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In the EnergyPlus Engineering Reference (pg 909), the reverse-cycle defrost power is given as as function of both fractional defrost time and Runtime-fraction (RTF)

However, in the current source code (DXCoils.cc, (https://github.com/NREL/EnergyPlus/blob/405295034523d273e87403a268c96107e2c0d224/src/EnergyPlus/DXCoils.cc#L8391C4-L8403C5) around lines 8391–8403 in commit 4052950), the defrost power for reverse-cycle on-demand defrost is implemented as:

FractionalDefrostTime = 1.0 / ( 1.0 + 0.01446 / OutdoorCoildw ); ... DXCoil(DXCoilNum).DefrostPower = DefrostEIRTempModFac * ( DXCoil(DXCoilNum).RatedTotCap(Mode) / 1.01667) * FractionalDefrostTime;

i.e., it multiplies by FractionalDefrostTime but not by RTF.

Which formulation is intended to be correct: the Engineering Reference equation including RTF, or the current implementation without RTF? If the code is correct, how should the Engineering Reference equation be interpreted?

In the EnergyPlus Engineering Reference (pg 909), the reverse-cycle defrost power is given as as function of both fractional defrost time and Runtime-fraction (RTF)

However, in the current source code (DXCoils.cc, (https://github.com/NREL/EnergyPlus/blob/405295034523d273e87403a268c96107e2c0d224/src/EnergyPlus/DXCoils.cc#L8391C4-L8403C5) around lines 8391–8403 in commit 4052950), the defrost power for reverse-cycle on-demand defrost is implemented as:

FractionalDefrostTime = 1.0 / ( 1.0 + 0.01446 / OutdoorCoildw ); ... DXCoil(DXCoilNum).DefrostPower = DefrostEIRTempModFac * ( DXCoil(DXCoilNum).RatedTotCap(Mode) / 1.01667) * FractionalDefrostTime;

i.e., it multiplies by FractionalDefrostTime but not by RTF.

Which formulation is intended to be correct: the Engineering Reference equation including RTF, or the current implementation without RTF? If the code is correct, how should the Engineering Reference equation be interpreted?

In the EnergyPlus Engineering Reference (pg 909), the reverse-cycle defrost power is given as as function of both fractional defrost time and Runtime-fraction (RTF)

However, in the current source code (DXCoils.cc, (https://github.com/NREL/EnergyPlus/blob/405295034523d273e87403a268c96107e2c0d224/src/EnergyPlus/DXCoils.cc#L8391C4-L8403C5) around lines 8391–8403 in commit 4052950), the defrost power for reverse-cycle on-demand defrost is implemented as:

FractionalDefrostTime = 1.0 / ( 1.0 + 0.01446 / OutdoorCoildw );
...
DXCoil(DXCoilNum).DefrostPower =
   DefrostEIRTempModFac *
   ( DXCoil(DXCoilNum).RatedTotCap(Mode) / 1.01667) *
    FractionalDefrostTime;
FractionalDefrostTime;