Heating a pool with an air conditioner

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Ask This Old House showed the installation of a system that captures the heat from the AC unit to heat a swimming pool. The AC refrigerant line runs through a coil inside a canister. The pool water runs through the canister and the heat is extracted.
OK, that's all well and good. Efficient, free heat heat for a pool which is shaded by trees and gets very little sun.
Let's think about this. When it's hot out, the AC is running and pool gets heated. When it's cool out, the AC is not running, so the pool does not get heated.
Sure, there's some advantage to heating the pool on a hot day, even into the hot night. However, on a cool day or cool evening, when the owner would really want the pool heated, he's right back where he was before the system was installed. Early and late in the season, when it's not hot enough for the AC to be running for any length of time, there is no heat available for the pool - right at the times of the season when you would want it.
Considering that it takes a certified AC tech to capture the refrigerant, adapt the AC piping and recharge the system, is it really worth installing one of these systems? I don't have a pool, so I don't know how cold the water in a shaded pool would be on a day hot enough for the AC to be running.
After a few days of cool weather, how long would would the AC have to be running for it to heat the pool to something that would be comfortable? Yes, I know it depends on the size of the pool and how cool it was. The one in the show was a decent sized in ground pool. Is it a matter of a few hours or would it take all day or longer? I know there's a number of variables involved...just looking for some idea.
It just seems kind of bass-akwards to only have heat available on hot days.
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I can easily see it in addition to fire, and the air conditioner will be more efficient when it's used. I guess fire takes over when the air is not used,but it has to do both ways.
Greg
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DD & Greg are both correct. In concept it's a good idea but whether it really works well & pays is all about the numbers. How much energy does the AC remove & when, seasonal & daily basis. How much energy does the pool need & when, seasonal & daily basis.
How well these two systems "match up" will determine viability.
Even a very large AC load (5+ tons) would still be much smaller than most pool heaters.
But, the "heat" from the AC is essentially free once the system mods were made. Providing a few tons (24,000 to 50,000 btu/hr) would lower your natural gas bill.
Like, Greg, I see this AC pool heater as supplying some sort of baseline heating with a gas fired unit also being required.
imo, the AC pool heater would lower yearly energy costs but not eliminate the need for a conventional heater... unless the owner was satisfied with a "greener" but lower performing pool heating system.
cheers Bob
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If we're talking a heat pump here, then in the winter, the HP is going to pull heat out of the pool which may have a very nice financial payback...it's going to work like a geothermal pump but not as expensive. Downside is that it may take longer to heat the thing up in the summer and will make the pool unusable in the winter
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Since the pool water is colder than the outdoor air, it could also lower your electric bill for the AC.
Liquid cooled condensors have been in use for years, but usually commercial applications.
My sense, is that there won't be enough return for the investment.
Christopher A. Young Learn more about Jesus www.lds.org .
But, the "heat" from the AC is essentially free once the system mods were made. Providing a few tons (24,000 to 50,000 btu/hr) would lower your natural gas bill.
cheers Bob
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They did indeed say the the AC unit will run more efficiently.
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On Sun, 9 Dec 2012 03:53:04 +0000 (UTC), DerbyDad03

That's the big advantage I see. Should be "Cooling the A/C With Pool Water." Whether it's worth the overhead is questionable..
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You may not have a pool, but I say you're on the right track. You're right, durintg the times you are most likely to want to heat the pool, the AC will not be running much. When the AC is running a lot, you're not likely to need it much to warm the pool. Here in NJ the AC is running a lot in Jul and Aug, precisely the time you typically don't need to heat the pool.
Also take a look at the BTUs of a typical pool heater. I have one here that is gas, 400K BTUs for a 48,000 gal pool. You can scale that for other sizes. They don't put 400K btu heaters in for nothing. It takes a hell of a lot of energy to heat all that water. A 4 ton AC by comparison is only 48,000 BTUs, an order of magnitude smaller
And also a lot of the heat from a pool is quickly lost, so you can't keep building it up over days. So, if you have a couple days of putting heat into it with the AC system, then days where it doesn't heat, in a day it will be cooled down again. That can be slowed by using a thermal pool cover, but that is yet another obvious pain to put up with. So, yeah, I'd say the whole thing is dumb and I would not spend a nickel on it.
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You may not have a pool, but I say you're on the right track. You're right, durintg the times you are most likely to want to heat the pool, the AC will not be running much. When the AC is running a lot, you're not likely to need it much to warm the pool. Here in NJ the AC is running a lot in Jul and Aug, precisely the time you typically don't need to heat the pool.
Also take a look at the BTUs of a typical pool heater. I have one here that is gas, 400K BTUs for a 48,000 gal pool. You can scale that for other sizes. They don't put 400K btu heaters in for nothing. It takes a hell of a lot of energy to heat all that water. A 4 ton AC by comparison is only 48,000 BTUs, an order of magnitude smaller ===================================================
Wow.... 400K btu's is a lot.... This might be an idear unique to your situration, but why don't you build a hot-air type heat exchanger for your pool, and just *talk* into it?? I'll bet your gas bill will drop to zero, and your pool temps will climb to, like, 110 F..... On a particularly loquacious day, you might be able to heat your neighbors' pools as well.....
--
EA







And also a lot of the heat from a pool is quickly lost,
so you can't keep building it up over days.
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If you don't have something to contribute, I suggest you just not post, instead of hurling insults for no reason.
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On 12/8/2012 5:08 PM, DerbyDad03 wrote:

I can see it working but, summer before last, I was trying to cool my pool down. Now I use "Sun Sails" and cover the majority of the pool with shade.
Nat. gas is so cheap here it doesn't seem like the savings would cover the cost of the conversion anytime soon.
Interesting idea though, and maybe I should be watching "TOH" more.
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Make sure you watch ATOH or the The TOH Hour. Just watching TOH won't get you what I saw.
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Is the refrigerant coil made of copper? How long will that coil last in chlorinated or salted water?
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On 12/8/2012 7:05 PM, snipped-for-privacy@gmail.com wrote:

I won't call you names over it because most folks don't know what's in the AC/pool heat exchangers. Here's a link for the type heat exchanger used for pool and marine applications. ^_^
http://www.pexsupply.com/Marine-Swim-Pool-Heat-Exchangers-MPN-Series-5x12-1065000
http://tinyurl.com/a7q9zbc
TDD
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http://www.pexsupply.com/Marine-Swim-Pool-Heat-Exchangers-MPN-Series-5x12-1065000
OP here...
On the show, Richard Trethewey specifically mentioned a coil and did that circular thing with his hand around the canister. Just sayin'
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On 12/9/2012 7:51 AM, DerbyDad03 wrote:

Was it stainless steel? A lot of guys I know will call any heat exchanger "the coil" even though the item may be in different forms but I did not pay close enough attention to the coil in canister bit, my bad but I'm sure the coil in canister wasn't bare copper. The flat plate exchangers I posted the link are not made of copper but rather stainless steel. **I found the heat exchanger you mentioned, it's not stainless steel, it's freaking "titanium". The video link is there too! I always use flat plate heat exchangers in the systems I work on so I automatically think of that type. I've never used one made of titanium and I think it's so cool(no pun). O_o
http://www.hotspotenergy.com/pool-heater /
TDD
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On 12/9/2012 7:51 AM, DerbyDad03 wrote:

I think this is the episode. It's the 3rd scene selection:
http://www.thisoldhouse.com/toh/tv/ask-toh/video/0,,20652494,00.html
Titanium.
FWIW: My pool heaters heat exchangers are copper.
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It's not about heating the pool, it's about the cooling the house. Air conditiioners are heat transfer devices. They move heat from one location to the other. Transfering heat by means of a fan to the outdoor warm air is far less efficient than transfering it to cooler water.
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No, it was about heating the pool. Watch the latest episode of Ask This Old House when you get a chance. The system was installed for the sole purpose of heating a shaded in-ground pool. It was plumbed in before the pool filter and included a sensor that only allowed the refrigerant to flow through the canister's coil when the pool water needed heating.
The fact that the AC would be more efficient when it was heating the pool water is just an added bonus. If it was about cooling the house, then the sensor would not have been installed.
The fact that
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On 12/9/2012 1:41 AM, DerbyDad03 wrote:

I just watched it and it sounds like it's both. It does make very good sense. Apparently it's nothing new.
http://www.thisoldhouse.com/toh/tv/ask-toh/video/0,,20652494,00.html
(3rd scene)
Thanks for posting BTW. It sure gives me something to think about.
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