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Abstract In order to solve the freezing damage problem of tunnel in cold region，an innovative heating system—tunnel heating system using heat pump was introduced for the first time to Linchang tunnel in Inner Mongolia Autonomous Region of China. Tunnel heating system consists of heating section，absorbing section，heat pump，collector and distributor line. The heating section is at the portal of tunnel and heated by the heating pipes located between secondary lining and insulation layer. The heat conduction of heating section is transformed to the heat conduction of composite medium in the cylindrical coordinate system. Its analytical solution was obtained using the finite integral transfer method. The yearly heating load is calculated by using the analytical solution under steady periodic conditions at different insulation layer thicknesses. These loads are used as inputs to an economic model including the cost of insulation material and the present value of energy consumption cost lifetime of 30 years of tunnel to determine the optimum insulation layer thickness. The investigation is carried out for Linchang tunnel in Inner Mongolia Autonomous Region of China. Results show that the energy costs decrease with the increasing insulation layer thickness；the cost of insulation material increases linearly with the increasing insulation layer thickness. Total cost，which is sum of insulation material cost and energy cost，decreases with the increasing insulation layer thickness. The optimum insulation layer thickness is obtained to be 8 cm；the yearly heating load is 580 MJ/m2.
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Received: 01 December 2011
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2012, Vol. 31 
