Friday, August 13, 2010

Hot Water and Heating with Heat pumps

Using only electricity for DHW and heat on our project results in a primary energy consumption of some 180kWh/m^2an, so this simplest of solutions is definitely not passive house.  Using heat pumps exclusively for both cuts the number in half (the limit is 120kWh...).

There are many types of heat pump module available.  Therma-Vent, Aqua-Plus, Heat Harvester, HotPlate...  The issue is heat pumps degrade in COP significantly as the output temperatures reach 55 to 60deg C for DHW (but they can still do this with a COP of about 2).

Anyway, we need to look at harvesting the incoming ventilation air heat in summer and the outgoing ventilation air heat in summer, and the outgoing ventilation air heat in winter - got that?

The other thing is to integrate this all with solar thermal, and a 600' 3/4" pex loop in the ground should provide a fair bit of the needed energy as well.  It would be nice to have an insulated concrete tank where we can dump excess heat in summer and recover it in winter.  The earthtube seems more and more of an impracticality, though it is still a minor possibility.

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