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First Active Solar Air heater question about temperature switch

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Posted by Stonecrop on January 2, 2009, 5:30 pm
I am planning on building an Active Solar Air Heater in Lena
Wisconsin.  I will be building an Active Solar Air heater in a few
weeks, and am in the process of gathering materials.  I was wondering
if anyone could suggest a good way to turn Computer Case Fans on, when
the temperature is above 80 degrees?  More about my potential design:

Flat panel solar heater using aluminum cans. (About 30 square feet to
start with)
I plan on using two 100cfm computer case fans to push air through the
system. (They will be powered by Batteries for now)
I want to have a way of automatically turning the fans on whenever the
solar collector reaches 80 degrees.
* I have many partially sunny days, and do not want to force air
through a system which will cool the air.
Why? I would like to see if using computer case fans is a real option
before building a larger system with pv panels to power the fans.
Thank you for your help

Posted by schooner on January 2, 2009, 5:45 pm

PC case fans wont give you enough outlet flow especially through a can setup
IMHO.  And the 100CFM rating is more than likely with no load, once you have
them in a panel with all the resistence there will be very little airflow.
We use a higher end Dayton or similar 120V fan which provides 150CFM on the
outlet of the panel.

You can get a snap disc controller to turn on fans or electronic switches as
well with temp probes.
We use  the following:


Hope that is of some help.

Posted by nicksanspam on January 2, 2009, 9:23 pm

Green Bay gets 800 Btu/ft^2 of sun on a south wall on an average 20.2 F
December day with a 27.7 high.

A toy. A 300 Btu/h-F house would need 24h(65-20.2)300 = 323K Btu/day of heat.
If 1 ft^2 of R2 glazing with 80% solar transmission gains 640 Btu and loses
6h(100-24)1ft^2/R2 = 228/day with a net gain of 412, you'd need 323K/412
= 784 ft^2 of glazing (26 times more than your 30 ft^2 :-)

Use a line voltage thermostat.

Of course they will, with a 412x30ft^2/6h/200cfm = 10.3 F temperature rise.


Posted by schooner on January 2, 2009, 9:32 pm

I doubt you'll get 200cfm on the outlet of a can based panel with PC case
fans when they are rates at 100cfm (ie with no load).

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