Re: [OM] OT: Air-source Heat Pump?

[Chuck Norcutt]

Make sure you understand the logic of the control system if you do this. 
  I had a hot water preheat system when I lived in Florida from 1985-95. 
  The water circulated from the hot water heater in the garage to the 
solar collector on the roof as long as the water in the collector was 
hotter than the water in the tank.

It all worked fairly well for a while until one day my wife complained 
that our electric bill had gotten astronomically large.  We couldn't 
figure out what was going on and it continued for 3 months until I 
finally solved it.  One night I went out into the garage about 9pm and 
suddenly realized that the pump was running feeding from the hot water 
tank up to the collector on the roof.  The sun had long been down and it 
was quite cool outside... no reason for the pump to be trying to collect 
non-existent heat from the roof.

I still had no idea what was happening and why but made a trip up to the 
roof collector the next day.  It took a lot of detective work but I 
eventually discovered that the temperature sensing wire that emerged 
from the collector and ran to the controller was short circuited against 
the aluminum of the collector frame.  Apparently expansion and 
contraction of the frame had been rubbing the wire between a sharp edge 
of the frame and the copper pipe carrying the water.  After some more 
detective work examining the operational specs I realized that no 
voltage signal coming from that wire was interpreted by the controller 
as "the temperature of the collector is at the boiling point of water". 
  Therefore the controller was dutifully pumping my expensive 
electrically heated water up to the collector where it acted as a very 
fine radiator for distributing all my expensive heat right back to the 
atmosphere.

Argghhh!!!  As my good friend Bob Burns said:
"The best laid schemes o' mice an' men
Gang aft a-gley..."

Chuck Norcutt


On 11/28/2012 2:44 PM, Ken Norton wrote:
> The side benefit is that the same collection
> system is used for hot-water preheat.
-- 
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