District-cooling distribution network: Optimal configuration of a double-pipe system in a rectangular trench

The optimal configuration, i.e. that which achieves the minimum steady-state rate of heat gain by the (colder) supply pipe for the considered conditions, has been determined experimentally. By using the displacement ratios of the two pipes as the experimental variables, the optimal configuration of the (colder) supply and (warmer) return pipes was deduced to occur for displacement ratios of 0·67 and -0·08, respectively, i.e. with the supply pipe in the lower region of the atmospheric-pressure air-filled relatively hot trench and the return pipe vertically above it, both symmetrically placed with respect to the side walls. This optimal configuration differs significantly from the traditional side-by-side arrangement of district-cooling pipelines and should prompt designers to become more aware of the prospective energy and financial savings which be achieved.