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Wind powered refrigerator ??

 
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Clocker



Joined: 18 Jun 2008
Posts: 5

PostPosted: Fri Jun 27, 2008 4:53 pm    Post subject: Wind powered refrigerator ?? Reply with quote

I was thinking recently about the woefully bad performance that the small scale domestic wind generators [B&Q Windsave !!] appear to have and I believe that their problems are due to the fact that they are attempting to generate some significant quantity of electricity and the financial return is ultimately dissapointing to the householder.

Perhaps a better use for a domestic wind turbine would be as an intermittent baseload compressor for a domestic refrigeration system. In such an arrangement, the turbine would directly compress the refrigerant with the mechanical power never having to be converted to electricity. In such arrangement, the heat exchanger could be mounted as part of the turbine assembly and with a significant airflow of external air, this would yield an effective reverse heat pump system.

The compressed and cooled refrigerant would then be piped to the evaporator coils in the refrigerator and then returned back in the loop circuit to the turbine.

Obvously such a system would need a backup electrically powered conventional compressor for non-windy days but if the refrigerator had suffcient thermal inertia and insulation, the turbine power would provide virtually all of the food refrigeration requirments for a typical home.

Refrigeration is an ideal use for an intermittent mechanical power source given that it is in any case an intermittent but not critically timed demand.

This setup would both give a much improved overall benefit to the householder in terms of enerygy and money saving whist providing essential refrigeration capability in a future where electricity supplies will inevitably become less reliable...
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JohnB



Joined: 22 May 2006
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Location: Beautiful sunny West Wales!

PostPosted: Sat Jun 28, 2008 12:27 am    Post subject: Reply with quote

Surely refrigeration is most needed when it's hot and the wind isn't blowing. Shouldn't we be adapting houses to reduce the need for refrigeration (larders, cold cellars etc) and using other techniques to keep food cool and preserve it, to minimise the need for a fridge. If that just means that a very small fridge is needed in the hottest weather, there could be enough surplus power produced from PV to power it.
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hardworkinghippy



Joined: 16 Aug 2007
Posts: 568
Location: Bergerac France

PostPosted: Sat Jun 28, 2008 8:19 pm    Post subject: Reply with quote

We hardly ever use a 'fridge except when it's really hot outside.

Right now we've got a little 12v car fridge running for cheese and milk, beer and leftovers. We'll probably use our gas/12v 'fridge in the next few days to get ice cubes and cool water and be able to cool chocolate mousse and fruit puddings and so on.

Normally, we use the cellar which is an even temperature almost all year round or we keep things outside and for convenience, in our "fridge" the coolbox in the kitchen built into an uninsulate part of the north wall with an insulated door.
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Mitch



Joined: 04 Aug 2006
Posts: 458
Location: Grand Union Canal, London

PostPosted: Sat Jun 28, 2008 9:26 pm    Post subject: Reply with quote

Personally, I think Clockers post has loads of merit. I would go one step further though, and suggest that instead of the heat exchanger being part of the turbine assembly, that possibly this be part of the hot-water tank system. Why chuck the heat away, when it could be used to assist with water heating? Otherwise a very sound idea indeed. Idea
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Clocker



Joined: 18 Jun 2008
Posts: 5

PostPosted: Sun Jun 29, 2008 9:42 pm    Post subject: Reply with quote

Mitch wrote:
Why chuck the heat away


Energy cannot be created or destroyed. (one of those Thermodynamics laws).

The overall effectiveness of a heat pump, which is what a refigerator compressor/evaporator is, is dependent on the gradient between the two temperatures. With a limited available quantity of free but intermittent mechanical energy, to give the best overall refrigeration performance, the hot end of the heat pump circuit should be in a relatively cool and ventilated area which would be the outside air, preferably free flowing. This is why air conditioning in buildings always has cooling towers with the heat dumped to the outside air.

This idea has the double advantage of no mechanical/electrical power conversions and eliminates these unavoidable losses.

For example, say a domestic wind turbine produces 250Watts of peak power output (say average 100Watt). Given a 50% conversion efficiency, this would mean that there would be an average 200Watts of wind energy available at the blades if it could be used directly without converting to electrical power.

Let's say a domestic fridge has a 200W compressor which runs at a 50% duty, then the the average electrical load is 100W. With a 50% conversion efficiency, the mechanical load output of the compressor motor is only 50Watts with the rest disipated as heat.

So we have 200W of FREE mechanical power from the turbine and only need 50W to drive the fridge (which saves 100W of electricity). If these are correct figures, then the turbine would be able to power a freezer as well.

Of course for non-windy days, a backup compress or power source would still be required.
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adam2
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Joined: 02 Jul 2007
Posts: 6467
Location: North Somerset

PostPosted: Thu Jul 03, 2008 8:36 am    Post subject: Reply with quote

Whilst the idea has some merit, I can forsee severe practical problems in attempting to drive a comppressor directly by wind power.

Firstly if the compressor is mounted atop the wind turbine tower, then very long pipes for the refrigerant gas will be required, longer pipes increase the risk of leaks, and of course require more refrigerant to fill them. Since all common refrigerants are expensive or flammable or toxic, or ozone destroying, this is clearly undesirable.

Alternativly the compressor could be mounted at ground level and driven by a shaft, this introduces considerable mechanical losses and complications.

Furthur, most compressors are best worked at either a constant speed, or at a speed varied according to the load. The output of a wind turbine varies according to the wind speed.
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Clocker



Joined: 18 Jun 2008
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PostPosted: Wed Jul 09, 2008 10:39 pm    Post subject: Reply with quote

I had thought about the problems that you mentioned and have also concluded that the compressor should be at ground level driven by a shaft from the turbine.

A vertical-axis wind turbine, or array of turbines, could eliminate the requirement for gears and there should be a mechical engineering solution to the speed/load issue you raised using a variable ratio transmission.

Since first suggesting the refrigerator idea, I have since pondered the idea of a turbine powered ground-source heat pump. In such a scenario the wind energy would be used to drive a heat pump and in this case, a 250W mechanical power input from the turbine[s] could generate an equivalent of up to 1KW of useful heat to heat a building. Due to drafts and wind chill, the need for heating IS more when the wind is blowing so this would be a better us for the wind power. The system could always be reversed in the summer and be used to cool the building...

There would still need to be an electrical backup to drive the compressor on still days.
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adam2
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Joined: 02 Jul 2007
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PostPosted: Thu Jul 10, 2008 8:57 am    Post subject: Reply with quote

Clocker wrote:
I had thought about the problems that you mentioned and have also concluded that the compressor should be at ground level driven by a shaft from the turbine.

A vertical-axis wind turbine, or array of turbines, could eliminate the requirement for gears and there should be a mechical engineering solution to the speed/load issue you raised using a variable ratio transmission.

Since first suggesting the refrigerator idea, I have since pondered the idea of a turbine powered ground-source heat pump. In such a scenario the wind energy would be used to drive a heat pump and in this case, a 250W mechanical power input from the turbine[s] could generate an equivalent of up to 1KW of useful heat to heat a building. Due to drafts and wind chill, the need for heating IS more when the wind is blowing so this would be a better us for the wind power. The system could always be reversed in the summer and be used to cool the building...

There would still need to be an electrical backup to drive the compressor on still days.


It would certainly be possible to use wind power to drive a ground source heat pump, though I have never heard of this being done.

It must be remembered though that heat pumps are expensive, and complex, one with direct mechanical drive would certainly be non standard, and probably more complicted than electric drive. It would also require long pipes (expense, losses, potential for leaks) into the house, unless the turbine was sited undesirably close to the building.

In some cases the cost of the heat pump might be better spent on a larger wind turbine, for direct electric heating.
One of the best uses for a wind turbine is to charge a battery bank for lighting and small appliances, in order that these may be used in calm weather.
When the batteries are full the surplus power can be used for space heating, thus saving coal/oil/firewood.
The weak point of any off grid system is the battery, and perhaps suprisingly, a larger wind turbine may need a SMALLER battery.

The reasoning being that doubling or tripling the size of the wind turbine, does not increase the lighting and small appliance load, which must be battery backed.
Suppose that the lighting and small appliance load averages 200 watts, with say a 2.5kw turbine, the battery might have to give a weeks standby, in case of calm weather.
If instead a 10kw turbine is installed, this will produce enough for essiential loads, for most of the time, the battery could then be reduced in size. The surplus power would be used for heating.
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gaby de wilde



Joined: 15 Jan 2009
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PostPosted: Thu Jan 15, 2009 1:16 am    Post subject: Reply with quote

Hello,

Interesting topic,

I just put a cardboard box in the lower part of my fridge and stuffed all the groceries in the top shelve. If I now open it it draws air from the kitchen behind the door. I figure A sliding door would be most ideal and some way to mechanically decrease the size to match the content. I know lots of people who never have anything in their fridge.

A freezer needs to be cool enough to preserve the food but cooling it a bit more doesn't have any negative effect.

I'm not sure but it seems historically pumping wind mills have a different design with lots of blades while electric mills work at higher speed. I'm not an expert on fluid dynamics but it seems a slow spinning pump mill should be cheaper and be able to cool much better than systems with generators, dynamos, batteries and inverters. It saves 90% of the material?

Batteries really are the bottle neck for domestic windmills but windmills still are the best way to generate raw wealth out of thin air. Not having a fridge will make it quite a bit harder to pull the economy out of the inevitable slump we are heading for. The only real problem I see is in the cost of the electronics.

Say we find some magic solution to fix that problem, Why would we then waste the magic pumping fluid though a fridge?

Makes me laugh actually, are we trying to salve a problem that doesn't exist?

It will take a bit more engineering and I''m not sure how to do it but with proper insulation it seems coolness could also be stored? Long ago we use to have an ice man delivering blocks of ice. Batteries are so expensive it might be worth looking into.

I'm new to the forum, excuse me if any of this was mentioned 100 times already. Laughing

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Last edited by gaby de wilde on Tue Jul 14, 2009 2:57 am; edited 1 time in total
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adam2
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PostPosted: Thu Jan 15, 2009 10:51 am    Post subject: Reply with quote

Some interesting points, and welcome.

I dont believe that driving a refrigeration compressor directly by wind power is likely to be viable, the output is too variable, and in the UK at least peaks when cooling demand is at its lowest.
The mechanical complications in driving a compressor from a wind turbine probably make the idea a non starter.

Ultra high efficiency electric refrigerators are available from a number of sources, though not being mass produced they are very expensive. They are availalable in 12/24 volts DC for off grid use and in 120volt and 240 volt AC for minimising use of grid power.

The battery is generaly the weak point of an off grid system, and every effort should be made to reduce the amount of energy storeage required.

Tradditional water pumping wind mills did indeed operate at low speed, they involved very considerable mechanical complication and were not very efficient by todays standards. To pump water useing wind power these days it is usuall to use an electric pump powered by a wind turbine.

To store frozen food for more than a few days, very low temperatures are required, it is not sufficient simply to freeze the food.
Domestic freezers work at about -18 degrees and for safe long term storeage this should not be increased.
Large industrial frozen food stores often work at about -30 degrees.
The ice making compartment of a refrigerator is often at about -5 degrees, and frozen foods may be stored thus but only short term.

To store "cold" is indeed sometimes more economic then storeing electricity in batteries.
Fridges and freezers are available to do this, when surplus wind or PV power is available.

Also disscussed here
http://www.powerswitch.org.uk/forum/viewtopic.php?t=3763
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gaby de wilde



Joined: 15 Jan 2009
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PostPosted: Tue Jul 14, 2009 2:56 am    Post subject: Reply with quote

I was looking at 50 Watt turbines (electrical output) and ran into this. Parrallel Wind Turbine. It's a 20 inch diameter turbine, that produces about half a kilowatt. Here is US patent 6616402: Serpentine wind turbine Douglas Spriggs Selsam. I love organic designs like this. It is stll about 10 times to big - funny.Laughing I'm not sure about stopping it in a storm. but for a camping/boat it would be perfect. For a house, if in stead(?) of insulation the box would have a lot of mass it would stay cool for days between wind. Cob and rammed earth pops to mind.

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