jeannieboef
commented
9 years ago Update to comments:
1) Cd is not calculated as per 3.5.3 of AHRI 210/240 (dry coil tests). The default value is also not used for when these tests are not conducted. Instead, the degradation is calculated from the model’s PLF(PLR) curve.
2) The code enters the PLR in to the PLF(PLR) equation where PLR = Part Load / Total Load, but the PLF(PLR) curve requires sensiblePartLoad/TotalSensiblePartLoad as an input. My spreadsheet shows that because the flowrates and the entering temperatures remain constant, the BFs and SHR remain the same at both the 100% and 50% TotalPLR points, thus the error cancels out, and the result is identical. This may not stay so for variable airflow units (including single speed compressor with variable speed supply fan).
As for IEER, I have only two issues:
1) There is no way to input auxiliary energy usages that do not add to the fan heat. E+ assumes that the condenser fan cycles on and off at the same time as the compressor, so I can’t add them here. The fan motor may not even be in the air stream, or the unit may even have a “power exhaust” where again the energies need to be included, but not the heat. This should be easy to add to the code.
2) The LF/Cd combination should only be used in the calculation when the equipment cannot "go" to that rating point (due to curve limits, i.e. due to machine limits). After that the current proceedure is correct, however before, the machines real degredation can be used as in the test.
Helpdesk ticket 10193 From user . . . StandardRatings.cc lines 1313 (or near) I've been going through some of these lines for the standard rating calcs and would make the following improvement. SEER = ( NetCoolingCapAHRI / TotalElecPower ) * PartLoadFactor However, PartLoadFactor is a function of PLR...and PartLoadFactor = CurveValue( PLFFPLRCurveIndex, PLRforSEER ); ...my improvement suggesting is to correct the code so that PLRforSEER = Sensible Capacity at Partload rating condition / Sensible Capacity at Full load at the same rating condition = 0.5
i.e. the PLFFPLR curve expects the ratio of Sensible Cooling not total cooling and so PartLoadFactor = CurveValue( PLFFPLRCurveIndex, 0.5 ) returns the PLF at the load condition where CapSENSpartload / CapSENSfullload is 0.5.
this PLF is being multiplied to ( NetCoolingCapAHRI / TotalElecPower ) where both NetCoolingCapAHRI is SENS+LATENT.
This is not consistant. In effect the PLFFPLR is being fed a PLR = CapTOTpartload / CapTOTfullload.
The error appears small in the case where the SHR at full load is similar to the SHR at partload. This may not always be the case...or is it, and this is an intentional simplification.
The rest of the code looks good. I still get other IEER values, and don't know why...will continue to search.