Issues with compressor nominal capacity mismatch and modeling a cold antechamber in EnergyPlus supermarket model
I am modeling a supermarket in EnergyPlus with two compressor racks (3 LT and 3 MT compressors).
For both LT and MT, I used manufacturer specs and generated bicubic performance curves (power and capacity) with the Bitzer software. The LT compressors supposedly have 10.7 kW cooling capacity each. I modeled this in the IDF, but I get the following warning:
* Warning * Refrigeration:System="REFLT", You may wish to check the system sizing.
Total nominal cooling capacity is 34483W.
Condenser capacity is 35055W.
Nominal compressor capacity is 20665W.
I don’t understand why the Nominal Compressor Capacity shows ~20.7 kW, while I expected ~32 kW (3 × 10.7 kW), even though it wouldn't be enough for the total nominal cooling capacity of 34kW.
I created three Refrigeration:Compressor objects (with the same curves but different names), grouped them in a Refrigeration:CompressorList, and referenced that in the Refrigeration:System object. Am I missing something about how EnergyPlus calculates compressor nominal capacity?
A second question: In the supermarket BackRoom zone, I have several walk-in coolers, modeled with Refrigeration:WalkIn. That worked fine. But I also need to model an antechamber (which is also a cold room) as a separate thermal zone because its doors lead to all of the walk-in coolers. I cannot use Refrigeration:WalkIn here, since the insulated panels are already modeled as BuildingSurface:Detailed, which would double-count the heat transfer.
So I tried using Refrigeration:AirChiller with ZoneHVAC:RefrigerationChillerSet. However, AirChillers cannot be mixed with WalkIns and Cases in the same CaseAndWalkInList. I then tried to create a new Refrigeration:System that uses the same MT compressor list, but EnergyPlus does not allow sharing compressors between systems.
Given that I only have 3 MT compressors in reality, how should I model this antechamber? I cannot simply dedicate one of the compressors to it, since its load is much smaller compared to the WalkIns and display cases.
Any guidance on:
Why the compressor nominal capacity doesn’t match the expected value?
How to properly model this small antechamber connected to the same compressor rack?
Thanks in advance!
