Certifugal drop-in replacement refrigerant

[Alwynb]

Hi there,

I have 2 off 450kW centrifugal chillers running at -25°C with refrigerant R12. I checked that R134a will give a 10% decrease in capacity and oil is also not compatible. Is R134a the best solution or is there something better?

Acc to me the drop-in refrigerant must have the following:

1) It must give the same capacity as R12 for the same compressor.
2) Evaporating and condensing pressures must be similar to R12
3) Compatible with the oil normally used for R12 centrifugal compressors.
4) Thermal properties must be equal to R12 in order to re-use existing R12 heat exhangers
5) Existing R12 line sizes be adequate for new drop-in refrigerant.

Regards
Alwyn

 

[simonho]

In commercial applications R134a is the only drop in for R12 chillers. However as you said there are problems with the capacity reduction and also oil changeout problems.

The characteristics are also not identical so you may also get head problems with a surging centrifugal compressor.

Why do you want to changeout R12 anyway ? If it is running OK and you have replacement refrigerant, let it be.

If you really want to change it out, it's best to buy new chillers with new refrigerant for this duty.

 

[Centrif]

Alwyn -
There are several ways to change your system over to R-134a. You do not need to replace the entire chiller.

First - you can just do a compressor upgrade..i.e. buy an entirely new compressor sized for your application. You do not need to go back to the original supplier of your chiller. You can retro-fit your chiller with a new compressor from one of the big three manufacturers.

Second choice - You can simply have a gear change to your current compressor to speed it up to make up for the loss of head with the R-134a. This is quite a common practice and works very well.

Several items to be careful of....

Oil. You must do a very thorough flush of the R-12 system and its mineral oil when you swap out to R-134a. Mineral oil in R-134a turns into a "slime" that will foul out your heat exchanger surfaces in your evaporator. This slime is very difficult to remove once created. The oil you must use is a Polyolester (POE) synthetic. You must swap out to a high viscosity POE and run your chiller with the R-12. Drain the POE and re-fill again..drain again. Do this about three times. When you swap out to R-134a you can then usew the proper viscosity POE. The reason for the high visc POE is that R-12 and POE have a great affinity for each other and the R-12 would thin out the POE too much. Be careful if you have a hermetic motor. Some of the older motor winding varnishes do not play well with the new chemistry.

If you can keep running with R-12 then by all means do so. But if you have to switch to R-134a - it is NOT a problem to overcome some of the m=noted issues. Thousands of chillers have been converted quite successfully and meet their original capacity.

One of the big three chiller manufacturers has a business group that specializes in exactly this sort of retro-fit.

-Paul

 

[imok2]

Thought this might interest you:

HCFC - R401B
Similar to R-401A except higher in R-22 content. This blend has higher capacity at lower temperatures (matches R-12 around -30F), and also provides a closer match to R-500 at air conditioning temperatures. This can be used with existing mineral oils

http://www.refrigerants.com/frame.htm

 

[briand2]

I had five centrifugal chillers converted to R134a about six years ago. They were all Sulzer chillers, each with motor size about 500 kW. Two of them were previously on R500; they needed gearboxes, impellers and seals changed. Three of them were previously on R12; they needed impellers and seals changed. All of them ended up with R134a and synthetic oil. They have all been OK for the last six years!

Brian