Fridge Fan Exhaust

[Roger]

So I was having some issues keeping my Domestic 3 way from freezing hard at night to barely keeping up if it got over 85.

Solving the freezing problem was easy, just turn it to Medium or Low at night.

After looking around here and other corners of the internet I found a solution to the daytime "not keeping cold enought" issue. The exhaust stack is right next to the cooling fins, on top of the fridge. Not very conductive for cooling the fins...

I bought the cheapest computer fan and rocker switch at Radio Shack ($15 total)soldered the wires nice and good and zip tied the fan right next to the cooling fans. I think the blue glow will be a nice reminder to turn it off at night.

Hopefully this helps keep the cooling fins cool on my next trip. I guess it took me 30 min to get this one up and running...

Fan Specs
.16Amps
1.92 watts
2000 RPM
27.8 CFM
63 grams
80x80 MM

 

[Desert Rancher]

Here is some interesting info I found regarding cooling / venting.

"The purchase of an add-on fan can solve a lot of problems in border line venting, but is not a cure all for terrible venting. The important thing to remember is that the fan should be installed above the cooling unit, preferably right at the roof vent. The purpose of the fan is to improve the draft, not to blow air onto the cooling unit."

http://rvmobile.com/Tech/Trouble/vent.htm

I'm currently reworking my reefer right now and adding a fan. Will see how much it helps!

 

[Roger]

Very interesting. I tried out the fan today in about 88 degree weather in direct sun. It did help the the fridge cool down to about 48, rather than 50 plus. I mounted the fan on the opposite side of the exhaust and could feel the heat being blown out by the exhaust stack. When I turned off the fan I could feel the cooling coils warm up in about 3 minutes. I am not sure if the fan improves draft, but it does remove heat from the the top side cooling coils. I am thinking that a "close" baffle between the exhaust stack and the cooling coils may help a lot.
Oh and we all seem to be "bad venting" by this web site's authority.(?)
Oh yeah, post pics of your project too...



Here is some interesting info I found regarding cooling / venting.

"The purchase of an add-on fan can solve a lot of problems in border line venting, but is not a cure all for terrible venting. The important thing to remember is that the fan should be installed above the cooling unit, preferably right at the roof vent. The purpose of the fan is to improve the draft, not to blow air onto the cooling unit."

http://rvmobile.com/Tech/Trouble/vent.htm

I'm currently reworking my reefer right now and adding a fan. Will see how much it helps!

 

[chnlisle]

My views of propane cooling are no secret on this forum. Roger's fan experience underlines what I've said previously. 30 degrees below ambient is about the best you can hope for and it goes up appreciably as the temps rise.
Again not an issue if you never camp in weather above 65 degrees. However in those temps you don't need a fridge either. A properly loaded Coleman Extreme with block ice will give you great service into the 90's and above for a few days depending on how often you open it, how well you cover it, etc. But if you're in Cayonlands et al in July & August or sitting on a remote beach in Baja and don't want to drive out to the local store for ice every couple of days a 3 way propane fridge won't do the job an Engel or other similar units will do.

Add an 85 watt solar panel and with enough water & Hornitos you can stay for weeks on end. Venting, fans and other fixes in my experience (and I've tried them all) are just putting a Band-Aides on a hemorrhage. I don't come by this position lightly. I've owned several 3 way fridges both used and brand spankin' new, all with the same results.

Now at the risk of being just a tiny bit self serving and in the interest of public service let me offer the following. The current MSAP of an Engel MT 45 is $910 plus shipping. For members of our happy little band of mis-fits, I will be glad to order them and get them out to you for $835 including shipping. To offer this price and because of shipping to me, I must order them 3 at a time. So if three or more of you guys are interested let me know. They take me about week to turn around. I can order all of the Engel line as well and will provide you with a price on other models if you wish.

 

[MarkBC]

30 degrees below ambient is about the best you can hope for and it goes up appreciably as the temps rise.
Again not an issue if you never camp in weather above 65 degrees.

I recently switched to a DC-only fridge, but the "30 degrees below ambient at best" was not my experience with a propane fridge (Norcold N300) in the 5 years I had it in my FWC Hawk. Maybe some brands/models work better than others...?

With my N300 I was able to keep the freezer at about 10° with the fridge in the upper 30s -- in all ambient temperatures, including days with highs in the mid-80s, maybe 90. The only tricky thing about it was the need to adjust the control dial, mainly if it was very cold outside, to prevent it getting too cold in the fridge, because that dial isn't really a thermostat. But I never had to turn the setting above 4 (on a scale of 1-5, 5 being coldest) even in mid-summer temps (not mid-summer in the Sonoran Desert...but certainly in the 80°+ range). Cleaning the burner-slots is important for proper function.
Maybe "never camp above 65°" refers to a daily-average ambient temp not above 65°? Like, a high of 85° and a low of 45° gives an average of 65°? Otherwise...I don't see how any propane fridges could be sold since almost all of the USA has summer highs above 75°. Everybody's food would be spoiling if that was true.

Really, if there are some lab tests of this I'd like to read them. I'm willing to be educated by a controlled study.

Seems like manufacturers of compressor fridges would feature those studies in their ads to show that their product cools cooler than a propane fridge, but mainly I just read claims about how compressor fridges work at steep angles compared to propane fridges, that they're simpler, and that they have actual thermostats.
As I said, I no longer have a propane fridge, but I have a friend who recently bought a $50,000 Airstream trailer, and it came with a propane/3-way fridge...so if his milk curdles when camping in the summer I'd like to be able to tell him why.

BTW: My 2005 FWC Hawk came with an auxiliary fan mounted behind the fridge, up near the top, to be turned on if it's hot outside and more circulation is needed, but I think I only turned it on one time -- camping in the Alvord Desert mid-summer. I never needed it otherwise.

 

[DLN]

The most important feature of propane fridges is the venting and baffling within the rear compartment. If you look up the manufacturer's specs for installation you'll find that nearly all RV builders install these units incorrectly. I rebuilt the compartment in our Eagle per specs and had much better performance from it.

The 8 cubic foot fridge in our Class C was installed with a proper roof vent and worked almost perfect in all temps. The 4 cubic foot in our current trailer was installed in the same half ass manner as the FWC. The large open space above the fridge traps hot air and should be closed with insulation and a sealed curved baffle. Also the space in front of the bottom coils is too large and needs to be baffled down to and inch or less. In addition the specs call for a fan a few inches above the lower baffle to help maintain the chimney effect.

In all the installation specs I've read the preferred venting method is through the roof. Impossible in a FWC and nearly so in our trailer, so alternatives are provided by the fridge factories.

 

[Roger]

Do you have any pictures for "inspiration"?

Thanks

Roger


...I rebuilt the compartment in our Eagle per specs and had much better performance from it.
...

 

[DLN]

Roger,

We don't own the camper anymore and unfortunately I didn't take any pics. I will look up the Dometic specs and see if I can get you link to the installation info.

 

[Roger]

Well instead of waiting for inspiration I decided to be inspired.

We are not the only ones having problems with these 3 ways it seems....

http://www.lets-getaway.com/caravanfridges.htm
http://www.fiberglassrv.com/forums/f56/improving-fridge-venting-34320.html

Thinking about the problem I realized a couple of thing.

1. I need to improve air circulation
2. I need to cool the entire system, not just the upper cooling fins.

I realized that I need to reverse the fan so it blows hot air out, not across the fins. Easy fix.

I noticed that the greatest point producer of heat was the exhaust stack; the cooling fins next to the stack were so hot I could not touch them. When running off electricity it produced some heat. When running off LPG it produced even more heat!

I altered a 3 inch adjustable elbow stove pipe and some Aluminum flashing to isolate and re-direct the exhaust directly outside. I noticed a dramatic decrease of heat in the box. The fridge dropped about 5 degrees in about an hour.

I also installed a baffle above the access vent to increase air flow.

Right now I can feel a strong hot air current coming out of the top of the top vent, something I know was not there before.

I think next project will be to put some insulation in the gaps between the sides of the fridge and the camper.

So far so good.

Roger

 

[billharr]

Also disagree with the 30 degree difference. My reefer gets too cold not too hot. Aunt had a houseboat on Lake Don Pedro for years with a OLD full size reefer stayed cold on 100+ days.

Bill

 

[leadsled9]

My Norcold N300 stays very cold (32-34 at setting 4) even on hot 100 degree days. It works real good as long as the burner slits are clean and free from corrosion.

It is a pain to have to remember to turn it down at night or everything freezes.

 

[Desert Rancher]

Rodger,

How about some pics!

Thanks~
DR

 

[Roger]

I only have a pic of the exhaust heat shield/isolator. It is ugly and probably needs improvement, but it seems to do the job. It is also 100% reversable.

I moved the fan next to it on the vent cover.


Rodger,

How about some pics!

Thanks~
DR

 

[Desert Rancher]

Thanks Rodger, that's sufficient to get the general idea. I was thinking about using the reflectex insulation on the sides and top, since there is very little room.

 

[Roger]

Just wanted to report back my findings over the past two days.

Yesterday I set the fridge to Med on the lpg setting and the fridge was about 48 degrees. The outside temp was about 86 degrees. Usually with the gas on high it would cool to about 50 degrees.

Today it is 90 degrees. The lpg setting is on high. The fridge has been in the sun all day. The temp inside the fridge is 40 degrees.

I may add another exhaust fan but I think I have resolved the main issue.

Roger

 

[Desert Rancher]

Good work!
FYI - I got this fan: http://www.amazon.com/gp/product/B002N5YDG2/ref=pd_lpo_k2_dp_sr_2?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B003UHTC8G&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=02EV73NC15J8KN28N1ED

It has two thermal switches (one attaches to the reefer coils) to turn on/off at a preset temp. The other one monitors ambient temp.

The ambient temp and the coil temp must be >80 to turn the fan on. Otherwise it not cool properly. After all it is a "still".

Seems to be a well thought idea.

 

[Roger]

DR,
I rolled up some reflectex and zip tied it in a roll to create dead are space in my unit. I had about 1 inch on the (facing the fridge from the outside) right and about 2 inches on the left. I didn't even bother with the top as it was less then a half inch. The two fans and the exhaust stack helped the most.

Thanks Rodger, that's sufficient to get the general idea. I was thinking about using the reflectex insulation on the sides and top, since there is very little room.

View attachment 12484

 

[cwdtmmrs]

DR,
I rolled up some reflectex and zip tied it in a roll to create dead are space in my unit. I had about 1 inch on the (facing the fridge from the outside) right and about 2 inches on the left. I didn't even bother with the top as it was less then a half inch. The two fans and the exhaust stack helped the most.


Where did you install the second fan and is it the same as the one discribed in your 1st post?


Thanks,
CWD

 

[Roger]

Where did you install the second fan and is it the same as the one discribed in your 1st post?


Thanks,
CWD


I installed a 120 MM case fan as the secondary. I think it was $7 at Fry's electronics, a way better deal than Radio Shack.
Specs
.33 AMp
57 CFM
140 Grams

You can see part of my Aluminum baffle in the "fridge bottom" pic. I installed the bigger fan on other side of the vent, again blowing out. I think I spent about $45 total on this project and I still have 8 feet of sheet aluminum left over, it was the most expensive item.

 

[cwdtmmrs]

Thanks Roger. I am still not sure I completely understand your baffle arrangement. Did your fridge come with the perforated metal wind shield on the burner or did you add that? Also what are the two red LEDs in the lower left and is the white thing a remote thermometer?

Thanks,
CWD