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Old 18-05-2016, 16:25   #1
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Internal Refrigerator fan placement

I'm currently monitoring my fridge temperature (using 12 highly accurate digital DS18B20 thermometers that read 0.0625&Deg C temperature changes) and have a very small fan to move air around.

I've searched using Google to see which fan placement is optimal -

a) Fan blowing onto the evaporator plate
b) Fan sucking air from the evaporator plate
c) fan blowing down onto the food area
d) fan blowing up from the bottom of the food area

and haven't found any useful information. So far I've got statistical data for temperature distribution inside my fridge with no fan running (sucks, about 5&deg C difference between high and low) and the most homogenous seems to be the fan in the middle blowing down on the food.

Does anyone here have any information on fan placement inside a fridge to make temperatures as evenly distributed as possible?
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Old 18-05-2016, 17:14   #2
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Re: Internal Refrigerator fan placement

I tried several and settled on a computer fan in a homemade rectangular plastic duct.
The fan runs continuously and pulls air from the bottom of the refrigerator box and blows directly on the thermostat sensor which is located at the top center of the box.

I have a keel cooled Vitrifrigo BD35 with an aluminum evaporator freezer.
It keeps ice cream nice and firm.

Temp differential top to bottom is about 1 f. Aerogel insulation on homemade box.
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Old 18-05-2016, 17:40   #3
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Re: Internal Refrigerator fan placement

We just installed a new stainless lobster controller, which includes a fan/thermocouple combo. In their instructions they recommend mounting the fan so it points at the evaporator to assist with the automatic defrost function. I suppose that any movement of air is good.
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Old 18-05-2016, 18:45   #4
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Re: Internal Refrigerator fan placement

Circulation helps to even out the vertical temperature gradient.

Baseline this without the fan. If the gradient is small a fan will make little difference. This isntypically a second order effect.

You should also measure the performance of your insulation. This is a first order effect.

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Old 19-05-2016, 04:11   #5
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Re: Internal Refrigerator fan placement

seniormechanico - I hadn't thought about actively ventilating the thermostat. I've got to think about whether that is a good things, but it does make sense to be certain that the thermostat is measuring the correct temperature.

zboss - I didn't know that any marine fridges using compressors had a defrost function! I feel that pointing the fan at the evaporator plate seems to make the most intuitive sense, as it forces more warm air to where it can transfer energy.

leftbrainstuff - I did a baseline without the fan and have about a 4C spread. I'm not sure why you want me to measure the insulation as I'm not looking to re-engineer my fridge but to optimize performance with what I have. The fan brings the temperature spread down a bit to 3C degrees but the standard deviation of measurements is much better with just one or two warmer spots.
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Old 19-05-2016, 05:53   #6
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Re: Internal Refrigerator fan placement

Richard Kollmann has a nice section about fans with 12V boat fridges here:


http://www.kollmann-marine.com/Fans.aspx
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Old 19-05-2016, 08:31   #7
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Re: Internal Refrigerator fan placement

Thanks for that link, it does reinforce my assumption that a more even heat distribution will lead to some energy savings. It doesn't recommend any specific fan placement; although Richard Kollmann might chime in on this thread with a recommendation based on his experience.
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Old 19-05-2016, 08:51   #8
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Re: Internal Refrigerator fan placement

Any (PC) fan will work, mainly if put along natural convection streams (to be checked)
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Old 19-05-2016, 09:48   #9
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Re: Internal Refrigerator fan placement

I would say in theory you would want to boost normal convection, which should be to blow down on the plates from above, as them being colder than ambient, there should be a descending column of air off of them.
In practice, I bet it doesn't matter, if you get air moving around, it will equalize in temp.
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Old 19-05-2016, 11:33   #10
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Re: Internal Refrigerator fan placement

If you have a compressor refrigerator like the Waeco for instance, it is essential to cool the condenser. This is where the heat from within the fridge is extracted to. As the ambient temperature rises so the efficiency of the fridge falls.
What I usually do is to put a simple computer fan, which takes virtually no current, and point it at the condenser. Then I make up a cowling to ensure that most of the air from the fan goes onto the condenser and is drawn from below the fridge ie the cool bilge.
Then I make sure that the air rising from the condenser, which will be warm, flows out into the cabin rather than remain behind the fridge.
The fan is wired up to the fridge so that when the fridge is on, so is the fan.
The ducting can be of any stiff material, taped into the shape that you need.
This has always turned my fridge into one that does not make ice cubes into one that does!
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Old 19-05-2016, 12:26   #11
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Re: Internal Refrigerator fan placement

Check out the Noctua line of fans on Amazon. I used them on my Isotherm Cruise 130 install (Danfoss BD35) to replace the factory fan on the compressor, one additional to help exhaust heat from the enclosure, and a tiny one inside, for what you describe, to circulate the air in the box. The inside one wired to the light fixture, the other 2 jumpered to the Danfoss controller.
These fans are more expensive than the typical crap supplied, but have ball bearings, are quieter, move more air, and draw less amps, all good.
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Old 19-05-2016, 12:53   #12
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Re: Internal Refrigerator fan placement

1affiah - I've already got an extra fan on the compressor , I'm using ahigh-quality computer fan from a German company (can't remember the name, and the fan is in the back of the compressor compartment and I can't read the name). This topic is for a fan inside the fridge itself. The ones I am using inside are from digikey and are rated to something like -30C. with PWM and a tach output.
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