How can I improve my fridge/freezer air circulation

[demonboy]

I've currently no sink in my galley which is offering me an opportunity to improve the air circulation of my two Danfoss compressors that sit in the cupboard underneath. They're both the same but for the sake of argument I call one my fridge and one my freezer, which sit on separate shelves. The cupboard door has a grille in it, supposedly to allow the hot air out but I'm sure I can improve the circulation somehow.

Here you can see from above how they have been installed. The compressor sits inside the boat and the condenser faces towards the hull, with the fan blowing towards the hull.

From the side you can see that the freezer compressor sits further in towards the boat and the fridge compressor, on the upper shelf, closer to the hull. The arrow indicates the movement of air from the fan between the compressor and the condenser.

And a view from the front with the door open (the closed door would have the grille somewhere in the middle.

My concern is that the hot air generated by the compressors is only being circulated within the cupboard with little escaping through the grille. My first thought was a fan on the back of the door so the hot air gets sucked out from the cupboard, through the grille and into the galley.

Another thought would be to run some kind of conduit from the condenser, but that's a bit more involved. If I did that, I'm not sure how much of the condenser/fan I could cover, if at all.

I did think about turning them around so the hot air is being blown straight at the door, but that's even more involved and requires extending and brazing new copper pipes.

Finally, there is a narrow cupboard to the left which houses a small rubbish bin and shelves. I wondered if putting a fan between the two would help, but can't decide if a) that would be any use and b) which way the fan should point (i.e. get hot air out or bring cold air in).

Any pointers/ideas gratefully received.

Thanks in advance.

 

[David2452]

The simplest way is normally to have a grille top and bottom to allow air to circulate by convection, but a small computer fan linked to the compressor(s) to operate when they do would obviously improve that and need a smaller opening too.

 

[demonboy]

The simplest way is normally to have a grille top and bottom to allow air to circulate by convection, but a small computer fan linked to the compressor(s) to operate when they do would obviously improve that and need a smaller opening too.

Hi David,

The compressors already have fans on them which turn on when the compressors run. The problem is the fans aren't blowing anywhere in particular, so the hot air is not escaping other than through the door grille. A top grille isn't practical as that's the sink area, but a grille in the lower shelf could be a useful option, thanks.

 

[vyv_cox]

I think that the ideal situation for an air cooled refrigerator compressor is for air to circulate from the hull, likely to be the coolest place, up through the heat exchanger and either out to the exterior or in some way allowed to return to the hull where it can be cooled again. The route out from the heat exchangers would ideally be at the top of the compartment of course. In many boats, including mine, this is an impossible situation to achieve, which is why I went to a water cooled heat exchanger.

 

[pvb]

Long ago, my parents had a mobo with a similar fridge problem. I fitted a 100mm computer fan, ducted to blow cool air from the bilges in to the compartment containing the compressor, and wired so that it operated whenever the compressor switched on. It significantly reduced the compressor running time.

 

[Heckler]

Bluddy heck, what a coincidence, write an article last night and sent it off! Similar thing on my bene. there is a series of 100mm holes in the bottom of the cupboards where the comp is on mine, I put an 80mm comp fan in one, it sucks air from alongside the cool water cooled hull and squirts it up towards the condenser fan. I wired it in to the existing fn. It transfirmed the performance of the fridge. It struggled in Faro to get to 10 deg C , it now goes down to 5 deg easily and cycles properly.
S

 

[charles_reed]

The simplest way is normally to have a grille top and bottom to allow air to circulate by convection, but a small computer fan linked to the compressor(s) to operate when they do would obviously improve that and need a smaller opening too.

Precisely what I did, but put some ducting, from back of compressor (I used spiral wound, tumble-dryer ducting) up to the upper grille with a 100mm computer fan,in suction, at the top - that was wired, in parallel with the on-board fan so only came on with more than 13.0v in the system.
It's been successful for 12 years 6/12 in the Med, and is, IMHO, a simpler and definitely cheaper alternative to water-cooling.

Reading Demonboy's subsequent post - mine was the same problem - exit the ducting somewhere else, in my case into the cockpit locker.
I'd not presume to tell Grandma how to suck eggs, but this is a a shining example of people thinking in self-installed boxes.
You can always vent higher and outside the boat.

 

[J Neeves]

It is possible to turn the fans on the compressor round so that instead of blowing toward the hull they blow toward the vent (the fans are simply bolted of screwed, easy to turn round (or reverse the wiring). We took hard plumbing pipe, must be about 6" (it covered the fan) and 'piped' that warm air right onto the vent. It depends on the vent but some really do not let much air in or out. We also have 2 compressors and have also used spiral wound tumbler drier ducting (as mentioned above) it depends on whether you need to add bends in the pipe to get at the vent. We feed our deep freeze warm air through the engine room direct to one of the engine vents. But this only gets the warm air out. You do not say describe your yacht nor where you are located but often the coolest air is outside (not in the bilges) and if you can duct from 'outside' that might be an interesting option. We duct from the anchor locker (which we suck with another computer fan) - but on many yachts this would be impossible - so we feed cool air from the bow and blow the warm air into the cabin or engine room. The air we draw from the anchor locker we duct right onto the compressor - so we have ducts up to the compressor and from the compressor (with a little gap in between). At anchor we are obviously bow onto the wind and have whatever airflow there is from wind adding to what we do with the computer fans.

A fridge and deep freeze use oodles of power and maximising anything you can do to reduce that power is worth all the effort (when you run your engine turn the thermostat to coldest - remembering to turn it back when the engine goes off!)

If I was starting again - I'd do what Vyv has done, water cooling but we would also fill any space round the 'boxes' with more insulation as well - but hindsight is marvellous and most marine fridges lack in insulation..

Jonathan

 

[superheat6k]

I am assuming the condensers are in the same cupboards. This being the case the greater requirement is to stop the air re-circulating back into the condenser. As David has mentioned an updraft is ideal.

Can you fit a grill in the top behind the sink, and a small inlet fan behind the existing grill.

As you have two separate condensers then you could control this extra fan with a thermostat.

 

[Breizh]

From looking at your diagrams it appears that the heat given off the freezer condenser is rising naturally over the fridge condenser / heat exchange and causing the fridge condenser / exchange to suffer from lack of cooling.

You need to try and place a barrier between them vertically so that the hot air from the freezer exits the top of your unit without touching the fridge condenser. it is very important to have vents up high to allow for the natural heat convection to occur an allow the hot air to escape.

I have had to fix no end of installations with this same issue. One of the easiest fixes is to put in a thick strip of rockwool or equivalent vertically from just below the freezer condenser to the top of the unit. Each side of the unit requires its own exit grill or a single long grill. The fan will push air up both side of the unit, if this isn't happening you may need small fan for each side, it doesn't require fast fans, as you only need to move the cool air across the condensers for the heat exchange to function.

Breizh.

 

[Monique]

Hi Jamie,

FWIW, I am installing Frigoboat keel cooling... if you want to be even more effective, add a keel cooler to your air/air heat exchanger.

Cheers and HNY

 

[demonboy]

Thank you all for your considered replies, there's some useful pointers among them.

The point about the freezer hot air rising to the fridge unit was my main concern. A water-cooled solution is something for the long-term, so in the meantime I will aim to put a computer fan in the floor to suck the cooler air up from the bilges; I'll see if I can add an exit vent behind the sink (there's a cupboard above which may offer a solution); and also look at using some flexible duct pipe to direct hot air from the respective units.