1 Extended Exam Problem Calculate The Heat Rate Through A Typical Home Exterior Wall As Shown Below Drywall Insulatio 1 (65.86 KiB) Viewed 28 times
1. (Extended exam problem) Calculate the heat rate through a typical home exterior wall as shown below drywall insulation Material k Drywall 0.17 W/(mK) Wood 0.14 W/(mK) Plywood 0.13 W/(mK) wood siding -plywood The wall is constructed using 2x4 wood studs on 16" centers (There is 16"= 40.64 cm between the centers of the studs. The studs are 1.5" = 3.81 cm wide). Fiberglass insulation fills the gap area between the studs. The interior surface is drywall, the outer surface is plywood, and there is vinyl siding over the plywood. You can ignore the vinyl siding as it has little insulation value. The data on the materials is given below. English thickness 1/2" 3 1/2" 1/2" SI thickness 1.27cm 8.89 cm 1.27 cm The thermal characteristics of the insulation are given as a thermal resistance Material R" (English) R" SI R15 Insulation 15 ft²° F/(Btu/h) 2.64 Km²/W The interior room temperature is 20C and has a convection coefficient of 8 W/(m²K). The exterior temperature is -15C and has a convection coefficient of 45 W/(m²K).
(a) What is the heat rate through a wall that is 16ft wide (4.88 m) by 8ft high (2.44 m)? (answer: 177 W) (b) What is the outer wall surface temperature? (c) What is the ratio of heat that passes through the studs to the heat that passes through the insulation? (answer: 0.43) (d) If radiation on the outer surface was included, redraw the circuit diagram for the wall and calculate the outer surface temperature (iterate) for a radiation emissivity € = 0.8
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