A chiller is used to cool products, machinery and factory equipment to a comfortable temperature. A variety of different types are available to meet specific cooling needs. They are a key component in most facility cooling systems, but can be a significant energy user if not properly managed.
Chiller efficiency has improved over the years due to advances in controls and refrigerants. However, a comprehensive preventive maintenance (PM) plan remains the best way to maximize chiller performance and efficiency.
There are several ways to improve a building’s chiller efficiency, including replacing an air-cooled unit with a water-cooled one, upgrading pumps, variable-frequency drives or piping layouts. Some of these improvements might reduce system energy use by as much as 20%.
A chiller operates by transferring heat from the equipment it is cooling to ambient air, according to the second law of thermodynamics. A chiller consists of an evaporator, condenser and compressor. Water-cooled chillers use a primary return water loop to preheat the refrigerant before it goes through the evaporator, while air-cooled chillers use fans to circulate outside air through the condenser. The condenser removes the heat from the chiller (remember that hot vapor turns to cold liquid) and then expells it into the atmosphere.
Centralized cooling systems often have multiple chillers that operate in parallel to meet various cooling load requirements. The energy performance of these chillers — measured as the coefficient of performance (COP) — varies hourly, depending on the temperature of the heat rejection medium, ambient conditions and chiller operating load. Austin and Kaya developed methods to evaluate optimum chiller loading points using cost-versus-load characteristics curves. chillers