Summary of Contents for Honeywell AUTOMATIC CONTROL SI Edition
NGINEERING ANUAL of AUTOMATIC CONTROL OMMERCIAL UILDINGS SI Edition...
Copyright 1989, 1995, 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: 97-77856 Home and Building Control Home and Building Control Honeywell Asia Pacific Inc.
Consideration of configuration, functionality, and integration plays a significant role in the design of building control systems. Through the years Honeywell has been dedicated to assisting consulting engineers and architects in the application of automatic controls to heating, ventilating, and air conditioning systems. This manual is an outgrowth of that dedication.
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.
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 ......................
Control System Applications ..................199 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 ..........
CONTROL FUNDAMENTALS Control Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................Definitions ......................HVAC System Characteristics ......................General ....................Heating ....................General ................... Heating Equipment ................. Cooling ....................General ................... Cooling Equipment ................Dehumidification .................. Humidification ..................Ventilation .................... Filtration ....................
CONTROL FUNDAMENTALS Control System Components ......................Sensing Elements ................Temperature Sensing Elements ............Pressure Sensing Elements ............Moisture Sensing Elements ............Flow Sensors .................. Proof-of-Operation Sensors ............Transducers ..................Controllers ................... Actuators ..................... Auxiliary Equipment ................Characteristics and Attributes of Control Methods ................
CONTROL FUNDAMENTALS INTRODUCTION Automatic controls can optimize HVAC system operation. This section describes heating, ventilating, and air They can adjust temperatures and pressures automatically to conditioning (HVAC) systems and discusses characteristics and reduce demand when spaces are unoccupied and regulate components of automatic control systems.
CONTROL FUNDAMENTALS Deadband: A range of the controlled variable in which no Load: In a heating or cooling system, the heat transfer that the system will be called upon to provide. Also, the work corrective action is taken by the controlled system and that the system must perform.
CONTROL FUNDAMENTALS Proportional-Integral (PI) control: A control algorithm that may be actuator driven, electronic, or directly activated combines the proportional (proportional response) and by the sensed medium (e.g., pressure, temperature). integral (reset response) control algorithms. Reset response tends to correct the offset resulting from Throttling range: In a proportional controller, the control point proportional control.
CONTROL FUNDAMENTALS HVAC SYSTEM CHARACTERISTICS GENERAL Figure 2 shows how an HVAC system may be distributed in 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.
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).
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.
CONTROL FUNDAMENTALS FINNED TUBE application, the refrigerant vaporizes at the lower end in the warm exhaust air, and the vapor rises toward the higher end in WARM AIR the cool outdoor air, where it gives up the heat of vaporization and condenses.
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 varying the An air handling system cools by moving air across a coil volume of refrigerant or controlling the compressor speed.
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...
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 DAMPERS FILTER...
CONTROL FUNDAMENTALS Self-powered systems are a comparatively minor but still SETPOINT important type of control. These systems use the power of the measured variable to induce the necessary corrective action. FEEDBACK SECONDARY For example, temperature changes at a sensor cause pressure CONTROLLER INPUT or volume changes that are applied directly to the diaphragm...
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 26 C, and to close the valve when the temperature drops to 25 C.
CONTROL FUNDAMENTALS BASIC TWO-POSITION CONTROL Figure 22 shows a sample control loop for basic two-position 23.5 control: a thermostat turning a furnace burner on or off in OVERSHOOT CONDITION response to space temperature. Because the thermostat cannot TEMPERATURE catch up with fluctuations in temperature, overshoot and ( C) 22.5 undershoot enable the temperature to vary, sometimes...
CONTROL FUNDAMENTALS Because the heat is supplied to the sensor only, the heat 22.5 anticipation feature lowers the control point as the heat requirement increases. The lowered control point, called “droop”, maintains a lower temperature at design conditions and is discussed more thoroughly in the following paragraphs.
CONTROL FUNDAMENTALS full on, the modulating stage returns to zero, and the sequence THROTTLING RANGE repeats until all stages required to meet 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...
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.
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)
CONTROL FUNDAMENTALS In an application requiring negative compensation, a change OUTDOOR AIR TEMPERATURE TEMPERATURE CONTROLLER in outdoor air temperature at the compensation sensor from – SENSOR 18 to 16 C resets the hot water supply temperature (primary sensor) setpoint from 94 to 38 C. Assuming a throttling range of 7 Kelvins, the required authority is calculated as follows: RETURN SENSOR...
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 normally band at twice the rate of shift for a two-percent deviation.
CONTROL FUNDAMENTALS PROPORTIONAL-INTEGRAL-DERIVATIVE (PID) The graphs in Figures 38, 39, and 40 show the effects of all three modes on the controlled variable at system start-up. With CONTROL 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.
CONTROL FUNDAMENTALS Adaptive control is also used in energy management programs The start value EPID setpoint sets the output to a fixed value at startup. For a VAV air handling system supply fan, a suitable such as optimum start. The optimum start program enables an value might be twenty percent, a value high enough to get the HVAC system to start as late as possible in the morning and still fan moving to prove operation to any monitoring system and to...
CONTROL FUNDAMENTALS COLD CONTROLLER FLOW (MANIPULATED WATER VARIABLE) TEMPERATURE VALVE HEAT LOSS (CONTROLLED 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.
CONTROL FUNDAMENTALS Figure 45 shows a high-velocity heat exchanger, which The difference between repeatability and static error is that repeatability is the ability to return to a specific condition, represents a process with a small thermal capacitance. The rate of whereas static error is a constant deviation from that condition.
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 where furniture loses heat.
CONTROL FUNDAMENTALS Each control mode is applicable to processes having certain poor rather than good control. Conversely, using a control mode that is too basic for requirements can make adequate control combinations of the basic characteristics. The simplest mode impossible. Table 3 lists typical control applications and of control that meets application requirements is the best mode to use, both for economy and for best results.
CONTROL FUNDAMENTALS FLAPPER The temperature sensor for an electronic controller may be a SPRING length of wire or a thin metallic film (called a resistance SIGNAL PORT temperature device or RTD) or a thermistor. Both types of BRASS TUBE resistance elements change electrical resistance as temperature changes.
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 called conditions.
CONTROL FUNDAMENTALS Applying the fluid jet principle allows the measurement of CONTROLLERS very small changes in air velocity that a differential pressure sensor cannot detect. A jet of air is emitted from a small tube Controllers receive inputs from sensors. The controller perpendicular to the flow of the air stream to be measured.
CONTROL FUNDAMENTALS ACTUATOR Electric actuators are inherently positive positioning. Some CHAMBER DIAPHRAGM pneumatic control applications require accurate positioning of the valve or damper. For pneumatic actuators, a positive positioning relay is connected to the actuator and ensures that PRESSURE the actuator position is proportional to the control signal. The positive positioning relay receives the controller output signal, reads the actuator position, and repositions the actuator according to the controller signal, regardless of external loads...
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...
CONTROL FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...
PSYCHROMETRIC CHART FUNDAMENTALS Psychrometric Chart Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................Definitions ......................Description of the Psychrometric Chart ....................The Abridged Psychrometric Chart ....................Examples of Air Mixing Process ......................Air Conditioning Processes ......................Heating Process .................. Cooling Process ..................
PSYCHROMETRIC CHART FUNDAMENTALS INTRODUCTION This section provides information on use of the psychrometric changes in relation to the performance of automatic HVAC control chart as applied to air conditioning processes. The chart provides systems. The chart is also useful in troubleshooting a system. a graphic representation of the properties of moist air including wet- and dry-bulb temperature, relative humidity, dew point, For additional information about control of the basic...
PSYCHROMETRIC CHART FUNDAMENTALS HANDLE WET-BULB THERMOMETER WATER-SOAKED WICK PIVOT DRY-BULB THERMOMETER RELATIVE HUMIDITY SCALE C1828 Fig. 1. Sling Psychrometer. (stocking or sock) and with an air flow of 4.57 meters Specific volume: The volume of air per unit of mass. Specific per second across the wick.
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.
PSYCHROMETRIC CHART FUNDAMENTALS — Enthalpy is 56.0 kilojoules per kilogram of dry air heat) line. The protractor nomograph, in the upper left corner, (Point D) is used to establish the slope of a process line. The mechanics — Density is 1.163 kilograms per cubic meter (reciprocal of constructing this line are discussed in more detail in the of volume) STEAM JET HUMIDIFIERS section.
PSYCHROMETRIC CHART FUNDAMENTALS EXAMPLES OF AIR MIXING PROCESS The following examples illustrate use of the psychrometric chart In this example, a ventilating system (Fig. 7) is used to to plot values and determine conditions in a ventilating system. illustrate how to plot data on Chart No. 2 and transfer values to The examples also show how to obtain the same results by Chart No.
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 9.4 grams of moisture per kilogram of 47.5 kJ/kg dry air.
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. 32 C DB 21 C DB 50% RH 95% RH 2. Read the enthalpy on the enthalpy scale. AIRFLOW 3.
PSYCHROMETRIC CHART FUNDAMENTALS SUPPLY FAN HEATING COIL 4700 L/s -18˚C DB 21 C DB 21 C DB 75% RH 35% RH 4.5% RH 0.55 g/kg FROM CHART 2 21 C DB C4330 4.5% RH 35% RH Fig. 14. Chart No. 1. 5.5 g/kg 4.5% RH 0.55 g/kg...
PSYCHROMETRIC CHART FUNDAMENTALS The air at Points A and B has 4.0 grams of moisture per If each kilogram of dry air requires 5.3 grams of moisture, kilogram of air. While the moisture content remains the same then the following moisture must be added: after the air is heated to 24 C (Point B), the relative humidity 5.55 kg/s x 5.3 g/kg = 29.4 grams of moisture...
PSYCHROMETRIC CHART FUNDAMENTALS REFERENCE POINT SENSIBLE HEAT TOTAL HEAT ENTHALPY 50% RH HUMIDITY RATIO 2675 kJ/kg THIS LINE IS 16 g/kg PARALLEL TO THE SOLID LINE C-B ON THE PSYCH CHART 6.5 g/kg 13 C DB 33 C DB 32 C DB M15331 CONSTRUCTION LINE Fig.
PSYCHROMETRIC CHART FUNDAMENTALS Figure 18 is the same as the chart shown in Figure 17 except The remaining 0.8 kJ/kg is sensible heat. The actual moisture that it graphically displays the amount of heat added by the added per kilogram of dry air is 9.5 grams. The specific volume process.
PSYCHROMETRIC CHART FUNDAMENTALS Recalling that the steam added 25.5 kilojoules per kilogram of dry air, the total heat added is: 5.4 kg/s x 25.5 kJ/kg = 137.7 kilojoules per second Summarized, a steam humidifier always adds a little sensible heat to the air, and the Process Line B–C angles to the right of CONSTANT ENTHALPY the 32 C starting dry-bulb line because of the added sensible...
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.
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 kilogram 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.
PSYCHROMETRIC CHART FUNDAMENTALS Figure 28 summarizes the process lines for applications using SUPPLY FAN washers for humidification or dehumidification. When the water recirculates, the process is adiabatic and the process line follows 14 C DB 32 C DB 85% RH 52% RH the Constant Enthalpy Line A-C.
PSYCHROMETRIC CHART FUNDAMENTALS HEATING COOLING SUPPLY FAN COIL COIL 32 C DB 9 C DB 15.5 C DB 21.6 C WB 8 C WB 11 C WB 40% RH 85% RH 56% RH C4337 Fig. 29. Fan System with Dehumidification and Reheat. Figure 30 illustrates cooling and dehumidification with reheat for maintaining constant relative humidity.
PNEUMATIC CONTROL FUNDAMENTALS Pneumatic Control Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................Definitions ......................Abbreviations ......................Symbols ......................Basic Pneumatic Control System ......................General ....................Air Supply and Operation ..............Restrictor ..................... Nozzle-Flapper Assembly ..............Pilot Bleed System ................Signal Amplifier ...................
PNEUMATIC CONTROL FUNDAMENTALS Sensor-Controller Systems ......................Pneumatic Controllers ................. Proportional-Integral (PI) Controllers ..........Controller Adjustments ..............Pneumatic Sensors ................Velocity Sensor-Controller ..............Actuators and Final Control Elements ......................Actuators ..................... General ................... Spring Ranges ................Control Valves ..................Dampers ....................Relays and Switches ......................
PNEUMATIC CONTROL FUNDAMENTALS INTRODUCTION This section provides basic information on pneumatic control — Many control sequences and combinations are possible systems and components commonly used to control equipment with relatively simple equipment. — Pneumatic equipment is suitable where explosion hazards in commercial heating and air conditioning applications.
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 pressure Manipulated variable: Media or energy controlled to achieve on a decrease in the variable.
PNEUMATIC CONTROL FUNDAMENTALS SYMBOLS MAIN AIR SUPPLY FIXED POINT RESTRICTOR FULCRUM NOZZLE PIVOT POINT C1082 BASIC PNEUMATIC CONTROL SYSTEM GENERAL In a typical control system, the final control element (a valve or a damper) is selected first because it must produce the desired control results.
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 or required. The restrictor and nozzle are sized so that the nozzle relays in other parts of the system.
PNEUMATIC CONTROL FUNDAMENTALS diaphragm is forced down, which opens the feed valve and SETPOINT SENSING ADJUSTMENT FORCE allows main air into the branch chamber. When the pilot pressure decreases, the pilot chamber diaphragm rises, closing the feed valve. If the pilot chamber diaphragm rises enough, it lifts the bleed valve off the feed valve disc, allowing air to escape from the branch chamber through the vent, thus decreasing the branchline pressure.
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.
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.
PNEUMATIC CONTROL FUNDAMENTALS Some applications require two compressors or a dual DRY AIR REQUIREMENT compressor. In a dual compressor, two compressors operate alternately, so wear is spread over both machines, each capable The coldest ambient temperature to which tubing is exposed of supplying the average requirements of the system without is the criterion for required dryness, or dew point.
PNEUMATIC CONTROL FUNDAMENTALS CONDENSING DRYING The heat exchanger reduces the temperature of the compressed air passing through it. A separator/filter condenses both water The two methods of condensing drying are high-pressure and oil from the air and ejects the condensate through a drain. A drying and refrigerant drying.
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.
PNEUMATIC CONTROL FUNDAMENTALS The oil coalescing filter continues to coalesce and drain off Two-Pressure Reducing Valve accumulated oil until solid particles plug the filter. An increase in pressure drop across the filter (to approximately 70 kPa) A two-pressure reducing valve is typically set to pass 90 or indicates that the filter element needs replacement.
PNEUMATIC CONTROL FUNDAMENTALS maintains a fixed branchline pressure for each temperature and raises the flapper off the nozzle. This movement causes within the throttling range (Fig. 17). The forces within the the branchline pressure to bleed down and a heating valve to nozzle-flapper-bimetal assembly always seek a balanced open.
PNEUMATIC CONTROL FUNDAMENTALS Controllers may also be classified as single-pressure or two- connected to the pressure to be controlled, and the other side is pressure controllers. Single-pressure controllers use a constant connected to a reference pressure. Pressures can be measured main air pressure.
PNEUMATIC CONTROL FUNDAMENTALS SENSOR-CONTROLLER SYSTEMS PRIMARY A sensor-controller system is made up of a pneumatic SENSOR controller, remote pneumatic sensors, and a final control MAIN AIR (125 kPa) element. The controller provides proportional or proportional- integral control of temperature, humidity, dew point, or pressure RESET SENSOR in HVAC systems.
PNEUMATIC CONTROL FUNDAMENTALS Reset authority, also called “reset ratio”, is the ratio of the The low-pressure sensor measures duct static pressure and effect of the reset sensor compared to the primary sensor. differential pressure. When the duct static pressure or the Figure 23 shows the effect of authority on a typical reset pressure differential increases, branchline pressure increases.
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.
PNEUMATIC CONTROL FUNDAMENTALS Actuators designed for special applications can move The position maintained by the valve stem depends on the through the full range, open to closed or closed to open, on balance of forces acting on it: a limited change in pressure from the controller. Such —...
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 300 millimeters, depending on the differential close-off rating of the valve.
PNEUMATIC CONTROL FUNDAMENTALS Figure 33 shows normally open and normally closed paral- For a more detailed discussion of dampers, see the Damper lel-blade dampers. A normally open damper returns to the open Selection and Sizing section. position with low air pressure in the actuator diaphragm chamber.
PNEUMATIC CONTROL FUNDAMENTALS HIGH-PRESSURE SELECTOR RELAY LOAD ANALYZER RELAY The high-pressure selector relay is a three-port relay that The load analyzer relay is a bleed-type, diaphragm-logic transmits the higher of two input signals to the output branch. pressure selector. The relay selects the highest and lowest branch The high sensitivity of the relay allows it to be used in sensor pressure from multiple inputs to operate final control elements lines with an accuracy of 1 to 1.5 degrees C.
PNEUMATIC CONTROL FUNDAMENTALS BLEED-TYPE damper precisely according to the branchline pressure from a THERMOSTAT thermostat or other controller, regardless of the load variations affecting the valve stem or damper shaft. The relay is typically used for large actuators for sequencing, or in applications DAMPER ACTUATOR requiring precise control.
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, THERMOSTAT 2 THERMOSTAT 1...
PNEUMATIC CONTROL FUNDAMENTALS HESITATION RELAY ELECTRICAL INTERLOCKING RELAYS The hesitation relay is used with a pneumatic actuator in unit Electrical interlocking relays bridge electric and pneumatic ventilator applications. The output pressure goes to minimum circuits. The electric-pneumatic relay uses electric power to whenever the input pressure is below the minimum setting.
PNEUMATIC CONTROL FUNDAMENTALS A resistance-type temperature sensor in the discharge air duct TEMPERATURE CONTROLLER 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 20 to 100 kPa output P/E RELAY to position the heating valve.
PNEUMATIC CONTROL FUNDAMENTALS Figure 56 shows the switch functioning as a minimum positioning switch. The damper will not close beyond the THERMOSTAT 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.
PNEUMATIC CONTROL FUNDAMENTALS — The controller must be located where the condition it cooling valve is closed. As the temperature rises, the branchline measures is uniformly affected by changes in position of pressure increases and the heating valve starts to close. At the multiple valves.
PNEUMATIC CONTROL FUNDAMENTALS Low-limit control applications typically use a direct-acting MANUAL SWITCH CONTROL primary controller and a normally open control valve. The direct-acting, low-limit controller can lower the branchline 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...
PNEUMATIC CONTROL FUNDAMENTALS CHANGEOVER CONTROL FOR TWO- according to a preset schedule. The system then provides the 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 TEMPERATURE 90 to 124 kPa in the mains.
PNEUMATIC CONTROL FUNDAMENTALS PNEUMATIC-ELECTRIC RELAY CONTROL started on low speed by Relay 1 which makes common to normally open. As a further rise in temperature increases the branchline pressure to 94 kPa, Relay 2 breaks the normally A P/E relay provides the interlock when a pneumatic closed circuit and makes the normally open circuit, removing controller actuates electric equipment.
PNEUMATIC CONTROL FUNDAMENTALS PNEUMATIC CENTRALIZATION Building environmental systems may be pneumatically The Discharge Air Temperature Indicator is fed from the automated to any degree desired. Figure 73 provides an pneumatic discharge air temperature sensor and the Three-Way example of the front of a pneumatic automation panel. This Valve Gauge is fed from the valve control line.
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.
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.
PNEUMATIC CONTROL FUNDAMENTALS SUPPLY FAN CONTROL SEQUENCE NOTE: 1. Because of varying exhaust between occupied and 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.
PNEUMATIC CONTROL FUNDAMENTALS RETURN FAN RETURN SA-1 B S M SNAP 20˚C TC-1 ACTING RELAY C-X < 21˚C C-O > 22˚C AIR DURING COLD RETURN AIR (WARM-UP) SUPPLY FAN OUTSIDE FROM TO COOLING TS-1 COOLING CONTROLS CONTROLS SR-1 20-55 kPa N.O.
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.
ELECTRIC CONTROL FUNDAMENTALS Electric Control Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................Definitions ......................How Electric Control Circuits are Classified ....................Series 40 Control Circuits ......................100 Application ................... 100 Equipment ................... 100 Controllers ..................100 Relays ..................... 100 Actuators ..................
ELECTRIC CONTROL FUNDAMENTALS Series 90 Control Circuits ......................107 Application ................... 107 Equipment ................... 107 Controllers ..................107 Actuators ..................107 Operation ..................... 108 General ................... 108 Bridge Circuit Theory ..............108 Basic Bridge Circuit ..............108 Bridge Circuit in Balanced Condition ........108 Bridge Circuit on Increase in Controlled Variable ....
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.
ELECTRIC CONTROL FUNDAMENTALS switching action dependent on the condition of the LOW-VOLTAGE CONTROL CIRCUIT controlled variable. Floating controllers (Fig. 3D) are spdt devices with a center-off position. Refer to SERIES 60 FLOATING CONTROL CIRCUITS for a discussion of floating control operation. MOTOR COILS Potentiometer controllers (Fig.
(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...
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 action closed, or single-pole, double-throw contacts.
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...
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.
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.
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...
ELECTRIC CONTROL FUNDAMENTALS SERIES 60 FLOATING CONTROL CIRCUITS ACTUATORS APPLICATION The actuators discussed in SERIES 60 TWO-POSITION A Series 60 floating control circuit is a line- or low-voltage CONTROL are also used for floating control. In addition, control circuit comprising a spdt controller with a center-off actuator assemblies are available with two, single direction (floating) position and a reversible actuator.
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. –...
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.
ELECTRIC CONTROL FUNDAMENTALS CONTROLLER CONTROLLER POTENTIOMETER POTENTIOMETER SENSING SENSING ELEMENT ELEMENT ELECTRONIC ELECTRONIC RELAY RELAY DRIVE DRIVE SHAFT SHAFT CLOSE OPEN CLOSE OPEN FEEDBACK FEEDBACK POTENTIOMETER C2522 POTENTIOMETER C2523 Fig. 21. Bridge Circuit on Increase Fig. 22. Bridge Circuit on Decrease in Controlled Variable.
ELECTRIC CONTROL FUNDAMENTALS BRIDGE CIRCUIT WITH LOW-LIMIT CONTROL has to go on each side of the bridge to rebalance the circuit, the 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.
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...
ELECTRIC CONTROL FUNDAMENTALS TWO-POSITION LIMIT CONTROL the controller and shorts R to W at the actuator. The actuator 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.
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...
ELECTRIC CONTROL FUNDAMENTALS position, and then permits the step controller to recycle to the A 135-ohm manual potentiometer provides up to a 50 percent minimum-position opening, and a 270-ohm manual potentiom- position called for by the thermostat. eter provides up to a 100 percent minimum-position opening. Step controllers can also be actuated by Series 60 floating controllers.
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.
ELECTRIC CONTROL FUNDAMENTALS MOMENTARY FAST-SLOW-OFF windings at the same time. Pressing the STOP button opens both holding circuits and stops the motor. START-STOP 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.
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.
ELECTRIC CONTROL FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...
ELECTRONIC CONTROL FUNDAMENTALS Electronic Control Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................120 Definitions ......................120 Typical System ......................122 Components ......................122 Sensors ....................122 Temperature Sensors ..............122 Resistance Temperature Devices ..........122 Solid-State Resistance Temperature Devices ......124 Thermocouples ................
ELECTRONIC CONTROL FUNDAMENTALS INTRODUCTION on microprocessor-based systems. The distinction between This section provides information about electronic control electronic control systems and microprocessor-based systems systems used to control HVAC equipment. An electronic control is in the handling of the input signals. In an electronic control system comprises a sensor, controller, and final control element.
ELECTRONIC CONTROL FUNDAMENTALS Electronic controller: A solid-state device usually consisting Proportional control (P): A control algorithm or method in of a power supply, a sensor amplification circuit, a which the final control element moves to a position process/comparing circuit, an output driver section, proportional to the deviation of the value of the and various components that sense changes in the controlled variable from the setpoint.
ELECTRONIC CONTROL FUNDAMENTALS TYPICAL SYSTEM Figure 1 shows a simple electronic control system with a ELECTRONIC FINAL CONTROL CONTROLLER DEVICE INPUTS controller that regulates supply water temperature by mixing return water with water from the boiler. The main temperature MAIN SENSOR (HOT WATER SUPPLY) sensor is located in the hot water supply from the valve.
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 CONTROLLER OR RELAY LED PANEL ANALOG TEMPERATURE SENSOR GAUGE ANALOG GAUGE POSITIVE RTD, OHMS THERMISTOR, OR DIGITAL TWO-POSITION...
ELECTRONIC CONTROL FUNDAMENTALS Another material used in RTD sensors is platinum. It is or small transistor) and provide quick response. 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.
ELECTRONIC CONTROL FUNDAMENTALS Thermocouples Transmitters measure various conditions such as 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.
ELECTRONIC CONTROL FUNDAMENTALS PROTECTIVE WIRES TO CONTROLLER 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 ULTRA THIN LAYER OF M10685 CONDUCTIVE MATERIAL...
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.
ELECTRONIC CONTROL FUNDAMENTALS INDICATING DEVICE ELECTRONIC CONTROLLER An electronic control system can be enhanced with visual OUTPUT MODULATING displays that show system status and operation. Many electronic VALVE ACTUATOR controllers have built-in indicators that show power, input signal, POWER deviation signal, and output signal. Figure 20 shows some types CHILLED WATER SUPPLY TO COIL of visual displays.
ELECTRONIC CONTROL FUNDAMENTALS TYPICAL SYSTEM APPLICATION Figure 22 shows a typical air handling system controlled by When the outdoor temperature is below the selected reset two electronic controllers, C1 and C2; sequencer S; changeover point set on C1, the controller is in the winter multicompensator M;...
MICROPROCESSOR-BASED/DDC FUNDAMENTALS Microprocessor-Based/DDC Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................133 Definitions ......................133 Background ......................134 Computer Based Control ..............134 Direct Digital Control ................134 Advantages ......................134 Lower Cost Per Function ..............134 Application Flexibility ................134 Coordinated Multifunction Capability ...........
MICROPROCESSOR-BASED/DDC FUNDAMENTALS Typical Applications ......................145 Zone-Level Controller ................145 Example 1. VAV Cooling Only ............145 Example 2. VAV Cooling with Sequenced Electric Reheat ....145 System-Level Controller ..............146 ENGINEERING MANUAL OF AUTOMATIC CONTROL...
MICROPROCESSOR-BASED/DDC FUNDAMENTALS INTRODUCTION This section discusses the types of microprocessor-based functions. A stand-alone controller can take several forms. The controllers used in commercial buildings. These controllers simplest generally controls only one control loop while larger measure signals from sensors, perform control routines in versions can control from eight to 40 control loops.
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 multi-loop. 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...
MICROPROCESSOR-BASED/DDC FUNDAMENTALS (IAQ), and/or building management functions. Changes in PRECISE AND ACCURATE CONTROL control sequences can easily be accommodated through software whether dictated by system performance or by changes Proportional control has the inherent problem of offset. The in the owner’s use of the facility. wider the throttling range is set for control stability, the greater the offset.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS Performance and reliability of temperature control range of outputs adequately covers normal control and display applications can be enhanced by using a single 12-bit A/D ranges for most HVAC control applications. D/A converters converter for all controller multiplexed inputs, and simple generally range from 6 to 10 bits.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS CONTROLLER SOFTWARE DIRECT DIGITAL CONTROL SOFTWARE Although microprocessor-based controller hardware governs, to some extent, how a controller is applied, software determines DDC software can be defined as a set of standard DDC the functionality. Controller software falls basically into two categories: operators and/or high-level language statements assembled to accomplish a specific control action.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS The use of preprogrammed operators saves time when writing Optimum Stop control sequences and makes understanding of the control sequence the equivalent of reading a pneumatic control diagram. The optimum stop program (Fig. 6) uses stored energy to Programming schemes often allow program operators to be handle the building load to the end of the occupancy period.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS Night Purge Load Reset The night purge program uses cool, night outdoor air to The load reset program (Fig. 9) assures that only the minimum amount of heating or cooling energy is used to satisfy load precool the building before the mechanical cooling is turned on.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS Sun, weather, and occupancy (building utilization) dictate The events of the first scenario occur within seconds because load reset demands. The sun and weather effects are relatively both loops (leaving water temperature controlling the chiller slow and occur as the sun and seasons change. Occupancy load and discharge air temperature controlling chilled water changes are abrupt and occur over brief periods of time.
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...
MICROPROCESSOR-BASED/DDC FUNDAMENTALS Distributed Power Demand BUILDING MANAGEMENT SOFTWARE The distributed power demand program (Fig. 12) is only Microprocessor-based controllers are used extensively as applicable to microprocessor controllers with intercommuni- data gathering panels (DGP) for building management cations capability. The demand program is resident in a single systems.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS PROGRAMMING CATEGORIES terminals are dedicated to a control relay or specific type of actuator. The need for data files is minimized. The processor always knows what to look for as it scans those points, and it Programming of microcomputer-based controllers can be knows how to process the data.
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...
MICROPROCESSOR-BASED/DDC FUNDAMENTALS Design, Write, and Compile Program other control blocks. Although this process requires little or no knowledge of programming, it does require in-depth knowledge The actual process of designing and writing the control loop of the control blocks and the specific HVAC process. programs can be a very complex or a relatively straightforward procedure, depending on the language processing software Debug, Install, Enter Data Files, and Test...
MICROPROCESSOR-BASED/DDC FUNDAMENTALS staged by a PI algorithm with software heat anticipation. See 4. Develop a detailed flowchart of the control sequence Figure 15. During reheat, the control mode changes to constant using either DDC operators or a programming logic flow volume, variable discharge temperature.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS If the DDC system is provided with a BMS having a color START monitor, a graphic may be required to be displayed with live, displayable and commandable points (12 total). If a BMS is O.A. not provided, the points may be required to be displayed on a TEMP text terminal (fixed or portable) at the system level controller.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...
INDOOR AIR QUALITY FUNDAMENTALS Indoor Air Quality Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL 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 ............
INDOOR AIR QUALITY FUNDAMENTALS 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 ............... 167 Operator Interface ................167 Graphic Displays .................
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.
INDOOR AIR QUALITY FUNDAMENTALS Dose: The amount of a given agent that actually reaches the site Micro-organisms: Life forms too small to be seen with the in the body where it causes an effect. unaided eye. Electrostatic air cleaner: A device that has an electrical charge Mitigation: A procedure or strategy aimed at reducing or to trap particles traveling in the airstream.
INDOOR AIR QUALITY FUNDAMENTALS Sick Building Syndrome (SBS): A term used to refer to the Threshold: The contaminant dose or exposure level below condition in which a majority of building occupants which there is no expected significant effect. experience a variety of health and/or comfort effects linked to time spent in a particular building, but where Total Volatile Organic Compounds (TVOCs): A measure no specific illness or causative agent can be identified.
INDOOR AIR QUALITY FUNDAMENTALS INDOOR AIR QUALITY CONCERNS bacteria. Gaseous contaminants such as methane are produced AIR CONTAMINANTS both naturally, by animals and decay, and by man made activity such as landfills. Location near a fossil fuel power plant, refinery, Air contaminants are categorized by location and type.
INDOOR AIR QUALITY FUNDAMENTALS Table 3. Sources, Possible Concentrations, and Indoor to Outdoor Concentration Ratios of some Indoor Pollutants. Indoor/Outdoor Sources of Possible Indoor Concentration Pollutant Indoor Pollution Concentrations Ratio Location Asbestos Fireproofing <10 fiber/ m Homes, schools, offices Carbon Combustion, humans, pets 3000 ppm >>1...
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...
INDOOR AIR QUALITY FUNDAMENTALS Gas And Vapor Contaminants BUILDING RESPONSES TO CONTAMINANTS The terms gas and vapor are often used to describe a common Building responses to indoor air contamination include visual state of a substance. Gas normally describes any mixture, except signs of fungus, mold, mildew, dirt buildup, corrosion, and atmospheric air, that exists in the gaseous state at normal discoloration The growth of fungus, mold, and mildew is found...
INDOOR AIR QUALITY FUNDAMENTALS Active pathways for air contamination include HVAC According to the EPA one half the population of the systems, cooling towers designed into the building, and local United States lives in areas that do not meet the National spot humidifiers, dehumidifiers, fans and heaters added by the Ambient Air Quality Standards with ozone being the most occupants after occupancy.
INDOOR AIR QUALITY FUNDAMENTALS OPTIMUM RELATIVE HUMIDITY RANGES FOR HEALTH DECREASE IN BAR WIDTH INDICATES DECREASE OPTIMUM ZONE IN EFFECT BACTERIA VIRUSES FUNGI MITES RESPIRATORY INFECTIONS # ALLERGIC RHINITIS AND ASTHMA CHEMICAL REACTIONS OZONE PRODUCTION # INSUFFICIENT DATA M10481 RELATIVE HUMIDITY, PERCENT ABOVE 50% RH Fig.
INDOOR AIR QUALITY FUNDAMENTALS VENTILATION RATE DESIGN PROCEDURE outdoor air and that the Indoor Air Quality Procedure must be used. The air cleaning equipment must be designed to reduce particulates and where necessary and feasible, gaseous The Ventilation Rate Procedure is deemed to provide acceptable contaminants.
INDOOR AIR QUALITY FUNDAMENTALS Recirculation Requirements ventilation fraction, and resets the outdoor airflow to the minimum outdoor air that will satisfy the critical space or spaces. See the latest version of ASHRAE Standard 62 for Recirculation of air in HVAC systems is regulated by additional information on critical zone reset application.
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 &...
INDOOR AIR QUALITY FUNDAMENTALS ASHRAE GUIDELINE 1-1989 deliver the design. The acceptance phase of the process 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.
INDOOR AIR QUALITY FUNDAMENTALS FLOW TRACKING CONTROL SYSTEM terminal box requirements that the fan supplies. Typically there are 30 to 70 VAV terminal units per fan system. The sample VAV terminal unit shown is a fan powered unit but the units Figure 4 provides a simplified hardware schematic of a could be non-fan powered.
INDOOR AIR QUALITY FUNDAMENTALS FLOW TRACKING SYSTEM WITH MIXING additional outdoor air. During non-economizer periods the EA/ RA dampers modulate to maintain static pressure constant at BOX STATIC PRESSURE CONTROL the filter inlet. This is accomplished by separating the control of the outdoor air damper from the control of the return and Figure 5 is the same as the Flow Tracking System except for relief dampers.
INDOOR AIR QUALITY FUNDAMENTALS ROOFTOP UNIT CONTROL SYSTEM OPERATOR INTERFACE Figure 6 shows a typical packaged rooftop VAV system Modern Building Management Systems (BMS) utilizing similar to the pervious system but with humidification and distributed direct digital controllers and personnel computer based without a return fan.
INDOOR AIR QUALITY FUNDAMENTALS Operator graphic displays with meaningful real-time dynamic For additional information on system configuration, network data displays can enable building operators to understand how communications, and specifying graphics, refer to the Building the building is operating. CO , VOC, airflow, DP, SP, filter, and Management System Fundamentals section.
INDOOR AIR QUALITY FUNDAMENTALS Figure 8 shows how dynamic data can assist an operator. This and allows the operator to adjust setpoints and review results in display provides the operator/engineer with the actual operating real time. This is one of many operator displays that can be values, at that instant, embedded in the sequence of operations designed to facilitate operator understanding and control of IAQ.
INDOOR AIR QUALITY FUNDAMENTALS A graphic such as Figure 9 can be automatically displayed as responsibilities. The acknowledgment of the alarm provides the an alarm on a quarterly calendar basis to remind the building necessary closure of the loop from the designer to the user. Alarm operators and owners that the maintenance of IAQ is one of their acknowledgment can be logged by the owner to verify compliance.
SMOKE MANAGEMENT FUNDAMENTALS Smoke Management Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................172 Definitions ......................172 Objectives ......................173 Design Considerations ......................173 General ....................173 Layout of System ................. 174 Codes and Standards ................174 Design Priniples ......................175 Causes of Smoke Movement ..............
SMOKE MANAGEMENT FUNDAMENTALS INTRODUCTION This section describes objectives, design considerations, building fires is carbon monoxide. Other toxic agents include design principles, control applications, and acceptance testing hydrogen cyanide, hydrogen chloride, sulphur dioxide, acrolein, aldehydes, carbon dioxide, and a variety of airborne particulates for smoke management systems.
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.
SMOKE MANAGEMENT FUNDAMENTALS Smoke management typically includes control of fires by According to NFPA 92A, control sequences should allow automatic sprinklers. Designing smoke management systems smoke control modes to have the highest priority; however, for sprinklered buildings is quite practical. However, designing some control functions should not be overridden.
SMOKE MANAGEMENT FUNDAMENTALS DESIGN PRINCIPLES plane, approximately midheight, and exits above the neutral CAUSES OF SMOKE MOVEMENT plane. See Figure 2. Air neither enters nor exits at the neutral plane, a level where the pressures are equal inside and outside The movement or flow of smoke in a building is caused by a the building.
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 is lowered due to heat transfer and dilution;...
SMOKE MANAGEMENT FUNDAMENTALS HVAC pressure differences while the building is under typical conditions of stack effect and wind. This table is for gas temperatures of 927 C adjacent to the barrier. To calculate HVAC systems can provide a means for smoke transport pressure differences for gas temperatures other than 927 C, refer even when the system is shut down (e.g., a bypass damper to data in NFPA 92A.
SMOKE MANAGEMENT FUNDAMENTALS The door widths in Table 2 apply only for doors that are SMOKE hinged at one side. For other arrangements, door sizes, or for hardware other than knobs (e.g., panic hardware), refer to SMOKE calculation procedures furnished in Design of Smoke Control RELATIVELY BACKFLOW LOW AIR...
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 than one floor.
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.
SMOKE MANAGEMENT FUNDAMENTALS 4. System enables damper operation as appropriate for EXHAUST DAMPER smoke control mode. 5. Operator verifies operation as appropriate (e.g., action SPRINKLER of differential pressure switch). 6. Operator cancels smoke control mode as long as initiating panel is not in alarm and FSCS is not in manual override. CONTROL OF MALLS, ATRIA, SMOKE PLUME...
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.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Building Management System Fundamentals ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................184 Definitions ......................184 Background ......................185 Energy Management ................185 Facilities Management Systems ............185 System Configurations ......................186 Hardware Configuration ..............186 Zone-Level Controllers ..............
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 —...
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.
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.
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.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS PEER COMMUNICATIONS PROTOCOL CENTRAL Peer communications protocol has the following advantages COMMUNICATIONS over poll/response communications protocol: SYSTEM/ZONE SYSTEM/ZONE — Communication not dependent on a single device as LEVEL LEVEL CONTROLLER the master. CONTROLLER — Direct communication between bus-connected devices without going through the BMS central processor.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS SYSTEM FUNCTIONS to interfacing with operating personnel rather that with GENERAL mechanical systems, as the controllers do in the lower tiers of the BMCS configuration. Each BMCS level provides some degree of stand-alone capability and collects and preprocesses data for other HARDWARE processing levels.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS — Transmitting requests for display data. • (Option) Automation Graphic Display. — Transmitting requests for report data. • Present button for operator graphic display request. — Uploading and downloading of controller software. — Present alarm status on graphics (point red if in alarm, —...
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Off”. Strong color conventions unclutter graphics by needing Controller Support less explanatory text, for example; a yellow filter may be clean, a red filter dirty, and a red and blinking filter dirty and A major portion of the BMS Software is the definition and unacknowledged.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS Operator selection of the “CHILLER A1 CHILLER A2” SYMBOL LEGEND: icon displays the graphic shown in Figure 7 which has 42 DYNAMIC VALUE data points and three icons for subsequent penetration, TEMPERATURE summarized as follows: HUMIDITY Cooling tower isolation valve position indicators.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS DUAL CHILLER PLANT CONTROL GRAPHIC DISPLAY LEAD CHILLER PRESSURE BYPASS SELECTOR & CHOKE VALVE COOLING CONTROL TOWER CONTROL 1 = CHILLER 1 LEADS DUAL CHILLER 2 = CHILLER 2 LEADS SETPOINT REDUCTION 72.4 CHILLED WATER SETPOINT PRESSURE BYPASS VALVE...
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS CONNECTED POINTS INPUTS APPLICATION SOFTWARE ENERGY MANAGEMENT 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.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS CONTROL GRAPHICS each specific operator type. For example, a security guard is 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.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS INTEGRATION OF OTHER SYSTEMS The advantage of surface integration is that limited GENERAL subsystem information is made available to the BMS. This type of integration is generally used to tie in existing systems to Information from other subsystems, such as fire alarm, eliminate the need to replace functioning equipment.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS ETHERNET LAN LEGEND PC - OPERATIONS/MANAGEMENT WORK STATION S - SYSTEM LEVEL CONTROLLER ZONE CONTROLLER ZI - ZONE CONTROL INTERFACE T - INTELLIGENT TEMPERATURE SENSOR A - INTELLIGENT ACTUATOR BI - BACNET INTERFACE BC - BACNET CONTROLLER LI - LONMARK INTERFACE 3I - THIRD PARTY (SUCH AS SWITCH GEAR) INTERFACE...
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL...
AIR HANDLING SYSTEM CONTROL APPLICATIONS Air Handling System Control Applications ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................203 Abbreviations ......................203 Requirements for Effective Control ......................204 Applications-General ......................206 Valve and Damper Selection ......................207 Symbols ......................208 Ventilation Control Processes ......................
AIR HANDLING SYSTEM CONTROL APPLICATIONS Cooling Control Processes ......................236 Control of Modulating Chilled Water Coil Three-Way Valve ....236 Two-Position Control of Direct Expansion Coil System ....... 238 Two-Position Control of Direct Expansion Coil System— Modulating Face and Bypass Damper ..........239 Cold Deck System with Zone Damper Control ........
AIR HANDLING SYSTEM CONTROL APPLICATIONS INTRODUCTION Also throughout the section, dashed lines indicate interlocked This section describes control applications for air handling links and solid lines functional relationships between control items. systems commonly found in commercial buildings. The basic processes such as heating, cooling, humidification, dehumidification, and ventilation are presented individually then Psychrometric aspects are included for most applications.
AIR HANDLING SYSTEM CONTROL APPLICATIONS REQUIREMENTS FOR EFFECTIVE CONTROL Effective control system performance requires careful design 3) Sizing the refrigeration equipment accurately. of the mechanical system and selection of components. 4) Providing minimum on and off time delays. Consideration needs to be given to the following by the 5) Providing a hot gas bypass.
AIR HANDLING SYSTEM CONTROL APPLICATIONS 9. CONSIDER THE PHYSICAL ARRANGEMENT OF 2) Providing failure alarms for pump, coils, and HUMIDITY SYSTEM COMPONENTS. other heating systems components. a. Locate humidifiers downstream from a source of heat. 12. ALLOW AIR HANDLING AND CONTROL SYSTEM DESIGN TO PROVIDE ENERGY CONSERVATION.
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.
AIR HANDLING SYSTEM CONTROL APPLICATIONS VALVE AND DAMPER SELECTION Pneumatic valve and damper actuators are shown in these actuator selection. The table indicates actuator positioning desired examples. If actuators are electric, certain ones need not be spring on system shutdown and loss of motive force. return unless a specific reason exists.
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...
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 FUNCTION AL DESCRIPTION SPACE PROPELLER TEMPERATURE EXHAUST 23.5 SETPOINT STATUS UNOCCUPIED LOW LIMIT FAN SYSTEM PERCENT SCHEDULE AND LOAD...
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 (hardwired). operate. 2. Optimized start-stop control of supply, return, and 2. On large 100% OA systems and systems where OA and exhaust fans.
AIR HANDLING SYSTEM CONTROL APPLICATIONS FIXED QUANTITY OF OUTDOOR AIR CONTROL Functional Description Example, calculate the mixed air temperature of a 4.720 m fan with 25% OA at –15 C. RA is 24 C. 1.180 MAT = 24 + [(-15) - 24] = 14.25 C 4.720 MAT = (24 x 0.75) + (-15x 0.25) = 14.25 C SPECIFICATIONS...
AIR HANDLING SYSTEM CONTROL APPLICATIONS OUTDOOR AIR FAN CONTROL FOR MULTIPLE AHU’S The OA fan loading shall be under EPID (see Control Fundamentals section) control with a start value of 25% and a Functional Description ramp duration of 250 seconds. NOTE: EPID was selected (and designed specifically) for this type of application because of the start-up nature of VAV fans.
AIR HANDLING SYSTEM CONTROL APPLICATIONS MIXED AIR CONTROL Functional Description NORMAL CONTROL PROGRAM OA MINIMUM SETPOINT M15153 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.
AIR HANDLING SYSTEM CONTROL APPLICATIONS SPECIFICATIONS See FAN SYSTEM START-STOP CONTROL. 17.5 C 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 MA RA 24 C DB, 15 C WB temperature setpoint down to a minimum ventilation position.
AIR HANDLING SYSTEM CONTROL APPLICATIONS ECONOMIZER CYCLE DECISION 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.
AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES the OA is between approximately 16 C and 25.5 C, and during the occupancy period. 1. Outdoor air is used for cooling (or to supplement the chilled NOTE: The dry bulb economizer decision is best on small water system) anytime the OA temperature is below the systems (where the cost of a good humidity sensor cannot economizer setpoint.
AIR HANDLING SYSTEM CONTROL APPLICATIONS Item SPECIFICATIONS Function A global economizer program function shall be provided to switch all AHUs from OA cooling to minimum OA based upon Sensor senses OA temperature. an OA enthalpy calculation setpoint, except the system shall be Sensor senses OA humidity.
AIR HANDLING SYSTEM CONTROL APPLICATIONS 6. Line 3 represents the dry bulb value, to the right of which ENTHALPY the cooling coil could not handle the sensible load, no CONTROL SELECTS RA matter how dry the air is. This is the high temperature economizer cutout line used with the enthalpy and OA/ 24 C DB, 54% RH RA enthalpy comparison economizer decision.
AIR HANDLING SYSTEM CONTROL APPLICATIONS Item CONDITIONS FOR SUCCESSFUL OPERATION Function 1. High quality RH sensors with at least 3% accuracy and long term stability should be selected. Sensor senses OA temperature. 2. Periodic maintenance of the humidity sensors is provided. Sensor senses OA humidity.
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) M15157 Item CONDITIONS FOR SUCCESSFUL OPERATION...
AIR HANDLING SYSTEM CONTROL APPLICATIONS PSYCHROMETRIC ASPECTS 7. The desired MA temperature can be maintained during economizer periods until the OA temperature falls below the temperature at which only minimum OA is admitted In the following chart it is assumed that: if the OA is less than 13 C.
AIR HANDLING SYSTEM CONTROL APPLICATIONS Item CONDITIONS FOR SUCCESSFUL OPERATION Function 1. Adequate mixing of OA and RA. Mixing may be obtained using a special mixing chamber. The temperature sensor Control system energizes when fan is turned should be in the fan discharge when possible. The fan in on (See FAN SYSTEM START-STOP a blow-through system usually provides adequate mixing.
AIR HANDLING SYSTEM CONTROL APPLICATIONS HEATING CONTROL PROCESSES The following applications show various ways to control CONDITIONS FOR SUCCESSFUL OPERATION heating in an air conditioning system. 1. A multiple inline coil arrangement should be used if a high temperature rise is required. CONTROL FROM SUPPLY AIR 2.
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 M15160 shall be reset from no lower than 13 C to no greater than Item 38 C as the space temperature PID demand for heating Function...
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 M15161 Item PSYCHROMETRIC ASPECTS Function The SA condition depends on the entering air condition and the temperature rise needed to satisfy the space heating Control system energizes when fan is turned on requirements.
AIR HANDLING SYSTEM CONTROL APPLICATIONS SPACE TEMPERATURE CONTROL OF ZONE MIXING DAMPERS AND RESET OF HOT DECK TEMPERATURE Functional Description SPACE SETPOINT OPEN TEMP. HALL LOBBY EAST CONTROL OFFICE PROGRAM WEST OFFICE SETPOINT NORMAL PERCENT OPEN TO HOT DECK ZONE DECK MIXING DAMPERS...
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.
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.
AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES The heating coil valve shall position from 0 to 100% open as the OA temperature varies from 10 C to 1.5 C. 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 10 C.
AIR HANDLING SYSTEM CONTROL APPLICATIONS CONTROL FROM PREHEAT LEAVING AIR Functional Description CONTROL PROGRAM OPEN N.O. N.C. NORMAL M15165 LIMITATIONS Item 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).
AIR HANDLING SYSTEM CONTROL APPLICATIONS The following results are obtained: Item Explanation RA 24 C DB, 17 C WB Heating of OA occurs along a line of constant moisture content from 1.5 C to 21 CF. This condition represents the mixing of PREHEAT AIR preheated air and RA supplied to the system.
AIR HANDLING SYSTEM CONTROL APPLICATIONS Coils 1 and 2 could be added to detect the loss of heating. OPTIONAL: Anytime the Coil 1 valve is full open and the If a Building Management System is included, the Coil 1 air differential temperature is less than a monitor could be two-stage to send an alarm warning Value V1, an alarm message shall be issued.
AIR HANDLING SYSTEM CONTROL APPLICATIONS YEAR-ROUND HEAT RECOVERY PREHEAT SYSTEM CONTROL Functional Description OPEN PUMP START SETPOINTS: EXHAUST N.C. COIL COOLING SETPOINT = ANYTIME OA TEMPERATURE IS DEGREES ABOVE RA TEMPERATURE. PUMP PERCENT OPEN TO SUPPLY COIL HEATING SETPOINT = ANYTIME OA SETPOINT TEMPERATURE IS DEGREES...
AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES In the heating season, the recirculating pump shall run 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...
AIR HANDLING SYSTEM CONTROL APPLICATIONS HUMIDIFICATION CONTROL PROCESS Humidification is a process of adding moisture to air. The most Although steam jet humidifiers are depicted, other modulating commonly used humidifier type is the steam jet. Humidifier types control similarly. On-off humidifiers require a differential requirements vary;...
AIR HANDLING SYSTEM CONTROL APPLICATIONS STEAM HUMIDIFICATION PROCESS SPECIFICATIONS DETERMINES SLOPE OF THIS LINE 1. The humidifier shall be modulated by a space humidity PI control loop to maintain the humidity setpoint. 2. A humidifier leaving air humidity high limit control loop shall disable the humidifier if the humidity rises above ENTHALPY HUMIDITY RATIO...
AIR HANDLING SYSTEM CONTROL APPLICATIONS 2. Design OA temperature is 35 C DB and 24 C WB. FEATURES 3. Air entering the system is from the ECONOMIZER CYCLE DECISION application. This system operates 1. Chilled water is supplied to the coil at a constant on 35 percent OA during the cooling cycle.
AIR HANDLING SYSTEM CONTROL APPLICATIONS TWO-POSITION CONTROL OF DIRECT EXPANSION COIL SYSTEM Functional Description COMPRESSOR START CIRCUIT RELAY TEMPERATURE CONTROL 24.5 COMPRESSOR DIFFERENTIAL VOLTAGE MONITOR (KELVINS) 24.5 CONTROL PROGRAM COMPRESSOR (MINUTES) RELAY MINIMUM MINIMUM ON TIME OFF TIME OPEN SUPPLY M15170 LIMITATIONS Item...
AIR HANDLING SYSTEM CONTROL APPLICATIONS The following results are obtained: PSYCHROMETRIC ASPECTS Item With on-off control, either cooled air or mixed air is supplied Explanation into the space. In the following chart it is assumed that: Mixed air temperature at cooling design condition.
AIR HANDLING SYSTEM CONTROL APPLICATIONS Item Anytime the face damper modulates up to 80% open, the refrigerant valve shall open and a relay shall enable the Function compressor to start under compressor controls. When the compressor system is commanded on, it shall remain on at least Control system energizes when fan is turned eight minutes and when it is commanded off (or drops off during on (See FAN SYSTEM START-STOP...
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...
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 35 C DB, 24 C WB be allowed to go out of control (storage rooms, etc.) should not be connected to the load analyzer program.
AIR HANDLING SYSTEM CONTROL APPLICATIONS DEHUMIDIFICATION CONTROL PROCESSES CONDITIONS FOR SUCCESSFUL OPERATION The following applications show various methods of controlling dehumidification in air conditioning systems. 1. If a chilled water coil is used, the water supply is cold DIRECT EXPANSION OR WATER COIL enough to produce the lowest required dew point.
AIR HANDLING SYSTEM CONTROL APPLICATIONS In the following chart it is assumed that: The following results are obtained: 1. Desired space condition is 24 C DB and a maximum of 50% RH. Item 2. OA condition is 27 C DB and 26 C WB. Explanation 3.
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.
AIR HANDLING SYSTEM CONTROL APPLICATIONS HEATING SYSTEM CONTROL PROCESS SPACE CONTROL OF HEATING, ECONOMIZER (FREE COOLING), AND HUMIDIFICATION Functional Description SPACE COOL CONTROL PROGRAM 23.5 HEAT N.O. N.C. SUPPLY AIR SPACE TEMPERATURE HEATING SETPOINT DEMAND NORMAL CONTROL PROGRAM SUPPLY AIR SPACE ECONOMIZER DECISION.
AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES 2. SA condition at design load is 32 C DB and 7.0 grams of moisture per kilogram of dry air. 3. Light load outdoor air condition is 13 C DB and 11.5 C 1. The outdoor air quantity is modulated from a minimum to take advantage of free cooling based on space 4.
AIR HANDLING SYSTEM CONTROL APPLICATIONS YEAR-ROUND SYSTEM CONTROL PROCESSES HEATING, COOLING, AND ECONOMIZER Functional Description 24.5 SPACE TEMPERATURE CHILLED WATER COOLING SETPOINT SETPOINT = FREE COOLING SETPOINT PLUS 24.5 (0.8 MINIMUM) FREE COOLING 23.5 SETPOINT HEATING SETPOINT = FREE SETPOINT COOLING SETPOINT MINUS (0.8 MINIMUM) SUPPLY AIR...
AIR HANDLING SYSTEM CONTROL APPLICATIONS 15,16 Hot water valve modulates to maintain SA The space temperature shall have a free cooling PI loop setpoint selected to provide optimum occupant comfort temperature. The temperature setpoint. space temperature shall have a chilled water cooling PI loop Free cooling demand varies SA temperature setpoint adjustable to no lower than 0.8 kelvins (minimum) above setpoint.
AIR HANDLING SYSTEM CONTROL APPLICATIONS MULTIZONE UNIT Functional Description 23.5 23.5 THE ZONE WITH THE GREATEST HEATING DEMAND HALL LOBBY RESETS THE HOT DECK TEMPERATURE FROM DEGREES AS REQUIRED TO 23.5 23.5 EAST OFFICE MAINTAIN ITS SPACE TEMPERATURE DEGREES BELOW SETPOINT. WEST 23.5 24.5...
AIR HANDLING SYSTEM CONTROL APPLICATIONS FEATURES In the winter, zone space temperature is maintained by mixing 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).
AIR HANDLING SYSTEM CONTROL APPLICATIONS HEATING, COOLING, HUMIDIFICATION, AND DEHUMIDIFICATION CONTROL WITHOUT DEAD-BANDS Functional Description SPACE N.C. 23.5 23.5 13.5 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...
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 35 C DB and 26 C WB. humidification and dehumidification.
AIR HANDLING SYSTEM CONTROL APPLICATIONS For heating conditions it is assumed that: The following results are obtained: 1. Design outdoor air condition is –18 C DB and 30 percent Item relative humidity. Explanation 2. RA condition is 24.5 C DB and 13.5 C WB. 3.
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 23.5 AIR REACHES PROPELLER PERIMETER EXHAUST ZONE WARM-UP 23.5 MODE SPACE...
AIR HANDLING SYSTEM CONTROL APPLICATIONS Control program optimizes duct pressure CONDITIONS FOR SUCCESSFUL OPERATION setpoint. 1. Airflow element and transducer must be kept clean and OA shaft static pressure point shared from OA calibrated. fan control system for this graphic (not a 2.
AIR HANDLING SYSTEM CONTROL APPLICATIONS During unoccupied periods, anytime the top floor west zone operating point. At this point the AHU fan would draw a small perimeter space temperature is greater than 25 C and the OA portion of its full-load amperage, good dehumidification would temperature is less than 22 C and the OA dew point is less than occur, and pumping energy may be reduced.
AIR HANDLING SYSTEM CONTROL APPLICATIONS VAV AHU WITH RETURN FAN AND FLOW TRACKING CONTROL Functional Description ZERO CALIBRATION EXHAUST 24.5 EXHAUST FAN "ON" DIFFERENTIAL SPACE PRESSURIZATION 1.274 DIFFERENTIAL 0.613 4.530 CONTROL PERCENT PROGRAM LOAD 14.5 6.423 NORMAL NORMAL PERCENT LOAD 0.45 0.060 0.45...
AIR HANDLING SYSTEM CONTROL APPLICATIONS SA temperature setpoint is reset based upon SPECIFICATIONS OA temperature. See FAN SYSTEM START-STOP CONTROL. 20-22 Mixing dampers modulate for free cooling. 23,24 Mixing box static pressure maintained constant Anytime the supply fan runs, the return fan shall start and during noneconomizer mode by modulation of the control system shall be enabled.
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 35 C DB and 26 C WB. 2. RA condition is 24 C DB and 14.5 C WB. RA mixes with 20 percent (minimum position) 3.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Building Airflow System Control Applications ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................265 Definitions ......................265 Airflow Control Fundamentals ......................266 Need for Airflow Control ..............266 What is Airflow Control ................ 266 Types of Airflow Systems ..............267 Variable Air Volume .................
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Airflow Control Applications ......................280 Central Fan System Control ..............280 Supply Fan Control for VAV Systems ..........280 General ..................280 Duct Static High-Limit Control ............. 281 Return Fan Control for VAV Systems ..........281 Open Loop Control ..............
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 air handling system, describes the various means of airflow types of space pressure control are static pressure, airflow tracking, and constant airflow.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Static pressure sensor or tube: A sensing device with several • Peak Velocity—The greatest air velocity occurring in an holes perpendicular to an airstream for measuring increment of a duct cross-section. Peak velocity is static pressure. denoted V Total pressure: The algebraic sum of Velocity Pressure (VP) plus •...
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS TYPES OF AIRFLOW SYSTEMS To ensure that all air terminal units have sufficient pressure to operate, a supply airflow control system is required. To monitor duct static, static pressure sensors are installed near the end of the An air handling system can provide heating, cooling, supply duct.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS OUTDOOR FLOW MEASURING STATION RETURN RELIEF (OR) AIR FAN 12.0 m MAXIMUM REMOTE EXHAUST FAN INLET VANE SUPPLY DAMPERS AIR FAN 0.7 m 14.0 m MAXIMUM FILTER FLOW 75% DIVERSITY, MEASURING COOLING AIR TERMINAL UNIT STATION COIL TOTAL19.0 m...
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS If this is done on a VAV system at design load, as the VAV Another positive method is to provide a small OA injection boxes require less cooling and less airflow, the supply fan fan set to inject the required OA into the AHU mixing box capacity reduces, and the inlet pressure to the supply fan during occupied periods (the OA damper remains closed).
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Theoretically, the mixing dampers may be modulated to Where: maintain a constant OA volume during occupied periods using F = Total door opening force applied at the knob an OA duct airflow measuring station. Since, in these examples, in newtons (N) the OA duct is sized for 100 percent OA, the minimum is usually = Force to overcome the door closer, applied...
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Where: WIND PRESSURE EFFECTS DP = Pressure difference in pascals (Pa) Wind effects generate surface pressures which can change = Outdoor absolute temperature in degrees supply and exhaust fan capacities, infiltration and exfiltration of kelvin(˚F) (273 + ˚K) air, and interior building pressure.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS FAN TYPES Two main types of fans are used in airflow systems centrifugal and axial: Centrifugal Fans: A centrifugal fan (Fig. 4) has airflow within the wheel that is substantially radial to the shaft (or PROPELLER FAN VANEAXIAL FAN TUBEAXIAL FAN...
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS FAN LAWS Fan power is the actual fan power required to drive the fan. Po = Theoretical Po Fan efficiency Fan laws (Table 1) are simple and useful when dealing with changing conditions. Three important laws deal with speed = (m /s x FTP) Fan efficiency...
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS The quantity of air flowing in a duct can be variable or constant, depending on the type of system. See TYPES OF AIRFLOW SYSTEMS. PRESSURE CHANGES WITHIN A DUCT For air to flow within a duct, a pressure difference must exist. The fan must overcome friction losses and dynamic (turbulent) losses to create the necessary pressure difference.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS TOTAL PRESSURE VELOCITY PRESSURE STATIC PRESSURE AIRFLOW A. PRESSURE IN THIS DUCT ABOVE ATMOSPHERIC PRESSURE STATIC PRESSURE TOTAL PRESSURE VELOCITY PRESSURE AIRFLOW C2643 B. PRESSURE IN THIS DUCT BELOW ATMOSPHERIC PRESSURE Fig. 8. Relationships of Total, Static, and Velocity Pressures for Positive and Negative Duct Static Pressures. FRICTION LOSS TOTAL PRESSURE TOTAL PRESSURE...
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS In transitions to and from equipment an attempt is made to spread the air evenly across the face of the equipment. If the FRICTION LOSS diverging section into the equipment has too great an angle, TOTAL PRESSURE STATIC splitters are often used.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS MEASUREMENT OF AIRFLOW IN DUCTS To obtain accurate velocity pressure readings, the pitot tube tip must point directly into the air stream. Figure 16 shows the error in static and total pressure readings when the pitot tube GENERAL does not point directly into the air stream.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS leveled 10:1 inclined manometer calibrated against a hook areas are taken. Readings are taken along at least two diameters gauge can read to approximately 1.25 Pa. A standard pitot perpendicular to each other. In rectangular ducts, readings at the tube with an inclined manometer can be used with the following centers of equal rectangular areas are taken.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Electronic flow stations use the tube type construction with AIRFLOW MEASURING DEVICES thermal velocity sensors instead of static and total pressure sensors. Other flow sensing arrangements use holes in round Various devices for measuring airflow are available. Figure 19 tubing (Fig.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS AIRFLOW CONTROL APPLICATIONS CENTRAL FAN SYSTEM CONTROL branch (Fig. 24C). Each sensed point should have its own setpoint in the control loop. This avoids the assumption that branches and multisensor locations have identical Figure 23 shows the net airflow balance for a building space requirements.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS A controlling high-limit application is used when the fan A wide proportional band setting (10 times the maximum duct static pressure at the fan discharge) on the fan control is a system must continue to run if duct blockage occurs, but its good starting point and ensures stable fan operation.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Since building static is controlled directly, the pressure remains constant even when exhaust fan airflow changes. Minimum outdoor airflow varies with changes in exhaust fan airflow and RETURN AIR TERMINAL DUCT STATIC building infiltration/exfiltration. In a control sequence where the UNITS PRESSURE SENSOR outdoor air damper is closed, the building static must be reset to...
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Duct Static Control RELIEF Duct static control is similar to supply fan duct static high- limit control, except return duct static pressure is negative. If individual space returns are damper controlled, return fan BUILDING SPACE control must use this technique (Fig.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS In systems not having a return air fan, the return damper RELIEF controls minimum outdoor airflow or building pressurization. FLOW Airflow tracking or direct building static pressure control can MEASURING be used to control the return damper, depending on which STATION parameter is most important.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS SEQUENCING FAN CONTROL Vaneaxial fan sequencing is also decided by total supply flow, 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.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS OUTDOOR SUPPLY RETURN RETURN INDOOR STATIC STATIC PRESSURE PRESSURE SENSOR SENSORS CONTROLLER CONTROLLERS DUCT STATIC REFERENCE AIRFLOW STATIC SENSOR (2) C2664 C2665 Fig. 40. Control of Return Dampers in Fig. 41. Control of Return Fan in Zone Airflow Control. Zone Airflow Control.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS Essentially, the increase of outdoor air above that required to FUME HOODS maintain building pressurization is done the same way as mixed air control except outdoor air is controlled by flow rather than Fume hoods are the primary containment devices in most mixed air temperature (Fig.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS The standard hood can be controlled either by adding a The subject of the “correct” face velocity is still debated. face velocity sensor at the sash opening or by installing However, most research now indicates that 0.4 to 0.5 meters per devices to measure the sash opening to calculate face second (m/s) at the sash opening provides a zone of maximum velocity.
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS 0.7 m CRACK AREA = 0.05 m LAB AIRFLOW AIRFLOW DAMPER ACTUATOR SENSOR CONTROLLER PANEL OR AIR VALVE DAMPER EXHAUST ACTUATOR 0.5 m OR AIR SUPPLY VALVE E X H 0.4 m A U S A I R AIRFLOW SENSOR...
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS CRACK AREA = 0.05 m 2 The significant issues are 1) how fast can the room pressurization system respond to upset (a door opening or several hoods being closed at once) and 2) what is the impact EXHAUST on adjacent areas and the rest of the building.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Chiller, Boiler, and Distribution System Control Applications ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTENTS Introduction ......................295 Abbreviations ......................295 Definitions ......................295 Symbols ......................296 Chiller System Control ......................297 Introduction ..................297 Vapor-Compression Refrigeration ............
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Boiler System Control ......................327 Introduction ..................327 Boiler Types ..................327 Cast Iron and Steel Boilers ............. 327 Modular Boilers ................327 Electric Boilers ................328 Boiler Ratings and Efficiency ............... 328 Combustion in Boilers .................
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Variable Speed Pump Control ............353 Decoupled Variable Speed Pump Control, Direct Return ... 353 Pump Speed Valve Position Load Reset ........355 Balancing Valve Considerations ..........357 Balancing Valve Effects ............357 Balancing Valve Elimination............
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS High Temperature Water Heating System Control ................... 374 Introduction ..................374 High Temperature Water (HTW) Heating ........374 High Temperature Water Safety ............375 HTW Control Selection ................ 375 HTW Valve Selection ................375 Valve Style ..................
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.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Primary Thermal Units: Thermal production water elements such Superheat: The additional heat contained in a vapor at a as chillers and boilers. Thermal production air elements temperature higher than the saturation (boiling) such as air handlers. temperature corresponding to the pressure of the vapor.
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.
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.
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.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS CONDENSER generator. In the generator the weak absorbent is heated to drive WATER IN (evaporate) the refrigerant out of the absorbent and restore the CONDENSER CONDENSER strong absorbent. The strong absorbent then passes through the WATER OUT heat exchanger, where it gives up some heat to the weak absorbent, and then returns to the spray heads in the absorber...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS internal control that transfers liquid from refrigerant circuit to Proportional-integral (PI) control improves the accuracy of absorbent circuit, transfers liquid from absorbent circuit to control. When integral control is used, provisions to prevent refrigerant circuit, limits heat input, or a combination.
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.
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 AUTO NORMAL ENABLED 10.5 BY REMOTE OPERATING STATUS PERCENT LOAD ALARM CONTROLS MODE STATUS CURRENT...
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 1545 THE CHILLED WATER PUMP STARTS AND ENABLES THE CHILLER SYSTEM CONTROLS.
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...
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 24 kelvins temperature when the first chiller reaches 100 percent load.
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...
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...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS NOTE: When using two-way AHU valves with this Anytime chilled water flow is proven via a chilled water pump current sensing relay, the respective chiller controls shall be coupled chiller configuration, exercise care in enabled to operate under factory controls, subject to a chiller optimizing the chilled water temperature.
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.
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 29.5 M15259 Fig. 18. Digital control of Sequenced Cooling Towers. Multiple Centrifugal Chiller Sequencing FUNCTIONAL DESCRIPTION % SPEED SECONDARY...
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 KELVINS FOR GREATER THAN MINUTES, BUT WITH NO LESS THAN MINUTES BETWEEN STARTS.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS DISSIMILAR MULTIPLE CENTRIFUGAL temperature and the entering condenser water temperature are frequently optimized and chiller capacity varies with changes CHILLERS CONTROL in either temperature, the per-chiller expected should be dynamically modified based upon manufacturers data regarding When a multiple chiller system consists of chillers that are these variations.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS 2.375 HIGH PRESSURE 2.250 STEAM SUPPLY PRV SET APPROX. 2.125 TO INLET VANE 69 kPa ACTUATOR SENSOR IN 2.000 TURBINE-DRIVEN CHILLED CENTRIFUGAL WATER BACK CHILLER 1.875 SUPPLY COMPRESSOR PRESSURE ABSORPTION TURBINE CHILLER RELAY 1.750 CENTRIFUGAL CHILLER...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS THERMAL STORAGE CONTROL – Charging Cycle: Valves V and V are closed and V controlled by T to maintain the flow rate at F . Pump is off. T controls chiller capacity to maintain 4.5 C GENERAL CHWS temperature.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS TEMPERATURE RANGE (KELVINS) COOLING TOWER AND CONDENSER WATER CONTROL COOLING TOWER PERFORMANCE CHARACTERISTICS SUMMER DESIGN CONDITIONS: ENTERING WATER, 32.5˚C The cooling tower dissipates the heat collected from the LEAVING WATER, 27.5˚C OA WET BULB, 24˚C building by the chiller and chilled water system by cooling the condenser water.
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...
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 used for single speed fan control. OA WB plus 3.5 kelvins, or the minimum temperature acceptable to the chiller, whichever is higher.
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.
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 25.5 25.5 SETPOINTS/...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS setpoint shall be determined by the tower free cooling control Features module. The OA WB shall be calculated from OA RH (the RH 1. Precise PI condenser water control above minimum load. sensor shall be of no less than 2% accuracy) and OA DB. The 2.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS than 7 minutes. The operating tower valves shall modulate to If both fans are off and the water temperature drops to the valve maintain the above noted valve control setpoint at anytime control setpoint plus 0.5 kelvins, the valves of Tower 1 shall regardless of fan operation.
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.
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...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS TOWER FREE COOLING, DUAL CHILLERS FUNCTIONAL DESCRIPTION FREE COOLING OA WB SETPOINT = CHILLED WATER TEMPERATURE SETPOINT MINUS DEGREES OUTSIDE CHILLER/ FREE COOLING SETPOINT DRY BULB CHILLER/ FREE CHILLER/ FREE COOLING COOLING CURRENT MODE CURRENT MODE COOLING COOLING...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Features Condenser water: 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.
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 A boiler is a closed vessel intended to heat water and produce are substantially surrounded by water.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Some modular boilers have very small storage capacity and Electric elements and electrodes are grouped to provide four very rapid heat transfer so water flow must be proven before or more stages of heating. A step controller responding to steam the burner is started.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS – Steam or air atomizing burners use high pressure air or COMBUSTION IN BOILERS 270 kPa 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.
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 SYSTEM boiler: CONTROL LINKAGE...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS OPERATING HI LIMIT CONTROLLER POWER FLOW SHUTOFF PRESSURE MAIN BURNER VALVE REGULATOR VALVE PILOTSTAT THERMO- AUTOMATIC COUPLE VALVE PILOT PILOT M15050 BURNER GAS LINE Fig. 45. Simple Flame Safeguard for a Gas Furnace. Figure 46 shows how flame safeguard controls are integrated APPLICATION OF BOILER CONTROLS with combustion controls on a small oil fired steam boiler.
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.
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 29.5 AUTO BOILER BOILER BOILER SYSTEM SYSTEM PUMP P1 BOILER -1 ON-OFF-AUTO OFF-AUTO SELECTOR SELECTOR AUTO AUTO OUTSIDE AIR TEMPERATURE...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Features Specification 1. Full flow through operating boilers. The heating plant shall operate under automatic control 2. Minimum temperature limit on boiler entering water. anytime the secondary pump ON-OFF-AUTO function is not 3. Variable flow secondary system with full boiler flow. “OFF”, subject to a heating system ON-OFF-AUTO software 4.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Boilers that are off have no flow and are allowed to cool. During boiler operation, a three way blending valve shall 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 63 C, intermittent operation prevents losses up the stack or to the at which time the blending valve shall modulate to maintain...
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...
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...
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 a Commercial pumps have performance curves showing the pump. Each curve of the family represents a different size impeller following data for a given pump speed: used with the pump at a specified rpm.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Figure 55 illustrates a pump fitted with a 165 mm impeller, Table 3. Pump Affinity Laws. operating at 130 kPa, and delivering 4.2 L/s of water. Specific Impeller Gravity Correct Multiply Water power = 4.2 L/s x 130 kPa Diameter Speed (SG)
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 pressure curve.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS 240mm BALANCED OPERATING POINT WITH 240mm IMPELLER DESIGN OPERATING POINT 220mm OPERATION WITH 220mm IMPELLER 200mm 185mm 11000W 9000W 7500W SYSTEM CURVE 5500W 4000W 6.25 12.5 18.75 31.25 37.5 43.75 56.25 C4093 CAPACITY IN (L/s) Fig.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS TYPICAL RANGE OF PERFORMANCE VARIABLE SPEED PUMPS FOR VARIABLE SPEED PUMP From the pump affinity laws (Table 3), pump power decreases by the cube of the decreased speed, and flow decreases linearly with speed; so at 80 percent flow, the power (kW) is down to nearly 50 percent (80 percent cubed).
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Table 4. Variable Speed Pump relationships Load (percent) Condition Flow (L/s) 31.5 0.80 x 31.5 = 25.2 0.60 x 31.5 = 18.9 0.40 x 31.5 = 12.6 Speed (rpm) 1750 0.80 x 1750 = 1400 0.60 x 1750 = 1050 0.40 x 1750 = 700 Total Pressure (kPa)
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.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS SUPPLY PIPING CONTROL VALVE(S) PUMP SERIES CONTROL PUMPS VALVES HEATING/ HEATING LOAD COOLING HEAT SOURCE COOLING EXCHANGER COILS BALANCING VALVES RETURN PIPING 2 PUMPS DESIGN PRESSURE DROP IN kPa FLOW CONTROL BALANCING ITEM COIL &...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS As flow through the system is reduced, a new system curve COIL, is established. See the 0.375 L/s curve in Figure 69. When the PUMP 1750 RPM SUPPLY/ CURVE RETURN flow is reduced, the new pressure loss in source and supply and SYSTEM CURVE PIPING 2.2 kPa return piping can be calculated using the formula:...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The Figure 70 supply piping runs out to the coils decreasing in Supply piping is the same for a reverse return system (Fig. 71) size between AHU 1, 2, 3, 4, 5, and 6. The return lines between as for the direct return system (Fig.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS METHODS OF CONTROLLING — Piping Cost. Costs are higher for three-way valves than 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.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The examples in this section on Flow And Pressure Control piping drops are 81 percent of design (90 percent squared). Solutions use a distribution system that has six equal loads The pump curve (not shown) indicates a pump pressure of (coils) as shown in Figure 73.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS TOP NUMBERS = FULL FLOW NUMBERS IN CIRCLES = GAUGE PRESSURES (kPa) BOTTOM NUMBERS = HALF FLOW, EACH COIL (PUMP INLET = ZERO kPa FOR SIMPLICITY) PD = PRESSURE DROP IN kPa 18 kPa DROP TOTAL 145.5 CHILLER HEAT/...
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 27.9 kPa, but across Coil 1 A reverse return system analysis equivalent to the direct return where the greatest differential pressure change exists (84 kPa analysis of Figure 74 would show that at half flow and no...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Dual Pumps, Dual Chillers, Pressure Bypass, With digital controls, the differential pressure setpoint offset 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 14.4 kPa) invoked anytime only one pump and one chiller are operating.
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 operation.
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 OPERATING POINT @ FULL LOAD AHU 1 requires a 84 kPa differential pressure (24 kPa for 25 L/s &...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS No pump pressure control example, so far, takes advantage FULL LOAD of both the variable speed pump and a digital control system. OPERATING POINT The digital control system VSD control algorithm adjusts the PUMP CURVE @ 1750 RPM differential pressure setpoint based on the demands of all the...
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.
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.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS The control objectives for a hot water distribution system Minimum flow (L/s) = providing space heating are: 4.2 x T Where: 1. Provide adequate hot water flow to all heating units. T = Low flow water temperature rise across the 2.
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.
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...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Supply Hot Water Temperature Control RATED OUTPUT 75% FLOW REDUCTION 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.
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).
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 90.5 RESET SCHEDULE PERCENT OPEN 1/3 CAPACITY PERCENT OPEN PUMP 2/3 CAPACITY START POINT AUTO CONVERTOR C-1...
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 the below the capacity of the small valve for five minutes, the large heat delivery from a heat exchanger or a secondary water pump.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS System Objectives The chilled water control and distribution system should: TERMINAL 1. Provide the minimum flow of chilled water through the UNITS chiller as specified by the manufacturer. 2-POSITION 2. Provide a stable pressure difference across supply and 3-WAY VALVE return mains.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS 1. Steam mains must provide adequate capacity so steam PUMP velocity is between 40 and 60 meters per second. PUMP PUMP PUMP 2. Water must not be allowed to accumulate in the mains. Provisions must be made for the use of traps or superheated steam to reduce or eliminate water in mains.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS STEAM SYSTEM HEAT CHARACTERISTICS EXAMPLE: The heat in 50m of steam: Figure 101 shows the characteristics of one kilogram of steam at 150 kPa is 43 kg x 2693 kJ/kg = 115 799 kJ as it travels through a steam heating system.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS STEAM DISTRIBUTION SYSTEMS The float and thermostatic trap (Fig. 104) can handle large 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.
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.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS TYPES OF LOW PRESSURE STEAM TYPES OF CONDENSATE RETURN SYSTEMS DISTRIBUTION SYSTEMS In addition to gravity return used for small systems, either open or vacuum return systems can be used. One-Pipe Steam Systems In open return systems (Fig.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Low pressure steam systems operate on pressures ranging from Table 7. Heat Output versus Steam Pressure for Coils. 100 kPa to 200 kPa. The steam main pressures are usually under Saturated Typical Steam 170 kPa and the returns are vented to the atmosphere.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Figure 114C shows the quarter-open valve position. Half of Oversized Valve the coil surface is starved of steam, the heat output is reduced to about half of the original value and the trap is full open. All In Figure 114A a large valve is used to ensure 128 kPa in the of the steam has been condensed in the coil before reaching the coil.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS Figure 115B shows the valve in the half-open position. The 2. Returns at atmospheric pressure, unless lifts (condensate output of the coil is cut approximately in half (16 kW). This is pumps) are required in the returns. in contrast to the oversized valve application (Fig.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS HIGH TEMPERATURE WATER HEATING SYSTEM CONTROL — Feedwater requirements are minimal, eliminating INTRODUCTION treatment costs and introduction of air which is a source of corrosion. HTW systems tend to remain clean. HIGH TEMPERATURE WATER (HTW) HEATING —...
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS HIGH TEMPERATURE WATER SAFETY HTW VALVE SELECTION A well designed HTW system with proper installation of Valves for HTW must be selected to ensure suitability for piping to prevent undue stress rarely fails. high temperature and pressure conditions.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS VALVE TRIM VALVE LOCATION Use stainless steel valve stems and trim. Standard trim for Always locate a HTW valve on the return side of the industrial valves is usually 316 stainless steel. Composition discs converter, coil, steam generator, or other equipment because it leak and corrode at the seat and disc and are not used.