Airside System–Type Prediction Enabled by Intelligent Pressure Independent Control Valves

Abstract

Low delta T syndrome, that is, the operation at low differences between supply and return chilled-water temperatures, increases the energy consumption of chilled-water systems. Numerous causes of low delta T lie at the cooling coils. As the load on the coil increases, more chilled water is sent through it. A point of saturation is reached when significant increases in chilled-water flow result in negligible increases in provided cooling power. The ability to recognize when such saturation is occurring and restrict flow in such situations is needed to combat low delta T. An intelligent pressure independent control valve attempts this by measuring and logging inlet and outlet water temperatures and water flow rates. Through nonlinear regression of measured coil data, a novel approach for the valve to predict saturation was developed and tested. The resulting curve fit was then used to predict whether a coil was operating in a constant- or variable-air-volume system. In total, 128 test coils over four climates and various system characteristics showed a 79.7% correct prediction rate.