A Computer-Based Monitoring system to Maintain Optimum Air Temperature and Relative Humidity in Greenhouses” international journal of agriculture

ABSTRACT The present study is concerned with the control and monitoring of greenhouse air temperature, humidity, CO 2 provision and irrigation by means of simultaneous ventilation and enrichment. A computer-based control and monitoring system was designed and tested. A microcontroller receives data on greenhouse environment conditions from a number of sensors installed inside and outside and transfers the data to and from a PC via RS 232 port. Accordingly, it changes the state of greenhouse control devices, heaters, fans, etc., to reach the desired condition. Performance of the controller was evaluated by installing it in a greenhouse. For the uncontrolled experiment, it was found that the outside or ambient temperature was always less than the temperature inside the greenhouse. This is a further confirmation of true greenhouse effect. It was found that the rate of change within the greenhouse in the upper part i.e. near the plastic cover, was higher than that of the height of plant. The temperature in the greenhouse increases along the height of the greenhouse due to receiving solar incident radiation. During the temperature decrease, it was found that the heat exchanges are mostly occurring near the plastic cover. When the controller was put into operation, it was found that contrary to the previous case. This is partly due to the use of re-circulating fan with an attached perforated polyethylene tube in guiding the air toward the plant root zone. In an attempt to control both the temperature and humidity inside the greenhouse fair results were obtained. The system response for temperature control was satisfactory, about 10 minutes. However, the time constant of mist and fog system was rather long, about 30 min, in reaching to the desired humidity