Altitude or attitude? - Page 4 - Fiberglass RV


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Old 06-27-2020, 09:16 PM   #61
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Name: Wil
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Originally Posted by Raspy View Post
Wil, I agree, but I think you are missing the point.

While heat is heat, let's say BTUs are BTUs, regardless of the fuel used, in this case, the delivery method may be the culprit.

The electric heater conducts heat from the heater well, to the refrigeration pipe directly. The heater, the well and the fridge pipe are all in physical contact. The propane heat is delivered by warm gasses rising past the pipe. If the rising pathway is disrupted, or blocked in some way, the energy may not be getting to the fridge pipe even with the burner burning.

I agree that it doesn't matter what the heat source is, but one method might work while the other does not, even if they are producing the same amount of heat. it certainly does matter how that heat gets to where it needs to be. A rats nest, for instance could stop the fridge from working on gas, but not on electric. And since it works on electric, but not on gas, the differences in the delivery systems becomes interesting.

In several posts the OP has stated that altitude seems to be the difference. At one point specifying 5,500 feet as the dividing line. That doesn't sound like rat's nests in the chimney.


On the other hand depleted oxygen at altitude does affect the heat/temperature produced by the burning gas. And, as I quoted from the manual, there may be ignition problems above 3,280 feet. By the way, the OP stated he had a "robust pilot light." I believe that fridge has electronic ignition; no pilot light. Even so, a heating flame that looks robust may not be hot enough to make the absorption system work. All things point to thin air at altitude.
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Old 06-27-2020, 10:26 PM   #62
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We all know that depleted atmospheric pressure reduces combustion energy. We all get that.

Unless you can tell us how many BTUs the flame is delivering and how many BTUs the system requires to operate, blaming flame power is just speculation. I can't recite those values, so I can't decide that is the only problem, and I don't think it is.

So what do we know? We know the fridge does work. We know the flame is robust. We know it was on continuously for many hours, so there is not an ignition problem. We know that other Dometic fridges work fine at altitude. My Black Series Dometic works fine at over 7,500', and my Oliver worked fine at 7,500 and at 10,000' at Saddlebag lake. We also know that the flame does not have to run continuously to cool the fridge. Mine, for instance, runs a while and is off for a while. Not sure of the ratio, but it certainly is off more than 15% of the time while the door remains closed. If running continuously it would more than make up for loss of performance at altitude, and it does make up for it as proven by actual use in both of my trailers, at higher altitudes than we are concerned about here. So, we can assume the flame is probably large enough. 10,000' at 3% loss per 1000 ft equals 30% loss of power, and that is still enough to easily freeze food. We also know the electrical heater delivers its energy to the system in a different manner than the flame does, and we know the electric heater makes the system operate. So the difference seems like it might be in the heat exchanger. Or it might be that the flame is so large it is overwhelming the cooling fins, as Myron reported a robust flame.

I'm suggesting he look at the heat exchanger to at least be able to check that off the list. It's not a generic problem related only to elevation, or everyone would suffer the same problem. And if it barely works at seal level, some elevation might make the difference and stop it. Barely working means a problem somewhere that would add to the elevation problem. That is the difference I'm interested in. Try to set aside the elevation issue for a minute, as everyone faces that issue but not everyone has the problem. What could be adding to the elevation problem to stop it? That is what we need to know. And again, we all know elevation affects combustion. We all get that. But something else is in play here too. What is that something? How about the heat exchanger? You have already written that off as not the problem, but I haven't. I haven't seen inside it to know for sure, and it could do what we are seeing. So maybe Myron can check that and we can eliminate it from the list.
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Old 06-28-2020, 01:01 AM   #63
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Originally Posted by MyronL View Post
I live here at an altitude of 6700 feet. Well today there seems to be only two conclusions to be drawn. As a 3-way, the Dometic RM8551 fridge in my trailer is a lemon, or, the fridge is adversely affected by altitude.

Note I did include the word “attitude” starting this topic.
Here is an explanation of why you are having propane difficulties at a higher altitude.
https://winnebagolife.com/2018/09/pr...high-altitudes

Yes Dometic does give you information about high altitude use. It is located in your manual. Basically says...forget that, you can't do it. So that is their attitude which is we are not going to make a fix for this issue because we don't have to, after all we did give you electricity to run it as an alternative to propane.

Here is an image from the section of a Dometic Fridge manual that says what you need to do at high altitudes.
Click image for larger version

Name:	dometic high altitudes.JPG
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Remember....don't shoot the messenger (me) just because you don't like the what Dometic says in their manual. I don't work for them. I don't own a Dometic fridge. Although I was given a Waeco which later became Dometic. I got it for free then immediately sold it and bought a used Engel with the money.
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Old 06-28-2020, 08:56 AM   #64
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I am still hoping some genius physics expert reads my initial post and after that understands the issue at hand and will offer useful advice. A real solution.

The prime question I guess, really is... why does altitude, it does seem to be altitude, that adversely affects performance? The magic number seems to be 5500 feet. Yes, my robust pilot light, as I have shown, seems to not produce the heat that produces coldness. But it just ain't going to burn any bigger or hotter. How about cutting open the cooler tubes and replacing the liquid inside with something that does a better job?

My fridge is well insulated, well ventilated (yes, got the two Texas fans in back), and though 6700 feet altitude is not down in the swamp it certainly is not up in the Rocky mountains. I do breathe quite effortlessly on the oxygen we got here so the thinking is if I can do it, so should my fridge.
The reason that few people answered technically is that there i#nt a lot of research on the subject. The technical answer is a combination of factors, I believe. Firstly, at 5500 feet, the air pressure is half that at sea level. Since the evaporate (stuff that causes the cooling) requires airflow over the cooling fins to reform into a liquid, the number of particles in the air that can absorb the heat and help with that process is less. Using the Texas fans will help, but itís all relative and if youíre using them at sea level, youíll notice the degradation in refrigerator performance similarly to if you didnít at both sea level and altitude. Secondly, the altitude also impacts the evaporateís kinematic viscosity, which likely impacts reabsorption.
A fridge using a compressor uses a mechanical process to run the refrigeration process, so it works almost as well at altitude (no system is perfect).
Regardless of altitude, two things really impact a propane fridge: Time since it stopped moving and level. As some folks have mentioned, just because your trailer is level doesnít necessarily mean that your fridge is. Since you donít seem to have a problem at sea level, I donít think this is your issue.
Hope this helps...
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Old 06-28-2020, 08:58 AM   #65
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I'm sorry I did, even though my suggestion is a valid one to consider. That is all I will say about this approach you are taking to getting advice.
Well said Gordon2
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Old 06-28-2020, 09:01 AM   #66
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Originally Posted by MyronL View Post
Roger that, Jon. No worries... this issue is a pretty old one. I am just hoping this thread piques the interest of any of the geniuses out there on line, gets them to read carefully, motivates and ponder a true remedy. Hey, geniuses, consider this a homework assignment. All others need not respond.

Got friends around Tucson... saw the news pix. You have my sympathy.
With this approach, why would anyone, genius or not? Perhaps you don't realize just how snarky, off-putting, and just a bit insulting your language reads.

Bravo to everyone who has responded to try to help you in spite of it.

With all due respect,

Harold
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Old 07-01-2020, 09:15 AM   #67
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re: "...Dometic does give you information about high altitude use. It is located in your manual. Basically says...forget that, you can't do it. So that is their attitude which is we are not going to make a fix for this issue because we don't have to, after all we did give you electricity to run it as an alternative to propane...."

I have read my Dometic manual, K, and a very frustrating, insulting experience it was.

Great explanations, thanks, K Band, Raspy, and all others who need not be listed, for they are forgiven.... much appreciated. Now, I will go over to the dark side, and buy a generator.
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Old 07-01-2020, 11:15 AM   #68
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I have this problem when at Yellowstone with my water heater pilot not staying lit. Works fine in the low lands of Minnesota.
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Old 07-01-2020, 02:35 PM   #69
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The reason that few people answered technically is that there i#nt a lot of research on the subject. The technical answer is a combination of factors, I believe. Firstly, at 5500 feet, the air pressure is half that at sea level. ...

At 2000 meters (about 6000 feet) ambient air pressure drops to about 80% of sea level pressure. It is at 5500 meters (about 16,500 feet) that the air pressure drops to half. If it was half at 5500 feet small planes (like I fly) would never get off the ground.


https://en.wikipedia.org/wiki/Atmospheric_pressure#/media/File:Atmospheric_Pressure_vs._Altitude.png


Edit: That link should take you to a chart in the article. If not, cut and paste into new page address. Or just scan down the article to find it.


Re. "the evaporate’s kinematic viscosity": Since the system holding the evaporate is sealed, outside air pressure has no effect.
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Old 07-03-2020, 09:14 AM   #70
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Raspy -- Where exactly is the heat exchanger? How do I check it out?
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Old 07-03-2020, 10:03 AM   #71
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I have this problem when at Yellowstone with my water heater pilot not staying lit. Works fine in the low lands of Minnesota.
Have you had the propane regulator tested for correct pressure output ?
It could be borderline at lower altitudes and when up high ; could be too loe. Get a certified tech to check it.
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Old 07-03-2020, 12:08 PM   #72
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Myron, I was referring to the gas passage through the chimney. Is that path blocked, or are the hot gasses being diverted away from the tube by insulation in the wrong place, a rats nest, heavy rust buildup, damaged baffles, or other problems? That is where the heat goes into the system. Somehow, in addition to the altitude problem, you are not getting sufficient heat into the system. It seems the altitude in only part of the problem.
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Old 07-03-2020, 02:51 PM   #73
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Myron, I was referring to the gas passage through the chimney. Is that path blocked, or are the hot gasses being diverted away from the tube by insulation in the wrong place, a rats nest, heavy rust buildup, damaged baffles, or other problems? That is where the heat goes into the system. Somehow, in addition to the altitude problem, you are not getting sufficient heat into the system. It seems the altitude in only part of the problem.

Jeez, give it up. The physics/chemistry of combustion says the heat of the flame diminishes as the air thins at altitude. At some (variable) altitude it just isn't going to be hot enough. The manuals say you may have ignition problems above 3300 feet. And the manuals say don't expect it to work at all above 5500 feet. Believe it. Live with it. Don't spend a lot of time and money trying to fix a "problem" that doesn't exist. Unless you want to get some high altitude modifications to your unit (and remove them at low altitude) just use electricity at higher altitudes. Those who have fridges that do work on gas at high altitudes are the exceptions, or have modifications.
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Old 07-03-2020, 03:15 PM   #74
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Actually Will, the problem does exist. And I like to solve problems. We have already covered, repeatedly that high altitude affects performance. I agree and have repeatedly agreed, but there is something more than that here. I don't accept generic answers when there is a hole in the logic.

Perhaps you can explain why three of my Dometic fridges worked fine at altitudes from 7500 to 10,000 ft. and Myron's does not work at 6,700 ft. Or should we all just not be curious and give up?

If this conversation bothers you so much, simply stop reading it.

Meanwhile, Myron asked me another question and my response was directed at him.
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Old 07-03-2020, 03:38 PM   #75
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re: "Or should we all just not be curious and give up?"

Contrarians included, love you guys. We're sheltering in place, are we not? Regardless of altitude or attitude, any altitude, a journey from this seat is at present the most fun we can hope for. For back-up, much as I find it distasteful, my WEN 56225i will arrive next week.

There's no insulation, etc., or batting, blocking air egress, Raspy. Spoke yesterday with the old trailer guy who taught my guy Tom everything he knows about trailers (lives 7 miles from me and still kicking) and he was speculating (from afar, of course) that the problem could be inadequate venting.

Or, pass the lemonade.
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Old 07-03-2020, 09:26 PM   #76
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Actually Will, the problem does exist. And I like to solve problems. We have already covered, repeatedly that high altitude affects performance. I agree and have repeatedly agreed, but there is something more than that here. I don't accept generic answers when there is a hole in the logic.

Perhaps you can explain why three of my Dometic fridges worked fine at altitudes from 7500 to 10,000 ft. and Myron's does not work at 6,700 ft. Or should we all just not be curious and give up?

If this conversation bothers you so much, simply stop reading it.

Meanwhile, Myron asked me another question and my response was directed at him.

OK. I just went out on the web and Googled "rv refrigerator for high altitude." Note, I did not specify brand. Lots of discussions about lots of problems with both Dometic and Norcold. (And gas appliances other than fridges) All fridges are not created equal, not even all fridges of the same make, and to a lesser extent not even all fridges of the same model. Unless your Dometics are the same model as the OP's all bets are off.


The gas/air ratio is critical to the operation of gas appliances. The size of the orifice in the burner is critical to that ratio. Some burners may operate over a wider range of altitudes depending the design of the burner and the size of the orifice. Hence some will work at a wider range of altitudes that others will not. The Op has said he has already taken everything apart and cleaned it and blown it out. It's time to try changing the orifice. If Dometic advises against that then you're on your own. But that is probably the only way to fix the "problem." And it may not, depending on the design. And if it does fix the high altitude problem then it may not operate satisfactorily (if at all) at lower altitudes. It's all combustion physics and chemistry.


Good bye and good luck.
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Old 07-03-2020, 09:55 PM   #77
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Dometic offers only one orifice for my fridge, and they sent it to me. By the way, it is smaller than a dime and they charged me $50bucks with shipping, from Denver. How's that for snarky?
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Old 07-04-2020, 03:12 PM   #78
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Dometic offers only one orifice for my fridge, and they sent it to me. By the way, it is smaller than a dime and they charged me $50bucks with shipping, from Denver. How's that for snarky?

Not being familiar with your particular fridge - the orifices I am familiar with are small brass/copper thingys much smaller than a pea with a small (tiny) hole drilled through them that fit inside end of the burner jet. Not anything near the size or shape of a dime. They are generally interchangeable with others with different sized holes. So I don't know what you've got. An independent refrigerator repair shop may be able to help. But, again, if a non-Dometic approved modification is made you're on your own. Good luck.
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Old 07-04-2020, 03:45 PM   #79
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Dometic offers only one orifice for my fridge, and they sent it to me. By the way, it is smaller than a dime and they charged me $50bucks with shipping, from Denver. How's that for snarky?
I have drilled holes for propane pilot lights and I would not undertake it for $50, it is quite difficult. The only reason Dometic can sell them for that price is that it is a production item.

The muffin fan is by far the easy solution.
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Old 07-05-2020, 07:05 AM   #80
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Hi there, little guy. I see you in there. Don't you fall out now. I know you want to.

Dometic sent me that orifice in a box so big before opening it I thought they sent not just the orifice but the entire propane assembly. Yeah, it was on my dime.
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