Hybrid Heat Pump

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When I was in school for heating and air conditioning, I learned that heat pumps are air conditioners that can run in reverse. The definition of refrigeration is to take heat from a place where it is not wanted and release it into a place where it is less objectionable. When a refrigeration machine( like an air conditioner) runs in reverse, the heat can be pumped to a place where it is wanted. I thought that all are conditioners should have a reversing valve because almost all applications need heat sometimes.

I began to wonder if an air conditioner that was not a heat pump from the factory, could be retrofitted in the field. The first one I did was an older model gas pack. I had an electronics firm custom make a controller that would use the heat pump until the outside temperature was 32 degrees. After that the furnace would come on just like it did before.

The results were even better than I expected. We were able to get heat down to 20 degrees. The savings in carbon equivalent was 90 %. The gas bill practically went away and the increase in the electric bill was not uncomfortable. We determined net savings in the range of 30% and the return on investment was within 3 years.
Since then, I have upgraded 23 air conditioners into heat pumps. The most recent was a five ton used on the offices of my church. It only had electric heat to begin with so the improvement was even more dramatic. That story will save for another day with hard data.