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A B S T R A C Twhich contain the main variable parameter. thus accomplishing adtive adjustment of the threshold level.District Beating and Cmling (DE) facilities produce heat in the lump and supply it for the heating and cooling of districts. A fault diagnosis system has been developed to enable DHC facilities to O B J E C T O F D I A G N O S I Sprovide stable heat supplies and this system has been proved using is a system diagram of the Hakozaki plant for the object of real facilities.diagnosis. These facilities used river water for heat rejectionTo minimize cost. the tvo heat pumps mainly use electric pover at Fig.1 and heat absorption for heat pump for the first time in Japan. ( I 'DHC facilities are provided for public utility. Their purposes are to save energy, to maintain the environment. and to equalize electric pover consumption etc.. They are compased of heat pumps for producing heat, storage tanks for storing hot and chilled rater. rater pumps for supplying buildings vith hot and chilled water. and di s t r i bu t ion pipes.The cooling capability of heat pump, and the condenser pressure are varied by the temperature and flow rate of the cooling water. The supply pumps operating at a particular time and their flow rate are also varied according to the load. Therefore, high sensitivity can not be realized by fault monitoring vith a fixed threshold. making it difficult to detect a malfunction early.night. Of the each four chilled-rater and hot-water pumps, three-are constarst speed pumps which are controlled stepwise. and the other is an inverter pump which strictly controls the supply pressure.Many kinds of faults exist and the requirements of fault diagnosis 1) Check mainly the process. but additionally the machine are as follows.character istks.-2) Predict the fault based on the detected symptom. 3) Guide the administration according to the cause and seriousness of the fault. From this viewpoint. we diagnosed the causes of reduced capability. pressure malfunction. etc., and judged their seriousness.This nev fault diagnosis system uses a causeeffect tree diagraa to find the causes of faults, and introduces.an analytical method for judging the malfunction rate.

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