Question

The wall has dimensions of 100 ft x 10 ft including window and door areas. The wall has a total window area of 80 ft2 and a door (8 ft x 2.5ft). The heat-transfer coefficients are 0.2 Btu/hr-ft2 –F for wall, 0.1 Btu/hr-ft2 –F for window, and 0.1 Btu/hr-ft2 –F for door. Determine the effective overall heat-transfer coefficient for the combination, U

Answer 1

Answer:

The effective overall heat transfer coefficient for the combination, $U = 0.19 Btu/hr-ft^2 -F$

Explanation:

According to the question, the total area includes the areas of the wall, window and door.

Total area, A = 100 * 10 = 1000 ft²

Area of the window, $A_{wind} = 80 ft^2$

Area of the door, $A_{d} = 8 * 2.5 = 20 ft^2$

Area of the wall, $A_{wall} = A - (A_{d} + A_{wind} )$

$A_{wall} = 1000 - ( 80 + 20)\\A_{wall} = 900 ft^2$

Heat transfer coefficients:

For wall, $h_{wall} = 0.2Btu/hr-ft^2-F$

For window,  $h_{wind} = 0.1Btu/hr-ft^2-F$

For door,  $h_{d} = 0.1Btu/hr-ft^2-F$

To get the overall heat - transfer coefficient for the combination:

$AU = A_{wall} h_{wall} + A_{wind} h_{wind} + A_{d} h_{d}\\1000U = (900*0.2) + (80*0.1) + (20*0.1)\\1000U = 190\\U = 190/1000\\U = 0.19 Btu/hr-ft^2 -F$