[Greenbuilding] Solar air heater efficiency vs absorber area and airflow

LarenCorie LarenCorie at axilar.net
Sun Feb 20 15:18:14 CST 2011


From: Clarke Olsen <colsen at fairpoint.net>

>    I built an air-cooled wall collector where the incoming air went
> up between the absorber panel and the glazing, over the top and
> down the back, for a double wash of  the absorber.

Hi Clarke;

  That is not a particularly good flow path, because the cool inlet
air is against the same absorber area that the heated outlet air is
against.  The absorber is a counter-flow heat exchanger, taking
heat from the outgoing air, to warm the incoming air. The result
is higher average collector glazing temperatures, and lower
outlet air temperatures.

>  Would collection be improved by making the spacing asymmetrical;
>  that is, making the air go faster on one side (glass side?) of the 
> plate?

Performance would be improved by allowing the air to evenly pass
through the absorber (Matrix flow-path) so that only the coolest air
is adjacent the glazing, with the heated air behind the absorber, both
flowing in the same direction. I suggest using vented aluminum soffit,
as your absorber.   It comes prefinished in satin black.

-Laren Corie-
   Natural Solar Building Design and
Solar Heating/Natural Cooling/Energy
 Efficiency Consultation Since 1975
        www.ThermalAttic.com

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