In-Situ Resistance Coefficient Curve and Experimental Analysis of a Virtual Chilled Water Flow Meter at Air Handling Unit Level

Abstract

In this paper, a virtual Air handling unit (AHU) level water flow meter using a control valve as a measurement device is experimentally validated through two different sizes of control valves on cooling coils. The flow through the valve is indirectly calculated using in-situ valve resistance coefficient curve, differential pressure over both the valve and its associated coil and valve stem positions. It was concluded in previous studies that the in-situ valve resistance coefficient curve is critical for determining the accuracy of the virtual valve flow meter. In this paper, an experimental approach and a theoretical approach of obtaining the in-situ valve resistance coefficient curve are introduced and as a result, accuracy of the virtual valve flow meters, using two different sizes of control valves: a smaller valve with design water flow rate of 25GPM and a larger valve with design water flow rate of 300GPM, is compared with an ultrasonic meter. The comparison show less than 4% of error over the full measurement range.