Auxiliary Refrigerator cooling fan?

[Rufus]

Our boat still has an old Norcold fridge that is working fine...and I want to keep it that way. As is evident in the photo, it is a tight fit in the surrounding cabinet structure. There are vent louvers on the side of the cabinet/enclosure to allow heat from the coils to escape (into the cabin), but I want to add a fan to pull warm air from the bottom of the unit and then exit it down into the bilge. There is a void behind the fridge that used to house a small Cadet electric heater (now removed). I'm thinking the fan should run on an AC pick off from the fridge as we rarely anchor anymore. And if we do, it cools well enough as it is.

So, I'm looking for advice as to a fan choice, and if anyone has a Norcold circuit diagram, perhaps a recommendation for the hook up.

 

[Comodave]

Don’t know anout Norcold, but I just put a fan on my Vitrifigo. It was simple. There is an F terminal and ground that will support a 500 mAmp draw and run a fan when the compressor is on. I found a computer fan on Amazon that draws 50 mAmps. I put it in on the bottom blowing air into the box and put an exit vent on the top of the box. Norcold probably has a similar setup on the control board. I just went to Vitrifigos web site and downlaoded the owners manual.

 

[O C Diver]

From your picture, there looks to be an upper vent on the side of the cabinet. I would try mounting a fan on the inside blowing out. Here is one I'm considering for a similar project. You don't need a lot of air flow and this one has a pretty low decibel rating.

https://www.acinfinity.com/115v-ac-...n-fan-80mm-x-38mm-low-speed/#product-warranty

Ted

 

[Comodave]

The one I added is so quiet you can’t hear it at all more than 2 feet away. It is a Noctura NF-F12 PWM Cooling Fan.

 

[Ex Sailor]

Our boat still has an old Norcold fridge that is working fine...and I want to keep it that way. As is evident in the photo, it is a tight fit in the surrounding cabinet structure. There are vent louvers on the side of the cabinet/enclosure to allow heat from the coils to escape (into the cabin), but I want to add a fan to pull warm air from the bottom of the unit and then exit it down into the bilge. There is a void behind the fridge that used to house a small Cadet electric heater (now removed). I'm thinking the fan should run on an AC pick off from the fridge as we rarely anchor anymore. And if we do, it cools well enough as it is.

So, I'm looking for advice as to a fan choice, and if anyone has a Norcold circuit diagram, perhaps a recommendation for the hook up.

View attachment 74754

We have a Novacool and I did the very same thing. Got a 4" DC computer chassis type of fan and mounted it inside the fridge cavity on the bottom. Our Novacool had a fan output terminal on the compressor module, but it will NOT support much of a load ( in our case, fan was too big and unit shut down ) as result I picked the feed from the incoming DC. Speed control is also nice as it will get a bit noisy if let run at full speed ..... fb

 

[Heron]

I've got a 30 year old Norcold that still works fine. As a few have mentioned, I mounted a 12v muffin fan blowing on the compressor that kicks in only when running on 12 volts.
I can't really tell if it saves me many amp/hours when anchoring out but it makes me feel better!
With the new dark blue hull, I also insulated the entire area where the fridge mounts and I can't help but believe that helps too..

 

[Comodave]

Our Vitrifrigo would support 10 of the fans that I used. I would be surprised if the Norcold would not support 1 of the fans that I listed in the above post.

 

[Rufus]

Thanks, everyone for the ideas and links. I'd actually like to reduce or even eliminate the warm air exiting the side vents in the fridge cabinet, as it dumps into the dinette seating area. The former electric heater cabinet/void for the forward cabin butts up to the backside/bottom of the fridge. Perfect spot to punch a hole in that adjoining bulkhead and hide a fairly powerful extraction fan. Then dump the warm air into the bilge via a 90 degree elbow. I'm thinking a larger, lower speed (quiet) AC fan offered in the link Ted provided might work well in the application. Shoot, with a "Y" valve the fridge exhaust could heat the forward cabin in cool weather... well, maybe not...

 

[C lectric]

I had a smaller Norcold #490 to which I adapted a fan which ran when the fridge ran.
My fridge used 20VAC to drive the compressor. THat voltage was supplied from 120VAC by a transformer OR by a pair of transistors creating a simple oscillating circuit producing 20VAC but from the 12VDC supply. The transformer was again was used to increase the 12VDC to the needed 20VAC.

I made my own little power supply which tapped directly off the two motor leads and then produced 12.8VDC to run a 12 VDC Muffin fan. It worked for many years untill I decided I simply wanted/needed a larger fridge which was less of an energy hog.

I found the actual Norcold circuit on the back of the fridge. Maybe there is one on yours also. Take a look.

Or you could , I think, try a 24VAC muffin type fan and wire it directly to the motor leads so it ran only when the fridge compressor motor ran. It would run somewhat slower than if it had a full 24VAC but it should run.

As for all the other ideas about using the excess heat I seriously doubt there will be enough heat to be of any value. DO it for fun if you wish but I would not bother and simply find the best way to exhaust the fridge off cast heat to the outside. All that extra plumbing/ducting will simply reduce the airflow from the fan, maybe enough to negate the effectivness..

If I can find my notes, circuit copies , fridge circuit copies I will post them. I don't think I have them anymore as I vaguely remember all that went with the still working fridge.

However if you have an electrically/electronics savvy friend it was a simply circuit. Just see if you have the circuit on the fridge back.

 

[O C Diver]

I would avoid pumping air into the bilge. The bilge should be operated in vacuum not positive pressure. You may find pushing air into the bilge helps odors work there way out.

I've often thought that venting the cabinet through the roof with one of those drip proof sailboat vents would be a pretty easy way to vent the heat outside. If it was tall enough, the pipe might act like a chimney and create a thermal syphon. Probably better leave that idea for the sailboat crowd.

Ted

 

[C lectric]

I should have added that a 4" muffin fan blowing air out of the cavity will do a good job.
It does not need a blast, just move the air out. A 4" muffin fan will move more than enough air to improve the fridges cooling in hot weather.

Try mounting it in front of one of those vents I see in the cabinet side. I doubt there will be enough heat to make anyone uncomfortable.

Anyways, your choice.

 

[Rufus]

I would avoid pumping air into the bilge. The bilge should be operated in vacuum not positive pressure. You may find pushing air into the bilge helps odors work there way out.

I've often thought that venting the cabinet through the roof with one of those drip proof sailboat vents would be a pretty easy way to vent the heat outside. If it was tall enough, the pipe might act like a chimney and create a thermal syphon. Probably better leave that idea for the sailboat crowd.

Ted

The engine room/bilge areas are open to atmospheric via the two large intake openings for the engines and genset. Might be a very slight vacuum with the engines running...which is not all that often these days. Actually a relative whisper of air, don't you think? Guess I could just port it into the forward cabin...better than the galley area. Or I could run a hose into the forward head...and then turn on the head fan, which exhales into the bilge (I'm kidding).

 

[Maerin]

I've got a 30 year old Norcold that still works fine. As a few have mentioned, I mounted a 12v muffin fan blowing on the compressor that kicks in only when running on 12 volts.
I can't really tell if it saves me many amp/hours when anchoring out but it makes me feel better!
With the new dark blue hull, I also insulated the entire area where the fridge mounts and I can't help but believe that helps too..

The insulation helps reduce the heat load on the box, the air blowing on the compressor won't do squat unless it's creating air flow that will remove the reject heat that the condenser coil is putting out. The compressor is cooled by the refrigerant flowing through it. The more heat you remove from the refrigerant as it moves through the condensing section of the circuit, the lower the head pressure will be on the compressor, and THAT is what will keep the compressor alive and happy. A fan blowing on the shell of the compressor is pointless. If the condenser coil must live in its own reject heat, it drives the head pressure up, and that is what will kill a compressor or at the very least will cause it to use more power.

The objective is to provide a path for the reject heat to escape, but that path MUST include a source for air. You must have FLOW. A way IN for cool air, a way OUT for the reject heat. Providing an exit high and an inlet low capitalizes on the chimney effect of convection. That alone can be enough, the fan helps. A single outlet, high or low, is pointless, fan or no fan. It's like blowing into a paper bag.

 

[C lectric]

Heron,

I missed the sense of your original post.

I absolutely agree with Maerin's post. Get the heated air out of the cavity or the fan is almost pointless.

FLOW coming in at or near the bottom and exhausting OUT of the cavity at/near the top.

That will help your unit in hot weather. The rest of the year when ambient is cool it may not matter nearly so much but it's in hot weather, especially when the sun is beating down, that the fridge needs all the help it can get.

 

[O C Diver]

The engine room/bilge areas are open to atmospheric via the two large intake openings for the engines and genset. Might be a very slight vacuum with the engines running...which is not all that often these days. Actually a relative whisper of air, don't you think? Guess I could just port it into the forward cabin...better than the galley area. Or I could run a hose into the forward head...and then turn on the head fan, which exhales into the bilge (I'm kidding).

There's probably a good reason you don't see anything else on a boat vented into the bilge (like you head fan). The other part of the equation is, how far do you think you're going to push air with a muffin fan?

Ted

 

[Rufus]

I'm 1300 miles from the boat, so cant' go look at the refrigerator...don't even know the model number. But I believe the air intake for the cooling coils is at the front below the doors just like a home unit. Likewise, I'm assuming the warm air would exit the unit at floor level at the rear like a home unit. I was thinking about a fairly powerful AC fan (more than a 3" muffin) to suck that warm air out (at floor level) before it ever rose inside the cabinet. Any left over heat would dribble out of the existing vents in the cabinet, but it wouldn't be much. I need to further ponder where to expel the warm air from the fan....there is an overhead void at the base of the windscreen that has an existing outside vent for the propane bottle overboard drain...

 

[Comodave]

My marine fridge does not have any intakes on the bottom of the fridge like a home unit. You have to do the venting yourself if the builder didn’t. These are not home refers. The heat is usually generated in the bottom in the back. Mine has about a 6”X6” area in the back bottom that has the mechanicals. You need to introduce cooler air into this area with a vent and then as has been said have a way for the hot air to flow up the back or sides to a vent up high so the hot air can escape. I would never pump air into my bilge as it will cause smells from diesel, holding tank, shower sump and just plain bilge stink up into the boat. Even if it is only part of the air that is pumped into the bilge that gets into the cabin, that is too much for my wife’s nose. If the refer heat is too much for your cabin area, then you need more ventilation in the cabin to let it out.

 

[FF]

The goal is not just to remove just the heat from the compressor, the air around the reefer needs to be removed as well.

The refrigeration expense is between the interior box temp and exterior box temp.

Most boats have cool bilges , sea water temp, and if the box can be surrounded with cooler air it will be less energy and less run time .

The NA that designed the boat should have worked the numbers and provided a natural cooling channel for the reefer , but stuff happens.

 

[Rufus]

The refrigerator is almost thirty years old, so the cooling system design (two big vents on the side of the cabinet) is arguably working fine. There is good cross flow across that area of the cabin from opening windows on either side of the galley/dinette area. The boat is air conditioned, so it's never uncomfortable. I simply want to improve the cooling for the fridge with a fan at the back...and I don't want a directed flow of air exiting toward the dinette seating area.


I think I found our fridge model on the Thetford site. Per Comodave's comments in post #17 it appears that there is no intake at the front of the unit. So, I guess the cooling is via the lower vent at the side and then convection via the upper exit vent. So sucking air out the bottom would effectively reverse the flow. I think it would work with a large enough fan at the bottom, but a new extraction hole at the back/top would make more sense for what I'm trying to achieve. And that's possible inside the adjoining cabinet in the forward cabin. Back to the drawing board.

Thanks all for the links to available fan solutions and potential pitfalls. Planning summer projects when the boat is five States away is a challenge.

 

[Lepke]

For moving air, I found that computer type fans are quiet, cheap, and available in 12 volts at various sizes. They are mostly silent and the speed can be regulated with a rheostat.
Because I have a wood boat, I power vent my bilge areas to control the "boat" odors. In dead areas I have 4x4 fans at reduced speed to keep all areas fresh and dry. The vents run about 10 cu.ft. an hour and draw air down the sides between the ribs from the cabin top.

 

[fryedaze]

Previous thread discussion.
http://www.trawlerforum.com/forums/s31/improved-refigerator-performance-7536.html

 

[Comodave]

I would either push air into the bottom vent or suck it out the top. Let physics be your friend...

 

[FF]

"Let physics be your friend..."

Hot air rises, a well designed reefer install should not require extra power to function.

 

[Rufus]

I would either push air into the bottom vent or suck it out the top. Let physics be your friend...

Sucking it out at the top looks like the ideal option. Would be easy if I was willing to live with more warm air dumping out of the upper vent next to the dinette seating area (where my spouse likes to read and work on her drawings). The challenge is finding a suitable exhaust exit in the forward cabin or head. On the other hand, since I'm not concerned about AC power consumption at the dock, and intend to use a fairly powerful (but quiet) AC fan, I could probably reverse the flow and suck it out the bottom. When at anchor and on DC (seldom) it would revert to the original non-assisted cooling.

 

[Comodave]

"Let physics be your friend..."

Hot air rises, a well designed reefer install should not require extra power to function.

Not many boat refer installs are very well thought out. The boat manufacturer does not usually really care about how it cools, just that it looks good when they sell the boat.

 

[FF]

"The boat manufacturer does not usually really care about how it cools, just that it looks good when they sell the boat."

Sadly this is true , but the new boat purchasers seldom seem to have enough experience to Demand a well engineered /constructed vessel.