Accessory List

Glossary
F-27382-1 © Copyright 2006 TAC. All Rights Reserved. 383
Abbreviations
ACU: Air Conditioning Unit
AHU: Air Handling Unit
ASHRAE: American Society of Heating, Refrigerating, and
Air-Conditioning Engineers; 1791 Tullie Circle N.E.; Atlanta,
GA 30329.
BTU: British Thermal Unit
C: Common
CCW: Counter Clockwise
CFM: Cubic Feet per Minute
CR: Condensate Return
CW: Clockwise
CWR: Chilled Water Return
CWS: Chilled Water Supply
DDC: Direct Digital Control
D.A.: Discharge Air, Direct Action, Direct Acting
ΔT: Temperature Differential or Change
DIFF: Differential
DPC: Differential Pressure Controller
DPDT: Double Pole - Double Throw
EA: Exhaust Air
EMS: Energy Management System
EP: Electric - Pneumatic Switch
FA: Fresh Air
GPM: Gallons Per Minute
h: Enthalpy
HVU: Heating and Ventilating Unit
HVAC: Heating, Ventilating, and Air Conditioning
HWR: Hot Water Return
HWS: Hot Water Supply
in. wc: inches of water column
mA: Milliamps
M.A.: Mixed Air
N.C.: Normally Closed
N.O.: Normally Open
NEMA:National Electrical Manufacturers Association
O.A.: Outdoor Air
PA: Percent Authority
PB: Proportional Band
PE: Pneumatic Electric switch
PID: Proportional, Integral, Derivative
PPM: Parts Per Million
PSI: Pounds per Square Inch
R: Ratio
R.A.: Return Air, Reverse Action, Reverse Acting
RC: Receiver-Controller
RH: Relative Humidity
RSES: Refrigeration Service Engineer Society, 960 Rand
Rd., Des Plaines, IL 60016
SP: Setpoint
SPST: Single Pole - Single Throw
TR: Throttling Range
SS:
Steam Supply
TR: Throttling Range
Vac: Volts Alternating Current
VAV: Variable Air Volume
Vdc: Volts Direct Current
VFD: Variable Frequency Drive
Absolute Pressure (PSIA): The sum of both atmospheric
pressure (14.7) and gauge pressure (psig). Example: If a
pneumatic gauge indicates 8 psig, the absolute pressure will
22.7 psia (8+14.7).
Action: The direction of magnitude change of the output of a
controller with respect to the change in the variable that is
being sensed. Example:
Direct Action (D.A.): Variable increases, output increases.
Reverse Action (R.A.): Variable increases, output decreases.
Actuator: A device which is mechanically linked to a damper
and positions the damper to regulate the flow of air; or is
mounted on a valve and repositions the valve to regulate the
flow of steam or water. Actuators are sometimes referred to as
operators or motors.
Adaptor (TAC System 8000): A device which conditions the
signal from a controller and it modifies this signal in some
manner before the signal reaches the controlled device
thereby accomplishing specific applications such as
sequencing, paralleling, minimum position, etc.
AHU (Air Handling Unit): A mechanical system usually
consisting of an enclosure housing a supply-air fan (or fans),
heating and/or cooling coils, filters, and outdoor air and return
air dampers. May include return air fan(s) and relief air
damper(s). May deliver air to a single space, to a number of
zones, or to numerous constant-volume or variable-volume air
terminal units.
Air Conditioning: The process of treating air so as to
control simultaneously its temperature, humidity, cleanliness
and distribution to meet requirements of the conditioned
space.
Air Handling Unit: Refer to AHU.
Analog: A proportional type of signal whose level varies
smoothly and continuously in amplitude or frequency.
Gl
o