Heating a pool with an air conditioner

[Existential Angst]

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.

No good deed goes unpunished.

 

[trader4]

It's also more efficient to move heat to a liquid rather than the air, plus most
of the time the water is going to be cooler than the air when the a/c is
running, another reason the a/c will be slightly more efficient.

The fact that it's more efficient to move heat to a liquid is
reflected in the size of the CONDENSER. The existing air
one is much LARGE. The replacment pool water one is much
smaller. As long as the temp of the refrigerant when it
reaches the air handler is the same, you're not gaining
anything in efficiency, except the previously noted issue
of using the pool pump
motor versus the AC condenser motor. And if you feel the
pressure line where it enters the air handler, it's already
close to ambient. At least mine is and I would hope it
is on any relatively modern AC unit.

As to the water being cooler, if the thing is doing what it's
intended to do and claimed to be capable of doing, then
it should be keeping the pool 80 to 80F. That doesn't
sound very much different from average ambient air temp
in locations that need pool heating, in the months when
they need it most.

That said, if you are going into this kind of setup thinking it will saveyou
money in heating a pool, you need a refresher course in basic thermodynamics.
Then look at what a PITA combo VCR/TVs were and consider what you'd be dealing
with with your average HVAC tech.

Absolutely agree with the last part.

 

[trader4]

"Ambient" pool water temperature normally isn't the same as ambient
air temp.

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.

 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.

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.

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.

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.

 I've seen estimates that water cooled condensers give 20-50% energy
savings.

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.

 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.

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.

 

[trader4]

Excellent points.
Bottom line, the pool will help the A/C  MUCH more than the A/C will help
the pool.

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.

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.

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

 

[gpsman]

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.

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.

 

[Existential Angst]

Excellent points.
Bottom line, the pool will help the A/C MUCH more than the A/C will help
the pool.

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.

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.

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.

 

[Existential Angst]

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.

You claim your return refrigerant is close to ambient....
If that's indeed true, you have a point, water cooling would be moot --
unless water temps were sig'ly below ambient.

But I seem to recall those return lines being perty warm, altho I wouldn't
bet the farm on it.
Also, eff w/ return temp might not be linear.
Inyway, no biggie, all this efficiency/ecology talk is inherently moot, with
7 billion assholes on the planet, every single one of them bucking for a
nice car....[/QUOTE]

 

[Dan Espen]

"Bruce L. Bergman (munged human readable)"

Another huge problem is the pool chemistry has to be kept Very Rigidly
Controlled or the pool water will rot out the water cooled condenser
REAL FAST - or clog it up with scale to the point it won't work
anymore, same outcome. Most people can't or won't be that anal about
the pool water, and the condensers can rot in a year or two.

It's not as huge a problem as you think.

For one, a pool should be kept near neutral.

I have a pool heater and years ago, after 2 years, the water manifold
developed a leak. The first thing the pool guy was asking is "did you
keep the water near neutral?". I did, but was unable to get any kind of
discount on the replacement.

When putting in the replacement, I noticed the interior is coated with
plastic. So, there's no water to metal contact.

I've been running heaters for more than 6 years now and I can tell you
the water in contact with a heated metal unit does not create any
special corrosion problems. A condenser shouldn't be any problem at
all.

I'm not sure what all the controversy is.

If this guy had his AC unit near his pool pump he just did what was
reasonable. The alternative would be to have a big fan roaring near the
pool with hot air being blown around. That's not something you want
near a pool.

Using water cooling is going to be quieter and save blower energy.
I believe other posters are correct, this won't heat the pool much but
it will save energy, be quiet, and not heat the air near the pool.

 

[Nate Nagel]

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.

It seems to me that the real advantage of a setup like this would be
that the pool water would act like a "ground loop" and make the air
conditioner more efficient, as the pool's temperature would likely be
less than ambient air on the hottest days when the A/C is likely to be
wanted most. I never did like the idea of using a big box sitting on a
pad trying to shed heat to 100F air on a hot day when you could shed it
deep underground where the temp is less. Simple thermodynamics tells
you which is going to be more efficient. I suspect that you would still
need some auxiliary method of heating the pool water either solar, gas,
what have you, but overall it still seems like a good idea.

nate

 

[gonjah]

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

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.

 

[Existential Angst]

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.

You keep saying the end result is same, but it's not.
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%.

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 **** 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..... **** 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.

 

[gonjah]

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.

I looked it up. Phoenix does have "time of use" billing.

 

[trader4]

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.




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.

You claim your return refrigerant is close to ambient....
If that's indeed true, you have a point, water cooling would be moot --
unless water temps were sig'ly below ambient.

But I seem to recall those return lines being perty warm, altho I wouldn't
bet the farm on it.

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

 

[trader4]

Another huge problem is the pool chemistry has to be kept Very Rigidly
Controlled or the pool water will rot out the water cooled condenser
REAL FAST - or clog it up with scale to the point it won't work
anymore, same outcome.  Most people can't or won't be that anal about
the pool water, and the condensers can rot in a year or two.

This is why water cooled condensers and the water tower used to cool
the water use liberal amounts of some really nasty chemical additives
to keep that from happening - and you sure as hell don't want to swim
in them.  And they still dump a lot of water and evaporate even more
on purpose (higher temps) and replace it with fresh every day.

Plus, you need to setup a variable-speed pool pump motor and link the
AC to the Pool

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

shift between the Water Condenser and the regular air condenser coils
on the condensing unit - Or it can't run automatically.

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

 

[trader4]

"Bruce L. Bergman (munged human readable)"


It's not as huge a problem as you think.

For one, a pool should be kept near neutral.

I have a pool heater and years ago, after 2 years, the water manifold
developed a leak.  The first thing the pool guy was asking is "did you
keep the water near neutral?".  I did, but was unable to get any kind of
discount on the replacement.

When putting in the replacement, I noticed the interior is coated with
plastic.  So, there's no water to metal contact.

I've been running heaters for more than 6 years now and I can tell you
the water in contact with a heated metal unit does not create any
special corrosion problems.  A condenser shouldn't be any problem at
all.

I'm not sure what all the controversy is.

If this guy had his AC unit near his pool pump he just did what was
reasonable.  The alternative would be to have a big fan roaring near the
pool with hot air being blown around.  That's not something you want
near a pool.

Using water cooling is going to be quieter and save blower energy.
I believe other posters are correct, this won't heat the pool much but
it will save energy, be quiet, and not heat the air near the pool.

If you watch the TOH video, the problem was not
the AC condenser unit making noise. It did not appear to be
particularly close to the pool. The problem was the pool is
shady and the homeowner wanted to heat the pool. The side
benefit was the alleged substantial savings in AC costs.

 

[trader4]

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?

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.

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.

In fact, I'm following them.

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.

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.

You keep saying the end result is same, but it's not.
Water cooling will provide lower condensed refrigerant temps
with less electrical energy expended.

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.

 

[trader4]

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 toan
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.

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.

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.

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.

 

[Existential Angst]

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.

I think someone here finally gets it! That is in essence
the point.
===================================================


And I owe it all to your very fine leadership and tutelage.
Plus, the REAL assholes all seem to be on rec.woodworking..... LOL
--
EA







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.

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.

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.

 

[trader4]

I think someone here finally gets it!   That is in essence
the point.
===================================================

And I owe it all to your very fine leadership and tutelage.
Plus, the REAL assholes all seem to be on rec.woodworking.....   LOL

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.

 

[trader4]

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.

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.