Heating a pool with an air conditioner

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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On Sat, 8 Dec 2012 23:08:36 +0000 (UTC), DerbyDad03

Isn't the purpose of a pool to cool off in hot weather? What's the point in heating it?
Sounds to me like another useless gadget to steal people's money......
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On 12/9/2012 6:26 PM, snipped-for-privacy@home.com wrote:

Sort of. When it's hot out (90+ degrees F) some pools still only get into the high 70's and low 80's depending on the amount of sunlight. My pool, when it's exposed to full sun, doesn't need any help. But, if you watch the video, he says this pool gets little sunlight. Some people want the pool in the high 80's. In that case it might push it up a few degrees. Plus he says it helps the AC, which would be my main concern.
Does it steal money? Maybe. I'd like to see some real stats before I invested. Plus. Your pool pump and condenser would need to be in the same location. That doesn't seem to be real likely unless you built your pool and a/c accordingly. In my case, it's pretty much out-of-the-question.
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Think about how it could help the AC. The current coils and fan in the condesner are perfectly capable of taking the heated, compressed refrigerant down to close to ambient temperature. The pool heat exchanger is going to do the same thing. Yeah, it's smaller because water can take the same heat away with a smaller heat exchanger. But, at the end of the day, all I see that's saved is the cost of running the AC condenser fan. Don't know how much that is in the whole AC scheme, but considering you have a compressor, big blower in the furnace, I'd be surprised if it's more than 15% or so.

Me too. You would think TOH would come back a week later to show the results.
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On Mon, 10 Dec 2012 07:43:07 -0800 (PST), " snipped-for-privacy@optonline.net"

"Ambient" pool water temperature normally isn't the same as ambient air temp. A pool provides an enormous heat sink, cooling at night, with evaporative cooling not requiring jumping through EPA hoops. Water is thousands (WAG) of times more capable of removing heat than air. And "perfectly capable" doesn't address the difference in time running to do the same job. Which gets to electrical consumption and compresser/fan wear.

I've seen estimates that water cooled condensers give 20-50% energy savings. It's all in the details - and climate. In some climates people want their pools chilled. Barring that, using pool water to cool the condenser is elegant and efficient if the bottom line works out The main issues are initial cost and maintenance. Those are the nuts to crack. It all gets to payback.
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wrote:

Excellent points. Bottom line, the pool will help the A/C MUCH more than the A/C will help the pool. BUT, it is proly unlikely this could be done economically, at least in a one-off basis.
But, if A/C mfrs would outfit the condensing heat exchanger with a water jacket, so that all's you needed was some fittings, plastic tubing and a small-ish pump, then indeed it would be economical, and likely radically increasing the SEER ratings.
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water

Yeah, but then they wouldn't work with air. There has to be intimate contact between the condensor tubing and the exchange medium.
If they were to outfit them with "Siamese" condensor tubing, so one line carried refrigerant, and the other a liquid exchange medium, AND put fins on the array -- then it would work, but would be quite a bit more expensive.
On a side note: With a little re-wiring of the controls, a large window unit AC makes a dandy monster-scale dehumidifier. Just situate the whole affair inside the conditioned space (instead of through a window or wall), and run the condensate outside. The wasted energy also heats the space (some).
I have dehumidified large industrial drying rooms for cheap that way.
Lloyd
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On Dec 11, 7:06am, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

> On a side note:With a little re-wiring of the controls, a large window

e
>wall), and run the condensate outside. The wasted energy also heats the

Does the evaporator still run cold? And if not, does any water condense inside of the unit (as the inside area's air is on its way out)?
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e
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the whole

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.
>Does the evaporator still run cold? And if not, does any water

Oops, didn't read that. You ran the thing with the windows closed.
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Yeah. The whole unit is inside the room. Both the evaporator and condensor are operating on the local air. So long as you isolate the two enough (with a plywood baffle to direct the hot exhaust away from the unit) so that they don't instantly swap air, it works a treat.
No... the evap doesn't freeze. If anything, it sometimes doesn't get cool enough -- as the humidity drops, the temp on the evap has to get lower and lower to condense, and the unit is heating the air at the same time it's cooling it <G>.
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

two

same

Lower the evaporator temp to the dewpoint by partially restricting mass airflow volume across the coil.
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yep. But it's a two-edged blade. Restrict it, and you get less dehumidification when you can use it most, and potentially can freeze the evaporator, if there's too little flow.
All-in-all, it works fine with no restrictions. There's just a limitation on how low a humidity you can accomplish.
And, of course, the usual AC doesn't have a humidistat, so it's just a matter of letting it run continuously, unless you want to do a bit more engineering.
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

Tried that.... for some reasons the units would ice up. An A/C guy told me that would be a common problem, forgot what the reason was. But, if they don't ice up, a useful application of an otherwise old beatup A/C unit. Also, if you turn them around in the window during the winter, you have a heat pump.... :)
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

The typical water-cooled condenser has the refrigerant tube threaded inside the coiled water pipe, so it is surrounded by flowing water.

The only problem is the typical window AC has the condensate rigged to flow back to the condenser fan and get slung around, to extract an evaporative cooling effect from the water. It probably wouldn't be real hard to defeat that, however. But, it would take a little hacking.
Jon
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wrote:

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radically

During the summer months, I use a geothermal heat pump to cool the house while simultaniously eating a 45,000 gallon pool; in the fall, I use it to heat the house with up until the point where the pool is colder than our well water at which point I start heating with well water, using surface disposal instead.
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PrecisionmachinisT wrote:

COOL! (pun intended) I'd like to hear more details about this system.
Jon
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Existential Angst wrote:

Adding a water-cooled condenser to an A/C system shouldn't be that big a deal. The problem is corrosion. I'd expect pool water running through condenser to shorten its life considerably. But, on the other hand, it might save enough energy to pay for a replacement condenser coil every few years. it would make a mess of the pool when it blew oil into the pool water, though.
Jon
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lp

No it won't. Because the refrigerant temp coming back to the air handler is going to be about the same in either case. The existing condenser is HUGE because it's air based. But it's sized so that the returning refrigerant is near ambient when it goes back. The pool water is going to be typically 80 - 85. At least it would be if this thing does what it's claimed to do. The refrigerant can't go lower than the pool temp, even if this small water based heat exchanger is 100% efficient. So, in my world, the bulk of the energy savings is from the AC condenser fan not running and instead the pool pump being used. The pool pump electricity isn't counted, because the pump would have to run 6 or 8 hours a day to filter anyway.

It ain't gonna do much for SEER, for the reasons noted above.
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wrote:

No it won't. Because the refrigerant temp coming back to the air handler is going to be about the same in either case. The existing condenser is HUGE because it's air based. But it's sized so that the returning refrigerant is near ambient when it goes back. The pool water is going to be typically 80 - 85. At least it would be if this thing does what it's claimed to do. The refrigerant can't go lower than the pool temp, even if this small water based heat exchanger is 100% efficient. So, in my world, the bulk of the energy savings is from the AC condenser fan not running and instead the pool pump being used. The pool pump electricity isn't counted, because the pump would have to run 6 or 8 hours a day to filter anyway.

It ain't gonna do much for SEER, for the reasons noted above. =======================================================I think you missed the basic point.
Heat transfer to air is *intrinsically* less efficient (by orders of magnitude) than it is to water. Add to that that the water is proly sig'ly cooler than the air to begin with, water cooling of the outside coils of an A/C is a no-brainer.
So no matter how the condenser is "sized" for air, a water bath would radically improve (lower) the returning refrigerant temps. And the hotter the day, the more improvement will be seen.
But, HOW this is actually executed is another story, as Vic implied. He was just making the thermodynamic point that, all other things being equal, the A/C efficiency, due to the heat transfer to water instead of air, would skyrocket. That the A/C exhaust fan is not needed is an added plus, as well.
OTHER things might negate the idea of water cooling, but that's another story.
Why do you think IC engines are water-cooled? Despite the fact that air-cooling technology exists? They've even gone to water-cooling motorcycle engines. Yeah, the analogy is not perfect, but it drives the point home.
--
EA



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Which, as I said, means that you need a bigger condenser coil/fan for air. Which the AC unit already has. It's the big thing with coils on 4 sides, fan on top.
You can transfer the same amount of heat with either water or air, given that they are sized correctly.

Significantly cooler? The whole purpose of this thing is to keep the pool warm. So, if it works, then the pool is gonna be 80 -85, which is not significantly different than the air temps. Sure, during some periods, the pool water could be 65, but that's going to be at the beginning of the season. And during those periods, how much do you think the AC is running? In my world, it's not enough so that whatever is going on is going to make a big difference in cooling costs.

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It's not going to change much at all, assuming the AC condenser already there is properly sized, which it is.
That the A/C exhaust fan is not needed is an added

Actually they are air cooled too. They have a properly sized radiator which takes all that heat the water picks up and transfers it to the air.

t
Have you felt the return line on a modern one, say 14SEER?
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