Fridge/freezer power use vs. 2 chest freezers

Stdyhand
Stdyhand Solar Expert Posts: 33
I have a standard AC fridge/freezer that uses 1-1.2 kwh in a 24 hour period. I've read that chest freezers are far more efficient and that some even convert a chest freezer into a fridge. Is it more efficient to use a standard fridge/freezer combo or go with two chest freezers with one being used as a fridge?

According to the energy guides on a few 5 cubic foot chest freezers I've seen, two freezers would still use less power than one standard fridge/freezer.

I considered the 12 volt freezers for less power consumption, but every one I've seen is just far too small for a family of 5.
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge/freezer power use vs. 2 chest freezers

    A few numbers I have read seem to indicate that a ~7 cuft chest freezer would run about 0.25 kWH per day as a chest refrigerator.

    The most efficient ~17 cuft refrigerator (cheap from Home Depot) I could find was rated about 0.9 kWH per day (no longer made).

    In real life, refrigerator/freezer operating power is very dependent on ambient temperatures, how often it is opened, and how it is used (making ice cubes, placing "warm food" in freezer to hard freeze, etc.).

    My suggestion if your numbers are within a factor of 2 between the high and low estimate--That is "almost the same" as the differences are not great enough to build a reliable system around.

    In the end, you may have to just get a small freezer, put it on a kWH type meter, and run it through hot and cold weather to see how it performs for you (and if a chest freezer is really acceptable to your spouse who may have to lift out baskets multiple times per day to access food on the lower levels).

    Some conservation projects are just not worth the family stress.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers
    Stdyhand wrote: »
    According to the energy guides on a few 5 cubic foot chest freezers I've seen, two freezers would still use less power than one standard fridge/freezer.

    One reason is that refrigerators use a lot of energy for their automatic defrost cycles. On most freezers, defrosting is a manual affair. If you convert a freezer to a fridge (lots written about it on this forum) beware of condensation issues.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    Instead of going with a chest freezer converted to a fridge and a separate chest freezer we went with a normal fridge/freezer that was very energy efficient. I really wish we went the chest freezer route. Our fridge uses a lot of power and we open the door all the time is it runs a lot more than I estimated. The chest freezers would have required a different kitchen layout and compromises (e.g. how do kids get stuff out of them) but I cringe every time the compressor on our fridge.
  • mahendra
    mahendra Solar Expert Posts: 177 ✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    Aren't the new Samsung inverter compressor refrigerators suppose to be really efficient.As i remembered i looked at a few and the energy ratings were about half of the regular energy efficient types that don't have inverter compressors.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    I looked at them before and they are REAL Pricey, ~ 3 times the others ( NA made)... mind you about half the price of an LG!
     
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  • Stdyhand
    Stdyhand Solar Expert Posts: 33
    Re: Fridge/freezer power use vs. 2 chest freezers

    My wife doesn't mind using a chest freezer. She is pretty strong in that she doesn't nit pick about little things and she isn't a material girl. We also had a chest freezer before that she regularly defrosted so the manual side of things is not new. This comes down to efficiency and storage space. We don't open the fridge/freezer too often, but this will be in Arizona where it will get fairly warm so I thought the chest freezer might be better suited. Most fridge/freezer combos also have a very small freezer and too much fridge space and we need the larger freezer more. It will be a 30 min trip to the grocery store so a chest freezer would serve us better. Like I said though, power consumption is very important. If we can get better efficiency while getting the extra space of chest freezers then we'll go that route.
  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    FYI, I picked up a cheap chest freezer at sears last summer and had a pile of 2" Iso board foam around the house. This unit has coil mounted under the back wall sheetmetal but I did glue on the 2" foam on 3 sides and ran it up 2" over the top cover after cutting a 1/2" thick shelf on the inside of the foam that was level with the top cover. I then have a removable 2" thick foam plug that sits on top of the cover and and catches the lip on the side foam. It is quite noticeable when I pull the cover that the top of the freezer is cooler than the surrounding area. On rare occasions in the summer I did get some minor condensation. I figure it cuts the power usage by about a 1/3. Sundanzer goes one step further and incorporates far thicker foam in their walls and also offers a model with built in ice packs that can run strictly off solar panels. They are pricey but may be worth looking at for an off grid install
  • mahendra
    mahendra Solar Expert Posts: 177 ✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    yes the inverter compressor are really pricey i like them not that that much because of the price was just trying to give info,
    Sundanzers are great several people here have them they are worth the money if you want to go dc and consider efficiency.
  • mahendra
    mahendra Solar Expert Posts: 177 ✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    sundanzers are pretty pricey too
  • Stdyhand
    Stdyhand Solar Expert Posts: 33
    Re: Fridge/freezer power use vs. 2 chest freezers

    I looked at the sundanzers and somehow overlooked the 8 cf model which would work for us. Do the sundanzers have a softer startup than the AC units? The thicker insulation reduces the amount of time the unit must run, but other than that reducing the energy consumption I don't see much difference from the AC unit.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers
    Stdyhand wrote: »
    I looked at the sundanzers and somehow overlooked the 8 cf model which would work for us. Do the sundanzers have a softer startup than the AC units? The thicker insulation reduces the amount of time the unit must run, but other than that reducing the energy consumption I don't see much difference from the AC unit.

    The Danfoss compressor in the sundanzers self configures to 12 or 24 volts. No startup surges. The compressor has a proportional control. The Danfoss compressor is used in several refrigerators and freezers. I recommend you look at the Steca freezers & fridges... they use the danfoss compressor and, in my opinion, have more features than the sundanzer. In particular, the steca thermostat can be set to fridge OR freezer temps. The Sundanzer cannot.

    One other thing I don't like about the sundanzer is the location of the thermostat... it is NOT inside the food compartment. That has some advantages under some circumstances, but the system does not work well if the fridge/freezer is at cold ambient temps. A smart strategy for northerners is to put the freezer in an unheated garage... it doesn't take much energy to keep food frozen if the garage temperature is near freezing, but that doesn't work with the sundanzer.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mmag
    mmag Solar Expert Posts: 57 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    is there a reason why none of these dc direct freezer/fridge manufactures make a model that runs on 48v? it seems that it would increase efficiency.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge/freezer power use vs. 2 chest freezers

    Danfoss does not presently offer 48 volt rated compressors:

    http://www.danfoss.com/

    I believe the reasons are several... The size of the 12+24 volt market is larger than 48 volt (but still microscopic compared with the AC refrigerator market). The highest rated voltage of the Danfoss product line is 45 VDC maximum--It is hard to get transistors that switch at >72 volts--Plus the higher voltage silicon devices have higher resistance, which makes them more difficult to use at 12 volts (low voltage, high current, more wasted heat/larger transistors needed, etc. to support a 12-48 VDC pump).

    In the end, most 48 volt systems are (usually) large enough to run a 24x7 AC inverter and a standard Energy Star rated refrigerator for the same overall costs (or even less) than the DC suppliers can offer at this time (high volume AC refrigerator market with much lower cost of production/distribution vs small DC market--even when AC inverter+solar array+battery bank costs are taken into account).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mmag
    mmag Solar Expert Posts: 57 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    Good points BB, although if a manufacturer were to build a 48v freezer why would it need to run on 12v too? Seems 24/48 would be a sufficient market, also there is not many options in an energy star chest freezers in the 7-8 cubic foot range, if any? and many of the 7 cubic foot chest freezers use 250-300 kwh per year, and the sundanzer 8 cubic foot uses 140-200kwh(im giving rough numbers) per year, and the soft start on the sundanzer reduces compressor surge, whether you have a inverter running 24/7 or not it seems to make sense to get the most efficient appliance you can find
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge/freezer power use vs. 2 chest freezers

    When designing power electronics (years ago), there was a definite change in the a availability of FETS that worked >~40 VDC. It was easy to find <40 VDC FETs that also had low internal resistance that would handle 2x the current on a 12 volt circuit--As well as still work on 24 volt battery power.

    Today--I am not sure--But I would still not be surprised that the price/components needed to run a 24 volt bank vs 48 volt bank are not really something that can be made to work cheaply (i.e., you need more >72 volt rated FETs and heat sinks to still function correctly at the lower voltage/higher current of a 24 volt battery bank--Again, just guessing.

    Another think to watch with some of the DC appliances... A few years ago when I looked, if you looked the Energy Star rated consumption of a DC Freezer, it was very close to the energy consumption of a "cheap" but efficient AC Freezer.

    The reason was that Energy Star ratings used a higher room temperature and the DC rated consumption was in a much cooler environment--Which naturally lowered the power consumption.

    A four year old thread: Is a Sunfrost Fridge worth it?

    I few years ago, I did look at Energy Star and the (I think) SunFrost website--And the Energy Star energy usage was the Right column which was 90F operation. Note the left column is only 70F and much less power usage. R19 is an 8cuf unit.



    Model
    Description

    Daily Energy Use
    (amp hrs @ 12 VDC /
    kwh @ 110 VAC)

    Dimensions
    (see clearances below)

    Shipping
    (export add 40 lbs.)



    at 70°F
    21°C

    at 90°F
    32°C

    Height

    Width

    Depth

    Weight

    Volume



    RF19*
    Half Refrigerator/Half Freezer
    62 amp-hrs
    .77 kWh

    82 amp-hrs
    1.02 kWh

    66"

    34.5"

    27.75"

    320 lb.

    46 C.F



    R19^
    Refrigerator Only
    28 amp-hrs
    .33 kWh

    47 amp-hrs
    .56 kWh

    66"

    34.5"

    27.75"

    310 lb.

    46 C.F



    F19
    Freezer Only
    100 amp-hrs
    1.25 kWh

    130 amp-hrs
    1.63 kWh

    66"

    34.5"

    27.75"

    320 lb.

    46 C.F





    Sun Danzer:

    http://sundanzer.com/wp-content/uploads/SunDanzerDCPowered1.pdf

    Daily Energy Consumption - Standard Test Conditions* 12VDC
    Model 21.1oC (70oF) 32.2oC (90oF) 43.3oC (110oF)
    DCR165 77Whrs / 6.5AH** 168Whrs / 14AH 348Whrs / 29AH
    DCR225 90Whrs / 7.5AH 198Whrs / 17AH 393Whrs / 33AH
    DCF165 272Whrs / 23AH 441Whrs / 37AH 766Whrs / 64AH
    DCF225 360Whrs / 30AH 532Whrs / 44AH 817Whrs / 68AH
    *Standard Test Conditions: No door openings, refrigerator 3oC (38oF), freezer -12oC (+10oF).

    Note Sun Danzer is +10F for freezer temperature... The optimum freezer temperature is ~0F or lower.

    As of today, I do not find Sun Danzer or Sunfrost listed in the Energy Star refrigerator or freezer site (that I could see)...

    http://www.energystar.gov/certified-products/certified-products?c=products.pr_find_es_products

    You can find lots of 7-9 cuft AC powered freezers in the 215 to 300 kWH per year or 590 to 820 WH per day range.

    And the 8cuft chest (AC or DC) freezers use 1/2 the kWH per day of the R19 vertical Sun Frost models.

    There is just not that much difference in power usage these days between the DC "high efficiency" and the AC "Energy Star" refrigerators/freezers.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mahendra
    mahendra Solar Expert Posts: 177 ✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    good info guys thanks
  • mmag
    mmag Solar Expert Posts: 57 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    does anyone have any real world experience with dc direct chest freezers, with actual measured energy consumption?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge/freezer power use vs. 2 chest freezers

    I have not seen any reports that cast doubt on the numbers given (both for AC and DC units)--At least when new... There have been some reports of one or two big AC refrigerator manufacturers gaming the AC Energy Start Ratings.

    Energy Star
    Labels Stripped from Five Fridge Models : TreeHugger

    According to both parties, LG rated the refrigerators on the basis of a standard test procedure that has been widely used for nearly 30 years. LG said it didn’t take into account different applications of the testing rules for newer technologies used in the latest energy-efficient products. Specifically, DOE said LG didn’t set the refrigerators’ temperature-controllable compartments to their coldest levels, a requirement for energy-usage measurements.

    Another company (as I recall--could not find link) turned off the anti-sweat heaters of the refrigerator when the room was at ~90F--Which lowered the energy usage during the Energy Star Testing.

    Here is a thread where I used a Kill-a-Watt meter to measure the energy usage of several refrigerators and a freezer in my home (around 70F):

    Daily Load Estimate from Energy Star label


    Overall, the numbers were pretty accurate (less than label or ~10% more than label at 70F)--And one (~8-10 year old) refrigerator (I am going to replace, may be losing refrigerant) that is using several times more than tag rating.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mmag
    mmag Solar Expert Posts: 57 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    i have a 8 month old 7 cu ft kenmore that is not energy star rated because i could not find one that size, it says it uses 282 kwh per year, the power consumption is rated at 1.3 amps but when the compressor turns on it surges enough to dim my lights bring my washer out of sleep mode and slow my bathroom fan down, i have a magnum 4448 and 16 brand new l16reb so power is not the issue, i am going to get a kill a watt to get some real world numbers.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers
    mmag wrote: »
    i have a 8 month old 7 cu ft kenmore that is not energy star rated because i could not find one that size, it says it uses 282 kwh per year, the power consumption is rated at 1.3 amps but when the compressor turns on it surges enough to dim my lights bring my washer out of sleep mode and slow my bathroom fan down, i have a magnum 4448 and 16 brand new l16reb so power is not the issue, i am going to get a kill a watt to get some real world numbers.

    The starting peak and running power are very different, and the kill-a-watt can't catch the peak starting surge.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge/freezer power use vs. 2 chest freezers

    Check the DC input to your AC inverter with a DMM (especially during surges). Perhaps your DC cabling has to high of resitance or your battery bank (more information?) is not large enough (or getting old?).

    Regarding Mike's comment. The Kill-a-Watt only takes readings about once per second. To accurately measure surge loads/voltages, you need peak capture volt/current clamp meters.

    There have been a few complaints here that Magnums did not regulate AC voltage during surges very well (I do not know if this is a problem or not)... Have tried calling Magnum support and see if they have any suggestions/solutions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Stdyhand
    Stdyhand Solar Expert Posts: 33
    Re: Fridge/freezer power use vs. 2 chest freezers

    Been looking at the steca vs. sundanzer freezers. The steca can be used as a fridge/freezer which is a huge plus. The steca also says it can run on a 70 watt panel whereas the sundanzer says it needs a 175 watt panel. Both freezers are 5.8 cu ft.

    It would be costly to get two of these and use one as a fridge, but if freezer went out I could use the other steca as a freezer.

    I am going with DC lighting and would like to use DC freezers. I might be willing to pay the price since their more efficient, but reliability is another issue. I have no experience with these so IF one were to break down the customer service and turn around time to get it fixed would become a very high priority.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers
    Stdyhand wrote: »
    Been looking at the steca vs. sundanzer freezers. <snip> Both freezers are 5.8 cu ft.

    They both make 8 cu ft models.
    Stdyhand wrote: »
    I am going with DC lighting and would like to use DC freezers. I might be willing to pay the price since their more efficient, but reliability is another issue.

    I would suggest you avoid DC lighting... Much better choices, quality and prices on 120 volt lights. Also, many DC lights do not tolerate the wide swings in DC voltages that you will have in a battery based system.

    As far as efficiency is concerned, DC fridges are not worth the price. The money you save on a AC fridge will buy you enough extra solar panels to make up for its inefficiency (and, as has been pointed out, its not much less efficient than a DC fridge).

    DC fridges may make sense in a very small system where an inverter, large enough for an AC fridge, is not otherwise needed.

    As far as reliability is concerned, I think the DC fridges are as reliable, or more so, than AC fridges. But you are correct that it will probably take longer to service a DC fridge in the unlikely event of a problem.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge/freezer power use vs. 2 chest freezers

    If I understand the ratings correctly:

    http://www.steca.com/index.php?Gefriertruhe_en
    http://www.steca.com/index.php?Gefriertruhe_en&repcode=b@wdownloadhinweis|2&dh=55/5540_0x0_Steca_PF_166_240_specification_EN.pdf

    You need a 50-70 watt panel minimum for refrigeration in a cool climate with a not too cool (inside) refrigerator to a 200 watt panel for a deep freeze in hot climate/weather.

    While I like the idea of running without a battery--There is real issues with cycling refrigerator and freezer temperatures (warmer food does not last as long, temperature cycling increases chances of freezer burn, long term freezing temperatures should be in the 0F range or colder).... If you keep your food/items short term (several days for refrigerator, a few weeks for freezer), then warmer temperatures and thermal cycling (warming at night/cooling during day) will be less of an issue for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mmag
    mmag Solar Expert Posts: 57 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers
    BB. wrote: »
    Check the DC input to your AC inverter with a DMM (especially during surges). Perhaps your DC cabling has to high of resitance or your battery bank (more information?) is not large enough (or getting old?).
    -Bill

    my post says i have sixteen brand new l16reb, which are trojans, i have about four feet of 2/0 600v welding wire from batteries to inverter, and my freezer is located about twelve feet away from my inverter/subpanel on 12/2 romex, my inverter could have problems with regulating voltage during surges but it does not happen when i turn other small loads on(but now i will look into it), but the point if my post was to show that the small freezer i have seems to surge alot when it turns on and the sundanzer and the steca have soft starts which should be easier on off grid systems.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers
    mmag wrote: »
    my inverter could have problems with regulating voltage during surges but it does not happen when i turn other small loads on(but now i will look into it), but the point if my post was to show that the small freezer i have seems to surge a lot when it turns on and the sundanzer and the steca have soft starts which should be easier on off grid systems.

    Hmmm, is this an issue of the inverter coming out of sleep or standby mode? If you have another load on the inverter would not be sleeping of in standby mode... therefore no surge?
     
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge/freezer power use vs. 2 chest freezers

    In general, a standard refrigerator compressor should have about 5x starting surge. Assuming ~100-120 Watts running, that would be 500-600 watt surge.

    It sort of sounds like the Magnum is not managing surge current well--And I have read of a couple of posts from others that had that complaint. I don't know if they resolved the issues or not.

    I believe the Danfos DC compressors are VFD (variable frequency drive) based--So, yes, they probably have much less (near zero) surge.

    And to answer another question, they do have a couple 48 Volt DC versions too (intended to cool telecom batteries/shelters)--I don't know enough about Refrigeration to guess if these compressors can be used in refrigerator/freezer applications.

    (product page) http://www.danfoss.com/Products/Categories/Group/ra/Compressors/Direct-Current-Compressors/Direct-Current-Compressors-Solar-Applications-10-45V-DC/ee06f4a0-0649-4e60-901c-8ea54593a573.html
    (literature page) http://www.danfoss.com/Products/Categories/Literature/ra/Compressors/Direct-Current-Compressors/Direct-Current-Compressors-Solar-Applications-10-45V-DC/ee06f4a0-0649-4e60-901c-8ea54593a573.html
    (PDF catalog page) http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/06/FRCC.PK.037.A1.02%20-%20Quick%20ref%20BD%2013-09-2012.pdf

    I wonder if it is cost effective/possible to swap in a DC compressor for a standard chest freezer/refrigerator...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mmag
    mmag Solar Expert Posts: 57 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers

    how would i check that? test the voltage output of the inverter under a surge?
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers
    mmag wrote: »
    how would i check that? test the voltage output of the inverter under a surge?
    BB. answered your question back in post #22 in this thread:
    BB. wrote: »
    The Kill-a-Watt only takes readings about once per second. To accurately measure surge loads/voltages, you need peak capture volt/current clamp meters.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Fridge/freezer power use vs. 2 chest freezers
    BB. wrote: »
    While I like the idea of running without a battery--There is real issues with cycling refrigerator and freezer temperatures (warmer food does not last as long,

    -Bill

    And I really had my eyes opened by the Dept of Health Food Handling course I recently completed. The results of storing, keeping, or allowing food temperature to rise above 40F can be deadly. And that includes foods not commonly thought of as tricky, things like cooked vegies, including cooked potatoes and even pasta products, NOT just animal products!