Gilbert Fritz wrote:How much heat would be given of by 55 gallons of water as it cools down from 130 degrees to 50 degrees F?
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S. G. Botsford wrote:
Now a 2000 square foot green house with 2 layers of poly will be about R2 per square foot.
At R2 it takes 1/2 btu/hour/degree F. to heat a square foot of greenhouse.
S. G. Botsford wrote:
So for spring and fall when nights roughly equal days we have 12 hours of night, so we need 12 * 1/2 = 6 btu per square foot per degree.
S. G. Botsford wrote:
Now no system is perfect, so I will add a third for inefficiencies. 8 pounds.
But that's a gallon
So 1 gallon of water per square foot, will heat a green house if the water is as much warmer as the outside is cooler.
S. G. Botsford wrote:
If you want a 60 degree greenhouse, then it takes a gallon of 90 degree water to keep it warm against 30 degree outside temps.
S. G. Botsford wrote:
If you are happy with the temp dropping to 50, then your water only needs to be 70.
S. G. Botsford wrote:
...a 16 hour night instead of a 12 hour night. It now takes 4 gallons for every 3 square feet.
S. G. Botsford wrote:
If the drop in temp outside is twice as much as the differnce between the desired temp and your source of hot water, you need twice as much water.
If your greenhouse is only R1 instead of R2 you need twice as much water.
S. G. Botsford wrote:
So How much water as thermal mass do you need to keep night time temps at 50F for a 5000 square foot green house. You want to run all winter, and it gets down to -10F in February.
You don't want greenhouse temps during the day to get over 85 -- plants stop working well. So the best case is that your water will get to about 80. That's 30 degrees above your minimum.
50 to -10 is 60 degrees below your minimum. That means a multiplier of 2.
So 5000 square feet * 2 gallons/square foot =10,000 gallons of water. If you did it all in 50 gallon barrels, it would take 200 barrels, which would cover 800 square feet.
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