Industrial Chilled Water system configuration

[dljtechnical]

Hi I'm looking for any recommendations on possible reconfiguration of our plant chilled water system.  We are currently using a 50HP Taco 1038B 4"x5"x13.3" impeller 750gpm pump with a redundant (identical) pump plumbed in parallel as a backup.  The system is "semi" closed-loop with a pit that the pumps draw out of, into the chiller(s), to the plant, and then drains back to the pit.  I say semi because there is a small portion of the plant that drains to the city sewer, so we do have a makeup supply controlled by a float in the pit.  We generally are pumping 400-500gpm with the entire plant running and the pump running full speed, 24/7.  The way we regulate pressure to approx. 60psi is with a bypass to the pit, located shortly downstream from the pumps, controlled by a manual butterfly valve.  We are also planning to add filtration between the pumps and the chillers.

Can you recommend a configuration with CSV's that would allow the backup pump to operate automatically as needed, as well as eliminate the need to adjust the bypass valve to regulate pressure.  I'm not sure if we can get away from using the bypass completely, since our chiller needs a minimum amount of load (high enough temp and flow) to operate.

Thank you

[Cary Austin]

We have done a lot of chillers over the years.  Put a 6" Cycle Stop Valve on the discharge of each pump and set it to maintain 60 PSI constant on the system.  The CSV will regulate the flow from the pump from 5 GPM to 750 GPM, maintaining 60 PSI constant on the system.  As the flow from the pump decreases, the amps or power consumed will also decrease.  This will work better and save a lot of money on energy compared to dumping the excess with a pressure relief valve.

A small 40 gallon pressure tank after the two pump manifold together can have two pressure switches.  These switches can be staggered so the secondary pump comes on when needed and goes off when not needed.  A good set up would be to run the CSV on the primary pump at 65 PSI with a 65/70 pressure switch setting.  If flow never get below 5 GPM this pump will never shut off.  When more water is needed the secondary pump will have a 60/65 pressure switch setting and the CSV will hold 60 PSI constant.  The CSV on the secondary pump will add what extra water is needed over the 750 GPM the first pump is producing (755 to 1500 GPM).  When less than 750 GPM is being used the CSV on the first pump will build the pressure to 65 PSI, which is what shuts off the secondary pump.

You can use a regular ball valve to bleed water from the system as needed.  The system would work fine without bleeding any water.  But you can bleed as much as you want as long as there is sufficient make up water added.