Cycling degradation in IEER calculation for variable/multi speed coils

[lymereJ]

Issue overview

The IEER calculation in EnergyPlus relies on EER values calculated using Equation 4 in AHRI Standard 340/360, see figures below. In this equation the EER is a function of C_D, the coefficient of degradation. That equation is used to calculate the EER values at different loading point (as per the Standard): 100%, 75%, 50%, and 25%. These different values are used to calculate the IEER, see Equation 3. However, the standard specifies that Equation 4 should only be use for units that "cannot be unloaded to the 75, 50, or 25 Percent Load".

EnergyPlus should not be using this approach to calculate the EER values used to calculate the IEER if a coil can unload at 75%, 50%, and 25% load, this includes the Coil:Cooling:VariableSpeed and other multi-speed/stage cooling coil objects. Otherwise a cycling degradation penalty is accounted which might not be representative of the actual simulated coil performance. Cycling degradation should only be accounted for if the coil cannot unload without cycling below the requirement percent loads.

Details

Some additional details for this issue (if relevant):

• Platform: All
• Version of EnergyPlus: 24.1

Checklist

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

• [ ] Defect file added (list location of defect file here)
• [ ] Ticket added to EnergyPlus Defect Complexity (Github Project)
• [ ] Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)

[lymereJ]

For instance, for variable speed coils, the IEER is calculated by this function which relies on CalculateInterMediateEER implements Equation 4 not matter what type of coil and its unloading capabilities.