Sequencing VSD and constant speed chillers
Sequencing VSD and constant speed chillers
(OP)
We have an existing central utility plant consisting of two York 1500-ton constant speed centrifugal chillers and a side-car arranged plate & frame heat exchanger (750-ton). There are VFD pumps on both the primary and secondary chilled water systems (which are de-coupled) and constant speed condenser water pumps feeding two Evapco VFD cooling towers utilizing an OA wetbulb reset of setpoint from 85-57DegF CWT (based upon temperature in Binghamton, NY).
We are going to add four additional York 1380-ton VSD chillers along with similar pumps/VFD's.
I am wondering what the best sequence would be to maintain efficiency with regards to chiller sequencing based upon chiller type/load/pump speed/etc.
Are the strategies between constant speed and variable speed chillers completely different? I haven't worked with the VSD chillers yet, and I am just beginning to explore them.
Thanks!
We are going to add four additional York 1380-ton VSD chillers along with similar pumps/VFD's.
I am wondering what the best sequence would be to maintain efficiency with regards to chiller sequencing based upon chiller type/load/pump speed/etc.
Are the strategies between constant speed and variable speed chillers completely different? I haven't worked with the VSD chillers yet, and I am just beginning to explore them.
Thanks!





RE: Sequencing VSD and constant speed chillers
Apart from this, a 1°/2° system with decoupling should stress the importance of proper 2° CHW D/P and flow control and proper chiller staging based on 2° CHW demand.
RE: Sequencing VSD and constant speed chillers
A few comments:
-Those kind of chillers, certainly have several thermodynamic groups working sequentially along the 1º('s?) circuit(s) temperature range.
-If we define/combine all the chillers we can put them to work sequentially to respond to all possible simultaneous demands. We have to exercise a global simulation to realise such "not so difficult and interesting data to get".
- Why to insist having VFD-pumps in the 1º('s?) circuit(s). Well, I can accept those expensive VFD-pumps in the cooling condensing circuits to the cooling-towers, because the atmospheric conditions can change a lot, as well.
- On contrary, it makes sense (at least to me) if we have VFD-pumps for the secondary/distribuition circuits in order to respond to the variable cooling loads.
- ...
zzzo
RE: Sequencing VSD and constant speed chillers
On the secondary side the system operated with 1 VSD chiller on all the time, to handle the in-between loads. The CVs would fire up one at a time once the load began to get beyond the 1st VSD, then the 2nd CV, then the 2nd VSD would come on-line if the load between the two VSDs was above their combined minimum.
Anyway, it's an interesting control scenario, but we split the primary side completely to eliminate potential hazards, let alone confusing maintenance.
RE: Sequencing VSD and constant speed chillers
In order to get you familier with your situation I urge you to go to this web site:http://www.automatedbuildings.com/ click on Tom Hartman and read his articles on All-Variable Speed Centrifugal Chiller Plants: Can We Make Our Plants More Efficient? Why the sudden change in attitude toward variable speed? and the 2 above it.Hope this helps
Roger
RE: Sequencing VSD and constant speed chillers
I tried to acess to the site http://www.automatedbuildings.com/,
and I was no able to reach it. Can you confirm that reference you gave?
Thank you!
zzzo
RE: Sequencing VSD and constant speed chillers
Click on the link in your own post.
Eng-Tips.com : Solving your problems before you get them.
RE: Sequencing VSD and constant speed chillers
Roger
RE: Sequencing VSD and constant speed chillers
It has worked this time!
Thank you!
Nice weekend to the Forum!
zzzo