Ventilation of Compressor Refrigerators

[@Michael]

Originally Posted by booster

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.
'''
...

The only fan in this system is the factory mounted one at the compressor assembly, right at the top of the added duct.

I'd rather not have fans...but...

The biggest issues is that there simply is no room to put in a decent sized exhaust vent above the microwave. All I have to work with is a 2.5 x 18" wide cabinet frame, which only leaves room for about a 1.25 x 14" vent. There isn't any place else to sent the air - the fridge compartment is boxed in by a cabinet on the left and the bathroom on the right.

With that small of an egress, the small amount of air convecting up and out is not enough to keep the exhaust air within 5 deg of the intake air, per Novakool's recommendation. Hence the forced air fans. I'll put as many or as few as I need to get the exhaust temp down to where it needs to be - or else lower the voltage and slow them down.

Originally Posted by peteco

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.

You might be right. I could put Reflectix to the outside of the pink insulation in several places, including the area behind and above the microwave. It should reflect heat back out to the van shell.

[peteco]

Nice sketch Michael. If you replace the pink with Reflectix or radiant barrier coated foam like Booster's it should work a lot better. Silver radiant part facing the outer wall. I think they make two-sided radiant barrier foam which would work even better. As I stated though, the silver surface can not be touching the wall. You may not be able to help that in some places but if the majority is not touching it should be much better than the pink insulation.

(Sorry, we are typing at the same time).

I would replace the pink insulation wherever possible.

[rowiebowie]

Michael. You did a nice job that Coachman should have done for you. My Airstream similarly lacked the manufacturer's minimum ventilation, plus they did not insulate the cavity adequately from van's hot outer skin.

I'm a fan of compressor fridges, but why upfitters think they can get away with stuffing them in tight, inadequately ventilated spaces is just idiotic.

[Bud]

"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.

Not sure how two fans draw air through 3 holes without allowing internal circulation between refer and microwave cabinets.

If the two fans are snug against some holes and air can Only enter the refer cabinet cabinet from below and Nowhere else, you're as good as it gets and all should be fine.

Bud

[booster]

Originally Posted by @Michael

I'd rather not have fans...but...

The biggest issues is that there simply is no room to put in a decent sized exhaust vent above the microwave. All I have to work with is a 2.5 x 18" wide cabinet frame, which only leaves room for about a 1.25 x 14" vent. There isn't any place else to sent the air - the fridge compartment is boxed in by a cabinet on the left and the bathroom on the right.

With that small of an egress, the small amount of air convecting up and out is not enough to keep the exhaust air within 5 deg of the intake air, per Novakool's recommendation. Hence the forced air fans. I'll put as many or as few as I need to get the exhaust temp down to where it needs to be - or else lower the voltage and slow them down.







You might be right. I could put Reflectix to the outside of the pink insulation in several places, including the area behind and above the microwave. It should reflect heat back out to the van shell.

My point was not about any particular system, but just a general comment that you don't need a door sized opening to cool a compressor frig if you can control the airflow well. If you look at the bottom of our duct, it is not really much larger, if any, than you could cut in your mentioned restriction area, but it works very well.


Why it works well is that is picks up cooling air that is not in any amount heated or mixed with air that the frig has exhausted before it gets to the condenser and compressor. The exhaust has no choice but to go out through the other vent away from the inlet.


Dumping air into a big area and then trying to pull out the hottest of that air is not going to happen very well, even with fans, unless you remove much more of the air than went in from the heat source. Fans certainly can compensate for a lot of that, but take power to run and will pull diluting air in every little gap which reduces their effectiveness. All the air we move is used for cooling and then exhausted completely, so the single fan is plenty big enough.



I have showed our ducting setup to quite a few people and most say it could not work as well as two big opening in the side of the van. Unfortunately, the two big openings made the frig run continuously and not stay cold all the time. That is where we started.

[@Michael]

Originally Posted by Bud

Not sure how two fans draw air through 3 holes without allowing internal circulation between refer and microwave cabinets.

If the two fans are snug against some holes and air can Only enter the refer cabinet cabinet from below and Nowhere else, you're as good as it gets and all should be fine.

Bud

I forgot to take a picture before I put the microwave back.

The back of the microwave cabinet looks something like this:



The fans blow air up through the fridge cabinet out into the microwave cabinet, which is vented to the coach above the microwave through the black vent in the pics above.

The angled board is sealed against the back, bottom and sides of the microwave cabinet (pink insulation and Gorilla tape) so the air can only go up and out.

If this doesn't work, I'll use the refrigerator cabinet to hold a couple of Yeti coolers and sell the fridge.

[@Michael]

Originally Posted by booster

My point was not about any particular system, but just a general comment that you don't need a door sized opening to cool a compressor frig if you can control the airflow well. If you look at the bottom of our duct, it is not really much larger, if any, than you could cut in your mentioned restriction area, but it works very well.

Why it works well is that is picks up cooling air that is not in any amount heated or mixed with air that the frig has exhausted before it gets to the condenser and compressor. The exhaust has no choice but to go out through the other vent away from the inlet.

Dumping air into a big area and then trying to pull out the hottest of that air is not going to happen very well, even with fans, unless you remove much more of the air than went in from the heat source. Fans certainly can compensate for a lot of that, but take power to run and will pull diluting air in every little gap which reduces their effectiveness. All the air we move is used for cooling and then exhausted completely, so the single fan is plenty big enough.

I have showed our ducting setup to quite a few people and most say it could not work as well as two big opening in the side of the van. Unfortunately, the two big openings made the frig run continuously and not stay cold all the time. That is where we started.

I agree - and I think what I have now is real close to what you recommend. The only air that can move through the fridge compartment is that which enters the bottom of the cabinet and exits the top into the microwave cabinet. The only egress from the microwave cabinet is out the top through the black vent and through two of the five silver vents built into the microwave frame.

Here's a shot of the back of the fridge, looking down from the microwave cabinet.



It's basically a sealed chimney 3 inches deep and about 21" wide.

This is a 6.8 cu. ft. fridge, presumably with a larger compressor, which Novakool says must have 120 sq. in. (60" top and 60" bottom). Coachmen says that Novakool told them that 30 sq. in. is enough, but Coachmen didn't say if that's 30" total or 30 top and 30 bottom. I'm assuming the latter.

Right now I have roughly 40 sq. in. below and above the fridge, but only about 20 sq. in. egress from the microwave cabinet out to the coach. If I could get 40 sq. in. of vent there, I don't think I'd need the fans.

So to your point, fans are a band-aid.

[avanti]

I don't think fans are a band-aid. A small computer fan is compact, quiet, and not power-hungry. Properly used, it can permit good cooling in configurations in which proper convection cooling is difficult or unsightly. Mine vents into an adjacent closet and works great. The closet leaks enough such that the small positive pressure is adequate without an additional vent.

[GeorgeRa]

My Isotherm fridge fan blows air directly across the condenser. I changed the factory fan to a quieter one.

[Bud]

Originally Posted by @Michael

I forgot to take a picture before I put the microwave back.

The back of the microwave cabinet looks something like this:



The fans blow air up through the fridge cabinet out into the microwave cabinet, which is vented to the coach above the microwave through the black vent in the pics above.

The angled board is sealed against the back, bottom and sides of the microwave cabinet (pink insulation and Gorilla tape) so the air can only go up and out.

If this doesn't work, I'll use the refrigerator cabinet to hold a couple of Yeti coolers and sell the fridge.

If this doesn't work, I would suspect what you have written or the Norcold thing is faulty.

If air out the refer compartment can ONLY come from the vents down low, then out the vents on top, you're good.

Thanks for the replies.

Bud