Ventilation of Compressor Refrigerators

[pattonsr]

If you want to eliminate venting problems, the Nova Kool RFU 7300 is a 6.8 cf which has dual compressors and front venting at the bottom. Air is brought in at the bottom sides and blown out by two fans over the two compressors at the bottom . The Fit RV and the Coachmen Galleria use this new model. The opening can be heavily insulated on all sides since no space is needed for ventilation. Great for hot climates.

[peteco]

Originally Posted by pattonsr

If you want to eliminate venting problems, the Nova Kool RFU 7300 is a 6.8 cf which has dual compressors and front venting at the bottom. Air is brought in at the bottom sides and blown out by two fans over the two compressors at the bottom . The Fit RV and the Coachmen Galleria use this new model. The opening can be heavily insulated on all sides since no space is needed for ventilation. Great for hot climates.

I just noticed this on the Novakool site. Looks like solar heating of the back cavity has caused efficiency problems with with some of their refrigerators. If venting of the back cavity is not possible it looks like the back wall should have as much insulation as possible or a radiant heat barrier.

http://novakool.com/products/two_doo...tional2015.pdf

[avanti]

Venting the back of the cabinet is indeed often very important. It is also usually easier than it looks, if you are using an exhaust fan. Don't be afraid to forced-vent to other cabinet space. In our case, we have a fan that blows into an adjoining closet. There is almost always plenty of leakage, and even if not you can usually create some.

[booster]

Originally Posted by peteco

I just noticed this on the Novakool site. Looks like solar heating of the back cavity has caused efficiency problems with with some of their refrigerators. If venting of the back cavity is not possible it looks like the back wall should have as much insulation as possible or a radiant heat barrier.

http://novakool.com/products/two_doo...tional2015.pdf

I think it is important on all of the styles and inside or outside vents. Beyond the radiant heat, the outside wall can get hot enough to create a large chimney effect that can cause backwards looping of the air you want going over the cooling coils or compressor(s). Insulation and baffles required in many cases I think. I know we needed to do both.

[GeorgeRa]

On my Isotherm fridge I replaced the factory fan with a quieter one, it pulls cooling air across the heat exchanger and warm air moves upwards by convection.

The convection heat transfer mechanism is your best friend in keeping a fridge efficiency up.

https://www.amazon.com/120x120x25mm-...ilpage_o06_s00

[peteco]

Originally Posted by GeorgeRa

On my Isotherm fridge I replaced the factory fan with a quieter one, it pulls cooling air across the heat exchanger and warm air moves upwards by convection.

How does the convection warmed air that has moved upwards exit the cavity?

[GeorgeRa]

Originally Posted by peteco

How does the convection warmed air that has moved upwards exit the cavity?

No cavity, the fan moves air back from the compressor cavity and convection moves it up.

My aluminum framed cabinetry is bolted to the floor so there is clearance between vans wall and cabinets.

[@Michael]

I'm struggling to get better performance from my Coachmen Crossfit/Beyond Nova Kool compressor refrigerator. It seems like the best I can get is around 40-45F colder than ambient with compressor running continuously.

I'd like to get an idea what a reasonable level of performance is, and if mine is performing below what's normal, strategies for improving performance, including improved venting.

Coachmen started out with no venting, then issued a bulletin to correct. The correction is to cut open the wood platforms above and below the fridge, and section off the back of the fridge with insulation, and put a small vent in the cabinet frame above the microwave. The theory seems to be that air will be drawn up from under the fridge, through the holes in the platforms, and egress above the microwave.

https://dealers.forestriverinc.com/d...in/2250901.pdf

My dealer drilled 3 - 2.5" holes in the top and bottom platforms, all of which are partly blocked by the fridge, and 3 - 1 1/4" holes above the microwave. They left me with no more than 6 sq in below the fridge, 12 sq in above the fridge, and 4 sq in above the microwave. The microwave has a bit of venting built into its chassis, perhaps another 6 sq in, so no more than 6 sq in available from bottom to top.

I've read through the various threads and Nova Kool docs, such as this and this and the installation guide for the fridge, where 60 sq inches top and bottom are recommended.

From the above links, it appears that:

To test the effectiveness of the ventilation, measure the exhaust air inside the enclosure. The temperature should be no more than 5 degrees higher than the air entering the enclosure (ambient air temp).

I've experimented a bit, and am certainly not meeting the 5F temperature rise parameter.

I sent Coachmen a request for more information or recommendations on refrigerator performance, and they punted the ball over to pretty much anyone other than them. So it looks like I'll deal with this myself.

• I've added 3 80mm computer fans directly above the 3 holes between the fridge and microwave compartments, first with high speed fans, and now with temperature controlled variable speed fans. This seems to help somewhat.
• I've opened up the cabinet frame above the microwave to approximately 1 1/4 x 14" and installed a vent cover with more free air that the one installed as a part of the Coachmen service bulletin.

I suspect though, that the bottom of the fridge compartment is still not opened up enough.

What' a reasonable expectation for cooling performance? Should I be able to do better than 40-45F of temperature differential?

I'm assuming that working out a venting strategy is the best path forward. Am I on the right track?

Any suggestions?

--Mike

[booster]

Originally Posted by @Michael

I'm struggling to get better performance from my Coachmen Crossfit/Beyond Nova Kool compressor refrigerator. It seems like the best I can get is around 40-45F colder than ambient with compressor running continuously.

I'd like to get an idea what a reasonable level of performance is, and if mine is performing below what's normal, strategies for improving performance, including improved venting.

Coachmen started out with no venting, then issued a bulletin to correct. The correction is to cut open the wood platforms above and below the fridge, and section off the back of the fridge with insulation, and put a small vent in the cabinet frame above the microwave. The theory seems to be that air will be drawn up from under the fridge, through the holes in the platforms, and egress above the microwave.

https://dealers.forestriverinc.com/d...in/2250901.pdf

My dealer drilled 3 - 2.5" holes in the top and bottom platforms, all of which are partly blocked by the fridge, and 3 - 1 1/4" holes above the microwave. They left me with no more than 6 sq in below the fridge, 12 sq in above the fridge, and 4 sq in above the microwave. The microwave has a bit of venting built into its chassis, perhaps another 6 sq in, so no more than 6 sq in available from bottom to top.

I've read through the various threads and Nova Kool docs, such as this and this and the installation guide for the fridge, where 60 sq inches top and bottom are recommended.

From the above links, it appears that:



I've experimented a bit, and am certainly not meeting the 5F temperature rise parameter.

I sent Coachmen a request for more information or recommendations on refrigerator performance, and they punted the ball over to pretty much anyone other than them. So it looks like I'll deal with this myself.

• I've added 3 80mm computer fans directly above the 3 holes between the fridge and microwave compartments, first with high speed fans, and now with temperature controlled variable speed fans. This seems to help somewhat.
• I've opened up the cabinet frame above the microwave to approximately 1 1/4 x 14" and installed a vent cover with more free air that the one installed as a part of the Coachmen service bulletin.

I suspect though, that the bottom of the fridge compartment is still not opened up enough.

What' a reasonable expectation for cooling performance? Should I be able to do better than 40-45F of temperature differential?

I'm assuming that working out a venting strategy is the best path forward. Am I on the right track?

Any suggestions?

--Mike

I can't speak for Novakool performance, but that sounds bad for any compressor frig.


We have a 3.0cf Isotherm with optimized venting to the outside of the van and we sat in Zion Nat Park at 100*F with frig side on the south facing full sun, for several days. Frig never went over 38*F the whole time, and the compressor speed was not even turned up off of minimum or up one step of 6. Duty cycle of the compressor was probably a bit over 50% but not near continuous.

[GeorgeRa]

If you calculate your vents openings you are about 35% undersized according to the Isotherm 3 Cu FT fridge 9 cm diameter hole requirements. I would suggest looking your fridge installation manual and follow vent size recommendation.

[VanFan]

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.

I added a fan to circulate air between the space behind the fridge and a space below an adjacent berth which is vented to the van's living area. Here's the fan I used:

https://www.coolerguys.com/products/...0mm-cooler-kit

Note that it has built in thermostatic control. On @ 88°F Off @ 81°F (+/- 1°). Very quiet (I can't hear it at all) and it only draws about a tenth of an amp. Moves a surprising amount of air.

[avanti]

Originally Posted by VanFan

I added a fan to circulate air between the space behind the fridge and a space below an adjacent berth which is vented to the van's living area. Here's the fan I used:

https://www.coolerguys.com/products/...0mm-cooler-kit

Note that it has built in thermostatic control. On @ 88°F Off @ 81°F (+/- 1°). Very quiet (I can't hear it at all) and it only draws about a tenth of an amp. Moves a surprising amount of air.

That is exactly what I did. IMO, forced exhaust from the fridge compartment is the easiest and most effective way to deploy a fan in aid of the fridge. Those little computer fan controllers are great--cost almost nothing and work perfectly in this application.

[@Michael]

Originally Posted by booster

I can't speak for Novakool performance, but that sounds bad for any compressor frig.

Thanks. I suspected that to be the case, and you've confirmed it.

Originally Posted by GeorgeRa

If you calculate your vents openings you are about 35% undersized according to the Isotherm 3 Cu FT fridge 9 cm diameter hole requirements. I would suggest looking your fridge installation manual and follow vent size recommendation.

It's a Nova Kool 6800, which as far as I can tell, is supposed to have 60 sq in bottom and 60 sq in top. So I'm way more than 35% undersized.

Originally Posted by VanFan

I added a fan to circulate air between the space behind the fridge and a space below an adjacent berth which is vented to the van's living area. Here's the fan I used:

Thanks. Right now I have three 80mm fans sucking air out of the fridge compartment:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

These are quiet, but don't seem to move as much air as the noisy ones that I had running for a week or so.

Originally Posted by avanti

That is exactly what I did. IMO, forced exhaust from the fridge compartment is the easiest and most effective way to deploy a fan in aid of the fridge. Those little computer fan controllers are great--cost almost nothing and work perfectly in this application.

Thanks.

I think my next step is to pull the fridge and figure out how to open up the bottom and see if that helps the fans move more air. AFAIK, it has the least sq in of vent. Otherwise, more powerful fans.

[GeorgeRa]

Originally Posted by @Michael

Thanks. ...........................
It's a Nova Kool 6800, which as far as I can tell, is supposed to have 60 sq in bottom and 60 sq in top. So I'm way more than 35% undersized.

........................

If you are within the ventilation specs of your fridge it should work great, good luck. Compressor fridges tend to be rather robust so if yours is not working as it supposed to perhaps it is the fridge.

[@Michael]

Update on my Coachmen Crossfit/Beyond Novakool refrigerator performance described here.

The TSB mentioned here had the dealer open up better vents below and above the fridge, and add a layer of insulation in the fridge cavity to help gain a chimney effect behind the fridge. My Crossfit was serviced, but fridge performance was still poor.

Here's what I did:

I pulled the fridge and set it on a plastic stool. It was surprisingly easy to pull, and lighter than I thought.



I reinforced the floor of the fridge compartment with some aluminum angle, and then opened up the entire back of the compartment floor, including removing what was the original wood bracing. The coach already has a large vent in the compartment under the fridge, but from there to the fridge cavity was only three 3" round holes that were half blocked by the fridge itself. So this allowed air upwards into the fridge cavity. I also re-positioned the insulation layer so that it was further back, re-positioning some electrical and plumbing to provide more clearance around the coils, and used insulation and Gorilla tape to secure and seal the compartment.

Fridge compartment floor:


Insulation - with Gorilla tape to keep it in place:


I then opened up the top of the fridge compartment with three 4" sq. holes up into the microwave compartment instead of the original three 2.5" round holes, securing the floor of the microwave compartment to the wall of the Transit with aluminum brackets in place of the original wood support:





I now have a straight shot bottom to top behing the fridge.



I re-positioned the insulation in the microwave compartment, and added a double layer of pink ridged insulation at the top of the microwave compartment to better isolate that compartment from heat being pushed down from the roof.



And placed two 120mm computer fans over the three microwave compartment holes to pull air from the fridge compartment and push it up through the microwave compartment and out the vent above that compartment. I used fans that are made for moving air against high back pressure instead of fans optimized for air volume (Arctic "P" series fans from Amazon) and built a duct to pull from all three holes with only two fans.

Today I left the campervan in the sun all day. When I got home, the inside temp was 100F, and the fridge was under 45F, so with the fans running I have at least 55f degrees of cooling performance instead of roughly 40F prior to re-doing the vents.

It's better than before, so I'll leave it this way for a while.

[Bud]

"And placed two 120mm computer fans over the three microwave compartment holes to pull air from the fridge compartment and push it up through the microwave compartment and out the vent above that compartment. I used fans that are made for moving air against high back pressure instead of fans optimized for air volume (Arctic "P" series fans from Amazon) and built a duct to pull from all three holes with only two fans.

I did not see pic's of the fans and the duct you built. I don't understand how these fans and duct work.

Bud

[booster]

I have always been one of the first to remind anyone looking at compressor frigs to be sure to address the ventilation issues because it is very important to get it right. If you don't get it right, you will either not be able to keep the frig cool and/or it will be costing more power to run than it should.


That said, for at least some of the compressor frigs, you really don't need a lot of air movement to make them run well if you are moving only the air you need to move.


Here are a few pix of our Isotherm that I put in a long time ago after a lot of airflow testing. It is on the bench in full insulation and ducted condition and will go right in place that way in our 07 Roadtrek 190P. They only thing you don't see is that I stuff the area between the upper and lower vent with fiberglass insulation to seal them from each other to prevent air looping, which forces the air to come in the bottom vent and out the top. The only fan in this system is the factory mounted one at the compressor assembly, right at the top of the added duct.











The air comes in the rectangular opening at the bottom of the duct, which as you can see is quite small, and out of only the area of condenser coils and over the compressor itself. The upper and lower vent in the van are totally stock with no blockoffs to alter size or such and no extra fans.


Unfortunately, this doesn't work on the frigs that have the conventional style large condenser on the rear of the unit as well as there is a lot area to cover and duct, plus the compressor is under it all so it's heat mixes in early unless ducted separately.


Our system will keep cool (37*)in 100* heat while facing the sun, on the lowest compressor speed setting, and it uses the same daily power with ducting, in the van, as it does in free air on the bench all other conditions identical.

[peteco]

Just curious: any idea why the big difference in the size of the condensor between Michael's NovaKool and Boosters Isotherm?

[peteco]

Originally Posted by @Michael

I re-positioned the insulation in the microwave compartment, and added a double layer of pink ridged insulation at the top of the microwave compartment to better isolate that compartment from heat being pushed down from the roof.

I am thinking you might have better external heat rejection using a radiant heat barrier instead of the pink insulation. Radiant barriers need an air gap (about an inch) between them and the heat source: the van walls and ceiling being a big heat source in your case. This is where many people make a mistake by placing Reflectix (or other radiant barrier) in contact with the hot wall.

[@Michael]

Originally Posted by Bud

"And placed two 120mm computer fans over the three microwave compartment holes to pull air from the fridge compartment and push it up through the microwave compartment and out the vent above that compartment. I used fans that are made for moving air against high back pressure instead of fans optimized for air volume (Arctic "P" series fans from Amazon) and built a duct to pull from all three holes with only two fans.

I did not see pic's of the fans and the duct you built. I don't understand how these fans and duct work.

Bud

I forgot to take a picture after the fans were installed.

Here's a side view:



I just took a 1/8" plywood board and put two 120mm holes in it and fastened the fans to the underside of the board. The board is propped up at a 45deg. angle at the back of the microwave cabinet covering the three holes between the fridge and microwave.

If I decide I need fewer or more fans, I'll just swap in a board with either more or fewer fan holes.

The reason for three holes in between the microwave and fridge compartments is because that's all that I could put in without loosing structure. Any larger and I'd loose the structure that holds up the cabinet shelf, or they would be blocked by the top of the fridge and/or bottom of the microwave.

I started with three fans, but because of the small size of the exhaust vent, I did not detect any more air flow that with just two fans. The reason for not leaving any holes open without a fan is that when I experimented with having more holes than fans, the fans just circulated the air between the cabinets instead of pushing it out through the exhaust vent. The board holding the fans acts as a duct that lets me have two fans drawing air through the three holes without allowing internal circulation.