PDA

View Full Version : Refrigerants and The Environment



Josip
07-03-2006, 09:51 PM
Economically sustainable - for mother nature

The refrigeration and air conditioning industries effect the environment all over the world, both directly with emissions and indirectly with their power consumption. The use of ozone destructive CFC's is not permitted in the developed industrial countries and the fade out for HCFC's is already decided. The discussion about the global warming effecting HFC refrigerants, however, is still in progress. These so called replacement refrigerants, like bromine and chlorine free HFC's, do not harm the ozone layer but have unfavourably high global warming potential. For this reason, the 1997 Kyoto Protocol called for a worldwide reduction of these greenhouse gases. Even new alternative refrigerants and blends like R134a, R404A and R507, each of them being HFC's, are less attractive for forward looking applications due to their relatively high greenhouse effect.

Against the backdrop of global efforts to protect the environment, natural refrigerants are the obvious choice as a sustainable and ecological alternative to HFC's. All natural refrigerants occur in nature's material cycle even without human interference. They do not contribute to the depletion of the ozone layer and have no significant influence to the greenhouse effect substantially less then synthetic refrigerants like HFC's. The natural refrigerant ammonia and carbon dioxide are highly important to the economy. Natural refrigerants have been used in food production and storage for more than 100 years. In recent times, technological progress and innovations have added new fields of application.

For all these reasons we are convinced that the natural refrigerants ammonia and carbon dioxide will be the most important for the future....................

Find this at http://www.grasso-global.com/Refrigerants.26.0.html

coments :)

US Iceman
07-03-2006, 10:24 PM
Natural refrigerants have been used in food production and storage for more than 100 years. In recent times, technological progress and innovations have added new fields of application.

For all these reasons we are convinced that the natural refrigerants ammonia and carbon dioxide will be the most important for the future....................

I could not have said this any better! :D :D
It is very interesting to see CO2 returning to favor.

I think what we will see is more CO2 systems being used for very low temperature applications as a cascade system. This would help to make the low-stage compressors smaller and probably more efficient.

Then we can use the ammonia system for the cascade condenser and the remaining higher temperature loads.

One question I am thinking about is how do we defrost coils when we use CO2? Water defrost???

What have you guys seen?

Andy
07-03-2006, 10:49 PM
One question I am thinking about is how do we defrost coils when we use CO2? Water defrost???

What have you guys seen?

That is the secret that makes it all work.

Star Refrigeration have a system using pumps to boost the R744 to a pressure several bar above the R744 condenser pressure, before they vapourize the liquid to produce the hot gas (I think patent pending is what they say):D
Others use electric heater, or a second coil in the evaporator with warm glycol defrost pumped in for defrosting:)

Kind Regards. Andy:)

US Iceman
07-03-2006, 10:53 PM
As you say, this is the hard part. The pumps would have to boost the pressure to a fairly high pressure, so that the flash gas formed during the expansion process would be able to provide defrost gas above 0C, right?

star882
08-03-2006, 05:14 AM
For higher temperature applications, could water be used as a refrigerant? Obviously, it'll be difficult to find a compatible oil, but it could work, right?

Josip
08-03-2006, 10:29 AM
Hello,

see this,

www.airah.org.au/downloads/2002-06-02.pdf

there are also some other systems like Andy said. Using CO2 people will find out how to make safety and cheap defrost :)

Star882 can you explain what did you mean about water as refrigerant. Why you need compatible oil?:confused:

star882
09-03-2006, 04:09 AM
Couldn't water be used as the refrigerant in a medium/high temperature application? (I have heard about a very large A/C that used water as the refrigerant.) The problem with the oil is that common refrigeration oils react with water.

Johnny Rod
09-03-2006, 11:13 AM
I theory there is no reason you couldn't use water as it has a high latent heat of vaporisation, but obviously the normal boiling point is high and there's the oil question. I think there is a design kicking about somewhere which I could look up, it's a bit different to usual, think it uses something resembling a big fan.

Josip
09-03-2006, 12:35 PM
Couldn't water be used as the refrigerant in a medium/high temperature application? (I have heard about a very large A/C that used water as the refrigerant.) The problem with the oil is that common refrigeration oils react with water.


I theory there is no reason you couldn't use water as it has a high latent heat of vaporisation, but obviously the normal boiling point is high and there's the oil question. I think there is a design kicking about somewhere which I could look up, it's a bit different to usual, think it uses something resembling a big fan.

Very interesting new idea, realy working but.....

http://st-div.web.cern.ch/st-div/workshop/ST98WS/technology/JacekK.pdf
http://www.arti-research.org/research/completed/exec-summaries/10080-es.pdf
http://criepi.denken.or.jp/en/e_publication/a2003/03setsubi3.pdf

So many pro&contra let's see :)

US Iceman
09-03-2006, 03:52 PM
Water as a refrigerant???

Why not? The evaporating temperature would have to be above 0C, but anything else above this temperature should be OK.

For oil selection you would have to find an oil that works and is compatible with H2O for the operating conditions and meets the compressor viscosity requirements.

Sounds a lot like a vacuum cooling system or a steam system.

In both of these water is the primary refrigerant.

Josip
10-03-2006, 10:44 AM
Hello,

Yes, I understand all of that but as you can see it is still under researching.

Using turbocompressors (like with old R11) or huge vacuum pumps.... whole plant is quite huge and very expensive, yet.

Maybe one day will be possible to use magnetic bearings for compressor and maybe some other improvments...

For all temperatures around and above 0C sounds very good.

Until that I prefer to do that on the old fashioned way :).
Definitely something what people can use in the near future.

US Iceman
10-03-2006, 03:33 PM
I agree that using water would be a very expensive task.

In principle it sounds very attractive, but in application it is a different story.

kasperDK
11-03-2006, 02:21 PM
Hello

At LEGO in denmark Sabroe+Soeby(now York koleteknik) have at large A/C system using H2O (R718)

“A 2682 hp Refrigeration Plant Using Water as Refrigerant,”

or se this:
http://www.arti-research.org/research/completed/finalreports/10010-final.pdf

Andy
12-03-2006, 10:10 PM
As you say, this is the hard part. The pumps would have to boost the pressure to a fairly high pressure, so that the flash gas formed during the expansion process would be able to provide defrost gas above 0C, right?

Pressure is about 6 to 8 deg c from memory, although it is highly superheated, I suppose you could use a lower saturation pressure, say -5 deg c, but you would need very large volumes of highly superheated vapour to perform any sort of defrost.

Kind Regards. Andy:)

Andy
12-03-2006, 10:13 PM
Hello

At LEGO in denmark Sabroe+Soeby(now York koleteknik) have at large A/C system using H2O (R718)

A 2682 hp Refrigeration Plant Using Water as Refrigerant,

or se this:
http://www.arti-research.org/research/completed/finalreports/10010-final.pdf


The worlds MAD I say MAD:eek:

You would want a non corrosive compressor, otherwise the steam condensate would eat the compressor from the inside out. I suppose that goes for all the system components:eek:

Kind Regards. Andy:)

US Iceman
13-03-2006, 12:11 AM
Hi Andy,


I suppose you could use a lower saturation pressure, say -5 deg c, but you would need very large volumes of highly superheated vapour to perform any sort of defrost

How do you defrost the coil with -5C vapor condensing? This could certainly warm the coil up to -5C, but the frost is still solid, not liquid.

Even with a lot of superheat at a -5C saturation pressure, the gas will still want to condense at -5C right?

Andy P
27-08-2006, 06:22 PM
You are right Ken - the liquid needs to be pressurised to about 45 bar before it is vaporised to create the "hot gas". For CO2 45 bar (about 675psig) is about 10C (50F) saturated, so the defrost works a treat. This seems to be much more efficient than a typical ammonia hot gas defrost, but I don't know why. Perhaps there is a lot less gas passing through the evaporator without condensing, so less dummy load on the compressor when CO2 is used?


Cheers
Andy P

US Iceman
27-08-2006, 09:21 PM
This seems to be much more efficient than a typical ammonia hot gas defrost, but I don't know why.


I think you answered your own question Andy.



Perhaps there is a lot less gas passing through the evaporator without condensing, so less dummy load on the compressor when CO2 is used?


I think the difference you may be seeing is due to how the condensate from defrost is allowed to pass. If a traditional pressure regulator were to be used on the CO2 system I suspect this would be similar to an ammonia system.

However, if a liquid drainer was used to pass the defrost condensate, the false load back to the compressors would be much less than the regulator.

I doubt the ammonia or CO2 are behaving much differently. I believe it is a function of the defrost system design.

jcook1982
18-12-2008, 06:53 PM
SO water as refrigerant could only be on a very large scale?

Why did the indunstry ever step back and re evaluate using CO2?

Sorry for silly questions i'm a little new to the field.