Chapter 3, Problem 3.5P

A dormitory at a large university, built 50 years ago, has exterior walls constructed of $L_s=25\text{-mm-thick}$ sheathing with a thermal conductivity of $k_s=0.1\text{W/m}\cdot \text{K}\text{.}$ To reduce heat losses in the winter, the university decides to encapsulate the entire dormitory by applying an $L_i=25\text{-mm-thick}$ layer of extruded insulation characterized by $k_i=0.029\text{W/m}\cdot \text{K}$ to the exterior of the original sheathing. The extruded insulation is. in turn, covered with an $L_g=5\text{-mm-thick}$ architectural glass with $k_g=1.4\text{W/m}\cdot \text{K}\text{.}$ Determine the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are $T_{\infty ,i}=22°\text{C}$ and $T_{\infty ,o}=-20°\text{C,}$ respectively. The inner and outer convection heat transfer coefficients are $h_i=5{\text{W/m}}^{\text{2}}\cdot \text{K}$ and $h_o=25{\text{W/m}}^{\text{2}}\cdot \text{K},$ respectively.