Design and application of temperature and humidity control system for environmental chamber on the determination of VOC emission from furniture

Based on SIMATIC S7-200 series PLC, a temperature and humidity control system was designed for the determination of VOC emission from furniture in environmental chamber (EC), in order to improve the level of internal condition control in domestic products. The sectional control strategy was employed using the combination of the PID arithmetic provided by PLC, and fuzzy control method. Simultaneously, the transformation of relative humidity (RH) control in EC into one of the temperature controls in the water tank was realized by applying the dew-point humidity control theory. The temperature and RH control in EC were decoupled and stabilized after employing this method. The results showed that the accuracy for temperature and RH was ±0.4℃ and ±3% when the system was applied to a 1m3 EC, which met the requirements of domestic and foreign standards. This system has high-quality performance which can be applied to other scales of EC.