COMPARATIVE LIFE-CYCLE COST-ANALYSIS OF UNDERGROUND HEAT DISTRIBUTION-SYSTEMS

An analytical model was developed to compare the life-cycle costs of t wo types of underground heat distribution systems: directly buried con duits and concrete trench installations. The costs of initial construc tion, routine maintenance, operation, repair, and replacement are repr esented in the model. Comparisons are made to explore the influence of failure rates, heat loss assumptions, the discount rate, and the poli cy on partial section replacement. Failure rate estimates are obtained from the literature and also from survey results obtained by the U.S. Army. Life-cycle cost computations indicate that, when initial constr uction costs are the same, concrete trench installations have a cost a dvantage of $18-$42 per foot over buried steel conduit when other cost components are taken into account over a 25-year lifetime. The cost a dvantage of concrete trench over fiberglass reinforcement plastic (FRP ) buried systems is $32-$133 per foot. The variation in the cost advan tage reflects the variation in the estimate of the failure rate for bu ried steel and FRP systems. Routine maintenance was crucial for the bu ried systems to avoid dramatic increases in operation and replacement costs that would make the cost advantage of concrete trench installati on even greater than stated above. In contrast, the low incidence of f ailure associated with concrete trench systems made their life-cycle c osts relatively insensitive to maintenance policy.