open loop

I want to put an open loop heat pump system in my house, however I didn't want to run my well pump all the time to do it. Approximately 80 to 100 ft from my new home location is a spring fed cistern (large concrete box that holds about 2000 gallons of water. The water flows into it year round at a rate of about 1.5 to 1.7 gallons per minute. The deed to the property shows that this spring has been there for approx. 150 years, so I don't think it is going to dry up soon.
My question is: Is the 2000 gal. resevoir with a flow of 1.5 gals a minute into it enough water to handle 8 tons of geothermal open loop system? Also, how small of a pump could you get away with if you only have to raise the water up about 20 ft. to get it to the system, instead of using the large well pump to pull it from deep in the ground?

What is the GPM required for the 8 ton unit? I am guessing 20 GPM, so 2,000 gallons will only last about an hour and a half.

Forget it!

Many states won't allow open loops today unless you return the water back into the aquifer which requires return wells that eventually stop up with iron.

Look into a Slinky Loop; pond loop or better yet closed loop. Closed Loop Systems cost more for installation but are more efficient and require only a small recirculator pump.

Porky

You need 2.4 GPM per ton at 10 degree F temperature difference.

If you have a spring then somewhere there is a source of water that may be an aquifer from which you could pump and to which you could return the water.

If the source of the spring is a trickle from somewhere (not a aquifer with a lot of volume in storage) you aren't going to be able to do anything to get 96,000 BTU per hour from it.

You would like to find an aquifer that is large enough and extends far enough below the surface to maintain essentially constant temperature while you are withdrawing heat.

If you can find a shallow aquifer you may be able to put in a couple of shallow wells so you could withdraw 20 GPM from one and inject it into the other.

If you can get to the area with a backhoe you might be able to bury a couple of large pipes in the aquifer some distance apart; one to withdraw water and one to reinject it.

Another possibility for returning water to the aquifer would be to make a small pond with a sand bottom that communicates with the aquifer. It will have a large area of reinjection and if it plugs up you can scrape the bottom to restore it.