Energy Matters Forums

[stivzor]

Hi everybody,
I am hoping someone has some experience that could help me because I've looked at quite a few options and I'm not particularly impressed with what is available.

I am hoping to set up several different types of refrigerator. Ideally I would like:
- a small freezer,
- a medium-sized refrigerator,
- a large "constant-temperature" cabinet or room. (This is not necessary but would be nice to have. It would need to keep a fairly constant temperature of about 15-18 degrees and would be used for long-term storage of perishables (and brewing). It may need to be heated in Winter.)

These will all need to run off solar power, and ideally they will run off 12 or 24 volts DC so that there is no need for an inverter and its inherent losses. I have plenty of roof area for panels and enough sunshine.

I am happy to build the cabinet(s) if necessary and I have ample room for them so I can use a lot of insulation.

I am looking for advice regarding the design of the system. Are there products available off the shelf that can do what I want? If I need to build it, what components should I use (and how do I put them together in the right order?)

I have heard of old chest freezers being used as refrigerators. Is this a good option? How is the temperature controlled? If I use an existing cabinet can it be improved by adding insulation?

If I build a refrigerator in a shed that can get hot, how do I best isolate the refrigerator's hot bits from the insulated areas?

I realise this is asking a lot, but I don't necessarily need everything at once. Can this sort of system be built up incrementally? Can the various cabinets share components? Any advice would be appreciated!

Thanks for reading this far...

Stivzor

[Tracker]

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These will all need to run off solar power, and ideally they will run off 12 or 24 volts DC so that there is no need for an inverter and its inherent losses. I have plenty of roof area for panels and enough sunshine.

I suspect that you are being a bit optimistic. You are asking for machines that will do a deal of cooling, and 12V is not likely to give "Economical Power". The compressors will be VERY expensive.
I suspect that Complete 12V fridges would be many times the cost of a 240V system, so you might have to rely on a 12/240V inverter.

The technical problems of DIY are one thing, and the LAW is another.. You MUST be licensed to deal with refrigerant gas, which you would need to DIY. ( Official Disclaimer )

I am not into the maths of energy conversion and BTU's etc. for a Walk-In cooler, so I won't attempt to suggest how you could design such, energy efficiently.
Chest freezers are always the most efficient, be they used as a freezer of a fridge.
It would not be impractical to get two freezers and simply add a different thermostat one freezer so that it only cools to +2c.. You could use a relay system so that ONLY one can run at a time.
An issue with the use of a chest freezer as a refrigerator will be CONDENSATION. It will eventually fill with water. One with a drain built in would be a really good first choice.

You might "search" for similar threads, as I do recall similar discussions some months ago.

[Gordon-Loomberah]

- a large "constant-temperature" cabinet or room. (This is not necessary but would be nice to have. It would need to keep a fairly constant temperature of about 15-18 degrees and would be used for long-term storage of perishables (and brewing). It may need to be heated in Winter.)
Stivzor

Have you thought of an underground/or dug into the side of a hill building? That will be somewhere in that temperature range assuming you live in a temperate part of southern Australia. You dont have a location in your profile, so its a bit hard to say exactly, but the 2 m underground temperature will be very close to your annual average temperature.
If that's not feasible then you could construct a well insulated building that is ventilated from an array of pipes dug ~2m into the ground and draw air through them to maintain that temperature in that room. The air will be quite constant all year round, so if it is sufficiently well insulated, you wont need summer cooling or winter heating.

Re your fridge and freezer ideas, as Tracker says above, low voltage fridges are extremely expensive- you'd be much better off buying an inverter and running a 240V fridge. Buy an older fridge and freezer, ones without the ridiculous radiator coils build into the walls nonsense that many modern units have, so you can add your own insulation. Its quite easy to modify a fridge to use in the order of only half a unit of power per day this way.
I have a 24VDC 10A fridge unit that dad gave me years ago that I've had re-gassed. I'll probably put it to some load dump/house cooling use one of these days, although I have used it as a fridge in the past and it worked quite well. I doubt its possible to buy anything similar these days though.

[stivzor]

Thanks for the replies.
Yes I'm being ambitious.
Yes I have considered building into the ground, and that is a real possibility.

I sort-of hoped that there must be a more efficient way than using 240VAC. If not, then that is that.

Can anyone quantify (in vague terms) the benefit of extra insulation around a refrigerator cabinet?

Stivzor

[Gordon-Loomberah]

Can anyone quantify (in vague terms) the benefit of extra insulation around a refrigerator cabinet?
Stivzor

my rough estimate using an old fridge: ~40% power usage savings from adding 50mm styrofoam on sides & top.
Most of the power use of a fridge is the loss through the walls, if you dont open it a lot, so the more you can reduce those losses, the less power it will consume. Even opening it doesnt really use all that much power depsite the claims you need to fill it full of containers to reduce the loss of air when you open the door.
I once calculated that for a 250l fridge, losing a fair bit of the cold air when the door was opened was the eqivalent of putting about 60ml of room temperature water in the fridge, ie not very much!

[Tracker]

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Gordon might be able to help in a more mathematical way, but the first thing in looking at any fridge/freezer, is that you need one with the black wires on the rear. ( or one with the heat-exchanger underneath )

If you wanted to "Insulate" an existing fridge/freezer, to increase it's efficiency, and you have one with NO wire-heat-exchanger on the back, then it will have the equivalent hot-pipes in the side wall skins.
Put insulation on top of that and you will lock the heat in, and dramatically reduce the efficiency of the refrigeration process. ( It will destroy the compressor - in fact )

To cut down the heat loss, from a fridge with a rear Condenser coil, it would just mean totally coating the top, back and sides with foam insulation. If you could shape it so that it protrudes past the door seal, that would likely help control loss via the door seal

I sort-of hoped that there must be a more efficient way than using 240VAC.

You are implying that the 240V way is less efficient. I suspect that even given the Inverter efficiency losses, using a 240V operation would still be more efficient than a 12V dc unit.

To build your "Cool-Room", the obvious bestest way would be to dig out the hill side, construct the room with normal Cool-Room sheeting, and then bury the whole lot. Sounds like a lot of work.
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[jayceeoh]

Stivzor-there are a couple of sites i have come across that sell/promote the type of regrigeration you may be looking for. If I understand what you are after correctly. One is solazone (or solarzone).Not quite sure of the spelling. I'm not sure how reputable they are or if anyone here has had any experience of them. And I think if you type in Mt. Best (Victoria) or Chalko - he sells some sort of conversion thingo for $150 to convert a chest freezer to a fridge that runs for next to nix. I think he has a very good reputation. Let us know how you go with those sites.

Cheers - Jaycee

[Tracker]

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Surely, all he can be selling is a replacement thermostat?
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Chalko - he sells some sort of conversion thingo for $150 to convert a chest freezer to a fridge

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[Gordon-Loomberah]

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Surely, all he can be selling is a replacement thermostat?
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Chalko - he sells some sort of conversion thingo for $150 to convert a chest freezer to a fridge

sounds like it... but its a very expensive thermostat!

Try this instead:

http://www.jaycar.com.au/productView.asp?ID=KC5476

[bradley.jarvis]

Danfoss make a efficient line of 12/24V compressors, one model is BD35F, there are a few others in this family of compressor. This is what is in out 50L 12/24V fridge/freezer. Works quite well, and we do get condensation buildup when running as a fridge(it has a drain plug in it. I believe it uses under 60W when running, it is connected to the 12V battery bank via a 10A 2 core cable off a ~12M length with no problem. The fridge has walls and lid that are about 100mm thick and it is a chest style cabinet.

I doubt the compressor would cool a room, and I believe the oil it uses has restrictions on its use in Australia.

Thanks Brad