Keeping the fridge cool!

Submitted: Monday, May 09, 2005 at 09:48
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Hi All,

Following numerous threads on this issue over the last 6 months, decided that with the big trip looming in the tropics, some additional cooling maybe warranted to keep the 2 Waecos cool whilst locked up in the car.

What we have is these 2 fridges (1 cranked right up to be a freezer) a tinnie on the car (keeping the direct sunlight off), tinted windows, and home made insulation bags over the fridges. What this setup missed however was some capacity to keep the heat out of the car when parked. So decided a fan was needed to pump the hot air out of the car.

Bought a big computer fan (12cm) and fixed this to some 4.5 mil perspex roughly the size of about half a rear window. A small strip of perpex glued to the inside and one to the outside allows it to be slipped over the existing window and wound up like the normal window (made it so it fits in the tracks). The fan displaces 6 cubic meters /minute for 0.52 amps. Figure that by leaving the car vents open the fan should be able to replace the hot air whilst parked.

Yeah, I know a bit over the top (the bride gave me a hard time about this as well) but I reckon that these fridges will find it hard to keep cool if the ambient temp reaches 40 to 50 degrees (close up car) Will let you know how it works on our return.

Kind regards
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Reply By: flappa - Monday, May 09, 2005 at 10:34

Monday, May 09, 2005 at 10:34
Sounds OK in theory.

A friend on mine had one of those Solar Fan things that you put into the windows of the vehicle , and it made a HUGE difference to the inside temp of the vehicle
AnswerID: 110403

Follow Up By: Member - Beatit (QLD) - Monday, May 09, 2005 at 11:06

Monday, May 09, 2005 at 11:06
Thanks Flappa,

I know its just a half baked theory at this stage. Kind off thought that the half amp power supply for the fan could well lead to a similar saving in fridge power if there were to be lower ambient operating temperatures.

Not a real big deal as I have plenty of battery power and was thinking of using this system only in areas where the car needed obvious locking for security reasons (if you know what I mean).

Kind regards
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FollowupID: 366929

Reply By: age - Monday, May 09, 2005 at 11:46

Monday, May 09, 2005 at 11:46
Just remember though - "for obvious security reasons" - you have in fact compromised security by fitting a piece of perspex where glass used to be. Idea is good though and should keep temps down a little.

Villains will just smash anything to get what they want anyway !!
AnswerID: 110417

Reply By: Drew - Karratha - Monday, May 09, 2005 at 12:52

Monday, May 09, 2005 at 12:52
I am trying to do a similar thing - I have a 12v .22amp computer fan that I am going to mount over the fridge to suck the hot air out. (The fridge is on a roller in an insulated bag with a shelf over the top). You can feel the hot air that builds up in the gap between the fridge and the shelf. I realise this wont cool down the interior temp but hopefully the air over the fridge motor/evaporator(whatever it is) will help it to work easier and draw less amps. I will hopefully do some testing over the next couple of weeks to test the theory......
Drew
AnswerID: 110430

Reply By: Lone Wolf - Monday, May 09, 2005 at 13:22

Monday, May 09, 2005 at 13:22
I too, have often given this some consideration.

Yes, the tinny on the roof will act as a safari roof.

The fan....... 1/2 amp......

I was seriously considering doing something with the Delica. Honda is good, it's got a sun roof.
Now, back to the Delica. What I had considered, was convection. I am thinking of cutting a hole in the floor, about 300 mm. square, and using a lid. Same deal on the roof, and a caravan type lid.

Gotta let some cooler air in, otherwise is will just try & vacuum.

Window tinting is damn good, but curtains will block out heaps more light, which in turn, stops heat ingress.

Wolfie
AnswerID: 110436

Follow Up By: flappa - Monday, May 09, 2005 at 13:49

Monday, May 09, 2005 at 13:49
Wouldn't be real waterproof though would it ?
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Follow Up By: Member - Beatit (QLD) - Monday, May 09, 2005 at 14:40

Monday, May 09, 2005 at 14:40
Wolfie,

I know that half an amp would probably run you cameras and the white lens for ever but my thinking was that if got the biggest meanest looking computer fan and it only sucks so little power it might just reduce the waeco's normal operating power consumption to something less than 5 amps (freezer mode and in 50 degrees). Felt it entirely possible to drop the internal car temp from 50 to 35 using this method. What do you reckon? Forget about cutting any holes though, surely having your air vents open would have the same effect?

Kind regards
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FollowupID: 366959

Follow Up By: flappa - Monday, May 09, 2005 at 15:25

Monday, May 09, 2005 at 15:25
Some more thoughts.

How much difference would 50 to 35 degrees make ?

Its the cycling effect you are trying to reduce isn't it ?

That is how many times the fridge cycles on and off to maintain the required fridge temp.

If it needs to run all the time at 35 degrees , then it would also run all the time at 50 , so really , it makes no difference. It wont run any harder.

I dont know the answer , its purely a thought.

My Evakool does cycle on and off at 35 degrees , but i haven't really used it in any higher temps , and its also not in the vehicle , its in the trailer. Temps seem to stay slightly cooler inside the trailer then the vehicle parked in the sun.

I can see good reasons for fitting a fan , at least it should reduce the time for the AC to cool the vehicle down , but , how much of an effect of the fridge , I dont know.
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Follow Up By: Lone Wolf - Monday, May 09, 2005 at 15:27

Monday, May 09, 2005 at 15:27
Actually, now you've put it that way, the air vents open, I think you are on a winner.

I also re looked at your figures, as in the current draw on 2 fridges, as against 1/2 amp overall, to have the fridges cycle less.......... I think this WOULD be an interesting thing to properly follow up on.

I, for one, would be interested to see any gains made, then .............. I may not need to cut a hole in Tracy's floor.................

Wolfie
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Follow Up By: Member - Brian (Gold Coast) - Monday, May 09, 2005 at 18:23

Monday, May 09, 2005 at 18:23
flappa said;
"How much difference would 50 to 35 degrees make ?"

Lots actually... hotter fridge condensor = less refrigeration effect and therefore longer run times = more power consumption.

My first attempt at fridge slide/drawer assembly worked ok but placed the fridge too close to the side section of the adjacent drawer. Subsequent modification gave me a 50mm breathing space in that area and I have noticed that the refrigerator works much more efficiently now.
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Follow Up By: flappa - Tuesday, May 10, 2005 at 09:03

Tuesday, May 10, 2005 at 09:03
Quote:

flappa said;
"How much difference would 50 to 35 degrees make ?"

Lots actually... hotter fridge condensor = less refrigeration effect and therefore longer run times = more power consumption.

But does it , thats the question I'm asking. ?

The question I guess is more about the efficiency of the fridge.

If it works efficiently at 35 degrees (as I suspect any decent fridge would) and cuts in and out as required . . . thats fine.

If it doesn't though , then really , does it matter whether its 35 or 65 , the fridge will still need to run flat out. You can go any more flat out then flat out.

You with me.
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Follow Up By: Member - Beatit (QLD) - Tuesday, May 10, 2005 at 09:17

Tuesday, May 10, 2005 at 09:17
G'day guys,

If my memory serves me at all, I remember something from the manual that suggested that this fridge can reduce the ambient temperature by 40 degrees (might have been 42 but it was something like that). So I guess that if the ambient temperature exceeds 40 then the fridge would be working the whole time. This is not overly hot as far as locked up car temps go (people are on record saying this can be as high as 60 in summer).

So if this is correct then one could assume that anything under 40 the fridge would cycle but how much and how often - no idea. The current Brissie weather doesn't permit a meaningful test but I would imagine that a reasonable test might be in-car temperature readings both with and without the fan. There are many other variables though such as the outside temp and the heat generated by the fridges. I'm guessing that if the inside temp = the outside temp then I've probably reached the limit.

Kind regards
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Follow Up By: Wok - Tuesday, May 10, 2005 at 15:48

Tuesday, May 10, 2005 at 15:48
Flappa,

From memory,my trials on a 60l Trailblazer gave 50% dutycycle for 45-50oC. This was on a modified unit. Your point of ' flat-out '
is valid, guess the fridge cavity would just rise in temp past this point.

cheers
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Follow Up By: Member - Brian (Gold Coast) - Tuesday, May 10, 2005 at 16:23

Tuesday, May 10, 2005 at 16:23
flappa,

yep... I'm with you on the "flat-out-is-flat-out" bit..... but I think that flat out "could" be interpreted to mean optimum effiency.... X amount of cooling watts at X deg C ambient.

And it depends on the rating of the fridge ....

E.G My Trailblaza is rated at 43 deg C or so it said on the sticker when I bought it... so up to an ambient of 43 deg C it will work fine..... ambient in this case refers to wherever the condensor of the unit is.... in our case the rear of the Patrol. As soon as the "ambient" rises above 43 deg C, I would expect the efficiency of the fridge to decline, and continue to decline in proportion to the rise in "ambient" to a point where the fridge will not cool anymore. This in turn directly affects two things.. firstly it will draw more current, because the higher the condensor temperature, the higher the condensor pressure and therefore the compressor has to pump harder. Secondly, due to the decreased refrigeration effect, the run time will lengthen, possibly culminating in constant running till the battery is flat. And it may do so WITHOUT maintaining cold temperaure within the refrigerator.

So............................ to go back to the original posting regarding the ventilated box on the trailer, say the trailer is sitting in the sun while the owner is having a countery, the temp inside the box could soar to 60+ deg C..... all this will do is eventually flatten the battery.... and NOT keep the stubbies cold! If it was vented and the temp kept down to a reasonable level, the fridge will do it's job and cause much less heartache!
Honest!
:-)
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Follow Up By: Wok - Wednesday, May 11, 2005 at 07:57

Wednesday, May 11, 2005 at 07:57
Brian[Gold Coast]

[Q] firstly it will draw more current, because the higher the condensor temperature, the higher the condensor pressure and therefore the compressor has to pump harder. [/Q]

Is this a refergeration fact? I measured a rise from 4.5A to 6A through the ON cycle...thought it was a problem with the Danfoss!?

Have you monitored your current ?
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FollowupID: 367185

Follow Up By: Member - Brian (Gold Coast) - Wednesday, May 11, 2005 at 08:44

Wednesday, May 11, 2005 at 08:44
Wok...
Strictly speaking I have not monitored this on my Trailblaza, but I have seen the effects of this on commercial refrigeration equipment.
Temperature and pressure have a direct relationship in the world of refrigeration. So as the condensing temperaure rises, the pressure rises within the system. As the condensor pressure rises, the compressor has to work much harder to pump the refrigerant around, i.e against the higher condensor pressure. Harder working compressor requires more current to operate.
As close to monitoring that I have done, is simply noting (roughly, not scientifically) how long the fridge runs now in comparison to before I gave it more "breathing" space and under what conditions. It works "better" now that it has a breathe space all round it, it works "better" when the fridge is extended on the slide (when we are parked obviously) and shaded from the sun, (we usually drape a tarp or a towel or something around the barn doors to shade the fridge and reduce the condensor temp), than when it is locked up in the back with no ventilation, or we are driving around without the air con on to keep the car cool. Bearing in mind that my Trailblaza is roughly 2 years old, the insulation is still in very good order, so shorter run times hopefully coupled with long off times (the insulation holding interior temp) should equal longer time till battery is flat! In theory anyway!

I think Nudenut (on this forum) is a fridgie as well.... he may be able to clarify it better than I have.....
Hope this helps anyway.
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FollowupID: 367189

Follow Up By: flappa - Wednesday, May 11, 2005 at 08:59

Wednesday, May 11, 2005 at 08:59
Brian,

So it seems we are on the same page.

Without arguing the specifics , which this wasn't what it was about , we seem to agree.

If you can reduce the temps to whatever is the Max Efficiency for your fridge (seems to be around that 40 degree mark) , then it will work as it should.

Therefore anything to reduce those temps , including this Puter Fan in the window , should be a good idea , and should have some effect.

If you do nothing , then in all likelyhood , whether its 50, 60, 70 degrees in the vehicle , no fridge will cope , and so things will get hot , and flatten your battery quicker.

Its all about getting the Ambient temps , into a reasonable working range.
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FollowupID: 367192

Follow Up By: Member - Brian (Gold Coast) - Wednesday, May 11, 2005 at 16:28

Wednesday, May 11, 2005 at 16:28
flappa.... yep.. we're definitely on the same page here. Not arguing, but discussing. And I must say I have enjoyed this discussion.... made me think hard before I posted to ensure I knew what I was on about! LOL...

I try hard to make things as easy as possible for my fridge... after all.... it keeps my beer cold!

:-))
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Follow Up By: flappa - Wednesday, May 11, 2005 at 16:33

Wednesday, May 11, 2005 at 16:33
Oh yeah , no issues this end . . . purely a discussion.

Only had my fridge for 12 months , wanna make sure the beers stay cold.
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Reply By: signman - Monday, May 09, 2005 at 16:19

Monday, May 09, 2005 at 16:19
Now if ya had a decent make fridge.....
nah..I won't go down that track !!!!
AnswerID: 110471

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