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Is it possible to manipulate EER in Energy Plus to see the effect on loads? I understand the variation of COP is possible.

asked 2020-03-17 14:10:49 -0500

bmjohn's avatar

updated 2020-03-18 18:20:55 -0500

Is it possible manipulate EER in Energy Plus to see the effect on loads? I understand the variation of COP is possible.

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answered 2020-03-20 05:54:48 -0500

Jim Dirkes's avatar

A couple of thoughts: 1) EER and COP do NOT affect loads. They affect the energy used to meet the loads. eg, the building cooling load (amount of cooling required) might be 100kW. The electric power needed by a chiller (COP = 3) to meet that load is 100/3 = 33.3 kw.

2) The conversion of chiller COP to EER is simple - as mentioned by Luis. For "packaged" equipment (fan, compressor, coil, condenser all in one piece of equipment), the USA rating agency (AHRI) defines the EER as a composite efficiency that includes compressor power AND fan power. Fan power, however, is assumed to be at a standard laboratory condition and normally is NOT the same as the actual fan power.

Confusing? Yes :)

For DX coils (those used in packaged equipment), E+ conveniently does the math to derive the manufacturer's EER for you in the background, but YOU must derive the compressor-only EER (which is what E+ uses), since the manufacturer uses the composite AHRI value. This is not too difficult once you understand the background assumptions made by AHRI. It's very helpful to have the calculations represented in a spreadsheet and I know that many modelers have done this.

If you would like my version of such a spreadsheet, please message me privately and I'll be happy to share it.

ps, kudos to you for working to understand the underlying assumptions!

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Thanks @Jim Dirkes, for that explanation. I really appreciate it! I will reach out to you soon!

bmjohn's avatar bmjohn  ( 2020-03-20 11:02:07 -0500 )edit

@Jim Dirkes, Could you please share an email, where I could get your version of the spreadsheet. It surely will strengthen my understanding of background assumptions. My email ID is Thanks in advance.

bmjohn's avatar bmjohn  ( 2020-03-23 08:48:40 -0500 )edit

answered 2020-03-17 14:45:29 -0500

You can just change the units. The formula is EER = COP * 3.412 BTU/W

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Thanks for responding. But the Cooling EER value in CBECC-Com and Cooling EER value (EER = COP * 3.412) from EnergyPlus don't align. I understand it is because the Cooling COP in EnergyPlus has only Compressor power in the denominator. But the Cooling COP from CBECC-Com (EER/3.412) has a "compressor" and "fan" power in the denominator.

Where can I find that specific "fan" power which is not being included in the denominator OR the specific "compressor" power which is only included in the denominator for Cooling COP in the EnergyPlus model?

bmjohn's avatar bmjohn  ( 2020-03-17 17:36:20 -0500 )edit

answered 2020-03-18 10:02:20 -0500

bmjohn's avatar

I was able to find the relation between CBECC-Com EER and the EnergyPlus Cooling COP. The EER in CBECC-Com gets adjusted, which is represented as EERAdj. This equation is present in section, eqn 15 from Nonresidential ACM reference Manual. A combination of eqns 6, 7 and 15 in Section 5.7.5 will give a relation that helps compute the Cooling COP, which is generated in the idf file.

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Asked: 2020-03-17 14:10:49 -0500

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Last updated: Mar 20 '20