An Analysis of Air Heating during Flow Through Ground Passages

During a 10 day period of below freezing temperatures, air was circulated through an underground tunnel. Under constant airflow rate, rock and air temperatures were observed every four hours at instrumented stations long the tunnel from the portal intake to the exhaust outlet. Tunnel ice formation and the depth of rock temperature cooling in from the tunnel surface were also recorded. The data were analysed to establish the heat low energy transfer characteristics between the circulating air and the rock. The day to day surface climatic changes were recorded and correlated to the air and rock temperatures within the tunnel. Comparisons were made with theory developed for use in hot underground mining conditions at depth, and a general equation formulated to describe the thermodynamic behaviour of the system. From this empirical base, suitable designs are pro-posed for ground tubes, or tunnels, to temper winter air for home heating. From the results of the study, the home owner should be able to design a ground passage air-tempering system with sizing appropriate to location and environment