Study of a new environmental chamber design

The present study develops an environmental chamber for temperature and humidity control (THCS) in which the condenser is divided into two parts. By properly adjusting the fan speeds of the outer and inner condensers, an enclosed chamber can obtain net heating or cooling effect and the temperature and humidity can be directly controlled. The system dynamics of the THCS is first studied. The temperature response models, G11(s) and G12(s), are shown to be of a first order. The humidity response models, G21(s) and G22(s), are of second order with a zero. It is found that the multiple-input-multiple-output (MIMO) control system can be decoupled into a temperature and humidity control loops. A control system using a PI controller is designed and implemented on a PC with an 8051 microprocessor. It has experimentally been shown that the chamber temperature and humidity can be controlled to within ±0.1 °C and ±1% R.H., respectively. In the presence of a heat load disturbance, the controller can restore the THCS to operate at the setting values within a reasonable transient time.