Fridge and freezer temperatures

[chrisr]

Our freezer (seperate unit to fridge) is set at abt -6deg C. sometimes gets up to -2 or -3 (C) before cycling on again

coldest i've ever seen it is -7.2 deg C

at these temps we have no trouble keeping everything frozen for months on end. can add fresh meat etc and will be hard frozen within 6hrs or so.

BUT (big but) it won't freeze icecream !!

oh well...nothing in life is perfect

cheers,

[Sojourner]

We have a standalone Waeco freezer which is a phenomenal piece of kit...runs on any voltage, super energy friendly, very well insulated and we built it in to take the place of the nav station bench seat, with a cushion on top. https://www.waecofridges.co.uk/freezer/cf50.htm

Anywhoodle, -15

[GordMay]

Originally Posted by a64pilot

Frozen food should be kept at negative Fahrenheit numbers for long term storage. But that’s tough to do. Our Engel stays at -5 F and that’s about as cold as it will get.
Actually you can use Ice cream as a gauge, if it will keep ice cream hard it’s cold enough, unless your wanting to store for long term...

Indeed.
Ice cream should be stored at as cold a temperature as possible (0 degrees Fahrenheit, or -18 C, or less) in a home freezer.
However, the ideal serving temperature for most packaged, scoopable ice cream is 5–10 degrees Fahrenheit (-12C to -14C).

See also ➥ http://www.cruisersforum.com/forums/...fety-2982.html

[sailorboy1]

I have a spillover system with a fan . The freezer has a mechanical thermostat and I have it set at the coldest setting, but don’t know the temp (stuff is like a rock). I dint think it ever shuts off. The spillover fan has an electronic controller and I have it set to maintain between 35-36. I know it’s time to defrost when the frig side starts being above 36 when nothing has been put inside or the door opened. Opening the lid to get something has a lot less impact than adding sodas to beer to the box.

[a64pilot]

My Cool Blue has a mechanical thermostat that senses the eutectic tank temp, freezer temp is a function of the eutectic tank, it’s not a set point.
My fridge is like Sailor Boys in that I now have a thermostatically controlled fan in the divider, temps swings were just to wide without it.
In the pic the white box is a thermometer that has wireless sensors you can place where you want and it has alarms too.
The little inkbird box is the inexpensive fan controller with individual on and off set points.
I know when it’s time to defrost when my freezer temp gets to about 10 or above, the ice layer that builds up on the eutectic tank is of course an insulator, the tank stays cold so the compressor turns off but the box will warm up.
I installed the fan and controller because like Sailor Boy said, toss in a case of beer and a watermelon and the fridge temp would skyrocket, but with the thermostatically controlled fan the fan runs and steals cold from the freezer, but I guess due to the mass of the eutectic tanks it doesn’t raise much as of course as the tanks warm, the compressor kick in and keeps them cold.

[tarian]

the temperatures of chilled and frozen cabinets must be checked to ensure they are operating correctly. Refrigerators should operate between 1 to 4°C and freezers below -18°C. Below 5°C the cold temperature slows down bacterial growth or makes it dormant. Below -18°C is very cold, this will prevent any bacteria from multiplying.

Pretty basic food hygiene , your life your belly but the science is science do not matter if a boat , a house a restaurant , them be the facts

Aslo any good biology graduate will tell you that there are places were bacteria live in extreme cold and extreme heat no such thing as killing them with a bit of heat of cold , oh wait I am a biology graduate

[Yellowjacket]

I've had two units, and the turn-on temp and cut-off temp DIFFERENCE for each was recommenbded to be 8 degress C.

I have eutectic plates, and the thermostat takes its reading from the plates, not the box.
Mine is a larger spill-over box. Actually, it's a conductive box: there's a stainless plate between freezer and fridge. There is also a circulation fan in the freezer to reduce stratification.

The latest install keeps the freezer at about -13 degrees C, and the refrigerator at about 1 degree C. I would like my freezer to be a few degrees colder, but I don't want to freeze my produce and the compressor sips power at about 6 amps, has about a three hour cycle, one hour on and two off, with the freezer mostly unloaded and not much in the fridge. So it consumes less than 50 amp hours per day that my solar array can handle that pretty easily.

I have yet to take boat out with both boxes full to capacity, but I think we'll be okay. Manufacturer says "Empty is the toughest thing to keep cold." Food could add to the thermal flywheel of the eutectic plates. We'll see.

[ayates]

For reference, here is real life logging of a Nova Kool RFU9000 refrigerator/freezer from this past summer. This is the OEM thermostat set at #4. The only modification in operation is the wrapping of the unit in 2" of Styrofoam SM. I can zoom in on the temperature and observe the compressor cycling.


Allan.

[Auspicious]

Originally Posted by tkeithlu

US Food and Drug Admistration standards are 40 F for refrigerating foods and 0 F for freezing them.

Fridge guidance is at or below 40F. See below.

Originally Posted by CassidyNZ

I want to know what you (and others) actually do, not what is recommended by the FDA and perhaps some gauge as to how that affects cycle times on the compressor.

I promise to answer your specific question. It just takes me a while.

The danger zone for food is between 40F and 140F. The FDA guideline for fridge is "at or below 40F." I've never taken and counted bacterial cultures. Flirting with the edge of even a conservative assessment of increased bacterial growth makes me nervous. So does the prospect of my lettuce freezing. Accordingly my target fridge temp is 36F. Hysteresis is real. 34F off, 38F on.

Frozen food lasts best when it is really frozen hard. Those 8x8 lasagna pans at the bottom of my freezer should be like bricks. Same with my steaks, loin, poultry, etc. I did some testing in my home freezer because the power consumption in my boat freezer at 0F is a bit high. I found 10F worked pretty well. Again, hysteresis, so 8F off, 12F on.

My experience is that reducing hysteresis (closer set points) results in more cycling AND increased power consumption for the same average temperature. I don't remember the exact numbers (it's been about five years since I last messed with this) but making the fridge a little colder had a noticeable but not significant impact on power. Increasing freezer temp had a bigger power consumption impact.

In the end, my goals are 1. food safety 2. food quality 3. food life 4. power. Sailing and cruising don't have to be camping, certainly not for me. If I had to add battery capacity and charging to meet life style expectations I would have done so.

I haven't found any other country (I've looked but not explicitly country by country) with the degree of specificity of US FDA guidelines for food storage or USDA guidelines for home canning. There is no question in my mind that they are conservative. We simply don't know how conservative. We know that bacterial growth doesn't explode at 40F and warmer and doesn't stop when chilled below 40F. A person, educated and trained, made a judgment and picked a number which was reviewed thoroughly.

We also know that there are cultural issues. Americans in particular refrigerate all kinds of things that need not be. It is a 'nanny state' problem. People can't be trusted not to put a utensil back in a storage container so better refrigerate the mayonnaise. For a relatively young country we have more than our share of old wives' tales. *sigh*

See? I said I'd answer your question and I said it would take a while.

sail fast and eat well, dave S/V Auspicious

[Auspicious]

Originally Posted by tarian

the temperatures of chilled and frozen cabinets must be checked to ensure they are operating correctly.

Definitely agree. All kinds of fancy ways to do this. I have mechanical thermometers on top of everything in both fridge and freezer. Like OP I have separate units (one fridge, two freezers). I also use the dime method for detecting power loss.

Something I meant to say before, changing temperature takes a lot more power than maintaining it. I'm always nice to grocers and restaurateurs. When I do a big cook I can usually schmooze space in someone's walk-in to get it frozen hard and down well below 0F. Even with transit issues, when it goes into my freezer it is a net contributor to cooling, not a drain. Sometimes I've helped out FOH or BOH in exchange; usually just being nice is plenty.

Story: In a marina in Panama the marina restaurant was going to be closed for three days. We'd been working on the boat for a week to get ready for a long distance delivery (I don't usually take "you have to fix it first jobs" but this one was special). We'd made nice with the locals, helped a bunch of people, been inducted into the 'Table of Wisdom.' Restaurant manager offered me the keys so we could cook over the weekend. He said cooking ahead and freezing was fine. Nice guy. The smells drew people in (no walls or doors - locks just on the gas valve and walk-ins). So I started cooking. And cooking. Two things on the menu I had no idea about but everything else I could do. Worked our prep into the other cooking. This was not a huge rush just a steady stream. My first real experience with a flat top. I was exhausted but had a great time. Tuesday morning gave the restaurant manager an envelope full of cash for payments, and envelope of tips (I was worried about work permit issues). Got the tip envelope back and a tip from the restaurant.

[handcrafter]

FDA range is 34-39 degrees for refrigerator.
Freezer range desired temp to maintain is -20 degrees F though -10 degrees F may be all your compressor can pull.
Try keeping the freezer compartment full at all times and use bags or containers of water-ice to fill the space. Everyone can use ice, right?
Keeping all items in vacuum sealed plastic will be a big help especially for preventing freezer burn. Your evaporator won't have much work to do.
A Seal-A-Meal unit doesn't take up much space.
You might find the freezer holding temps better when you're away from the boat, etc.

[CassidyNZ]

Originally Posted by ayates

For reference, here is real life logging of a Nova Kool RFU9000 refrigerator/freezer from this past summer. This is the OEM thermostat set at #4. The only modification in operation is the wrapping of the unit in 2" of Styrofoam SM. I can zoom in on the temperature and observe the compressor cycling.


Allan.

Hey Allan. I’m not sure of the relevance to boat units - is this a domestic fridge/freezer being logged? The consensus here so far appears to be that a freezer needs to run at -15C to -20C to be safe. The logger indicates that this unit cycles mostly between -3C and -12C. Can you fill in some background as to use, contents, storage time?

As I said in my original post, I’m not looking for any long term freezer storage, ten days max. My most common proposed use will be for enough frozen pre-cooked meals to get me to the islands with one easy dinner per day. By the time we reach the destination those meals will have been replaced by freshly frozen fish caught on the voyage (we can take in frozen fish caught en-route but not frozen meat).

Once at the islands it’s largely just for luxuries - ice cream for meals, ice for drinks, freezing cold Slivovitz and still freezing what’s left of the “daily catch”, maybe some frozen veggies for when we’re away from fresh produce markets.

Seems though that I’m going turn the temp down to ice cream levels (-15C). Thanks everyone for your input so far, valued as always.

[ayates]

Originally Posted by CassidyNZ

Hey Allan. I’m not sure of the relevance to boat units - is this a domestic fridge/freezer being logged?

This is marine/RV unit, installed on a boat, and run on 12V all summer (July/August), mostly around Lake Ontario.

Yes, it would be nicer to have the freezer at little lower in temperature., but if the thermostat is set any lower, the fridge goes below zero. Looking at the graphs, and my end of summer photographs, I see the thermostat was set a #5, so I suspect someone was playing with it near the end. It can be seen that freezer gets to a better temperature, but at the expense of freezing the fresh food.


I would much prefer separate compressors and thermostats for fridge and freezer...


Allan.

[CassidyNZ]

Originally Posted by Auspicious

Something I meant to say before, changing temperature takes a lot more power than maintaining it. I'm always nice to grocers and restaurateurs. When I do a big cook I can usually schmooze space in someone's walk-in to get it frozen hard and down well below 0F. Even with transit issues, when it goes into my freezer it is a net contributor to cooling, not a drain.

Yep, that’s been our modus operandi up to now. Before this freezer, we used a local butcher to prep meat for individual meals for the trip north and vacuum pack it then freeze down to -40C. By day 4 or 5, the last of this, in the fridge still partly frozen, would be cooked.

But our crossings are normally 7 to 10 days so the freezer will enhance this process. I usually sail with two unskilled, inexperienced crew who almost always have some level of mal-de-mer to contend with and having pre-cooked meals will save me having to cook a full dinner every day.

Also, by day 5 or 6 the fridge contents are getting lower so I hope to use the fridge space to pre-chill fresh catch before putting it into the freezer. I believe this freezer is about to revolutionise my voyaging

[CassidyNZ]

Just for some additional background, our fridge and freezer used to be a eutectic spill-over with air holes in the common dividing wall. The compressor unit was a really clunky, noisy, seriously power hungry monster that just had to go.

All the bleed holes have been sealed off and now two 12v condenser units with seperate evaporators enable me to keep better control. That said, there is still quite a bit of temperature sharing between the spaces. I’ve seen a much better cycle time on the fridge now that it’s getting some bleed-through from the much colder freezer.

The down side of course is it places all the insulation under scrutiny and I believe I’m getting similar bleeding off of temperature through some of the other walls as well. An example was quite a lot of condensation on the work top above the freezer when it first went to work. That has slowed now but still evident on a humid day.

But it is what it is - I’m not about to rip everything out and re-insulate to get a 5% performance improvement - my solar array easily manages the power used so the only negative for me is the longevity of the compressors running perhaps for longer than they should. In 10 years I probably won’t need this boat (or it’s fridges) anymore