Ventilation of Compressor Refrigerators

[peteco]

I am starting this thread because I have seen different recommendations regarding venting of the condensor units on a compressor refrigerator. The factory installed units appear to have no ventilation through the wall to the outside of the unit. Yet some people on various forums that have replaced the absorption fridge with a compressor unit recommend using the existing through-the-wall vent to provide ventilation air to the condensor. My absorption fridge is borderline working so I may replace it soon with a compressor unit and I would like to have the venting figured out before I replace.

[avanti]

If I had outside vents, I would certainly use them. However, internal venting works just fine also, when properly set up. So, I wouldn't cut holes in my van for this purpose, but if you already have the holes, you may as well use them.

[booster]

I would also say that if you have the outside vents, use them, but I don't think I would cut the van either if they weren't there.


I think the outside vents have some good advantages as long as you get the airflow working well in the less controlled outdoor environment. You normally have cooler air available through the large openings, you can seal up the frig to the inside so it is quieter and add some insulation if there is space to improve it's efficiency, you don't add heat an already hot van, etc.


The downside in the venting is that you have to deal with wind, driving time airflow, hot van sides, etc. Careful use of baffles, ducts, seals, etc is needed, but certainly not overly difficult.


We have an Isotherm which uses the Danfoss compressor/condenser/fan as a small box shaped assembly that is mounted on the upper rear corner of the frig. Quite efficient use of space and cooling air because of the fan blowing right on the hot parts. Ventrifigo, I think, uses the same style.



We did have trouble in the beginning as the air would not get out of the vents and would just loop around the compressor area. It blew in toward the center of the van and came out all around the assembly and needed to change direction to get to the top vent in the wall. The air would not get to vent, going back into the inlet of the fan getting hotter and hotter.



The final solution, after lots of experimenting, for us was to make a duct out of 3/4" foil faced insulation board that picks up air at the bottom vent and goes to the fan inlet and is sealed to the inlet. A baffle was added half way up the van wall to separate the bottom vent from the top vent and fiberglass insulation put around it to seal it up well.



The cooling air now has no choice than to come in the bottom vent, go through the cooling assembly and out the top vent with no chance of looping.



We had run baseline testing on the bench as the first thing when we got the frig, to be able to know how well it worked in place, and with the duct system we are essentially identical to the best case testing on the bench, so we are about as good as we can get. We don't see any real difference in hot, cool, wind, no wind, driving or not, even in the sun or not, so very happy with the results. Along the way when trying to find the best fix, I had added a fan to the upper vent, which we never have needed to use since the duct was installed. I tested a while ago with it for fun and it power but didn't save any.


I think the units that have the separate compressor from the condenser, with the coils on the back of the frig would be harder to control the air as precisely, but I don't have any experience with them to know how they run in the van compared to best case on the bench.


Our only trouble with our frig is has been with failures of the mechanical thermostat a couple of times. It is right inside the door, so it appears to get a lot of condensation on it.



We have also experimented quite a bit with the sensor position in the freezer, on the freezer, in the frig, etc to try to get the most uniform temp in the frig. It is a tough deal as we tend to have a lot of stuff in bags that block air circulation.

[peteco]

Nova Kool discusses ventilation somewhat:

Nova Kool, refrigerators, freezers, Marine, RV, Truck

I think this is directed at separate component units for boat installations but the principles are the same as for an all-in-one unit.

[peteco]

Interesting (long) discussion here on ventilation issues with Nova Kool fridge in Airstream class B. Airstream did not have any ventilation on some installations. Several owners installed internal vents which improved performance greatly, but had some minor problems in hot weather. There was some discussion about adding external ventilation, though no one had gone to the extreme of cutting openings, which I would definitely not do.

Refrigerator ventilation - Airstream Forums

[booster]

Originally Posted by peteco

Interesting (long) discussion here on ventilation issues with Nova Kool fridge in Airstream class B. Airstream did not have any ventilation on some installations. Several owners installed internal vents which improved performance greatly, but had some minor problems in hot weather. There was some discussion about adding external ventilation, though no one had gone to the extreme of cutting openings, which I would definitely not do.

Refrigerator ventilation - Airstream Forums

Just a thought based on our Roadtrek configuration from the factory. They had added an opening in the floor of the frig compartment to let more air into the lower vent area, maybe to get it to a different pressure area than having it on the same side as the outlet. Especially if you were fan forced, some sort of floor in and out system might help.


This is one of those cases where those of us with the big holes already in the side of the van came out better, maybe.

[rowiebowie]

RV makers often fail to provide adequate (or any) ventilation, especially for compressor fridges. Your existing external vents should be adequate for a compressor fridge replacement. You'll need to have a standard plug that converts from 12v to 120v when plugged in. The power should be there from your 3-way fridge.

Here's another related thread.

http://www.classbforum.com/forums/f5...html#post83678
.

[booster]

Originally Posted by rowiebowie

RV makers often fail to provide adequate (or any) ventilation, especially for compressor fridges. Your existing external vents should be adequate for a compressor fridge replacement. You'll need to have a standard plug that converts from 12v to 120v when plugged in. The power should be there from your 3-way fridge.

Here's another related thread.

http://www.classbforum.com/forums/f5...html#post83678
.

If he is getting and aftermarket install unit, he would be able to get a 12v only unit if he chose to. They are usually a little less expensive and the Danfoss is a native DC system anyway, so why convert twice to get what you started with. You also wouldn't need to to ever supply 110v. We have had 12v only for years and wouldn't go any other way, as it is just a waste of money and wiring.

[GeorgeRa]

I agree with comments above to keep outside venting if already present. The key is to keep a good airflow by convection, so there needs to be provision for air intake below the condenser and exhaust above to enhance a chimney effect - height will help to move air.

My Isotherm fridge condenser has an electric pancake fan blowing air across it, I changed the fan with a quieter and more efficient one. Due to my galley aluminum framing there is unobstructed flow in the back side of the fridge.

If you go with Danfoss type of a fridge consider replacing the electromechanical capillary thermostat with modern electronic one like for example the Smart Energy Controller for additional energy savings. It allows variable speed of the compressor making it more efficient and quieter.

https://www.youtube.com/watch?v=F2hAWqFVkUI

[rowiebowie]

Originally Posted by booster

If he is getting and aftermarket install unit, he would be able to get a 12v only unit if he chose to. They are usually a little less expensive and the Danfoss is a native DC system anyway, so why convert twice to get what you started with. You also wouldn't need to to ever supply 110v. We have had 12v only for years and wouldn't go any other way, as it is just a waste of money and wiring.

My Novacool does not runs off inverter. Either 120v when plugged in or 12v DC directly off batteries. Seems like the best of both worlds.

.

EDIT: From my Novacool Manual - It has a Danfoss compressor with AC option.

2. Electrical:

When fitted with the optional AC/DC module, both AC & DC power can be connected to the module at the same time. The unit will always run on AC when AC is available. Should the AC be disconnected there is a 1 minute time delay before the unit continues running on DC. If AC power is reestablished there is no delay, and the unit will immediately resume running on AC.

The DC models are 12 & 24 VDC (the only consideration is the models supplied with an interior light, either 12VDC OR 24 VDC). The AC/DC models work on both 12 & 24 VDC as well as from 100-240 VAC 50/60hz. (The interior light on the AC/DC models is always 12vdc regardless of the DC supply voltage). Both modules “auto” sense the supply voltages so no wiring adjustments are necessary other than following the guidelines for DC fuse sizing.

[booster]

Originally Posted by rowiebowie

My Novacool does not runs off inverter. Either 120v when plugged in or 12v DC directly off batteries. Seems like the best of both worlds.

.

Except that when you are on shore power, the frig is just running a converter to DC, so there is really no reason to pay for that converter. It is running on DC anyway, and your main charger is generating DC from the 110v so the same thing. Less electronics is always a good thing, IMO.

[avanti]

I agree with Booster (although I also agree that it makes little difference one way or the other). With the Danfoss compressor, if you have 12VDC available, you should use it. It doesn't matter whether it is coming from the battery or from a converter. The 120VAC input is just a power brick. It makes little sense in an RV. I guess the exception might be if you are parked somewhere in storage and want ONLY the fridge running. In that scenario, the smaller power brick might be more efficient than the big converter.

[rowiebowie]

My comments were to assist the OP's understanding of how mine works.

My point is simply that I don't have to engage my RV's inverter and thus another source of drain on my batteries. When hooked up to A/C, I don't care if it is powering directly from AC or if the AC is charging the batteries which are then powering the fridge. Either source is automatic and of no detriment to me. Mine came with the AC option standard, so I did not have to make a choice.

If the OP wants to order his without the AC option, and it saves a few $, that's his call.

[GeorgeRa]

I purchased my Isotherm 85 with AC/DC option. Mostly the fridge is powered by DC, but often, I have it powered by AC via shore power plugged-in with everything else being turned off, only the fridge is on.

When we comeback from a trip I turn off the main battery disconnect (Intellitec) primarily due to safety concerns. The fridge is on the dedicated CB on the panel which is easily accessible, so only the main CB and the fridge CB are on. If the van is parked inside, I disconnect the Morningstar solar charge controller (CBs) and batteries will stay charged for long time, if parked outside I leave solar charging active.

If I had a DC fridge only, I wouldn’t leave it on, I like turning DC off when not in use.

[thanasis]

My Dometic fridge has the compressor located high. I drilled vent holes right next to it ( click on link below for photo) and installed the fan next to the vent. I left a gap at the floor of the cabinet above the sliding door step to allow air in. That fan is not the factory one but one from a PC that has 2 speeds governed by a temp sensor. It runs in high in speed only if the temperature inside reaches 90F. At low speed is a lot quieter than then factory one. I have had this setup working w/o any issues for years.

Class B Forums - thanasis's Album: D - Picture

Thanasis

[peteco]

Originally Posted by thanasis

It runs in high in speed only if the temperature inside reaches 90F. At low speed is a lot quieter than then factory one. I have had this setup working w/o any issues for years.
Thanasis

How did you do this? I run a ventilation fan now on its highest speed and it is loud. It would be great to have it run at lower speed at lower temps.

[avanti]

Originally Posted by peteco

How did you do this? I run a ventilation fan now on its highest speed and it is loud. It would be great to have it run at lower speed at lower temps.

This is easily accomplished using one of several temperature-controlled fan speed controllers available on eBay and Amazon. They are very inexpensive and work well. I use this one:

fan controller.jpg

It will make you fans dramatically more quiet.

[thanasis]

Originally Posted by peteco

How did you do this? I run a ventilation fan now on its highest speed and it is loud. It would be great to have it run at lower speed at lower temps.

My fan has a built-in-temp sensor located on the fan frame near the center. I wired it the same way as the original one, nothing special.

BTW, I just found this one on Amazon that has a sensor at the tip of a wire offering the flexibility of sensing the temperature not only at the fan's location ( as mine) but anywhere the wire can reach.
According to the chart printed on the box, it runs slower and quieter as long as the temp at the sensor's location is less than 32C ( 89.6F)

Avanti's recommendation would probably give you more flexibility, if it provides a way to set the trigger temp

[peteco]

Originally Posted by avanti

This is easily accomplished using one of several temperature-controlled fan speed controllers available on eBay and Amazon. They are very inexpensive and work well. I use this one:

Attachment 6715

It will make you fans dramatically more quiet.

I could not find this one on ebay. Do you have a link?

[avanti]

Originally Posted by peteco

I could not find this one on ebay. Do you have a link?

That stuff comes and goes. Looks like that one is gone. There are many other choices, though. Some are even programmable.
Just do the following eBay search:

fan speed controller temperature