I burped my Baby
Neon John
that is :-)
This is a 20 year old strictly manual three-way refrigerator. It had
faithfully maintained the cabinet temperature at a balmy 32 degrees ever since
I've owned the rig. A couple of weeks ago it started drifting upward. By
last weekend, it had hit 50 inside and last night had risen to 55.
No sign of leakage so I decided to try the burp technique. Itasca practically
embedded the cabinet in RTV as part of the mounting scheme so the couple of
hours it took to dig all this stuff out was the worst part of demounting the
fridge.
Once on the bench, the first was to disassemble the burner and chimney to
clean and inspect it. The flue was clear but the burner tube and generator
were quite rusty. I gave it a very good wire brushing. Then to discourage
further rust, I gave it several coats of LPS cold galvanize. I know from
experience that this stuff will withstand the heat and provides excellent
galvanic protection against rust. The flue assembly was packed with very
crufty fiberglass insulation. I replaced this stuff with some new fiberglass
insulation.
Next to the burping. The objective is to break up any gas pockets that may be
blocking circulation and to re-dissolve any crystallized chromate solution.
There is a wide variety of suggestions on how to do this on the web. All
seemed excessively complicated and time consuming so I devised my own.
What I did was to put the refrigerator on its side, left it there until the
gurgling stopped (NOT overnight as some of the procedures indicate), then
turned it upside down until the gurgling stopped, followed by placing it on
its other side until the gurgling stopped.
To aid the fluids' return to their proper places, I then rocked the 'fridge
between lying flat on its (looking from the rear) right side to just a bit
past upright. All the plumbing is on the right on my unit so this was
designed to let the fluid flow freely. On each move, I again waited for the
gurgling to stop.
The final step was to sit the cabinet upright and let the gurgling stop. I
then hooked up propane and lit the burner. I placed a data logger in the
cabinet along with a gallon jug of water, my standard test condition.
When I first got the rig, one of the tests I did on it was to run the data
logger and measure the cooling capacity (by looking at the delta temperature,
if anyone here cares). I set up the same conditions and am proud to say that
the unit now cools a bit better than it did 4 years ago when I bought the MH.
Notice that I did NOT leave the thing lying on its side overnight, as some
burping procedures recommend. I could see no logical reason for waiting that
long. In any event, I decided to do the short program, knowing that I could
always go back and do the long program if the short one didn't work.
A half hour to stick the thing back in the rig, light that puppy off and set
the thermostat. It's now sitting there right at 32 degrees like it's supposed
to.
I love it when a plan comes together....
John
---
John De Armond
johngdDO...@bellsouth.com
http://personal.bellsouth.net/~johngd
Cleveland, Occupied TN
D Phillips
Dometic in a 94 trailer that I bought that isn't working. I've decided that
I will probably have to have the cooling unit refurbished. I AM going to try
this before I do even though everyone says it only works on the older
models. I think the trailer was setting up prior to my buying it a couple of
months ago. It's certainly worth a try.
Thanks for the post!
Dawn
"Neon John" <johngdDO...@bellsouth.net> wrote in message
news:7r0dcugqa6ul4mp65...@4ax.com...
mo_drew@yahoo.com Mo
Mo
"Neon John" <johngdDO...@bellsouth.net> wrote in message
news:7r0dcugqa6ul4mp65...@4ax.com...
No Spam
I have read several times that this doesn't work.
Good to see it worked for you. Especially after all you went through.
I'm so dam lazy I would have left the thing in the trailer and turned the
trailer on it's side.
I guess it pays to do it right.
Neon John <johngdDO...@bellsouth.net> wrote in message
news:7r0dcugqa6ul4mp65...@4ax.com...
Neon John
>Nice Job!
>I have read several times that this doesn't work.
Well, you know what they say about things you read on the net :-)
>Good to see it worked for you. Especially after all you went through.
Actually I had called to see if the $CW$ in Nashville had a new one in stock
:-) But either way the fridge had to come out so little labor lost. I
figured it was worth a try. It'll be interesting to see how long the burp
lasts. The 'fridge is almost exactly 20 years old so I figure it's done its
duty.
>I'm so dam lazy I would have left the thing in the trailer and turned the
>trailer on it's side.
>I guess it pays to do it right.
I thought about that. But in my MH, I'd have had to stand the darn thing up
on its nose and that might have turned into actual work.... :-)
John
No Spam
> >trailer on it's side.
> >I guess it pays to do it right.
>
> I thought about that. But in my MH, I'd have had to stand the darn thing
up
> on its nose and that might have turned into actual work.... :-)
>
> John
Oh My! Your right. On it's nose is really asking too much.
Hope it stays running!
TBFisher
practical to build an absorption AC
system for an RV? Looks like Honda
and others have considered it:
http://world.honda.com/news/1998/p980312.html
http://www.pnl.gov/microcats/fullmenu/compheatpump.html
Tom Fisher
Dallas,TX
Neon John
Possible? Probably.
Practical? Probably not, at least not now.
First thing to understand is that very, very little of what comes out of the
national labs has any commercial viability. Funding the nat labs now consists
of little more than scientific welfare.
Honda doesn't tell us enough about the unit to see if it is practical or not.
Conventional absorption systems are quite inefficient. Not an issue when
running on exhaust heat but very important when fuel powered.
I have a friend who owns a farm up in Kentucky who has several gas wells. In
other words, his energy is free. He has two approx 3 ton absorption AC units
on his house and shop. I can't quote figures from afar but I can say the
things are horribly inefficient. Of no concern there, of course.
I think we'd be a lot better off if effort were to be put into a system
similar to what the trucking industry is gradually adopting to end idling.
These systems involve a small engine, a 12 volt alternator, a refrigeration
compressor and if operation on shore power is needed, an electric motor.
Always seemed odd to use a generator to turn rotary motion into electricity,
only to turn it back into rotary motion in the AC compressor. From the units
I've seen at the trucking shows, the things aren't any larger than a typical
RV generator.
TBFisher
an AC compressor for a 30KBtu/hr system?
Tom Fisher
Dallas,TX
"Neon John" <johngdDO...@bellsouth.net> wrote in message
news:vhiscuohgqn2ilrf2...@4ax.com...
Neon John
> So, how many HP are required to power
>an AC compressor for a 30KBtu/hr system?
>Tom Fisher
>Dallas,TX
The basic measure of efficiency is the COP or Coefficient of Performance which
is the number of watts pumped divided by the number of watts consumed.
Measured under conditions specified by ASHRAE. A COP of 3 is pretty good for
an air conditioner and can roughly be equated to a SEER (seasonal energy
efficiency rating or COP modified by a bunch of fuzzy seasonal factors) of 10.
For a given refrigerant, the only way to improve COP is to make the condenser
larger and/or more efficient.
The problem for RV units is there is not enough space to achieve a high COP in
a package unit. If we deviate from the package unit format so that a larger
condenser and higher air velocity could be used, we could improve the COP to
the equivalent of high efficiency home units. That we could either get more
cooling capacity or else reduce the power drawn at the same cooling capacity.
I've never measured my AC's COP. Guess that would be an interesting thing to
do sometime. I'm going to bet that it's down around 2.25-2.5.
John
David Osborn
> So, how many HP are required to power
>an AC compressor for a 30KBtu/hr system?
>Tom Fisher
>Dallas,TX
Runing the numbers and assuming reasonable efficiencies indicates that an
engine of probably somewhere between 12 and 15 hp would required to operate
that compressor and provide the electricity for the required blowers.
--
David, N8DO; FMCA 147762
djosborn at aol dot com
TBFisher
needed to produce 30KBtu/hr of cooling.
Tom Fisher
Dallas,TX
"Neon John" <johngdDO...@bellsouth.net> wrote in message
news:brbucusv55nqa14np...@4ax.com...
TBFisher
engine to drive an AC unit. This 5hp engine
will need at least .25gal/hr of diesel to run
not to mention the increased maintenance,
noise, etc, etc,etc. I think it would be better
to use an absorption unit powered by diesel.
.25gal/hr should produce the 30KBtu/hr
needed with much lower maintenance, noise,
etc, etc,etc. Now who's gonna get busy and
design one for an RV??
Tom Fisher
Dallas,TX
"TBFisher" <tbfi...@swbell.net> wrote in message
news:sDHz8.3299$Tp4.23...@newssvr11.news.prodigy.com...
Neon John
> So assuming a COP of 3 would give 3.92594 horsepower
>needed to produce 30KBtu/hr of cooling.
>Tom Fisher
>Dallas,TX
Sounds about right. Rule of thumb is 1 HP per ton of cooling. BUT! The
problem still remains of having enough condenser area to achieve this level of
efficiency. Take a look at your home unit and see the size of condenser on
it. Unless your unit is very new, it's likely not much better than SEER
10-12. The ultra-efficient SEER 13-14 units are HUGE for the capacity. I
think that obtaining a COP of 3 on an RV would be a major trick. I'd have to
run some numbers to be sure but my gut tells me so.
The next issue is noise. Given the size limitation on an RV, the other way to
achieve reasonable efficiency is to move more air across the condenser. If
you've ever had to sit near a home central unit, you know what kind of noise
I'm talking about. My last home had the condensing unit right under the deck.
I HATED that unit!!!! I really don't like listening to the fan in my little
Coleman unit which means that it's turned off most of the time I'm not
actually inside. I'd hate to think of the noise from a large, high efficiency
unit.
Absorption type cooling would be even worse. Plus the absorption process is
much less efficient than the carnot cycle stuff. At least for existing
technology.
The advantage to be had with an engine-driven compressor is that the engine no
longer has to run at a synchronous speed (3600 or 1800). Experimenting I've
done with my cordless battery charger project has shown me that the sync
speeds are particularly annoying, probably because we all are subjected to 60
hz buzz so much in our daily life. Dropping the speed of my CBC even a few
hundred RPM makes it a LOT less annoying. You could use a low speed, high
displacement engine to get the necessary power. Using a water cooled engine
would make it even quieter. This is what I'm planning for when I start
building my custom coach.