Heat Pump Auxiliary Heat (UNCLASSIFIED)

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Classification: UNCLASSIFIED
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Short question:

What is the easiest way to have the electric heat to provide heating for packaged rooftop when the outside temperature is less than 40 degrees? Or is this even what the review is looking for?

The full comment from my good magnanimous friend from LEED.

6. It is unclear if the packaged rooftop heat pumps in the Baseline model were modeled according to Section G3.1.3.1, which requires that the electric air?source heat pumps are modeled with electric auxiliary heat that only energizes on the last thermostat stage and when the outdoor air temperature is less than 40 degrees F. This means that the heat pump and auxiliary heat should operate together at low temperature conditions, with the compressor as the lead machine. The outside air cutoff temperature for the compressor must be no greater than the temperature associated with the low-temperature heating efficiency requirements of Table 6.8.1B (17 degrees F). Note that for packaged heat pump units smaller than 65,000 Btuh, the HSPF rating accounts for electric auxiliary operation, and includes test conditions at 17 degrees F. Please indicate the modeled characteristics of the electric auxiliary heat in Table 1.4 including the temperature at which the auxiliary heat engages, and the outside air temperature cutoff for the compressor. If the compressor low temperature cutoff is modeled as greater than 17 degrees F for packaged heat pump units smaller than 65,000 Btuh, describe how the Baseline efficiency of the heat pump was modeled to reflect the HSPF rating including auxiliary heating energy.

John Eurek

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Jeurek's picture
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Forgive my memory skills here, but I think you get 2 coils for a HP. You can reassign the electric coils to an electric plant and leave the others on your boiler. Then I think you can assign the schedule of the elec plant to not activate unless the OAT < 40°F. Clear as mud, I'm sure, but I have not seen this comment on the past 10 of my geothermal LEED projects. Also look at possibly creating your own schedule or power curve for these plants. Good luck.

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