240v Fridge vs. 1v Fridge

[Tim Good]

240v Fridge vs. 12v Fridge

I posted recently that I had a 240v watermaker. The consensus was that keeping the 240v and a genset might be a good idea due to high outputs.

However, my fridge and freezer are also 240v. Yes I have a freezer. Long term I do not intend to use the freezer and just use it for food storage. The system is a 90's Frigoboat system which is powerful with a large waterpump and compressor. I have found that I can run it for a couple of hours a day and keep it cool but it does need 240v.

Since I have never been a liveaboard before, but will be next year whilst starting a circumnavigation, would you recommend, ripping out all the old 240v system, saving some weight and then putting a more simply 12v system in maybe with a keel cooled plate instead of a waterpump?

 

[Trident]

Re: 240v Fridge vs. 12v Fridge

If cost is not an issue then a keel cooled 12v will be much less power hungry and work extremely well. I have two non keel cooled 12v fridges and my friends have a larger single keel cooled which uses under half the power mine do (they estimate around 24 amps a day for an ice cold fridge of round 120l capacity)
After summer in the Med I plan to add a keel cooler this winter - I have 600w of solar so keep up with the fridges ok but I'd rather not use power I don't need to

A keel cooler and suitable compressor and fitting will be around £800 or more though...

 

[Tim Good]

Re: 240v Fridge vs. 12v Fridge

A keel cooler and suitable compressor and fitting will be around £800 or more though...

Yeah it is coming in at about £1000 at the moment plus the lift needed to put the keel cooler in. I was hoping not to come out of the water again this year but it is beginning to look likely.

Maybe I could keep the huge existing fridge water pump as a spare emergency bilge pump run from the inverter

 

[macd]

Re: 240v Fridge vs. 12v Fridge

If cost is not an issue then a keel cooled 12v will be much less power hungry and work extremely well. I have two non keel cooled 12v fridges and my friends have a larger single keel cooled which uses under half the power mine do (they estimate around 24 amps a day for an ice cold fridge of round 120l capacity)
After summer in the Med I plan to add a keel cooler this winter - I have 600w of solar so keep up with the fridges ok but I'd rather not use power I don't need to

A keel cooler and suitable compressor and fitting will be around £800 or more though...

Possibly 24 amp-hours per day?

 

[affinite]

Re: 240v Fridge vs. 12v Fridge

If cost is not an issue then a keel cooled 12v will be much less power hungry and work extremely well. I have two non keel cooled 12v fridges and my friends have a larger single keel cooled which uses under half the power mine do (they estimate around 24 amps a day for an ice cold fridge of round 120l capacity)
After summer in the Med I plan to add a keel cooler this winter - I have 600w of solar so keep up with the fridges ok but I'd rather not use power I don't need to

A keel cooler and suitable compressor and fitting will be around £800 or more though...

I agree on the merits of the keel cooler if power is at a premium but if you have 600W of solar and are generating enough power to run an aircooled fridge OK I'm not sure of the logic of spending £800 to reduce your (free) power consumption.

 

[GrahamM376]

Re: 240v Fridge vs. 12v Fridge

We have a BD50F (fan assisted air cooled), with large "O" ring, draws about 7 amps when running and keeps our 170L box cool enough, the large O ring freezes food indefinitely and makes ice OK. 200W solar + Aerogen 4 keeps up with it but more would be better.

 

[ip485]

Re: 240v Fridge vs. 12v Fridge

I have two very well insulated chests, one fridge, one freezer or fridge, with top opening lids and a keel cooler for each. I must measure the draw but the panels more than cope with the combination and other services in a UK summer. It is worth the investment. The only draw back is the sintered plates seem to love fouling, not that it seems to reduce their performance.

 

[geem]

Re: 240v Fridge vs. 12v Fridge

Just a thought. Keel coolers get their efficiency from the fact that the sea is cooler than the air in the boat. This reduction in condensing temperature is where the reduction in amps comes from. Once you get up to high air temperatures in you boat the compressors on air cooled condensers start to draw more amps and/or runs for longer. When you get to about 40 degrees they really start to struggle.
If you sail in the Caribbean, the efficient benefit of keel coolers is not so great. The sea temperature is typically 28 degC and so is the air temperature. Condenser efficiency should be pretty similar for air or water cooled. Keel coolers have a great advantage where the sea is relatively cool so if you cruise around the Algarve for example they would be a great solution. Air cooled can work very well if you can install the condenser such that it will pull cool air from the bilges. The air in the bilge will be similar to the sea temperature that it is immersed in. We have an air cooled condenser on our fridge. Efficiency is not of any concern since the setup is very efficient. The small freezer is inside the fridge and the fridge tub is super insulated. The downside of air cooled in a hot climate is the noise of the cooling fan and the heat that is discharged to the cabin. Next time I will go water cooled for these reasons

 

[GrahamM376]

Re: 240v Fridge vs. 12v Fridge

The downside of air cooled in a hot climate is the noise of the cooling fan and the heat that is discharged to the cabin. Next time I will go water cooled for these reasons

That's why I moved our compressor into the cockpit locker which made a big difference. Been getting above 40 degrees on a few days over the past couple of weeks and although running time increased, fridge worked OK. Unfortunately, the box is badly insulated and would be major surgery to strip it out but when I suggested adding extra insulation internally and relining, SWMBO didn't like the idea of reduced space - can't win.

 

[geem]

Re: 240v Fridge vs. 12v Fridge

That's why I moved our compressor into the cockpit locker which made a big difference. Been getting above 40 degrees on a few days over the past couple of weeks and although running time increased, fridge worked OK. Unfortunately, the box is badly insulated and would be major surgery to strip it out but when I suggested adding extra insulation internally and relining, SWMBO didn't like the idea of reduced space - can't win.

Unfortunately It's not an option to move ours as distance to the cockpit locker is too great and I am not sure I could get rid of the heat without ventilating the locker.

 

[Chris_Robb]

Re: 240v Fridge vs. 12v Fridge

A couple of people have mentioned insulation as important. I cannot stress how important it is. All round us last night (Turkey) boats had their engines going charging batteries till after 10. This is almost entirely due to the failure of yacht builders to insulate their fridges.

The proper thickness should be 4 inches (100mm) all round including the tops. The other common problem is they are too big. Westerly, Moody fr example like most 90's boats have 1 inch of insulation with the westerlies having just plywood across the top. I

So before doing work on making the compressor more efficient, do something about the insulation. On very large fridges you can put a layer of insulation inside which is better than nothing but can look a bit of a bodge. The Oceanlord fridge was so large and so badly insulated that I just ripped it out and started again from scratch with 4 inches all round. Perfect.....

Some indications as to efficiency: If you have ice build up on the plates, the compressor is working too hard; it should always melt as the end of each cycle and should be free of ice. ONLY solution Insulate.

 

[RobbieW]

Re: 240v Fridge vs. 12v Fridge

.... The only draw back is the sintered plates seem to love fouling, not that it seems to reduce their performance.

My fridge uses an Isotherm system with a cooling coil in the sink water drain, that doesnt foul and I think its to do with the heat generated - they little critters dont like it! It also works well enough when on the hard as air is drawn over the coil, there power usage is less of an issue as shore power is usually available. I certainly see the problem with sintered plates on the SSB ground plate though

EDIT: Just had a look at the latest Isotherm catalogue and there is a sea water temp limit of 28C - that may be why my overall power usage has gone up in the last couple of weeks as the sea has about reached that temp all the time!

 

[vyv_cox]

Re: 240v Fridge vs. 12v Fridge

Mb

Just a thought. Keel coolers get their efficiency from the fact that the sea is cooler than the air in the boat. This reduction in condensing temperature is where the reduction in amps comes from. Once you get up to high air temperatures in you boat the compressors on air cooled condensers start to draw more amps and/or runs for longer. When you get to about 40 degrees they really start to struggle.
If you sail in the Caribbean, the efficient benefit of keel coolers is not so great. The sea temperature is typically 28 degC and so is the air temperature. Condenser efficiency should be pretty similar for air or water cooled. Keel coolers have a great advantage where the sea is relatively cool so if you cruise around the Algarve for example they would be a great solution. Air cooled can work very well if you can install the condenser such that it will pull cool air from the bilges. The air in the bilge will be similar to the sea temperature that it is immersed in. We have an air cooled condenser on our fridge. Efficiency is not of any concern since the setup is very efficient. The small freezer is inside the fridge and the fridge tub is super insulated. The downside of air cooled in a hot climate is the noise of the cooling fan and the heat that is discharged to the cabin. Next time I will go water cooled for these reasons

The reason that seawater cooling is more efficient than air cooling is not because of temperature but specific heat. The specific heat of water is around 1000 times that of air, so that transfer of heat from a warm condenser is considerably more effective. To test this, put your hand inside the fridge at 4 degrees C, then put it in a bucket of water at the same temperature. Which do you think will make it cold first?

 

[jordanbasset]

Re: 240v Fridge vs. 12v Fridge

Mb

The reason that seawater cooling is more efficient than air cooling is not because of temperature but specific heat. The specific heat of water is around 1000 times that of air, so that transfer of heat from a warm condenser is considerably more effective. To test this, put your hand inside the fridge at 4 degrees C, then put it in a bucket of water at the same temperature. Which do you think will make it cold first?

On our old boat we changed from air cooled to keel cooled and found a big drop in energy consumption. Never really thought about why it should drop so much, bearing in mind what people have said about the ambient sea temperature. But now you have said this it all make sense. Should have worked it out myself but never gave it much thought.

 

[geem]

Re: 240v Fridge vs. 12v Fridge

Mb

The reason that seawater cooling is more efficient than air cooling is not because of temperature but specific heat. The specific heat of water is around 1000 times that of air, so that transfer of heat from a warm condenser is considerably more effective. To test this, put your hand inside the fridge at 4 degrees C, then put it in a bucket of water at the same temperature. Which do you think will make it cold first?

I don't believe its simply about specific heat capacity. Assuming the fridge manufacturer has sized the fins on the air cooled condenser to match the refrigerant cooling needs of the system the fin area and fan volume will normally be sized to reject the heat.
Rule of thumb below;
Tc = condensing temperature
Ta = ambient temperature
te= evaporating temperature
tei = air inlet to the evaporator

TDc = Tc - Ta
TDe = tei - te

For air cooled condensers :
Hot climates ------- TDc = 6 to 8°C
Normal climates ------ TDc = 8 to 10 °C
cold climates ---------- TDc = 12 to 15 °C

For water cooled condenser :
TDc = 15°C

 

[GrahamM376]

Re: 240v Fridge vs. 12v Fridge

I don't believe its simply about specific heat capacity. Assuming the fridge manufacturer has sized the fins on the air cooled condenser to match the refrigerant cooling needs of the system the fin area and fan volume will normally be sized to reject the heat.

In a boat situation, air circulation to the fins is usually restricted by the compressor being located in a cupboard which I'm sure the makers haven't allowed for in their calcs. so, compared to being in water not good. In our case the original fit was not fan assisted and mounted in a small cupboard directly under the cool box, plain stupid .

 

[geem]

Re: 240v Fridge vs. 12v Fridge

In a boat situation, air circulation to the fins is usually restricted by the compressor being located in a cupboard which I'm sure the makers haven't allowed for in their calcs. so, compared to being in water not good. In our case the original fit was not fan assisted and mounted in a small cupboard directly under the cool box, plain stupid .

I have mine mounted in a duct that is quite like a chimney. Air is pulled in from low level and discharges through a grille in the top of a cupboard. It works pretty well as long as you don't put clothes on top of the cupboard and block the discharge vent!

 

[Max K]

Re: 240v Fridge vs. 12v Fridge

Just a thought. Keel coolers get their efficiency from the fact that the sea is cooler than the air in the boat. This reduction in condensing temperature is where the reduction in amps comes from. Once you get up to high air temperatures in you boat the compressors on air cooled condensers start to draw more amps and/or runs for longer. When you get to about 40 degrees they really start to struggle.
If you sail in the Caribbean, the efficient benefit of keel coolers is not so great. The sea temperature is typically 28 degC and so is the air temperature. Condenser efficiency should be pretty similar for air or water cooled. Keel coolers have a great advantage where the sea is relatively cool so if you cruise around the Algarve for example they would be a great solution. Air cooled can work very well if you can install the condenser such that it will pull cool air from the bilges. The air in the bilge will be similar to the sea temperature that it is immersed in. We have an air cooled condenser on our fridge. Efficiency is not of any concern since the setup is very efficient. The small freezer is inside the fridge and the fridge tub is super insulated. The downside of air cooled in a hot climate is the noise of the cooling fan and the heat that is discharged to the cabin. Next time I will go water cooled for these reasons

One of the first mods I made to our boat when it came out of warranty. Not only does turning the compressor's fan round draw "Cool air from the bilges", it also avoids blowing warm air into the boxing around the fridge insulation and heating it up. We are on Kefallonia at the moment with the sea temp. 28.5 and the air 33.0. The thermometer in our fridge hovers around 0C most of the time but we do keep a slab of foil coated foam on top of it to augment the insulation and compensate for the lack of a thermal break in the metal lid edging and frame. Every calorie of energy saved is so important with low power refrigeration. Another tweek is to get the correct "Battery cut-out voltage" selected by altering the resistor (yellow link in thermostat housing) going to terminal "T". These units are made primarily for RVs where a deeply discharged automotive battery is likely do much more harm than it is with a marine system and proper deep cycle batteries.

Max.

.