1 A rectangular outside wall 3mx3m has one doublepane glass

1. A rectangular outside wall 3mx3m has one double-pane glass window. The cement wall (k=1.1W/mC) is 10 cm thick and it is covered on the inside with 1 cm layer of plaster (k=0.2)W/mC). The 2mx2m window consists of two 5mm glass panes separated by 3cm of air. Find the total heat lost in one hour through the wall if the inside temperature is 20 C and the outside temperature is 0C. Find the equivalent R factor for this wall. Use the table in your textbook for the physical constants.

Solution

Equivalent R = 0.1/(1.1*9) + 0.01/(0.2 *9) + 0.005/(0.078*4) + 0.005/(0.078*4) + 0.03/(0.026*4) + 1/(10 * 9) +1/(25*9)

                       =   0.0101 + 0.0055 + 0.016 + 0.016 + 0.2884 + 0.0111 + 0.00444

                        = 0.35154 °C/W

total heat lost in one hour through the wall =   (20 / 0.35154) * 3600

                                                                    =   204813 .11 J