Methods of Heat Transfer Analysis of Buried Pipes in District Heating and Cooling Systems

District heating and cooling system is an energy-efficient and environment-friendly way of energy supply. Transmission and distribution pipeline system is an essential part of district heating and cooling system. Underground buried laying is the prevailing way of transmission and distribution pipeline system in district heating and cooling systems. Heat transfer calculation of pipeline is very important to determine the thickness of the insulation layer, accessory load of central plant, and the possibility of thermal damage. There are some factors that influence the heat transfer calculation of underground buried pipeline, including: temperature difference between fluid and soil, pipe insulation properties, burial depth, soil thermal conductivity and distance between adjacent pipes. Numerical methods to compute transient heat gains or losses in underground piping systems, is complicated and time consuming. To simplify the calculations, this paper introduces the steady-state thermal calculation method based on thermal resistance formulations that, that avoids the complex calculation process, and greatly simplifies the computational effort, and the calculated results can meet project needs. This method is suitable for the majority types of buried pipeline, so it can be used as reference for engineering design