The most commonly used compressors are screw or centrifugal types, with an indirect central cooling system design. This means that secondary circuits are also installed, where the condenser is cooled via a seawater cooling circuit and the chilled water circuit (evaporator side) uses cold water to cool the air handling units.
Main benefits are the following:
- Installing VFDs on chilled water pumps and on the evaporator cooling side provides accurate control and energy consumption based on process demand. In most cases, the typical payback time is less than one year. On average, savings are between 30 – 40% of total power consumption.
- Using VFDs for supply and exhaust fans, rather than relying on inlet vanes and two-speed motors, generates energy savings in every case. The payback time is less than one year.
- In theory, installing a VFD on a centrifugal compressor can reduce power consumption by as much as 25%. This depends heavily on the chiller plant’s control strategy. The investment cost of a chiller upgrade is relatively high, generating a payback time of between 2 – 2.5 years.