[Greenbuilding] Solar air heater efficiency

[Clarke Olsen]

    Laren,
       Thanks for your assessment. I always assumed that a mesh  
absorber, like a
    few layers of expanded metal lath, would generate the air  
turbulence desired
    for efficiency. But how can we overcome the be the conflict of  
the coolest surface
    (the glazing) being opposite the hottest? How does the matrix  
flow-path keep the
    coolest air next to the glass?
      One of my rationales for the counter-flow design, was  
elimination of ductwork:
    the inlet and outlet are side-by-side at the bottom of the wall.

    Clarke Olsen


On Feb 20, 2011, at 4:18 PM, LarenCorie wrote:

> 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-
>
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