Variable Flow Chiller Water System

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Permalink Reply by Mark Mimier on January 14, 2009 at 9:37pm

In the past we have always discouraged variable flow thru the chiller evaporator which can cause the evap flow switch to trip or surging in low load conditions. But according to Trane, if it's done right they dont have a problem with it. see acticle in link:
http://www.trane.com/commercial/library/vol31_4/index.asp

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Permalink Reply by Chillerman on January 14, 2009 at 10:10pm

Hi Antonio,
Are you dealing with the system that uses a variable flow on the primary system, i knw something about it but never been involved to that type of system before, i usually work with decoupler system with a variable flow on the secondary side. I added this topic, actually a copy of ASHRAE journal (check forum ) about variable flow system. I appreciate if you can share with us some of the updates on this one.

Cheers

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Permalink Reply by Chillerman on January 14, 2009 at 10:30pm

That system works well i guess on screws and recips, if the instrumentation is properly fine tuned..proper sequencing of the equipment rely on the 3rd party automation right? and if you are using a multiple centrifugal chiller, if the flow rate drops faster than the unloading timing of the chiller, and the lift goes up beyond the surge line, i guess a centrifugal surges.

I'd like to learn more about that, very interesting.

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Permalink Reply by Chillerman on January 14, 2009 at 11:41pm

You are right Mark the flow switch reacts and trips the chiller unless the flow switch is wired into the 3rd party control system, and i guess they have an algorithm designed for that.

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Permalink Reply by Sotes on January 15, 2009 at 8:02pm

The first chilled water system was the "constant-volume single loop system." In this configuration, water flows through the chiller evaporator and air handling units in a single loop. Water gpm is constant.

When variable speed pumps became available, the "primary-secondary" configuration came into place. The "secondary loop" is driven by variable speed pump so gpm could be varied depending on the cooling demand at the AHUs. This configuration saves energy because only the "primary pumps" run constantly and could be sized down to the minimum gpm requirement that could prevent adverse effect to the chiller/s. The "secondary pumps", on the other hand, could be slowed down when cooling demand is low, thus saving energy.

Lately, variable speed compressors became available. Energy managers, engineers, and designers took advantage of this technology by using variable pumps on the primary loop in order to save energy. Again, the idea is to reduce pumping power when load is low. There had been proposals to remove the secondary loop and revive the single loop system, only this time, it would be variable flow.

Source: conducted dozens of energy studies on chilled water systems.

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Permalink Reply by Jun A. on February 22, 2009 at 3:47am

With regards to Variable Primary Pump System, do you mean Variable Primary Flow?
Well if you do, you may also read the article "Varying Views on Variable-Primary Flow.
See the link below.

http://www.engr.psu.edu/ae/iec/publications/articles/varying_views.pdf

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