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


Chiller VFD installation

Chiller VFD installation

Chiller VFD installation

All you HVAC engineers! Question? Can a VFD or soft start controller be installed on a Rotary Liquid Chiller? I have received conflicting info regarding this action. We are trying to reduce the initial elec. demand on startup. Any ideas?


RE: Chiller VFD installation


First of all, if your system is not a primary/secondary system, I am not 100% convinced variable flow through a chiller is all that great.  I know that some manufacturers say that it can work with their chillers, but some manufacturers still don't believe in it.  The only place I have seen VFD's on pumps work is on a primary/secondary system (or as ASHRAE calls it now, a "decoupled system").

My personal opinion is that water flow should be constant through the chillers for stable control.  A chiller typically controls discharge water temperature, and the heat exchange rate in the evaporator is directly related to flow.  Therefore, your system is trying to control too many variables.  Control becomes unstable, and if your system is even semi-critical, unreliable.

With a decoupled system, your chiller circulating pumps are lower head pumps and therefore have smaller horsepower requirements.  The main system pumps are then VFD.  This reduces starting hp for the chiller pumps and gives you lower operating hp's on the delivery side.  This way the chillers only have to control leaving water temperature with a constant flow.

Not sure what your system is or how it operates, but hopefully this gives you some insight as to some of your choices.  Maybe a little more detail on the system could help to get more detailed answers.

RE: Chiller VFD installation

We have scheduled VFD on chillers and pumps for soft start.
It does help. The other $ saver is not to start the pumps and chiller all at the same time

RE: Chiller VFD installation

We are about to upgrade our Mcquay Screw Drive Chillers with "soft Start" kits from the manufacturer as an upgrade due to previous compressor failure after starting up with liquid at the intakes. THEY claim this will curb the problem, it has only been out for about a year from Mcquay but with positive results, howeve it is noted certain internal compressor modifications have to done as well.

RE: Chiller VFD installation

The chiller in question is a Trane model RHTB 300 ton unit 274 KW, 480 v


RE: Chiller VFD installation

I have a site w/ 4 rthb 250  that have soft sart and have had no problems with them, they are cutler hammer and were factory installed.I believe they are availible as after maket products through your local trane rep.As far as vfd`s, I don`t think they are availible for screw chillers at this time just centrifugals.  

RE: Chiller VFD installation

Thanks, David.

As far as I have been able to determine York is the only manufacturer that has taken on solid state controls for screw chillers. I have been told that due to the pressure imbalances that can exist in a screw chiller (front to rear) it is a difficult design challenge to achieve equal pressure before starting. I was just looking for a way to reduce the amount of inrush current needed as we are on a demand meter system. I have been told a "hot gas bypass" can run the chiller in a constant state at a limited load. It is more expensive for us to start the unit than it is to run it.


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


White Paper - Understanding Critical Specifications for Dynamic Metrology Applications
Different types of metrology have different critical specifications to consider when determining which actuator technology to use. This white paper goes into detail on the demands of dynamic metrology applications as they apply to the selection of precision linear motion control components and systems. In addition, the relevance of Moore's Law is examined in the context of the industry. Download Now
White Paper - Permanent Non-Welded and Cold Bent Piping Solutions
Commonly used welded piping connections come with skilled labor, validation, inspection, and long commissioning times, as well as the workplace hazards associated with welding. Non-welded permanent mechanically attached fittings offer a viable alternative to welded piping systems that greatly reduces the time to commission piping systems through reductions in many of the time-consuming steps required in welding. Download Now
White Paper - Take Mobile Hydraulic Systems to a New Level
The introduction of digital ecosystems connecting electronic control hardware and software to the Cloud is catalyzing a new era of mobile machine and equipment design innovation. This is enabling OEMs across industries to develop customized solutions that digitally integrate hydraulic and machine controls with the Internet of Things (IoT). Download Now
White Paper - The Evolving Landscape of Commercial Battery-Powered Trucks
What’s driving the evolving landscape of truck electrification? What are the barriers, motivators and strategies for accelerating the electric transition? What insights and resources are available for today’s design engineers working to achieve industry disruption and evolution? For answers to these and other pertinent questions, read this white paper. Download Now

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