The estimation of heat outputs for road heating installations

Heat transfer coefficients relating heat losses from surfaces of heated roads to wind speed and the difference between air and surface temperatures have been derived from measurements made during icy conditions. The magnitude of the heat flow downwards from the heating grid is discussed and a method of calculating the extra heat output required for installations on elevated roads is given. Solutions of the equation of heat flow in a semi-infinite medium under simple boundary heat flux conditions are used to illustrate the effect of heater depth and output on the rate of response, snow melting capacity and thermal storage of the system. Operating conditions required to provide adequate thermal storage in off-peak installations are examined in the light of this analysis and the observed heat losses from existing installations, and heater outputs required in different situations are estimated both for continuously available supply and for off-peak supply. (A)