Quote:
Originally Posted by AC_Hacker
I haven't actually talked this issue over with Daox, but it seems pretty clear that he is working on the principle that a highly efficient house, coupled with a highly efficient floor, means that sufficient heating can be achieved at very low feed temperatures.
That is at the core of 'low temperature heating'.
With fossil fuel, the difference in lowering feed temperatures a degree or two is pretty small.
With a heat pump, lowering the feed temp a few degrees makes a big change in efficiency.
With solar, it means that you can heat directly with solar heated water down to a lower temperature before you need to either extract more heat with a heat pump or else rely on a back-up heat source.
-AC
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This statement fits perfectly in BBP's other thread, concerning the operation and design of his combo system. Just as with very low (outdoor/source) temperatures, the efficiency of the heat pump suffers when you demand high heating temperatures out of it. He was concerned on how to efficiently source 130+ degree domestic water from the heat pump. When I suggested running a gas boiler when the sun source ran out, the wolves jumped on me.
At a certain point, the gas boiler would do a better job than the heat pump at providing hot water. Especially when the hot water tap is running, the heat pump may just not keep up with demand. It is better doing the recovery of the hot water tank after the demand has stopped. In any case, the heat pump would just rob more solar energy from the solar heat store, where the boiler would not.