> What about heat pumps then, where the heat "output" exceeds the energy
> input?  - A heat pump driven from (mainly) hydro power must be close to
> optimum overall "efficiency".

Yes, depending on the outside temperature (assuming the desired inside
temperature is usually about the same, about 70F or 21C), a heat pump can be
a more efficient way to heat a house than a resistor.  That's because when
the temperature differences are low, it is easier to move heat energy around
than to convert it from incoming energy.  For example, it may only take 50W
of electric power to bring in 100W of heat from outside whereas it takes
100W of electric power to produce 100W of heat inside.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olin@cognivis.com, http://www.cognivis.com

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