Chapter 4.2, Problem 13P

Under many conditions, the rate at which heat enters an air conditioned building on a hot summer day ta proportional to the difference in temperature between inside and outside. $T_h-T_c$. (If the heat enters entirely by conduction, this statement will certainly be true. Radiation from direct sunlight would be an exception.) Show that, under these conditions, the cost of air conditioning should be roughly proportional to the square of the temperature difference. Discuss the implications, giving a numerical example.