Temperature control for a vehicle climate chamber using chilled water system

The effective temperature control of a vehicle climate chamber was investigated. The temperature was regulated by electrical heater power and valve opening in the chilled water system. Cooling load and water flow rate through the adjusting valve were studied based on the distributed parameter model developed in a previous article. In order to ensure the flow capacity and increase linearity between the cooling side control output and the air temperature, two equal percentage valves were applied. The climate chamber has characteristics of large thermal inertia and non-linearity. Performance of a proportional-integral-derivative (PID) controller used in the existing system was not satisfactory, so a fuzzy self-tuning PID controller was designed. The PID gains were tuned online according to temperature error, error change rate, and air velocity using fuzzy logic. Model predictions showed that the fuzzy PID control stabilized the air temperature in a shorter time and with smaller overshoot and undershoot. The time averaged temperature error was reduced from 0.37 °C to 0.09 °C in the high temperature test, and that of the low temperature test was reduced from 0.42 °C to 0.18 °C.