Normal Heat Pump Control
Normal Heating
In the Normal Heating state the following are accomplished:
• Compressor capacity (INV and Comp 3) is regulated to maintain the DAT at either the Discharge Air Temperature Heating
Setpoint (Unit State=Heating) or the Minimum Discharge Air Temperature Spt (Unit State=MinDAT)
• Outdoor coil expansion value (EVO) is modulated to maintain the suction superheat at the suction superheat setpoint
• Indoor coil expansion valve (EVI) is controlled to maintain indoor coil subcooling at the indoor coil subcooling setpoint (heat
pump)
• Outdoor fan(s) are set to maximum and then decreased if the suction pressure is high (above 162.2 psi) or increased back
toward the maximum if the suction pressure is low (below 106.7 psi).
When in the Normal Heating state the action of the heating control devices is as follows:
Table 68: Normal Heating State
Device Action
Compressors
Inverter Compressor Speed Controlled with PI Loop to maintain DAT Setpoint
Comp 3: Turned On when Inverter Compressor at Maximum
Comp 3: Turned Off when Inverter Compressor at Minimum
Outdoor Fan A
4 Way Valve
(HeatPump)
ON
Outdoor Coil Expansion Valve (EVO)
(HeatPump)
EVO Controlled With PI Loop to maintain Suction Superheat Setpoint
SVR
(HeatPump)
Closed
SVB
SVB is normally closed during the Normal Heating state
except in the following cases:
SVB is opened for one second before and after Comp 3 is stopped.
During Low Pressure Unloading Control SVB is opened if PTS <147.1 kPa
(21.34 psi). It is closed again when PTS>294.2 kPa (42.67 psi).
Indoor Coil Expansion Valve (EVI) B
Time Duration While in Normal Heating state
A. Outdoor fan(s) are set to maximum and then decreased if the suction pressure is high (above 162.2 psi) or increased back
toward the maximum if the suction pressure is low (below 106.7 psi).
B. The indoor expansion valve is either driven fully open or varied based on indoor coil subcooling as follows:
When the Htg EVI Method is set to 100%, the indoor expansion valve is driven to the 100% open position.
When the Htg EVI Method is set to SbC, the indoor expansion valve is controlled to maintain the indoor coil subcooling at
the indoor coil subcooling temperature setpoint.
OM 1141-3 • MICROTECH UNIT CONTROLLER 118 www.DaikinApplied.com
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