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Old 12-26-19, 10:42 PM   #11
Helper EcoRenovator
Join Date: Dec 2019
Location: Northern Utah
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Originally Posted by jeff5may View Post
The important thing to know here is the heat capacity of running water. 1 BTU =1 pound of water changing 1 degF. A gallon of water weighs close to 8 1/3 pounds, so the harvestable heat is 8 1/3 BTU per degF per gallon. This will tell you how much water (at the very least) you need to flow to move your heat.

The heat flow follows Fourier's law of thermal conduction. If you buy copper tubing, the manufacturer publishes tested specs for it. Do a little math and find out if you are in the ballpark as far as surface area and flow rate.
I'm not good with math but I do appreciate how it can save time.

I took some measurements off my radiator well water geoheater in the greenhouse tonight. Its been running about 2 hours.

Single wall polycarbonate 14' x 14' greenhouse
outside air is 26F
inside air is 37F

Heater output is 45F
No sure of CFM
Input air temp measured 38F
Water inlet temperature is 55F
Water outlet temperature is 46F
Flow is 1.2 GPM

So to figure BTU's per hour

60min x 1.2 GPM = 72 gallons per hour
BTU's per Gallon @ deg per gallon extracted = 9 deg x 8.3 per gallon= 74.7
BTU's per Gallon 74.7 x GPH 72 = 5378 BTUs per hour

This is equal to about 1.57 Kwatts per hour of electrical heating. I'm using .2KWH with the blower and well pump running.

So my COP for just using a radiator and fan is 7.85 ???

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