geothermal loop using 5000 gal irrigation well tank
Last Post 31 Aug 2014 08:27 AM by ACES-Energy. 6 Replies.
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SteveDIYUser is Offline
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30 Aug 2014 10:06 PM
I am wondering if I can use my irrigation water tank as a heat exchanger.  My well is 640 ft deep and the water in the tank stays cold. On any given day my low usage of irrigation water is approx 1000 gal and on my high usage days 7,500 gal. My refresh rate is 40 gal/min. On my heavy pumping days the tank will stay at or above 1/2 full. If I pump over 10,000 gal/day the water level in the tank will drop lower.

15-20 days/yr daytime temps 95-102 degrees
5-10 days/yr nighttime temps below 32 degrees

If this is feasible, I was thinking of using maybe copper or some other material that readily transfers heat.

I am looking to use a geothermal heat pump for heating and ac.

Thank you for any help or ideas you may have.

Steve
engineerUser is Offline
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30 Aug 2014 11:45 PM
Sounds theoretically possible, depending on load and water temperature. If the water quality is good enough, use it directly. Snatching some numbers out of the air:

a 4 ton geo heat pump in cooling mode operated 12 hours in high stage (really hot day) could reject about 750,000 BTU. That would raise the temperature of 2500 gallons of water by 36*F degrees. Try to do that 2-3 days in a row while only pulling 1000 gallons per day off the tank and the design would fail.

Other scenarios might be made to work. A 2nd water tank in parallel might sufficiently smooth the peaks. If your load is only 2 or 3 tons then the numbers get easier.

Do you irrigate 365 days per year? What is your well water temperature? Where are you located?
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
jonrUser is Offline
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30 Aug 2014 11:54 PM
Figure ~6000 gal/day for the continuous use of a 2 ton geothermal heat pump (scale as fits your case). Look at heating numbers, where typical well water has less btus available (36F isn't going to work).

With your deep well, it might not be cost effective to pump more water than you need for irrigation. Consider air source or horizontal closed loop geo (as a comparison on practical and cost issues).
jonrUser is Offline
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30 Aug 2014 11:54 PM
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engineerUser is Offline
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31 Aug 2014 12:17 AM
Jonr's figure is likely based upon 1440 minutes in a 24 hour day and a rule of thumb that calls for 2 GPM per ton for conservative open loop designs.

1440 x 2 x 2 ~6000 GPD...easy math.

However the underlying assumptions are flawed: No properly sized system runs 24 hours / day, and his resulting "2880 GPD / ton rule can be bent a bit as long as system entering water temperature is held within a broad range, on the order of 45-85*F.

While it may be possible to compensate for low irrigation flow days by dumping extra water somewhere, it would be well to consider both the extra pumping energy and impact of that extra discharge water.

This is an intriguing idea; it may well fail when site-specific values are applied, but it could also pass with flying colors - configuring an existing regular flow of water to drive a really efficient heating and cooling system.

Do the project specific math; don't rely on simplistic rules of thumb.
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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31 Aug 2014 01:45 AM
No reason why this should not work. 40 gal/min as a refresh rate is a lot of water to work with. Put some appropriate controls in, and ensure you do not go below freezing and not above the max op temp. The key are the actual loads. How much cooling and heating do you need>
www.buffalogeothermalheating.com
ACES-EnergyUser is Offline
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31 Aug 2014 08:27 AM
This should work. This spring/summer I had a 100-ton geothermal job that my vertical loops were not yet done (still only have 10-ton drilled). We utilized a much smaller tank but put a few cheap JCI A419 that open and closed some cheap $15 irrigation valves to either dump water, turn on a boiler, force water to an air cooled HX, put water directly to the loop, etc...We had 5 different possibilities to either heat or cool the water down and where we injected the water. our loads were fairly small as building was under construction, it was maybe 30-tons at the peak, but i would say we saw a 20 ton load just a few times and everything was less than that...
www.ACES-Energy.com
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