Variable flow chilled water system - Question? 3

[HamBurger]

Dear fellow sloggers,

I am designing a variable flow chilled water system with four cenrifugal chillers, one dedicated constant volume pump for each chiller, and two sets of three parallel pumps (serving two diffent buildings).

As you know, there must be a common pipe between the return water and the common supply (chillers), before the secondary variable volume pump takeoffs. The position of the common pipe will affect the method of unloading on the chillers.

Try and picture the following:

1. Four chillers in parallel, each with it's own constant volume pump, discharging into a common header pipe.
2. One common return from two independant buildings with takeoffs to each chiller.
3. Two variable volume pump sets consisting of 2 parallel pumps each, supplying water to the two buildings.

My question is this:

1. Can the secondary pump systems (variable flow) be connected anywhere in the common header i.e. even between chillers or should the pumps be positioned at the end of the header line?
2. Can a common pipe between supply and return be introduced on both sides of the chilled water headers or should they be combined first and then taken to the chillers?

Hope this makes sense......

Your feedback would really be appreciated.

Thanks,

Hamburger

 

[remp]

firstly you need to positin a bypass line at the end of the 4 chillers between the flow and return headerso as to seperate the primary from the secondard side. This bypass line should have a flow metre so as to operate the staging of the chillers on the primary side depending on flow direction and quantity.
The secondary pumps should be located off the primary header behound all the chillers and the bypass, otherwise you are letting yourself i for a lot of trouble.Deffinatly dont take the secondary pumps off between the 4 sets of chillers.

 

[SAK9]

The chillers should connect to a common header(suction and discharge).The bypass line should be installed parallel to chiller.The by pass line can be sized for about one chiller's flow.If budget allows ,install a flow meter in the by pass line to turn on/ off chillers.

The secondary pump's suction line should be connected to discharge header after the bypass pipe T connection.The return line from the building loop will go into the chiller suction header before the bypass pipe T connection

A single common header is sufficient for the system.Try to keep the distribution loop delta 'T'higher than the production loop(chiller loop).This would keep the distribution loop flow rate less than the production loop flow rate and would ensure there is flow in the 'right direction'in the bypass pipe.

 

[imok2]

You might enjoy reading this article by Thomas Hartman

http://www.automatedbuildings.com/news/apr02/art/htmn/htmn.htm

 

[HamBurger]

Thank you for your contributions remp, SAK9 and imok2, I really appreciate it!

You re-affirmed my notions about this design and it is re-assuring that one can draw on the expertise of specialists in this wonderfull forum!

Thanks again.

Hamburger

 

[Rhonda2]

Looks like a lot of extra pumps. Why not consider variable primary flow instead?