Abstract
Factors influencing the steady state heat transfers from a horizontal hot-water (or to a chilled-water) pipeline within a relatively cold (or hot) horizontal rectangular trench filled with either (a) atmospheric pressure air or (b) hollow plastic spheres or Lytag in order to simulate a buried district heating (or cooling) distribution network have been considered. A series of experimental measurements as well as finite element and finite difference predictive analyses revealed the optimal configuration, for each set of considered circumstances, is that which achieves the minimum steady state rate of heat exchange between the supply pipes and their surroundings under the considered conditions. The recommended configuration for both the district heating and cooling systems is to place the two pipelines one above the other in the trench, the hotter pipe being the upper member. This differs radically from the arrangement of the pipelines traditionally adopted in district heating or district cooling designs (the pipes being placed side by side), and its adoption leads to at least a 4 per cent improvement in energy thrift. Such a saving can be achieved with no extra constructional costs, and the savings should be significant over the lifetime of either the district heating or cooling system.
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