Fridge using lots of amps in the hot weather

[coopec]

Insulation

The first step that can be taken to reduce the power needed to run a fridge is improving the insulation. In many cases this is woefully inadequate – ideally a marine fridge will be encased in four-inches of insulation. Smaller units – those below around 100 litres – may be able to get away with less than this. However a freezer should ideally have some six inches of insulation.

If yours has less than this, improving the insulation may be easier than you think. Many units have a big air gap between the refrigerated box and the surrounding joinery. This allows for a very cost effective solution of simply gluing the type of extruded polystyrene insulation you can buy from builders’ merchants around the outside of the box. More awkwardly shaped gaps could also be filled with expanding foam.

Efficient boat refrigeration: a how-to guide - boats.com

 

[JumbleDuck]

As Paul says, all the cold falls out of a front opening fridge every time you open the door.

Don't worry about it. The amount is negligible.

The heat capacity of air is about 1 J / g / K, so replacing 10 litres (10g) of air at 0C with 10 litres of air at 20C only introduces 200J of heat into the system, which is enough to melt 0.6g of ice.

 

[PaulRainbow]

I don't see any reason why an air cooled "out of the box" fridge could not be converted to water cooled condenser.

This could be a submerged condenser of a onboard tube in tube heat exchanger a I posted in an early thread.

No reason why it cannot be converted, technically.

Other than, you'd have to dissect the the fridge, re-locate the condenser (or whatever you were replacing it with) pay to have it all silver soldered or brazed together, pay to have it re-gassed etc etc. You also need to find space to fit it, not the easiest task on a 26 foot bilge keel Westerly Centaur.

A little bit of overkill perhaps for an East Coast UK boat, where we get enough hot weather to cause the OPs "issue" for about a week, once every three years.

 

[LadyInBed]

The heat capacity of air is about 1 J / g / K, so replacing 10 litres (10g) of air at 0C with 10 litres of air at 20C only introduces 200J of heat into the system, which is enough to melt 0.6 of ice.

Is that 0.6 of an ice burg or cube

 

[rogerthebodger]

This usually requires an electric pump to circulate seawater, so additional electricity consumption.

As I said in the previous thread but saves any external evaporator to be fitted.

It could also be designed to fit to an existing sea cock blow the water thus possibly eliminating the need of the pump.

Like this

Or you could buy one.

 

[PaulRainbow]

The OP owns a Westerly Centaur, 26 foot bilge keel boat. He weekend sails on the East Coast of the UK. The last few days have been abnormally hot for here, the hottest few days since the 1960s.

I'd suspect the OP wants a viable and not ruinously expensive solution to his "problem". Are solutions for live-aboard Caribbean cruising, cruising in South African waters, solutions applicable to 40--50ft yachts really the best answer here ?

 

[rogerthebodger]

No reason why it cannot be converted, technically.

Other than, you'd have to dissect the the fridge, re-locate the condenser (or whatever you were replacing it with) pay to have it all silver soldered or brazed together, pay to have it re-gassed etc etc. You also need to find space to fit it, not the easiest task on a 26 foot bilge keel Westerly Centaur.

A little bit of overkill perhaps for an East Coast UK boat, where we get enough hot weather to cause the OPs "issue" for about a week, once every three years.

The OP asked " Is there anything else, other than insulation, that I should be looking at? "

So I gave him something else he could look at plain and simple

Yes it would cost and it again up to the OP to decide if he can justify the cost.

The fact you only get hot weather for about a week, once every three years. why I chose to take a job in a warmer climate rather than go to Canada or stay in the UK.

So what's the issue.

 

[PaulRainbow]

The OP asked " Is there anything else, other than insulation, that I should be looking at? "

So I gave him something else he could look at plain and simple

Yes it would cost and it again up to the OP to decide if he can justify the cost.

The fact you only get hot weather for about a week, once every three years. why I chose to take a job in a warmer climate rather than go to Canada or stay in the UK.

So what's the issue.

He asked is there was anything he could look at, i imagine he meant anything sensible.

 

[rogerthebodger]

He asked is there was anything he could look at, i imagine he meant anything sensible.

Sorry Paul I didn't realise that I had to run my suggestions past you to ensure you consider them sensible.

 

[JumbleDuck]

Is that 0.6 of an ice burg or cube

Sorry. 0.6g. Now sorted. Thanks.

 

[TernVI]

As stated above the air falling out doesn’t matter as it‘s heat capacity impact is immeasurably small compared to the contents.

The heat capacity of the contents is not the issue. The question is the heat capacity of the the incoming air, vs the power of the fridge.
If the incoming air is humid, then the latent heat of its water vapour content can be significant..

On the subject of fans on the back of the fridge, even if the air is the same temperature, moving air will cool the condenser more effectively than relying on convection. Every little helps!

 

[RupertW]

The heat capacity of the contents is not the issue. The question is the heat capacity of the the incoming air, vs the power of the fridge.
If the incoming air is humid, then the latent heat of its water vapour content can be significant..

On the subject of fans on the back of the fridge, even if the air is the same temperature, moving air will cool the condenser more effectively than relying on convection. Every little helps!

Sorry but that is very wrong. To give an idea of how wrong, would you like to tell me the weight of this warm water replacing the cold air in a 50 or even 100 litre fridge and compare that to my hypothetical single can of Coke.

 

[Boater Sam]

If your fridge is one of the daft new ones with the condenser in the cabinet sides, adding insulation will make it even worse.

 

[Boater Sam]

I used to think the air falling out of a front loader fridge/freezer would be significant but if you only opening a couple of times a day I wouldn't worry. Anyway it is only a bit of cool air that is lost as most of the coolness is retained by the cool/frozen goods.

The more insulation the fridge has the less time the compressor will have to work. My fridge is custom built and has 4 inch insulation. As others have said it is vital that air is able to circulate. My unit is a Waeco and they said not to install the unit in a compartment less than 100 cu ft.

Just looking at your fridge (with minimal insulation) your compressor is going to be working overtime in hot weather.

Here is an excellent article on marine fridge/freezers.

MARINE REFRIGERATION

That is a hell of a big fridge to have on a boat, or is it a cold store ship?

 

[[70521]]

Friends have sailed from France to the Pacific and back to France without a fridge.

 

[TernVI]

Sorry but that is very wrong. To give an idea of how wrong, would you like to tell me the weight of this warm water replacing the cold air in a 50 or even 100 litre fridge and compare that to my hypothetical single can of Coke.

50 litres of air, changing ever few seconds, that might be a mol per second at 29 J/mol/K. Maybe 25k difference? That's 700W for the time the door is open, just for the air.
The condensation, let's guess it's 30degC i nthe cabin, air holds 4% water so maybe thats up to around a gram per second coming in at around 2420 J per gram latent heat. So with air flowing while the door is open, we can be looking at 3kW

It might not chage the temperature of the coke very quickly, but it takes the fridge a long time to get back to how it was after the door has been open a little while.
It will be exaggerated by the efficiency / COP of the fridge going to ratshit as the condenser temperature rises in hot weather. People may have notied that the fridge's duty cycle increases rapidly as the ambient gets above a certain point.
A boat fridge is what? 50W DC in? COP about 3 in good conditions, falling below 1 as the condenser gets too hot.

 

[Catalina36]

Seems to be some peoples out of the box solution.

How sensible would you say that was for someone with cabinet fridge (like the OP has) on a 26 foot bilge keel boat ?

The smaller the boat, the less space you have to add inches of insulation or extra batteries. I first did all this in a Jag 27. Sure it costs money to instal a keel cooler and compressor but it's only done once and then you know you have the most efficient system you can get.

 

[pvb]

The smaller the boat, the less space you have to add inches of insulation or extra batteries. I first did all this in a Jag 27. Sure it costs money to instal a keel cooler and compressor but it's only done once and then you know you have the most efficient system you can get.

People don't normally add keel coolers to cabinet fridges.

 

[sailorman]

Extra insulation will help, if the cold doesn't escape you won't need to spend power replacing it

Bare in mind though, insulation a cabinet fridge like yours has to be done bearing in mind that you still need to keep the compressor and condenser cool.

Top loading fridges can have some benefits, it can be easier to add insulation, you can keep the compressor and condenser remote and that makes it easier to cool them, plus, when you open the lid, all of the cold doesn't fall out on the floor.

add a PC fan in the compressor locker

 

[Catalina36]

People don't normally add keel coolers to cabinet fridges.

Indeed so. They find a locker, or in my case at that time the original coolbox in the galley, and convert it into a fridge. Then they don't have space taken up by a cabinet fridge.