Heat recovery chillers - entering vs leaving chilled water control

[immsk]

Hi folks, I'm in the process or recommissioning a multistack heat recovery chiller Link

The chiller wasn't commissioned/set up properly and hasn't run much since it was installed.

I'm wondering if anyone could shine some light on entering vs leaving chilled water control? The chiller can be set up for either option but I haven't been able to find much information either in the manual or online on what are the pros and cons of either option. Or when to use one vs the other.

 

[EnergyProfessional]

You need the model#, and contact Multistack for more information. Read the design guideline and Installation manual and other documents to understand what this specific chiller requires. Obviously assume noting will be set up properly since you say it wasn't done properly. So need to re-do all that.

they have varying control options in that either the chiller controls certain things, or the Building Automation System. Also depends on specific piping and valving in your system. They can be operated in different ways.

 

[Rputvin]

Trane has an engineering article on heat recovery chiller applications. It discusses the need for entering-water-control on centrifugal compressors to prevent surge conditions on page5, and moves on to the difference between entering vs. leaving water control scenarios.

Might not be 100% applicable to the Multistack, but hopefully it helps with your understanding of the problem.

https://www.trane.com/content/dam/T...letters/waterside-design/admapn023en_0207.pdf

We recently fired Multistack as a vendor, too many service issues, no response from their service team or weeks on weeks of scheduling, terrible factory schematics/prints, warranty issues not being fixed for months, etc. Best of luck dealing with them. Hopefully it's a recent change due to the current situation and not indicative of their overall decline.

 

[EnergyProfessional]

I think most Multistack chillers are smaller units and not centrifugal. Their whole schtick is that they use modules that fit into an elevator. So if you have a "large" chiller, you have many smaller ones coupled together. That comes with the disadvantage of using many small compressors.
We don't have too much chiller experience. And in some cases the problem is on the design side by choosing the wrong type. But we've had our fair share with Multistack problems that were based on their firmware etc. They did make effort to resolve the issues quickly, though.

But if you don't need the modularity for space reasons, you may be better off looking at more traditional chillers. Carrier et al now also make smaller chillers you can combine to larger units.

But I think the OP just wants to make the existing one work. So you need to look at the documents for that specific chiller.

 

[immsk]

I have read through the IOM. But it didn't explain when to use entering vs leaving chilled water control.

Was hoping to hear people's experience using one vs the other.


@rputvin that article is super helpful thanks

 

[EnergyProfessional]

The manufacturer or the rep often have design guidelines that are not on the manufacturer website.