Refrigerator circulation fan placement question

[Joliba]

We are currently completing the installation of refrigeration in our E38-200. We are planning to add a small computer fan with a tube (duct) to act as a circulation fan running continuously in order to improve uniformity of temperature distribution through the box. This diagram depicts the way I would expect the natural convective flow in the box to occur. The sequence I would expect is as follows:1. The lid has just been closed (on the upper right) and the warmest air is at the top on the right. 2. The thermostat turns on the compressor and the evaporator becomes cold. 3. The cold air descends, setting up the circulation seen in the diagram. (Because it is a completely closed system, any moving air must be filled in "from behind" thereby initiating circulation.)
Because this circulation is not strong, the box temperature will most likely never become uniform without assistance. My question is this: If a fan is added as in the diagram below, SHOULD THE SMALL COMPUTER FAN DIRECT THE FLOW IN LINE WITH THE NATURAL CIRCULATION TO AUGMENT THE FLOW OR AGAINST THE NATURAL FLOW TO BEST IMPROVE CIRCULATION IN THE BOX?

 

[Joliba]

this message should have the diagrams attached

We are currently completing the installation of refrigeration in our E38-200. We are planning to add a small computer fan with a tube (duct) to act as a circulation fan running continuously in order to improve uniformity of temperature distribution through the box. This diagram depicts the way I would expect the natural convective flow in the box to occur. The sequence I would expect is as follows:1. The lid has just been closed (on the upper right) and the warmest air is at the top on the right. 2. The thermostat turns on the compressor and the evaporator becomes cold. 3. The cold air descends, setting up the circulation seen in the diagram. (Because it is a completely closed system, any moving air must be filled in "from behind" thereby initiating circulation.)
Because this circulation is not strong, the box temperature will most likely never become uniform without assistance. My question is this: If a fan is added as in the diagram below, SHOULD THE SMALL COMPUTER FAN DIRECT THE FLOW IN LINE WITH THE NATURAL CIRCULATION TO AUGMENT THE FLOW OR AGAINST THE NATURAL FLOW TO BEST IMPROVE C

IRCULATION IN THE BOX?

View attachment box.pdfView attachment fan.pdf

 

[Greg Ross]

My common sense tells me......

These are not very large volume enclosures so variation in temperature will happen via loss when the cover hatch is opened or through variations of the effeciency of the insulation surrounding the box. Based on your sketch and if the representation is reaonably accurate I would be inclined to have the fan fitted in behind the idebox where you show it and exhausting in an upwards direction. This will move cooler air from below (theoretically!) and move it over the surfaces of the Icebox to further chill it.
I would also be inclined to have the fan connected in series with the compressor fan such that it only comes on when the thermostat calls for cooling. Only problem I can see is whether the fan runs full time or icrementally with the compressor it's likely to frost up eventually and quit. Second guessing that, it's likely to run longer before frosting up and seizing if it's powered all the time.
I've considered this as well and do have the fan in inventory, it just hasn't percolated to the top of the "To Do" list yet.

 

[Frank Langer]

While not the answer you are seeking, we actually like the fact that the area near the evaporator plate is colder than the other area of the refrigerator. This allows us to put the stuff that really needs to stay cold (eg. frozen meat, milk, etc.) in the colder area and other stuff that is less sensitive (eg. cheese, eggs, some vegetables, etc.) in the warmer area where they won't freeze. We also put a sheet of bubble wrap on top of the contents of the fridge to minimize heat loss through the door and other areas near the top.

Back to your question about the fan, will it circulate air in the way you are wanting when the fridge is full? I'll be interested in what others think on this.

Frank

 

[Blue Chip]

We're with Frank on this one. The liquids, pop, beer etc go close to the plate...veggies and stuff further away. Bubble wrap really made a difference in our situation.
I would try both (placement and BW) before I went to the trouble of a fan. In that small a space etc I really don't think you will gain much except possibly frost or condensation that you don't expect....if it ain't broke.....

 

[tcooper]

Few facts
Each hp of fan even if fractional adds about 3300 btu per hp so a fan adds heat load and it's not an insignificant load
Heat rises cold falls if door is in top as in most sailboat ice boxes very little cold is lost when top is opened.
Ice boxes are designed to be colder at bottom than top IE beer always goes close to bottom.
Fan in box may make temperature more stable but average temperature will be warmer.
If you really want to get complicated you can make two separate temperatures in a ice box but it's done with isolation wall and dampers that opens and closes to maintain temperatures without adding heat load.


Tom