Analysis of heat losses in underground tunnels for preheating of ventilation air

Methods for calculation of thermal conditions and heat loss parameter for an underground tunnel into surrounding sub-soil were developed in the first half and in the middle of the 20th century [18-20], when the study of complex heat-and mass exchange processes between underground tunnel, sub-soil and outdoor air was started. In a tunnel it is important to meet specific microclimate parameters such as air temperature and temperature surfaces of the protecting designs in order to reach thermal comfort. In that regard it is necessary to use climate control system, which in turn increases the capital expenditure. The article is based on analysis of the existing methods of heat loss in the underground tunnel. The complexity of the calculations is in the fact that there is soil of varying thickness between the underground tunnel and ambient air, which causes the attenuation of outdoor temperature variations. This heat transfer process is associated with a large thermal massiveness of soil layers, which absorb warmth. (Less)