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From: John De Armond
Subject: Re: Hot Weather Cooling Problems
Date: Tue, 25 Jul 2006 13:24:22 -0400
Message-ID: <>

On Tue, 25 Jul 2006 16:00:36 GMT, (Harry
Chickpea) wrote:

>Another trick I use to lower cooling costs is to mist the sealed can
>containing the compressor itself.  Although they are designed to
>operate at high temperatures, the heat of compression and motor losses
>has nowhere to dissipate other than the small interface the can has
>with the surrounding air, and the compressor is constantly working
>against its own build-up of heat.  Misting it drops the temperature by
>a significant amount.

It's an odd compressor these days that has the can high side
pressurized.  Those are the only ones that run hot cans.  For the more
normal compressor, the can and the motor and compressor rely almost
exclusively on the incoming cool refrigerant for cooling.  Essentially
all the heat losses dissipated in the compressor motor are carried out
by the high pressure gas and then discharged to air (or water) in the
condenser.  Misting the can on one of these will have no effect either

Misting the condenser WILL have a significant effect.  If your water
is quite soft then misting the condenser directly will work.  If the
water is hard at all then mineral buildup will quickly ruin the
condenser.  In that situation I've built a sheet metal box around the
condenser designed to hold swamp cooler media.  cool air from that is
pulled across the condenser by the fan.

I had a rather ancient 60s vintage unit on my house in Atlanta.  It
had the typically undersized condenser typical of the era.  I had soft
water so I set up a misting system (actually a fogging system) using
very fine fogging nozzles.  These discharged directly in front of the
condenser and were controlled by a solenoid valve connected to the
thermostat lead so that it misted only when the condenser unit was

I don't recall the exact numbers but the actual power draw (measured
with a wattmeter and not just an amp-clamp) dropped over 25% and the
supply air temperature dropped a few degrees to boot.  It dropped the
monthly bill by about a third.  The misters used only a couple gallons
of water per hour so the water cost was nominal.


From: John De Armond
Subject: Re: Hot Weather Cooling Problems
Date: Tue, 25 Jul 2006 17:59:01 -0400
Message-ID: <>

On Tue, 25 Jul 2006 19:36:19 GMT, (Harry
Chickpea) wrote:

>Neon John <> wrote:

>I agree with you right up to that last sentence.  The refrigerant gas
>going into the compressor is relatively cool, since it has just exited
>the evaporator coil.  However, it has picked up the heat from the
>house, and that heat is what gets concentrated by the compressor,
>concentrated enough that it can then cool in the condenser and liquify
>at temperatures of 90 and 100 degrees.
>Touch the high pressure line coming out of the compressor and you'll
>find just how hot that is.  As you point out, systems are designed so
>that almost all of that heat gets dissipated in the condenser and
>liquification occurs there.
>If the walls of the piston in a compressor are cooled, the compressor
>can dissipate a part of that heat on its own, and thus reduce the
>load.  The effect is much less in a small canned compressor that a
>large one that can be cooled with a chiller, but it still exists.

I hate to say this but you don't have a clue.  Consider the
construction of a hermetic compressor:

This is an old illustration but it serves.  There is no connection
between the compressor itself and the walls of the hermetic can.
Reducing the can temperature to absolute zero would have such an
insignificant effect on the compressor operating temperature as to be

In fact, it's probable that wetting the can will have a small negative
impact.  The suction line gas temperature should be in the 40-45 deg
range for a normally designed AC unit.  This gas is in contact with
the can which means that the can temperature approximately follows. If
the can is artificially heated by "cooling" it with ambient
temperature water then some amount of refrigerant is actually warmed
(given more enthalpy) more than what it received in the evaporator.
This very slightly reduces the operating efficiency and very slightly
ups the operating cost.

In practical terms, the effect is too small to matter.  If heat
through the can did have any significant effect then the mfr would
insulate the can the same way he does the suction line.  In practical
terms, wetting the can has no measurable effect.


From: John De Armond
Subject: Re: Hot Weather Cooling Problems
Date: Wed, 26 Jul 2006 13:44:22 -0400
Message-ID: <>

Window units and many packaged units (all the components inside one
case) do use the condensate to help cool the condenser.  The
condensate is routed to the condenser area where a rim on the
condenser fan, called a slinger, slings the water up and about.  It
helps a little but there just isn't enough water available from that
source to make much of a difference.

With hard water you can use the swamp cooler pad option that I
mentioned before.  Simply frame in the condenser inlet (I used sheet
metal but outdoor grade plywood will work) so that you can mount a
swamp cooler evaporator pad in front of the condenser.  Arrange to
keep that pad wet.  That way the evaporation takes place in the pad
and not on the condenser so the minerals stay on the pad.  Simply
replace the pad when it gets crudded up enough.

If you live in a low to moderate humidity area then this will make a
significant difference.  Even under high humidity conditions it helps
a little.


On Wed, 26 Jul 2006 09:45:28 -0700, "Ulysses"
<> wrote:

>> That is my experience as well.  During July thru September, I have a
>> constant mist going on the compressor and the hottest part of the
>> compressor coil.  I have a filter to prevent mineral buildup and I
>> leave the mist going all the time to give it a chance to wash down any
>> deposits that start.  It is one of the more effective ways to reduce
>> power costs.  I monitor it fairly closely, and haven't seen any
>> serious corrosion or buildup.  Once weather starts getting cooler, I
>> cut off the misting.
>I have extremely hard water so misting with it would probably be a bad idea,
>but I'm thinking that it might be possible to collect the condensed water
>and use a small pump to mist it.  After all, the condensed water comes out
>of the air so it must be fairly close to mineral-free.  It sounds like there
>might not be quite enough water available from that source though...

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