A general process engineering simulation program for a microcomputer is used to evaluate the response of a cooling system to changes in load, setpoint, and controller tuning parameters to better understand the control stability of a supply air cooling system used in the Mobile Windows Thermal Test (MoWiTT) Facility. A detailed system model is built out of standard components and is used to plot the steady state performance under different operating conditions. The response of the cooling coil output depends strongly on the transport delays. For a system with a linear control valve, the process gain of the cooling coil increases rapidly as the valve flow fraction decreases. A system that is stable at mid-range is shown to become marginally unstable at the low end of the control range. The  applications of both an equal percentage valve and reheat are shown to improve the control response of the system under low cooling load conditions.

Units: SI