On Dec 13, 2:19*pm, Vic Smith wrote:
On Thu, 13 Dec 2012 07:53:13 -0800 (PST), "

wrote:

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.

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.