geothermal heat pump insufficient

My home has a geothermal heatpump that is about 2.5 years old. The heat pump cannot keep up when it gets too hot out. I live in Tennessee, and the temperature was in the high 80s and low 90s for significant portions of this past summer. During those times, my whole house heats up to around 6-8 degrees higher than I've got the thermostat set, and the heat pump runs constantly. Needless to say, this jacks up my power bills, and that kind of defeats the purpose of having the geothermal heatpump in the first place.
I've talked with the contractor that installed the heat pump, and they insist that it is the right size for my house. But they say that it just won't be able to keep up when it gets that hot. honestly, this seems like BS to me, it seems to me that either the heat pump can keep up, or it is undersized.
Anyway, I wonder if anybody has suggestions for how to improve the situation. Is there any kind of supplemental system that can be used with a geothermal heat pump, something along the lines of the aux heat coils that standard heat pumps use when it gets too cold?
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With a geothermal installed properly though, that is with the coils at least 4 feet underground (deeper in some areas and the proper length), you should not have any problems as at that depth the ground should be a constant 45 degrees or so, optimal for a heat pump to heat and cool.
If you have a geothermal heat pump, my guess is that the coils weren't installed properly, in which case if you have a warrenty you should be able to go back on the contractor and get it fixed.
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DragonKnight wrote:

More like 55F at best at 6' or deeper...

I'm guessing it's more than likely the heat load analysis wasn't done well (as in accurately) and the unit actually is lacking in transfer area. It is possible they also buried them too shallowly, of course, but more likely is simply not enough area and possibly a too-small unit as well.
One way to guesstimate would be whether it is adequate heating from the ground loop source during really cold weather or does it also require the "emergency" heat a lot? In that case, I'd say it's clearly under-powered, so to speak.
I'd first go to the manufacturer if the local installer isn't being cooperative/helpful and ask for an evaluation. I had a Water Furnace unit in E TN and it was quite capable in the hottest weather and we never had the strip heating come on except for the one night Knoxville reached -24F! It handled even the near-zero nights adequately. Water Furnace is very good in their support of their selected dealers/installers and (at least at that time) were pretty selective in who represented them. I don't know whether they're still as good or whether any other is (or was) as good.
I would also include the complaints in a written, documented form to both the dealer and the manufacturer, not just rely on telephone/verbal communications. This will help to establish the longevity of the problem at least from this point on although sooner would have been better, obviously.
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dblho39 wrote:

In addition in to other note...was the put in for you or for a previous owner? If not, can you find out from the previous owner whether it was satisfactory during a previous summer indicating there's been a change in function or was weak to start with?
The installer should be able to compare measurements of flow and loop temperatures with those after initial installation as well in order to confirm operation. These should match manufacturer's spec's for the unit if properly sized/installed.
Other alternatives as well include a possibility of circulation pump or the "ordinary" heat pump problems--low charge, dirty exchanger, dirt filters, etc., etc. All these diagnostics and maintenance items should also be checked and taken care of.

Of course one could add additional cooling but I'd certainly want to eliminate the possible problems with the system first. As noted in the other thread, had the Water Furnace unit in E TN and was absolutely great so it _can_ work, but also as noted in the other note will need support from the dealer/manufacturer to find out the "why" in the present system and then decide what to do.
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A simple test. Air conditioner outlet air should be about 20 degrees colder than input air. If system is dropping the air temp this much and your house is too warm then it is undersized. If not then it has a problem.

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dblho39 wrote:

Doubtful that it is an undersized or underperforming loop as the ghp just won't operate without sufficienct loop capacity for it's size once it is in extreme temps.
As others have mentioned here, it sounds like the system may have been undersized for the home. Did the contractor do a heat loss/gain calculation before quoting the system? Did he do an energy analysis showing what the run times and capacity of the ghp would be at both the high and low temps? He should have.
Were there any improvements to the home that were agreed on prior to the installation that you haven't yet made (insulation, caulking, etc.)?
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