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re: commercial air-air exchangers ?
21 dec 1996
david j. wingert  wrote:

>we are looking to provide ventilation for a 20,000 sq. ft. building that
>is being used for machine work... the owners don't want to spend any money
>on heating/cooling all that make-up air... if you know of anything that
>might work...

how about running a few concentric polyethylene ducts from side to side near
the building ceiling, with greenhouse fans pushing outside and inside air
into opposite ends of each tube?  

a $50 100' section of 36" diameter duct with 8 mph air has au ~ 5000 with
1600 cfm = cmin = cmax, roughly, and z = 1, so ntu = 5000/1600 ~ 3, and the
ashrae hof says e = 3/4 for this counterflow heat exchanger, so 30 f entering
air would be raised to about 30 + 0.75(70-30) = 60 f with 70 f exhaust air... 

they might heat the building this way, if both airstreams ended up at opposite
ends of a $1/ft^2 lean-to commercial plastic film greenhouse bolted on to the
south side of the building, to collect the solar heat equivalent of about a
gallon of oil per square foot per year, with the plastic film covered with
shadecloth in the summer, to make it last longer than 3 years and reduce the
solar heat gain of the building. 


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