Fuzzy logic controller design for staged heating and ventilating systems

Conventional stage controllers (CSC) for interior environment control of ag ricultural facilities are prevalent and well suited for slowly varying load s, smaller facilities with few stages of control, and in cases where "discr ete proportional control" is deemed adequate. Ad hoc implementation schemes for using the same CSC over a range in size of building heating and ventil ating systems, from one hearing and cooling stage to many are practiced in the industry. A fuzzy logic controller (FLC) was developed to satisfy a bro ad spectrum of installation sizes without any modification. Principles for designing an environment controller that can mimic CSC behavior over a broa d range of system size were applied. By adjusting a single additional input this controller provides users with a trade-off between energy use and con trol precision. Simulations were conducted using the same FLC in a greenhou se and a broiler house; these two examples were selected for their consider able difference in magnitude of energy transfer and loads. Disturbances inv estigated included: variations in outside temperature, internal heat load ( or solar load), and step changes in set point temperature. FLC system respo nses are compared with a representative CSC for stability, overshoot and me an square error from set point temperature. The FLC was able to keep the ro ot-mean-square errors to 1.0 to 4.0 degreesC, depending on different energy use settings. The FLC provided useful improvements in performance over a C SC, and is readily implemented in modem electronic controllers with floatin g point arithmetic capability.