Naked Science Forum
Non Life Sciences => Technology => Topic started by: Chemistry4me on 13/01/2009 07:39:20
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We've just got a new fridge the other day and I was reading the manual. Below the tips and information bit, this is what it said:
• Coldest freezer setting is not recommended in normal and very hot climates.
• In very cold climates (where the temperatures are below 10°C) the freezer may need to be set colder.
Is there something that I am not getting here? Why do you not set the freezer to the coldest in hot climates and why wouldn't you set the temperature to normal in cold climates, instead you have to set it even colder? [???]
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Well I can understand the first one (maybe). It may be saying that the freezer can't cope if it is too warm and there maybe an unfortunate failure mechanism that they are not quite revealing, if only that if the motor runs too long continuously in hot weather, it can overheat and operate a thermal cut-out.
The second condition, and the one you ask about, is a bit baffling. However, I think it maybe to do with there being a combination of fridge and freezer, if this is the case. In cold weather it is possible that the fridge does not have to work so hard to maintain the +5 degress (or whatever it is) in the main refridgerator. However, it is likely that the fridge/freezer only has one cooling circuit. It maybe "difficult" to control the fridge temperature (for example if the outside temperature is close to, or even below, the required fridge temperature, and at the same time get the freezer to its required temperature. It could be that (from an engineering perspective) that the two control loops are note wholly independent in that they almost certainly share a good deal of their functionality.
So, am I right that this is a fridge/freezer and not just a freezer?
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Yes, it is a fridge/freezer.
It maybe "difficult" to control the fridge temperature (for example if the outside temperature is close to, or even below, the required fridge temperature, and at the same time get the freezer to its required temperature.
So, am I right that this is a fridge/freezer and not just a freezer?
Can you please explain that bit again? In a bit more detail?
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I think graham.d is right; Your fridge-freezer combo has just a single cooling system, with just a single temperature sensor in the fridge compartment, and relies upon a certain duty-cycle for the fridge to ensure that the freezer compartment is kept below the maximum (high-temp) limit for the freezer specifications.
For example, if the freezer compartment is supposed to maintain a temp below -10C but you keep the fridge-freezer in an environment where the ambient temp is only +5C, and you have the fridge set to maintain +5C, the cooling system will never need to switch on. As a consequence, the freezer compartment will not be chilled and it's temp will rise to +5C too.
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That sounds a good reason: The freezer needs the cooling motor to run for such a short time that the fridge may not get cool enough.
My hotpoint has a single compressor but controls the fridge compartment cooling with a flap which controlls the amount of cold air entering the fridge from the freezer. The control circuit sometimes goes wrong but it's basically a good design.
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Don't those systems work just like Air Conditioners? were the gas transports heat from the inside to the outside, maybe it has to be set up that way so the pump knows how much gas needs to flow, in that way there will be enough temperature differential to perform its function. [:)]
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Don't those systems work just like Air Conditioners?
Do they??? [???][???]
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They use a 'heat pump' in conjunction with a thermostat which turns it off when cold enough. It's only in extremely hot conditions that the motor is running continually.
In cold conditions, the motor may run enough to keep the freezer compartment cold but that may not be enough to keep the fridge part cold.
However, The design would have to a bit odd for this to be the case.
I think the instructions, quoted in the original post, were basically 'arse covering' on the part of the manufacturer.
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...arse covering
I love it when you talk kinky
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In cold conditions, the motor may run enough to keep the freezer compartment cold but that may not be enough to keep the fridge part cold.
Shouldn't it be the other way around?
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Yes, of course - all things being equal.
If both compartments keep gaining heat at rates proportional to temperature difference and they get fixed proportions of the 'cooling', then the heat pump needs to work less under cold conditions. However, if the freezer gets the lion's share of the cooling when the motor starts (it is more critical and could be built in by including some 'flap' mechanism, the motor may not be running long enough each cycle to cool the fridge compartment. i.e non-linear conditions.
Not likely but possible - and the warning could refer to an ancient design which demonstrated the fault once.
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Coldest freezer setting is not recommended in normal and very hot climates.
Well I can understand the first one (maybe). It may be saying that the freezer can't cope if it is too warm and there maybe an unfortunate failure mechanism that they are not quite revealing, if only that if the motor runs too long continuously in hot weather, it can overheat and operate a thermal cut-out.
Is this true? [:-\]
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I believe you're all on the wrong track here and don't think it has anything remotely to do with temperature differences betweem fridge and freezer compartments.
This clearly has something to do with the compressor and heat radiator that sit outside of the fridge/freezer compartments and as such are in contact the ambient air.
Simply check out how refridgeration actually works and you will find the answer.
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does this help?
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http://www.passiveaggressivenotes.com/2007/06/03/when-phds-get-frustrated/
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Farrah day
"Simply etc."? LOL
Did YOU find the answer?
In cold conditions, the motor just has to run for less of the time to maintain the freezer at a desired temperature. The 'heat pump' principle isn't hard, qualitatively - it's a bit harder quantitatively.
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Coldest freezer setting is not recommended in normal and very hot climates.
Well I can understand the first one (maybe). It may be saying that the freezer can't cope if it is too warm and there maybe an unfortunate failure mechanism that they are not quite revealing, if only that if the motor runs too long continuously in hot weather, it can overheat and operate a thermal cut-out.
Is this true? [:-\]
Paul. Is that a diagram of an air-conditioner? [:-\] What does it have to do with the fridge/freezer?
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C4Me, the relevance is that an air conditioner works on exactly the same principle.
It seems that the second reply on this thread was just about right. Here is the definitive answer:
With fridge freezers where there is only a single compressor (easy to spot as there’s only one black “bottle” at the back and/or generally only one control for fridge and freezer) this means that all too often the ambient can be lower than the cut in point for the fridge. Since the fridge thermostat controls the on/off for the freezer as well it means that, for long periods during the colder winter months, the freezer won’t cut in and the food will defrost.
Hence the cut-in temp of the fridge (not freezer) thermostat must be lower than the ambient air temperature. So, in colder climes or times the fridge thermostat may need to be set colder to prevent the freezer from defrosting.
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But, if the room temperature is lower than you would need for a fridge compartment, the stuff in the fridge will be just fine! Cold enough without the fridge having to operate.
It would be a pretty naff machine which didn't ensure the freezer compartment was monitored correctly.
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I believe that most fridge/freezer combos work this way, or at least they used to, and mine certainly does. Having said that, my fridge/freezer is pretty old now (a little over 20 years) but the only thing that has gone wrong with it was the temperature sensor, which is located in the fridge compartment (I removed it myself to check if that was where the fault lay). The temperature sensor used on my fridge is a very simple device; basically, a long flexible gas-filled sealed tube with a plunger on the end, so that as the gas expands or contracts the plunger makes or breaks the compressor circuit. The failure in the sensor on my fridge was a leak in the gas-tube.
Fortunately for me, I had a friend who was a refridgeration engineer and who replaced the faulty sensor for me and it's worked fine ever since. There is no sensor in the freezer compartment.
Actually, I've just remembered another fault I've had with it; the light has blown, but I've never bothered to replace it, and so I've not had to worry about whether it goes out when the door is shut [;D]
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It really comes down to a factor of insulation. The better the insulation of the fridge/freezer compartment from the outside ambient air, the higher the efficiency rating of the unit will be.
A fridge/freezer with an extremely high insulation factor would be far less prone to the effect of ambient air temperature - high or low.
The vast majority of the cooling fins are located within the freezer compartment, so this compartment sees by far the greatest amount of cooling. Engineers will have designed the machine so that over any given temperature setting of the fridge compartment, the compressor will still be switched on enough to maintain the freezer.
Of course this does mean that there will generally be a compromise in effcicency as the compressor is more than likely being switched on more than necessary.
The problems occur when the ambient air is too cold and fridge is being asked to worked outside the limits of it's thermostat setting. Without the compressor being turned on by the fridge compartment, although the fridge compartment will be fine, freezing cannot be maintained within the freezer - again down to insulation.
It might seem pretty naff, but this is why there are guidelines as to ambient air operating temperatures for each particular unit.
In order to have temperature control over both fridge and freezer compartments, you would need separate cooling systems for each. On a single cooling system, the fridge compartment is where you are likely to want some control - as long as the freezer freezes the food, then why would you want to alter this setting.
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LeeE
I can see how your, relatively simple, system would need to be turned down in cold weather. What you say makes perfect sense.But I haven't come across a FFr that had no regulation of the freezer section. I bet the freezer isn't rated as ****.
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Coldest freezer setting is not recommended in normal and very hot climates.
So basically, if it was 35°C in the room you wouldn't set the freezer to the coldest because...? [???] The hot air will get back in? [???]
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It has got an energy rating of 463 KWh per year if that means anything...
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Coldest freezer setting is not recommended in normal and very hot climates.
So basically, if it was 35°C in the room you wouldn't set the freezer to the coldest because...? [???] The hot air will get back in? [???]
I think it's because it would cost a lot to run and the temperature of the freezer (not the fridge) would end up lower than necessary.
Basically, it sounds like a rather rudimentary temperature control system. Thermostats are supposed to do the work for you to get the temperature right in both compartments.
Did you pay a lot for the item?
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Did you pay a lot for the item?
It was in the medium price range, $1400 NZD there and there abouts...
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LeeE
I can see how your, relatively simple, system would need to be turned down in cold weather. What you say makes perfect sense.But I haven't come across a FFr that had no regulation of the freezer section. I bet the freezer isn't rated as ****.
It's rated as *(***), which seems to be the highest rating according to
http://en.wikipedia.org/wiki/Refrigerator#Temperature_zones_and_ratings (http://en.wikipedia.org/wiki/Refrigerator#Temperature_zones_and_ratings)
Note that the freezer compartment isn't full-sized though; it's only about one third of the size of the fridge compartment, which may be a factor.
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Sorry for dissin your white goods bro'.
I guess we'll never know the real answer - I bet the warning is based on a poor past design and they never thought to take it out of future handbooks.
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Sorry for dissin your white goods bro'
No problem. It doesn't seem to be sulking or anything atm, but if it breaks down tomorrow I'll know who to blame.
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(...)
The problems occur when the ambient air is too cold and fridge is being asked to worked outside the limits of it's thermostat setting. Without the compressor being turned on by the fridge compartment, although the fridge compartment will be fine, freezing cannot be maintained within the freezer - again down to insulation.
It might seem pretty naff, but this is why there are guidelines as to ambient air operating temperatures for each particular unit.
In order to have temperature control over both fridge and freezer compartments, you would need separate cooling systems for each. On a single cooling system, the fridge compartment is where you are likely to want some control - as long as the freezer freezes the food, then why would you want to alter this setting.
I am sure glad I found this thread again. I vaguely remembered the gist but it explains perfectly what was going on with my fridge.
I noticed the other day that in my house (which is at 4 Degree Celsius when I am not there - which is a lot at the moment) that the stuff in my freezer seemed to be thawing. It made no sense! Why would my fridge have a harder time cooling the freezer if the ambient temperature is colder? But I believe the answer is that the thermostat is in the fridge compartment and the fridge does not kick in often enough to keep the freezer cool enough and its contents deep frozen. I turned it higher and all is well.
BTW, not an old model. Energy star rated and bought 3 months ago. But it seems this company does not plan for anyone letting their house temperature drop to just above freezing.