Piping design question

[D.D.KORANNE]

I have an application that needs to select suction , discharge & liquid pipe sizes :

The application is as follows :

a) multi temp rack
Evap temp : ( 27) deg C ,
cONDENSING TEMP : 40 DEG c
Comp capacity : 52 KW
Refrigerant : R-404a
Suction header selected : 64 mm , discharge header : 35 mm
b) Ante-room
Copm cap : 65 kw
Evap : (-3) deg C
CONDENSING TEMP : 40 DEG c
R-404A
Suction line 54 mm , dis line 42 mm



Both these systems will be operated by three semi-hermetic compressors each with a compressor having 122.2 meter cub per hour displacement

Question is :
Individual system (a) & (b) suction / discharge pipe selected are given above .

But how to calculate suction & discharge header sizes when all three compressors are connected to a common suction & discharge headers ?

[D.D.KORANNE]

Evap temp is -27 deg in the first application & not 27 deg c as mentioned

[NoNickName]

Based on ASHRAE tables, 67mm suction is suitable for 54kW @ -30°C evaporating temperature, while 35mm discharge is only suitable for capacities up to 41kW. I would suggest to use 42mm wide pipe.

For the ANTE, I would suggest 54mm for the suction and 42mm for the discharge.

Common headers shall have the same speed than individual pipes, so the cross section must be triple (for a three compressor multipack).

35mm --> 67mm
42mm --> 76mm
54mm --> 105mm
67mm --> 105 or 130mm

[lana]

Hi,

What is the pipe length and number of fittings?
Is there suction or discharge vertical risers?
Is there capacity control, if so what is the minimum capacity?

For the common suction line you have to consider full load capacity then calculate the correct size.

Cheers

[D.D.KORANNE]

Thanks , nonickname !

All three compressors will be connected to a common discharge & suction headers . Individual compressors will have indepedent oil separator, suction accumulator , oil reservoir and oil level regulator for each compressor through an oil filter .

Appreciate your response !

[D.D.KORANNE]

Hi lana,

all compressors will operate on capacities between 80 to 100% . The water cooled condenser will be mounted on frame work ; in other words the discharge piping will not be more than about 4 to 5 meters .
I had selected pipe sections through a solken software .

Thanks for your response !

[lana]

Hi there,

My calculation shows the followings :

First system : suction 67mm and discharge 35mm.

Second system : suction 54mm and discharge 28mm.

Cheers

[D.D.KORANNE]

Hi lana ,
thanks . However all the compressors will be connected to a common suction & discharge header . Hence the question prtains to how to work out a common header size with multi temp application . Each system will have its own mass flow ; -27 deg c & -3 deg c systems in this example ; but need to connect all the compressors to a common header , suction & discharge .
Any suggestion how to proceed ?

[chemi-cool]

How do you intend to controll rooms temp and defrost?

[D.D.KORANNE]

We are offering only the rack system i.e. High side equipment to the customer . The low side evaporator coil will have electrical defrost & coils will operate through tex valves with individual capacities & settings .as a rack provider , not much info is disclosed to rack designer .

[Zpoint]

Sir,

If you are only supplying the rack, the lengths of piping you are dealing with are minimal. Size them for the total capacity of all compressors. Oversizing them slightly won't hurt, but undersizing them will cause unwanted pressure drops under full load conditions.

You're no "Alfred Einstien" are you? :)

Jeff P.

[dougheret0]

Get a copy of TRANE "Reciprocating Refrigeration", Chapter 14, Refrigeration Piping. This provides copper tubing and pipe sizing as a function of refrigerant type and tonnage for liquid, suction, and hot gas piping as well as oil return requirements and recommendations. Another source is the Carrier Refrigeration Handbook, Piping Section. These charts, for whatever refrigerant you are using, are probably available on line.

[D.D.KORANNE]

Thanks Zpoint . We normally allow the loss of pressure in suction line since pipe lenghts are not really known to the designer . Hence 1 deg k penalty on suction may not be sufficient . Besdies, a size higher is offered for suction piping .

[D.D.KORANNE]

dougheret0,
Thanks !
However , do not know whether these two handbooks can be sourced . Any suggestion how to access these two books ?