I live in mid NC where it gets hot but actually most energy goes into heating - roughly 3x the cost on average. Think 50/30 as typical temps. I think we are at 3300HDD and 1400 CDD

I have a new construction house with Seer 15 HPs and I was looking at putting in a pool. I got to thinking that I'll probably want to heat the pool and I am needing to plan my roof now (for PV). The typical plan would be to heat the pool with solar which would eat up a lot of available roof.

But I wanted to consider using the pool as a water source for the heat pump. In the summer, it will almost always be cooler than the air and the HP would heat the pool as a side effect of using the a/c. In the winter, with a solar cover, the pool will be warmer than the air at night when most of the heating is used (and the COP of the HP starts falling off). My father mentioned putting 2 heat exchangers in the circuit and use temp data to decide whether to use air or water (ie run the fan or the pump).

Pitfalls - the extra heat exchanger stresses the compressor as we were thinking to plumb in series.
      - the pool temp drops significantly at night and can't recover during the day. I calculated a 5 degree drop on a bad night in addition to usual losses. This could be lessened by solar panels to heat the water which would help to heat the pool before the a/c gets kicking in the spring and fall. It is fairly sunny around here and my solar panels for DHW were at 250 in mid feb (that was a really nice day). I think on a sunny day, the amount of btus hitting the pool could easily make up for the lost heat. I've done the calcs and it shouldn't be a problem - sort of like a 800 ft solar collector - although not a very efficient one.
      - the pool could easily get too hot in the summer but the air temps are not much of a problem. I am more looking to the "free" side effect of heating the pool.

Thoughts. Crazy?

Likely your pool won't be a large enough heat sink for the heating need and you could end up with a block of ice, not good for the pool and the geo system. In summer if you had no other source of heat it would probably work if you don't mind warm pool water, leaving the pool uncovered to dissipate the heat, especially at night would help. Or using a fountain at night might keep the pool cooler as well.

We have an indoor pool in Wisconsin and by late June / early July we are overheating the pool to keep the house cool. So cooling might work, but heating I wouldn't think you will have the recovery to make it work.

Actually I think the heat recovery should be pretty good on a sunny day, if not then solar panels could supplement. A solar panel area of 400 sq feet would take care of the heat for the house and the pool is planned to be 800 sq feet. I doubt the cover would be 50% as efficient as panels but they might be. If not, a couple of solar panels would heat the pool a few degrees. Obviously we are a pretty mild climate so the need is not all that great. I've done the calcs and I'm not worried about the heat amount. What I'm more concerned with is the practical part of having both a water and air exchanger.

I am very confused about the logic of trying to improve the efficiency of a SEER 15 heat pump, but at the same time dumping a huge amount of solar PV energy from most of a roof into heating a swimming pool. I would be wary of breaking a good heat pump just to salvage a few btu's.

You can ask your HVAC guy to size and splice in a refrigerant/water heat exchanger.

PV to heat a pool? No way.

I think the confusion came from my post. I have to plan my roof and I may need to split between PV and thermal panels for the pool. The PV is not really an efficient use of limited space if I need heat and can use it reasonably efficiently. PV is great and all but it only becomes financially viable with incentives on purchase price and selling it back to utility. For the greater good - I'd rather save a "few btus" with my roof if the $$ winds up being pretty even.

jonr (or anyone else) - would this void the warranty? I hate to bring it up if it would but of course that is the right idea. I didn't know what to call it so I appreciate that.

I am guessing on a 20% improvement in efficiency (in the winter) which makes it a viable option. I mean why not if it has a reasonable payback.

ahhhh I get it now, using the solar water heaters all winter to keep the pool warmer.

I would think as long as the heat exchanger is large enough you shouldn't have an issue. You could leave them in series and then only turn the air fan on when necessary, that should eliminate any concern about altering it to much. But it might not be as efficient as using just the pool since some heat might be lost in as they pass the cooling fins in the air coil.

I'm a bad one to ask about warranty effects - but I expect the installer would know.

Ok, I see know. I though you were going to use PV to heat your pool, I should have known solar water heaters for the pool make more sense. I would calculate how many btu's you heat pump has to produce to heat/cool your house on a given day, then calculate how many btu's it takes to change the temperature of the pool one degree. Those ideas should give you a good idea of how well your idea will work. What if on a cold day you could even run the hot water off your rooftop heaters through the heater on the way to the pool? Heating the other side of your heat pump with 90+ degree water would really improve efficiency.

And make sure they don't insulate the pool walls. It is becoming more and more common, but in your case you would like the added mass of the earth surrounding the pool.

Interesting about insulating the walls - I never would have thought they would do that. I guess in my situation, I want the ground to help warm the pool in the winter. Sure, there will be some loss in the summer but that is nothing. Far and away, the biggest loss is evaporation and easy enough to rectify.

As far as insulating, what I really would want is a nice solar cover during the day and then a thick foam for night time - like a hottub would have. Add a few solar panels and I suspect you could beat geothermal (because of less pumping losses).

We are currently having 60 degree sunny days and 30 degree nights. So I have my backup NG coming on in the morning but the pool would have been over 50 I'm sure just with a good solar cover.

aardvarcus - interesting thought about daytime use. I don't know if I am going to need solar panels to heat the pool. That is the big question. The pool would cool down about 5degrees at night from the heat pump. What I need to find out is the temp of a pool with a solar cover in my climate in the winter. And the bigger question is how many btus can I salvage from a solar cover and the surface area. Losses are easy enough to calculate.

Probably - there will be some advantage to heating the pool with solar thermal panels in the winter and it should be easy enough to direct that warm water to the heat pump on the way down.

Before I came up with the pool possibility, I was trying to figure how to add some supplemental solar heat to the system. Obviuosly during the day, if you have a fluid heat exchanger, that would be easy with the heat pump. Then the excess heat can be put into the pool. So these panels would be way south facing - I have some room on a southern wall but no room on a southern facing roof. Since I am just looking for winter heat, I suspect a southern wall (unobstructed) would be fine. At some point, it might make more sense to store some heated water underground and skip the pool for this part of the system entirely.

So - solar panels to underground tank to be used for heating the house in winter. You could mix water in from the pool if it was warmer to help capture some of the solar gain of the pool surface. Same fluid heat exchanger could then heat the pool and cool the house in the summer.

push through with it! you are not crazy! just innovative! - Pool Parts

I like this idea of getting some use out of the pool water for a form of heating and cooling. Could you also install a water system that circulates the water through the ground during filtration at night with cooler temps for cooling the house. Now that I see the pool as something besides a money pit there could be all kinds creative energy savings just sitting in the back yards of so many people.

Have worked on several of these installations over the years.The maintenance costs need to be factored into the total picture. Water chemistry of pool can be a real problem. You may be better off circulating the water heated from the solar into a radiant floor. On the a/c side of the equation, install a small cooling tower to reject the added heat to maintain a comfortable pool temp.