Venting hot air from refer coils

[Al Bear]

My Trillium has a 12-volt refer. The hot coils are on the back of the unit, that is, inside of the fiberglass cabinet/kitchen counter which also contains the sink and stovetop and some drawers. When the refer is running, the hot air is trapped inside the cabinet, unless you leave one of the drawers open.
That seems really dumb to me. Should I cut into the cabinet to allow the air to circulate? I would not install a refer in my kitchen at home inside of a completely sealed closet or cabinet, so why would I do that to my 12-volt in the Trill, especially since I would like the battery to last a few days before it's run down?
Note that a 3-way has venting to the outside built in: it's unavoidable because a 3-way burns propane. But this is a new Trill, it never had a 3-way. The only holes in the outside wall on that side are hookups for water and shore power.

[Borrego Dave]

Albert you should have two vents in the outside wall, one low and one higher. Are you saying there are no outside vents? Can't see a manufacturer doing that. Did you install this refer ? Heat from propane use is normal but shouldn't be vented or go to the inside. How about a picture from the outside behind the refer. Dave, the Trill king will chime in soon.

[cpaharley2008]

I'd cut a hole in the cabinet to let all the heat to escape as it will get worse in hotter weather. They have a lot of nice finished round vent covers at Home Depot and on line. The unit will run more efficient with less heat build up.

[Timber Wolf]

I have plans to install a 12V refrigerator in my Scamp some day. The location is right below a window so I plan to have an air intake vent in the bottom of the cabinet below the fridge and one in the top back of the counter top. This way in the summer I can crack the window and just by convection (I think that is the term, hot air rises anyway) it will draw and vent outside.

[Bob Miller]

First I'd check the MFG's installation instructions. Some refrigerators vent under the bottom. They may think it's an OK installation.

But, rather than using a hardware store vent, I would check with the local RV store and/or on-line suppliers for an appropriate vent to install to move more air behind the refrigerator.

[kirkman]

Originally Posted by Borrego Dave

Albert you should have two vents in the outside wall, one low and one higher. Are you saying there are no outside vents? Can't see a manufacturer doing that. Did you install this refer ? Heat from propane use is normal but shouldn't be vented or go to the inside. How about a picture from the outside behind the refer. Dave, the Trill king will chime in soon.

This is a 12 volt fridge..NOT a propane one.


Sent from my iPhone using Fiberglass RV

[Raz]

The California Trilliums came with a Dometic DC compressor fridge. No vent. I asked about venting and was told they had "run the numbers" ??? and that it was fine. The manual suggests venting at the bottom, which is difficult once the fridge is in place. Since heat rises, it's also inefficient. I would remove the fridge and place a standard fridge vent as high as is practical. I believe I got the only trailer they made with a 3 way. Raz

[Al Bear]

Not a diy, fridge came like that. See Registry for exterior pix, including one showing driver's side. That part of the hull is as smooth as the head of ... your favorite bald actor. (The fridge is in front of where you see the water and electric hookups.)
The reply from Raz gives a flavor of what some mfgr's think of the laws of physics. I wonder what "numbers" they ran: my inconvenience (batteries run down faster) vs. theirs (they gotta figure out where to put the vents)?
The Dometic manual that I have shows input venting low, output venting high. Low could be under the fridge, which sits on legs, just gotta make sure it's not blocked by the rug. Where to put the high vent will be the challenge, the higher the better. Haven't yet decided whether it should be interior or exterior. If I go with exterior I will certainly use an r.v. part intended for this application. You want a vent that will not admit rain easily.
Although an interior vent might allow more compressor noise into the living space, I'm reluctant to do much cutting in the outer hull. I don't want to compromise strength or cause cracks to develop over time.
In any case, "convection" is indeed the word.
Dometic says you could leave a gap in the cabinetry at the top of the fridge so that the hot air can vent towards the front. Not the best solution because the flow over the top of the fridge would give at least some of the heat back to the interior, from which your battery will need to pump it out again. I might be able to just replace the solid trim that closes that gap at present with a grill of some kind.

[Al Bear]

"... heat back to the interior ..." I mean back to the interior of the fridge via conduction through the top. I'm not too concerned about a little extra heat in the living space. Can just leave a window open a crack, like T. Wolf says. Plus those Trillium jalousie windows, which we love for the way they admit the breezes, are not all that airtight anyway.

[rbryan]

Originally Posted by Bob Miller

First I'd check the MFG's installation instructions. Some refrigerators vent under the bottom. They may think it's an OK installation.

But, rather than using a hardware store vent, I would check with the local RV store and/or on-line suppliers for an appropriate vent to install to move more air behind the refrigerator.

Great advice. If you want to retrofit with a compressor based fridge, check to see if it's "self venting" or vents to the outside. Some will require a vent to outside, and some will not.

[redbarron55]

You could vent to the outside or the inside, but the top and bottom vents are neceessary.
I have a 12 volt swing compressor Norcold and it's book gives the dimensions required and as a part of the base there is a grille that the electronics live behind for the bottom and you have to make accommodations for the top venting in installation.
A small 12 volt fan could help reduce the need for vent space if installed.
My Norcold has a 12 volt power inlet along with a 120 VAC plug and it switched between the two with preference to the 120.
While driving the 12 volt will keep the reefer cold and the question would be does the heat build up in the camper during this time?
I think that 110*F is close to the limit for the Norcold with the electronic oscillator, but I don't know about your unit if it is a 12 volt motor directly off the 12 volt. The hotter the environment the harder the reefer will have to work both because of the heat conduction into the unit and the differential temp for the coils.
You have to make accommodations for the cooling flow through of the air rising as it is heated or the thing won't work well. The Norcold book covers this as the main reason for dissatisfaction with their units. It is up to the installer to make certain that the ventilation is adequate.

[Mike Magee]

Some of us are experts at venting hot air.... not necessarily from the backs of refrigerators, though.

If your concern is operating the fridge within allowable parameters without damaging the unit, you would want to run the unit under normal (for you) camping temperatures and measure the temperature at the rear of the fridge; then compare that to the mfr's specs for allowable operating temp. If it's exceeding the allowed upper temp limit, you'd have to vent it in some manner. If it is not, you have no problem.

Absent some hard data, it becomes a question of "how do you feel about it." In other words, if the specs and measurements will not be available to you, go with your gut... and err on the side of caution.

(Now, how much have I heated up this thread with all that verbiage?)

[Raz]

Unfortunately because of the construction you will have to pull the fridge to see what can be done. There is not a lot of room between the top of the fridge and the bottom of the sink. This may force you to vent outside. If it were me I would add one vent and see how it works.



For what it's worth Trillium didn't do a great job installing my 3 way either. I had to remove the vent and cut a much bigger hole to get my fridge to work right. Two 4" holes weren't enough.

[redbarron55]

For the Norcold unit the problem is not the coil or the compressor, but rather the inverter oscillator under the refrigerator. This part is transistorized and produces the 22 volt 60 HZ chopped DC that runs the swing compressor (a special little thing that vibrated back and forth to pump instead of going round and round).
The Dometic may use this or a Danfoss type compressor that goes round and round. That compressor will not care so much about the temp either, but either system will be very much more efficient with cooler air passing over the coils and to do this there has to be convection cooling taking place behind the fridge.
The rising hot air brings cooler air in at the bottom.
Even with the camper traveling along the road (closed up) the coolest air will be at the bottom. Probably enough leakage with the florida windows keep the air temps from going too high,

[Al Bear]

I might go with one exterior up high. Looking at the second pic in Raz's last post, you can see that there is a double hull behind the stove/sink that goes up to the overhead cabinet. I think there is a couple of inches of empty space between that hull and the outer hull. I could cut a hole in the outer hull about 2 feet above the belly band. That would give a relatively tall air column for convection effect. Warm air in the space behind the fridge should rise up into that space and out the vent.
I would just need to make sure there is enough opening down low to suck in make-up air for what is venting out the top.
I also need to make sure the space behind the fridge actually communicates with the space above. Feeling around with my hand it seems like there is a horizontal fiberglass panel that separates the two. Maybe I could drill a bunch of holes in in.
I'm not worried about overheating the unit. I'm not planning to take it to Death Valley in the summer, or to Phoenix. I would just like to not run down my batteries so quickly.

[tractors1]

Hot air tends to rise according to my Physics 101 class. I'd vent it outside the shell and provide an outside air inlet vent below the cooling fins, again outside the shell.
Any other method is less efficient as far as the thermodynamics of cooling.

Charlie Y