Concerning variable primary flow system!

[ananinii]

If I would design the variable primary flow system for hi-rise office building based on maximum cooling load 4000 ton and the chiller plant comprises of 4 sets of 1000 ton chiller, 2 sets of 500 ton chiller, 4 sets of 2400 gpm chilled water pump and 2 sets of 1200 gpm chilled water pump. All chilled water pumps will be connected to main header before distributing water to each chiller. I am concerning whether different chiller capacity may cause problems! What is your advices or any related articles to come up with ideas? By the way, my country has no heating.

 

[imok2]

This may be of some help:

http://www.automatedbuildings.com/frame_resources.htm

 

[south4scuba]

I have some limited experience with variable flow primary systems. I am not an expert.

I assume you know that the control sequence is very important for VFP systems. You have to carefully control the CHW flow when you stage chillers on and off.

In your case you seem to have enough chillers (4 x 1000 ton and 2 x 500 ton) that staging of the chillers can be achieved with minimal impact. I have mostly read of problems when capacity is added or dropped in 50% increments (such as systems with only two chillers).

Write a very good control sequence and allow for dead bands while system stabilizes and you should be OK.

 

[KiwiMace]

Provided that the pumps are dedicated to the respective chillers, there shouldn't be any fundamental problems. I take it that you are connecting all the pump inlets to a return header and piping from each pump to the equivalent chiller.

Design your system so that it can be balanced hydronically.

 

[imok2]

http://www.automatedbuildings.com/frame_resources.htm

When you get to the above web page scroll down to Thomas Hartman's article on " All-Variable Speed Chilled Water Distribution Systems: Optimizing Distribution Efficiency" from April 02. Notice he has other articles on this subject

 

[ananinii]

Thanks you all!