Thermal Insulation The number of Btu/hr conducted outward through a surface such as a wall is given by Qt=kA(T1-T。)/l Where k is the thermal conductivity of the wall material in units of (Btu in.)/(hr ft*.F) a is the area of the wall surface in square feet, l is the thickness of the wall in inches, and (t - To)is the temperature difference in degrees Fahrenheit between the inside and outside Degree days For each day of the heating season, the number of degree days accumulated is given by the average temperature difference between inside and outside with the inside temperature taken to be a constant 65 F For an entire heating season, the total number of degree days is obtained by summing these degree days for the individual days of the heating season 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan UniversityThermal Insulation k l i o Q/t = A(T − T )/ (Btu in.)/(hr ft F) 2  ⋅ ⋅ ⋅ The number of Btu/hr conducted outward through a surface such as a wall is given by : Where k is the thermal conductivity of the wall material in units of : A is the area of the wall surface in square feet, l is the thickness of the wall in inches, and (Ti -To) is the temperature difference in degrees Fahrenheit between the inside and outside. Degree days For each day of the heating season, the number of degree days accumulated is given by the average temperature difference between inside and outside, with the inside temperature taken to be a constant 65 ̊F. For an entire heating season, the total number of degree days is obtained by summing these degree days for the individual days of the heating season