A building tune-up of the Health and Human Science (HHS) facility at Western Carolina University (WCU), which included air economizing and chiller optimization—cut energy usage by 15 percent, slashed chiller starts by 77 percent and earned an ROI of 127 percent.
In 2008 the university installed a 600-ton chiller sized to accommodate three new buildings on the new Millenium Campus. Because of the recession, only one facility—the HHS Building—was completed. During the building tune-up the team realized the chiller, which serves only the HHS building, was running for only 30 minutes each time it started. According to the manufacturer, at least two-hour runs per start are optimal; less than that creates excessive wear and tear on the equipment.
The pull-down demand limit on the chiller was set for 60% for 15 minutes, meaning that the chiller ran at 400 tons of capacity for 15 minutes and then switched into full 600 tons. By changing the demand limit to 30% for the first 240 minutes, the team was able to reduce demand by 30%. This 80 kWh reduction at $12/kWh saved $960 per month.
By improving this economizer logic, chiller starts were reduced from 488 (November 2016 – March 2017) to 112 (November 2017 to April 2021), which is a 77% reduction.
The tune-up also revealed that the economizer wasn’t working as expected. The team discovered that one of the three criteria to economize was that there could be no calls for heating. That meant that if there was even one call for heating amongst 40 zones, the system would not economize and would use the mechanical chiller instead. By removing that third criteria, WCU was able to make more use of free, cool, comfortable outside air instead of mechanical cooling whenever outside temperatures were sufficiently cool and dry.