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virgoblue2

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Reply with quote  #1 
I read the items on calculations and decided to build a solar air heater,  The first one was square  and the second one was longer. The square model gave interesting results but the long model did so much better 
 with exactly the same space [[3100squarein.]], same two black screen,  same cfm , same automatic solar powered  fan,  same angle at 41  degrees

yet the long one put out a much higher temperature, anyone found this to be  true or are my calcs off some how

300 Btu for the square  model
674 Btu for the long model

gbwillson

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Reply with quote  #2 
Virgoblue2-

The longer the time and distance the air is inside a collector, the hotter air gets. So your results seem reasonable. Keep in mind that if the time and distance are too long, you will lose efficiency as heat is lost through the glazing. So you want a collector that gets very hot, and a fan powerful enough to extract the heat before it gets wasted. 

Greg in MN[wave]
stmbtwle

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Reply with quote  #3 
Interesting, but higher temperature by itself is no measure of heat gain, as you need heat TIMES mass. Long skinny collectors have more resistance, so with the SAME FAN they will have less airflow and higher temperatures than a short wide one. Does this mean you're getting more heat? Not necessarily.

Until you can measure the ACTUAL air (or water) flow you don't really know.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
gbwillson

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Reply with quote  #4 
Very true Willie, but he stated he had the same CFM, not just the same fan. It's hard to get accurate readings on such small units. But it does give further questions to explore. 

Greg in MN
stmbtwle

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Reply with quote  #5 
He did say he had the same fan, and we know a fan will deliver different CFM under different conditions. I'd question the CFM until we know how it was measured. If it wasn't a simultaneous side-by-side test it could have been the weather. Something isn't right.
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
virgoblue2

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Reply with quote  #6 
Quote:
Originally Posted by gbwillson
Virgoblue2-

The longer the time and distance the air is inside a collector, the hotter air gets. So your results seem reasonable. Keep in mind that if the time and distance are too long, you will lose efficiency as heat is lost through the glazing. So you want a collector that gets very hot, and a fan powerful enough to extract the heat before it gets wasted. 

Greg in MN[wave]
thanks for input, today the temp got up to 47F with wind at 25-30 miles and hour and I disabled the square model and checked  the long model [94 inches]. installed new measuring devices so tomorrow I can tell exactly what this heater can produce and whether such a device can be as efficient as some folks claim.  but the old numbers 275 ft./per/min at  125F. the warm air  felt very nice BUT is it really worth the investment.
Location is northern Arizona at 5500 feet .
The VDC is direct to solar panel thru a 10.5 Zener Diode  so only comes on when sun shine is bright enough.
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