I wonder if anyone has thoughts on improving the heating efficiency of a normal heat pump by warming the air around the outdoor unit? It seems like a "poor man's" version of the geothermal heat pumps to me.
Here's the idea. For a few $ build a passive solar water heater with antifreeze in the water. Let the water circulate through radiators positioned around the standard outdoor heat pump.
Of course you could more directly use the energy in your house but that requires modifying the inside, things the wife might not approve of. Heating the air around the heat pump could all be done outside with cheap surplus parts.
Possibly not worth the trouble but it might make a fun experiment.
gb