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Old 03-21-18, 01:22 PM   #3
Tpm
Lurking Renovator
 
Join Date: Mar 2018
Location: Pennsylvania
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I don't need reliability from the sun in a heating mode I select (vs wood stove boiler) because I've looked outside and seen that bright yellow ball. And it appears right along in the shoulder seasons. With passive solar keeping things toasty in the afternoon and evening, and heat loads in the upper teens of kbtus/ hour overnight, solar assist could make a difference.

Towit: by heating the entry air with solar thermal does not the heat pump operate at a higher COP, in effect multiplying solar output by some fraction of it?

Yes, the heat pump at two tons will handle the whole load. That would be the definition of backup. The question I asked is best and highest use, as measured first in fewer trips to the woodshed, and second in electric bills that don't appear horrific next to my normal central heat use of about 400w/hr - intermittent -- plus chainsaw gas.
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