The study reported here was conducted in an effort to obtain data for comparing the combined owning and operating costs of two different types of air-conditioning systems in two elementary schools. Both schools were built during 1969-70 in the same geographical area along the southeast coast of Florida and are also served by the same electric utility company. They have been exposed to the same seasonal weather changes, building conditions, and economic impact. Since these schools are also similar in educational requirements and architectural planning, although completely dissimilar in air-conditioning or mechanical design concepts, a basis was established for a realistic, meaningful, and valid comparison. To carry out the study (1) energy consumption of equipment was metered, (2) replacement costs because of differences in longevity of equipment were adjusted, (3) first costs because of differences in design and owner requirements were adjusted, (4) "money costs" based on available funding options over an extended period of time were considered, and (5) maintenance costs were applied to operating costs. Study results show that it is more economical to own and operate the roof-mounted, multizoned, unitary type air-conditioning system than to own and operate the central, chilled water, terminal heat/reheat, type. (Author)