Improving Fridge Cooling

beemerphile1 wrote:

dougrainer wrote:

...The Interior refer relies on Convection air to flow from the bottom of the refer box UP the back wall and THRU the Evap fins and that removes the heat as the fins are 10 degrees colder than the interior temp...

The part quoted doesn't sound quite right. I'm not being argumentative but cold air falls. Seems to me that cold air would go down the rear wall.

Cold air does fall, but when it's falling then there is warm air rising, on the other side.

No, the light still turns on and off. I tapped the power before it goes to the switch.

I wouldn’t want the light to stay on all the time.

:):)

NRALIFR wrote:
The RV fridges I’ve seen with a factory installed fan inside them has been at the very top, with the air blowing towards the fins. The one I’m thinking of was in a Norcold fridge, and it looked like a centrifugal fan laying flat against the top of the reefer compartment. It was inside a plenum box that directed the air across the width of the fins.

I made one for my fridge with a small 12v fan that was in my junk pile. I used it because it’s small, and it’s the right voltage. I tapped into the power going to the interior light, and it runs full time when the fridge is turned on.



:):)

Since you are using the interior fridge light as a 12vdc power source I assume the light does not go off when the fridge door is closed?

dougrainer wrote:

...The Interior refer relies on Convection air to flow from the bottom of the refer box UP the back wall and THRU the Evap fins and that removes the heat as the fins are 10 degrees colder than the interior temp...

The part quoted doesn't sound quite right. I'm not being argumentative but cold air falls. Seems to me that cold air would go down the rear wall.

The RV fridges I’ve seen with a factory installed fan inside them has been at the very top, with the air blowing towards the fins. The one I’m thinking of was in a Norcold fridge, and it looked like a centrifugal fan laying flat against the top of the reefer compartment. It was inside a plenum box that directed the air across the width of the fins.

I made one for my fridge with a small 12v fan that was in my junk pile. I used it because it’s small, and it’s the right voltage. I tapped into the power going to the interior light, and it runs full time when the fridge is turned on.



:):)

If you put a small fan inside the fridge to blow on the fins where is the ideal location? Is it bad to blow directly onto the temp sensor?

pianotuna wrote:

cooldavidt wrote:
Correct me if I'm wrong- I think a 12v fridge comes only in beer cooler sizes. Totally impractical to run an RV fridge on 12V alone.David

You are incorrect--though there are small units availble:

https://youtu.be/jMCdrE-4jBI

Segue - The Danfoss company has been making refrigerant compressors for many years. They don't kame refrigerators or A?C units, but their compressors are used by many companies.

Their 12VDC compressors are very interesting. They take 12VDC and run it into a 3 phase inverter. (3 phase motors are much mire efficient than single phase.) The 3 phase AC has variable frequency so that the compressor motor can spin at different RPM as the load requires.

bob_nestor wrote:
First, absorption units do better on propane and 110v than they do on 12v. The 12v is only there to try an maintain temps while traveling.

Second, minimize putting warm things in, so limit the number of times and the length of time you have the unit open and try not to put a lot of things in at the same time that aren't already cooled down.

Third, they all work by transferring the heat to the outside via the cooling coils in the back of the unit. For most installations that uses just normal airflow over the coils - since hot air rises it brings in cooler air at the bottom and exits at the top. Units installed with a top roof vent work better than units with the top vent on the side. Most manufacturers don't follow the recommendations for clearances in the back where the coils are and usually allow too much space. Limiting the space to the recommendations using baffles and such helps with the airflow. Adding fans can help, but be careful. Just moving a lot of air may not be as effective as moving the right amount of air over the coils. Faster air can create a turbulent airflow and a laminar airflow is what you want for maximum heat transfer.

Finally, since the unit's performance is based on the ability to transfer the heat outside thru the coils, the temp difference between the air at the coils and the outside air is important. Try not to park your RV in such a way that the sun is heating the area where the refrigerator is located. And remember that at most the unit can probably create about a 40 degree F temp difference, so it will work better when the outside temps are around 70 than it will when the temps a pushing triple digits.

Your description is inaccurate. The Refer REMOVES the heat Internally from the objects in the refer. The interior of the refer is SEALED from the outside. The OUTSIDE condenser fins do remove the heat. But they remove the heat from the OUTSIDE cooling unit assbly. The Interior refer relies on Convection air to flow from the bottom of the refer box UP the back wall and THRU the Evap fins and that removes the heat as the fins are 10 degrees colder than the interior temp. This is why it is important to NOT block the rear 1 inch of space on the back wall. Plastic bags are a no-no on the back wall. This is a very simple version of RV refer operation. Doug

Edd505 wrote:

dougrainer wrote:

bob_nestor wrote:
First, absorption units do better on propane and 110v than they do on 12v. The 12v is only there to try an maintain temps while traveling.

Second, minimize putting warm things in, so limit the number of times and the length of time you have the unit open and try not to put a lot of things in at the same time that aren't already cooled down.

Third, they all work by transferring the heat to the outside via the cooling coils in the back of the unit. For most installations that uses just normal airflow over the coils - since hot air rises it brings in cooler air at the bottom and exits at the top. Units installed with a top roof vent work better than units with the top vent on the side. Most manufacturers don't follow the recommendations for clearances in the back where the coils are and usually allow too much space. Limiting the space to the recommendations using baffles and such helps with the airflow. Adding fans can help, but be careful. Just moving a lot of air may not be as effective as moving the right amount of air over the coils. Faster air can create a turbulent airflow and a laminar airflow is what you want for maximum heat transfer.

Finally, since the unit's performance is based on the ability to transfer the heat outside thru the coils, the temp difference between the air at the coils and the outside air is important. Try not to park your RV in such a way that the sun is heating the area where the refrigerator is located. And remember that at most the unit can probably create about a 40 degree F temp difference, so it will work better when the outside temps are around 70 than it will when the temps a pushing triple digits.

Are you stating that if the outside ambient temp is 95 degrees then (using your 40 degree), the Interior refer temp will at best be 50 degrees? If so, go back to school and learn RV refers. While outside ambient will affect the capability of an RV refer, I have to check and repair refers in 100 degree Texas heat all thru the summer. With all parameters(install and ventilation at spec), I can get a good cooling unit to produce 28 to 32 degrees in the lower section. There is No such thing as a "40" degree difference in RV refers. Doug(41 years working on RV's and Refers)

Mine must be broke, I get zero in the freezer & 35-36 in the refer.

Notice I stated GOOD COOLING UNIT. RV'ers ALWAYS run their RV refers off level at times. Even that 30 minutes or 2 hours will start a small degrade in operation. Then add up years of those short times running off level and the COOLIN unit cannot perform as required in hotter operations. Your refer is OK. Anything below 40 degrees in the lower section is adequate and good. Doug

PS This type discussion is difficult. Kind of like arguing Gas mileage. There are so many variables that will affect Gas Mileage on the same model car.

This blog post may be of interest:

Fridge mod -- insulation and deflector

It definitely improved the performance of the fridge, but I did not measure the before and after temps or energy usage.