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Aircon or fridge compressor to solar? Answered

Sometimes I get weird ideas that I can't shake off :)
When I was looking into options for a 12 compressor fridge freezer combo I was stunned.
You a get a fullsized frrezer for far less!
A further check revealed that it is mainly the linear compressor that makes the price plus the usual mark ups.
Efficiency and especially start up is far better with thes compressors than out standard rotary and piston drive models.
But why would it be so impossible to replace the motor from a standard compressor with a brushless DC one?

I focussed on three things for the start:
Lubrication, cooling and sealing.
There is no such thing like a simple compressor with a piston system that does have some leaking.
So apart from the noise the enclosure really needs to be welded and sealed again.
Everything moving inside is lubricated by the drive shaft - it acts like a little pump.
Same for the cooling of these vital parts.
The oil flow exchanges heat through the big metal housing.

A replacement motor would need to be suited to run in such a messy enviroment.
Of course something to provide a proper oil flow needs to be created too if the drive shaft is replaced.
With some basic enineering this might be possible, same for the motor mount and wiring to the outside.
But what to do about the full load starting conditions that can happen?
Even with no load from the cooling system the motor needs massive torque to get the piston moving.
A bypass valve that closes once the motor is at proper speeds might work but hard to implement in a tight space.

Any ideas?
Did you ever try something that stupid?
Could you make it work?

What about a rotary compressor with external drive?
We use ice blenders that have a magnetic base and the actual connection is made through the magnetic forces alone.
A scroll compressor has lots of space without the original motor inside.
Plus, a round pipe is easier to work with when it comes to adding or removing things.
Small scroll compressors from an airconditioner or small industrial freezer wouldn't have to do much work in a small setup.
Best thing is that with a variable speed the cooling power can be adjusted.
How feasable would it be to use some polycarbonate end plate and a magnetically coupled drive ?
Modern BLDC motors offer great performance and suitable gear systems are readily available.
N52 neodymium magnets of the block type provide several kg of force if close enough to each other - should be enough to make a compressor spin...

In return it could mean to have a nice freezer or even airconditioner that runs directly on solar power.
No massive losses from inverters, no need for huge battery banks either.
As long as the sun is out you have free power, once down you can still switch to a power supply for the motor or use battery power.
Just imagine you come home after long day of work and the house is already cool.
And you did not have to pay a cent to get it cool or wait for hours for it to reach this temperature!
We love to add solar panels to our houses in the hope to get a few cents back from our energy providers.
The sad reality often is that you might be able to power all your needs during the day but the excess that goes back to the grid often pays next to nothing.
But if you could power a lot more things like a compressor directly with the electricity from your panels....
Then these kWh would not appear on your usage bill either.
Means you neither use what the power provider compensates you for nor is it "wasted" thorugh this bogus compensation.
The normal solar setup can then provide you with this little extra money while an additional set powers the motors for your big freezer or little airconditioner - little being relative to what you make of the idea ;)
If you really dare than you could even use your bike and legs to power your fridge directly ;)

Use your imagination :)


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2 years ago

I tried some digging on the web and seems my idea is quite outdated already, at least in the modern world.

We have many areas in this world where the people living there are at a dis-advantage.
Be it the aftermath of war, femine or a non existing income for the country...
Some people in these regions found ways to make even the worst of scrap and rubbish useful again.
For example one poor but very inventive old guy build his own ammonia based cooler.
But where the usual types have the reservoir to heat the stuff he made a custom flat container.
To get the required safety margins under pressure he placed lots of short rods insdie to keep the sidewalls stable.
Not sure if drilled holes in the plates and then welded it all up with the rods in place but it seemed to work fine.
Ingenious was the use of a crystal ball - not for furtune telling though.
Must have been some clear plastic and no clue where he found it ...
As a sphere is a perfect lens in terms of angle the focussed beam heated up a suffiently big area of the box during the day at all times.
According to his old school thermometer his contraption is able to get the inside of the fridge down to about 7° celsius - at an ambient temperature of around 35° C !
And for the colder times he uses a simple kerosene lamp to supply the heat.
As the fridge then needs far less energy anyways the fridge appearently makes it down to freezing temperatures once the ambient temps are below 20° C.

Now I need to find an old ammonia fridge somewhere on the scrap or caravan second hand sites.
With the lack of big spheres around here I guess I will have to settle for a bunch of slightly parabolic mirrors and a simple tracking system.
But at least that way I can have the fridge in the shade :)


Reply 2 years ago

The gasses inside an Ammonia fridge are very toxic and corrosive I certainly would not be playing around with that stuff. You could get an upright freezer, (the insulation is much thicker than a fridge) pull out the AC compressor and put a DC compressor in it and use LPG as a refrigerant.
LPG is more efficient as a refrigerant you can use it at a lower pressure, and this company sells it in a can , at a highly inflated price as "hydrocarbon refrigerant" .
there web site has lots of pressure charts and Data which is handy.


Reply 2 years ago

Toxic is always relative, especially in a closed system.
Have fixed a few ammonia based fridges back in the day after they got dropped or similar and got a leak.
It is even possible to do this without much stink and gas / vapours escaping - I prefer to put my ammonia in the freezer over night ;)
The key is to "fill" the fridge system twice so to say.
Ammonia always needs a tiny amount of water but you really need to get all air out the system first to prevent corrosion.
A flush with Argon or Helium is a good idea ;)
The first fill is with an open system and the concentrated ammonia/water solution.
Then all is cooled down big time.
The next "fill" is by bubbling ammonia through the reservoir, preferably under slight pressure to prevent air entering the system.
You want to fully saturate the water with ammonia and fill the system with ammonia vapour - the fill level in the reservoir should then be leveled correctly or you have to go by weight and mol.
It is far less critical as a compressor system in terms of overfilling but underfilling will give bad performance.

I know the 12V compressors but for a few bucks more I prefer the liniar models as they use far less energy and are almost silent.
Considering the prices I have a reason to go old school and with ammonia ;)
No moving parts, no electricity, several options to actually heat the system.

Ammonia based system were abandoned mainly due to safety concerns, especially in caravans and campers.
A total failure in a home is almost unreal as these things prefer a slow coorosion from the outside.
I do admit it still is not the best option for a safety concious mind but there are not too many options that wouldn require a compressor...
Check the Icy Ball - those things never failed.... ;)