Perpendicular Horizontal Vertical South 60° South October 21 2454 1348 1654 2074 November 21 2128 942 1908 December 21 1978 782 1646 1796 January 21 2182 948 1726 1944 February 21 2640 1414 1730 2176 March 21 2916 1852 1484 2174 The perpendicular surface is steered so that it is perpendicular to the suns rays. The vertical surface is south-facing. The 60 south surface is south facing and slanted back 30 from the vertical (Adapted from Kreider, J F, and Kreith, F, Solar Heating and Cooling. New Yourk: McGrawOHill, 1977 Insolation in Btu/ft2 per Day on Various Surfaces for winter Months under Clear Sky conditions at 40. N latitude 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan UniversityInsolation in Btu/ft2 per Day on Various Surfaces for winter Months under Clear Sky Conditions at 40。N latitude. The perpendicular surface is steered so that it is perpendicular to the sun’s rays. The vertical surface is south-facing. The 60̊ south surface is south facing and slanted back 30̊ from the vertical. (Adapted from Kreider, J.F., and Kreith, F., Solar Heating and Cooling. New Yourk: McGraw0Hill, 1977