUTPUT Supply Hot Water Temperature Control With Flow Control Combining flow control with supply water temperature reset from outdoor air temperature or any other measurement of load results in effective control. Figure 93 shows output of a typical air heating coil with flow and supply water temperature control.
  • Page 374 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Another digital control function is steam valve demand FROM ADDITIONAL limiting. Water systems are usually balanced such that if all PANELS water valves are full open, design flow is delivered to all load coils (unless diversity is used).
  • Page 375 CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Dual Valve Converter, Demand Limiting, Setpoint Shift Functional Description H.W. SETPOINT SEQUENCE OUTSIDE WARM-UP OCCUPIED OPERATION PERIODS PERIODS OUTSIDE AIR TEMPERATURE SETPOINT RESET SCHEDULE PERCENT OPEN 1/3 CAPACITY PERCENT OPEN PUMP 2/3 CAPACITY START POINT AUTO CONVERTOR C-1...

  • Page 376: Three-Way Valve

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS With both valves operating, as the total demand drops below Hot Water Control Method Selection the capacity of the large valve for five minutes, the small valve shall close. With the large valve operating, as the demand drops Supply water temperature control is suitable for controlling below the capacity of the small valve for five minutes, the large the heat delivery from a heat exchanger or a secondary water...

  • Page 377: System Objectives

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The same equation expressed in MMBtuh (million Btu per DUAL TEMPERATURE SYSTEMS hour) is: Figure 99 shows a typical arrangement where the same pipes 2000 gpm = MMBtuh x carry hot water for heating or chilled water for cooling to the TD W same terminal units.

  • Page 378: Steam Distribution Systems And Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Figure 100 uses three-way valves V1 through V4 operating are not considered in this section. Not all of Objectives 1 through two position to accomplish zone changeover. In large systems, 7 may apply to any given distribution system. two-way valves may offer a tighter isolation of the hot and chilled water circuits than three-way valves.

  • Page 379: Steam System Heat Characteristics

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS STEAM SYSTEM HEAT CHARACTERISTICS STEAM QUALITY Figure 101 shows the characteristics of one pound of steam Steam tables generally show properties of dry-saturated as it travels through a steam heating system. steam. Dry-saturated steam has no entrained moisture and is at the boiling point for the given pressure.

  • Page 380: Steam Distribution Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The float and thermostatic trap (Fig. 104) can handle large STEAM DISTRIBUTION SYSTEMS amounts of air and condensate and is commonly used on steam coils in air handling systems. In this trap, the thermostatic STEAM PIPING MAINS element passes air until it senses steam at which time it closes the valve.

  • Page 381: Pressure Reducing Valve Station

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The disc trap (Fig. 106) is a device with only one moving part. As steam in the chamber above the disc cools and condenses, the disc snaps open releasing condensate. These traps cycle CONTROL CHAMBER independent of condensate load.

  • Page 382: Types Of Low Pressure Steam Distribution Systems

    C2928 Fig. 113. Typical Two-Pipe Vacuum Pump System. Two-pipe systems (Fig. 111) are used for all systems using automatic control of terminal units. A trap at each unit removes The vacuum in the return line draws a condensate/air mixture condensate.

  • Page 383: Variable Vacuum Return Systems

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Low pressure steam systems operate on pressures ranging from vacuum steam system. In an atmospheric-return low-pressure 0 psig to 15 psig. The steam main pressures are usually under 10 steam system, when the thermostat turns the burner off, boiling psig and the returns are vented to the atmosphere.

  • Page 384: Control Principles For Steam Heating Devices

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Figure 114C shows the quarter-open valve position. Half of CONTROL PRINCIPLES FOR STEAM the coil surface is starved of steam, the heat output is reduced HEATING DEVICES to about half of the original value and the trap is full open. All of the steam has been condensed in the coil before reaching the GENERAL trap.

  • Page 385: Correctly Sized Valve

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Correctly Sized Valve SUPPLY AND RETURN MAIN PRESSURES The valve in Figure 115A is sized for a 4 psi pressure drop The supply main pressure should be constant and sufficient when it is full open leaving 1 psi of steam for the coil and the to allow an 80 percent drop through the control valve and still trap.

  • Page 386: Low Temperature Protection For Steam Coils

    Vacuum systems are adaptable to responds to the coldest portion of the capillary sensing element, automatic control valves, since usual practice is to maintain a should be part of the design. For addition examples of control controlled difference between supply and return main pressures with freezing air conditions entering a coil see Air Handling while varying supply main pressure with heating load.

  • Page 387: High Temperature Water Safety

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS PRESSURE CONTROL MANUAL AIR VENTS AT HIGH POINTS OF UNIT EXPANSION OTHER HEATING COILS SUPPLY AND RETURN HEATERS TANK EXPANSION LOOPS LOAD BOILER NITROGEN BOTTLES INSTANTANEOUS CONVERTER SYSTEM DOMESTIC HOT WATER CIRCULATING FOR BUILDING PUMP PIPING FOLLOWS CONTOURS OF...

  • Page 388: Valve Style

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS VALVE STYLE VALVE FLOW CHARACTERISTICS Single seated valves are recommended because of their tight The flow characteristics of a valve is the relationship between shut-off and availability with equal percentage and reduced fluid flow expressed in percent of flow and valve stem travel capacity (Cv) trim.

  • Page 389: Instantaneous Converter Control

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS 1. The primary sensing element must be located in outlet INSTANTANEOUS CONVERTER CONTROL water as close to the converter as possible. 2. A stainless steel well that matches the element with heat An instantaneous converter is the standard type of converter conductive compound in the well must be used.

  • Page 390: Htw Coils

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS LOW TEMP CONTROLLER PREHEAT OR of the coil. The low-temperature limit controller senses the air TO SHUT DOWN FAN TEMPERING temperature leaving the coil and opens the valve on sensing a COIL freezing temperature. Use of a glycol solution as shown in Figure 120 is recommended.

  • Page 391: Multizone Space-Heating Htw Water Converters

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS TEMPERATURE CONTROL MULTIZONE SPACE-HEATING HTW RELIEF VALVE WATER CONVERTERS BUILDING Figure 124 shows a storage converter application. It is 120°F FROM BUILDING controlled as a conventional converter with only the HTW valve and pump interlock having special requirements because of STORAGE the heating medium.

  • Page 392: District Heating Applications

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS OPTIONAL RELAY ALARM CLOSES VALVE IF SAFETY LIMITS RELIEF EXCEEDED PRESSURE VALVE PRESSURE HIGH LIMIT CONTROL HIGH TEMPERATURE STEAM WATER VALVE MAKE UP WATER LEVEL CONTROL STORAGE CONVERTER WATER CUT OFF STEAM GENERATOR HTWR HTWS FEED...

  • Page 393: The Substation

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS LOSS 10% OTHER LOSSES 5% POWER 35 – 40% STEAM TURBINE GENERATOR BOILER FUEL 100% COOLING WATER LOSS 10 – 35% FEED WATER HEAT GENERATION HEAT 40 – 10% DISTRIBUTION BUILDING SUBSTATION M11434 (CUSTOMER) (HEAT EXCHANGER) Fig.

  • Page 394: Definitions

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Heat Exchanger Substation: Compact Station, controls the DEFINITIONS radiator and DHW loop in a building. Booster Pump station: Maintains sections of a network (return Heat Exchanger: Also called a convertor, transfers heat from or supply pipe) in required pressure conditions.

  • Page 395: System Configuration

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS SYSTEM CONFIGURATION STEAM SYSTEM VS HOT WATER SYSTEM Steam networks differ mainly in the following points from HEAT GENERATION hot water systems: Excess heat is produced in steam electrical power generating – No pumps are required, the pressure difference between stations which can be reclaimed as in Figure 126 and sold to boiler and consumer drives the movement of the steam.

  • Page 396: Pressure Reducing Stations

    CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS KEY POINTS PRESSURE MAXIMUM Key points are locations where pipelines branch off (Fig. 129). SAFETY They consist of valves for supply and return flow which can LIMIT SUPPLY separate the branch line from the main line. If a branch line is FLOW shut down, the pressure ratio in the entire network is affected.