Compressor duty and suction temp
This thread contains 9 post(s).

Author
Message
2008-08-26 18:46:31
Compressor duty and suction temp
Hi,
could anybody tell me a calculation for the loss of duty for a reciprecating compressor if the suction line temp is 5k above designed temp? Say for theory sake unit evaporating at -8'c expected gas return to comp 2'c, however gas returning at 7'c.
Many Thanks Rowan
2008-08-28 21:08:38
RE: Compressor duty and suction temp

Rowan
I'm not sure I understand your question right.

If you have an evaporating temperature of -8C and you have a suction gas temperature of plus 7C you have superheated the gas 15 degrees. This can happen in an internal heat exchanger which I assume you have in the system. If you expect a temperature of +2 and get 7 your system can be a bit undercharged or some insulation on the suction line has fallen off so you get heated up the suction gas to a temperature that the system is not designed for. However superheat in CO2 systems is not always bad

Alex.

 
2008-08-29 21:43:55
RE: Compressor duty and suction temp
The problem i have is with a co2 pack running 50 or so cabs. the pack seems to be struggling on duty, as the controls system is not what i'm used to I stand to be corrected. Cabs are making temp however run with very wide superheats. Thought that if the gas was returning warmer than the design that this would mean that the gas would be less dense than design and knock the duty of comps?? Just didnt know by how much. Co2 is very new to me so i'm still trying to grasp it and any advise would be great.
Cheers
2008-08-29 22:01:00
RE: Compressor duty and suction temp
Hi Rowan,
as Alex mentioned a bit more superheat is not bad for CO2. The power of the comps doesnt
suffer much. Generally in DX systems you can go down to a coefficient of about 0,8 (comp-power/consumer-power), this is also valid for CO2.
What you  can try is to minimize the superheat in the cabs by adjusting it in the
electronic controls of the cabs. But be careful and watch that the comps dont become white.
We experienced that a superheat of 7-10 K at the comps should be kept, not less. A little bit more is also OK.
Matthias
By the way, may I ask you for which company you are working ? (Just curious)
2008-09-02 22:58:42
RE: Compressor duty and suction temp
Hi Matthias thanks for your help. I work for a Project First Facilities Management. We work supermarkets mainly.
2008-09-09 22:39:11
RE: Compressor duty and suction temp??
Hi Rowan,

I take it we are talking R744 Transcritial application here (Dry suction)?

If you let me have the compressor details (It may take me a while to trawl through my info) I will come back to you. 


Regards


Martin Ritchie
2008-09-14 09:30:14
RE: RE: Compressor duty and suction temp??
Mr. Martin Ritchie posted on 2008-09-09 22:39:11:
Hi Rowan, I take it we are talking R744 Transcritial application here (Dry suction)? If you let me have the compressor details (It may take me a ...
Jump to Post

Hi Martin, hows tricks?

Yep, should be a dry suction.

The comps are Bitzer, mod; 4HTC-20-40P. No rush for the info mate just something I'm trying to justify something in my head.

Cheers Rowan
2008-11-19 16:39:22
RE: Compressor duty and suction temp
I am currently trying pipe sizing calculations for R744, is there a Nomograph available to check computer caculations?
2008-11-21 03:36:52
R744 pipe sizing for both transcritical and subcritical
We are in the beginning stages of designing a transcritical 4C chamber.  What are the expe cted velocities we should design to for oil movement.  With R404a we have had good results at 1500 FPM vertical and 750 FPM horizontal.  Is there line sizing criteria available I here the sizes will drop but want to size the lines properly especially since this is an R&D project.
Thanks for your help


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