Refrigeration Compressors

I have been in the field of refrigeration for quite some time. Now I need help for a very peculiar problem. Some refrigeration engineers have suggested to one of my prospective clients that for temperarures below -20 Deg. C he should install two stage compressor using R 22. I have in all my years of experience used single stage refrigeration compressors upto -40 Deg C and have selected all the equipments properly. Could some one help me with some standard documents to substantiate my statement. Unfortunately my client is totally confused and has no knowledge of refrigeration.

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Originally Posted by Samarjit Sen

Some refrigeration engineers have suggested to one of my prospective clients that for temperatures below -20 Deg. C he should install two stage compressor using R 22.

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Since you did not specify, I am assuming you mean a two-stage system using booster compressors and hi-stage compressors, not an internally compounded two-stage compressor.

I agree with the use of two-stage systems below -20C. A two stage will will cost more to install, but less to operate.

A single stage system down to -40C is quite possible with screw compressors, but the thrust bearings absorb a lot of additional loads, which tend to require more frequent repairs. This is also cheaper to install, but does cost more to operate.

If the system is only being used for ~2000 hours per year, then a single stage system may be more cost effective. However, if the hours of operation require a full time system (~8760 hours a year) I would suggest the two-stage system.

I would not recommend R-22 for this now with the eventual phaseout of the refrigerant.

I would use ammonia.

I agree with the Ice Man, 2 stage systems are better efficency wise, plus ammonia is a much cheaper refigerant

It all depends on the size of the system: if it's for 50 kW, then a NH3 freezer will be far too expensive.

In another century, we installed many freezers - and many one stage - on R22 and if you can keep discharge pressures low enough, then I don't see any problems.

Copeland had the 'Demand cooling' for this in the past with liquid injection in the compressor it selves.

Speaking of efficiency is of course another point of view. But there's always the economical aspect: is the extra cost worth for a two stage compared to the savings it will make over the years. It's sometimes better to add a big oversizes condenser.

But a two stage in this application - espacially low temperature on R22 - is always more energy efficient.

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Originally Posted by Peter

It all depends on the size of the system: if it's for 50 kW, then a NH3 freezer will be far too expensive.

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You are right of course Peter. Size does matter.:D

A small ammonia system can be more expensive than a R-22 system of the same capacity. Since the original post was made in the "Industrial Compressors" area I assumed (there's that word again) that we were dealing with a large ammonia system.

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It's sometimes better to add a big oversizes condenser.

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Agreed. Another consideration would be the condenser type. An R-22 system (single stage) using an evaporative condenser may be just as efficient as an air-cooled two-stage system.

We have gotten ahead of ourselves, since the gentleman didn't provide enough information. But in relative terms, I think we are saying the same thing.

You can show your customer compressor rating tables. The tabless of 'Bitzer' / 'Bock' show capacities at -40 Deg. C evaporating (in single stage compressor) for R-22.

'Kirloskar Pneumatic' KC series compressors and 'ACCEL' compressor tables show capacities at-30 Deg. C evaporating in single stage for R-22.

Of course all these will be with a watercooled system with
condensing temperatures preferably not exceeding 40 Deg. C

It doesn't matter whether your application is a chilling plant or a freezer.

Thank you friends. The capacity of the plant is 26 kw. Using ammonia is not possible. Bitzer, Copeland and Bock shows a rating of -45 Deg. C Evap and 40 Deg. C Condensing with R 22.

Rather than using R-22 which most countries are scheduling to pahase out (2010 on new equipment and 2020 as a seervice refrigerant in the USA) why not look at R-507. I am not a proponent of the 400 series fro a system of any size over a residential unit since they are all blends.

Ken

Welcome back TXiceman. I was wondering how your move back to Texas went. I hope you have settled into your new position and home.

Please send me your new email address, when you have a chance.

Best Regards,
US Iceman

Hi Samarjit - you will find the Bitzer single stage limits at the bitzer website - look for /_doc/k/kp-520-3.pdf This shows as you pointed out earlier that you can run at -40/+40C if you want to, but you are giving the compressor a pretty rough time, even if you use the additional cooling and limit the suction superheat as recommended. Your condition is right on the limit for this machine. I would suggest keeping at least 5K away from the extreme: you could drive your car at 6000rpm all the time, but would you?

Its all about discharge temperature at this point - not good for the refrigerant or the oil! Some of the new blends - despite what Ken says - are chosen to produce lower discharge temperatures. This seems to have a really good effect on compressor reliability, so worth a try.

Cheers
Andy P

I feel operating at -45 Deg. C Evap. and 40 Deg. C with a single stage is not advisable, si I have decided to go in for two stage Semi Hermetic Compressors and play safe.

Thank you all for the valuable adice given.

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Originally Posted by Samarjit Sen

I feel operating at -45 Deg. C Evap. and 40 Deg. C with a single stage is not advisable, si I have decided to go in for two stage Semi Hermetic Compressors and play safe.

Thank you all for the valuable adice given.

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Samarjit

I have never worked on 2 stage systems, but for my constant thirst for knowledge, would it be possible to show a diagram the system layout, operational characteristics, etc.

Nothing detailed, just rudimentary. I know you guys are busy

Thank you

Dear Abe,

I am terribly sorry for not replying to your post. I have been kept pretty busy with my various projects that it had completely slipped my mind. I am attaching a bulletin from Copeland which will give you a detail idea about 2 stage refrigeration system. Sorry could not download as the forum allows only 100 kb whereas the file is more than 500 kb. Could you please send me your e mail address to me at so that I may mail this and some others also.

With best wishes

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Samajit Sen:
Some refrigeration engineers have suggested to one of my prospective clients that for temperarures below -20 Deg. C he should install two stage compressor using R 22.

I have in all my years of experience used single stage refrigeration compressors upto -40 Deg C and have selected all the equipments properly.

Could some one help me with some standard documents to substantiate my statement. Unfortunately my client is totally confused and has no knowledge of refrigeration.

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Samarjit Sen:
The capacity of the plant is 26 kw. Using ammonia is not possible.

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Samarjit Hi,

I have seen system (small & large) with two stage compressors operating just below -20C te.
But, I still have to see a document that will say that at this Tevap the single compressor should be use instead of a two stage compressor or vise versa.
Maybe, somebody out there knows better. Would appreciate to see that document.

For me, it all depends on the designer and, of course the customer, if the customer wanted to pay more for a two stage instead of single stage.

The largest i saw: used 2 units GRAM two stage recip each with 75KW motor for one room @ -18C room temp.
This is not my design. . . i usually design up to -35C te using one stage open type recip. Of course, this is for halocarbon & not NH3. From -40C te up to -55C te, i would of course use a two stage.

This is my personal opinion and are very subjective. I would love to hear other fridge guys opinions on this. . . :confused:

In my experience, the best way is to first educate the customer with value engineering.

- he can use a 26KWR SINGLE stage recip (R22 or NH3) with a budget of
USD ______ for R22 (hermetic compressor)
USD ______ for R22 (semi hermetic compressor) or
USD ______ for R22 (open type compressor)
USD_____ for NH3 (open type). Just email if you will need to use NH3 for 26 KWR. This might be of same price with R22 using open type compressor.

- he can use a 26KWR TWO STAGE recip with a budget of
USD ______ for R22 (semi hermetic) or
USD ______ for R22 (open type) or
USD ______ for NH3 (open type)

With the above presentation with budgetary pricing you can do no wrong.
The final decision on what system to use is from the customer and not yours. Anyway he is the one eventually paying (or suffering)
Also, the customer will be able to see through the motives of the other design engineers.

Hope to have contributed something to this nice thread. . .:)

Dear Fredy,

I myself am already executing a project for -45 Deg C Evap with R 22 single stage semihermetic compressors of Copeland make. I have successfully many a smilar projects in the past. So when this customer of mine told me about the opinions other people in the refrigeration trade has given me, I myself was taken back. I told hom that I would like to meet the person who has made such comments. Further surprisingly the refrigeration guys in that State or even here are still tinkering and using with old models of Grasso compressors which used to be made in India in collaboration with Kirloskar. Surprisingly there are very few engineers who are aware much advanced compressors that are available today.

So you see what hardship I have to face to convince a client specially when he has an EXPERT associated with him.

My referring this to the forum was purely to have some documentary evidence from real experts in the field of refrigeration, which I can put up before my client. Your post is going to be of great help so are the others in this thread.

With best wishes,

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Samarjit Sen:
. . . old models of Grasso compressors which used to be made in India in collaboration with Kirloskar. . .

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Thanks for that piece of info, i did not know that.

I used to be connected with KOPPEL Inc, a local distributor of Grasso since the 80's until early 90's. We sold a lot of RC11 for block ice plant. Since mid 90's till now Grasso Phils is selling direct to customer with RC12 as their latest model.

Even until now, am using RC612 in a new 30Ton/day Block Ice Plant, maybe will finish it by next month.
Here, Grasso has a solid reputation in ice plant application.

But, none in single stage models for application near -20C Tevap. Grasso is not pushing the RC12 single stage at Tevap lower than the iceplant application.
They suggest a 2 stage unit for approx -20C Te.

Maybe this is what they mean. . .

But you have a very small requirement which is not within Grasso range. Better use Bitzer single stage open type with your required capacity (26 KWR).

For the -45 TeEvap. what would be your opinion if I opt for Vilters two stage. I am expecting the rating chart and the technical details tonight. Two stage semi hermetic with R 404 A models are also available with Dorin, Copeland and Refcomp.

Can any one advice as to which would be suitable.

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Samarjit:
For the -45 TeEvap. what would be your opinion if I opt for Vilters two stage.

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Hi Samarjit,

I cannot give an objective opinion on this as i have not designed a system using Vilter compressor.

If it will be installed in my area and my customer would ask, i will cite the ff:
1) There are not much Vilter around.
2) The guys selling vilter is 1,500 kms away.

Maybe a Vilter guy can give some suggestion on your predicament. . .

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Originally Posted by TXiceman

Rather than using R-22 which most countries are scheduling to pahase out (2010 on new equipment and 2020 as a seervice refrigerant in the USA) why not look at R-507. I am not a proponent of the 400 series fro a system of any size over a residential unit since they are all blends.

Ken

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Yes i agree with this refrigerant being used as i have had a bit to do with a small system using R507 on a small glycol chiller and it worked very well.:rolleyes:

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Originally Posted by Samarjit Sen

Can any one advice as to which would be suitable.

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Hi :)

Bitzer Screws with economisers either R404a semihermetic or NH3 on open drive.

Kind Regards Andy:)

I'm not a fan of R-4-4a as it is a blend where R-507 is an azetrope. You have to be careful recharging blends as you do not know what percentage of which component leaked. To stay on R-404a properties you should remove the refrigerant and recharge with new. R-507 does not behave in this manner.

And I like the idea of ammonia on an open drive compressor. Smaller screws are not much of an option, but Mycom, Vilter and Grasso all offer pretty large recips for ammonia.

Ken

Doesn't Bock and Bitzer offer small open drive recip. compressors for NH3? Depending on the system capacity, this might also offer a decent alternative.

hello guys,

if u want to ensure the operation cost different betwen single stage and two stage (booster+high stage), you can plot the operational temperature on moiller chart, u can see the power consumption of single stage higher than two stage. so the operational cost and lifetime of the two stage compressor cheaper than another.

operational low side pressure should be come to consider in choosing the system, if the pressure to far away below atmosphere pressure ( vacum ) might be selected the two stage system more valuable.

please help me

can i convert to R-22 from ammonia in a flake ice amchine with the capacity of 30 us ton north star branded

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Originally Posted by Rajeevcoldtech

please help me

can i convert to R-22 from ammonia in a flake ice amchine with the capacity of 30 us ton north star branded

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Are you converting only the ice machine or the whole refrigeration system?


Ken

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Originally Posted by Rajeevcoldtech

can i convert to R-22 from ammonia in a flake ice machine with the capacity of 30 us ton north star branded

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If you are referring to the North Star Icemaker itself, the answer is yes. You might have to replace the feed control, depending on its type.
You also have to follow North Star's recommendations for oil return piping for your system.
When doing these conversions we always circulate solvent through the drum (internally) for several days, in order to make sure it is clean.
You may experience some loss of capacity going to R-22. They do tend to be a bit more difficult to operate when using R-22 than on Ammonia.

Here's a bit of history and contacts if you need them.

RefComp and Thermokey form together the RTH group which is an independent group which has one owner who is the original founder Mr. Candio.
RefComp makes the very same screw and piston compressors at their factories both near Vicenza in Italy and in Shanghai in China while Thermokey makes many types of heat exchangers for Air Con, Refrigeration , Process Control, Close Control , Power and Energy and Solar Energy markets and manufactures in Italy , China and Brazil.

About 30 years ago Mr. Candio used to own Artec (heat exchangers) which he after sold to Alfa Laval. After RefComp was then founded and was a pioneering company with screw compressor technology specifically designed for HVAC and Refrigeration applications. During this past century Bitzer used to sell the large RefComp screw compressors through their sales network because back then they did not manufacture yet this kind of new screw compressor.
After Thermokey was then founded. Nowdays Thermokey is pioneering in large aluminium microhannel heat exchangers specifically designed for HVAC and Refrigeration applications

you can contact them at :

sales@refcomp.it
sales@thermokey.it