Compressor Sequence Code for RSLOGIX5000

asterof

Member
Join Date
May 2007
Location
Califonia
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Anyone have some code I can use for refrigerant Compressors
Sequence Control

IE an example

Cascade Sequencers

The simplest sequencers use a “cascade algorithm”. It is the sequential starting and loading of compressors based on falling pressure, and the reverse for rising pressure. It works like this: as pressure drops, the next compressor starts and loads, and then the next starts and loads if pressure drops further. As pressure rises, the reverse occurs. The last on will load and unload once the number of compressors running stabilizes. The sequencer swaps the order around to even out wear.
 
Asterof,

Are you actually using these compressors for True "Cascade Refrigeration System"?
In other words putting refrigeration systems in series to achieve a temperature lower than you could with a single loop.

OR

Are you simply putting many compressors in Parallel so you have enough capacity to keep up with your max load?

I am just curious because in your other thread on SCT you are looking for a way to calculate Saturated Condensing Temp.

But if you are just putting compressors in Parallel, then I am not quite sure why you need to have this calculation in the PLC.

My past experience and my license are only for <25 ton capacity systems, so I am not well read on larger capacity, multi-compressor systems, but the ship I now work on has a refrigeration plant much larger than that with multiple compressors in parallel.

We load and unload our compressors (5 of them) in auto using A.B. PLC (8 of them) by looking at the load of one compressor and once it has reached 95% load then we start the next compressor and begin loading it.
This is done until all 5 compressors are running at 100% if needed.

Unload is done the same way but in reverse and we stop one and start unloading another when it hits 5% load.

The signal (pulse) given to Load or Unload is determined by a dead-band set around the Suction Pressure.
If it gets X amount higher than set point then Load signal.
If it gets X amount lower than set point then Unload signal.

Head Pressure is controlled by varying the speed of water pumps through Shell-in-Tube Condensers to try and maintain a sufficient, set head pressure.

Our load can vary, very rapidly.
We maintain a 1500 metric ton cargo hold at -30c at all times, but we also have 9 plate freezer racks that get loaded with around 2 tons of blocked, fresh, fish fillet or surimi and frozen to -20 C in about 1 hour each.
These plate freezers go around the clock when we have fish and sit empty when we don’t.

If you are installing a True "Cascade Type System" then this may be another animal all together and not relevant to our system in any way.

Can you give a bit more detail about the process you are working on?
Don't know if I will be a lot of help but I am curious at the least.

BCS
 
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