cooling capacity variation in compressor using R22 & R134a

[nambiandy]

hi

I have 2 doubts

1. why is same compressor Running on R22 Refrigerant gives more output compared to R134a ?

2. Can R 22 be used for -40deg appication , why is R404a prefered for low temperature application.

anand

[LRAC]

Hi Nambiandy

The easiest way for you too see is on your gauges, select a pressure and read off the corresponding temperature, you will see different temp readings at the same pressure for different gases. Which should explain that different refrigerents have different properties and their ability to absorb heat.

This should also explain why R22 is not normally used for -40 C applications because of the pressure differences, another gas may be more suitable which provides better low temp stability which may include oil properties as well.

Regards
Lrac

[NH3LVR]

Here in the States we use R-22 at -40. R502 was the Refrigerant of choice, but there are few of those systems left running.
I have used it in DX systems and it worked fine, as long as the system was designed with oil recovery in mind.
One contractor installed continuous freezing systems with flooded evaporators and no means of returning the oil. I operated one for a couple of years and had no problems. I simply pumped it down a once a month and drained the oil from the accumulator.
Another system I work on has a oil still, which is disconnected. It has no skimmer. The operator does not remove the oil. Dare I say it is getting a bit thick?

[The MG Pony]

Temprite to the rescue! (They're oil seps fyi)

[NH3LVR]

Oil Separation is not the problem unfortunately.
And Temrite does not make anything that big.
The basic problem is operator error on the night shift. The night guy keeps overpumping the Cornell Reservoir and pushing the O ring out of the seal chamber. Why he needs a oil pump is beyond me. But he either breaks a O ring or seal once a month. Then they pump oil in it at the rate of 1/2 gallon a day until they decide to shut down and have me fix it again. I think they have pumped about 30 gallons this year so far. Adds up quick

[Peter_1]

What about discharge temperatures when evaporating at -40°C and if your compressor is a 1 stage machine and needs suction gasses of +/- 0°C(32°F)?

Discharge temperatures of +/- 140°C (284°F):eek:

We then use liquid injection in the suction gasses or a 2 stage machine

[US Iceman]

What about discharge temperatures when evaporating at -40°C and if your compressor is a 1 stage machine and needs suction gasses of +/- 0°C(32°F)?


Peter, if a single stage screw compressor is used for R-22 (or ammonia, etc) at this low of a suction pressure the discharge temperature is controlled by the oil injection. This actually becomes part of the oil cooling load, so the oil cooling capacity is increased to compensate for the additional heat. Otherwise, for a recip. compressor liquid injection cooling must be used.



1. why is same compressor Running on R22 Refrigerant gives more output compared to R134a ?


This is somewhat of a open-ended question. First, I'm going to assume you mean the compressor is being compared at the same operating conditions for two different refrigerants. If this is the case then you are correct.

The compressor displacement is fixed (no speed increase possible) and will not change. The variation in capacity is a result of the different mass flows and refrigerant properties for the two different refrigerants.

Each refrigerant will behave a certain way and have different properties (enthalpy, desnity, etc).



2. Can R 22 be used for -40deg appication , why is R404a prefered for low temperature application.


R-22 can be used for low temperature applications. However, how the system is designed will determine what additional steps are required to maintain the system in good condition.

A single stage reciprocating compressor will require a different method than a single stage screw compressor (for the same refrigerant).

You have such factors as the specific heat ratio of the refrigerant. The higher this value is, you will see higher discharge temperatures as a result.

The main problem is how to control the discharge temperature at the compressor for low temperature applications.

On recip. compressors you need to either use a compound two-stage compressor, or, a two-stage compression system (individual low and hi stage compressors), or a single stage compressor with liquid injection (which is essentially used to keep the discharge temperature down to reasonable limits).

[Samarjit Sen]

Dear Anand,

The difference in capacities for different refrigerants is due to the chemical and physical propeties of the refrigerant.

With R22 you can go down to - 40 Deg. C Evaporation. However whenever you are working at a temperature of below - 10 Deg. C I would suggest you to use Oil Separators. I myself always install an Oil Separator for temperatures below 0 Deg. C and I have achieved good results. Further I have designed and installed a number of projects using single stage compressors with R 22 for _ 40 Deg. C Te.

All that you have to be careful for such applications are that you select the controls properly. Using Temprite Oil Separators are the best option. For your information I am installing a refrigeration plant suitable for - 40 Deg. C Te and another for - 35 Deg. Te using R 22 as a refrigerant.

With best wishes,

[nambiandy]

thanks everyone,
US iceman

as i understand from the comments that with R22 refrigerant ,specially in negative temperature has high discharge temp and more so where the ambient is close to 42degC it is must to have liquid injection which would reduce the discharge temperature .

Mr.Samarjit sen.

You mentioned about doing the project withR22 ref for -40 degC application ,is compressor with liquid injection used in your case.

regards

Anand

[US Iceman]

as i understand from the comments that with R22 refrigerant ,specially in negative temperature has high discharge temp and more so where the ambient is close to 42degC it is must to have liquid injection which would reduce the discharge temperature .


It depends on the type of compressor being used and the system deign. You cannot make broad assumptions without telling us all of the details.

All of the members who post responses to questions have different backgrounds. Some work on commerical equipment, others work on only indutrial equipment. It's all refrigeration equipment, but the various types of systems are designed differently.

Someone may answer a question based on what is done in commercial refrigeration, where another may respond from an industrial viewpoint.

The answers can be different.

If a question is asked, and answered, the answer is normally based on the responders background and experience.

I'm not comfortable with issuing statements that some may consider to "cover all situations". Or, providing information without knowing more details.

My reason for saying this is; I don't want you to do the wrong thing, for the right reason. Because... If what you try does not work, it makes it more frustrating for you!

From your replies, it looks like you are asking for confirmation of using liquid injection cooling for low temp. R-22 applications. My answer is.... it depends on the compressor and system design.

[Andy]

Hi Nambiandy:)

R22 is a good refrigerant, but one that is not ideal for low teperature operation.

Liquid injection is used on commercial equipment and some industrial screw compressors.


Two stage recips are a partial answer with liquid injection and a subcooler operation and the intersage pressure.

Energy consumption is lower on two stage recips, but they are less relyable and harder to maintain (commercial refrigeration).

Better not use single stage compressors below -33 deg c evaportion

Kind Regards Andy:)

[Samarjit Sen]

Hello Anand,

I think US Iceman is correct in his comments.

No I did not or do not use liquid injection for my - 40 Deg. C jobs with R 22. I use a single stage semi hermetic compressor with additional cooling by way of providing a fan over the compressor. As I said before, you have to be very perfect in your system design and use of controls. Different engineers will have their individual views which they get out of learning it the hard way and with experience.

With best wishes,

[nambiandy]

Thanks for the genuine advice

I only wanted to understand the behaviour of Refrigerant for negative application..


Anand

[Samarjit Sen]

Dear Anand,

Using liquid injection depends on which compressors are you using. I am using Bock semi hermetic compressors in which liquid injection is not required. The best thing for you will be to contact the manufacturers of the compressors, and they will tell if liquid injection is required for their make or not.