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[EnergyPlus_Support] DX:Multispeed power at low PLR



I am trying to understand how cooling power is calculated in EnergyPlus for a DX:Multispeed system at low part load ratio.


The Engineering Reference shows the following formula for the first speed range:

CoolingPower = (TotCap1)(EIR1)(SpeedRatio)



TotCap1 = f(RatedCap1,TotCapTempModFac1,TotCapFlowModFac1,BypassFactor1)

BypassFactor1 = f(RatedBypassFactor,RatedFlowRate,ActualFlowRate)

EIR1 = RatedEIR1 * EIRTempModFac1 * EIRFlowModFac1

Where “1” designates speed range #1.


Elsewhere, I see a formula for speed ratio that appears for the first speed range to be:

SpeedRatio = (CoolingLoad – FanHeat)/(FullCoolOutput1)



I can extract most of these parameters or the basis for the parameters with Output:Variable, but I can’t seem to get at the Bypass Factor.  


Is there a way to get the bypass factor at each time step?  Can it be calculated from other variables?


Also, when the coil is in the first speed range, my Output:Variable data shows:

SpeedRatio = 0 and

CyclingRatio = CompressorPartLoadRatio.  


So should the SpeedRatio be replaced by CyclingRatio in CoolingPower equation for the first speed range?



Doug Maddox, PE

5800 Baker Road
Minnetonka, MN 55345
T 802-262-1033
F 952.938.1480



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