157
29. Abbreviations
A55 M3 board. Main RTU control board
AI Analog input
AO Analog output
BL Blower
C3
Add on board for third and forth compressor and second-stage heat (A178).
C1 1st stage cooling
C2 2nd stage cooling
C3 3rd stage cooling
C4 4th stage cooling
CAI Combustion air inducer
CAVB Constant air volume with bypass damper
COM Electrical common
CL Cooling
CP1 Compressor 1
CP2 Compressor 2
CP3 Compressor 3
CP4 Compressor 4
CSP Cooling setpoint
DAC Discharge (supply) air control
DACC Discharge (supply) air control cooling
DACH Discharge (supply) air control heating
DAP Discharge (supply) air pressure
DAT Discharge (supply) air temperature
DB Deadband
DCV Demand controlled ventilation
DDC
Direct digital control
DI Digital input
Diff Differential
DO Digital output
FAC Fresh air cooling control
FAH Fresh air heating control
FAT Fresh air tempering control. See FAC & FAH
FC Free cooling
G Thermostat demand, blower
GLO Global mode or input (economizer)
H1 1st stage heating
H2 2nd stage heating
H3 3rd stage heating
H4 4th stage heating
HP High pressure
HSP Heating setpoint
HT Heating
IAQ Indoor air quality. Often synonymous with CO
2
level in ppm
IDE Indoor enthalpy. Depends on temperature and humidity
“w.c. Inches of water column
LED Light emitting diode. An indicator light, found either as individual elements or grouped together as segments to form
characters
LP Low pressure
LT Limit
M3 M3 Unit Controller - main controller board (A55)
MGV Modulating gas valve
MSAV Multi Stage Air Volume
OAC Outdoor air control
OAS Outdoor air suitable for free cooling
OAT Outdoor air temperature
OCP Thermostat demand, occupied mode
ODE Outdoor enthalpy. Depends on temperature and humidity
PID Proportional, integral and derivative based control loop
PPM Parts per million (mostly used for CO
2
measurements)
RAP Return air pressure
RAT Return air temperature
RH Relative humidity
RS Reset
RTU Roof top unit
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