Heat Pump supplemental heating

   I'm getting ready for Winter in Atlanta.

   What I have is about a therm/day (150 ft2) of solar air heating and
will be finishing a therm of solar hot water (120 ft2). I think that may
leave me a little shy of my needs.

   So what I am thinking about is adding a homebrew heat pump to add
heat to the water store. That would only be run during the warmest parts
of the day and only when the evaporator is above freezing. I've got
several big old AC 220v window units I can scavenge parts from.

  It seems to me that the heat pump will be delivering a lower temp
water than the flat plate solar collectors could.  That would give two
options, a larger lower temperature store which would also yield a
higher collector efficiency. Or a seperate store for the heat pump
heated water.

   Any thoughts, or is this just too crazy?

   Jeff

 

It seems a bit crazy, with a COP of 3 vs 100+. Maybe you can combine your
air and water heaters in an interesting way, or add an auto radiator, and
end up with a higher efficiency and higher-temp water.

Nick

 

With warm water and cool outdoors, it would be difficult to get a very
impressive COP from such a heat pump.  The usual heat pumps used for home
heating have a much lower 'discharge' temperature (something like just 80F
as opposed to +100F).

Another idea is to reduce your need for hot water.  Low-flow shower heads
and grey-water heat recovery come to mind.

daestrom

 daestrom wrote:

   I'm actually thinking of staple up underfloor radiant, But if 80F out
is all I'm going to get then that is not good. I was hoping for 50F in
and 110F out for a 60F "head" and a COP of 2.5 or so...

   Cheers,
Jeff