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re: solar power greenhouse fan?
6 apr 1999
jiva  wrote:
>scot leith  wrote:
>>is there such a thing as a solar powered greenhouse fan kit? i recently
>>built a small greenhouse and must put a fan in...

maybe not...

>i wonder if you might want to explore a vent opened with a temperature
>controlled/powered actuator. don't recall the manufacturer but they
>are around and i don't think they're too expensive ($50us range?)

jade mountain 800-442-1972 sells passive $54 #fc115 thermofor vents that
can lift a 15 pound hinged window 15". the catalog says "select a
temperature between 55-85 degrees." 

this might work well with some square vents at the upper gable ends, say
4' tall x 4' wide panels that rotate to open on a horizontal axis in the
middle, and roll up sides. our new 14x96' greenhouses will have plastic
film sides that roll up to about 4' above the ground with 100' of thinwall
swedged pipe duct-taped to the poly film every 2', with a right angle
connector and handle at one end. 

an 8'x16' greenhouse covered with 50% shadecloth might collect 20k btu/h of
peak solar heat on summer day. cfm = 16.6 av sqrt(h dt) for a chimney, with
a vent area of av ft^2, height h feet and temperature difference dt f. the
heat removed is roughly cfm dt btu/h, so with two 4'x4'vents and an 8'
height, 20k = 16.6x32ft^2 sqrt(8) dt^1.5, dt = 5.6 f, max. 


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