Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/22/1999
Publication Date: N/A
Citation: Interpretive Summary: Our greenhouse control system used traditional pneumatic control technology for temperature control. This technology responds only to the difference between the set-point temperature and the current actual temperature. The greenhouse operator had difficulty adjusting the pneumatic-electric (PE) switches that turn on the various cooling and heating devices such as fans, pumps, windows, fresh air intakes, and steam valves. The optimum settings were very different depending on current conditions (i.e. whether it was a cloudy cool day or a sunny warm day). We needed a system that could automatically adjust to the current weather conditions. We developed a personal computer based system that used the existing heating and cooling devices and used the existing pneumatic system for a backup. We used fuzzy control to incorporate the practical experience of the greenhouse operator into the control program that varied its response base on the current heating or cooling load on the greenhouse. Initial test results indicate the personal computer system will provide accurate control and will be simpler to operate. Further tests with be required to document the expected potential energy savings with the new system. Greenhouse system designers, scientists and growers will benefit from what we have learned in the design experience. Leveraging personal computer technology can provide economical solutions for precise and flexible control systems.
Technical Abstract: We developed a Personal Computer (PC) based control system to upgrade an existing pneumatically controlled greenhouse. The objectives were to maximize control precision and energy savings, and to increase operator flexibility. The goal was to create a controller that could adapt to the current heating or cooling load on the greenhouse. This system requirement and the resulting fuzzy controllers incorporated into the new system were based on the request and practical knowledge of the operator. The resulting system combined data acquisition, a state transition process for discrete control, and simple fuzzy controllers for analog control outputs. We describe the system hardware and software and preliminary test results.