Everyone, I made an energy model of a building being served by water source heat pumps attached to a typical water loop with a fluid cooler and a boiler. I let eQuest size all the equipment including the boiler and water source heat pumps. The PS-H Water Loop report showed the following:

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Notice that in January, the peak heating load is -991.9 kbtu/hr, the peak net load is -576.1 kbtu/hr, and the peak over load is -355.6 kbtu/hr. eQuest sized the water loop boiler to be -576.1 kbtu/hr. I believe these numbers are correct and the boiler size is correct but I cannot find an explanation in a document telling me how net load and over load is calculated and what they mean. I can explain how eQuest develops the heat load, but not the other two loads. I know a typical hot water coil system has heat load peaks equal to net load peaks and the over loads are usually zero. I am pretty sure the over load value is related to the heat pump COP, but I would like to be able to point to a written piece of documentation explaining this. Anybody know where to look?

Thanks.

P.S. the energy model ran successfully with less than 10 heating hours out of throttling range.

Kathryn Kerns
Systems Specialist
BCE Engineers, Inc.
| Ph: 253.922.0446 | Fx: 253.922.0896 |