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re: solar heating for barn
12 feb 2004
ecnerwal   wrote:

> "gary"  wrote:
>> it would be nice if there was some way to also measure and log the velocity
>> of the air through the collector.
>you have temp sensors. look up "hot wire anemometer"...

or maybe "thermoanemometer." dwyer makes a $400 version. you might add
a small resistor next to a temp sensor and measure the temp diff with
and without a fixed voltage across the resistor to add some heat (0.1 w?)
to the combination. after a few time constants, smaller temp diffs would
indicate greater air velocities.

you might calibrate it with a 4" diameter x 5' tall thermal chimney. page
43 of passive solar energy (bruce anderson and malcolm wells, brick house,
2nd edition, 1994) says v = 486sqrt(h(to-ti)/(ti+460)) feet per minute,
where h is the height difference in feet between intake and outlet vents
and to and ti are (f) air inlet and outlet temps. for example, h = 5',
ti = 80, and to = 70 would make v = 486sqrt(5(80-70)/(80+460)) = 148 fpm.
heating 148pi(4/12/2)^2 = 13 cfm 10 f takes about 130 btu/h or 38 watts.

scientific american (80s?) described how to build one in a 1" steel ball.


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