Altitude or attitude? - Page 2 - Fiberglass RV


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Old 06-20-2020, 03:28 PM   #21
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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.
I made an effort to assist yesterday by posting a link to a Google search that showed many RV forum discussions regarding the issue the OP is having, and a relevant quote from the Dometic manual, etc. Personally, I found that a quick reading of a couple of the forum posts yielded useful, and perhaps actionable, advice and information. However, I deleted my post after reading the above-quoted reply.

Here's some information for those who might be interested.

Absorption refrigerators require a careful conformance to the required heat input in order to function properly.

Too much heat at the burner creates results in excess heat in the back of the refrigerator which (surprise!) reduces cooling. The excess heat needs to be removed as per the many, many threads on this subject concerning 1) proper venting, 2) proper baffling and 3) muffin-fan installations which are made to improve poor performance.

Poor performance is actually often caused by improper installation; the refrigerators are often installed too far from the outside wall of the trailer, so the air does not pass through the fins to remove heat as it should (looking at you Casita). The fans compensate for these poor installations to some extent, at the expense of additional battery consumption.

My earlier post also specifically mentioned how Dometic's "chimney pipe" fix as sold in the Australian market can be cheaply duplicated, but is designed to remove excess heat, so it will not address the altitude problem.

In brief, Liquefied Petroleum (LP) gas combustion is poorer at high altitudes, in part due to the lower oxygen content. This results in the burner producing less heat, which fails to properly drive the absorption cycle.

As regards "cutting open the cooler tubes", the refrigerator manufacturers advise operating the refrigerator burners on 120 VAC above 5,500 feet. In other words, it's not what's in the tubes, but the LP gas burner's poor function at high altitudes which is causing this known problem. This known problem continues to be described in the operating manuals.

All of this information is relevant to the altitude problem.

That leaves us with the attitude problem. As far as that goes, I'd say that the OP is certainly entitled to sit on the roof and wait for the boat and helicopter. Please refer to the following link if the "boat and helicopter" reference needs explaining.

https://www.reddit.com/r/Jokes/comme..._will_save_me/
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Old 06-20-2020, 05:38 PM   #22
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To sum it up, then, you are saying ...
  1. There is no known altitude cure.
  2. My best move is to sit on my roof and wait for a helicopter rescue.

Raspy, there's no way to adjust the pilot light intensity. It is what it is. I have considered pulling it out and turning it upside down but...maybe just buy a generator.

Appreciate the candor. Especially yours, Gordon.

Hoping for a second or third, or fourth opinion.
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Old 06-20-2020, 05:55 PM   #23
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Originally Posted by MyronL View Post
To sum it up, then, you are saying ...
  1. There is no known altitude cure.
  2. My best move is to sit on my roof and wait for a helicopter rescue.

Appreciate the candor. Hoping for a second opinion.
(Or, buy a generator.)
Actually the moral of the story is that one should NOT sit on the roof and wait for divine intervention (or some genius physics expert to chime in) but instead graciously welcome the help which was offered.
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Old 06-20-2020, 07:57 PM   #24
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This may not add too much to the conversation, but is my experience.

I don't see where removing your fridge and turning it upside down will do any good, as you stated it works OK on electricity.

I have a Servel absorption fridge at my camp which is probably from the 30s or 40s which works great regardless of the temperature. It sometimes gets to cold. The flame is modulated by the cold control and goes quite low once it cools down. I also had an absorption fridge in my HiLo which worked like crap. I did install a baffle so the air moving up the rear of the unit was forced over the cooling fins. I got another 7-8 degrees of cooling. According to the manual, the manufacturer installed the unit too far from the back wall.

I can attest to the performance of the compressor fridges, which you may want to ponder while waiting for divine intervention. You just need to make sure you have enough generating and storage capacity. My Truckfridge 4.6 cu ft uses around 40 Ah a day.
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Old 06-20-2020, 09:00 PM   #25
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To sum it up, then, you are saying ...
  1. There is no known altitude cure.
  2. My best move is to sit on my roof and wait for a helicopter rescue.
To be clear, I actually did not say either of those things. In fact, I specifically noted that there was some potentially actionable information in the forum posts under the original link that I had posted and deleted yesterday. This 2017 post from another forum is one example:

Quote:
When I call Dometic to see if there was a kit, so I could use at higher altitudes on gas. I was told they did not have one. He also said if I changed the jet it would void the warranty. He also said I could take it to a shop here in Denver and they most likely would know which jet would make it work better at high altitudes, but it would be a pain to change back when going lower altitudes
So, I expect there is a means to make an absorption refrigerator operate properly at higher altitudes. Norcold apparently even offers a high-altitude kit for their models 3163T and 3163G.

I don't have all the information to know how practical it would be to adapt just any refrigerator. But clearly, one of the basic issues is that changing the piloting or other changes to operate better at higher elevations can be expected to degrade the performance at lower elevations. Otherwise, they would have simply piloted them that way from the factory, right?

The fact that no absorption refrigerator manufacturer appears to sell a unit which will automatically compensate for altitude strongly suggests that it's not viewed by manufacturers as something which is 1) practical and 2) economical to do as there's certainly a natural market in RV's for units that will operate at higher elevations.

Regarding the second bullet, I think my point was plain enough as originally stated. You sound like a pretty intelligent guy, but I think that perhaps you aren't applying your full energies to the problem.

I'm actually grateful that you have brought this issue up as we have reservations to spend a week at 9,000 feet. So, I intend to do some further work on the issue. So, thank you for your help in identifying the issue.

As I mentioned to another member the other day, being friendly on this forum is about the only currency we have. It's amazing how some people will research information or prepare lengthy, detailed posts sharing some expertise or skill they have just for the vibes that come when someone seems to appreciate their effort. Isn't that something?
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Old 06-20-2020, 09:29 PM   #26
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Originally Posted by CarlD View Post
This may not add too much to the conversation, but is my experience.
I agree with your observations and was interested to hear about the power consumption on the larger Truckfridge. The Danfoss 12V compressor is a tempting proposition.

I was able to greatly improve our Casita refrigerator's performance as you did with the Hi-Lo. The Wikipedia article has a great thermal-imaging illustration of the surplus heat which needs to be removed from the back of the refrigerator. When they install the refrigerator too far from the trailer sidewall with no baffle and the air bypasses the fins, this is the heat that's defeating the refrigeration process.

https://en.wikipedia.org/wiki/Absorption_refrigerator
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Old 06-20-2020, 11:49 PM   #27
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Myron,

Here's the link to a complete upgrade or conversion kit from JC Refrigeration. Maybe you should talk to these people.

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Our Dutch Aire Cooling Units (gas/elect or Hvac )have gained popularity and are often referred to as the Amish RV Cooling Unit. We have risen in popularity because our refrigeration units are superior alternatives to the factory installed models.
https://jc-refrigeration.com/product-information/
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Old 06-20-2020, 11:54 PM   #28
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Mike and Gordon covered most of you question I believe. I will add that you loose about 4% of BTU value per 1000 feet of elevation change so when you combine the fact that the fridge air/gas mixture is set to work between sea level and 5500 feet and the loose of BTU value of the gas your thermal efficiencies required to operate the absorption system are lost.
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Old 06-21-2020, 11:44 AM   #29
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The following quote is from the conclusions section on the last page of this linked publication:

The Effect of Altitude on the Limits of Safe Operation of Gas Appliances

Quote:
To construct an appliance for safe use at high altitude, it must be designed as a whole to burn safely at sea level an appropriately greater quantity of gas.
Designing an appliance to burn a greater quantity of gas would basically offset the 4% loss of BTU value per thousand feet of elevation. So an appliance that would provide 100% of the heat required to operate properly at 10,000 ft would have to produce roughly 5/3 or on the order of 166% of the target heat required for operation at sea level.

This is commonplace practice with furnaces for buildings, which are re-jetted and de-rated for use at higher altitudes in accordance with published tables in the manufacturer's manuals and associated code standards.

In the case of an absorption fridge, the issue would be to have the unit operate properly at various elevations by either diverting or limiting the excess heat produced at lower elevations, excess heat meaning that beyond the amount necessary to drive the refrigeration cycle.

Earlier posts here, and countless posts on various forums through the years, illustrate the frustrations of absorption refrigerator owners whose poor installations fail to properly divert excess heat.

As diverting excess heat would increase inefficiencies and propane consumption, it would seem best to develop a variable-output burner assembly which could be readily controlled to limit the heat produced in accordance with the varying requirements of different altitudes.

The fact that the industry has not done so to date is suggestive that such an endeavor is either futile, impractical, or a sparkling opportunity for a new innovation.
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Old 06-21-2020, 12:33 PM   #30
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Back in the pre-fuel-injection days automobiles had a similar problem coping with changes in altitude. SU carburetors incorporated a variable venturi design which successfully compensated for altitude. I dont guess that altitude compensation was a design criterion since, to the best of my knowledge, they were only used on British and Swedish cars. (Volvo used a Zenith(?) variable venturi instead of SUs). Eventually fuel injection made this a non-topic.


If there were a larger market for roving refrigerators then perhaps someone will try to improve the product.
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Old 06-21-2020, 12:47 PM   #31
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re:...The fact that the industry has not done so to date is suggestive that such an endeavor is either futile, impractical, or a sparkling opportunity for a new innovation...."

...hoping for the latter, or, divine intervention.

That Amish site's videos? ??-? -thanks anyway for the link. They do a great job.
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Old 06-21-2020, 02:28 PM   #32
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We live near sea level and generally camp below 5,500 ft even when we are in the Cascade Mountains. We did spend a week on an electric hookup in West Yellowstone at 6,700 ft, and we expect to spend more time in the Rockies and Sierras. But, that will only be for limited periods of time overall.

If they don't cancel our one-week reservation in September at 9,000 ft, I might just use the Escape's refrigerator as an ice box as there is a general store nearby. I could buy a small 12V chest cooler to supplement it.

I would have been tempted to get a 12V refrigerator in the Escape if that had been an option as I've long heard good reports on the Danfoss compressor. (They seem to be getting ever more popular, with less expensive off-brand options beginning to appear over the past several years. I was surprised when a web search yesterday pulled up a 6 CF 12V upright refrigerator at Home Depot for $999.)

Quote:
Unique
6.0 cu. ft. 170 l
Solar DC Top Freezer Refrigerator Danfoss/Secop Compressor in White
I don't think I'm ready to convert our Escape fridge to a 12V system as I don't know that the scope of the problem merits the cost and effort for us.

In the end, I think I'll consider that forewarned is forearmed and use what we have until it fails, supplementing with ice and perhaps a chest fridge whenever we spend time at higher elevations.
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Old 06-21-2020, 05:18 PM   #33
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While I haven't decided on the fridge for my Boler 1700. I did put a 12 Volt Danforth Compressor refrigerator in my Airstream Argosy to avoid many of the absorption refrigerator issues. They typically draw about 4 amps once running and you can have it running while driving with no worries.
I would think the main reason no one has worked on developing a fridge that will work from sea level to 10,000 feet is about 98% of requirements are below the 5500 foot elevation levels so demand isn't that great. The requirements would require an ECU which would add about a $1000 dollars to the fridge making them cost prohibitive to develop.
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Old 06-22-2020, 12:26 PM   #34
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Myron,

I think you are barking up the wrong tree with the propane issue.

You obviously have the burner working as good as it can, and the flame picture shows a nice clean looking burn. And it had no affect on the outcome. You didn't get a percentage reduction in cooling, you got nothing. Altitude will not just stop it at some magic elevation, it will maybe reduce the performance. The amount of cooling is based on the size of the flame, so it should just reduce cooling and not stop. As an example, we live at 5,000 ft and the fridge works fine. We like to camp at Twin Lakes, which is above 8,500 ft and it works normally there too. My freezer temp a couple of days ago was 6 degrees F. Remember too, the fridge is a closed loop system that is not affected by atmospheric pressure changes. The only reduction in performance I've seen was due to high ambient temps where the system could not get rid of the excessive heat.

And just as an additional note, the compensation made in carburetors on engines, for elevation, do not restore power as seem to be suggested in an earlier post. They correct the mixture. This makes the engine burn correctly and prevents carbon buildup, but it does not add back power lost to elevation, which as a rule of thumb, decreases by about 3% per 1000 ft elevation. Even fuel injection engines that run very well at altitude, lose the same amount of power, based on reduced atmospheric pressure.

You commented that there is no way to adjust the flame. Well, of course there is. You might change the regulator setting, change the jet or deflect some of the heat out of the normal path, to run a test. But either way, the propane system seems to produce no cooling, while the electric works OK. And again, in your case, it is not a percentage change based on elevation, it just doesn't seem to work at all. And your burner seems to be running very well. So I'd say, there is something else wrong. Have you taken the chimney apart to see how it works or if it is blocked? Have mice moved in? Is there any way the heat from the flame is not getting to the right place as it is with the electric heater?

Finally, since it works on electric, it is not being stopped by a bubble, so there is no need to turn it upside down. That is a last ditch effort when all else fails. In your case it does work.
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Old 06-22-2020, 12:38 PM   #35
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Originally Posted by widgetwizard View Post
Please answer post #12.
I cannot tell if you ever answered this simple question......
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Old 06-22-2020, 04:56 PM   #36
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The amount of cooling is based on the size of the flame, so it should just reduce cooling and not stop.
Is this a true statement considering the whole system and the various external conditions which can influence boiling ammonia out of the mixed solution? I'm not trolling, I just don't know. A bluish flame's temperature will generally be the same, but the amount of the heat will vary with the flame size.

It seems that vaporization requires both a threshold temperature and adequate heat, so it seems that there could be some threshold point at which the system fails to boil enough ammonia out of the working fluid solution to condense and adequately feed the evaporator; an sharp inflection in the process curve if you will.

I do agree that "fiddling" with the flame might be productive; however, I'm not clear if it poses risks.

Furnace derating kits seem to typically include replacement jets, new pressure-monitoring switches, and sometimes new springs for the gas regulators. But in general, it seems the thinner air and less dense gas continue to feed and mix at compatible ratios at elevation; at least I don't see reference to fiddling with air shutters to compensate for altitude.

These refrigerators don't appear to much in the way of failsafes; witness the market for the Fridge Defend by ARP which basically monitors the temperatures at the boiler.

Failing to monitor boiler temperature is arguably unconscionable, something that Norcold and Dometic could have implemented as part of their equipment, but apparently "value-engineered" out of their designs, leading to the class-action settlements for refrigerator fires.

Anyway, I'd consult regarding potential impacts on safe operation before I got too far out on a limb re-jetting or tinkering with the burner assembly or pressure regulator. I'd be happy to find my fears are misplaced, I just respect that what I don't know can hurt me.

Quote:
Originally Posted by widgetwizard View Post
I cannot tell if you ever answered this simple question......
This is probably one of the most sensible things I've seen posted. (Which is admittedly kind of a low bar given all of the blather I post! )

Demonstrating that the refrigerator runs successfully on 120VAC electric at altitude eliminates many potential causes of a failure to cool properly.

Operating properly on LPG at sea level (or at least at much lower elevations) would then eliminate a number of issues which would only be related to gas operation.

After all this, Myron's probably ready for a quick spin down to the beach anyway!
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Old 06-22-2020, 05:03 PM   #37
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Actually I did, Widge--- post #20. (--Note Indicated at the much lower altitude at the ABQ Home Depot and then over to Cabellas - even lower altitude - Fridge began to cool steadily on propane. Then, leaving it on propane and driving back to 6700 ft home, when I got there it had spiked back up.) ABQ is about as close to sea level as I can get to around here.

I have been very reluctant to pull the fridge out and inspect the chimney. Looking like that's the only stone left uncovered, Rasp.

re: "...it just doesn't seem to work at all. And your burner seems to be running very well. So I'd say, there is something else wrong." --Have to agree. As far as changing the regulator pressure - since my "robust" pilot light picture was taken at home, the 6700 ft altitude, think that would not accomplish anything.
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Old 06-22-2020, 05:22 PM   #38
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Originally Posted by MyronL View Post

It does work great on shore power and on battery power. On propane? Not!
Myron did answer the question in post number 1, or he stated that is worked fine on shore power, before being asked if it did.

I thought that question was already settled, and so moved on to gas issues.

Since mine works great to up over 8500 ft, in my search for an answer, I was willing to assume the design was capable of working fine at 6,700', and therefore, it must be something other than altitude. And since Myron has a pretty and large flame, that is not the issue. What is left? Too much heat? Heat bypassing the heat exchanger in the chimney? Mice, obstruction, phase of the moon?

It's time to disassemble the chimney, or vary the heat being delivered by the flame in a desperate attempt to get some data. Do something that makes a change that can lead to an answer

The pressure of the propane coming out of the bottle is not related to atmospheric pressure, only ambient temperature and and boiling rate in the bottle due to the heating load. The regulator could and must be related to atmospheric pressure, but the flame looks good. I'm confident there is plenty of energy in the flame, but can't prove it.

Has anything changed since the last time it was run on shore power? Will it run fine on shore power now? Maybe that is the question widgetwizard is asking and I misinterpreted. That might be the best test. Switch it to electric and see what happens without changing anything else.

If it cools on 120 volts, with no other changes, I'd then look in the chimney.

Whew!
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Old 06-22-2020, 05:37 PM   #39
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Shore power has always done a beautiful job of cooling, at any elevation, and continues to do it. A reason why I am now thinking to kill two birds with one stone and go over to the dark side and buy a generator for boondocking the fridge and using the air conditioner.
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Old 06-22-2020, 06:46 PM   #40
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Regarding the chimney issue. Once again you stated it works ok on electric. If it is a chimney issue wouldn't it also have reduced performance running on electric at altitude?
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