Improving fridge efficiency

[GHA]

I just love all thse discussions regarding refrigerators on a boat in the UK. I have never used one and very rarely felt the need for one. The sea temperature around the UK is low enough to adequately cool drinks (in a water filled bucket, on a lanyard over the side or in the bilge). I always overnight in harbour so shop daily for fresh food.

Am I alone?

If the boat next to you has cold beer you will be

interesting discussion for a liveaboard, I can feel some measuring coming up..

 

[coopec]

This is almost always obtained from the hull in contact with the sea, maybe the bilge but maybe somewhere else on the hull. Air should rise from this point but needs somewhere for the warm air to exit after passing the heat exchanger. even more.

Darwin Sea Temperature
(Today) 6th Mar 2014
29.4°C
85°F

I have a refrigeration mechanic helping me with installation of my fridge/freezer and he has worked on a lot of boats in Darwin. He says you need an absolute minimum of 4 in (100mm ) insulation and keep it away from the hull.!! Of course the waters are cool around the UK but not in the tropics where many fridges are useless.

 

[vyv_cox]

Darwin Sea Temperature
(Today) 6th Mar 2014
29.4°C
85°F

I have a refrigeration mechanic helping me with installation of my fridge/freezer and he has worked on a lot of boats in Darwin. He says you need an absolute minimum of 4 in (100mm ) insulation and keep it away from the hull.!! Of course the waters are cool around the UK but not in the tropics where many fridges are useless.

My boat is in Greece where we experience similar water temperatures, maybe one or two degrees lower. As said in an earlier post I use a standard Waeco fridge that has only 20 mm or so insulation but I use a water cooled heat exchanger. It runs for about 1/3 of the time, day and night, and consumes about 3 amps when running. The statement you are replying to (and criticising?) referred to the cooling air, nothing to do with the fridge or the insulation.

 

[coopec]

My boat is in Greece where we experience similar water temperatures, maybe one or two degrees lower. As said in an earlier post I use a standard Waeco fridge that has only 20 mm or so insulation but I use a water cooled heat exchanger. It runs for about 1/3 of the time, day and night, and consumes about 3 amps when running. The statement you are replying to (and criticising?) referred to the cooling air, nothing to do with the fridge or the insulation.

I am using a Waeco too in the yacht I am building so what you say is re-assuring. I wasn't really criticizing your statement that the coolest air is near the hull because where do you get cool air in a yacht in Darwin Harbour!!

My yacht has a sandwich hull and deck, all ports open and I have 6 dorade vents so the yacht is quite cool but imagine a steel yacht in the tropics without proper ventilation.

 

[vyv_cox]

I am using a Waeco too in the yacht I am building so what you say is re-assuring. I wasn't really criticizing your statement that the coolest air is near the hull because where do you get cool air in a yacht in Darwin Harbour!!

Everything is relative! The coolest air is presumably nearest to the water. In Greece there is perhaps a 10-15 degree difference between water and air temperatures at midday, maybe nothing at all at night. Many boats have air cooled heat exchangers but unless their refrigerator is very well insulated they will be running constantly.

 

[GHA]

So to actually measure any benifit, what would be the best way to go about it? Measure volts and amps with the extra fan only on for 50% of the time?

 

[vyv_cox]

So to actually measure any benifit, what would be the best way to go about it? Measure volts and amps with the extra fan only on for 50% of the time?

In the end the critical measurement seems to be how often the fridge cycles on and off once it is running in a stable condition. I time mine regularly to make sure all is well and as a guide to when it needs defrosting. I think you will find that the consumption of the fan is negligible: even my little pump only consumes 0.5 amp compared with the 3 - 3.5 amps of the fridge. A fan is probably a lot less than that.

 

[rogerthebodger]

In the end the critical measurement seems to be how often the fridge cycles on and off once it is running in a stable condition. I time mine regularly to make sure all is well and as a guide to when it needs defrosting.

What do you consider is an acceptable duty cycle.

In summer (Dec ,Jan, Feb) in Durban Mine runs at about 70% on time rest of the year about 45-50% on time.

 

[Colvic Watson]

The little fans use almost nothing.

 

[vyv_cox]

What do you consider is an acceptable duty cycle.

In summer (Dec ,Jan, Feb) in Durban Mine runs at about 70% on time rest of the year about 45-50% on time.

Mid summer in Greece about 30 - 35% of the time. Water cooling makes a huge difference to a standard fridge.

 

[rogerthebodger]

Thks a lot.

Is yours water cooled or air cooled

Mine is water cooled using a Sintered bronze Frigoboat keel cooler.

http://www.veco.net/index.php/en/pr...ration/refrigeration-systems-eng/keel-coolers

I have looked at Owen's write up and the refrigerant level seems OK by that but still seems to me to have too high a duty cycle.

When I built the cabinet I used 150mm thk expanded polyurethane foam surrounding a stainless steel liner. We only get a small amount of external condensation during the summer when the humidity is very high other times other the year we don't get any.

Any thing else I could check.

Thks again for your help

 

[vyv_cox]

Water cooled, once through driven by a PAR Max 1 pump.

 

[geem]

Mid summer in Greece about 30 - 35% of the time. Water cooling makes a huge difference to a standard fridge.

I would concur with regard to duty cycle. We built the fridge on our last boat. Keel cooler, danfoss compressor and 90 litres fridge. The tub had a minimum of 100mm kingspan insulation. I reckoned on 1amp per hour average for a 2.5 amp compressor. Turning 1/3 of the fridge into freezer rather than just a frozed icebox increased duty to 2amp/hr. Fridge at -4degC