21 replies to this topic

[Cpt Davenport]

Keeping direct sun/heat off the side with the refrigerator makes a BIG difference.  I just returned from a wonderful father daughter trip in the Painted Hills, and the first night was brutal.  I parked with the refrigerator facing west.  My thermostat controlled fan kicked on about 1:30 PM and ran until 10:00.

 

I repositioned so the refer was shaded in the afternoon, and the fan never came one.  That said, the refrigerator kept things wonderfully cold.  The fan is very helpful!

I think that facing the fridge side of the camper away from the sun is the most important part. We set up on the lake with fridge on the north side. Even though we were only getting 3-4 hours of full sun on the panels the fridge and battery kept up way better. When we left the camper in the parking lot of another lake, because of the boat trailer and oneway situation, we were forced to park with the fridge facing SW. Even though we had sun all day on the panels, the all day sun on the fridge side was our demise. I'm looking into some kind of shade to deploy in these situations.

 

I store my collapsible grey water jug and hose in the side compartment were the fan is. I think this is limiting the circulation and also part of the problem. I will relocate these items. 

Edited by Cpt Davenport, 24 July 2023 - 02:46 PM.

[JaSAn]

I have always kept the fridge stuffed to the max thinking the same thing. I did just watch a video that explained the need for some space around the edges in there so the cool air can circulate. This was for an absorption style fridge. I wonder if the same need for circulation is present with the compressor style.

Air is what does the cooling of the contents of the fridge:  air is cooled by the heat exchanger (evaporator coils), circulates past contents removing heat.  So there needs to be room for air to circulate past all the contents of the fridge.

Some guys add small muffin fans inside to help this process and to equalize the temperature in the fridge.

[Ted]

I know it would not look great, but would putting something like a 1" thick piece of insulation on the outside of the refrigerator door help? This way you can still use the door storage and add insulation to a poorly insulated side of the fridge. Maybe glue a piece of corkboard to the fridge door and use it as a bulletin board, or something to that effect.

[Casa Escarlata Robles Too]

I know it would not look great, but would putting something like a 1" thick piece of insulation on the outside of the refrigerator door help? This way you can still use the door storage and add insulation to a poorly insulated side of the fridge. Maybe glue a piece of corkboard to the fridge door and use it as a bulletin board, or something to that effect.

Good ideas Ted.Duel usefulness. I like that.

Frank

[Cpt Davenport]

I know it would not look great, but would putting something like a 1" thick piece of insulation on the outside of the refrigerator door help? This way you can still use the door storage and add insulation to a poorly insulated side of the fridge. Maybe glue a piece of corkboard to the fridge door and use it as a bulletin board, or something to that effect.

Great idea!

[ckent323]

JaSan, et. al.

I know that a residential type refrigerator with a freezer needs to allow internal air circulation from the freezer compartment to the refrigerator compartment but I am not convinced that is necessary for a 12 v refrigerator that does not have a freezer compartment.

The small volume of a 12 v refrigerator compartment is cooled by the compressor system and in turn the contents will cool by convection and conduction.  Unless the small volume food compartment of the 12 v refrigerator is stuffed so full that no air can move (which would require something solid or nearly solid) I suspect there is plenty of air space to allow for convection to occur.  In addition the food would be in contact with other cold items and would cool by conduction which is a superior heat exchange mechanism in air.  

I confess that I am no expert on this so if you have a reference you can share to help my understanding of why a fan is needed inside a 12 v refrigerator compartment I would appreciate you posting a link or sending me a PM so I can read it.

Thank you

Craig

 

Edited by ckent323, 26 July 2023 - 01:50 AM.

[JaSAn]

Craig,

 

The only test I know of was done by a guy going by Sternwake in the old Cheap RV Living web site about 8 years ago.  I don't remember the model of upright RV refrigerator he tested.  The web site has changed owners and name (currently vanlivingforum.com).  My testing followed his except for the addition of fans (I'm going by a very creaky memory here).

 

My testing was as follows:

Norcold  DE-251D 1.9 cu.ft upright loaded with 12 oz water bottles, cold soaked for 24 hours.  Fridge temperature set to be ~34ºF.  Internal temp variation was about 4ºF.

Temperature was measured with a IR temperature gun; each water bottle measured in situ.

External refrigerator temperatures were also measured: door, door gasket, door frame, sides, top, bottom, back behind condenser.

Test was run twice.  I don't remember the ambient temp but it was run in winter, in my basement so probably ~68º

 

Results (as I remember them):

Coldest water bottles were in the rear bottom of the refrigerator and in the top left (right next to the freezer).

Warmest were in the top door shelf.

There was ~8º difference in temperature of the water bottles.

 

Exterior sides were all about the same temperature with the top left being the coolest of the sides (close to heat exchanger).

Rear exterior was the warmest (behind the condenser).

Front door was at about the same temperature as the sides (I did add a plywood facia to replace the metal door skin).

Door frame and rubber seal were coolest of all external surfaces (leakage?).  The door eventually did warp enough to require pinning at the bottom.

 

Both my refrigerators (Norcold and current cheap dorm fridge) have tiny (and almost useless) freezers so didn't test freezer-less refrigerators.

 

I don't think conduction has much cooling effect as there is little contact between the odd shaped items in the fridge.  The only real surface contact is on the bottom where they rest on another surface.  Air to item convective heat transfer is the main mechanism.  There should be sufficient air circulation unless things are jammed tightly.

 

[ckent323]

JaSAn,

 

Interesting test.  Thanks for sharing. 

It seems that the closer the items are to the heat exchanger the colder they are.  

 

Conductive heat transfer through the sides, door and seals for sure.  You did not say what the temperatures were of the various exterior surfaces of the refrigerator.  I would be interested to see the data if you still have them and would share.

It does appear convection is cooling the interior contents and there was plenty of room for unassisted convective air flow.  Coldest at the heat exchanger and at the bottom below it. The cold air is heavier and drops to the floor setting up the convective air circulation.

The warmer items appear to have been closest to the sides with the most conductive heat loss (i.e. those without a heat exchanger).

Did you measure the temps of the interior walls, floor and door surfaces?  That would be informative.   

Did you run the test with and without a fan inside? 

Since there is clearly convective air flow I am wondering how much difference the fan would make.  Seems to me the temperatures of the contents might get closer together and bring all of the contents closer to the average temperature (slightly warmer for the items in the back and slightly cooler for the items in the front).  I do wonder if the little bit if heat from the fan motor would raise the average temp a bit.


Looking at my own Norcold refrigerator and my dometic portable 12v refrigerator I see that the heat exchanger plate in the Nordcold is small relative to the total interior surface area.  Also it is at the top of the back wall and there is a small freezer so the refrigerator works just like a residential type refrigerator where there has to be a path for cold air to flow out of the freezer into the refrigerator compartment.

The surface area of the walls in my Dometic cooler is much less but I think the cooling surface is in the vertical wall of the step of the interior compartment over the compressor.  Some models may have a cold plate that wraps around the sides of the larger compartment and I know that one model has a separately controlled cold plate in the bottom of the compartment over the compressor with an added ice maker compartment.  The sides of the box (under the exterior cover) are covered by industrial foam insulation so it is better able to keep up with the conductive heat loss through the sides and door (top door) of the refrigerator).  The contents of the dometic fridge also seem to have less variation in temperature.

I do not know what the difference in insulation may be between the Norcold and the Dometic fridges and if that is also a factor in the heat flow through the sides but area wise the ratio of cooling plate to interior wall surface is much more favorable in the Dometic portable fridge than it is in the Norcold built in fridge.



 

Edited by ckent323, 26 July 2023 - 04:58 PM.

[Vic Harder]

130L Truckfridge in my rig.  I added a small squirrel cage fan inside my fridge that runs whenever the compressor is on.  It is positioned between the small freezer compartment and the top inside of the fridge next to the compressor indent.  It keeps the temps more consistent in our fridge, as evidenced by less frozen veggies in the crisper (bottom) and colder beer in the top door compartment.  Readouts on the temp sensors are more consistent too.

 

fan i used - Vic's Puma (Grandby) build - Gallery - Wander the West

[JaSAn]

 . . . You did not say what the temperatures were of the various exterior surfaces of the refrigerator.  I would be interested to see the data if you still have them and would share.

Did you measure the temps of the interior walls, floor and door surfaces?  That would be informative.   

Did you run the test with and without a fan inside? . . . 

I did measure surface temps (inside and out) but I don't know where that data is (if I even kept it).  This test was done 7 - 8 years ago.  I did add 1" formular around the sides, top, and bottom (on the Norcold).

I did not use an interior fan.  I had planned on installing one but my supply of round tuits has been depleted for some time.

 

. . . I do not know what the difference in insulation may be between the Norcold and the Dometic fridges and if that is also a factor in the heat flow through the sides  . . .

I would guess there is some variation in the insulation and thickness among makes, models, and years of refrigerators.  Each manufacturer would have their own spec on insulation effectiveness.

 

This experiment is so easy to do and there would be variation among refrigerators.  I should do it on my current dorm fridge.  The outside temps might not tell much because it uses the skin as part of the condenser.