Plastic KETER sheds

[fixitflav]

I'm no expert in these matters but is not at least part of the issue related to the fact that the sort of refrigeration appliances we're talking about depend upon 'phase changes' - i.e.. repeated changes of the refrigerant from liquid to gas and then back to liquid again - 'absorbing' ('latent') heat when it goes from liquid to gas (within the fridge or freezer) and then 'releasing' that ('latent') heat when it next goes from gas back to liquid (outside of the fridge or freezer). It is a combination of temp and pressure that governs those phase changes.

Good explanation!

That being the case, if the ambient temp outside of the fridge or freezer is too low, then the compressor may not be able to increase the pressure enough to liquify the gaseous refrigerant - so the 'cooling cycle' will grind to a halt.

I don't think that's quite right, as lower temperature makes it easier to liquefy the refrigerant (in the heat dump grid on the back of the freezer). I would guess it's down to the choice of refrigerant. The temperature in the evaporator must be something like -25°C (at a guess) for usual compartment setting -18°C, but it must still be liquid at the higher pressure in the heat dump. I don't know any figures.
I believe early ones used ammonia refrigerant, but not too good if it leaked, though at least you'd smell it! I don't know whether CFCs are still used, or changed to eg hydrocarbons because of the ozone layer. Probably refrigerants vary in low ambient temperature performance, maybe there are other design factors, like pressure.
My Bosch fridge/freezer has temperature range +10° to 32°. It's in a utility room so OK, but it would be a non-starter for an unheated shed or garage. I don't remember minimum temperature being mentioned when I bought it 20-odd years ago.

 

[JohnW2]

Good explanation!

Thanks!

I don't think that's quite right, as lower temperature makes it easier to liquefy the refrigerant (in the heat dump grid on the back of the freezer).

You're right. I need to ask my brain to revisit that - since, as you say, it seems that my thinking got back-t-front!

In the meantime, and particularly 'today' this makes me wonder about the other end of the environmental spectrum - i.e. when the ambient temp may be 'too high' for a refrigeration appliance to work (and I mean 'too high for the refrigeration cycle to work', not simply the affect of have hot air surrounding the appliance!).

For most of today, a room in which I have a fridge-freezer has been well above 35 degrees, but it's carried on working OK (cavity temps remained much as they should be). If the ambient temp keeps rising, presumably one then does (with thinking the right way around this time ) eventually reach the point at which the compressor cannot re-liquify the refrigerant?

I would guess it's down to the choice of refrigerant. ..... Probably refrigerants vary in low ambient temperature performance, maybe there are other design factors, like pressure.

Well, yes, I think the two primary issues (in determining ambient temp performance) must be the characteristics of the refrigerant and the pressures, mustn't they?

My Bosch fridge/freezer has temperature range +10° to 32°. It's in a utility room so OK, but it would be a non-starter for an unheated shed or garage. I don't remember minimum temperature being mentioned when I bought it 20-odd years ago.

I have to say that over the past 50 years or so I've lived with countless fridges and freezers in garages, cellars and various outhouses (some of which must have got very cold at times) but have never become aware of any malfunction as a result - and, like you imply, doubt that I would even have thought about the potential issue until quite recently!

 

[mikehammer69]

I’ll hazard a guess that freezers don’t work as efficiently at lower temps

All I knew was that compressor dehumidifiers work on a similar principle and are suitable for temps above 15c

 

[fixitflav]

In the meantime, and particularly 'today' this makes me wonder about the other end of the environmental spectrum - i.e. when the ambient temp may be 'too high' for a refrigeration appliance to work (and I mean 'too high for the refrigeration cycle to work', not simply the affect of have hot air surrounding the appliance!).

As well as more heat entering when ambient is higher, it has to reject heat via the heat dump grid, which also gets harder.

For most of today, a room in which I have a fridge-freezer has been well above 35 degrees, but it's carried on working OK (cavity temps remained much as they should be). If the ambient temp keeps rising, presumably one then does (with thinking the right way around this time ) eventually reach the point at which the compressor cannot re-liquify the refrigerant?

It seems to be doing pretty well! We're not suffering quite as much round here, but it's bad enough.

I have to say that over the past 50 years or so I've lived with countless fridges and freezers in garages, cellars and various outhouses (some of which must have got very cold at times) but have never become aware of any malfunction as a result - and, like you imply, doubt that I would even have thought about the potential issue until quite recently!

I've had a few, but none has lasted as long as the current Bosch. Some years ago I bought a Brandt, thinking it sounded reassuringly Germanic, but it failed after about 3 years, and turned out it was made in France. Beko seem to be good, especially on minimum temperature, I have a Beko larder fridge, must be 5 years old now, and it's fine.

 

[JohnW2]

As well as more heat entering when ambient is higher, it has to reject heat via the heat dump grid, which also gets harder.

Agreed - but, as I said, if ambient temp continues to rise, making it 'harder' (ultimately impossble) for heat to be lost from the 'dump grid' to the surrounding environment, one presumably may get to the point at which the compressor is unable to liquify the gas, bringing the 'refrigeration cycle' to a halt?

 

[fixitflav]

Agreed - but, as I said, if ambient temp continues to rise, making it 'harder' (ultimately impossible) for heat to be lost from the 'dump grid' to the surrounding environment, one presumably may get to the point at which the compressor is unable to liquefy the gas, bringing the 'refrigeration cycle' to a halt?

Well yes, there must be a limit on ambient temperature above which it can't do the job

 

[JohnW2]

Well yes, there must be a limit on ambient temperature above which it can't do the job

Quite, but my point (which many people may not realise) is that such is the case not simply because of a hot environment 'leaking heat' into the fridge or freezer but, more fundamentally, that, with a given compressor, one will eventually reach a point at which the entire (Physics-based) concept of this method of refrigeration 'ceases to work'.

 

[fixitflav]

Quite, but my point (which many people may not realise) is that such is the case not simply because of a hot environment 'leaking heat' into the fridge or freezer but, more fundamentally, that, with a given compressor, one will eventually reach a point at which the entire (Physics-based) concept of this method of refrigeration 'ceases to work'.

I wouldn't disagree with that

 

[JohnW2]

I wouldn't disagree with that

Thanks. I have to wonder whether, like so many things that are discussed here (and elsewhere) the potential 'problem' being discussed mnay perhaps be more theoretical that something which is actually significant in the practical real world.

As I've implied, over the years and decades I've had fridges and freezers running in places where the ambient temp must sometimes have got very low or very high, but have never been aware of any consequential issues. I may, of course, have 'missed' those consequences at times, but I'd be very interested to know if anyone has actually experienced a known problem due the ambient temp?

 

[fixitflav]

I'd be very interested to know if anyone has actually experienced a known problem due the ambient temp?

So would I

 

[JohnW2]

So would I

That makes two of us, then! However, there is a problem ....

I strongly suspect that, in terms of 'the question' as I worded it, we would probably struggle to find poplewho had (knowingly) 'actually experienced' any problems with a fridge or freezer due to low ambient temp. However, I also strongly suspect that even IF such problems do sometimes arise, it is very likely that they will have gone 'unnoticed'. Lots of 'no' answers to my/our question therefore would not neceessarily mean very much.

I presume that there must have been a fair bit of 'testing', which will have included active/objective identification of any real problems -so I suppose it's really the results of that which we probably should be most interested in!

 

[fixitflav]

Lots of 'no' answers to my/our question therefore would not necessarily mean very much.

You've been reading your Karl Popper!

 

[JohnW2]

You've been reading your Karl Popper!

I haven't really needed to do so to any significant extent, since I have decades of personal experiences which has taught me essentially what he has formalised as 'theories' ... but I wouldn't claim that that makes me a 'Philosopher'

 

[SUNRAY]

Agreed - but, as I said, if ambient temp continues to rise, making it 'harder' (ultimately impossble) for heat to be lost from the 'dump grid' to the surrounding environment, one presumably may get to the point at which the compressor is unable to liquify the gas, bringing the 'refrigeration cycle' to a halt?

This isn't something I'd ever thought about as it's not my boat. However I don't know how dependant the process of liquification of gas is on temperature.

I assume the gaseous part of the cycle has little viscosity variation so feel there is no issue until it forms into liquid, My prediction would err on the expansion/decompression part where the thinner fluid will pass through the constriction more easily and therefore not allow pressure to build high enough.

BUT this is supposition and I don't know.

 

[fixitflav]

I assume the gaseous part of the cycle has little viscosity variation so feel there is no issue until it forms into liquid, My prediction would err on the expansion/decompression part where the thinner fluid will pass through the constriction more easily and therefore not allow pressure to build high enough.

I assume it's that with the installed compressor power there is a maximum heat flow, at design maximum ambient temperature, and minimum freezer temperature. If the ambient temperature goes higher, the heat flow falls, because the grid cannot dissipate the heat. But it would be nice to think there's a bit of a margin in the stated performance figures.