Peltier Fridge

[Mark Parsons]

Anyone in the group with experience similar to this E-bay seller?
http://cgi.ebay.ca/Cooler-Heat-sink-peltier-for-ice-chest-refrigerator_W0QQitemZ180109115668QQihZ008QQcatego ryZ13807QQrdZ1QQcmdZViewItem

Take a non-functioning fridge and retrofitting with a Peltier unit and powering from a Solar PV panel or system?

Solar PV powered fridges like SunFrost or Sundanzer are very expensive. This DIY option appears to fit a very low budget. Wondering if more than just the defrosting issue the seller mentions - which should be eliminated with a precise solid state thermostat with sensor mounted on the heat sink that keeps the heat sink from frosting up. This would also likely eliminate the need for a fan on the cold side unless the peltier unit is unable to keep up with the heat loss passively.

Thanks,
Mark

[Paul Bailey]

Fridge size and the cooling unit would need to sized (matched BTU output) for unit to meet the design load on the warmest day. Unless you can control the humidity the unit will frost on the coldest plate,and your stuck with a manual defrost. What do you do on the sunless days if it is PV tied and or at night.? Personnaly I think it would be a great test but focus on the fridge R-value as being very high.(comparable to a sunfrost) then size the plate acordingly for max efficiency. Paul;)

[Paul Bailey]

Take a standard chest freezer(in the basement). Envelope it in another layer of foam on the cold surfaces. Save .5 KW /day for rest of its life for 14 bucks worth of foam. Paul:)

[Joe Blake]

I experimented with a Peltier unit (in fact two of them) a few years ago, comparing them to an Engel freezer (40 litre).

http://www.engelaustralia.com.au/

Whilst I was able to get the temperature of a water filled "wine cooler" silvered bladder (4 litres I think it was) down to almost freezing I found that the "energy:cooling ratio" was very poor compared to the "swing motor" of the Engel.

The Engel draws 30 watts at maximum and gets down to -20 degrees Centigrade and has been running almost continuously since Christmas '05 (99% of the time off solar panels and/or batteries with a back-up mains charger).

As much as they are silent, and have no moving parts, I'd give the Peltier a miss and go for the Engel, despite the high cost. The little Sawafuji swing motor has only one moving part, and is a beautifully designed piece of engineering.

http://www.i-m-d.com/engel/Tech.htm


Joe

[Mark Parsons]

Thanks Paul for good design direction. I know the SunFrost fridge is designed to keep the cold plate above freezing thereby eliminating the frost. This lack of humidity removal (via no frost) in the compartment is also supposed to keep your food fresher longer. So the marketing spin states:
http://www.sunfrost.com/refrigerator_features.html

Hi Joe,
I should have remembered your earlier post with this info. Must be some inherent inefficiencies in the Peltier effect if a compressor type heat pump is more efficient. Is the Engel unit available as a kit to retrofit to a DIY fridge? Checked your link again and answered my question - http://www.engelaustralia.com.au/cgi-bin/search.cgi?id=17542-209216155215-1177640614&category=Conversion+Kits
AUD$899 for conversion kit. Quite expensive. I can see the capital cost benefit to a USD$40 Peltier conversion kit.

Mark

[Joe Blake]

I should have remembered your earlier post with this info. Must be some inherent inefficiencies in the Peltier effect if a compressor type heat pump is more efficient.

I think the comparison of efficiencies comes from comparing the Peltier to a ROTARY compressor. Whilst I haven't actually pulled one apart (never had to - and hopefully won't have to), the "swing motor" seems to get around the problem of a high initial current, because the rotary compressor has to do a full 360 turn, whereas the swing motor, with its "linear" design only has to move a short distance in a straight line, then reverse direction, then as it builds up the distance it travels increase until it reaches its full stroke.

This of course is just what I've garnered from reading the literature available, plus experience in other areas, such as computers, where I discovered that I needed a far larger solar array than I'd calculated I SHOULD need since on boot up, the electric motors (hard disk drive, fans etc), plus the boot-up sequence itself causes a large increase in the work of the central processing unit, with all the testing, mounting various programs and systems etc consume relatively high amounts of power, but once everything is running, the power consumption drops dramatically. I got around this by using a "store bought" uninterruptible power supply which had its own internal battery. The idea was that when the mains power went down, I would have about 5 minutes to shut everything down, before the battery went flat. However, by putting the UPS between my array and computer, the UPS had sufficient grunt to handle the boot-up procedure, and then there was sufficient solar power to enable everything to keep going. The battery to the UPS of course was still delivering power to the computer, but the array was putting in more than went out, so in short order the UPS was recharged.

So this meant that I could get away with using only a 500 Watt sine wave inverter, since this delivered more than adequate "running power", whereas I would otherwise have needed 800 watts or there about, even though only for a few seconds.

Getting back to the Engel, as I say it's been running now for over a year, and performs it's task admirably. Strange as it may seem, I'd have to say that it seems to be more efficient than the Peltier system, but the Peltier would appear to have the edge over a rotary compressor.

Hope that assists.

Joe

[Joe Blake]

Of course, if you're after a fridge rather than a freezer, I'm actually considering buying a larger Engel, and using the smaller one to freeze bottles of water which I can then put into my (turned-off) mains powered fridge as a type of ice-chest. The trick with that is the loss of automatic temperature control, and that could be dangerous with some foods getting too warm and spoiling.

But a thought to consider.

Joe

On edit: If I were going to do THAT then I'd use a non-working chest freezer, rather than upright. They seem to be more efficient at reducing heat loss, since the cold air doesn't "spill out" when the door is opened.

I remember reading an article in a magazine last year about a guy converting a chest freezer into a chest fridge, and having a very high drop in power consumption. He said the thing ran for about 1 minute per hour or something. I'll see if I can track it down.

J

[Ralph Day]

Hi Joe

Have you ever seen an Engel in larger than "cooler" size? Maybe there are limitations to size of operation. We in North America (home of the power hogs) are usually looking for reefer units 18 cu ft or larger. The bolt on conversion looks promising but no size limitation info anywhere. As it's a Japanese developed product perhaps they are more aligned with small apartments, cars, and such.

ralph

[Joe Blake]

Hi Ralph,

Can't I've seen anything bigger than the 60 litre one shown in the brochure on the link above. My local 12 Volt Shop has (or had) one in stock which I've been casting a covetous eye over.

I suppose if one had a largish amount of $$$$, one could jury rig something up using a conversion kit or two using a chest freezer, but other than that I'm afraid I can't help you on that one.

But of course, there's a difference 'twixt fridge and freezer, which I keep forgetting.

;)

Joe