An office is maintained at 25°C in winter by electric resistance heaters. If the outdoor temperature is 10°C, the second-law efficiency of the resistance heaters is
A)5.3%
B)5.0%
C)60%
D)67%
E)100%

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
TL=10+273 "K"
TH=25+273 "K"
To=TL
COP_rev=TH/(TH-TL)
COP=1
Eta_II=COP/COP_rev
"Some Wrong Solutions with Common Mistakes:"
W1_Eta_II=COP/COP_rev1; COP_rev1=TL/(TH-TL) "Using wrong relation for COP_rev"
W2_Eta_II=1-(TL-273)/(TH-273) "Taking second-law efficiency to be reversible thermal efficiency with C for temp" 
W3_Eta_II=COP_rev "Taking second-law efficiency to be reversible COP" 
W4_Eta_II=COP_rev2/COP; COP_rev2=(TL-273)/(TH-TL) "Using C in COP_rev relation instead of K, and reversing"

An Office Is Maintained at 25°C in Winter by Electric