Temperature field and system efficiency of a ground source heat pump heated tunnel drainage ditch

Abstract Freezing of central drainage ditches constitutes a significant cause of freeze damage in tunnels located in frigid climates. Traditional passive insulation methods, such as thermal insulation layers, are inadequate to prevent the freezing of central drainage ditches in these harsh environments. This study investigates the effectiveness of ground-source heat pump-based active heating systems in enhancing frost resistance for tunnel central drainage ditches in cold regions through laboratory tests and numerical simulations. The impacts of various parameters, including the volumetric flow rate of the circulating medium, heating system supply water temperature, heating pipe linear density, and heating pipe layout, on the temperature differential between the supply and return water of the heating system, heat exchange power, and the temperature field of the central drainage ditch, were analyzed. A novel sectional layout method for heating pipes within the central drainage ditch was proposed. Furthermore, the study explored how the wind speed inside the tunnel affects the temperature field of the central drainage ditch, the annual running time of the sectional heating system, the heating power of the system, and its energy consumption under active heating conditions. The results indicate that the temperature differential between the supply and return water of the heating system diminishes as the volumetric flow rate of the circulating medium increases, yet it escalates with higher supply water temperatures and increased linear density of heating pipe. The heating power of the ground-source heat pump system initially rises before declining as the volumetric flow rate of the circulating medium grows, while it consistently increases with elevated supply water temperatures and greater linear density of heating pipe. Results also highlight that helical heating pipes in the ground-source heat pump system outperform U-shaped heating pipes. The annual operating time of the heating system lengthens with higher tunnel wind speeds and shortens with increased distance from the tunnel inlet. Lastly, the average annual energy consumption of the heating system rises with increased tunnel wind speeds and declines as the distance from the tunnel inlet increases.