Even Compressor Fridges Need Venting

[DrJ]

15% less amps used

That's the amount I used less in power once I added my fan system to my dometic 110 litter compressor fridge. I think you could do even better in a hotter environment.

I ran an experiment in a controlled temperature shop over several days with and without my fan system.

Here's what I did:


This is the top vented area. I have removed the prewired fan wiring on the left. You can also see a temperature sensor on the left as well. More on that later.


Another view of it



Then I secured 3 computer fans to a metal trim that would be added at the top of the fridge compartment.



Here are the fans installed before the cover is back on:



I added a temperature sensor to turn on off it gets to 80 degrees and turns off at 65 degrees. So it doesn't run all of the time.



I had to add the switch to my bank inside the camper.


Finished outside:



Over several days I had the fridge on 110 volt power overnight to cool the fridge. It was never opened and was empty during the week. It is challenging for a fridge to keep constant cool with nothing in it so it runs a lot under these times.

The first 24 hours with no fans, I used 66.5 amps of power to run just the fridge. It got up to 91 degrees in the back of the fridge compartment despite only 69 degrees in the shop.

The second day of experiment I used only 55 amp hours with the fans running essentially the entire day. They do not shut off until 65 degrees. The shop stayed at 69 degrees. The fridge compartment also only reached 71 degrees with the fans.


A few things I learned:

The dometic fridge can use a lot of juice. 66.5 amp hours over 24 hours in a 69 degree shop is a lot.
Hard to run that thing without lots of solar and batteries.

Fans makes difference. Hot air is trapped in the top compartment that needs to be removed to increase efficiency. It can be 20-30 degrees warmer in that area.

I noticed similar if not better efficiency in my prior hawk with the old fan system. I think warmer weather would make the fans even better.

The fans only draw 0.3 amps per hour. I really like having them run only when it's too hot in there. The temperature sensor is a nice way to use the power only when you need it.

I am still doing my experiments to verify the data and will post updates as I get more data.






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[97grandby]

Great report on your findings. I can't say the exact amounts of battery power savings like you did, but mine was night and day between no venting and a vent and a fan.

 

[Alley-Kat]

The next test should be with the fridge filled with items.
Perhaps pre-chilled water bottles would be good, mimiking our pre-chilled food that gets loaded before we head out to camp.
As you say and know "It is challenging for a fridge to keep constant cool with nothing in it so it runs a lot under these times."
Let's see how many amps are used this way, with something in the fridge. A little difference or a big difference from an empty fridge to a full fridge?

- - - - - - - - - -

Another test might take a little effort, however, there are two modes of operating.

1) The start up mode where the fridge is first turned on with the inside at ambient temps and goes to the desired inside cool temp with the pre-chilled water bottles. How long does that take in time, and how many amps did it use to get to the desired inside temp?

And;

2) The normal running mode, which is once at the inside desired temp, how many amps does it use in the next 60 minutes? If we go on a more than one day camping trip, the normal running mode will be a more accurate reading of how many amps per day will be used, because the start up mode will only happen once for each camping trip (the first day).

I've found that the start up mode uses a lot of amps per hour compared to the normal running mode.
It would be interesting to see what your numbers are.

Thanks.

 

[DrJ]

Alley-Kat,

I like your ideas. Thanks for the input.
The normal running mode experiment will probably be my next one to try.

 

[68 Siesta]

I love it. My gut always led me to believe the fans would make a big difference. Glad to have some data to back that up!


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[DrJ]

I know 68Siesta and 97Grandby have noticed improved performance with a fan system for their fridges.

Anyone else install fans and notice improving fridge cooling or decreased battery usage doing this?

I think FWC should consider adding fans even on their compressor fridge systems. They already prewire it and install fans on the absorption models.
Why not use the fans on the compressors too?

It gets pretty hot in that compartment.
When we stayed at Valley of the Gods, it would get around 100 degrees in there when the outside temperature was 75 degrees. I can't imagine that helps with cooling.

 

[Stalking Light]

My Dometic 65 has a fan by the coils, looks to be a part of the fridge itself. I'm wondering if a second fan would help since the fridge is not a model of efficiency.

 

[97grandby]

My Dometic 65 has a fan by the coils, looks to be a part of the fridge itself. I'm wondering if a second fan would help since the fridge is not a model of efficiency.

Stalking Light, I have the same Dometic 65 with the factory fan from Dometic(Not FWC) and I first only added a larger vent and that helped some, but when I added the fan(on top of my vent), I noticed a large differance in power draw along with the fridges ability to keep up in hot weather. My entire mod cost less then 30.00 and 30 mins of time. Worth a shot to me.

 

[Stalking Light]

I already have an extra fan and a relay so I might just see what happens.

 

[Kodachrome]

My Dometic 65L has always done fairly decent with just the stock fan, gobs of reflectix insulation and existing vents but I do think I am seeing a bit of an improvement with the new 140mm fan. I can feel hot air coming out of the vent and with the fridge about half full the battery has not dropped below 70%, been on for a couple weeks now.

I just had my Trimetric 2030 delivered so I will have a better idea once that is in.

 

[DrJ]

Kodachrome,
Did FWC install your fan or did you do it aftermarket like the rest of us?

 

[DrJ]

My compressor fridge modification was entered into the Truck Camper Magazine competition.
It's #5.

Thanks for everyone who gave me help and advice with this one.

It still works great!

Here's the link if you are interested:

http://www.truckcampermagazine.com/camper-mods/january-super-mod-cup-contest-medium-mods/

 

[Happyjax]

Like your mod and voted for it

 

[97grandby]

Made a huge difference in my camper as well. I have voted for your mod. Good luck!

 

[Redfish]

Thanks, DrJ, for posting this great mod. I'll be doing this very soon.

Would you mind providing links to the fans, temp sensor and switch you used? Also, I assume that I can find temp sensors with a different range; can you recommend a good source?

In doing a bit of research, I found that some folks wired their new fan(s) to the existing compressor fridge fan wiring so that the added fan(s) only come on when the compressor and existing fan turns on.

I live in Florida but travel to the SW, PNW and Rockies in the spring-summer. I have a 2016 Fleet with the new 65L compressor fridge. I'm traveling and camping many days when the temps are in the mid-upper 90s and nighttime temps are in upper 70s and low 80s, particularly during my long E-W-E transits. I don't know what the temps are in the fridge compartment, but there are days and nights when the fridge rarely cycles off. I like that your approach that reduces cycling caused by the heat generated by the compressor when ambient temps are otherwise reasonable.

After reading about your mod, I'm considering a hybrid approach--one fan wired to the manual switch with a sensor to reduce cycling at lower temps and another fan wired to the existing compressor fan to boost cooling at higher temps. I like the option of being able to turn off one of the fans if parked for a long time unattended (i.e., backpacking and river trips).

Any thoughts or recommendations on this approach?

Thanks,
Jeff

 

[DrJ]

I bought all of the parts off amazon.

Here is the temperature control:
Thermostat Switch - Circuit On At 80°F and Off At 65°F - Large Flange https://www.amazon.com/dp/B0026RSBUQ/ref=cm_sw_r_cp_api_ep5GybMP1EGM2

I believe this is the correct fans:
Cooler Master Sleeve Bearing 120mm Silent Fan for Computer Cases, CPU Coolers, and Radiators (Value 4-Pack) https://www.amazon.com/dp/B000O8I474/ref=cm_sw_r_cp_api_9t5GybG61MD14

There appear to be lots of options for the fans and temperature control sensor. This is just what I used.

Your hybrid approach sounds like a good idea for your area.

My system was designed to be totally off by the switch inside. Or just to run if the temperatures became too high and automatically turn off if it gets below 65 degrees.

I turn it off when it's cold or when I am driving.

The temperature control is very easy to switch out for another one too if I didn't like its performance. But so far it's been just right.

Hope that helps you.


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[Redfish]

Yes, it does. Thanks very much.