9 Water Chillers in Turndown: Calculating Time Required for a Chiller to Draw Down the Temperature of an Insulated Closed Water Reservoir to a Relatively Low Value (Near Chiller Minimum Discharge Ability)

Modern packaged water chillers come equipped with a variety of talented microprocessor and/or PC-based internal controllers and system controls, which can be interfaced with building automation systems and other networks quite easily.

These controls, in conjunction with modern, throttleable-by-inlet-vane-or-other-means refrigerant compressors (or their equivalent) such as the high-efficiency centrifugals, scroll-types and screw machines, make something not only possible but easy and relatively efficient, which was previously difficult and risky: operation at a heat transfer rate much smaller than the chiller's maximum capacity.

Commonly called “turndown,” or “part-load operation”, the ability of a chiller to run continuously at only a small fraction of its design capacity is very important to the system designer. Precision HVAC systems often need to maintain tight control of room air dry bulb temperature and humidity. The HVAC system control must be continuous and simultaneous, able to adapt rapidly and effectively to changes over a wide range of air-cooling and moisture-removal loadings.