Improving the dimensioning of piping networks and network layouts in low-energy district heating systems connected to low-energy buildings: A case study in Roskilde, Denmark

The paper presents a method for the design of a low-energy district heating (DH) system, concerning the studies of different pipe dimensioning methods, substation types and network layouts. Computations were carried out separately on each of the pipe segments of which the DH network consisted. A simultaneity factor was taken account in connection with each of these pipe segments. The applicability of the developed optimization method was investigated with outcomes of its being highly useful in the pipe dimensioning and of its being superior in respect to traditional dimensioning methods. It was shown that an appreciable reduction in heat loss from the DH network could be achieved. The optimal pipe dimensions found were evaluated by use of the commercial software Termis with input of several randomly generated heat demand scenarios involving peak winter conditions. The effects of the network type on the pipe dimensions were investigated for substations of different types containing buffer tanks and heat exchangers and for booster pumps installed at the DH network. Two types of network layouts were compared in terms of satisfaction of customers concerning the supply temperatures and heat loss within the DH network to prevent excessive drops in supply temperature during the summer months.