An expert system has been developed to help diagnose operational problems with solar domestic hot water (SDHW) systems. The intended audience for this program is the novice and intermediate level solar service technician, the homeowner who has a SDHW system and a personal computer, and schools that offer courses in trouble-shooting solar systems. The sphere of interest, or domain of the program, called SDHWPROB (Solar Domestic Hot Water Problem), is the analysis of operational problems with active, two-tank, flat-plate collector systems that utilise 120-volt AC power for pumping and controls. The system types can be either recirculation, draindown, drainback, or closed-loop antifreeze. Rules covering more than 125 of the more commonly encountered problems have been encoded. During a consultation, the program draws from more than 200 available questions in order to arrive at a diagnosis. There are about 375 rules that govern the paths of logic that the program can follow. During a consultation session, the typical number of questions asked is about 12 to 18. Consultation times on a 6-bit personal computer require from about 2 to 20 minutes. The structure of the program is such that it can easily be expanded to include more solutions. Expansion of the program to include other types of SDHW system is also feasible.

KEYWORDS: expert systems, computer programs, solar water heating, domestic, microcomputers, monitoring, failure, operations.