CO2 System Design

[iansuffield]

Hi all,
I am trying to design my first CO2 side of a CO2/134a cascade system and am having some trouble with the calcs required for pipe selection. MT refrigeration is by pumped liquid CO2 @ -10C with LT refrigeration by DX CO2.

Does anyone have some std calculations or recommend a pipe selection program for these as the figures I am getting at present are of concern.

Thanks in advance,

[750 Valve]

what figures are you getting - small pipe sizes? big pressure drops with the sizes you want to limit the installation to without going steel?

This area is a bit cloak and dagger right now, its a bit of a touchy area till all competitors are putting forth completed systems - at least in this country (Australia) at this point in time

I'll give you the heads up on the hi stage though, plant shutdowns are a bugger on R134a... better off with R507 (I know its not as green as R134a) but you WILL have headaches with the R134a, got screws on the hi stage? WW or Coles or someone else?

[iansuffield]

I am comparing to some figures I have heard in the past. The figs I get have high velovities, high pressure drops and are just wrong... I know I need to keep my LR pipe to 7/8" max to keep within the SWP of the pipe. I am 100% confident we do not need steel pipe anywhere in the system as even a transcritical system only needs stainless pipe on the high side - low side is still soft drawn copper (saw one operating last week).

Any advice on recommended selection programs used in the past would be appreciated!

We have gone with 134a screws at the request of the client (not Coles). I have delt with 134 screw racks in the past and am aware of the gremlins that can pop up in the system - eapecially when using VSD's...

[US Iceman]

I guess I'm confused as to what you might consider too high for pressure drop or velocity. You still need to account for the pressure loss so it does not affect the performance of the item (evaporator, condenser, compressor, etc.).



Any advice on recommended selection programs used in the past would be appreciated!


Don't take this the wrong way, but how will this help you?

[750 Valve]

What store did you visit?

Its not the fact they are screws that causes the hassle but I guess everyone is hell bent on green so R134a gets the gig, but unfortunately when compared to R507 cascade systems they are very tedious and leave absolutely no room for error, unless of course you run the occasional vacuum.

Are you seeing high pressure drops in pumped liquid, return or suction lines... what sort of velocities are you shooting for in each line?

Maybe you might have to take a shot at it and hope that it all works, this is what the rest have done on their first system and then fine tuned from there. Have you got a test plant up and running to refer to or trial a setup?

[iansuffield]

The transcritical store I visited was at Angle Vale, on the north side of Adelaide - it was an independent store.

As for the velocities I am trying to achieve, I am aiming for <1.0m/s for pumped liquid at -10C fluid temp.

no test plant as yet - we have visited other co2/134a stores that have been completed and noted some pipe sizes, which I agree with, its just getting the calculations to spit out the numbers I am expecting.

[Frigosoft]

Hi all,
I am trying to design my first CO2 side of a CO2/134a cascade system and am having some trouble with the calcs required for pipe selection. MT refrigeration is by pumped liquid CO2 @ -10C with LT refrigeration by DX CO2.

Does anyone have some std calculations or recommend a pipe selection program for these as the figures I am getting at present are of concern.

Thanks in advance,

You could try the FrigoSim program that I am developing (frigosoft.no/frigosim). It is not a "quick and dirty" program, rather an advanced tool for design of thermal plants.

[Andy]

The transcritical store I visited was at Angle Vale, on the north side of Adelaide - it was an independent store.

As for the velocities I am trying to achieve, I am aiming for <1.0m/s for pumped liquid at -10C fluid temp.

no test plant as yet - we have visited other co2/134a stores that have been completed and noted some pipe sizes, which I agree with, its just getting the calculations to spit out the numbers I am expecting.

Hi Ian:)

you could use Danfoss Dircal, free off their web site.

Kind Regards Andy :)

[Samarjit Sen]

Yes , Danfoss DIRcal is suitable for pipe sizes, and the software can be downloaded free from Danfoss web site. I find this very useful in my work.

[Guy Hodgins]

Here in the UK a pipe work design package called Micropipe is extensively used, particularly in the supermarket sector. I know that the latest version contains CO2 pipe work design data. Not used that part of the programme yet but if it as good as the rest of the refrigerants it wiil be spot on. Not cheap to buy but it does save a lot of time and mistakes.