Downshifting: Green fridge DIY

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- CommentAuthorbetterroof
- CommentTimeAug 17th 2009
Just saw this while I was browsing the internets and felt it was relevant and interesting - there's a pdf with instructions that you can download...

http://www.homedesignfind.com/appliances/green-fridge-invention-uses-almost-no-electricity/

why we can't buy at this level I don't know - it would be interesting to see if there are any food storage safety implications...
- CommentAuthorJulian
- CommentTimeAug 17th 2009
Thanks BR - very interesting. As it refridgerates the contents like a normal fridge I can't see why there should be and food storage safety implications. It's so simple I'd feel confident to do the same and modify a chest freezer.
- CommentAuthorjon
- CommentTimeAug 17th 2009
Great idea... if it were actually true that this happens: I have a very large fridge that happens to be Australian:

0.001297 J/(cm3·K) x 1000 x 300 litres (half full fridge)= 387 J/C
Maintain at 30K differential & assume complete flush:
11170 Joules = 11170 watts.seconds
= 3.1 watt.hours = 0.003 kwh

Opened 10 times a day: 0.03 KWh

Total due to opening my fridge door 10 times a day in summer: 1 kWh per month (not the 30 claimed)

So the 30 kWh/month seems a bit of an overestimate. And our temp differential in the UK isn't that high. And we don't generally have 600 litre Westinghouse fridges in the UK

Looks to me as if the inventor multiplied by 30 days twice. Anyone see an error in above?
- CommentAuthorDaveOxford
- CommentTimeAug 17th 2009
Jon,

Can you set out the assumptions you have used in your calculation? I'm not sure I understand your method, but it looks as though you have assumed that no heat is lost between door opening episodes, and also that no new 'hot' objects are added to the freezer. Are you saying that it takes 387 joules to re-cool your 300 litres of air, or have I got the wrong end of the stick.

Bosch claim (and they are boasting) that one of their modestly sized upright freezers uses just over 200 kWh per year. If you are running a giant freezer on 1kWh per month, I want to know your secret, please.

D
- CommentAuthorCWatters
- CommentTimeAug 17th 2009
His

Posted By: DaveOxfordJon,

Can you set out the assumptions you have used in your calculation? I'm not sure I understand your method, but it looks as though you have assumed that no heat is lost between door opening episodes..

Jon has calculated the energy cost of loosing the cold air and shown that that alone doesn't account for the claimed energy saving.

My guess is that chest _freezers_ are better insulated than upright _fridges_ and that this is where the real saving comes from.

Chest fridges aren't common because not everyone likes having to move all the baskets to get to things at the bottom. Chest freezers also take up more floor space in the kitchen.
- CommentAuthorbetterroof
- CommentTimeAug 17th 2009
so is it good or not? and would the same technique work on an upright?

I'm afraid my science/maths interface is in for repair ...
- CommentAuthorJulian
- CommentTimeAug 17th 2009 edited
Posted By: betterroofso is it good or not? and would the same technique work on an upright?
>

Well the originator claims that some of the saving comes from gravity - i.e. the cold air stays in the chest type freezer when it would fall out of an upright fridge or freezer. He does accept in his description of the process that the insulation in a chest freezer is probably better than in many fridges. But that can't be the whole story. Overall, if you were prepared to have the less convenient footprint that a top loading model would give, it does seem an improvment.
The originator may have exaggerated the effect as Jon suggests above but that doesn't mean it isn't an improvment.
- CommentAuthorbetterroof
- CommentTimeAug 17th 2009
jolly good!
- CommentAuthorjon
- CommentTimeAug 18th 2009
Hi Dave,

Yes, as CWatters says, all I did is look at my fridge to see if opening the door 10 times a day in mid summer really made that much difference:

I would guess freezers are much better insulated and it's the better insulation of the freezer (that he's using as a fridge) that cuts his costs down.

So the summary of it all seems to be that your fridge could be constructed like a chest freezer but that doing that won't make a huge difference (unless you have an empty fridge that you open 40 times a day and there happens to be a fan next to the fridge to flush out all the air): OTOH, the better insulated the fridge is, even if upright, the better the energy savings will be.

A better idea might be to have upright fridges with compartments and internal compartment doors?
- CommentAuthorCWatters
- CommentTimeAug 18th 2009
Ahhh Now I understand why the baskets in my upright freezer have those clear plastic fronts on them.
- CommentAuthordjh
- CommentTimeAug 18th 2009
There's an interesting fridge here http://www.rmi.org/sitepages/pid399.php
- CommentAuthorDaveOxford
- CommentTimeAug 18th 2009
Aha,

Thanks both for explaining that.

The internal compartment doors idea is interesting. The problem is that the air has to circulate (yes?) so that heat can be transferred efficiently. We already have open-topped trays that can be pulled out in our upright freezer. But, I notice my feet still get chilled when I open the thing, and this must be because there are gaps built into the design for the air to circulate above and around the food. A really clever design would block these gaps as the door opens, but open them again when the door is closed. I can imagine levers attached to the door that slide sheets over the vents to close them off when the door opens. Could the James Dyson among us comment on the trade-off between added complexity/cost and the savings? And would those savings be surpassed by adding more/better insulation?

D
- CommentAuthorTerry
- CommentTimeAug 19th 2009
This principle is used to promote drawer fridges
see www.adande.com
- CommentAuthorbrig001
- CommentTimeAug 20th 2009
DaveOxford, how about roller blinds fixed beneath the drawers so that when a drawer is opened, it unrolls and forms a bottom to the drawer. Shouldn't be too hard to do, but might be difficult to clean...
- CommentAuthorDaveOxford
- CommentTimeAug 20th 2009
Brig001, if I understand your proposed design, then there would also have to be some sort of bottom to each drawer (e.g. a basket type arrangement) or all the fridge contents would drop to the bottom. I had not thought of roller blinds, but, as you say, probably too difficult to clean. A chest of drawers arrangement, but with sufficient space round the sides to permit air flow when closed, and a large 'back' which is larger than the front aperture (so blocks it off when the drawer is fully open) should do it. Consumer perception might be that too much space is wasted though. It looks as though the Adande folks, mentioned by Terry, have already cracked this, though in a squat design with quite a large footprint to volume ratio. Their graph showing internal temperature is quite impressive.

D
- CommentAuthorTerry
- CommentTimeAug 20th 2009
They did look to be very efficient etc and are stackable/clusterable in various ways, but the most impressive thing I recall was the price - ouch.
- CommentAuthorscott
- CommentTimeAug 21st 2009
dc solar fridges as used to store medicines and vaccines in hot climates
have been about for years , powered by pv panel
- CommentAuthorCWatters
- CommentTimeAug 26th 2009
How many fridge are installed over UFH I wonder? We only remembered at the last moment.

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