The previous posts addressed the number of wells wcih is the problem I've hads trouble with. I've been trying to find contractor who will install a "storage tank" that runs 24/7 and can provides the HP with groumd water temperature when it needs it. All I've succeded in getting back from several contractors is "it won't work".

They are nearly correct.....Unless you have a tank similar in size to a 1 acre pond (depending on size of system, depth of tank....all the usual disclaimers). Problem is that even in a thousand gallon tank or more the amount of btus available is finite and not likely to heat anything larger than a dog house.
More importantly is your real question which I think is with X and Y available to me how do I make a heat pump work at my place? Why not start a thread about your situation and see if we have any ideas to help achieve your goals.
Good Luck,
Joe

You might mean a storage tank to allow buffering and continual (vs intermittent) extraction of heat from a traditional ground loop. This provides some efficiency increase although it's probably not worth the cost.

Yes jonr, I'm thinking in terms of continuous extraction. My current air source heat pump (36000 BTU) runs about 1/3 the time on the hottest day. This equates to transferring 12000 BTU/hr. My thinking is that a 200 gal tank would lose about 15 deg. when the HP is running. My lot is such that I have to drill wells - and it's rock ledge so the well cost is almost 2/3 of the total system cost. geowanabe

Okay,
Many contractors have suggested your plan won't work. Jon was told his storage system is impractical as well.
Would you prefer to believe a lot of pros or........?
btu extraction from the ground is based on a lot of contact with surrounding soil. A big tank of water in the ground will eventually move to ground temp but not as quickly as you would extract the btu's......
Or you can have jon tell you about all his successful installations.
J

Joe, I should have explained that the tank would be in the basement next to the HP and well insulated. I agree with you that burying it in the ground is of NO value. I'm hopeful that someone has/can tell me how to size such a tank. geowanabe

Tank in the basement is of slightly more value....almost none. This is because of the finite number of btus you will be able to store and the conflict between peak usage and availability of replacement btu's. As an added bonus you may begin to add load to the conditioned space with the giant icicle in your basement.
j

Or you can listen to "installers" who don't understand thermodynamics and try to play engineer. It's as I said - yes, there is an efficiency gain in longer heat extraction cycle from the ground and no, it probably isn't worth the cost. An indoor tank would be less valuable because of the insulation losses.

so after two  or three days the tank will be frozen.  Then what will you do?

O'contrair! The ground loop is continuously putting heat into (winter) or removing heat (summer) from the tank. Assuming the HP is only operating a part of the time (like my current unit), the tank will recover during the OFF period.

Ummm, why not just let the GROUND recover during the off period?

Nah, that's what everyone else does, so it must not be right.

if you are thinking that by having a tank, you can have a smaller ground loop, you are sadly mistaken. What is the logic behind the tank?

I can supply my family's hot water needs with a 20 KW tankless instantaneous electric water heater. However, by storing hot water in a small tank, say 65 gallons or so, I can cut hot water electricity demand to 5 KW or so. As it turns out, such devices are readily available at places like Lowe's or Home Depot.

So, since I can reduce the size of the heating elements in my water heater by a factor of four or more by incorporating a storage tank, I must be able to reduce the size of a geo loop field by the same factor by similarly incorporating a storage tank.

Of course the foregoing analysis fails to account for crucial difference that hot water use is rapid but extremely intermittent, whereas house heating and cooling loads are variable but continuous.

In an odd and utterly unrelated coincidence, I just noticed that this post raises my total post count to 1065, dead even with DeWayne...

Oh stop poo-pooing good ideas guys and let jonr tell us about all his great storage tank installs.......
go ahead jon we're anxious to hear about all your projects.....
okay 1 project......
anything?
nothing?
really?
oh well my post count went up.
j

I'm sorry GW but what you seem to miss is that a tank again has minimal btu storage capacity and ultimately adds to house load.
A heat pump that does not run much of the time during peak requirement actually costs more to run during other times.
There are no short cuts to foot print (contact with the earth).
If you can get good loops in your yard; forget the tank, if you can't; go ASHP.
j

To answer a question in your first posts - you can eliminate the strip heat by over sizing the unit. I believe Bill (a regular poster here - and I am surprised he has not weighted in on this) oversized his system and got a two speed unit to elimiante the heat strip issue. A optimal system will probably have your heat strips come on 1-4 days a year on the coldest nights. Get a manual J calculation and then upsize your unit by 1/2 ton and you should eliminate almost all the heat strip usage except on maybe the absolutely coldest night of the year. I don't recommend over sizing but if you are that adverse to any strip heat use that is your option.

I doubt the payback on +25 SEER unit is there. Once you hit about 18 you are near the payback maximum. Also keep in mind that the unit is only gets the highest rating during a very narrow temperature range (about 80 F).

I hesitate to jump into this thread now that I have read it but here goes. Continuous extraction means continuously running the pump (using energy). You also modify the ground temperature somewhat thus reducing the efficiency of your loop. You would be better off just oversizing your loop a bit (add a couple of shallow well loops) instead of buying a tank.

Now if you are really into the tank idea, you might research standing column wells.

Best of luck (and I am out of this thread).

Alex