12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaFig. 4 In-house heat exchanger (HE) in DH systemTable 1 Simultaneous FactorsDistrict Heating NetworkThe DH network and the connection to the end usersare shown in Fig. 6. The house is designed to connectto the plant directly through different diameter pipeswhich were optimized with the simulation program. Thedirect connection allows the primary DH network tocirculate water directly into the end user installation. Itis suitable for a moderate pressure level network andthe differential pressure of DH network is sufficient tocirculate water to the house installation. The networksand house installations are assumed to withstandmaximum pressure 10 bar. The consumer differentialpressure is set as 0.5 bar. It is controlled at the enduser along the network critical route which is shown ingreen color.Three network design scenarios were investigated foreach house installation:Case 1: It is the reference case. The totalnetwork length is 3080 m and the network lineheat density is 177 kWh/year. Network wasdesigned in the traditional way for two pipeswith one supply and one return, respectively.The differential pressure is controlled at userA. Twin pipes were selected for theDH network. They are called ―reference pipe‖in this paper.Case 2: By-pass water recirculation. A thirdpipeline (Fig. 6 grey color line) was introducedto separate the by-pass water with returnwater and re-circulate the by-pass water backto the plant. The third pipeline was sizedbased on the summer by-pass water flow rate.The differential pressure is controlled at pointB.Case 3: Double pipeline supply. The main pipe(from plant to the junction point at each street)in the third pipeline which was sized in case 2functions all year round. It acts as supply pipeduring winter season and functions as supplywater recirculation pipe when there has bypasswater demand. In this case, the mainpipe in the reference case was resized as aportion of supply water is shared by therecirculation pipe. The connection ofrecirculation pipe to the reference pipe isshown with red color.Fig. 5 Domestic hot water storage (DHWS) in DH systemThe thermal by-pass temperature was set as 50 °C forHE and 60 °C for DHWS with dead band 2 °C. The bypassis placed on the end user at each street in case 1,while at the virtual point adjacent to the end user incase 2.75