×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Variable flow vs. Constant flow through centrifugal chillers

Variable flow vs. Constant flow through centrifugal chillers

Variable flow vs. Constant flow through centrifugal chillers

(OP)
I need some opinions on variable flow vs. constant flow through centrifugal chillers.  Trane says they can do it, York prefers not to.  The Tranes would use R123 and the Yorks would use R134A.  Our hydraulic analysis says that variable flow will work, however, we are developing some conflict as we get closer to construction.

RE: Variable flow vs. Constant flow through centrifugal chillers

Constant flow has worked for years.
We have done a varable flow job and found that we cound only vary the flow 25% and keep the chillers on-line. It was hardly worth the design time for variable flow.
R123 is a better refrigerant for variable flow but the market in moving toward R134a.

RE: Variable flow vs. Constant flow through centrifugal chillers

jad747
Are you referring to variable refrigerant flow or variable flow of chill water through the evaporator or variable flow of cooling water through the condenser.  I am working on a system that reduces overall electrical power requirements by reducing the water flow to the condenser and am interested in finding some other views on the matter.

RE: Variable flow vs. Constant flow through centrifugal chillers

I use a Chilled water pump on VFD, to augment my chilled water system, and it seems to work pretty well. Over the years, systemic changes to the building have seen an increase of fan coil unit use (they are practically everywhere!), and this was putting our system out of specification (at some point, operator would have to put on another chiller, even though from historical perspective in the building, you didn't need to). The VFD pump running with the constant speed pump, would provide enough GPM to fulfill capacity needs, without putting another chiller on. I prefer to run the VFD in manual so I have tighter control of the system, but the auto mode functions fine, as well.

RE: Variable flow vs. Constant flow through centrifugal chillers

(OP)
I think you have to look at your system to see if its worth while using variable flow. It seems to me the whole basis is to save energy on the pump side.  If you get a 25% saving in flow rate then this equates to a pump power saving in the ratio of its cube.  This is pretty substantial savings. There is a newsletter on the trane web site that goes into it, but it does say only to use variable flow if close control is not required.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources