How cold should a refrigerator/freezer be?

[rhizomatic]

Experimenting with conservation, I currently am monitoring ~45*F in the fridge and 10-15*F in the freezer. Online they call that too warm. And I might agree. I wonder if anyone has experience to confirm or refute the "answers.com" position.

With the above temperature change, two liters of water in freezer and two in fridge, and a old timer to shut it down for short stretches during the night I brought my so-so fridge down in power draw 15%. ($10-$12 per year). But if I ruin food or make myself sick... well, it's obvious I want to avoid that.

[Daox]

I keep my fridge at 40F and freezer at 5F. I haven't run into any issues with food spoiling abnormally quickly.

[AC_Hacker]

The way many people think about refrigeration is kind of curious... It's almost like it's a magic box that prevents bad things from happening to food. But it just slows down bad things from happening. In fact, some foods suffer from refrigeration. In France, putting good cheese in a refrig is considered a bad idea. Also, certain produce, like melons for instance, don't taste as good after refrigeration.

But back to the question, I tried experimenting with various refrig settings, and found that food like meat & dairy does degrade somewhat faster in a warmer refrig, but the vegetables were just fine. The real problem I encountered was that ants were able to survive at temps a little above 45F, and for me, they were a worse problem than spoilage.

So, I run my refrig at 40F now... it is an ant-free zone.

My freezer (which is down cellar), I keep at 0F. I put a kill-a-watt on it and it consumes about $26 per year, so I'm not very motivated to try to beat that.

* * *

Additionally, I have drastically down-sized my refrigerator. I now use a refrigerator that is 19" wide x 32" high x 18" deep. At first, I was in a panic, because I had to completely rethink how I use a refrigerator. But by being careful how I stack things in the little refrig, and by tossing things that are no longer good, and by being selective what I refrigerate, and by putting things in my separate freezer that should be in the freezer, things are working out very well. The only thing I would change would be to select an Energy Star 'all refrigerator' (that's the trade term for a refrigerator with no freezer), as the freezer compartment in the little fridge is pretty much worthless... an all refrigerator would allow me to have more useful room.

I got the idea of the tiny refrig by watching some BBC TV shows and I saw that families of two adults and three children were able to get by just fine with a tiny refrig... now I am, too.

I actually went shopping recently for a larger refrig, and was put off by the huge amount of space that they occupy. I think I have been forever changed.

-AC

[RobertSmalls]

Milk spoils a few days faster at 36°F than at 32°F, according to my observations. Therefore, I always keep the milk at the back of the fridge, and never on the door. Meat, stew, and dinner items also keep best when just above freezing. Considering how energy intensive (and expensive) food production is, I don't feel bad about setting the fridge as low as I can go without freezing things.

When it comes to the freezer, I've read that 0°F retards spoilage better than warmer temperatures, and that milk can be kept safe (though perhaps not delicious) indefinitely at that temperature. However, the failure mode I usually see in the freezer is dehydration/freezer burn, not spoilage. I'm not sure how to delay the onset of freezer burn.

[rhizomatic]

These are all useful responses guys. Thanks. I moved the thermostat back to the "2" mark. It is 42*F in the fridge and 5 or 7*F in the freezer. I have four liters thermal mass water in there (2 fridge and 2 freezer). And it's on a timer to shut off for 5 hours a night, with a half-hour "on" period at 230am. That'll do.

[MN Renovator]

"it's on a timer to shut off"

Why? I keep reading this here. We've got a bunch of people who are running thermostat settings with temperatures right on the edge of quick food spoilage and they use a timer so that there is a period of the day where you let the refrigerator and freezer get even warmer than the marginal temperature for safe food storage.

Take this thought for a moment. If you have a timer that shuts off your freezer/fridge for, say even only 4 hours, and right before the fridge is about to lose its power, it goes into a defrost cycle, then a minute after the defrost cycle is over and the compressor and fan are churning the hot air in the coil chamber into the fridge, you cut the power to it. Whenever my refrigerator runs its defrost cycle, the refrigerator temp raises about 5 degrees and it takes about 5 minutes of compressor operation to even hit the peak temperature before it even begins to cool back down. It takes about 30 mins of running to recover from a defrost cycle.

Running these timers is a great way to destroy your food. Why don't you let your thermostat hold the temperature where it should be rather than thinking you have something to gain by powering the refrigerator off at a point when it might have just about turned on, or worse been in the middle of a defrost cycle or its recovery.

My milk jug recommends milk temperature to be 34-38 degrees. I make sure that my refrigerator starts the compressor to cool things off right before it hits 38 degrees. Even then I'm a little concerned about my food in case there is a power outage right when I took off for work when I set it that close.

We are talking about a temperature difference of 60 degrees outside to inside for the freezer and about 35 for the refrigerator. 5 degrees isn't going to be that much additional energy and the cost will be minimal, far less than what it costs to get sick or to stuck with throwing away food.

[AC_Hacker]

I think that refrigerator design should be seriously reconsidered.

Start with size... If your refrigerator regularly contains spoiled food, it's not because you are running it at too low a temperature, it's because your refrigerator is just too big.

Then there is the Saga of the Decline of Good Refrigerator Design. Things began to go downhill when the compressor was moved from the most energy efficient location (Top, where heat could move away from the food) to the least energy efficient location (Bottom, where heat flowed around the food), and things have continued their decline ever since.

Insulation was made as thin as possible to allow for more room inside.

Then the condenser coils that were first on the top, were moved to the back where they were in closer proximity to the food, and the final brain storm was to put the condenser coils inside the sheet metal body where they are in contact with the insulation, and surround the food. Each 'improvement' has led to lower efficiency. Why, you'd think that the power companies were paying the refrigerator companies to be stupid.

Then, the act of monthly defrosting was determined to be too burdensome, so heaters were put inside the refrigerator to periodically melt the frost, so not only do we have resistance heaters with their notoriously high current draw, we also have the extra refrigerator run time required to eliminate the heat that was generated by the defroster feature.

* * *

Some wonderful work has been done in converting chest type freezers into ultra high-efficiency refrigerators, by simply adding a separate thermostat that will accurately hold temperatures in the 35 to 40 degree F range.

Quite a few people have done this conversions, HERE is the most recent conversion I know of.

Mr. Dirty Boots reports that his yearly cost to run the converted freezer is $6.63 (calculated at a power cost of 0.11 $/kw-hr)... that's some serious EcoRenovating!

And all of this with a freezer that most likely has all of the design sins cited above. So Mr. Dirty Boots extremely good low energy mark could be improved still further...

It's well to note however, that this conversion will not need defrosting, because it will not frost, because there is sufficient chill plate area inside to supply cooling, that the temp does not need to go as low as 32F, so no defrosting and also longer vegetable life.

* * *

And then there is Sun Frost...

These admittedly expensive refrigerators & freezers are designed for folks who live off-grid and must bear the price of site generated electricity, which is usually much higher that grid power... so

Here is a photo of one that is currently on ebay:

Note that the compressor & condenser coils are on top, note the very thick insulation that is used. Also, not so obvious is that the large cooler plate for the refrig area does not get to the point where water vapor will freeze, which means no defrosting and it also means longer vegetable life.

We can do this!

Best,

-AC

[Vlad]

The main problem as I can see is your thermostat. Usually home fridges have a junk thermostats with on/of difference as much as 10 F.

So, when you set up your temperature make sure the ON temperature is still in safe range.

Also there is a defrost relay which starts 4-6 times a day. YES EVERY 4-6 HOURS. This brings your temperature even higher....

For this reasons fridges set up lower then you even need to keep your food safe.

If you want to make it work like Swiss watch you have to replace junk thermostat with good one and play with defrost timer.



This will pay off in couple years....

[MN Renovator]

You actually want the temperature to swing a bit, it takes some time before the compressor reaches a more solid state efficiency and it definitely isn't in the first 5 minutes of operation. You need long runtimes to get good efficiency and long compressor life.

Mine will swing about 3 degrees from hottest to coldest, which works for me, it runs about 10-15 minutes at a time.

The defrost timer that mine came with defrosts every 10 hours, no matter how much the compressor runs. I used to think it was based off of runtime but found out it isn't. A quick search on ebay for "defrost timer" yields results that are almost all 8 and 10 hour timers. I've taken the defrost timer and timed how long the defrost cycle lasts, 23 minutes, then I pulled the pin that controls the timer and I manually cycle the defrost once a week. Nice thing now is that when I defrost, it's actually defrosting something off the coils instead of just warming them up and then running the compressor for 30 minutes to cool things off again and in the process wasting loads of energy. ...that was the thread I was going to make but then later forgot about. I'll still post it because I've got pictures, but it will be once I've got a month of usage out of it since I now have my Kill-a-watt back to do an 'after'.

[AC_Hacker]

Originally Posted by MN Renovator

You actually want the temperature to swing a bit...

So, it looks like the 'defrost feature' is the real problem here...

I still maintain that a properly designed refrigerator will never need any defrosting at all, because the chill plate will be of sufficient size that it will be able to remove heat from the refrigerator without ever getting to 32 degrees F.

Implementing a precision thermostat may be an improvement, and manually controlling the defrost cycle may also be an improvement, but they are both partial compensations for poor basic design.

In addition to bad placement of the compressor & condenser coils, the glaring design flaw is the freezer/refrigerator 'combo feature'. With this 'feature' the chill plate that cools the freezer is the same chill plate that cools the refrigerator (lower production cost) and of course it must have a temperature much lower than 32 degrees F to function, which necessitates the 'defrost feature', which is just a bandaid for the 'combo feature'.

I have discovered that there is a class of refrigerators called "All Refrigerator" which means that they do not have the cursed 'combo feature', but are actually all refrigerators with no freezer at all... it also looks like the buying public is so hypnotized into thinking that the combo is the only way to go they they have to say it twice, "Full Refrigerator Refrigerator" to indicate the difference.

I just saw that these are also named "freezerless refrigerators".

Here, a company has taken the chest type freezer and put in a different thermostat:

LINK to chest type Full Refrigerator Refrigerator

These units may or may not use freezer grade insulation, and may or may not use a freezer grade compressor, but they do save the agony of installing a precision thermostat in a chest freezer.

And HERE is a link to many models of All Refrigerators...

Even though almost all of the compressors are on the bottom (BAD), if the condenser coils are mounted on the back (MEDIUM GOOD), and not integrated into the sides (WRETCHED), some of these units might be pretty good. Since these do not have the 'combo feature', the chill plate should not need to go below 32 degrees F and the refrigerator will not need to do duty as a vegetable dehydrator, so it will not need the 'defrost feature'.

[EDIT: l have noticed that these configurations also offer the 'defrost feature', so it looks like they are sticking with the small, very cold chiller plate, and that frosting is still an issue... whether it is reduced, I can't tell... Sun Frost has found a way around the frost problem, so it is possible.]

Best,

-AC