Design of Low-Energy District Heating System for a Settlement with Low-Energy Buildings

With the integration of new low-energy buildings the traditional district heating (DH) systems with high operating temperatures will have significantly higher heat loss according to the heat supplied to the district. The relatively higher heat loss could be reduced with low operating temperatures of 55 °C and 25 °C in supply and return line of DH network, respectively with a convenient control of in-house installations (substations).

Traditional DH pipe dimensioning methods were based on size searching algorithm in which lowest possible pipe diameter was defined according to the limit of max velocity and/or max pressure gradient. Since traditional dimensioning methods cause over-dimensioned network, special attention has to be given to lower the dimensions and as a consequence heat loss from the DH network further.

In this investigation pipe dimensioning method of low-energy DH system was developed with an optimization method in the objective of minimizing heat loss from the network while pressure drop values were kept as the constraints through the DH network. In the dimensioning method also descending pipe dimensions were formed in the branched type DH network by taking into account simultaneity of heat load, according to the cumulative consumer load, on each pipe segment separately.

According to the traditional dimensioning method, 14% reduction in the heat loss was achieved with the developed optimization method. The resultant pipe dimensions were evaluated via hydraulic and thermal simulation software Termis with simultaneity factor based randomly generated heat demand scenarios for peak winter situation.

The simulation results were re-sampled with bootstrapping method and confidence interval of the reliability of the DH system was presented as a result.