Introduction; Abbreviations; Definitions - Honeywell AUTOMATIC CONTROL Engineering Manual

INTRODUCTION

This section provides descriptions of and control information
about water chillers, cooling towers, hot water boilers, steam
boilers, and water, steam, and district heating distribution systems.
It discusses various methods of controlling and distributing steam
or water to heating and cooling coils, and methods of ensuring
safe and proper control of boilers, chillers, and converters. Sample
system solutions are based upon digital control systems and
networks. These digital control strategies may not be practical
with other forms of control, and may not be possible with all

ABBREVIATIONS

AHU — Air Handling Unit
BMCS — A Building Management and Control
System, including digital controllers
and communication networks.
CHW — CHilled Water
DB — Dry Bulb
DP — Differential Pressure
Delta T (∆T) — Differential Temperature
EPID — Enhanced PID. A PID algorithm which
includes integral component windup
prevention, user defined initial value,

DEFINITIONS

Approach–
1. The temperature difference, in a cooling tower,
between outdoor wet bulb and condenser water
leaving the tower.
2. The temperature difference in an air cooled
condenser between the liquid refrigerant leaving the
condenser and the entering air dry bulb.
3. The temperature difference in a conduction heat
exchanger between the entering working fluid and the
leaving treated fluid.
Central plant–An area or building where the chillers and boilers
for a building or group of buildings are located.
Compressor–A mechanical device for increasing a gas pressure.
• Centrifugal compressor–A device which uses
centrifugal force to compress refrigerant vapors in a
vapor-compression cycle chiller. This is not a positive
displacement compressor.
• Positive displacement compressor–A compressor that
reduces the volume of a compression chamber to
compress a gas.
• Reciprocating compressor–A positive displacement
compressor which uses the reciprocating motion of one
or more pistons to compress a gas.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
digital controllers or by all digital controller programmers. Many
solutions are portrayed as they may be specified to be displayed
on a PC based BMCS color graphic monitor. The data points
shown on the color graphics are still recommended for systems
without color graphics, and may be specified via a points list or
by publishing the graphic picture. The values (setpoints, timings,
parameters, etc.) shown in the examples are arbitrary. Values for
any given project must be specific to the project.
Constant speed pumping–A pumping system where the system
Deadband–A range of the controlled variable in which no
Diversity–A design method where building elements (such as
Double bundle Condenser–A chiller condenser having two coils
Head–Pressure of a fluid
297
and user defined start-up ramp time.
See CONTROL FUNDAMENTALS
section.
HW — Hot Water
HX — Heat eXchanger
NPSH — Net Positive Suction Head
OA — Outside air
PID — Proportional-Integral-Derivative
SG — Specific Gravity
VAV — Variable Air Volume
VSD — Variable Speed Drive
WB — Wet Bulb
• Screw compressor–A positive displacement compressor
which uses the rotary motion of two meshed helical
rotors to compress a gas.
pressure is maintained by a constant speed pump.
corrective action is taken by the system and no energy
is used.
chillers and pumps) are sized for the instantaneous
building peak load requirements (rather than the sum of
all the loads, which may individually peak at times other
than when the building peaks). Diversity does not allow
the use of three-way AHU control valves.
in the shell to allow the chiller to dissipate heat either to
the cooling tower or to a heating load.
• Head pressure–The pressure measured at the discharge of
an operating pump or compressor.
ENGINEERING MANUAL OF AUTOMATIC CONTROL