|Chao, Kuanglin - Kevin Chao|
Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2000
Publication Date: N/A
Citation: Interpretive Summary: In enclosed livestock facilities and greenhouses, a ventilation control system uses a series of discrete stages of ventilation and heating to add air conditioning capacity. Such a staged control system is highly nonlinear, not readily analyzed with classical control techniques, and presents some problems in field operation. For example, in larger facilities, there has been a tendency toward a greater number of stages of ventilation. This means that either a larger deviation from set point is accepted for significant periods of operation, or temperature differentials between stages must be reduced. In the former case, there is a risk of animal suffering from heat stress. In the latter case, there is a limit to how small the differentials can be made without excessive switching of large ventilation loads. This research is conducted to design an intelligent control strategy for agricultural ventilation systems. A fuzzy logic controller was designed to provide an alternative to conventional stage controllers. By suitable selection of input/output linguistic variables and a rule base, a broad range of desired control outcomes was achieved. Intelligent features include user-specified overall control "tightness" analogous to a control range, optional close adherence to set point conditions, and the ability to explicitly set the trade-off between energy costs and interior environment. The design illustrates an original approach, which can be applied to the new generation of environmental control systems. The design examples present in this paper can be useful to the environmental control designers.
Technical Abstract: Design parameters are identified for fuzzy-based control of staged ventilation systems. A simple non-steady state heat balance is used in conjunction with a building simulation model, and coupled with a model for the control system, to simulate performance. Difficulties with implementation of conventional staged ventilation control, and the proposed fuzzy inference technique, arise because of the discontinuous nature of these highly nonlinear systems. Comparisons between the new fuzzy stage controller and conventional staged control are made. Effects of varying the identified design parameters for the fuzzy stage controller, including different degrees of control precision and energy use, effect of rule base complexity, and the rate of change of house temperature are discussed. The fuzzy logic controller was able to keep the root-mean-square error to 1.0 to 2.7oC, depending on different energy use settings. Results indicate that existing staged ventilation control systems, which utilize microprocessors could realize significantly enhanced control flexibility by a simple software modification to incorporate the fuzzy staged controller method.