The diagnosis method using qualitative reasoning is one of effective techniques for diagnoses of complicated systems such as air conditioning systems of buildings. In this technique, the target system is modeled qualitatively, and possible behaviours of the target model are generated by the qualitative reasoning. By comparing the results of reasoning with the real measured values, a part in failure is identified.
However, the qualitative reasoning has its short-comings. That is, the possible behaviours of the model tend to increase enormously because of ambiguity of qualitative reasoning.
To solve this problem, we propose the stochastic qualitative reasoning method in this paper. In this method, the existence probability is introduced. The states that have small probability are eliminated through the process of qualitative reasoning. Moreover the agreement degrees between results of reasoning and real measured values are calculated by existence probability of each states, so the cause of failure is identified in justifiable order.
We have applied this method to fault diagnosis of a building air conditioning system practically and confirmed its effectiveness.
