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, EstoniaTable 3 Simulation results in Case 1Table 6 Simulation results in Case 1Table 4 Simulation results in Case 2 (First 5 rows) andCase 3 (Last 3 rows with italic)Table 7 Simulation results in Case 2 (First 5 rows) andCase 3 (Last 3 rows with italic)Domestic Hot Water Storage TankTable 5 shows the pipe types and corresponding lengthin the DHWS installation. Alx 14 was selected asbranch pipe due to the smaller design heating load.Similar to the HE, the by-pass flow rate exceed theactual flow rate through the consumer in summerseason. The plant mixed return water temperature incase 1 is 46 o C. The introduction of the recirculationline can keep the plant return temperature in referenceline as low as 30 o C, while increases the returntemperature in the recirculation pipe to 54 o C at theplant. Extra heat loss has to be tolerated due to therecirculation pipe in both case 2 and case 3.Table 5 Selected pipe types and length in Case 1–3Further Discussion on Heat TransferAs shown in Eq. 1–3, the simulation program simplifiesthe calculation of the heat loss in the twin pipe as thatin the single pipe. The influence of the adjacent pipewas accounted through converting the linear thermaltransmittance U ij to the overall heat transfer coefficientsU s and U r , with pre-assumed constant networksupply/return temperatures. To assess the influence ofthis simplification on the temperature predication, thethermal interaction between the supply and returnpipes was calculated by solving the coupled pipe heattransfer differential equations. The governing equationsfor supply and return pipes can be expressed as:[4][5]The boundary conditions can be expressed as:The dimensionless temperature is introduced with:[6][7]78