Field tests and analyses of thermal and humidity environment and heating and cooling capacity of air intake tunnels into underground plants

The underground air intake tunnel is a natural source of heat and cold that can be utilised to significantly condition the air entering the underground plant, thereby reducing the energy consumption of the plant. The heat and humidity environments of three underground tunnels were tested in winter and summer. The tunnels belong to Jiangxi Hongping Hydropower Station, which has significant cooling and heating characteristics in the air intake tunnel, Sichuan Xiluodu Hydropower Station, the world’s largest underground power station, and Hainan Qiongzhong Hydropower Station, the southernmost in China. The heat and humidity exchange pattern between the underground air intake tunnel of the power station and the air was analysed, including temperature and humidity trends, condensation zoning, inter-seasonal thermoregulation effect. Furthermore, the cooling and heating capacity of the air intake tunnel was calculated and analysed. The results show that: the greater the length and cross-sectional area of the tunnel, the greater the cooling and heating quantity; there is a noticeable difference in heat transfer capacity between different air intake tunnels, and the tunnel length is not a decisive factor for the heat transfer capacity, the heat transfer capacity (enthalpy difference) per unit mass flow rate of air in the air intake tunnels of Jiangxi (1500 m) is more than twice that of Sichuan (2800 m); the test cooling capacity of the Hainan (1400 m) tunnel reaches 606 kW (while the plant chiller rated cooling capacity of 2082 kW), the air intake tunnel can be used as an underground plant energy-efficient air conditioning, the equipment selection of plant mechanical air conditioning should take into account the air handling capacity of the air intake tunnel.