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Old 08-25-2012, 06:34 PM   #81
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Yes, very. Isn't dissipation of heat, still dissipation of heat no matter if the system is closed or open?
Well yes, but.
These fridges are really two systems. An ammonia cycle heat pump
which is closed and an "ammonia gas generator" which is an open
system. Open in that it requires outside heat input.
What does that mean? Well........??

The question still remains why on most days/nights my little pop up camper fridge would work well, then with no setting changes, it would start to warm up. Then the following day in most cases it would start to cool down. This was fairly random.
Insufficent data.

The only thing that was not consistent was the weather,

A clue? A data point?

so I'm still unsure why ammonia fridges vary so much in cooling.
I think the amazing part is not that they work so well, but that they
work at all........

cheers,
johnd
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Old 08-25-2012, 06:34 PM   #82
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Quote:
Originally Posted by Mark S
So after 8 pages of discussion, numerous scientific theory, scores of photographs and even a little bit of debate, the answer to my original question that started this thread, "are two fans better than one" the answer is a definate maybe. I am glad we got that resolved

I added the second fan just above the intake and will know for sure when I camp again at the end of September how it works. I may try moving it up to the horizontal exhaust vent if it's not as good as I hope . Thanks for all the input.

Ps. Man, there are some very intelligent folks on this forum. What a great resourse and source of entertainment.

Mark
I'm with ya Mark on all counts. My personal favorite MAGIC! Really though I think you're right. Because of different configurations, designs, and location of use (altitude, temps, humidity) and other factors and personal experiences, the best method is just try it and see what works and what doesn't. Do let us know what worked for you.
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Old 08-25-2012, 06:38 PM   #83
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Quote:
Originally Posted by dnaraG_1M
Yes, very. Isn't dissipation of heat, still dissipation of heat no matter if the system is closed or open?
Well yes, but.
These fridges are really two systems. An ammonia cycle heat pump
which is closed and an "ammonia gas generator" which is an open
system. Open in that it requires outside heat input.
What does that mean? Well........??

The question still remains why on most days/nights my little pop up camper fridge would work well, then with no setting changes, it would start to warm up. Then the following day in most cases it would start to cool down. This was fairly random.
Insufficent data.

The only thing that was not consistent was the weather,
A clue? A data point?

so I'm still unsure why ammonia fridges vary so much in cooling.
I think the amazing part is not that they work so well, but that they
work at all........

cheers,
johnd
Great responses and thanks...you're right...not enough data, so much of it is educated guesswork. It's interesting trying to explain to someone how heating ammonia with a flame can cause an insulated box cool down, so yes it's amazing they work at all.
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EPDM Rubber Roof Installation - https://www.youtube.com/watch?v=xbraK...hannel&list=UL Pulled by a 2002 Chevy Avalanche, 496cid Rat motor, 12k Lb. tow package, leveling hitch, dual sway controls & electric brakes.
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Old 08-25-2012, 06:58 PM   #84
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Here is how it was Explained to me.


A gas refrigerator uses ammonia as the coolant, and water, ammonia and hydrogen gas to create a continuous cycle for the ammonia. The refrigerator has five main parts:

Generator - creates ammonia gas
Separator - separates the ammonia gas from water
Condenser - where hot ammonia gas is cooled and condensed to create liquid ammonia
Evaporator - where liquid ammonia converts to a gas to create cold temperatures
inside the refrigerator

Absorber - absorbs the ammonia gas in water
It works like this:
1. Heat is applied to the ammonia and water solution in the generator. (The heat comes from burning gas, and\or electric heating element in the case of a RV frig.)
2. As the mixture reaches the boiling point of ammonia, it flows into the separator.
3. Ammonia gas flows upward into the condenser, dissipates heat and converts back to a liquid.

4. The liquid ammonia makes its way to the evaporator where it mixes with hydrogen gas and evaporates, producing cold temperatures inside the refrigerator's cold box.
5.The ammonia and hydrogen gases flow to the absorber where the water collected in the separator in step No. 2 mixes with the ammonia and hydrogen gases.

6. The ammonia forms a solution with the water and releases the hydrogen gas, which flows back to the evaporator.
7.The ammonia-and-water solution flows toward the generator to repeat the cycle.
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Old 08-25-2012, 07:19 PM   #85
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Quote:
Originally Posted by Mark S View Post
Ps. Man, there are some very intelligent folks on this forum. What a great resourse and source of entertainment.
Mark
Indeed there are. The amount of info and help that I have gotten
here is immense. What did I do before the Internet allowed me
to "gather it all in"!!! And nobody, but nobody has anything like
the Herk Information Super Library.

Yesterday, I finally got around to powering up my FOUR fan
array from Allelectronics and I was amazed at how quiet they
are. So......I'm now gonna try to duplicate what ya'll are doing.
The Texas 100+ heat really does a job on my fridge..........


In a less serious vein:
Entertainment??? Oh yes. In my personal case, I know that I
am a great source. Every time we go to leave, my DW just roars
laughing at me.

But then I remember my pants and......................

cheers,
johnd
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Old 08-25-2012, 07:24 PM   #86
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Best and simplest explanation I've seen. Complete with picture of the back of a refrigerator.
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Old 08-26-2012, 08:50 AM   #87
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I just crawled up on the back of our trailer to investigate the possibility of installing another fan under the roof vent for the refrigerator. After removing the top cover, I discovered a molded collar with a screen in it. I will NOT be removing the collar. The chimney uses the back of the trailer as the back side of the chimney which curves at the top with a large hole cut in the ceiling to dump the hot air.

I will add the extra fan beside the one already installed and wire them together. Using a mirror, and looking up from below, there are no baffles or deflectors blocking off from the back wall of the chimney to the back of the refrigerator. It is clear from the bottom of the compartment to the hole in the roof.
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Old 08-26-2012, 04:06 PM   #88
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Going to have to remove the existing fan and come up with a dual mount to get both fans mounted side by side where there is room.
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Old 08-27-2012, 04:27 PM   #89
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With my two fans outside blowing air up the vent pipe and one inside fridge I maintained 32 degrees in my fridge today.
Temp was 91 today with the fridge side in the sun.
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Old 08-27-2012, 04:56 PM   #90
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I almost forgot I started the fridge at 6;30 am today and at 4;30 pm this is the temp.
Also note that the a/c was off in the unit today .
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Old 08-27-2012, 05:26 PM   #91
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Got my two fans mounted and operational, 1) 80mm and 1) 90mm. With both fans going, you can feel the heat coming out of the roof vent. Temp inside frig is holding @ 33 with the control set at 2 and outside temp @89. Very pleased with the setup. I may bolt a deflector to the outer edge of the fans so the air is directed straight up so it does not deflect off the accumulator and out the lower vent. I want all the air going up the chimney and out the roof vent.
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Old 08-28-2012, 06:03 PM   #92
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At 89-91 degrees could you not get those temps before the fans?
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Old 08-28-2012, 06:08 PM   #93
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At 89-91 degrees could you not get those temps before the fans?
1) I could not maintain a temperature .
2) fridge temp ran mostly in the 36 to 38 range

my fridge cooled to 32 degrees in about 9 hours . it could have been less but I only checked when I got home from work .
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Old 08-28-2012, 06:24 PM   #94
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At 89-91 degrees could you not get those temps before the fans?
I could get the temps, but the control had to be set @4 instead of 2 and if the outside temp went to the high 90's and low 100, I had to set the control to 5 to hold the frig at around 34-35. It just makes the whole system work so much more efficient for our situation. For no more expense and effort to install, I think it it well worth it.

The gas burner just does not cycle as much. As far as saving propane, I imagine it is negligible, but every little bit helps.
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Old 08-28-2012, 06:44 PM   #95
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Cool, glad you got the results you needed.
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