Case Study: WSU Campus Chilled Water System Redesign for Operational Improvements & Energy Savings

During the 2023-2025 biennium, Millig worked closely with the WSU Pullman project team to develop and implement an operational redesign and expansion of the campus’s chilled water system. The issues and strategies identified for the Pullman Campus applicable to any water-cooled chilled water system.

WSU’s Pullman campus consists of 8M sqft of facilities served by four chilled water plants with nine individual chillers with a combined capacity of 12,800 tons of cooling. A 2M gallon thermal energy storage (TES) system was intended to store chilled water generated overnight, for deployment during afternoon peak loads.

The following operational issues were uncovered:
– System pressure issues in the distribution network meant that the TES was discharged primarily to satisfy chilled water demand in the loop and deployment of the stored chilled water did not coincide with the peak need.
– Chillers were staged on and off to supplement the TES tank.
– Chillers were experiencing flow control issues between their primary and secondary loops, causing significant levels of return water to be bypassed around the chillers and mix with supply water.
– The chillers were staged on based on their size and location, not based on their individual operating characteristics or efficiencies.
– There was no high-efficiency winter-baseload chiller.

These issues led to a lack of cooling capacity during high temperatures, leading to significant load shedding in the summer, as well as excessively high year-round energy use.

Identifying and addressing these issues required extensive due diligence and the generation of an innovative 8,760-hour digital model of the operation of the entire system using actual performance curves, trend data, and chilled water metering data.

All new controls language and an open-source supervisory controls system were developed to optimize the operation of all chiller plants. Millig also designed a new, highly efficient 500-ton chiller that also has the ability to operate at very low condenser water temperatures to provide additional capacity in the summer and serve as the winter baseload chiller.

The Results:
– Reduction of system-wide energy consumption by 22%
– $216,377 of annual utility cost savings
-$641,117 utility incentive
– Increased the cooling capacity on hot days and no more load-shedding
– Completed for a cost of $1.77M with a simple payback of 5.2 years