Mycom question and Manuals (Compound two stage)

[henry.zhang]

Dear all,
1,My question is on MYCOM compound two-stage screw compressor 2520LSC. Why the oil heat rejection load almost does not vary with evaporating temperature?
ET/CT Oil load
-40/40C 132kw
-45/40C 130.7KW
-50/40C 130.3KW
Is it reasonable?

2,Anyone here has selection software of Mycom compressor and mycom screw compressor Installation & Operation manual, especially for Two-stage? Compound two-stage screw attract me a lot. Thanks in advance.

Henry.

[Camille]

Henry

A two stage compression system either a direct injection interstage cooling, or open flash interstage cooling, at the booster as the evaporating temperature goes down, say at constant discharge temperature as you have shown, many things are happening that are related. The compression ratio between the suction and discharge goes up, the discharge temperaure rocket up, as the compressor is doing more work, less mass flow rate to carry the heat, and the oil heat required to be rejected by the machine oil cooler is higher. The horsepower is down as the evaporating temperature goes down which help the oil heat rejection little bit; but also keep in mind that every refrigerant reacts differently to above scenarios.

anything else copy me

Camille Zabbal

[henry.zhang]

Thanks for your reply,Camille.
Yes,Many things will happen when ET goes down. But this phenomen on mycom is totally different with on Bitzer hermetic screw compressor. I post the data of HSN8571-125(125HP,single stage,W/ Eco) here.
ET/CT Oil heat load
-35/38C 33.2kw
-40/38c 35.8kw
-45/38c 37.8kw
-50/38c 39.2kw

I don't intend to know every details in compressor theory,but wonder the reason of this difference and make sure the oil load data is correct for designing.

[henry.zhang]

And wonder any friend has selection software of Mycom and IOM of Mycom screw compressor unit.This document will be very useful for me.

Many thanks!

[Sandro Baptista]

Maybe, on the MYCOM WEBPAGE...

[charlie n]

Henry,
Contact Mayekawa office in Shanghai. They should have the manuals and their selection software CD. Tel: (86) 21-5116-8958.

[henry.zhang]

Many thanks for your information,Charlie.I will try,and BTW,we decide to start this project.

[tabreed717]

Hi Henry
My question to you is;
How did you measure the oil heat rejection load at different ET? Is it from the specification manual or software?
If we take it as you said, I think the oil cooler is over sized to be able to handle the oil heat rejection at different loads.
I am totally agree with Camille and thanks to him for the clarification

[RANGER1]

henry ,
The oil cooler heat load is correct according to the mycom programme ( for R22 ) .

When you select oil cooler , select it for higher suction pressure to allow for a pull down .
Also a bit of tube fouling if water cooled .
R22 has a lot less heat rejection than say ammonia .
Also a booster compressor if used seperately has small oil cooler load , so not much changes .

If it was a Howden booster its completely different again to Mycom , but similar design !

Bitzer has roller bearings which require very small amount of oil compared to Mycom whitemetel bearings .

[henry.zhang]

Many thanks all for helps!

Yes,tabreed717,it's from selection software.
Thanks you for your double-check,Ranger1.
For oil cooler selection,I use ET setting +5K to calculate targeted oil load.

[henry.zhang]

Yes,Ranger1,different bearing types may lead to different oil mount. But i think it doesn't mean oil load must be different,because the oil load is determined by De-superheating load for refrigerant gas. Is it correct?
thanks!
right?

[RANGER1]

I think less oil through oil cooler less load .

In the mycom programme total oil flow is for bearings etc only , as it does not require
oil injection into rotors at all . Its using all oil to bearings to cool machine .

Also compound mycom is 2 compressors not 1 as with Bitzer single stage economized .

Do Bitzer make machines this big , or would you have to use several ?

[Camille]

Henry

As I said the higher the compression ratio the more work the compressor has to do , more heat to be rejected from the oil
At constant discharge and intermediate temperature for two stage compressor, as the suction drops down so is the horsepower so is the oil heat rejection.
Now by changing the intermediate to higher temperature [constant discharge], we get higher tonnage, mind you it is more horsepower to produce that tonnage; but the compression ratio to the intermediate is less, so the oil heat rejection is down as the mass flow rate intermediate is less

very unfortunate that the refrigeration engineer web will not allow more that 1mg file to be sent as I amde you sketches to understand the concept

best regards
Camille Zabbal

[henry.zhang]

Hi,Ranger1,Bitzer does not have the compressor as big as Mycom.



I think less oil through oil cooler less load .

In the mycom programme total oil flow is for bearings etc only , as it does not require
oil injection into rotors at all . Its using all oil to bearings to cool machine .

Also compound mycom is 2 compressors not 1 as with Bitzer single stage economized .

Do Bitzer make machines this big , or would you have to use several ?

[henry.zhang]

Thanks,Camile.
I fully agree with more oil heat rejection needed if higher compressoion ratio.
While I am a little confusing on the results in case of increasing intermediate pressure. Yes oil load is less for high stage compression,but the oil load is more for low stage compression. Not sure how the total oil load will change.

You could send email to me at shgzhang@hotmail.com at your convenience if you have some file to show me.

Thanks again.
Henry



Henry

As I said the higher the compression ratio the more work the compressor has to do , more heat to be rejected from the oil
At constant discharge and intermediate temperature for two stage compressor, as the suction drops down so is the horsepower so is the oil heat rejection.
Now by changing the intermediate to higher temperature [constant discharge], we get higher tonnage, mind you it is more horsepower to produce that tonnage; but the compression ratio to the intermediate is less, so the oil heat rejection is down as the mass flow rate intermediate is less

very unfortunate that the refrigeration engineer web will not allow more that 1mg file to be sent as I amde you sketches to understand the concept

best regards
Camille Zabbal

[gpeterman]

Did you get the manuals you needed? I have the 2520/3225 manual in electronic format.

[HAROLDMYCOM]

Dear Henry,

Where did you found your information ?
ET/CT Oil load
-40/40C 132kw
-45/40C 130.7KW
-50/40C 130.3KW

Cause in my selection software taking in mind I selected the N2520LSC with random discharge port on Nh3, with open flash and oiltemp set at 50°c I have following results.

Oil load heat rejection calculated is at

-40/40C = 197.9 Kw
-45/40C = 185.7 Kw
-50/40C = 175.7 Kw

Kind regards,
Harold