First we develop a suitable method for determining the optimal size for a single pipe segment independent of any others. The method is general enough to allow for any set of economic or physical parameter values. In addition, any form of load management, i.e. temperature and/or flow modulation, can be accommodated by the integral form of the coefficients in the cost equation. We then present an example which shows a 17% savings in life cycle cost over a design based on a common rule-of-thumb.; Following the treatment of the single independent pipe we study the heat consumer and the effect he has on the piping system. We develop a new model for the consumer's heat exchanger which uses the geometric mean temperature difference as an approximation for the logarithmic mean temperature difference. We integrate our new consumer model into our previous single pipe model and for a sample case determine its effect.; For systems with multiple pipes and consumers we first develop the constraints and subsequently our general solution strategy. The method makes use of the solution to the unconstrained problem as a starting point for the constrained solution. Monotonicity analysis is then used to prove activity of some of the constraints, and thus simplify the problem. Finally, the branch-and-bound technique is shown to be suitable for finding a design with discrete values for all the pipe diameters. A simple example is provided. In addition, a method is also demonstrated for further refinement of the pipe network to eliminate excessive throttling losses in the consumer's control valves.; We feel that the method developed is feasible for use in designing the piping networks for district heating systems of moderate size. The major advantage of the method developed here is felt to be its flexibility to accommodate any set of economic and physical parameters and operating strategy. In addition, it is felt that the approximations, where used, are much more suitable than some made in the past.
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