Report on use of Internal fridge fan and venting

Submitted: Friday, Dec 01, 2006 at 04:22
ThreadID: 123095 Views:4893 Replies:5 FollowUps:5
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Some people are skeptical of venting their 12 volt compressor fridges internally and or fitting a fan inside the fridge to circulate air so this is a report of what we found in recent hot conditions.

We have just returned home from a 4 day stay in our caravan at Boondooma Dam where the day time temperatures in the van were mid to high 30’s and under the awning were between 38 and 43oC. We were running completely on solar and no air-conditioning was used.

About 3 years ago acting on advice from our club president, Bob Pollock, we blocked off the 2 external fridge vents and vented our 190lt 2-door Waeco fridge completely inside the van. It now obtains fresh cool air from under the front of the fridge and this air is then free to flow past the hot compressor and up the back of the fridge and exit the fridge cabinet at the top rear. Placing your hand over the top vent does NOT give you any indication of warmer air rising.

Inside our fridge mounted on the underside of the rear centre top shelf is a 90mm computer fan that blows air downwards over the cooling plate on the rear of the fridge. This fan then circulates air around the entire cabinet of the fridge in much the same way as domestic fan forced fridges do.

At the front of the top shelf I have placed a thermometer probe (that has been tested and found accurate against a commercial unit) and this can be read on the outside of the door. When the under awning temperature was between 38 and 43oC the inside temperature of the fridge was between 0 and 3oC with the fridge thermostat set at the lowest setting of “1”. Prior to installing the internal fan the temperature in the same location was always about 7 or 8oC with the thermostat set higher on 3. We used to find some things freezing and others not getting cold enough, but that is now a thing of the past.

Up until just prior to this trip the aluminum vent cover plates were not insulated, but I have just taped some 25mm thick poly styrene foam to the inside. It is just taped there as the adhesive that I tried to use just melted the styrene foam.

It should be noted that the most common installation of the lower external vent is just above the black rubber along the side of the van and that is completely above the hot compressor of the fridge so air can not flow past the compressor in the same manner as it can when it flows under the fridge.

If anyone is contemplating having there van built with internal vents or changing their current setup, there needs to be a lower inspection opening to the outside so that repairer can access the fridge while still in situ.

I am not saying that anyone should change to this, just giving a report on what we have found in reasonably hot conditions.

Brian
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Reply By: 12tony - Tuesday, Dec 05, 2006 at 00:47

Tuesday, Dec 05, 2006 at 00:47
i have my fridge vented inside and have no probs at all .I like the idea of the internal fan.Have you got it so it switches on and off with the compresser? Thanks
AnswerID: 569858

Follow Up By: Noosa Fox - Tuesday, Dec 05, 2006 at 02:44

Tuesday, Dec 05, 2006 at 02:44
There is a way of having the fan come on only when fridge compressor is running, I think Neil Mattews (Boystoy) has done it, but I was not able to get a fan to work that way. The electronics are such that when it senses an extra load of normal fridge fan that it cuts off the fridge.

In order to prevent any voltage drop in the fridge circuits, I picked up power from the lighting circuit and as it only draws 0.3 amps it is not a big problem over a 24 hour period.

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Reply By: Bushtracker - Tuesday, Dec 05, 2006 at 02:09

Tuesday, Dec 05, 2006 at 02:09
Bushtrackers Position on this... (And I would rather our R&D stay on the Owners Forum) But here you go, a repeat of TIP # 99. We are not here to argue the point, just to tell of our experience over the ten years and why it is not standard for us.... And why it is not in our own vans... AM I BEING FAIR DINKUM? Well, I just reviewed this with Tracy (the other Director) to see if our position has changed any in the year since TIP # 99 was out... And it has not... SO IS IT ABOUT DOLLARS? No, it would be CHEAPER FOR US TO INTERNALLY VENT THEM ALL AS A STANDARD..! So what then? Here is our view on the matter:

TIP # 99 Internal or External Venting on the Fridges

Hello Boggers in planning! There is a good argument about the advantages of interior venting for the fridge instead of the external venting as we normally do. Here are the summary of good points and bad points for internal venting:

Good points:
1) The idea is that the internal venting allows better heat exchange with the condenser coils on the back of the fridge. In normal running conditions this may be true, as you can get a higher volume of convection air flow.
2) Another argument is that it eliminates the bull dust entry into the condenser and compressor area.

Bad points:
1) Refrigeration is not about making cold, it is a process of removing heat… The idea of better heat removal goes to pieces, when the van is locked up, and the internal temperatures in the van can soar to 50 degrees or more. Then, when the van is locked up while you are on a Tour somewhere, in town shopping, off fishing or exploring, the fridge is struggling against the heat of the locked up interior generated by the sun. Even on trips when you are driving, the van is all locked up in the bull dust or desert crossings; ever feel that warm blast in the face when you open the van door? The fridge is struggling to cool itself in those conditions… You are making an artificial 50 or 55 degree heat wave the fridge has to work against. Refrigeration is not about making cold, it is a process of removing heat…
2) Bull Dust? On 10,000 kms across the Red Centre, we pulled the vents and looked inside expecting to find a lot of dust… Maybe we found ½ to 1mm to vacuum out? It seems that whatever blows in, blows back out and most does not settle in the fridge compartment.
3) Maintenance and repairs or just checking something out? A lot can be done to check things out, through the external vent at the bottom of the fridge, instead of having to pull the fridge out….

The short answer and our analysis?
Well, if you were going to summer over in Arnhem Land, living on 240v power with air conditioning on, then yes the internal venting makes sense. The load on the fridge would be alleviated with the cool air supplied by the air conditioning. Then it definitely works better and lessens the loading on the fridge itself as the air conditioning dissipates the heat. Also, that far north in summer and the fridge would struggle anyway, and might not shut off at all during the day. The air conditioning would be working in favour of the fridge.

The problem is that most people are not going to summer over in the far north. In normal conditions, with the van locked up in heat during the day when you are out, it might just burn more power as the interior of the van heats up working against the efficiency of the fridge. The fridge will produce heat on its own, but the raising of the internal temperature is negligible compared with the heating up of the van in the sun with all windows and such closed as in travel or sitting somewhere closed up for security reasons while you are away. Then the interior temperatures can soar, and the fridge will struggle, using more power. I would say that internal venting is an Option, and we will do it, no charge, but it should be restricted to the far North and living on AC. Otherwise it is another idea that could be counterproductive for majority… However, you may chose to disagree, and we will now do it as an option F.O.C….. But not in my van.

While we listen to all ideas, we test them in time, and the “proof is in the pudding.” I think we will stick to the external venting and access to the back of the fridge as our Standard, with internal venting upon request.

Regards from the Ranger.
AnswerID: 569859

Reply By: Noosa Fox - Tuesday, Dec 05, 2006 at 02:57

Tuesday, Dec 05, 2006 at 02:57
I believe that both Turist Bob and I have used our vans for extended periods in both hot and dusty conditions as described above by Bushtracker, with and without external vents. As such we are both in a position to be able to compare fridge operation with and without external vents.

I believe Bob did a test once with his internally vented van and Tracy's externally vented van and found the internal venting to have a lower temperature behind the fridge than the externally vented one.

My finding was a far greater amount of dust in the rear of the fridge than described above, and I believe the fridge works more efficiently with internal venting than with external venting. I must have a better insulated van as I haven't noticed the van temp inside being hotter than outside. When we are parked we always have the 4 season hatch open, and when travelling on sealed roads the rear shutter of the 4 seasons hatch is open, so our van is only ever sealed up on dusty roads.

It is good to see that people can now opt to have the fridge vented internally if they wish to do so. At least everyone ordering a new van now can make an informed decision on which way they wish to go.

Brian
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Reply By: Bushtracker42 - Sunday, Jan 21, 2007 at 23:27

Sunday, Jan 21, 2007 at 23:27
We have had an item to improve the fridge cooling, mainly to reduce how often it runs on hot days, on our list for a couple of years. Initially we were going to try to force more air past the evaporator and/or improve insulation.
I was going to try to find some of my old uni books on thermodynamic and consider building a passive device to increase the air flow by causing a suction on the top vent.

As our fridge cupboard is the height of the fridge, we can't lift it for feet without lifting the shelf above the fridge, so I was wondering how much improvement is in the internal fan and how much is in the internal venting i.e. how would I go with the fan and leave it as external venting.

I can see one difference with the external venting that is not mentioned. Looking at the arrangement and positioning of the upper external vent, one advantage of internal venting is that if forces air up past a larger area of the condensor. Also I suspect it 'draws' better than the external vent i.e. improves flow velocity.
I have always considered my problem is that I have hotter air outside the van than behine the fridge and no real difference between the upper and lower vent.

AnswerID: 569861

Follow Up By: Noosa Fox - Tuesday, Jan 23, 2007 at 23:11

Tuesday, Jan 23, 2007 at 23:11
Gary,
It is hard to say how much if any better the fridge works with Internal venting as apposed to external venting, as to do the test properly would require several fridges vents in each manner and travelling together in the same weather conditions to be able to make some sort of comparision.

The fan circulating air inside the fridge is another story all together.
I can guarentee that if you fit a fan inside the fridge to blow air over the cold plate at the rear, that the whole fridge compartment will be at a lower temperature than without and that it can be run on setting 1 instead of around 3. It also prevents items at the rear being frozen.

It is one of the best improvements that I have made to our van. What it requires is a few more people to do it and give the information to BTi then they as a major purchaser of the fridges could make representation to WAECO asking that a fan be fitted inside as standard.

Brian
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Reply By: TroopyTracker - Wednesday, Jan 24, 2007 at 03:00

Wednesday, Jan 24, 2007 at 03:00
Brian,
We have noticed our fridge struggles to stay cool on the top shelf (remote thermometer). The internal fan sounds great. Any chance of a photo or at least a description of how you got power into the fridge neatly?? Any reason why you couldn't use the power at the internal light if you wanted it on all the time??

Thanks
Matt
AnswerID: 569862

Follow Up By: Noosa Fox - Wednesday, Jan 24, 2007 at 04:05

Wednesday, Jan 24, 2007 at 04:05
The only NEAT way that I can think of to get the power inside the fridge is up through the drain hole. As the power draw is only 300 MilliAmps the wire size required is only very thin so it should not cause a problem restricting the hole by that amount.

The way I did ours was pick up power from the lighting circuit and then ran it through the overhead cupboards and into the fridge caverty. As our fridge is internally vented, we don't have any dust sealing problems so I was able to run the wire out beside the fridge near where the door clip is and then in through the side of the door and wired it to the top shelf. This was done while we were on the road with limited tools so it is not as neat as it could have been if done at home. I also put a switch in the circuit.

The electronics in the fridge appear to be sensitive so I didn't want to interfere with any of that circuitry in case it shut the fridge down. I once tried to connect another fan up to the fan near the compressor and all that did was stop the fridge working all together.

Someone else told me some time back that they had also put a fan inside and had run it so that the wires could not be seen so maybe that person might be able to help. It may have been Neil Matthews.

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Follow Up By: TroopyTracker - Thursday, Jan 25, 2007 at 02:46

Thursday, Jan 25, 2007 at 02:46
Brian,
The drain hole sounds like a good idea to me being teeny tiny wire.

Thanks for the reply and the photos via email.

Whether or not to let it run full time or intermitantly(but how) is the only other question.

Thanks again,
Matt
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Follow Up By: Noosa Fox - Thursday, Jan 25, 2007 at 03:08

Thursday, Jan 25, 2007 at 03:08
Matt,

When you look at the bigger picture with power usage, @ 0.3 amps per hour for the fan, if you had 12 hours of darkness then the fan would only take 3.6 amp hours and you may even gain about that by not having to run the fridge thermostat on as high a setting as it is now. During the day the solar input takes care of this power usage easily.

We got a cheap fan first and it failed, but later got a better quality one from Dick Smith and it has lasted well.

Brian
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