Heating a pool with an air conditioner

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First the use of isolation reservoirs are very common.
One pumps hot coolant into a tank of say salt solution but keep all of the coolant in the pipe. In another loop that goes in the tank and outside of the system - is other coolant. So coolant A never touches or mixes with coolant B.
One is drawing heat off and putting it into the salt. The other takes the heat from the salt and dumps it in the pool or in a water cooled chiller.
Many machines work that way and every NUKE works that way as well.
Martin
On 12/13/2012 9:30 AM, snipped-for-privacy@optonline.net wrote:

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First the use of isolation reservoirs are very common.
One pumps hot coolant into a tank of say salt solution but keep all of the coolant in the pipe. In another loop that goes in the tank and outside of the system - is other coolant. So coolant A never touches or mixes with coolant B.
One is drawing heat off and putting it into the salt. The other takes the heat from the salt and dumps it in the pool or in a water cooled chiller.
Many machines work that way and every NUKE works that way as well.
Simply put the solution you want in place of the efficient salt.
Martin
On 12/13/2012 9:30 AM, snipped-for-privacy@optonline.net wrote:

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On Dec 12, 3:23 pm, "Bruce L. Bergman (munged human readable)"

There is no need for a variable speed pump. Any existing pool pump is going to be just fine. With a single speed pump, the water just goes at full speed. What's wrong with that? It's going already, probably 6 - 8 hours a day to filter the water.
- and you'll really need a computer to know when to

The installed unit comes with a controller that does exactly that.

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On 12/11/2012 2:19 AM, Existential Angst wrote:

Maybe it depends on where you are, but in Phoenix, our pool needed cooling in the summer just from the heat load from the sun. In July and August, the water temperature would be 98+ in the evening. We had a mister hooked up to the filter return that would take a few degrees off when the pump ran at night. Pumping more heat into the pool would make it unusable for swimming.
Also, we ran the pump late at night when electric rates were lower. That would not be possible if you were using the pool as a heat sink.
Boiled, BobH
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On 12/12/2012 5:29 PM, BobH wrote:

Yeah. Central TX here and same thing. Last 2 summers I got "Sun Sails" and that made quite a difference. HD sells them for $35. I got mine back when they were cheaper. They hold up remarkably well.
Are you sure they lower the bills at night? Here it just looks like they do and it fools a lot of people. Even the guys at the pool store thought it was lower at night but, actually, here, they tier the rates based on usage, not time of day.
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On 12/12/2012 5:56 PM, gonjah wrote:

I looked it up. Phoenix does have "time of use" billing.
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On 12/12/2012 6:37 PM, gonjah wrote:

Yes, we were on APS in the east valley. As long as we used more than 1/2 the daily KWH between 8PM and 8AM (or something similar), the nightime rate was about 1/3 the daytime rate. Running the pool pump from midnight to 5AM used enough power that we almost always made the required distribution, even when we were pounding hell out of the air conditioner.
BobH
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wrote:

I never said they were. Only that they are, fairly close. If this thing works, then it should keep the pool at 80 - 85. That isn't all that much different than the ambient air temps when the AC is going to be running. Sure, the pool could be 65 in May. But then the AC isn't running or isn't running enough to make any impact anyway.

That is reflected in the size of the CONDENSER. The existing on is sized based on AIR. The pool water one is sized based on using WATER. So, of course the pool water one is much smaller. But if the temp of the refrigerant when it leaves the condenser and returns to the evaporator in the air handler is the same, then the only thing you've accomplished from an energy standpoint are replacing the fan motor with a pump motor. As previously noted, that is a benefit as long as the pool pump would be running to filter the water anyway.

Yes it does address it, because, again, the refrigerant temp is still going to be about the same temp when it returns to the air handler. Whether it got to that temp by a large air based heat exchanger or a small water based one doesn't matter, the pool pump motor replacing the fan motor being the essential difference.

Anybody can give you "estimates". I'd like to see real data on this pool thing. And as I've said, you do get some savings. It's due to the fact that you no longer have the fan on the condenser running. Instead you're using the pool pump motor, which you can assume is paid for by it having to run for pool filtering, anyway.

Do you have a pool? Pool heater? What size is the pool and what is the pool heater in BTUs? In my world, there is no way this computes.
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wrote:

No way. An inground pool pump pumps in the vicinity of 40 gpm.
The HVAC line through that tiny heat exchanger seems it would have to attain a temperature approaching 1000°F to make -any- difference. -----
- gpsman
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On Wed, 12 Dec 2012 05:19:15 -0800 (PST), " snipped-for-privacy@optonline.net"

I never mentioned heating the pool, only AC efficiency. But even with water and air temps the same, water cooling is a much more efficient means to remove heat. Why do you think many commercial enterprises use water cooling for AC? Building logistics, local electric and water costs, and salesmen. Cooling towers aren't put up capriciously.

You seem to be denying common precepts of thermodynamic laws. Energy is being used and transferred in all cases. Water transfers heat much better than does air. Beside the fan, a bigger condenser also usually means a bigger compressor, and more energy use.

Water cooling will provide lower condensed refrigerant temps with less electrical energy expended. You can cut down a tree with a sharp blade or a dull blade. The tree goes down in either case. But the dull blade will tire you out more.

You probably won't find data on residential pool-cooled AC condensers, because air-cooled AC does the job, electricity is pretty cheap in most places in the U.S., and residential pools are very small in number. The southwest U.S. might be the place to look. Here's a "study" done in Kuwait showing `40% energy savings using water cooled AC. Click on the pdf link. http://repository.tamu.edu//handle/1969.1/4621 I don't vouch for it.

No, I don't have a pool and never wanted one. And I'm not saying I would cool my AC with pool water. But if I lived in the right climate and had a pool, I would look into it. But a hard look at cost vs savings. Chlorine interaction with the heat exchanger might be the biggest issue, BTW, I don't know who said it, but I think somebody said the air handler uses the bulk of the electric energy in the AC system. Not true from what I've read. Compressor uses `70%.
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wrote:

All true (proly). But Trader's point was, if the return refrigerent is already at ambient temp (and assuming water is at the same ambient temp), adding water cooling to an existing system will provide no benefit. This is correct. I don't know if return refridgerant of an air-cooled A/C *is* at ambient temps, but if it is, ADDING water coolant won't do anything further.
If the pool water is below ambient temp, then better effic would be realized, but it would remain to be seen if the increased effic was worth the monkeying around.
But, from an original design pov, water (or whatever the liquid coolant) will undoubtedly allow the inherent design of the system to be more efficient.
Energy usage: In my 5 ton A/C unit, the blower draws about 10 A at 120 V, the compressor 20 A at 240, for a total of 6,000 W. 4800/6000 = 80%. 6,000 W.... holy shit....
And if the fukn installer -- Yost & Cambpell, Westchester, Bronx, NYC, NY -- didn't fuck up the installation so royally, the blower could have been under 5 A instead of over 10 A, so the compressor usage ratio would have been higher. In fact, the original blower WAS under 5 A..... Fuck Yost & Campbell, the worst HVAC company I've ever seen.
Inway, I don't know if that ratio holds in commercial buildings, etc, but my installation supports your figure.
--
EA




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I think someone here finally gets it! That is in essence the point. That the existing AC system is going to get the refrigerant down to just above ambient. But in your above statement, the pool water cooling could still have benefit IF the pool water was substantially below ambient. But as I've said, that couldn't be during most operating times, if the thing does what it's supposed to, ie heat the pool. If it works, then the pool should be 80 -85 most of the time, right? Which sounds like ambient air temp.

Per the above you have the catch 22. The system was installed to heat the pool. If it's effective doing that, then most of the time the pool should be at ambient.
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It's typically within a couple degress of ambient. If it's higher than a couple degrees, I know there is other problems going on. That;s one of the things I check on systems that aren't working.
Christopher A. Young Learn more about Jesus www.lds.org .
If someone here is in a warm climate, has a decent efficient AC system, perhaps they could measure the temp of the refrigerant pressure line just before it enters the air handler. I'd love to do it, but it's too cold here. It would be interesting to see how much above outside ambient the temp is.
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You need to get a grasp on efficiency and what it actually means. In this case, the fact that water can absorb a lot more heat than air means that you can use a much smaller heat exchanger with water to transfer the SAME amount of heat. That is why the pool heat exchanger is SMALL, the AC condenser with all it's coils on 4 sides is LARGE.
I could construct a variety of heat exchangers to take away the heat from the compressed AC refrigerant. It doesn't matter how large or small they are. All that matters is how much heat they remove and how much energy goes into doing that. You have two differenct heat exchangers:
A - Existing AC coils with fan
B - Pool water, using pool pump.
As long as the temp of the refrigerant going back to the air handler is about the same, the only efficiency that comes into play is that the AC coils have a fan that must be powerd. The pool pump also must be powered, but since the pool water has to be circulated 6 or 8 hours, you can attribute the electricity that it takes to run the pool pump to the pool, so it's already paid for.
For there to be any other "efficiency" involved you would have to see a difference in the temp of the refrigerant where it enters the air handler. If the pool heater works as claimed, then the pool is going to be 80 - 85. The refrigerant can't be any cooler than that. And from holding the line on a new AC unit, the line isn't hot going into the air handler. It might be a little above 80 - 85, but I don't belive you're typically going to have it be substantially hotter than what you get with the pool water. If it were, AC manufacturers could get that same improved performance by just making the AC coils, fan, etc larger. They have already done exactly that, to get the most efficiency possible out of the unit. It would be pretty stupid to send hot refrigerant back to the evaporator.

In fact, I'm following them.

Well, duh! And a bigger compressor, bigger coils means the unit has more capacity. Of course a 5 ton AC is bigger than a 3 ton. But that isn't the issue. For a given capacity, say 4 tons, the condenser and fan are sized to remove all the heat required. That unit sends the refrigerant back to the evaporator at close to ambient.

I said the result is close enough to being the same that it's not going to make much difference. If the refrigerant is about the same temp when it gets back to the air handler, then the only difference in efficiency is going to be the difference in energy it takes to run the AC fan on the condenser versus the energy it takes to run the pool pump. And I'll bet in the energy comparisons they don't count the pool pump, attributing it to running anyway. That in turn does give you some energy savings.
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On Thu, 13 Dec 2012 07:53:13 -0800 (PST), " snipped-for-privacy@optonline.net"

Right. Water cooling means a smaller condenser, a smaller compressor and compressor motor, and `30% less electrical consumption than an air-cooled unit producing the same cooling capacity. But that has nothing to do with efficiency. And all the HVAC engineers are wrong. And I "need to get a grasp on efficiency .." Got it. Dream on.
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Tthere is no such thing as just "water cooling". You have to look at the whole system, how it's sized, what temp the water source is, where the heat from the water goes, what temp the water is when it returns, etc.
Let's start with the basics of that home AC as it currently works, with air being used to transfer heat at the outside condenser, OK? The refrigerant comes into the air handler evaporator as a liquid. Let's say it's 85F. It expands, cooling the air. When it leaves the evaporator it's a gas and cold, let's say 40F. The compressor draws it back via the suction line. The refrigerant gas enters the compressor and gets compressed back into a liquid. In doing so, it's temp rises substantially. That's most of the energy consumption right there, compressing the refrigerant. Now it's a liquid again, at 140F. Now we have to get rid of that heat, cool it down. Are you with me so far? We're going to cool it down. We can do that in one of two ways:
A - Pass it through a larger heat exchanger which is a coil with ambient air flowing over it.
B- Pass it through a smaller heat exchanger with pool water flowing over it.
In case A, the governing factors that effect the efficiency are the electricity that it takes to run the fan and the temperature of the air. The refrigerant can't be cooled below the temp of the ambient air, but with a properly sized coil and fan, we can get it close to that.
In case B, the governing factors that effect the efficiency are the electricity it takes to run the pool pump and the temperature of the pool water. The refrigerant can't be cooled below the temp of the pool water, but with a properly sized coil and fan, we can get it close to that.
That is the essential energy difference. Now let's say that the ambient air is 80F and the pool water is also 80F. In that case it's perfectly possible and reasonable to get the refrigerant down to close to 80F using either approach. Now the cooled refrigerant at 85F goes back to the evaporator at the air handler. It enters the evaporator, expands, cools the air and leaves the evaporator at 40F, completing one whole cycle. That's it.
So, the cycle works exactly the same either way. You still need the same size compressor motor. You still get the same cooling capacity. The only difference is that you've used a large air based heat exchanger with an electric fan in one case and a much smaller water based heat exchanger with an electric pool pump in the other.
Now, if you attribute the pool pump motor electricity to the pool operation instead of the AC, which is reasonable, then you can say you've "saved" the cost of running the air fan in the AC condenser. That's reasonable. And you could say that the system is saving x percent in energy because it no longer has the AC fan running. Actually, now that I think about it, I wonder if the fan isn't really running all the time anyway. Because to stop it is going to require modifying the AC electrical system. Every one I've seen the fan runs when the compressor runs.
But otherwise, the operation of the system is EXACTLY the same whether you air cool it or water cool it. I don't see a magical improvement in efficiency, no smaller compressor, etc. In fact, it's bizarre to drag a smaller compressor into this at all, because no one is proposing to change the size of the compressor in the home AC, are they? Could I design a water based system, with a smaller compressor, less electricity? sure. Just use ground water that is 50F. But that isn't what we're talking about doing here.
Now, in actuality, the temp of the refrigerant going back to the evaporator may be slightly lower with the pool water based system. But IMO, it's not going to be so much lower that it makes a significant difference. And it can't be lower than the pool temp water, no matter what. If the thing is doing what it's supposed to be doing in the TOH application, then the pool water should be about 80 - 85 most of the time, ie not much different than ambient.
And the returning refrigerant temp can't be too much above 85F, ie ambient, because obviously the existing system has a properly sized air based heat exchanger to take away as much of the heat as possible, ie get it down close to ambient. That's one of the ways to get higher SEERs out of the system and it would be pretty dumb to be selling systems that don't bring the temp of the refrigerant down as close as possible to ambient when you can do it by just using a bigger condenser, more airflow from the fan, etc.
That's the physics as I see it.
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I've seen this stated a few times in this thread and I don't think it's true. The pool temperature is going to be the average of daytime and nighttime temperature plus the effect of evaporative cooling at the water surface, plus the effect of cooling due to ground temperature.
All and all, I'd expect the pool water during the time the AC is in use to be significantly lower than the air temperature.
Before I had my heater, with air temps in the upper 90s I'd still have the water at 80 or so. If I remember right, 82 was an all time high.
The heating from the AC system heat exchanger isn't going to make much of a difference for pool temperature but the AC system will cool better.
--
Dan Espen

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That depends on the particular climate and if the pool is shaded or full sun. Here in NJ/NYC for example, pools that have mostly sun are in the low 80s without heat during July and Aug. And that is with daytime temps in the 80s. If it's upper 90s for a couple days, pool could be 85+ with no heater. The time folks here typically use a pool heater, if at all, is in the beginning of the season, ie late May, early June and again going into Sept. The problem with that is during those periods the AC is running the least. It's a mismatch between when it's needed most and when the most heat is available.
I agree there are going to be some days when the pool water temp will be below the air temp. But look at it from this perspective. If the system works to do what is wanted, then the pool should be 80+, no? Isn't that a purpose of the pool heater? So, if the water is 80 - 85, reagardless of how it gets there, I don't see that as being a big difference versus the ambient air if you average it out. For example, at night, the pool at times could actually be above the ambient air temp, right? If you;re saying, well the pool could be 75 and the ambient air 90, sure I could see that, but that situation has to be an exception, or else the thing isn't heating the pool enough, right? If it's working, then you should have 90 air, 85 water.

But the main point of the whole TOH project was to heat the pool. That was the original problem, not that they wanted to lower the AC bill. The lowering of the AC bill was an additional benefit.
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I have no delusion that this thing heats the pool to any significant temperature.

TOH never said heating the pool was the _main_ point at least I didn't catch it. Maybe they mentioned pool heating first?
I think they were wrong to mention pool heating at all because this isn't going to heat the pool enough to make a difference.
I'm in central NJ (like you).
I didn't see where they mentioned the location of the house in question but since it's TOH, it's likely it's New England. Like us in NJ, only worse. With the trees that guy had next to the pool, that water must be freezing. Reminds me of swimming in the cold clear lakes of New England. Nice water but cold, cold, cold.
--
Dan Espen

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Yes, that's how it started. TOH plumber, Richard T meets the homeowner and the discussion is about heating the pool. The HO says it's been hard keeping the pool warm enough, the backyard is shady, that he has researched other pool heating systems, wood burning, solar, hasn't got a roof with exposure for solar, etc. Richard adds the benefit of making the AC more efficient when he describes to the HO how the thing works.
And then to confuse things even more, Richard also says that the AC will use the same electricity as before, but you'll be getting heat for the pool too. So, which is it? That it improves the efficiency of the AC, or not? I think it does. One thing I think everyone agrees on is that when the pool is heating you could turn off the AC condenser fan. That for sure saves money. But, I wonder if they even do that? It would save energy, but it would also complicate the install because now you have to modify the AC equipment to selectively kill the fan. What about things like AC warranty? What about that for the system anyway? I mean if say the compressor fails, what if Trane says the system was modified, screw you? Maybe that wouldn't happen, because the servicing company would just put it in as a warranty claim anyway.....

Yeah, I was wondering where it was located too. I came to the same conclusion, that it was probably NE.
The big thing missing here is any report on how well it worked. You would think they would come back after a week to see the results. I don't doubt that it will heat the pool some. The real question is whether it's enough to make the whole thing worthwhile.
I think we're on the same page with regard to that. Around here a typical inground pool has a 200K to 400K btu heater. And if you've used one, you know that it takes it many hours running full blast to heat the thing. With say a 3 or 4 ton AC, you're getting what, 45K maybe 55K btus? And most of the time the typical AC is not running anywhere near constant. Mine on typical summer days runs maybe 25% of the time, from 11am until 8pm or so. And very little at night. So, you get it part time.
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