Variable-speed drives (VSD) offer many advantages in a heating, ventilating, and air-conditioning (HVAC) system. However, they are seldom used with centrifugal chiller systems. One of the reasons for the low number of VSDs in chiller systems is unfamiliarity with these systems. This research project was initiated to establish a base of accurate and detailed information for building owners and HVAC consultants to realize the benefits of VSDs. A 200 hp variable-speed drive was retrofitted to a 615 kW (175 ton) centrifugal chiller and monitored for one cooling season. Results show that VSD retrofits do work in HVAC centrifugal chillers. The VSD operated without problems during the test period and successfully met the air-conditioning requirements of the building. Energy savings are estimated to be approximately 41% at this particular site. The power quality effects also were studied and do not appear to be a concern. The total harmonic distortion is less than 2.5%.

Units: Dual