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McQuay OM 751 19
Description of Operation
Figure 12: Cool mode super state diagram
Econ State (State 3)
The Econ state is a “normal” state during Cool mode. The Econ state typically is active in the
Cool mode when primary cooling (economizer) is available and adequate to meet the cooling
requirements.
When the Econ state becomes active, the UVC uses economizer cooling (see “Economizer
Operation” on page 32) as needed to maintain the effective cooling set point (see “Space
Temperature Set Points” on page 26). If cooling is not required while in the Econ state, the
UVC can “idle” in the Econ state until cooling is required or until there is a call to switch to
another mode or state.
The UVC monitors the DAT to ensure it does not fall below VCLL.
The CO
2
demand controlled ventilation function (optional) will be active (see “CO2 Demand
Controlled Ventilation (optional)” on page 34) and the OA damper is adjusted as needed to
maintain the CO
2
set point.
Econ
EconMech
Mech
3
1
2
CantCool
C
CoolMode
SuperState
DAHeat
LowLimit
4
F
LLPI=SatLow (2min)
AND
DAT>(VCLL+1.8F)
HeatPI=SatHi(2min)
AND DAT<VCLL
Space
≠
HighCO2
AND
HeatPI=SatLow
AND
DAT>VCLL
Space=HighCO2
OR
DAT<VCLL
UVCMode
≠
Cool AND UVCMode
≠
Auto
OR
UVCMode=Auto AND Space=Cold AND
MechPI=SatLow(3min) AND
EconPI=SatLow
UVCMode=Cool
OR
UVCMode=Auto AND Space=Warm
Econ
≠
Available
AND
MechCool
≠
Available
Econ = Available
AND
MechCool
≠
Available
Econ
≠
Available
AND
MechCool=Available
MechPI=SatLow (3min) AND
EconMechTimer=Expired
(3 minutes) OR
MechCool
≠
Available
Econ
≠
Available
Econ=Available
MechCool
≠
Available
Econ
≠
Available
AND
MechCool=Available
Transition
Point
EconTimer=Expired
(3 minutes) AND
EconPI=SatHi AND
MechCool=Available