Figure P6.2-5 illustrates a single-paned glass window that is L = 6 ft high and

Question

Figure P6.2-5 illustrates a single-paned glass window that is L = 6 ft high and W = 4 ft wide; the glass is thg = 0.25 inch thick and has conductivity kg = 1.4 W/m-K. On a typical winter day, the outdoor temperature is Tair, out =10 degree F and you keep the indoor temperature at Tair, in = 70 degree F. On a still winter day, estimate the rate of heat loss from the window. Winter lasts twinter= 90 days and you are heating with electrical resistance heaters. Electricity costs ecost = $0.12/kW-hr. How much does the heat loss through the window cost you over the course of 1 winter? Assume that 50% of your heat loss in your house is through your windows and that you have Nwindow = 10 single paned windows in your house. Prepare a plot showing the cost of heating your house as a function of the thermostat set point (i.e., the indoor air temperature).

Explanation / Answer

I can help you with first two parts.!!

1.Heat lost due to conduction,Q= (Tin - Tout)/ R

R= t/k*A

t=thickness=0.25 inch=6.35*10^-3 m

L=6ft=1.82m

W=4 ft=1.21 m

R= 6.35*10^-3/1.4*(1.82*1.21)=2.05*10^-3

Q= 70 - 10/2.05*10^-3= 29131.46 W=29.131 KW

b) for 1 day= 29.131.46*0.12=$3.49

for 90 days=$314.61

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