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(no email)
Date: Mon Oct 11 2004 - 23:52:07 EDT
I suppose you're talking about the camper roof models as I'm not familiar
with Coleman RV style.
"it's more efficient (though this may be because we're in Texas waters, and
of course the warmer it gets in
summer, the less efficient marine systems are)."
I am however a little familiar with water cooled vs. air cooled heat
exchangers. And that's what an air conditioner is. A heat exchanger. Size
for size there is no comparison in efficiency. Water cooled wins hands down.
To began with even in Texas I doubt the water gets to the same temperature
as the air. It takes a lot more 90 degree air moving over the condenser
coils than 80 degree water simple because of the laws of heat transfer.
Liquid will absorb heat better than air.
"it requires no maintenance;"
Maybe you haven't done any yet but the time will come. The condenser coils
should be cleaned periodically. There is also more area of condenser coil
that is subject to a leak, most of it very thin so as to make it efficient
as possible. So be careful when you do start cleaning.
I'm not sure why a marine unit's filter would need to be cleaned more often
that the RV style. The type cooling for the condenser shouldn't effect the
filter. Yes maybe a 16K BTU unit needs to move more air over the evaporator
than a 13 K and therefore more air goes thru the filter but aside from that
the filter cleaning/changing should be very close to the same. Both should
be cleaned/changed regularly.
I regret your problems with weeds. My first thoughts are that the system
needs a little tweaking to try and keep the weeds out of the hoses.
Different strainer maybe? I can't give any advice there because in the
nearly five years we've had ours we haven't had to backflush weeds once.
(Knock on wood or I'll be down next week doing it.) And we're on Lake
Guntersville- Milfoil and duckweed capital of the world.
I've also heard numerous stories about airlocks but so far have never had
one.
I have to think it has something to do with installation design. (I didn't
have anything to do with the way ours is laidout so I'm not saying I could
make anybody else's work better.)
"Isn't it possible to install an air-cooled unit in a dedicated inboard
space, with perhaps a blower to force outside air in and out for cooling?"
Sure but can you imagine the size of the blowers and the noise they'd make?
"but why not?"
Like I said the size of the blowers and the noise. And why would someone
want to when they are sitting in an almost unlimited amount of cooling
liquid that will take away the heat much better than air.
On another note, if the unit is a reverse cycle one that will heat, then
there is a definite advantage to the water cooled coils. Or as the case of
when it is heating, the water heated coils. You can rest assured that the
water will be warmer than the air when the air is 25-30 degrees. The water
stays about 46-50 degrees all winter at Guntersville but 20 degree air is
not unusual so the water heat exchanger has a big advantage. It heats the
boat great.
I'm happy that you are pleased with the roof mounted unit but I don't
believe its because its more efficient than a similar sized marine unit.
Some of the things that might be making it stand out right now are:
1) Because its mounted in the roof, its cold air vent is ideally situated in
the ceiling. Where is/are the outlet/s for the marine unit?
2) You state its in the V-berth. What's the comparably volume of the V-berth
to the volume the marine unit is cooling? Unless your boat is different from
most, the V-berth is probably 15-20% of the total boat's volume so you've
got a 16K unit cooling 4 times as much as the 13 K unit. Or put another way
you have 29 K BTUs of capacity but 45% of that capacity is cooling 20% of
the total need. Oh! and the V-berth probably has 5% of the window area.
3) What are the ages of the two? If the marine is 12 years old and the RV 2
years old then there is a difference in technology in the systems. A 2 year
old system will be more efficient when compared to the same type system that
is 12 years old. Consequentially a 2 year old water cooled system will
knock-the-socks-off a 12 year old water cooled system.
Are we comparing today's technology with yesterday's?
4) (And to me a biggie) Installation! A lot of HVAC installations in boats
are poor at best and bloody awful at worst. The vents are poorly placed.
Many are right down on the sole if not up thru it. In our boat the outlet in
the aft cabin was on the same level (about 12" above the floor) and only a
few feet from the air return. All that happened was that the air came out
the vent and right back in the return. It made a terrific difference when I
elevated the outlet to almost ceiling height. Gives the cooled air a chance
to distribute before being sucked back thru the unit.
We have the same situation in the galley/salon area. The outlet is literally
three feet from the return, maybe a foot higher. So far I haven't worked out
a way to move it but a small fan sitting in front of the outlet blowing the
cooled air away from the return makes a big difference.
And while I have said I'm not a system designer I do recognize good pump
placement and hose routing. As well as a amply sized sea strainer. None of
which you will find on most boats. Particularly if the installation was post
factory.
Again good luck with the RV unit. Let us know how its doing when it gets the
same age as the marine one.
Bill
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