2 years ago I built a house with a gravity well (actually a spring) on the property. At the house I have a 1" line with about 30 psi before the pump for domestic water. The spring is 1600' away with a 75' vertical drop over that distance. I've been researching geothermal water to air units for the past several years and have decided to seriously pursue installing a pump and dump system. my house is about 2000sq ft and is well insulated. I've had an energy audit and need a 2.5 ton unit. The question is since the the domestic water is pulled off of the same water line, how to I create a buffer so that if the bladder tank pump kicks on it doesn't rob water from the geo unit? or don't I need one? I'm also curious about what pressures the geothermal unit will run at. any other design aspects you can think of? Oh, it's Buffalo (no jokes about the Bills! please...) so it's cold here. For those you you who would like to see me hire a professional, it just isn't possible financially. Thanks -Aaron

You can use a large pressure tank and throttle the pump - but first, how many GPM can you get from the current system on a continuous basis? I calculate around 6 gpm. So the heat pump draw + filling the tank need to stay less than that. Doable with proper tuning.

2.5 tons requires as little as 4 GPM with nominal pressure.
Regarding hiring a professional, you will get some help here, but you are already asserting a size that sounds possibly smallish for your area. putting out as little as ~24kbtu in the middle of winter, if you have high cost/kwh I would load up a little bit bigger geo particularly since you are going open loop (since it adds little cost to equipment). Further you can't get 2.5 tons in 2 stage which creates greater water demand on open loop. So you might want to think again about employing a pro as you are headed down what appears to be a poor path.

Companies like ours offer services from design to turn-key and by purchasing a heat pump from a dealer you keep warranties in tact.

While you may think you can save $5,000 installing this yourself, what happens as you need repairs or something is wrong? $5,000 can be used up very quickly in energy bills and repairs with a system as complex as what you are looking at.
I always say do it once and do it right and with help from forums that is not going to be enough for you to do it right the first time.

what happens as you need repairs or something is wrong

Isn't one of the nice things about DIY that you are prepared to service it yourself?

If I read this right, you have 30 psig available upstream of the pump? Typical geo needs just 5 or so psi across heat exchanger, so you could do dump without the pump.

I have an artesian well with just 9 psi, and it feeds my geo with pressure enough to spare to push water out a 100' X 3/4" hose for irrigation, kiddie pool, etc.

Of course, here in Florida, the price of failure is much lower than in Buffalo. Our climate annoys, but never kills. Even in January, the only pipes that freeze are hose bibbs and those in mobile home crawl spaces.

Unless the spring is very low flow, there should be plenty of pressure / volume still available upstream of the pump even when it is running. If not, look into downsizing well pump, many are oversized.

Thanks for all the replies. I've been doing more research and I've narrowed my search. I have an open basement that would be perfect for radiant heat. Last week we installed the onix in my brother-in-law's basement. He's a certified industrial boiler technicial so he set up a propane boiler. Anyway, it went really well (and really easily). Two days of install on the onix and it was all stapled up. So that's what I'm thinking of doing with the Geothermal. Using a pump and dump (yup, without the pump) system to feed a water to water unit. Some more info: There is 30lbs before the pump inside of the house for the domestic water, all from gravity. Does anyone have an opinion on how best to give priority to the geothermal? I would need to set up some sort of buffer as well so that the house would have water available when the unit is running. a large bladder tank? As far as the pump for domestic water. It is way over sized at 1hp, but it was free so.... thanks for all of the help so far! I'm looking into hiring someone to help me set it up. Anyone in the Buffalo/Rochester area?

The problem is that your 30 psi is likely to go to negative psi (gauge) when the domestic water pumps starts up. That's why you probably want to throttle the pump and use a large bladder tank (didn't I say this above?).