At issue, our proposed system (chilled water) is paired against a System 5 (non-residental < 5 floors & 25,000 < SQFT < 150,000) but we are having a problem with the energy modeling which was confirmed by the Carrier HAP customer support personnel. The way ASHRAE 90.1-2007 derives the compressor + cond fan kW from the full load EER is a bit flawed and ASHRAE has recognized this. This results in the Packaged DX RTU being a far more efficient system compared to a chiller operating at the same EER. This is because the RTU total energy includes the indoor fan energy and the chiller energy does not. When you subtract out the indoor fan kW allowance from the RTU the resulting compressor + condenser fan kW of the RTU is much less than the chiller.
Summary: Because of the nature of the code and how software interprets it, it seems untenable to pit a chilled water system that does not include fan energy in its EER calculation against a DX packaged system that does include fan energy.
Request: We would like to pair up our proposed chilled water system again System 7 for a more logical comparison. This is my first foray into the LEED online portion, does anyone know how I go about getting a formal answer?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
October 19, 2018 - 1:55 pm
You cannot use a System 7. No formal answer needed unless you want to throw away $220 on a LEED Interpretation. This is not a known issue or a flaw or anything ASHRAE has recognized as a problem. Not sure where all that is coming from?
HAP should be separating the fan energy automatically. Not sure why you are having this issue. You should selecting the automatic baseline system within HAP which should be separating the fan energy. Some software does require that you do this manually but I don't think that is the case with HAP.
Alejandro Vera
Mechanical Designer20/10 Engineering Group
October 19, 2018 - 2:42 pm
"This is not a known issue or a flaw or anything ASHRAE has recognized as a problem. Not sure where all that is coming from?"
This was from an e-mail exchange with Carrier HAP customer support personnel.
"HAP should be separating the fan energy automatically. "
I completely agree with your statement. HAP is absolutely separating the fan energy. But it is then using that fan energy calculation as part of the total EER as a "package" for the packaged DX. The EER for DX = compressor + fan energy. And the chiller EER = compressor | then add unit fan energy on top. E.g., if the fans accounted for half the energy, HAP was subtracting out the half and saying the same tonnage compressors were running artificially more efficient.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
October 24, 2018 - 3:14 pm
I think the reason you are having this comparative issue is that you are trying to compare two things that are inherently different. Sometimes the smaller air cooled chillers are less efficient than DX units and therefore you should be paying an energy saving penalty. DX systems are rated in EER and this includes the fan energy. Chillers are typically rated in COP or kW/ton and do not include the fan energy. Even smaller air cooled chillers rated in EER do not include the fan energy.
If you think HAP is not accurately separating the fan energy you can manually use the formulas in 90.1-2013, Section G3.1.2.1 to separate the fan energy. Make sure to provide the calculations and an explanation to the reviewer.