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Heat-transfer calculation methods for underground piping systems differ from those for aboveground systems because of the earth envelope and its moisture content, and the thermal effect of each pipe on adjacent pipes through the earth heat sink. The calculation methods are not well known and are scattered through the literature, usually with a minimum of theory and detail. This paper reviews the choice of ground thermal conductivities and temperatures so important to accurate results. It also gives simple, once-through analytical methods for one-pipe and two-pipe systems along with basics for a currently used iterative computer program for systems of two pipes or more. The paper does not cover theory or derivations, but lists references for this information.
Comparisons of the results of each method on specific problems indicate reasonable results of analytical methods under many conditions, but also show that the computerized iterative results are always best.
thermal transfer, underground piping, calculation methods, computer programming, hand calculator programs
Market manager, Mechanical Piping Systems, Pipe Division, Johns-Manville Sales Corp., Denver, Colo.