converting a chest freezer into a fridge

[Tim+]

We have a small unused chest freezer in our garage. We also have a tall fridge/freezer combo that we use for beer and wine. The freezer part of it really can’t be relied on in cold weather so we don’t use it. As a beer fridge, it’s probably not terribly efficient.

That got me wondering if I could just change the stat on the chest freezer to turn in into a fridge. I presume being top opening it would avoid all the cold air loss that the upright one suffers from and might be better insulated and hence cheaper to run.

The only thing stopping me just swapping the stat is that there is no sign of an internal temperature probe inside the chest freezer. It’s just a flat sided box. Where is the temperature probe hidden in chest freezers?

Any reason NOT to convert it to a fridge?

Tim

[Brian]

The fridge / freezer that doesn’t work as well as you’d like, have you checked it is rated to work in an outbuilding?

If you plan to use a fridge or freezer in an outbuilding / garage etc, you should check it is rated to work at lower ambient temperatures. If it isn’t, odd as it seems, it may well not cool properly.

As for converting the freezer, possibly but it may tend to over shoot. I would assume, having switched to cooling, it would be set up to ‘work harder’ as a freezer than you will need as fridge.

[Tim+]

It’s definitely not! It was just a redundant fridge/freezer that got stored in the garage and became our beer fridge.

Well that’s kinda why I’d like to ditch it.

Well with an appropriate thermostat I don’t see why it would overshoot.

Tim

[Chris Hogg]

Not quite answering your question, but if all else fails you could use an external temperature controller like this

. I have something similar to control a plant propagator. Plug the controller into a mains socket, plug the freezer into the controller and hang the probe in the freezer.

A similar one by the same mfr claims to be able to control 3000W so should cope with the compressor surge, and it controls down to 0C, but it's brand new and more expensive.

[farter]

Not by enough to matter.

Access with a top door is much less convenient.

[farter]

I do. Fridges are carefully designed to ensure you dont accidentally freeze the liquids like drinks and stuff that doesnt like being frozen like lettuce.

It is unlikely that a converted freezer will be that well designed circulation of cootth wise.

[Brian Gaff]

Yes you would get the heat equivalent of servo hunting I'd imagine. No idea where the thermostat might be, but also of course, being designed to be a freezer it will probably have a more capable compressor and pipes in the sides more numerous than a fridge would have. Can you not flog them and buy what you really need instead? Brian

[Brian Gaff]

More thermal lag, I'd imagine. Freezers can vary in different parts of their storage and do vary in temp quite a bit in normal use. the tend to stay below what you need, but from experiments the fluctuate all the time. Most fridges and freezers do have histeresis though, bit like most thermostats do. Brian

[Brian]

Control systems are more complex than that.

A simple thermostat is essentially a hard switch. Ideally, when heating or cooling something, you want to gradually slow down the heat / cooling as you approach the target temperature. Even better, you look at the long term error (by integrating it and adjusting it to zero) and adjust to compensate. Look up three term or PDI controllers.

The cooling mechanism in a freezer is designed to hold things around -18C not fridge temperatures. The rate of cooling may cause the overshoot I referred to.

[John Walliker]

If overshoot does turn out to be a problem, the easiest solution would be to put more beer in the freezer - or if you want to drink most of it, then put some large plastic containers of water in there. They will have two effects:

1) The extra thermal mass will make overshoot less likely. 2) If it does happen, the water will buffer the temperature at around freezing point as the water in the containers freezes. Beer will not freeze until the temperature gets several degrees below freezing. Wine is good to around -10 deg C.

Conventional refrigerators can also freeze water if the thermostat is set too low. I have found it to be more likely in hot weather where heat leakage near the thermostat causes it to think the 'fridge is warmer than it actually is and overcompensate.

One time this happened the water in a plastic bottle became supercooled and had a viscosity like glycerin. A few tens of seconds after I picked it up the whole lot froze, almost instantly.

John

[Brian]

Increasing the thermal mass by either keeping the converted freezer full is a good idea. I’m not really a beer drinker but freezing point seems a bit cold, I would think more like 4 / 5 C would be better. 4 degrees C is the triple point of water.

[Pamela]

You probably mean PID controller.

[Fredxx]

0.01C is the triple point. And 4C is the nominal temperature at which density inversion takes place.

I understood that the biggest risk associated with freezing cans or bottles is the CO2 suddenly comes out of solution? Hence why I have seen cans with their bottoms 'popped'. BICBW.

[Martin Brown]

The most obvious ones are that its designed to pull down temperatures much lower than in a fridge and its internal surfaces will all be aggressively cold. You may need to stand off any produce to avoid it being in direct contact with below zero metal in normal operation.

The expansion of its refridgerant will be designed to pull the metal down to -20C or thereabouts so you will have to limit its on time rather carefully with pulse width modulation rather than a simple bang bang thermostat. I'd say it probably wasn't worth the bother - just use it as extra freezer space.

Your other minor problem is that stagnant water will accumulate in the bottom of it rather than frost. Apart from that and the logistics of making good use of the volume it should function OK if you can get the temperature control right (which may be harder than you think).

The thermostat sensor will be glued against the inner metallic surface somewhere with tails going off to the controller.

Redundant freezers make good places to store apples in (at least until squirrels learn how to open them).

[Animal]

I'll be curious to hear how well it works. On the face of it it ought to be ok, except for lack of condensate drainage. You'd need to wipe that out, perhaps using bleach. The sides will get cold, but not excessively, the stat will stop it when it gets overly cold. Fridges require a controlled amount of hysteresis in the stat, so use a fridge stat rather than a central heating or uncompensated stat.

[John Walliker]

My chest freezer has a drain plug in the bottom for defrosting. Simply removing the plug might be enough (to ruin the floor underneath). The condensate drains in refrigerators drip onto a tray above the compressor to evaporate the condensate.

John