How's this for thick?

Submitted: Sunday, May 01, 2005 at 17:05
ThreadID: 22548 Views:2830 Replies:6 FollowUps:11
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I went to the show yesterday with some friends (Al's, Glenn and Crazies) and then all back to Crazie's for a great barbie (thanks Adam and Kir) where Eric and family joined in; great night.

Anyway, back to the point. Glenn and I were looking at a camper by a new manufacturer and it had a steel box fitted on the drawbar with a fridge in it. Big problem was the box had no ventilation. Would anyone really spend over 20 grand on a camper built by someone who would overlook something as elementary as that? What else would be wrong with it I ask myself?

Apparently he hadn't sold one during the show.

Hmmmmm?

Cheers,

Jim.
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Reply By: Nudenut - Sunday, May 01, 2005 at 17:16

Sunday, May 01, 2005 at 17:16
mmm may be it wasnt really made for a fridge...but one was handy and of right size?
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Follow Up By: Member - Jimbo (VIC) - Sunday, May 01, 2005 at 17:21

Sunday, May 01, 2005 at 17:21
You're being very kind to him Nudie, but he had a sign saying fridge extra $1200 or whatever it was.

Cheers,

Jim.
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Follow Up By: Nudenut - Sunday, May 01, 2005 at 20:35

Sunday, May 01, 2005 at 20:35
.... i'm a nice bloke
havent they told you this!
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Follow Up By: Member - Jimbo (VIC) - Sunday, May 01, 2005 at 21:22

Sunday, May 01, 2005 at 21:22
You're allright Nudie.
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Reply By: Mike Harding - Sunday, May 01, 2005 at 17:17

Sunday, May 01, 2005 at 17:17
I wouldn't be too worried by the lack of ventilation, fridges don't dissipate a lot of heat and that may well be transferred by the heatsink effect of the steel box anyway and keep in mind; ventilation (without filters) = dust.

However I would be very concerned about the box being in a location which may expose it to direct sunlight! In an Australian summer I'll guess the internal temperature of a steel box in direct sun may reach 80 deg C? And no amount of natural ventilation will bring that down to an acceptable level.

Mike Harding
AnswerID: 109086

Follow Up By: Member - Jimbo (VIC) - Sunday, May 01, 2005 at 17:26

Sunday, May 01, 2005 at 17:26
Agree with some of that Mike, but Collyn Rivers (where is he these days?) says that the most important factor to fridge performance is allowing cool air to the condenser. If the fridge can suck some cool outside air through the vents it will work much better.

I've actually seen this work quite well. Diamond has his in a steel box with ventilation next to the condenser and leaves the lid open a few inches when stopped to allow airflow and the lid of the box stops direct heat hitting the fridge. He gets amazing battery life out of an old start battery.

Cheers,

Jim.
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Follow Up By: Redback - Monday, May 02, 2005 at 09:26

Monday, May 02, 2005 at 09:26
He's in the campertrailers forum most of the time Jimbo and is keeping a low profile.

Baz.
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Follow Up By: Member - Brian (Gold Coast) - Monday, May 02, 2005 at 17:24

Monday, May 02, 2005 at 17:24
Hotter condensor = lower efficiency = longer run time = shortcut to flat battery.... simple as that!
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Follow Up By: Member - Jeff M (WA) - Monday, May 02, 2005 at 17:38

Monday, May 02, 2005 at 17:38
I agree with Brian, and think of this if fridges did not need ventilation why would Waeco be fitting fans to their new models? What's it going to do, circulate the hot air round and round, might as well not bother.
Air cons, fridges, thermo coolers. It's transfering hot air from inside the fridge to the outside of the fridge either through gas and a compressor/condensor etc or a Peltier, either way the proccess is inefficiant meaning that not only are you removing the heat you are generating more heat. If there's nowhere for it to go it's going to get hotter in the box, then the cycle starts again only making it worse and so on.
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Follow Up By: Mike Harding - Monday, May 02, 2005 at 20:43

Monday, May 02, 2005 at 20:43
It's not about ventilation it's about dissipating heat and ventilation _may be_ one of the ways of doing that.

Consider a fridge dissipating 30W in a closed steel box but with an ambient outside temperature of 0 deg C - what do you think the internal temperature of the box would be?

The same situation but with an outside temperature of 30 deg C - do you think the internal temperature of the box would be hotter?

The same fridge dissipating 30W in a glass box with an outside temperature of 0 deg C - would the internal temp. be the same as in the steel box?

The steel box will have a heatsinking effect but that will be proportional to the temperature differential across the box and most of the time in Oz that differential won't really be good enough for a fridge to work very well - for a steel box in sun the fridge wouldn't have a chance because now the heat transfer process is working in reverse.

Passing ambient air through the enclosure will help but it would probably have to be forced air from a fan to get sufficient heat transfer to make any noticeable difference.

Well that’s my take on thermal thingies – but it’s not really my area and I would welcome corrections?

Mike Harding
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Follow Up By: Member - Brian (Gold Coast) - Tuesday, May 03, 2005 at 07:10

Tuesday, May 03, 2005 at 07:10
Never bothered to work out how many watts is dissipating but as a Refrigeration Technician I do know about heat from condensors and the efficiency involved/affected. With commercial refrigeration, the efficiency of the system is greatly decreased by inadequate air flow across the condensor. The same with a car refrigerator, whether it is a fan cooled condensor or not.
Over the course of our just completed holiday i noticed this with our Trailblazer........
On Fraser Island, where ambient o/nights were in the 17-19 deg C range, I would turn the fridge off at night before turning in, say 10 PM. In the morning at say 6:30, I would turn the fridge back on and the compressor would start immediately and run for some time to bring the temp inside the fridge back down. On the days where we were stationary, I had the rear doors of the truck open, the fridge extended out on the fridge slide and the fridge "shaded" and it operated quite efficiently. On the days where we were driving around the island ALL day, with the rear door shut and not as much airflow around the condensor, I could hear the compressor running longer during it's "run" time. This is simple "Fridgie" rule.... reduced effiency condensor = longer run times.
Part 2 of our trip was at Gorge River Staion near Bonalbo NSW... o/night ambients of 11-12 deg C.Turned off the fridge at 10ish, back on at 6 or 7am and each day the compressor didn't start until after we had opened the fridge to get breakfast food out. During day when doors were opened and fridge out on slide, compressor run times very short compared to almost continuos running when out on the tracks.
The short answer is that the condensor has to "breathe" to be efficient. Try blocking the condensor of your kitchen fridge and see how efficient that is then!
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Follow Up By: Member - Jeff M (WA) - Tuesday, May 03, 2005 at 11:15

Tuesday, May 03, 2005 at 11:15
Mike, the motor in the fridge is generating heat, along with other inefficancies. Sure if it is 0c outside the box will be cooled by the lower outside ambient tempeture but just imagine how much cooler the inside of the box would if there was a vent at the bottom and a vent at the top to let the hot air be drawn out.

How does a blanket or sleeping bag work? Heat rises, but the heat is trapped in by the blanket. You have a sealed metal box, it is trapping more heat than it is disapating I'm sure. Maybe if you put big heatsinks and a fan stuck to the outside of the box it would be an effeciant heatsink, but then your using power to run the fans and it would look pretty bloody werid! LOL And of course as you mentioned, if the sun is belting down on it... Well then it's going to be pretty useless anyway.
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Reply By: Bob of KAOS - Sunday, May 01, 2005 at 18:24

Sunday, May 01, 2005 at 18:24
I'd be very concerned at what may happen to the fridge on a rough track. The trailer tends to have a rougher ride than the tow vehicle. The contents of the fridge would be homogenised at the very least. The compressor would be shaken off its mountings.
AnswerID: 109100

Follow Up By: Member - Jimbo (VIC) - Sunday, May 01, 2005 at 19:48

Sunday, May 01, 2005 at 19:48
"homogenised"

ROFLMAO

Nearly as good as your explanation of foul tasting water in the caravan tank a while back LOL.
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Reply By: Diamond (Vic) - Sunday, May 01, 2005 at 20:54

Sunday, May 01, 2005 at 20:54
yep me got one of them boxes with a big fridge.
i got a certain mr al to get me a vent for the side.
minimal dust gets in and it does get hot in there id hate to see how hot with out vents.
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Reply By: muzzgit (WA) - Monday, May 02, 2005 at 00:38

Monday, May 02, 2005 at 00:38
And then there is the added weight on the draw bar !!
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Reply By: Member - Crazie (VIC) - Monday, May 02, 2005 at 08:34

Monday, May 02, 2005 at 08:34
Hey Jimbo

yep there were some strange things at the show, i like how we found the map on the way out hahaha. I couldnt get over some of the asking prices for some of the camper trailers. Anything with a hard floor started at $21000 and they were crap lol
I cant believe i didn't buy anything..... let alone that big steel box.

cheers
Crazie
AnswerID: 109169

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