Cost effective heat pumps

[premzee@juno.com (s premena)]

Thanks Norbert for the needed discourse on energy...

 I'd like to add an emphasis that the COP - indicating the BTUs out for
BTUs in ratio of the complicated heat pump apparatus - is very dependent
on the actual input temperature to output temperature diferential of the
working fluid [usually refrigerant]. The efficiency drops off fast with
increasing temperature difference!

In a practical situation this is not *just* the temperature difference
between the inside air [or floor] and outside air [or pond or whatever]
but that difference PLUS the temperature difference across the heat
exchanger at *each* side of the system. To have small differences at
these points implies large areas of heat exchange surface and therefore
expensive heat exchangers. With time crud of various sorts reduces this
efficiency - be it dust or spider webs or corrosion or algae or
mineralisation etc.

 BEGIN ENERGY RANT

If you enjoy playing with this, have fun! [I once built a number of small
heat pumps from scratch]. However nothing beats good thermal design and
insulation and this is, in part, what strawbale is about. Remember also
that typically for every hundred watts of electricity you use 200 watts
is thrown out in power genertion and transmission so to get 100 watts you
burn 300 watts worth of coal etc.,.

To give a small idea of how energy spoiled we are; I once considered
building a mechanical toaster [for bread] and calculated it would take
the energy of a 20,000 pound weight falling 10 feet to toast the toast.
Crank it up the night before breakfast! [1000 watts for 3 minutes]

 One square foot of sunlight is about equivalent to one manpowr [75
watts]. We lead tremendously energy-rich lives; please don't waste it!

 END OF RANT 

Best wishes to all you wonderful people.... Premena