Experimental Performance Investigation of Cooling or Heating Coil Valves and Their Impact on Temperature Controls

Hysteresis and nonlinearity exist in most valves that are utilized in building HVAC systems, such as in cooling or heating coil valves. The hysteresis mainly comes from the manufacturing clearance in an actuator gearbox and nonlinearity in the variation of the regulated flow with respect to control signal originates from valve design. The combination of valve hysteresis and nonlinearity poses significant difficulties in obtaining satisfactory control performance when utilizing a conventional PI controller. This paper presents experimental testing results for a set of valves in an operating HVAC system serving an office building. The test valves include VAV reheat coil and AHU cooling coil valves provided by two mainstream manufacturers. Open-loop experiments were carried out that are used to analyze valve performance in terms of hysteresis and nonlinearity. Valve closed-loop performance was also investigated and the results showed that valves with significant hysteresis and nonlinear characteristics lead to unsatisfactory supply air or zone air temperature controls with severe temperature oscillations and control chattering.