A university campus has 200 classrooms and 400 faculty offices. The classrooms a
ID: 1605035 • Letter: A
Question
A university campus has 200 classrooms and 400 faculty offices. The classrooms are equipped with 12 fluorescent light bulbs each consuming 110 W, including the electricity used by the ballasts. The faculty offices, on average, have half as many light bulbs. The campus is open 240 days a year. The classrooms and faculty offices are not occupied an average of four hours a day, but the lights are kept on. If the unit cost of electricity is $0.075 kWh, determine how much the campus will save a year if
(a) the lights in the classrooms and faculty offices are equopped with light sensors that turn off the lights during unoccupied periods
(b) the fluorescent lamps are replaced by LED lights each consuming an average of 10 W
Explanation / Answer
The Power consumed by the light bulbs in the class rooms is
Pclass room = (No. of light bulbs)(Power consumed by each bulb) = (200 x12 x 110 W) = 264000 W =264 kW.
The power consumed by the light bulbs in the faculty offices is
Poffice = (No. of light bulbs)(Power consumed by each bulb) = (400 x 6 x 110 W ) = 264000 W = 264 kW
Total power consumed in the campus is
Ptotal = Pclass room + Poffice = 264 kW + 264 kW = 528 kW.
a) The energy saved per year after the classrooms and faculty offices are equopped with light sensors is
Esaved = (No.of non working hours / day ) x (No .of working days per year ) x (Total power consumed in the campus)
Esaved = ( 4 h /day ) (240 days) (528 kW) = 506880 kW h
Total cost saving per year is
Cost saving per year = (Esaved ) (Unit cost of electricity ) = (506880 kW h )($0.075 / kWh ) = $ 38016
Therefore total cost saving after using of light sensors is $ 38016 per year .
b) By replacement of fluorescent light bulbs the power saved by each LED light is
Power saved by each LED light = 110 W - 10 W = 100 W
The Power saved by the replacing the fluorescent light bulbs by LED lights in the class rooms is
(Pclass room)saving = (No. of LED lights)(Power saved by each LED light) = (200 x12 x 100 W)
(Pclass room)saving = 240000 W = 240 kW
The power saved by the LED lights in the faculty offices is
Poffice = (No. of light bulbs)(Power consumed by each LED light) = (400 x 6 x 100 W ) = 240000 W
Poffice = 240 kW.
Total power consumed in the campus is
Ptotal = Pclass room + Poffice = 240 kW + 240 kW = 480 kW.
The energy saved per year by replacement with LED lights is
Esaved =(No.of non working hours / day ) x (No .of working days per year ) x (Total power consumed in the campus)
Esaved = ( 24 h /day ) (240 days ) (480 kW) = 2764800 kWh
Total cost saving per year is
Cost saving per year = (Esaved ) (Unit cost of electricity ) = (2764800 kWh )($0.075 / kWh ) = $ 207360
Therefore total cost saving after replacement with LED lights is $ 207360 per year .
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