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-   -   Simple Survey on Fridge Performance While on Propane (http://www.airforums.com/forums/f404/simple-survey-on-fridge-performance-while-on-propane-169937.html)

OTRA15 07-27-2017 11:18 AM

Great point Bob. Indeed, is the new Basecamp the only Airstream with the fridge vent on the front of the trailer? Almost all others have side vents (or flues through the roof) which would more likely promote the exhaust gases leaving the fridge's system.

:blink::wally::blink:

uncle_bob 07-27-2017 11:44 AM

Quote:

Originally Posted by OTRA15 (Post 1984273)
Great point Bob. Indeed, is the new Basecamp the only Airstream with the fridge vent on the front of the trailer? Almost all others have side vents (or flues through the roof) which would more likely promote the exhaust gases leaving the fridge's system.

:blink::wally::blink:

Hi

It certainly is the only version I've ever seen with the fridge right up front. Given that AS has made a few billion variations over the last 80 or so years, I'd never say "only one" :)

The gotcha is that they have designed themselves into a corner. Flue through the roof? Not so much. Remove the propane tanks? Nope. Jet engine loud blower(s) that will handle lots of back pressure? good luck ... Even with a compressor based design the exhaust heat has to go *somewhere*.

If they were paying me to do this, I'd put a baffle half way down the tank cover / trailer gap. Then start looking at mods to the tank cover to change the airflow pattern. It might be as simple as drilling a couple of 1 or 2" holes. Working out where to put those holes ... not simple at all. Note: I'm retired and *not* looking for work harder than lifting the odd can of beer each evening ... :)

Bob

OTRA15 07-27-2017 12:55 PM

Needs a total redesign to get the fridge to one side, and ideally have a flue through the roof. I think I noticed on another thread that some of the 2018 AS models are going back to having a fridge flue through the roof. Hopefully the entire fleet will revert back to this simple and time-proven design, like our 1985 25' AS had back in the 90's.

If it ain't broke don't fix it. The new BC is a classic example of too many designers trying to cram too much into a small space, without proper review and field testing. Really poor management to let such an unproven design hit the market IMO.

A fleet-wide axle recall because the tires hit the wheel well?

:blink:

Say no more . . .

:mad::wally::mad:

uncle_bob 07-27-2017 01:18 PM

Hi

Between the wrap around windows and the rear door, there's not much space in a Basecamp to get to the roof for a roof vent. Changing the design to accommodate one would be a pretty massive redesign. Simply getting vents to either side of the tank cover (intake left / low and output right / high) is about all I suspect they could do and keep the fundamentals intact. Not much of a chimney, but they are off to fan land already.

Bob

Rzr1999 07-27-2017 01:42 PM

We landed on the moon 48 years ago, you would think engineering a frig to cool in any condition would be a simple task

OTRA15 07-27-2017 01:56 PM

Bob, the frontal air pressure/vacuum issues you raise demand that the fridge vent move entirely to the side IMO. Yes, a total redesign . . . IMO.

Troutboy 07-27-2017 05:31 PM

The Ultimate Fix, yes, no?
 
Quote:

Originally Posted by OTRA15 (Post 1984133)
You are being optimistic IMO, and have not examined the problem closely, in terms of the BC fridge exhaust vent being about an inch away from the back of the propane cover. With no room for the exhaust air to flow freely, it is stifled, and the hot air stays trapped, stagnant in the cabinet space. ESPECIALLY if the front of the trailer is in direct sun.

With your design and fabrication skills, in my opinion you would appreciate this if you examined the problem more closely.

The Basecamp Issues thread has more details on the fridge problem as well.

No quick and easy fix here, again in my opinion, short of a substantial redesign of the layout of the components they are trying to JAM so close to each other. Also, Dometic's design parameters seem to conflict with the fridge's layout and venting system IMO.

Peter

PS see Post #600 et seq. on the Issues thread:

[click on arrow in quote to go there]

Peter,

I don't have enough information to be specific. i was likely to general in my response. Its a simple mass transfer/heat transfer issue, so what I was trying to state was it should be solvable by moving the right amount of air through it.

If I had the dimensions of the vent, understood the space the fridge is in, the gap between the cover, I am confident I could design a simple fix with fans and aluminum sheet metal.

As discussed by others, you need a cool/fresh air intake, and a hot air exit. They need to be designed such that there is no short circuiting and so the air crosses past the coils to remove the heat as its generated.

Air does not have friction losses like water, and you would be surprised how much flow you can get through a small space. its all about the flow, the transfer, and optimizing hot/cold input/exit.

Without seeing one in real time, a potential fix would be as follows:

1. Use the Propane cover as part of a duct. Imagine closing off the sides bottom and top and making a square thin metal box with the existing fridge vent on one side, and the back of the propane cover as the other side.

2. divide that space in two, a a separate, isolated top and a bottom, and the make the bottom the fresh air intake, with vents on the thin sides (both) to let the air in at the bottom of the fridge vent compartment. could even do a vent on the bottom of the gap.

3. create the similar top part for hot air exhaust, vents on the side and or top.

4. Place 2-4 fans at the top of the existing fridge vent and seal it off such that fresh air is drawn into the new created fresh air duct, passes over the coils, and exits out the new hot air vent.

maybe i will draw a picture if anyone really wants to see this. I am confident this would work very well, as not as much air is needed as one thinks if the flow is optimized across the coils. If the air gap is like 1/8 inch between the propane cover and the basecamp fridge vent, then yes an issue. all I think I would need is a 1 inch gap to make this work.

If I could see one in real life, I know I could design a, cheap, easy fix that would work well. And it would be quiet.

if I was retired I would go to the AS dealer, measure everything up , design and post this fix. It would cost less than $100.

the issue of battery draw still remains, and could be significant for boondocks with stock battery and no solar system.

As currently designed or without major redesign, i do not see a passive air system (i.e. no fans) solution with the existing fridge.

uncle_bob 07-27-2017 07:43 PM

Quote:

Originally Posted by Rzr1999 (Post 1984345)
We landed on the moon 48 years ago, you would think engineering a frig to cool in any condition would be a simple task

Hi

Well, the software to do a basic analysis is about $150K to purchase and roughly $50K a year in maintenance. Somebody who is trained on that software likely makes > $100K a year. Running a first pass mock up is at least six months of work. You then do testing to validate the model and likely spend a similar amount of time / money on that. Loop through the process three or four times and you will have a pretty good idea of what's going on. Net result, you spent a bit over $1,000,000 checking out a hunch about a fridge. I don't know of any company on the planet that would toss that amount of money and time at a hunch.

No that's not to say it's a great design. It's simply to say that doing a "perfect" design costs way more that anybody would want to pay. Would you pay $100,000 for a Basecamp? Of course not ... There are literally hundreds of "possible issues" like this that pop up as part of any design.

Bob

Gail Miller 07-27-2017 07:56 PM

Quote:

Originally Posted by uncle_bob (Post 1984280)
Hi

It certainly is the only version I've ever seen with the fridge right up front. Given that AS has made a few billion variations over the last 80 or so years, I'd never say "only one" :)

The gotcha is that they have designed themselves into a corner. Flue through the roof? Not so much. Remove the propane tanks? Nope. Jet engine loud blower(s) that will handle lots of back pressure? good luck ... Even with a compressor based design the exhaust heat has to go *somewhere*.

If they were paying me to do this, I'd put a baffle half way down the tank cover / trailer gap. Then start looking at mods to the tank cover to change the airflow pattern. It might be as simple as drilling a couple of 1 or 2" holes. Working out where to put those holes ... not simple at all. Note: I'm retired and *not* looking for work harder than lifting the odd can of beer each evening ... :)

Bob

Someone, and I have forgotten now who it was, took their tank cover off to see if that would help with air flow and it did not.

uncle_bob 07-27-2017 08:08 PM

Quote:

Originally Posted by Gail Miller (Post 1984500)
Someone, and I have forgotten now who it was, took their tank cover off to see if that would help with air flow and it did not.

Hi

I suspect the "airflow in motion" with some TV's is down over the front of the trailer regardless of the propane cover or even without the bottles. When not in motion, the cover certainly does not help the situation any. Since there are multiple issues with the fridge, the solution is an A + B + C sort of thing. Doing any of the three by themselves may not be a very big deal.

All that said, this is only a wild guess. It's something I'd bet a six pack of beer on.

Bob

Gail Miller 07-27-2017 08:17 PM

Quote:

Originally Posted by uncle_bob (Post 1984507)
Hi

I suspect the "airflow in motion" with some TV's is down over the front of the trailer regardless of the propane cover or even without the bottles. When not in motion, the cover certainly does not help the situation any. Since there are multiple issues with the fridge, the solution is an A + B + C sort of thing. Doing any of the three by themselves may not be a very big deal.

All that said, this is only a wild guess. It's something I'd bet a six pack of beer on.

Bob

Since the Basecamp seems to be the only AS with the refrigerator in the middle, instead of on the side ... one would think they could have put the sink in the middle and the refrigerator on the side. I've decided their engineers must have gone to Trump University. To me, it's insane that I paid $40K+ for so much trouble. I'm watching AS's bragging Basecamp ads on Facebook and I have to bite my fingers to keep from typing my opinions! I've had to buy yet another 12 pack of beer, but in all honest, I really just hate the hot Arkansas summers! :-)

Gail Miller 07-27-2017 08:32 PM

Quote:

Originally Posted by uncle_bob (Post 1984280)
Hi

It certainly is the only version I've ever seen with the fridge right up front. Given that AS has made a few billion variations over the last 80 or so years, I'd never say "only one" :)

The gotcha is that they have designed themselves into a corner. Flue through the roof? Not so much. Remove the propane tanks? Nope. Jet engine loud blower(s) that will handle lots of back pressure? good luck ... Even with a compressor based design the exhaust heat has to go *somewhere*.

If they were paying me to do this, I'd put a baffle half way down the tank cover / trailer gap. Then start looking at mods to the tank cover to change the airflow pattern. It might be as simple as drilling a couple of 1 or 2" holes. Working out where to put those holes ... not simple at all. Note: I'm retired and *not* looking for work harder than lifting the odd can of beer each evening ... :)

Bob

I commented in message #19, that I read the following in my Dometic refrigerator installation booklet. I also commented that I wondered if any of us have box baffles: More on page 11 on the upper and lower SIDE vent application, talking about adding the box baffle at the back. "If required, install a box baffle above the lower access vent extending within 1/2" lower than the condenser fins".

Gail Miller 07-27-2017 08:39 PM

I know the service manager of a local RV place here in my town. It is not an Airstream dealer but I've thought about having them pull my refrigerator and seeing just how poorly the design/installation is. Of course it would cost me, when it really should be AS's $$ to fix the problem, but I sort of want to know WHAT the real problem is. Is it a lack of insulation? Is there no box baffle? Are the vents too close together? Does the refrigerator have a connection for a chimney, that isn't connected, so heat is just pouring into the cabinet space instead of escaping via a chimney, causing the counter top and front outside of the camper to feel warm? Just how stupid is it?? I'm not sure AS will admit that.

uncle_bob 07-27-2017 08:40 PM

Hi

A *lot* of engineering errors are "obvious" when you look back at them. Trust me, they are far from obvious from the other end of the process .... There are generally three drivers:

1) How soon does it need to be done
2) How much do you want to spend
3) How well do you want it done

Yes, you will see different labels on each of those. Two out of three with no limit on the other one is easy. There are *always* practical limits on all three of them.

None of this is to excuse the situation. AS certainly is not addressing any of this in a fashion that reflects well on them.

Bob

Troutboy 07-27-2017 09:15 PM

Trust me when I say this is a very simple problem to solve, I'm not over simplifying. Heat removal across the coils is the key. Anyone who is an engineer will get this. Mass transfer calcs are easy, and for this you don't need a complicated model.

As designed the heat being generated in the small pace is not being removed. The ability of the fridge to cool is based on the temperature differential between the air temp of the coils and the air around the coils. The temperature difference (delta) drives how cold the fridge will get.

The current design, with or without the propane tank covers in place does not allow air flow across the coils. Passive or they way they have the single fan designed is inadequate given all the dimensions and aerodynamics.

A design fix is required that will increase the heat removal across the coils. This involves the right air flow, no short circuiting, and the ability to keep the air temp in the fridge compartment space at a specific temperature. This is Not rocket science, and does not require $1M in costs to figure out.

I really question whether the AS factory has the right type of engineer to look at this issue and figure out a fix, or if this is in their top priority list. This is something that 4 people on this thread, if in the right place together could figure out likely in less than one day.

They keep selling these things as is, so what incentive do they have to make it work for the dozen or so on this site that boondock and are having issues? In my opinion if they really cared about this issue and put a few resources on it, it is a quick fix.

I have worked in industrial plants where you loose $1M an hour for down time, and we have solved issues 100x more complex than this in hours. It just baffles me why they can't figure it out and issue a quick fix? It has to be that it's not a big issue to them at this time.

OTRA15 07-28-2017 06:49 AM

Quote:

Originally Posted by uncle_bob (Post 1984525)
. . . AS certainly is not addressing any of this in a fashion that reflects well on them.
. . .

In a nutshell . . . yes . . .

;):wally:;)


PS -- Thanks TB.

Gringo 07-28-2017 10:34 PM

We just today went to the dealer here in Missoula to look at a BC in person for the first time. We were unaware of some of the issues at that time, so didn't know enough to discuss them with the Airstream guy who was showing us the trailer. I think I do understand the problem with getting the heat out and bringing in cool air to ventilate the rear of the fridge.

Is there enough room inside the Airstream wall for a vent channel ? I'm thinking about the double aluminum wall space probably filled with insulation at the moment. And Possibly pulling in fresh air through a slot in the floor?

Troutboy 07-28-2017 10:57 PM

Quote:

Originally Posted by Gringo (Post 1984991)
We just today went to the dealer here in Missoula to look at a BC in person for the first time. We were unaware of some of the issues at that time, so didn't know enough to discuss them with the Airstream guy who was showing us the trailer. I think I do understand the problem with getting the heat out and bringing in cool air to ventilate the rear of the fridge.

Is there enough room inside the Airstream wall for a vent channel ? I'm thinking about the double aluminum wall space probably filled with insulation at the moment. And Possibly pulling in fresh air through a slot in the floor?



That could potentially work if you can get the air to then flow over the coils and out the vent.....

Bborzell 07-29-2017 01:49 AM

We showed up at Jackson Center this morning. In addition to the fridge issue we took the opportunity to get a few other small issues addressed.

My service tech was Joel. If you should show up for service at Airstream and you draw Joel, you should have a good day. He is everything that today's service folks have failed to aspire to. Thoughtful, attentive and skilled are three important attributes and he has them all.

The fix considered that the fridge creates heat that fills the cavity between the unit and the front wall. Much at that heat fails to exhaust itself through the forward vent because it has the upward path which heats up the counter top.

As I understand the issue, AS engineers got together with Dometic engineers and decided to limit the volume of space available for the heat to fill. Instead of adding fans (Joel pulled the noisy fans that were initially added) Joel placed deflectors between the fridge and the forward vents. They also insulated a top deflector that is supposed to eliminate the hot countertop.

In effect, the design should fill the considerably smaller space which has been created by the deflectors. In addition, itappears that the deigners sought to take advantage of the expansion of the heated air to drive movement from the fridge through the deflectors andout the vent.

By the time we were walked through the fix by Joel, the fridge had cooled fromthe low 50s to 43. Two hours later it was at 40 and, after 3 hours on the road, it was 37.

Joel says that ours ws the first to get the redsign in the service department. However, all the new BCs are seeing the mod.

Tomorrow, we will get more heat and I will continue to monitor temps. So far so good, and no fan noise.

xrvr 07-29-2017 03:30 AM

That sounds like good news for all of you.


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