Question - Best Freezer Temperature
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Question on accepted "standard" of zero deg. F. as the best temp to keep frozen food in a freezer.
All my life, I have accepted, without question, the "wisdom" of always keeping the freezer set to 0* F. Now, I have a question. If "0" is the best temp, then why does SunDanzer list their freezer temp as 12*F, when listing their energy use. Is there a good reason for the 0* F, or is it just done that way to give some room when the power goes off? Or, was 0 pushed by the utilities because that uses more power that they can bill you for?
Anyone know the real answer without BS?
Thanks a bunch.
Wayne
All my life, I have accepted, without question, the "wisdom" of always keeping the freezer set to 0* F. Now, I have a question. If "0" is the best temp, then why does SunDanzer list their freezer temp as 12*F, when listing their energy use. Is there a good reason for the 0* F, or is it just done that way to give some room when the power goes off? Or, was 0 pushed by the utilities because that uses more power that they can bill you for?
Anyone know the real answer without BS?
Thanks a bunch.
Wayne
Comments
you know wayne i've asked myself that question a few times. just kicking it around you have stuff that needs to stay below 32 degrees f. opening the door obviously raises that air temp and could raise the temp of the contents some. now add to it the fact that you just put some stuff in there, maybe a bunch of leftovers or whatever. this raises it too. ahh, but it's running you say. yes it is, but it takes a bit of time to reduce the temperature. let's also not forget those defrost cycles also heat up the freezer section some before it goes back to cooling it again.
do i think it needs to be 0 degrees f. nope as i feel that even with putting new stuff into the freezer it'll still cool it in time before the already cold adjacent items hit 32 degrees f so i'm with SunDanzer on this one. i guess we could compromise and go 6 degrees too. as you mentioned if your power goes out and there's no other power source, the 0 degree f temp would keep the food longer though. i would think experimentation could select a good temp for your use with thermometers(handheld infrared is great) or genericly by observing ice cubes placed in certain sections.
in fact you've got my curiousity as i've never checked the temp on my own freezer or frig. i'll update here with my results.
ok, i did it with an infrared and measured 1 and 38 degrees respectfully. now my handheld ir thermometer is off some as i found i have to add 3 degrees to get it right. that makes it 4 and 41. by that i can make the freezer slightly warmer and the frig slightly cooler. it wasn't where i originally set my freezer/frig by seeing the dial positions as the other half messes with things. typical. :roll:
do note that the temp reading on my ir thermometer was rising quickly when i opened the freezer door and was aimed at a pizza. that's the biggest factor of any frig or freezer is keeping the doors closed as much as possible. standing there deciding for 5 minutes will raise the temp of the food quite a bit.
A little googling found this (sorry, it is in PDF and, so far, I have only found page 1--I think):
http://pubs.acs.org/cgi-bin/abstract.cgi/iechad/1948/40/i08/f-pdf
Updated link (10/11/2019):
https://pubs.acs.org/doi/pdf/10.1021/ie50464a017
Update again. Found full file for free, and attached PDF to Post #28 below:
https://forum.solar-electric.com/discussion/comment/403789#Comment_403789
This test apparently was performed around 1945--I think...
interesting, as back then no frig could run that long without having to pull it all out to chip away all of the ice that had formed. i'd also think the insulation wasn't good in 1945 if there was any. everytime you open the door the temps fluctuate and why they didn't explore below 0 temps i would be curious to know. i think those tests need to be run again in this day and age for accuracy, don't you think?
actually those nutritional losses make 0 sense to me. where did the ascorbic acid go to?
I looked around some more, and it turns out the whole article is available for $25.00--I am not that interested.
I believe these were lab tests, so they probably took quite a bit of care to ensure that the temperatures were maintained as stated (they even had a zero degree room to do their measurements of weight to measure dessication of food/packaging). And if this is just at the end of WWII, the government would have great interests in how to ship frozen food to troops in a cost effective manner.
More quotes from page 1:
At this point, it appears that there is some scientific data to backup the Zero Degree setting for a deep freeze when attempting long term storage of food.
And SunDanzer is either assuming short term storage of frozen food (less than 4 months), or they are stacking the specs. to make their unit look more efficient than it really is...
-Bill
PS: Article is dated 1948...
:-) Thanks a lot BB, that's the kind of info I was looking for and it makes sense. Even though the info is old, I expect it was a well done study, so the info would still hold today.
Hummmm, I wonder just how much energy those SunDanzer freezers REALLY take if run at what appears to be the required 0* F. ?
With over 4 inches of insulation, should be better than your average, that's for sure, but how much do they really save? We may have to do our own testing to find out.
Thanks again for your responses.
Wayne
I try to stay closer to 0F, because buying a steak, and thawing it on a perfect BBQ evening, and finding it's "turned" and not as tastey, well, crank the freezer down, and instead of tossing a $5 steak in the trash, use the $5 for an extra 5 degrees.
And the ice cream needs to be solid, not mushy.
Mike
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
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Looking at Sundanzer's PDF spec. sheet:
http://www.sundanzer.com/PDF/SunDanzerDCPowered.pdf
It appears that 10F for the freezer, assuming 70F to 80F is an equivalent model for the difference in power for 0F vs 12F:
500Wh/400Wh=20% power increase (6.8 cuft freezer)
660Wh/540Wh=22% power increase (8.1 cuft freezer)
182.5 kWhrs/year (5.8 cuft @ 0F) (31.5kWhrs/cuftyr)
240.9 kWhrs/year (8.1 cuft @ 0F) (29.7kWhrs/cuftyr)
From ACEE, some cheap energy efficient chest freezers (assuming US testing is done at 0F):
http://www.aceee.org/consumerguide/freezers.pdf
Wood's 9 cuft = 251 kWhrs per year (28kWhrs/cuftyr)
Various 15 cuft = 354 kWhrs per year (24kWhrs/cuftyr) (number seem to match my measurements vs my AC freezer "tag")
The Sun Danzer's are 1/2 the size (6-8cuft), and 3x as expensive ($974-$1074 list price) as the el-cheapo 15 cuft chest freezers ($300 or less???), and use more power per cuft (although 12vdc vs 120vac has its own issues of inverter efficiencies)...
Going through this page:
http://www.sundanzer.com/prodinfo.htm
It appears that the SunDanzer compressors are actually 3 phase motors with a variable frequency inverter/controller to operate the unit (there is also a mandatory (?) fan required for cooling the electronics/compressor. Makes sense, you would not want a brushed DC motor in a sealed refrigeration system.
So insulation is only part of the equation--Volumetric efficiency (volume/mass of food goes up with the cube of the size of the freezer, the walls only go up with the square of the size), and the losses of a dedicated inverter/controller for the motor (plus required fan--not used on standard AC freezers), mass production and engineering vs the much smaller market for "solar" powered freezers--all probably come into play here.
I would say, at this time, that SunDanzer is playing pretty fast and loose with specifications and when compared apples to apples, they do not appear to offer any real savings in power usage over a standard energy efficient chest freezer.
Using their own sizing chart for a 5 hour solar day, the difference in size for a solar array would only be a 40 watt larger solar panel--at $5 per watt, that is only $200 more (plus probably less than $100 for more batteries)--certainly a questionable cost savings of spending $2,100 for 16 cuft of SunDanzer (two 8 cuft freezers) vs $600 for one 15 cuft freezer that would use quite a bit less power (or if DC off-grid system--the two 8 cuft SunDanzers would use almost exactly the same amount of power as one 15 cuft no-name freezer with inverter).
I would also question SunDanzer's Freezer spec. range of 0F-23F range--from the early food testing link I provided, pork went rancid after 4 months in a 0F-20F test, whereas it lasted for more than one year when kept at 0F or less... Unless the SunDanzer spec. is the adjustment range rather than representative of its ability to keep food cold.
-Bill
I thought Sunfrost http://www.sunfrost.com/ was the leader in low power fridges, but they are REALLY pricey.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
bb,
i do want to commend you on researching this some as it's good info. i suppose i can still keep mine around the compromise of 6 degrees f because i don't keep foods that long. i'm lucky if something stays in there for a month so i'll bet i could go the 12 degree f mark that SunDanzer uses. i would suspect they are relying on both short term storage and better figures by having a higher internal temperature.
in any event even if you have a 25 year old energy hog the main culprit is to have the doors open. an energy efficient frig/freezer with the doors open frequently and for longer periods of time can do worse than the energy hog with doors not opened much or for long when they are.
it should also be mentioned that a near full frig/freezer will do better than one nearly empty and that you must not block the key areas of the frig/freezer that circulate the cold air.
An upright 16.1 cuft freezer F19:
http://www.sunfrost.com/refrigerator_specs.html
1.25 - 1.63 kWhrs / day (70F-90F room temp, freezer temp not stated)
= 28.3 kWhrs/cuftyr - 37 kWhr/cuftyr for Sun Frost upright freezer... (no chest freezers listed).
Actually, if I take a 15 cuft Woods freezer (above) and run it on an 85% efficient inverter:
24 kWhr/cuftyr / 85% = 28.3 kWhr/cuftyr for the Woods cheap chest freezer.
The SunFrost uses the same amount (or slightly more--don't know the test conditions) as the dramatically cheaper Wood's freezers...
Even my 1 year old on-sale Maytag 15 cuft frost-full freezer (in insulated outside tree shaded shed bought on clearance at Home Depot), from 5/24 to 10/20 (today) used only 320 kWhrs/year (this is only based on the warm seasons here) or 21.3 kWhrs/cuftyr (pretty close to the 24 kWhrs/cuftyr based on the US Energy Star Ratings) for somewhere around $350...
From the Energy Star Guide... Their 14.3 cuft RF-16:
http://www.energystar.gov
Uses 254 kWhrs per year (working backwards, it appears that the Energy Star number for the RF-16 is equivalent to the 90F temperature rating of Sun Frost).
My Maytag 20 CuFt with ice maker, frost free, fridge uses 555 kWhrs per year (per hang tag)... Roughly:
SunFrost = 254 kWh/yr / 14.3 cuft = 17.8 kWhrs per cuft
Maytag 20 CuFt loaded = 555 kWh/year / 20 cuft = 27.8 kWhrs per cuft
Yes the SunFrost is more efficient (36% less energy per cuft of food) but for about the same cost as my loaded 20 cuft fridge (and somewhat overpriced because it is a counter depth fridge), I get less storage space, manual defrosting, no ice, no cold water...
I am sure that the SunFrosts are nice for what they do---but they also demand an arm and a leg for what they do--and for the upright freezers, I would have to pay ~$2,800 for the SunFrost, or ~$400 for a similar freezer that uses the same amount (or less) power.
There are a few web sites out there that offer the Wood's models and dropped the others (like SunDanzer) because of the huge differences in value and the small (if any) energy savings...
-Bill
Thank you Niel. I will answer in this second post, since the previous post is already getting pretty long.
I am going to shamelessly quote myself from a post I did last year on www.candlepowerforums.com on exactly how much energy is lost opening a freezer door (hint--seems to indicate about 20% of the energy is lost through opening an upright freezer door vs a chest freezer--some $$$ lost, but not as much as anyone thinks):
PS: I am going to fix my post below with the real 144 BTU per pound of water to freeze (I originally used 212 as an estimate, and that was too high)...
Again, a kill-a-watt or old utility meter can quickly show how much power is used for our major appliances... A twenty year old fridge/freezer really does use 3x the amount of energy as the same (or larger) current model fridge/freezer--ignoring the amount the doors are used.
Also, we had a very old ice cream freeze years ago (cold enough to liquefy propane on F-21 or something)... Years later went to chuck it as it was just getting too rusty--found the lower 1/3 of the freezer's insulation was ICE! The old rusty cabinet, the fiberglass insulation (instead of closed cell foam), the condensation, then freezing of water just attracting more water/ice to all added to make this one inefficient chest freezer (this was back in the 1960's--so power was much cheaper then)...
It is possible that a new, properly operating fridge/freezer will actually save you money in a relatively few years--especially for those folks that pay more than base-line for energy usage and/or have AC (where you have to pay to use AC to get the excess heat from the fridge/freezer out of the home in hot weather)...
-Bill
i have no doubt a more modern frig/freezer draws less as my key word down there was 'can'. i was making an analogy that if i'd put it to cars would be the equivalent of expecting good milage from a hybrid when you are racing it around with the pedal to the metal while the large block car run correctly and conservatively could outdo the hybrid under those circumstances. in other words don't abuse it.
you are also right that putting alot of new stuff into a fridge that is at room temperature will cause it to run quite a bit, but you can't avoid the needs for some things to be refrigerated. on that note people should know that and would certainly hope to not be dumb enough to take something from the oven and put it into the frig/freezer either.
btw, for water it's 1lb up 1 degree f = 1 btu. 1 gallon of water is 8lbs and in my frig it would be about a 30 degree difference. 8x30=240btu's. to freeze it it would be about double that.
Niel,
I was making a big estimate above about the amount of energy to freeze water... The actual number is 144 BTU per pound of water (latent heat of fusion)... So, to freeze 1 gallon of water and take from 62F to 0F would be:
62F-32F * 1 BTU * 8 lbs = 240 BTU
32F-32F (freeze) * 144 BTU * 8 lbs = 1,152 BTU
32F-0F * 1 BTU * 8 lbs = 256 BTU
Total: 1,648 BTU per gallon of water (62F-0F)
-Bill
:-) Thanks a lot guys for all the very interesting information. Very much appreciated indeed and goes along with what has been floating around in my mind for some time.
Thanks again
Wayne
I'm looking for refrigeration for my off grid cabin.
I looked at small refrigerators and chest freezers (thinking I may replace the freezer thermostat if it turns out to be more energy efficient than the refrigerator) and noticed that the current draw as shown on the tag on the back of the units is twice as high for freezers as it is for refigerators of the same size.
I know these numbers may not show the actual current use and since the chest freezers are easy to clad in more insulation and open from the top they may have some advantages over the front opening refers.
I think some of you guys have been experimenting with freezer conversions.
My question; is it worth the effort?
In a word - - - - YES!!!!!
I perverted a 5 cu ft chest freezer early this Summer and am VERY pleased with it's operation and how little power it uses. Yes, it MAY, or may not use more power while it is running, bit it runs so little that the savings are huge.
I used a modified house thermostat, adjusted to center at about +1 F and find it far better at keeping things than a standard fridge. Installed 2 shelves across the back half, so am able to reach down the inside front to access the lower shelf and the biggest things go on the floor. It only runs for 12 minutes, then goes to sleep for the next 90 minutes (after initial cool down). And it's far quieter than a regular fridge.
There is one problem you will have to look after though and that's condensation on the inside upper walls. I solved it with a small, "V" shaped, stick on weather stripping, mounted about one foot down from the top of the inside wall, which acts as a catch for any moisture running down the inside wall and drains it into a small tube which takes the water through a hole drilled through the lower wall where there are no freon pipes and into a container from where it evaporates away. A "normal" fridge has evaporator plates that run so cold that all moisture collects on them as frost. I find the chest fridge keeps veggies far longer because of the higher ambient moisture. They don't wilt. sure, it's perhaps not a convenient to use as a regular fridge, but the efficiency is so high, that I can't see me ever going back to a standard energy pig. Would I do anything different? yes, get a 7 cu ft instead of the 5 and one that has 3 inches of insulation instead of the 2 that this Woods one has.
Oh yes, I installed a 200MFD motor starting capacitor in series with the compressor start winding, gives much quicker starts, with a lot less surge. Also, the inverter is controlled by the thermostat, so it only runs when needed and I used a delay relay which holds the power from the fridge for a couple of seconds, to give the inverter time to start and stabilize before the load is connected.
Am I happy with it? YES!!!!
Go for it, you won't be sorry.
Oh, and check out this thread, page 2: http://www.wind-sun.com/smf/index.php?topic=1073.15
Wayne
Thanks for the solid info, Wayne.
My neighbor added two inch foam board to the outside of his refigerator and covered it with the bubbly looking plastic paneling that they use on bathroom and shower walls.
He claimed that it ran only 8 minutes and hour off his MSW inverter but he sold out and moved before he had it long enough to be sure if this was correct.
I'm not clear about the 200mfd cap you added. You said you put it in series with the compressor motor? Am I correct in understanding that you put the cap in one line, not across the line?
No, not in series with the motor, rather in series with the START WINDING of the motor.
Most compressors (refrigeration) have 3 terminals. One is "common" another is "run" and the third is "start". If you unplug whatever is plugged into the actual compressor, you will most likely see three pins sticking out of the compressor, arranged in a triangle. The upper pin is usually the "common" connection, the bottom one on YOUR left, is usually the "start" connection, going to the start winding, while the other bottom one on, on your right, is usually for the "run" winding. Disconnect whatever is connected to the bottom LEFT (your left) terminal and install a 200 MFD capacitor between that terminal and whatever was connected to it. EXCEPT, there MAY be a MOTOR RUN capacitor that was connected to the start terminal, if there was, reconnect it, but nothing else, back to that same terminal, as it was before you did anything and leave it there. It would have been connected across the bottom two terminals on the compressor.
Confused? Clear as mud? Take your time and look things over well before you try anything.
You do not need to make this modification, but if you do, it really reduces the big surge on start up and greatly shortens the time it takes for the motor to come up to speed, thus saving power. Power saved, is power you don't have to make.
By the way, I've been running mine all summer on a 1000 watt MSW inverter, because I still can't afford a pure sine unit, but hope to go sine in the next few months, which I understand will reduce power consumption of motors, by about 20%.
Good luck
Wayne
Thanks for the clarification, Wayne.
Since I'm often off line for weeks at a time my replies are sometimes late.
Have you considered placing capacitance accross the line to smoothe out the "bumps" from MSW inverters or improving power factor?
Has anyone done this to see if it works?
I've been looking for a 1:1 xfmr to see if it would round off the edges of the waveform enough to cut the noise from some of my flourescent fixtures.
After blowing up the battery charger for my DeWalt battery drill I'm shy about plugging appliances into my MSW inverter.
TCurran,
I am not sure that a standard transformer will really do much to round off the square wave edges... depending on the construction, transformers transmit higher frequencies better than lower frequencies... So, either nothing will happen, or you will just be heating another thing (the transformer) with the MSW inverter...
One suggestion, look at a propane powered refrigerator instead... If you have propane available, they seem to be a good alternative (something like 1/2 to 1 lb of propane per day--depending on size and model?). A standard 20 lb BBQ tank will last 3 weeks or a month for some of the fridges I have seen. And it might be cheaper than sizing solar panels/batteries/inverters/generators when compared to the cost of bottled propane.
-Bill
A transformer will indeed round off the edges for you, but 2 problems
1) the inverter may shut down or fry
2) the transformer will get really warm.
"Modified Sine Wave" is a really POOR term, it actually looks much more like a square wave, which is why transformers/heavy wall warts die, and the switching power supplies are OK.
Whichever is stronger, will win : Inverter or inductive load.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
"depending on the construction, transformers transmit higher frequencies better than lower frequencies" from bb
not necessarilly so as it depends on how things are wired. in general a standard transformer with primary and secondary will pass low frequencies better. series choke coils are based on this so that they would attenuate higher frequencies, but if a choke coil would be wired between hot and ground this will pass low frequencies to ground leaving the higher ones to pass on.
capacitors are similar in that it would depend on how it is wired. a cap from hot to ground will pass the higher frequencies to ground and lower frequencies allowed to pass onward. a cap in series will pass only ac frequencies with less resistance the higher in frequency it goes. i'm sure you know this, but it may have been either an oversight or just said wrong by you.
I run my converted freezer and submersible pump (1/2 HP) on modified square wave inverters, only because I still don't have the money to get a good pure sine. I realize the motors uses about 20% more power this way and in time hope to go pure sine. Neither run long enough to get more than the chill off.
Re capacitor across the output of the inverter, I tried from 0.1 MFD, up to 33 MFD (started with 33) and the only result was the instant shutdown of all 3 MSW inverters I tried, on "fault". So, I gave up.
Re transformers passing HF audio range, for years the older, high quality, tube tube audio amps used an output transformer to drive the speakers, then along came transformerless solid state outputs. In fact, those audio xformers passed HF better than bass in most if not all cases. The transformerless ones could and would pass DC to the speakers if you weren't careful with what you fed in to the amp. You could actually watch the speaker cone very slowly move in or out, or move out and stay out, something that would never happen with an xformer. They actually had to design in low frequency filters to prevent this. But yes, those xformers were designed for audio. Tube type audio - - hummm, I think I'm getting old!
Wayne
Ideal transformers are not chokes/inductors--they are designed to transform the voltage and current by the turns ratio--and within the design bandwidth of the transformer, its response should be relatively flat...
As the frequency goes down (towards DC), there will be a cutoff point where the core saturates and no further power can be transformed (transformers will not pass DC, a choke will just fine)... High frequency will be limited by the ability of the magnetic core material to switch states without heating losses... So, a power transformer at 50/60Hz is going to be sized for the minimum frequency (50/60 Hz) at the low end of the bandwidth, and at some higher frequency cutoff by the design/selection/windings/etc. and material (I have yet to find the bandwidth for a 60Hz transformer
If you want a "transformer" filter, then you can look at ferroesonant transformers... They are designed to filter high frequency harmonics (don't know what will happen when fed a modified square wave) and (relatively) accurately regulate voltage.
However, a 2kVA rated ferroesonant transformer is going to be very big (110 lbs) and expensive ($2,319 list price). Low frequencies at high currents requires a lot of copper and steel/iron.
You can read about their capabilities here- (but I don't think I would even bother trying to use one to "fix" a MSW output inverter):
http://www.solaheviduty.com/support/faq.html
Just to show you how sensitive transformers are to their low frequency ratings... From the above FAQ:
You can also read here about how harmonics cause havoc with transformers (causes them to run hot):
http://www.solaheviduty.com/products/transformers/KFactor/index.html
Got to go now... Back later.
-Bill
reguardless of the responce of a transformer you will get only a limited benefit from trying to shape the waveform or smooth it out so to speak. the bigger the load the worse the waveform will get.
wayne,
those caps are shorting the high frequencies to ground through the ac resistance of the cap. this represents current being shorted to ground. that is consistant with the results you got. the larger the value the more power will be fed to ground due to a lowering of the frequency responce. also note there is more power available at the lower harmonic frequencies than higher frequencies from the inverter. that makes doubling the value of a cap to ground up to quadruple the power to ground. yes the modsines are more efficient, but start shorting out the harmonic energy and you are left with far less usable power than you thought.
Thanks Niel, That's what was floating around in the back of my head, but I wasn't able to put into words. Very well explained, makes perfect sense!
Wayne
https://datapdf.com/effect-of-fluctuating-storage-temperatures-on-quality-of-fro.html
And I have attached the file here (let me save and test). Yep--Works!
-Bill
That said, I think most food would keep better at the 0F setting rather than 20F even though in theory 20F is still well below the freeing point.