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Old 06-14-14, 08:31 AM   #2
stevehull
Steve Hull
 
Join Date: Dec 2012
Location: hilly, tree covered Arcadia, OK USA
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Remember that the higher the temperature of the circulating fluid, the lower the efficiency of the collector. This is not trivial.

The efficiency drops rapidly as collector temperatures go over 100 C (212 F). The lower the collector temp, the higher the collector efficiency and the fewer number of panels need to be installed.

This is why I advocate "drain back" collectors. Water (cheap) can be used as a collector fluid and problems with heat exchanger corrosion (and subsequent introduction of toxic materials) become moot.

Drain back collectors are one of the simplest type of collector, yet few consider their utility. They are also the longest lasting of collectors with some in Israel lasting more than 50 years! Those areas have cold winters and hot summers.

Drain back only pump when the collector temps will support water fluid movement; easy to do.

So my suggestion is - just water!

Alcohol based mixtures are my second choice as gycols tend to gum up at high temperatures.


Steve
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