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Old 01-16-20, 01:17 AM   #1
Lurking Renovator
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Default geothermal water temp minimum

I have been watching for a while.
I am thinking of making a heat exchanger.
I would like to start small and move on from there.
I would like to heat my 3 ft crawl space.
approx 600 square feet.
our house is on an alluvial fan with high water table and natural flow down hill.
I am wondering what is the lowest temp that would be reasonable for this to work.
I plan on digging a hole and placing a thermometer in the water to check the temp.
I can place pipes uphill and use it as a horizontal well to provide a water source.

my theory is to direct the water from an up hill source to a storage unit with 2 inch pipe.(approx 150 ft run)

build the heat exchanger to use the storage as a source.
this way I could control sediment in the supply.

or I could just make trenches near the house.
typically if I dig a hole 1 ft deep, water fills the hole half way.
I have a mini excavator and could make trenches 4 ft deep and 2 ft wide.

average low temp is minus 2 c. but it can drop to -20 in an extreme typically for less than a week

It appears to me the most important thing is to know if the water has enough temp to work.

any info is appreciated

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Old 01-16-20, 09:30 AM   #2
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I think you will need at least 7c but also the flow rate/volume is important. Warmer water temp if flow is limited

If you have enough flow and it is high enough up the hill, have you considered a hydroelectric generator after the heat pump?
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Old 01-16-20, 11:29 AM   #3
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Ok so the main question is related to size and scale. How much heat do you plan on extracting from the ground? The higher the demand, the more water you will need. If you are planning on using a tank and coil heat exchanger, your cyclic demand will most likely dictate the size of your tank (unless you have a river flowing rapidly through the tank). Cooler entering water, lower flow rate, more demand for heat, all of these equate to more surface area and a larger tank volume.

Next question is: freezing or no freezing? With your big flood bed, and perpetual flow of water, a submerged dx loop or conventional glycol or brine ground loop and a brazed plate heat exchanger could bounce against zero Celsius and provide a literal wall of heat. At the phase change temperature, there is a boat load of heat to be had at constant temperature.

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