10.8. Abbreviations
Table 9.
Abbreviation
Definition
A55
M3 board. Main RTU control board
AI
Analog input
AO
Analog output
BL
Blower
C3
Add on board for third and fourth 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 CO2 level
in ppm
IDE
Indoor enthalpy. Depends on temperature and
humidity
"w.c.
Inches of water column
Abbreviations
Table 9.
Abbreviation
Definition
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
M4
CORE 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 CO2
measurements)
RAP
Return air pressure
RAT
Return air temperature
RH
Relative humidity
RS
Reset
RTU
Roof top unit
RT6
Discharge air temperature sensor
RT16
Return air temperature sensor
RT17
Outdoor air temperature sensor
SMK
Smoke detection mode (alarm)
SP
Setpoint
Stg
Stage
Tb
Terminal block
UnOCP
Unoccupied
W1
Thermostat demand, heat stage 1
W2
Thermostat demand, heat stage 2
W3
Thermostat demand, heat stage 3
W4
Thermostat demand, heat stage 4
VAC
Alternating current voltage
VAV
Variable air volume. Accomplished with a variable
frequency drive (VFD)
VDC
Direct current voltage
VFD
Var. frequency drive. An AC inverter used to vary
motor speed
VT
Ventilation
Y1
Thermostat demand, cooling stage one
Y2
Thermostat demand, cooling stage two
Y3
Thermostat demand, cooling stage three
Y4
Thermostat demand, cooling stage four
ZAT
Zone air temperature
35
Abbreviations
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