Thermal storage in district heating systems

Large hot-water reservoirs can be very attractive components of medium-sized district heating systems as they offer a good means of uncoupling timewise demand and occurrence of heat and electricity from one another. The most cost effective solution is offered by pressureless hot water tanks. In special cases batteries of cylindrical pressure vessels can also be advantageous. Stratification is very important for the reuse of the stored heat. Different load-changing devices have been developed and tested and proved successful. The design, construction, and operation of four recent hot water storage systems in Germany are discussed. At the Pforzheim reservoir a comprehensive experimental program demonstrated that existing and amended computer models can also predict the thermal behavior of large thermal stores with great confidence. Finally the economical advantages of thermal storage were studied and resulted in a very short payback time.