Optimizing the design of a district heating network

District heating (DH) system is one of the most important infrastructures in cold area. It is very important to balance the initial investment and the pumping cost in the DH network design. Currently, this design is mostly based on a recommended value of R=?P/L (specific pressure loss) in the main lines. This will result in a feasible network but probably not the optimal in most cases, which means that it is still possible to improve the design further. The aim of this paper is to develop a multi-objective optimization model to facilitate the design considering the initial investment of the pipes and the pumping cost for heat distribution. The main line in the optimization method is generating all possible network scenarios consisting of different series of diameters for each pipe in the network. Then for each DH network scenario, the annuity of initial investment, the pumping cost and the total annual cost will be calculated using different combinations of steel prices and pump operating time levels. Finally, we can obtain the optimization results and find out the overall optimal design. The optimization method is demonstrated in an example DH network and the optimal scope of R values is found from 44.9 Pa/m to 79.3 Pa/m which justify the recommended R values. But we conclude that on one hand R should be less than 100 Pa/m but on the other hand it should not be too small, otherwise the total annual cost will increase due to the large initial investment. In addition, we find that the pumping cost percentage is always increasing along with the increasing R values. This percentage increases from 41% to 82%. Therefore, pumping cost is a more important factor when designing a DH network and it should be given more considerations compared to the initial investment.