Multisection or onesection condencer for two systems.

[Aik]

Have one refrigerating plant with two compressors Q=40 kW, Te=-10 C, Tcond=+45 C and one refrigerating plant with two compressors Q=30 kW, Te=-35 C, Tcond=+45 C.
I have place on roof only for one condencer, and I want to use one condencer for two plants. There is question: what is more preferable to use multisection or onesection condenser?
I understand that multisection condenser more preferable, but how can I regulate condencing pressure in two different systems with own circuits?

[Yuri B.]

...... how can I regulate condencing pressure in two different systems with own circuits?

I offten see condensers let "live" their "condensation-pressure-regulated lives" on roofs almost fully independently from other parts of the system.

[Sandro Baptista]

Aik,

You can for example use KVR + NRD for each section. This is DANFOSS equipment.

If you have any doubt about this tell me.


Sandro

[Aik]

Of caurse I can use KVR+NRD for each circuits, but there is interesting question: how can I regulate fans working? At what condencing pressure low or medium plant?

[Aik]

I also think so, but for automatization I need controller with two analog inputs (0-20 mA or 4-20 mA) or two controllers with one analog input or something else...
What do you think about onesection condencer?

[Sandro Baptista]

Of caurse I can use KVR+NRD for each circuits, but there is interesting question: how can I regulate fans working? At what condencing pressure low or medium plant?

What's narkom said is very correct. If you don't want to do it like that way just consider a low condensing pressure set-point in on the "more important" plant just to ensure that you don't have lack of condenser when this "important plant" is at low capacity and the other is at 100%. Of course in that way certain is much fans will work without be necessary. Don't hurry if the condensing pressure is too low the KVR+NRD will do its job.
The problem is if the "important" plant stop and well in that case you can force an certain number of fans to work.

[mad fridgie]

I assume you want to keep the two refrigerant circuits seperate, so lets look at the application, the LT system has the biggest pressure ratio and with the correct expansion valve selection, is less likely to be grossly effected by changes in liquid pressure, I see no real issues in letting the LT system high side pressures fall, far better for efficiency and performance, how ever your MT system due to small pressure ratios will need some form of control. I would then control your fans using the MT system, with a simple override for when the LT is running and the MT is not.
You will need to consider where your liquid reciever is placed, if directly next to the condensors not an issue, but if are remote from the condensors (in a warmer area) then you wll have to consider a balancing line, to reduce the likelyhood of "liquid hangup" liquid sitting in the condensor due to warm vapour traveling back up the condensate line (line between cond and reciever)
You need to understand how the combined systems are going to work, "process time lines"
Or you could simple purchase a special (which is about every one in NZ) where effectively you have to complete seperate conds built into a single case, two sets of fans and baffled air flow (one set for MT one set for LT), the refrigerant distribution of the 2 systems are not interwoven

[Aik]

Thanks guys for answers, it's more simple than I thought...