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salahzantout
25-08-2013, 09:55 PM
Hi Guys

Im trying to make a design for two compressors built in parallel... now the problem is that i must connect the suction and discharge to headers and i can not find the way of calculating the size of the header...

I hope any of you can give any procedure or lead me to any reference, Ashrae or trane or any other reference...I have all of them but they only state the way of sizing a single discharge or suction line,

much appreciated

Thanks in advance :)

moideen
26-08-2013, 04:12 AM
go to this link,it may help you....

http://www.bitzer.de/eng/productservice/p4d/KT-600

salahzantout
26-08-2013, 06:08 AM
hey moideen,
Thanks but i already have this catalogue from bitzer, but it never states any rules or calculations for it.
I need some rules, lets say i have the 3 compressors ( same type and capacity ) in parallel and i want to connect the suction lines ( must ) to a header as well as the discharge lines...
How to choose the correct size of headers ?

nike123
26-08-2013, 07:11 AM
hey moideen,
Thanks but i already have this catalogue from bitzer, but it never states any rules or calculations for it.

Yes, it states! Suction header=<4m/s rule, discharge header=sum of individual pipes rule. Read carefuly!

salahzantout
26-08-2013, 08:58 AM
Yes, it states! Suction header=<4m/s rule, discharge header=sum of individual pipes rule. Read carefuly!

hey nike,

yea ive seen this... and actually i already know this... its in 2.6 and 2.9 i think
but i want little more details...

lets say i have two suction lines of identical compressors in parallel
1 inch suction line with capacity of 15 kw each

do i select the header as 30 kw with velocity restrictions ??

salahzantout
26-08-2013, 09:04 AM
also note that im working with screw compressors....

nike123
26-08-2013, 09:38 AM
You should size suction header in such way that maximum velocity of gas does not go above 4m/s.
You need to select moment in operation of such tandem in which you have maximum mass flow of refrigerant and size header pipe to have velocity in that moment less than 4m/s.

In your example, yes you size it at 30kW if that is maximum sum of individual capacities.

salahzantout
27-08-2013, 01:13 PM
what about minimal capacity ??

is there any manual you have for exact calculations ?

Josip
27-08-2013, 04:38 PM
Hi, salahzantout :)


what about minimal capacity ??

is there any manual you have for exact calculations ?

It is easy...when you make drawings of your plant you can upload them here and we'll tell you what you can do in some better way, if ... it is a game, unfortunately the best is not always acceptable by client due to high price ;)


You can try this software ...

ftp://software.danfoss.com/RA/DirCalc/DirCalc.zip

Best regards, Josip :)

nike123
27-08-2013, 09:40 PM
I am not construction engineer. I cannot tell you with 100% certainty what you should do in that case. I just interpreting what is said in that paper from Bitzer and what I saw in practice on few installations, that work satisfactory.
In today discussion with my colleagues, minimal capacity is not of concern in designing that, only maximal! And that correspond with what is written in that Bitzer manual.

Also, as in that manual, discharge header should be dimensioned as sum of cross section of all individual discharge pipes and not less than that.
Discharge pipe on individual compressor should not be smaller than factory prepared (proscribed) connection at compressor discharge isolation valve for single use.

salahzantout
28-08-2013, 01:12 PM
hey nike

actually mimimal capacity is important so that you insure sizing the pipes for getting oil back to the compressor

Also note that bitzer recommendation is for reciprocating compressors and not screw...

but thanks anyway

salahzantout
28-08-2013, 01:16 PM
Hi, salahzantout :)



It is easy...when you make drawings of your plant you can upload them here and we'll tell you what you can do in some better way, if ... it is a game, unfortunately the best is not always acceptable by client due to high price ;)


You can try this software ...

ftp://software.danfoss.com/RA/DirCalc/DirCalc.zip

Best regards, Josip :)

Hey Josip...
thanks for that... i ll try to learn on using it... but i wish you just link me to some manuals or ebooks for calculating the pipe sizes... i am not asking for sizing a single compressor one capacity system... i am asking for multiple compressor system which requires headers and so on

ive seen ashrae, carrier, trane, mc quay and some more but nothing states some real calculations with examples for multiple compressors or evaporators... etc etc

so if you would link me to any valuable book or even you own calculations ( if it is possible ) I woulld be so thankful

Josip
28-08-2013, 10:31 PM
Hi, salahzantout :)



Hey Josip...
thanks for that... i ll try to learn on using it... but i wish you just link me to some manuals or ebooks for calculating the pipe sizes... i am not asking for sizing a single compressor one capacity system... i am asking for multiple compressor system which requires headers and so on

ive seen ashrae, carrier, trane, mc quay and some more but nothing states some real calculations with examples for multiple compressors or evaporators... etc etc

so if you would link me to any valuable book or even you own calculations ( if it is possible ) I woulld be so thankful

I'm glad you found Danfoss software useful ...

this one CoolPack 1.5 is very good too ... very complex too ....
http://en.ipu.dk/~/media/koele-og-energiteknik/downloads/coolpack150.ashx

maybe you can find something here too ..
http://softadvice.informer.com/Refrigerant_Line_Sizing_Program.html

With books you can start here ...

http://www.gobookee.net/refrigerant-pipe-sizing-calculator/

then visit this very valuable link ....

...http://www.refrigeration-engineer.com/forums/forumdisplay.php?24-Refrigeration-Books

here you will find links to books ... need some time to read all threads and much more time to read books ;) but that time is not a lost time at all ...


Sorry, my calculations are not of any value for you ... my systems are completely different of yours and it is not written like a school book with explanation why this and why that ... more like small notes .... and it is useless for any other person too ... I'm using above software too

It is not hard to calculate, pipe or header sizes ... more important and harder is to make complete piping layout, with slopes, vertical distances for risers, bottom, side or top pipes joint, supports ... etc ... this is something what is not possible to learn from books or some software ... to design refrigeration plant it is a must to have a lot of experience ....

again, my suggestion, the best is to make your "homework" and then we can advice you, but this is only my opinion and I can be wrong, anyhow, it is your decision what you'll do ...

Best regards, Josip:)

salahzantout
31-08-2013, 07:54 AM
ok will check the links

thanks alot Josip
much appreciated