freezer efficiency

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freezer efficiency

Postby eileen » Tue Jan 31, 2012 9:10 pm

We have a freezer which I bought before I realized how important it was to check for energy usage.

We also have solar panels and receive a net feed in tariff and have a time of use meter.

I am wondering, given that the freezer is now at 90% capacity, is it feasible to run it only at night, on a time switch? That would mean that we would pay a fraction of the cost of electricity to run it. But I am concerned that the food might spoil if it gets a little warmer during the day.

The freezer contains mostly fruit and veggies, home grown, which will last us through the winter.
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Re: freezer efficiency

Postby Gordon-Loomberah » Wed Feb 01, 2012 8:12 am

Since I'm off-grid, it is best for me to use power when it is available, ie not at night, but the same technique will work. For you, turn the freezer to its coldest setting overnight and turn it right back to 1 or 2 - just enough to keep everything cold enough during the day, and not a total disaster if you turn it off and forget to turn it back on! I find that when running it at 6 or 7(the max) through the day and 2 at night here, the compressor rarely if ever comes on during the night.
A technique to help keep things colder when it is off/turned right down, is some concentrated salty ice blocks (in plastic bottles that wont split). These melt, ie absorb most heat, around -20 to -30C, depending on salt concentration. Regular ice melts at 0C, and is not really very useful for keeping things colder than 0C, which is required in a freezer.
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Re: freezer efficiency

Postby Smurf1976 » Wed Feb 01, 2012 7:58 pm

I've heard of people hard wiring chest freezers to the off-peak meter with no apparent problems in Queensland. I'm not sure how widespread it is, but I know that it is not unheard of.
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Re: freezer efficiency

Postby bpratt » Thu Feb 02, 2012 10:21 am

Smurf1976 wrote:I've heard of people hard wiring chest freezers to the off-peak meter with no apparent problems in Queensland. I'm not sure how widespread it is, but I know that it is not unheard of.


If you don't open up the lid whilst the off-peak has been turned off for the couple of hours that it does, then it shouldn't really be a problem.

It'd almost be like having a regular blackout, and if it is kept close during that time a chest freezer tends not to lose much chill.
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Re: freezer efficiency

Postby Gordon-Loomberah » Thu Feb 02, 2012 1:12 pm

Given how miniscule the heat capacity of air is compared to water (which the food contains a lot of), and the freezer being fairly full of food, an occasional brief opening would have negligible effect on the average temperature in the freezer.
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Re: freezer efficiency

Postby Smurf1976 » Thu Feb 02, 2012 7:48 pm

If an off-peak HWS can be on for 6 hours a day and remain hot 18 hours later with only a few degrees lost, then it stands to reason that a freezer should be able to stay off for a few hours with no real consequence. The key is making sure it is well insulated.
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Re: freezer efficiency

Postby Tracker » Fri Feb 03, 2012 9:00 pm

.
Could I suggest an alternative.. Fit two thermostats and a timer with change-over contacts..

Off-Peak is 10pm to 07am.. Set the timer to that period.
Adjust one thermostat to say -25c and connect it during the Off=Peak period, after that the -15c thermostat will be connected.
Now you have the best of both worlds.. Things will not go above 15c, ever...

I don't like the idea of turning it off completely, as it's possible to get larger temperature swings that COULD create health problems..

Incorporate Gordon's suggestion of saline solutions and you might sustain things even better..
..
.
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Re: freezer efficiency

Postby bpratt » Fri Feb 03, 2012 9:39 pm

Shame they are on a TOU tariff, as the ordinary off peak(tariff 33 13.673c kw/h) we have in Qld (dunno the OP's location), runs for around 21 hours a day, and that's nearly 10c kw/h cheaper than tariff 11 at 22.759c kw/h.

We've got a few things hardwired in to use that tariff, such as a/c's and tumble dryer, and should we get a chest freezer I'll get that hardwired in too!

Tariff 31 is cheaper still at 9.284c kw/h, but is only on from 22:00 to 07:00 (although the Origin site states that sometimes it may not get turned off at all by Energex).
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Re: freezer efficiency

Postby Gordon-Loomberah » Sat Feb 04, 2012 2:59 pm

As bpratt points out, the rates you are paying for power at various times, and how much you are being paid for your FIT also come into the equation of how worthwhile it is. Can you tell us that information? Location would be useful too! you can put that into your profile so people can see it and don't have to guess ;)
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Re: freezer efficiency

Postby eileen » Mon Feb 06, 2012 9:39 pm

Hi,

I am in Melbourne.

Tarriffs here are

Peak: 0.295
Off peak: 0.167
FIT: 0.66

I think that most of our energy usage during the day is by the freezer - we have a 2 kw solar system but are only generating about 5 KWH to send back to the grid each day. I would have expected it to be a little more, as we do get full sun on our panels.
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