Very cheap to operate that is - After reading articles I have seen on the web I bought a conventional 5 cubic foot chest freezer for $160, a used one may have been cheaper but wanted the newest in insulation and compressor technology as they have been improved greatly over the last twenty years.
I choose a 5 cubic foot model because I measured what I actually used in my regular fridge, why waste power on something you don't use especially when I will be running it from very expensive solar panels. Getting your butter from the bottom of a chest refrigerator will be a bit of an inconvenience but the payback is many for my application.
The freezer as it is coming out of the box boasts only $2 a month in electricity usage. My modified temperature controller brought that down to 50 cents a month, my regular 20 cubic foot refrigerator freezer drinks $8 a month in coal juice. I very seldom use a freezer and doubt that I will have one at the new cabin, I may make a small one for the times I want an ice cube for some adult beverages.
All I did was wire up a stand alone temperature controller with a type J thermocouple and a 10 amp slave relay powering a receptacle in a small box to cycle it at 40F, most freezer will not go to that high of a temperature. Since most of the temp controllers in these units are capillary tube it would be too hard to change them.
As a side note: Since the infamous ice storm of 2009 and power was lost to hundreds of thousands of people with some being without up to a month (I had a generator and a wood stove) I decided to test how long this box will stay cool with just 8 pounds of ice (a two liter bottle is 4 pounds) I never opened the lid and it stayed at 40F for a full week.
The theory behind how cheap you can operate this is many but here's a quick breakdown:
1) the insulation in a freezer is much better, plus there are no sty, mullion, or defrost heaters.
2) chest styles will not drop all the cold air out when opened, with cold air being heavier it will stay in the box.
3) Newton's law of cooling plays a huge role too - basically it states that the less of a temperature difference between the inside and the outside the more efficient it will be.
What does that mean? cold will migrate to hot and visa versa, that's a law of thermodynamic equilibrium, but it is the rate at which it does that is of concern. A freezer at 0F will gain heat at a much faster rate than a refrigerator at 40F meaning it will take a lot more power to keep food at zero than at 40F (obviously).
A better example with no math involved would be trying to keep your house at 80F while 10F outside, with all that kinetic energy of the hot air it will bounce everywhere and leave the house using up 100 units of heat in 1 hour, the same house kept at 70F will also do the same but at a much slower rate and burn up the same 100 units of heat but taking 3 hours instead.
This is why turning your thermostat down 1 degree can save you up to 3% on your heating costs. Which is what works for this fridge conversion, it was designed for 0F but kept at 40F.
I choose a 5 cubic foot model because I measured what I actually used in my regular fridge, why waste power on something you don't use especially when I will be running it from very expensive solar panels. Getting your butter from the bottom of a chest refrigerator will be a bit of an inconvenience but the payback is many for my application.
The freezer as it is coming out of the box boasts only $2 a month in electricity usage. My modified temperature controller brought that down to 50 cents a month, my regular 20 cubic foot refrigerator freezer drinks $8 a month in coal juice. I very seldom use a freezer and doubt that I will have one at the new cabin, I may make a small one for the times I want an ice cube for some adult beverages.
All I did was wire up a stand alone temperature controller with a type J thermocouple and a 10 amp slave relay powering a receptacle in a small box to cycle it at 40F, most freezer will not go to that high of a temperature. Since most of the temp controllers in these units are capillary tube it would be too hard to change them.
As a side note: Since the infamous ice storm of 2009 and power was lost to hundreds of thousands of people with some being without up to a month (I had a generator and a wood stove) I decided to test how long this box will stay cool with just 8 pounds of ice (a two liter bottle is 4 pounds) I never opened the lid and it stayed at 40F for a full week.
The theory behind how cheap you can operate this is many but here's a quick breakdown:
1) the insulation in a freezer is much better, plus there are no sty, mullion, or defrost heaters.
2) chest styles will not drop all the cold air out when opened, with cold air being heavier it will stay in the box.
3) Newton's law of cooling plays a huge role too - basically it states that the less of a temperature difference between the inside and the outside the more efficient it will be.
What does that mean? cold will migrate to hot and visa versa, that's a law of thermodynamic equilibrium, but it is the rate at which it does that is of concern. A freezer at 0F will gain heat at a much faster rate than a refrigerator at 40F meaning it will take a lot more power to keep food at zero than at 40F (obviously).
A better example with no math involved would be trying to keep your house at 80F while 10F outside, with all that kinetic energy of the hot air it will bounce everywhere and leave the house using up 100 units of heat in 1 hour, the same house kept at 70F will also do the same but at a much slower rate and burn up the same 100 units of heat but taking 3 hours instead.
This is why turning your thermostat down 1 degree can save you up to 3% on your heating costs. Which is what works for this fridge conversion, it was designed for 0F but kept at 40F.
