Would there be any problem with using a solar air collector or green house to pre-heat the airstream that feeds the standard heat pump condensing unit? Wouldn’t this keep it running at very high COP’s? – Tom B., Seattle, WA
According to Dr. Tom Henkel, you should look at: Kreider and Kreith “Solar Energy Handbook” discusses solar-assisted heat pumps on pp 13-19 to 13-20), and Donld Rapp’s “Solar Energy” devotes a full chapter (9) to this topic.
These references point out that such solar assist systems significantly raise the heating COP. So, the answer to the question is YES, it’s possible to direct solar-heated air to the condenser of a heat pump and raise the heating COP.
But Henkel says, “What may be difficult is engineering a workable system”. While I always support innovative solutions, I want to emphasize that it is always safer to buy existing solar thermal systems whether they are for water heating, hydronic or air space heating systems, or augmenting absorption cooling systems for larger buildings.