Fridge Temperatures❓

[nortada]

Summer temperatures still continue in the Algarve. Hence my question.

Clearly to produce ice for the G&T the ice box has to be kept around 0C but what is the maximum the fridge box can be run at to keep food fresh

The fridge is our biggest onboard electrical consumer so with fewer sunshine hours for the solar panels, fridge running times on anchor becomes increasingly significant.

For every degree down the fridge running time increases exponentially. ?

 

[GHA]

I go for between 4º and 6º, still alive

Ambient temperature makes big difference, up above 30º my duty cycle will be up near 50% against more like 20% at the end of a cool night.

 

[nortada]

I go for between 4º and 6º, still alive

Ambient temperature makes big difference, up above 30º my duty cycle will be up near 50% against more like 20% at the end of a cool night.

I do find playing a small free standing fan powered by a Solar Charger, BERNET 24000mAh Portable Solar Power Bank, has a significant impact on the duty cycle.

 

[GHA]

I do find playing a small free standing fan powered by a Solar Charger, BERNET 24000mAh Portable Solar Power Bank, has a significant impact on the duty cycle.

Don't doubt that at all, one of these months I'll get round to mounting a little computer fan to suck hopefully slightly cooler air from the bilges over the evaporator. My thermostat is an arduino & logs duty cycle so would be interesting to see the difference it makes.
Maybe not much at the moment in a boatyard

 

[Mistroma]

Increasing insulation is the obvious answer but unfortunately it's usually not a simple job. However, there is one part that can usually be improved at little cost on many top opening fridges and that is the top.

The worktop above our fridge used to get very warm in summer whenever the sun shone through the hatch or windows. I bought some foam and my wife made up a cover from vinyl. This helped greatly as the lid felt cold even when the top of the vinyl cover was warm. It was improved further by cutting up a cheap reflective car windscreen cover and sliding 2 pieces inside the vinyl cushion.

The cushion also helps improve the door seal, though I've already installed extra seals on the hatch and the freezer lid inside the fridge compartment.

It's a minor nuisance moving the cushion to access the fridge but it is still firm enough to act as a worktop when access isn't required. Our freezer compartment usually manages -5 to -10C with the fridge around 4-6C.

 

[Daverw]

It’s all about the TD(temp difference) of inside to outside and the insulation properties of the box. Maximise this and refrigeration duty requirement drops dramatically. Insulation is very high tech these days and does not need to be thick, don’t forget you have a six sided box and any sides improved will make a difference

 

[Heckler]

Summer temperatures still continue in the Algarve. Hence my question.

Clearly to produce ice for the G&T the ice box has to be kept around 0C but what is the maximum the fridge box can be run at to keep food fresh

The fridge is our biggest onboard electrical consumer so with fewer sunshine hours for the solar panels, fridge running times on anchor becomes increasingly significant.

For every degree down the fridge running time increases exponentially. ��

Most domestic fridges on land run at or about 8 deg C. Its too warm really. Commercial fridges have to be run at 4 deg C or lower. At that temp beef ages nicely. My fridge on the boat is set at 5 on the temp control. It keeps it at 7 - 8 deg halfway up the deep Bene fridge which is very cold beer temp at the bottom. It cycles nicely. I improved things by putting a computer fan in the compressor compartment to suck air from the cool bilges.
Stu

 

[Flica]

Ideal fridge temperature, as suggested, is 4C. My automatic unit thermostat is set to that temperature @ voltages between 11.8 and 13.0v. Below that the unit cuts out. In fact the top is at 8-9C and the bottom @ 0C.
Above 13.1 system volts the thermostat only cuts out the compressor @ -4C. That happens when motoring or connected to shorepower, when the charger is in operation.
This latter setting means that weak beer freezes.
I have in my power budget allowed 40 amp hours in 24 for the fridge - that's reasonably accurate when day temperature are <26C and night temperatures >16C. At 34C ambient, I guess that estimate is half the actual.
There is a 140mm computer fan blowing air over the heat-exchange matrix, that works at the higher voltage only, when the compressor is running. Air is ducted, by a tumble drier extractor tube from the bilge under the sink to the fascia at the sinks. That exhausts noticeably warm air.
Water-cooling might appear to be more efficient, but with sea temperatures at 28C and the need for a raw-water pump, I doubt the extra complexity justifies the gain in efficiency and the increased capital cost.
This system has been in use in the Med for the last 12 years and, apart from two re-gasses since new in 1997, has proved reasonably reliable, except on those occasions when water leaks short out the solid-state transformer converting 12v dc to 240v ac for the compressor. The whole unit is made by Indel-Isotherm.
The internal fridge temperature can be over-ridden manually - on this setting the fan runs continuously.

 

[geem]

Ideal fridge temperature, as suggested, is 4C. My automatic unit thermostat is set to that temperature @ voltages between 11.8 and 13.0v. Below that the unit cuts out. In fact the top is at 8-9C and the bottom @ 0C.
Above 13.1 system volts the thermostat only cuts out the compressor @ -4C. That happens when motoring or connected to shorepower, when the charger is in operation.
This latter setting means that weak beer freezes.
I have in my power budget allowed 40 amp hours in 24 for the fridge - that's reasonably accurate when day temperature are <26C and night temperatures >16C. At 34C ambient, I guess that estimate is half the actual.
There is a 140mm computer fan blowing air over the heat-exchange matrix, that works at the higher voltage only, when the compressor is running. Air is ducted, by a tumble drier extractor tube from the bilge under the sink to the fascia at the sinks. That exhausts noticeably warm air.
Water-cooling might appear to be more efficient, but with sea temperatures at 28C and the need for a raw-water pump, I doubt the extra complexity justifies the gain in efficiency and the increased capital cost.
This system has been in use in the Med for the last 12 years and, apart from two re-gasses since new in 1997, has proved reasonably reliable, except on those occasions when water leaks short out the solid-state transformer converting 12v dc to 240v ac for the compressor. The whole unit is made by Indel-Isotherm.
The internal fridge temperature can be over-ridden manually - on this setting the fan runs continuously.

A raw water pump for water cooled is a thing of the past. Modern water cooled fridges use a keel cooler. The compressor pumps the refrigerant directly through a bronze heat exchanger mounted on the outside of the hull. These are called keel coolers but this description is a little misleading since they have little to do with your keel. I fitted one to our last boat but went air cooled on the current boat. I think that was a mistake in hindsight. The keel cooled fridge was super quite and didnt push hot air into the boat. I would go keel cooled next time even with the 30degC water temperatures we experience in the Caribbean.

 

[NornaBiron]

A raw water pump for water cooled is a thing of the past. Modern water cooled fridges use a keel cooler. The compressor pumps the refrigerant directly through a bronze heat exchanger mounted on the outside of the hull. These are called keel coolers but this description is a little misleading since they have little to do with your keel. I fitted one to our last boat but went air cooled on the current boat. I think that was a mistake in hindsight. The keel cooled fridge was super quite and didnt push hot air into the boat. I would go keel cooled next time even with the 30degC water temperatures we experience in the Caribbean.

We fitted a keel cooler this year, it's made a massive difference to the energy consumption of our fridge. The thermostat is set to cut in at 4.5C and out at 2.5C, lovely and cold, within the recommended limits for refrigerated food and and plenty of ice - definitely worth spending the money on the bronze plate.

 

[srm]

Keel cooler plus lots of insulation. Run fridge just warm enougn to stop ice forming on inside - otherwise the deep drawer sticks. Installed 2010 and run it 24/7 - even for a week at anchor in Scotland on solar (too sheltered for wind turbine to do much) without any concerns for the batteries.

 

[Yngmar]

Re: Fridge Temperatures?

Electronic thermostat is set to keep the temperature at the sensor between 7 and 9°C. The sensor is mounted about halfway up the fridge, not at the evaporator like the old one was. Also added a small radial fan inside the fridge that circulates air (unless packed to the brim with booze). Works well, and the IR thermometer reports 0°C on the bottom where we keep the meat, 6°C in the middle where the drinks and milk are (although it's UHT milk anyways which lasts years unrefrigerated in the bilge before opening) and around 11°C at the top where the butter, veggies, cheese etc. are. Works well and no health problems.

Insulation could be better. PO tried to squirt PU foam into the surrounding areas but missed some spots and made a huge mess in the bilge which I had to stab at for hours with a putty knife to remove. The compressor with condenser is stupidly located underneath the fridge, so warms it from below, derp. There are two fans on the evaporator too, but they're not well placed to move air out of the compartment, so room for improvement there as well.

When we were up the Rio Guadiana and it was stupidly hot, the compressor ran non-stop during daytime hours and it got pretty warm in the below-fridge compartment where it lives. Leaving the access door open and pointing the 12V fan in helped it (but we missed it cooling us).

 

[nortada]

Re: Fridge TemperaturesBugger

Hey ho, as I feared when I started this thread, the temperature rheostat in the fridge box which was becoming increasingly temperamental has given up the ghost in the off position so will now have to dump all of the perishables (fortunately beer doesn’t go off) and more importantly source a new rotary temperature control switch.

Emergency action to sustain ice for SWMBO’s G&T - shorted out rheostat with a jump lead and fridge runs as normal so to my simple mind, this switch needn't be specific to type so any temperature sensitive on/off switch should doWould appreciate other lechie views.

Any other thoughts and yes, why do these things always happen late on a Friday evening - after the pub Fortunately we were not at anchor

Break out the Portuguese - now what is that word for rheostat.?

 

[Yngmar]

Re: Fridge TemperaturesBugger

Emergency action to sustain ice for SWMBO’s G&T - shorted out rheostat with a jump lead and fridge runs as normal so to my simple mind, this switch needn't be specific to type so any temperature sensitive on/off switch should doWould appreciate other lechie views.

Exactly. I've fitted and would recommend one of these. Cheap enough to carry a spare, although so far the first one is doing just fine. Also gives you a nice external temperature readout.

Break out the Portuguese - now what is that word for rheostat?

It's a thermostat, so termostato

 

[Daverw]

Re: Fridge TemperaturesBugger

+1
That’s a better option and makes your thermostat a standard item and as said gives you a temp display, they are avsilable from and fridge supplier, makes sure you have one that allows off cycle defrost, that’s just a timed period off cycle of the compressor.

 

[nortada]

Re: Fridge TemperaturesBugger

Many thanks thanks for all of the advice, I can source a replacement Danfoss Service Thermostat No.3 - Fridges with Auto Defrost - 077B7003, in Portugal for a mere €54.5 but get the same item sent from the UK for just £11.30 + p&p so no brainer! But as it is the weekend, I have yet to place the order.

Is the suggestion rather than go for like for like a better plan would be something like a KKmoon 10A 12V Digital Temperature Controller Thermocouple -40℃ to 120℃ with Sensor Delay Protection Function? Agree it is very cheap.

Not interested in an external readout so rather than cost, what would be the over all benefit and would it be compatible with the instillation?

 

[GrahamM376]

Re: Fridge TemperaturesBugger

Many thanks thanks for all of the advice, I can source a replacement Danfoss Service Thermostat No.3 - Fridges with Auto Defrost - 077B7003, in Portugal for a mere €54.5 but get the same item sent from the UK for just £11.30 + p&p so no brainer! But as it is the weekend, I have yet to place the order

There's a fridge repairer in Portimao, got a new thermostat from him a few years ago, not very expensive. He's (assuming still there) on the road roughly behind the sailing club, which about half way between the marina and the town.

 

[nortada]

Re: Fridge TemperaturesBugger

There's a fridge repairer in Portimao, got a new thermostat from him a few years ago, not very expensive. He's (assuming still there) on the road roughly behind the sailing club, which about half way between the marina and the town.

Many thanks Graham; I will check him out when next over that way (which won’t be long as the other half of the team likes to shop at the new Waitrose/Iceland) and report back.

 

[Daverw]

Re: Fridge TemperaturesBugger

You can fit a temporary switch just to get system running, just switch off for periods. The advantage of electronic control is longer term reliability and better temp control. I would however use a proper refrigeration controller , Dixcell, elliwell, danfoss etc rather than any temp controller as these have defrost options as standard, cost about £30 or more though so more than mechanical stat.