In the Northeast US where deep earth temp is about 50*, could the vertical closed loop field water, be circulated through a duct coil, and just the fan of the furnace be used for summer cooling? Without the compressors running, I would think this might be cost effective. Any thoughts or comments?

Thanks, Paul Campbell

cost effective, perhaps. Comfort effective, maybe not.

Systems operating on chilled water typically use it at an entering temp of 42. Reason for this is need to bring air down into mid 50s or so to wring uncomfortable humidity out of it.

Earth temp of 50 might yield loop water temp of 60-70 when loaded. That could cool air to 70 or so, best case. Little or no dehumidification would occur, and that is critical for summer comfort in all but the driest climates.

Some heat pump manufacturers offer a water only coil as well as regular fan coil. Other manufacturer's have a water coil that can be installed instead of conventional a/c. There are a few around in mid mi. Not everyone has the ability to dispose of thousands of gallons of water in a day. Well pumps can easily cost 40% as much as a low end airconditioner and fail prematurely from extra load. Air conditioners work better for reasons Engineer points out, so not a good trade in my mind.
j

Another thing to consider is with a closed loop your temp will not stay at 50°.  My closed loop ended the summer at 65° last year.  The air blowing across a 65° coil is going to be around 75°.  You just can't cool your house with 75° air.

I'm not so sure about this. Since he's not using his heat pump to extract heat from his house and dump it into the ground, the ground wouldn't warm up as quickly as when your using your heat pump. The inefficencies of not using a heat pump would be beneficial in keep the ground temperatures lower.

I do however question the effects this method would have on the overall health of the system. If he's stealing heat from the earth during the winter and not giving any heat back in the summer, how long could you continue to keep this imbalance before the ground gets too cold to extract any heat from it. Since the load of the house affects the temperature of the ground loop over time, how you use you system has a definite impact on ground temperature.

In the north there is great asymmetry between the heating and cooling seasons. Where I live we have around 4000 HDD and 400 CDD (these are Celsius degree days so make that 7200HDD and 720CDD to compare with US locations) so there's no way we put a winter's worth of heat back during the summer.

Even if you're using as passive cooling mode (by passing the ground loop liquid through the air coil) you're still extracting heat and putting it into the ground - if you weren't it wouldn't be doing any cooling!

By the way, Maritime Geothermal who make the Nordic range of heatpumps up here in Canada do have a heatpump that does do the passive cooling - works well up here since ground temperatures are much cooler - in the 40s and more like high 30s at the start of the cooling season. The EER of the passive mode is enormous!! They quote cooling COPs of greater than 8! Note, though, that this is only for an open loop system. See http://www.nordicghp.com/mg/nordicJul-25-04/O_series/O%20series%20brochure%20(R22).pdf

Paul.

The heat from the sun of course gives it's donation to heating the ground during the summer, but since the temperature of the ground loop changes over the course of the heating or cooling season, the house must have some impact on the overall termperture of the ground. At least locally where the ground loop is installed. If you only used your geothermal system to heat and not cool, would the system continue to operate just as efficently heating year after heating year, or would you begin to see lower and lower EWT over time?
  

We do this with our system. Basically our water to water heat pump is connected with the hot side to the pool/hot tub. The cold side is in parallel to the geo field and to a furnace coil. We have on peak / off peak rates so I only run the pool heating during off peak or cheap rate times. Depending on how much cooling the house needs I let the heat pump cold side go out to the field and the furnace coil. If I need more cooling I run it just to the furnace coil. During the day or on peak, I run a smaller circulation pump from the field loop to the furnace coil completely bypassing the heat pump.
During most of July the field was in the low 50's and all the heat pump cooling was going to the house. If I ran the field to furnace coil the house would gain about 2 degrees on a sunny 80F day, if I didn't do this it would easily gain 8F over the day. The warmest the field got all last summer was 58.9 at the end of August, which doesn't do much for cooling, but better than nothing. As a side note if we have a bunch of people over in winter I usually shut off the heat early in the morning and while everyone is over I usually circulate field water through the furnace coil, right now the field is in the low 30’s.

So while it doesn't "cool" per say, it does help, it doesn't dehumidify much, most of that is done at night when I am running the heat pump so I get the dehumidification that way.

Brock don't you heat the pool with that system as well?
Paul now I notice you said closed loop. It would be about footprint and design. More than one system offers passive cooling coils. How well it would work would depend on the size of your heat exchanger.....notice the less help we give heat transfer, the bigger your condenser has to be...Air source systems help with a fan small coil, unassisted air source coil takes up the back of a refrigerator to cool a modest amount of space, take away the assistance of the compressor at the other end and now how much ground coil do you need?
TG while Earth's heat may not be infinate, heat migrates to areas of less heat in perpetuity, so providing we have adequate ground loop, you do not need to run airconditioning at all in the summer to have heat in the winter. As you get closer to the dividing line of heating or cooling dominated climates, you will notice ground loops get much shorter.
You may remember a thread or two on "heat banking" in which we are quick to point out that gains are very short lived and you still need foot print.
Joe

Yes, the "hot" side of the geo is only connected to the hot tub / pool.

Oops, yep I see that now, it certainly does keep your summer ground temps lower.

Yup, that is the dilemma, right now we never put heat in the ground. Last summer for about 3 weeks we needed more cooling then the pool needed heating even with running the pool radiant heat in the garage floor (got the garage nice and toasty). Our HVAC guy wants to plumb the coil so it could switch sides of the geo unit and then reverse the heat pump and bypassing the pool, basically turning it in to a traditional geo setup. I am sure that would work, but I would no longer have a cheap way to keep the house cool during the day (on peak).

I'm sorry, are you suggesting that you are out of heat in the ground in February (after the coldest winter this century), because you heated your pool last summer?

Brock
What type of control system are you using for your setup?

I am fine, I am getting this thread off topic with my odd system. I am just saying you can cool or maybe a better word, temper your house with 50-60F water, but it won't dehumidify, but it is better than nothing.

Joe, no we still have heat left, the field is coming back about 34F right now. But I don't put heat in the field during the summer, not sure if that would really matter or not right now, ground temp wise.

zircote, mostly the system is controlled by the pool. Basically if the pool system calls for heat it turns on the geothermal. In summer I break that line with a call for cooling from the house, so the pool has to be calling for heat AND the house has to be calling for cooling. I manually open the furnace coil valves and then close the field valves as it is warmer outside. I would be neat if this could happen by itself, but it would be a LOT of valves and confusing control wise.

Brock
Thanks for the reply. I hope you won't mind another question.
How much heat are you putting into the pool?
Is your heat load 4 tons for the house and pool combined?
As for the control I think you will find it easier than you think.
Would be interesting to pursue, but in another thread maybe.

In the spring and fall when I am not cooling or heating the house I run the 4-ton unit on the hot tub / pool about 35 hours a week. In the middle of summer I was running just over 100 hours a week, I was dumping the excess heat to the radiant in the garage floor and a small outside 1000 gallon pool. I just hit 95 hours two weeks ago, basically running all the in house radiant 24x7, 6 zones on the main floor under tile and 4 zones in the basement slab. In winter I don't need the furnace until about 5F night time and 15F daytime temps, and then I just let the natural gas forced air furnace make up the difference.

I am open for ideas on how to control the system to use geo cooling in summer. I am at the point where I would rather reverse the heat pump and dump heat to the field. It was neat to have a nice and warm outside pool, but a pain to run pool lines out there and back in. The one place I didn’t think of to run empty pipes or conduit.

I started this all thinking if I had to heat the pool 35 hours a week, why not use that same 35 hours to cool the house. You can’t get much more efficient pool heating than that (or house cooling and pre hot water tank heating).

Be happy to look at your set up and suggest some control.