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How Are Prototype Cooling Coil Efficiencies Determined?

asked 2021-01-14 18:10:25 -0600

willyJohan's avatar

updated 2021-01-14 18:13:20 -0600

Working with the latest DOE prototype for stand alone retail, I find the following COPs listed for the cooling coils:

PSZ-AC:1 --> 3.80
PSZ-AC:2 --> 3.40
PSZ-AC:3 --> 4.12
PSZ-AC:4 --> 4.12

These seem to all exceed the minimum efficiency listed in ASHRAE 90.1-2019 for single packaged air cooled air conditioners, of any size. Of course this comparison requires some awkward conversions (SEER or IEER to COP) but these COPs don't even seem close the the EERs specified for units above 65k btu/hr.

Based on the specified EERs only, the minimum efficiencies range from a COP of 2.784 for units over 760k btu/hr up to 3.22 for units between 65k and 135k (smaller units only specify a SEER 14, which i calculate as 3.45, roughly).

What am i missing? do the numbers in 90.1 include fan energy that has to be removed from the coil COP in EPlus?

and, while were talking about prototypes and efficiency determinations, if a model has one large zone served by 1 HVAC unit where in real life that 1 zone would most likely be served by a few smaller units, does the prototype use the minimum efficiency appropriate for the unit sized to serve the entire zone or for some assumed number of smaller units that add up to the modelled capacity?


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answered 2021-01-14 19:29:30 -0600

Jian Zhang's avatar

Hi there, Thanks for your interest in the DOE Prototype Models. EnergyPlus takes COPnf (no fan) inputs for the cooling coil objects and models fans in packaged systems as sperate objects. Therefore, the COP in the prototypes are COPnf. In the current models

COPnfcooling= (EER/3.413 + R) / (1-R) R is assumed to be 0.12

See PDF page 46. Thornton B.A., M.I. Rosenberg, E.E. Richman, W. Wang, Y. Xie, J. Zhang, and H. Cho, et al. 2011. Achieving the 30% Goal: Energy and Cost Savings Analysis of ASHRAE Standard 90.1-2010. PNNL-20405. Richland, WA: Pacific Northwest National Laboratory.

ASHRAE Standard 90.1-2016 Appendix G has a new formula. See Section G3.1.2.1. Our prototype simulation team plan to adopt this new method in the future prototype updates.

For your second question, when a large thermal zone is expected to be served by more than one packaged single-zone systems, the autosized capacity of the large zone is used to determine the EER from the code table. Although it is reasonable to split the large capacity to multiple smaller units, our team has not used that approach to the published prototype models. In some special analysis projects, we have done the split using a rule of thumb approach.

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Asked: 2021-01-14 18:10:25 -0600

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Last updated: Jan 14 '21