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


Differential pressure switch

Differential pressure switch

Differential pressure switch

Hi ,

We are installing a primary/secondary chiller plant . As known , the secondary pumps must be variable speed type and its VFD is controlled by a differential pressure switch .

My problem is where i should install this DPS and what is the optimum pressure setpoint so teh system will work properly and efficiently .

Thank you .

Hassan Naim .

RE: Differential pressure switch

Hi Hassan,

I think you mean "differential pressure transmitter" instead of "differential pressure switch." You'll also need a controller (your VFD on the secondary pump(s) will probably have one built in).

Best place to put the dp transmitter is across the valve/coil combo that is physically the farthest from the pumps - or if you study the piping system, you may come up with a different worst-case coil. This way, you are controlling the secondary pumps to produce adequate pressure for the worst-case coil. Note that your transmitter goes across both the control valve and the coil, not just the coil.

Good luck with your project!

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Differential pressure switch

You'll find there are multiple answers that will end up giving you a system that works. But I would you should put the differential pressure (DP) sensor/transmitter (not switch) where your system has the most consumers that are representative of your typical system loads. Then go 2/3 down that supply/return pipe and put it there.

As for your pressure setpoint, you can't really know that for sure until the balancing contractor gets there. In theory it would match the pressure drop you calculated from your supply branch takeoff, through all the coil valving, through the coil itself, and back to your return branch takeoff. But calculation and actual don't always line up. As far what is optimal, without a complicated optimization strategy where you track control valve positions - you are looking for a target differential pressure that leaves your worst case control valve satisfied at 95-100% open.

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! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close