Freezers: keep warm or keep cold?

[John]

We got a new freezer - it's a John Lewis Frost-Free job. We keep it in the utility. When my wife told the salesman this, he asked about the ambient temperature of the room (which is very cool, not to say cold.)

He seemed to imply it would be better if the room that the freezer is kept in should be warmer rather than colder. This doesn't seem to make sense to me.

I wasn't there, and I figure it is more useful to get a consensus here than go back and ask a random salesman in a shop (even if it is John Lewis).

The instructions for the freezer aren't a lot of help (produced in the same country the freezer was made: very terse as well as poor English). However it does state preferred ambient temperature ranges ... all I have to do is find the serial number plate to find out which grade ours is -- I am suspecting the plate is underneath the damn thing, having failed to find it on the back.

ANYWAY: what's the story? I would have thought that the colder the room, the better. The thing is: this freezer seems to be running its condenser quite as much as our ancient thing, that we swopped it for.

Cheers John

[Matty F]

The salesman is wrong. The colder the air is around the radiator, the less work the motor has to do to keep the food at the same cold temperature.

[Richard Downing]

It's b....locks. The physics is easy. A freezer is a heat pump, it pumps heat from the inside to the outside. The cooler the outside is the less energy is required to attain the correct temperature inside.

Other considerations: The running temperature of the pump - better in a lower temperature as long as any grease used in the bearings doesn't freeze (no liquid nitrogen in your utility is there?).

The working fluid (Ammonia usually) doesn't freeze, or fail to evaporate. (Only a problem in the Outer Planets, and certainly not your utility room)

R.

[MikeH]

Keep it in a cool place. Not only will the condenser be able to dump heat easier in a lower ambient temperature, but the heat energy passing into the freezer from the surrounding air in the first place will be reduced as well.

Frost-free freezers are less efficient than ones that have to be manually defrosted. Ours has a heater element (about 300 watts) that runs round the evaporator (the bit that cools the air inside the freezer). Every eight hours or so the compressor switches off and the heater is turned on for a few minutes. This melts the ice build-up on the evaporator which then drains away through a pipe into a tray on top of the compressor from where it naturally evaporates. Because the heater is part of the evaporator assembly and is inside the freezer compartment, inevitably that extra energy (300 watts for a few minutes three times a day) than has to be removed when the compressor switches back on again at the end of the defrost cycle.

Mike

[nafuk]

Some freezers will not work if kept in a very cold (less than around

4=B0C??). There have been cases of people replacing old freezers in outhouses, where it gets very cold in winter, with newer freezers which have a minimum temp requirement, and the freezers not working. Check the instructions of phone the manufacturer.

MikeH wrote:

[Guy King]

The message from John contains these words:

Nor should it. The device is trying to shove heat out the back - the cooler the surroundings the easier this is. The warmer the surroundings the harder it has to try - and use more power in the process.

The only gotcha is that some fridge-freezers only have one thermostat and that's in the fridge bit. If the ambient is below the set-point for the thermostat in the fridge it'll never switch on so the freezer bit will never get cooled as it operates as a side-show to the fridge. But that doesn't appear to be the case in your situation.

Whichever course you take, ensure there's good airflow over the back of the unit - don't pile the top up with stuff that goes back to the wall, and don't block round the sides/bottom.

[lairdy]

I'd follow the manufacturers recommendations over bar-room science. Fridges and freezers *do* have specific operating temperatures, and it's fairly well known that fridges in particular can struggle in a very cold environment. Freezers should have more leeway as they are cooling to a much lower temperatures.

How inefficient is a badly frosted-up unit, though? Generally, they start to cut in more and more often to less and less effect as the plates freeze up.

[Edgar Iredale]

I asked a similar question here over a year ago just after I bought a new freezer. In the manual my new Frigidaire said it needs a minimum ambient temperature of 16degC. I was very cross - and still am - with Currys for not telling me this before I bought it and then for refusing to take it back without a large surcharge.

I think there are two reasons:

First some fridge/freezers use only one mechanism to work both parts. If the machine doesn't run enough one part remains cold while the other part gradually defrosts and the food rots. Or something like that.

Secondly cold ambient encourages condensation inside the freezer case but outside the main storage compartment. This either rusts the machine or builds up into a large block of ice underneath which never seems to get melted.

With some encouragement here I mended the old freezer and now use both freezers on the approach to Christmas then switch off the Frigidaire until the spring when I swap over. (I'm fortunate to have the space to keep two freezers.) This allows both freezers to get a really thorough defrost each year.

In my old Hotpoint the block of ice in its innards took a very long time to completely defrost and dry out. Not days but weeks in summer.

Edgar

[Dave Liquorice]

Looked inside it? That is where it is for our fridge and fridge/freezers.

Is it cooling to the same, measured, temperature or lower?

There is information on the web about why fridges and freezers have a designed ambient temperature range. Have a dig for the facts rather than the unsupported guff already posted. For single compressor fridge/freezers it is a very real issue as the freezer is part only cooled when the fridge wants cooling. With a low ambient temp the heat gain in the fridge will be longer than designed and thus the freezer will also warm up, possibly above "safe" levels.

[marvelus]

A week or so ago Will Dean gave a respose to thread "freezer operation at low ambiant temp"

"I suspect that one reason for the caution about extreme temperatures is that domestic fridges/freezers use a capiliary tube as an expansion device, rather than the more sophisticated thermostatic devices used in commercial plant. Because the capiliary is just a fixed flow restriction rather than a proper temperature/pressure regulator, it's specified on the basis of fairly narrowly constrained pressure/temperature conditions throughout the plant.

A very cold condenser will give low high-side pressures which might be outside those for which the capiliary was designed - it can also cause an excessive proportion of the charge to hang around within the condenser.

All they're really saying in the instructions is that they designed the freezer to perform to specification with a certain external temperature range, and that outside that range it may not meet the spec."

[John]

ACH! So he did! I forgot to Google Groups for 'freezer' before I posted: my sincere apologies (though I think I've got answers more suited to my simpler mind).

Cheers John

[Ian_m]

Correct, my mates fridge/freezer in his outside shed, defrosts the freezer when the temperature drops below about 5°C. This is because the compressor no longer runs as it thinks the fridge is cold enough ie below 5°C. It does state a minimum of +15°C so he wasn't too surprised. So after piddling around with a 100W tube heater set to 5°C and getting variable results he moved it back indoors where it now works perfectly.

If you shop around you can get fridges and freezer that do work at lower temperatures but tend to be commercial models with commercial price tags.

[Andrew Gabriel]

The engineering is not so easy though. Units are somewhat constrained on temperature range they can cover, so they are designed to cover the most common temperature range in a home, i.e. 16-35C.

Pumps usually outlast a freezer at normal ambient temperatures, so there's not much to be gained trying to make one last longer.

Ammonia hasn't been used in domestic fridges or freezers for over

50 years (except adsorption fridges). It is still used in some very large industrial fridges and freezers.

[L Reid]

Salesman is probably correct. I'd suggest you try to keep within the ambient range of temperatures which will be mentioned in the instructions. Alternatively you could try and find out the exact refrigerant used by the freezer and work out what the minimum temp will be based on Pressure and type. Some fridges these days use R134a, which has a boiling point of -26 deg C at atmospheric temp and 5 - 10 deg C when under pressure in a Fridge, hence the minimum 15 deg ambiant temperature requirement to ensure the refridgerant vaporises when it leaves the freezer compartment.

[Guy King]

The message from "L Reid" contains these words:

The refrigerant is supposed to evaporate inside the cold compartment - that's how they work. The refrigerant draws the energy needed to go from liquid to gas from the heat in the bit you're trying to cool.

If you were to evaporate the liquid elsewhere you'd get lumps of ice forming outside the compartment at whatever point it's mistakenly doing it.

[jim]

This problem reared its head when shopping for a replacement chest freezer [no fridge] 3 years ago or so. There was a big sign up in the elec section of a dept store saying none of their freezers were suitable for outside use.

I didn't believe it but after some querying & searching about, it did indeed turn out that there are 2 types of freezer - ones which work at any ambient & ones which need a minimum temp. We found Iceland sold some (at least over the web) which were suitable for outside use - NB that was 3 years ago. It is just possible the more expensive ones don't have this problem.

I didn't discover the reason, but there were suggestions that it was due to the change from CFC gases. Some replacement gases - no doubt the cheaper ones - apparently forced this limitation. OTOH it could simply be that some freezer control systems cannot deal with temp inversion (or it could be both reasons).

Long ago we had a plain fridge which didn't like temp inversion, so it didn't work overnight in midwinter - that was before CH came our way. But there's quite a number of other operational conditions in practical refrigeration cycles which defeat the assumption 'colder is better'. One I've seen in a southern Europe in a hot summer was due to ice formation due to the fridge/freezer running too long. Ice is a thermal insulator, which if it forms & doesn't have a chance to melt/evaporate, stops the thermostat sensing the correct temp & so the fridge never stops running, forming more ice over the thermostat....etc etc.

BTW SFAIUI in fridge a temperature control is applied to the freezing section & the rest of the fridg is cooled relatively. So the temp in the ice box is the key factor, not the temp in the fridg itself.

Good news is that the freezer we have that seemed to be failing 3 years ago is still going :-))

[Matty F]

I am sorry that I butted in. I never considered such low temperatures outside. It's not a problem here in New Zealand, where I grow tomatoes outdoors in winter.

[Pete C]

Hi,

I think the problem is that if the temp difference between condenser and evaporator is too low for too long (low 'superheat'), there's a chance liquid refrigerant will get back to the compressor, and jam it or at least reduce it's life expectancy.

At a best guess, this is because the condenser and compressor condenses refrigerant more efficiently at low ambient temps and so the pressure in the evaporator rises.

As the pressure rises so does the boiling point of the refrigerant, until it's too high to evaporate, and liquid refrigerant gets back to the compressor.

One way round it might be to time the run time of the compressor at say 5°C, then when it gets colder add _some_ insulation to the condenser to trap heat and raise it's operating temperature.

As long as the run time at lower temps then stays above this figure, it implies the condenser is working at a high enough temperature due to the insulation.

With the old style black finned condenser, just adding some polystyrene to the outside and leaving the inside free may be enough.

A more elegant solution would be making an insulated box around the condenser ventilated by a thermostatically controlled fan

Needless to say, no responsibility accepted if anyone blows up their freezer doing the above!

The forum at would be a better place to get a definitive answer.

cheers, Pete.