Generator advice needed - thinking of buying one for a small bungalow

[JohnW2]

Buy a medical one. If it's at -60 when the power goes it will probably last more than 24 hours.

Undoubtedly true, but I think that a fair few food items tend to become somewhat unpleasant (although perfectly safe) when exposed to such low temps.

 

[robinbanks]

thereis an immediate loss of cold air

Though it's a small amount of air, really, and a consequently small amount of heat energy admitted to the compartment by the warm air flowing in. There isn't going to be enough energy in it to defrost the contents

 

[JohnW2]

Though it's a small amount of air, really, and a consequently small amount of heat energy admitted to the compartment by the warm air flowing in. There isn't going to be enough energy in it to defrost the contents

True but, as Harry pointed out, it does depend to some extent on how full the freezer is - if it is 'lmost empty,there's a fair bit of air to be 'exchanged' when the door opens.

 

[robinbanks]

fair bit of air

If it were a totally empty 140 litre freezer that you completely evacuated of all its cold air and replaced with air at 20 degrees, it's only about enough energy to defrost a tenth of one beef burger

Don't worry about it

 

[JohnW2]

If it were a totally empty 140 litre freezer that you completely evacuated of all its cold air and replaced with air at 20 degrees, it's only about enough energy to defrost a tenth of one beef burger

You're probably right

Don't worry about it

It's eric you should tell that, not me

If you've read what I've often written, I don't worry in the slightest. I'm happy with stuff that's been in a non functioning freezer for at least 24-48 hours and, indeed, am also perfectly happy re-freezing stuff that has more-or-less completely thawed, should that ever happen!

 

[ericmark]

OK energy monitor on the chest freezer

120 watt start and 60 watt run. The chest freezer was a lot cheaper to the upright, and about the same size, I have put both on an energy monitor before, and average the upright uses more power even without opening the door.

How you can measure energy lost by opening a door I don't know? The more the door is opened on an upright freezer, the more often the defrost cycle is initiated so not only measuring heat gained, but also cost of defrost cycles. The defrost cycle is not a simple timer, when I had the energy monitor on the upright, sometimes 36 hours between defrost cycles, other times only 6 hours, so something measures something, be it how long door open, or how much frost, not a clue.

Note the second start it does not show hardly any in-rush, I have four screens and last time I tested I had each freezer run for a month to get a better average, the monitor was on a paper cutting machine before, so only the one screen tells us anything.

 

[Harry Bloomfield]

I'm happy with stuff that's been in a non functioning freezer for at least 24-48 hours and, indeed, am also perfectly happy re-freezing stuff that has more-or-less completely thawed, should that ever happen!

I have never quite understood, why they suggest never to refreeze, nor the logic, but I tend to follow the rule.

 

[morqthana]

Undoubtedly true, but I think that a fair few food items tend to become somewhat unpleasant (although perfectly safe) when exposed to such low temps.

I didn't know that.

I wonder if any lab workers have found that out the hard way after a lunchtime shopping trip to Iceland, thinking "I'll just stick this in the freezer until I go home.."

 

[JohnW2]

I have never quite understood, why they suggest never to refreeze, nor the logic, but I tend to follow the rule.

Most people do ('follow the rule'), However, like you, I don't really understand how the rule came about ... and, indeed, there are now a good few things (particularly fish) which (if one looks carefully!) say that the have previously been frozen but are nevertheless safe to 're-freeze'!

The basis of the concern is presumably that once products thaw, any viable bacteria within them will start proliferating, so that a lot more bacteria will be re-frozen' than were originally there - but, provided it is something that is going to be 'properly cooked' once it is ultimately used, I think that that represents a minimal risk.

I am far more nervous about freezing and thawing (just once, let alone multiple times) products that are going to be eaten without any further cooking.

 

[JohnW2]

I didn't know that.

I'm not certain that it's true - but I have certainly heard it suggested a good few times.

I wonder if any lab workers have found that out the hard way after a lunchtime shopping trip to Iceland, thinking "I'll just stick this in the freezer until I go home.."

Possibly

 

[morqthana]

Most people do ('follow the rule'), However, like you, I don't really understand how the rule came about ... and, indeed, there are now a good few things (particularly fish) which (if one looks carefully!) say that the have previously been frozen but are nevertheless safe to 're-freeze'!

And if you look carefully you'll also see something about having been defrosted under controlled conditions. i.e. not in a warm oven/microwave/water bath/left out overnight...

But AIUI the main concern is quality, not safety.

 

[JohnW2]

And if you look carefully you'll also see something about having been defrosted under controlled conditions. i.e. not in a warm oven/microwave/water bath/left out overnight...

Indeed so - but I think all that probably means is that during previously de-frosting its temp was not allowed to rise to appreciably more that 0°C. The problem with trying to thaw something big (like a turkey) by leaving it in a warm (or even hot) place is that the outer parts will get quite warm (hence a lot of bacterial replication) long before the inner parts have thawed. However, again, that's probably not much of a problem if it is subsequently going to be 'properly cooked'.

But AIUI the main concern is quality, not safety.

Indeed so - anything significantly below about 0°C is probably pretty 'safe'. I think that at temps between 0°C and about -18°C, deterioration of 'quality' (taste and/or texture) may occur, hence the normal temp of 'food freezers'. However, as I said, I've also heard it said that 'quality' will again deteriorate if the temp gets a lot below -18°C - but, as I said, I don't know if that is true.

 

[ericmark]

I would have thought the act of freezing damaged the food. But it may be more down to the speed at which things are frozen, I tried freezing milk, and a 1 litre bottle works, but as you go up in size, the time to freeze and defrost gets close to the life of the milk, so if when it arrives at the door step it is frozen it seems to work, but by time you have a glut of milk, it's too late. Commercial, they use blast freezing.

The major problem is in the main, we don't know if defrosted, OK two of my freezers will show the highest temperature it reached before the power came back as long as no one opens the door.

However, I had an upright freezer literally go bang when I was in the room. I had a fridge freezer in the garage used to brew beer in, so beer came out, and it was switched on to cool down, I waited ½ hour for it to cool, and then started the transfer of food. Food in the lower part was frozen solid, but food in the top foot of the freezer had started to defrost to extant it was floppy, no longer rigid.

This was a surprise, as I had heard so often, that unless the door is opened, food would stay frozen. I will guess it went bang as it started to refreeze after a defrost cycle. But can only guess. But where is the sensor which tells us the maximum temperature reached?

I also had a freezer, which I was testing with the energy monitor, if a freezer has lost gas, then it may never turn off, so I want to see the motor cycling, I can see it cycling and that average is 20 watt so I am reasonably sure freezer is OK, but one freezer was not cycling, it was on all the time, so either the thermostat was faulty, or the whole freezer was faulty, but which? I tried to borrow or buy a thermometer, I could not believe how hard it was to find a high street shop that sold them, I failed, however the freezer temperature should be -18ºC and the freezing point of brine is also -18ºC, so I mixed up some salt with water, stuck it in freezer, and it froze solid, so ordered new thermostat, and at same time ordered a thermostat to control another fridge for brewing, the freezer had got down to -24ºC, but the new thermostat was the other way around, and only getting it to -16ºC when at lowest setting.

Now I use a redundant beer thermostat and set to +4ºC as don't really need 4 freezers. And use it as a fridge. That was another point, the very small freezer was using nearly as much as the big one.

I keep lolly ices in top of upright freezer, as these will malformed if defrosted, I note if you freeze beer, don't do this as illegal, but the water freezes out of the alcohol, making the pints drawn to start with higher in alcohol and the latter ones watered down, I know a pub where this had happened, and landlord taken to court for watering down the beer. So what can one home freeze?

Anyway time to swap the energy monitor to other freezer, and see results in the morning.

 

[SimonH2]

Probably true but, as I observed, having 'auto defrost' must result in at least some rise of cavity temp during the 'defrost cycle'

I guess it would depend on the design of the freezer. I assume ours is similar, but I know for certain that my parents old upright had an expansion coil in the top (above the storage cavity) and a fan to circulate the air internally. The defrost would only heat that expansion coil (electrically) to melt off any ice, and that would not warm up the storage cavity much, or probably not at all.
We got to know more than we should have needed to about that one as it had a "design issue". It would work fine for ages (years), then if you were noticing, the compressor would start running longer and longer, eventually not keeping the temperature down while running continuously - and plugged into an energy monitor, not actually using much power. Basically the defrost didn't work properly, eventually the expansion coil fins would get blocked by ice, and as the airflow reduced, the effectiveness would reduce. The fix was to simply transfer everything into another freezer, and leave it switched off with the door open - after a couple of days water would start to appear, and when that stopped it was defrosted and would work normally again for ages.

The more the door is opened on an upright freezer, the more often the defrost cycle is initiated so not only measuring heat gained, but also cost of defrost cycles. The defrost cycle is not a simple timer, when I had the energy monitor on the upright, sometimes 36 hours between defrost cycles, other times only 6 hours, so something measures something, be it how long door open, or how much frost, not a clue.

If it has a pressure sensor on the low pressure (LP) side of the refrigerant loop then it can calculate the temperature of the evaporator coil from that - given a known relationship between the boiling point of the refrigerant and the pressure. This is far more effective than trying to measure the actual temperature - which will be different in different parts of the expansion coil.
Basically, as you release (either through a capillary tube or expansion valve) the high pressure liquid into the LP zone, it will immediately start to boil off until it is unable to draw any more energy from the surrounding pipework. So when the system is running, some of the expansion coil will carry a mix of liquid and vapour at the boiling point of the refrigerant at the pressure in the coil. How far that goes will depend on the mass flow rate or refrigerant, and the airflow (and humidity of the airflow) over the fins of the coil. Once all the liquid has boiled off, then the vapour can start to rise in temperature as it passes through the remainder of the coil - it's bad news if liquid gets carried over as (unless there's a design to avoid it) it will wreck the compressor.
With an inverter drive and pressure sensor, you can control the expansion coil temperature by controlling the compressor speed to keep a certain pressure in the LP side.

So, after that ramble round the workings of the LP side of a refrigeration circuit, back to defrost.
If you find that the pressure is dropping, then that means the temperature is dropping. At some point, you can infer that the coil is icing up - at which point you either stop the compressor and turn on the defrost heater for a while (freezer), or in an aircon system you temporarily reverse the system to heat whichever coil you were cooling (indoor coil in cooling mode, outdoor coil in heating mode).

As an aside, you can pull more heat out of wet air, and in fact some systems rely on this to not freeze up.
Cool wet air and you get condensation, and you have to extract the latent heat of vaporisation from the water in order to do that. So you get more heat extracted, at the same time as a higher "off coil" air temperature. There is thermal resistance from the inside of the refrigerant pipes and the fins on the coil - so if the air is wet enough, and some other conditions are met, the coil doesn't freeze up even though the LP side has boiling refrigerant well below 0˚C. With dry air, you have less latent heat from condensing water, so the coil runs colder, and what condensation there is freezes in the fins and eventually blocks the coil.
Once your coil is blocked by ice, if the system isn't reversible (such as in a car system) then it's hard to defrost. By the time you realise there's no cold air coming out, you have very cold ice and no airflow through the coil. So it can take ages to warm up enough, and thaw enough, to let air through (the problem we had with my parents freezer). So (and this is one of those "getting to know your vehicle" type things), if you are in a situation where this is likely, then it pays to turn off the cooling periodically to let air through the coil warm it up and melt any ice that's formed - and it'll be a very quick process.

Most people do ('follow the rule'), However, like you, I don't really understand how the rule came about ... and, indeed, there are now a good few things (particularly fish) which (if one looks carefully!) say that the have previously been frozen but are nevertheless safe to 're-freeze'!

The basis of the concern is presumably that once products thaw, any viable bacteria within them will start proliferating, so that a lot more bacteria will be re-frozen' than were originally there - but, provided it is something that is going to be 'properly cooked' once it is ultimately used, I think that that represents a minimal risk.

I think it'll be one of those "it depends" things where it's simpler to have a simple rule (don't do X) rather than a complex list of rules (don't do X with Y, but you can do it with Z, and you can so it with W if you follow these precautions). Like "don't reheat chicken" - I suspect that's more because people have been doing it badly (i.e. not getting things good and hot to kill bugs) and then getting ill. Much easier to say "don't reheat chicken" than "if you're going to reheat chicken then you must do A and B".

 

[SimonH2]

I note if you freeze beer, don't do this as illegal, but the water freezes out of the alcohol, making the pints drawn to start with higher in alcohol and the latter ones watered down, I know a pub where this had happened, and landlord taken to court for watering down the beer.

And it's also an (illegal) way of home fortifying wine. Freeze it, pick out the ice crystals, wine now has a higher alcohol content.
Many years ago (back when 8 bit computers were still something of a luxury as a home item), a friend told me how he'd written a program to calculate how much ice to take out to reach a certain level of fortification - and sent it to one of the magazines. They got a polite letter back telling them it was illegal (so they weren't printing it), and enclosing a relevant C&E leaflet on the subject.
And if you freeze milk, you see the same effect - and it's easy to be pouring off quite nice milk when you think it's thawed, then look in the carton and see you've a lump of ice in the middle (which thaws to something resembling skimmed milk (yuck)).