Cost-Benefit Analysis

Chris and I worked on a Cost-Benefit Analysis for using motion sensors in the hallways of the dorms. This was applied to one hall in the Babcock dorm.

Info:

$ 100 – Motion sensor

36-W twin light bulb

$.09 per kWh, average cost for power in NC in May 2006

-Average 6 hours a day of lights off (best estimate based on observation of hall usage assuming the lights will be mostly off during the hours of 3AM-8AM) / leave the lights on during peak times 10AM-10PM, put it on timer the rest of the day, go to timer from 10PM-10AM

Initial Calculations:

72 (amount of watts per hour for light bulb due to two tubes in each) x hours = number kWh per light

24 hours a day = 1.73 kWh

18 hours a day = 1.30 kWh

Formula:

Number of lights in hallway x (1.73 or 1.30) = per hour for the hallway

Hallway x 24 or 18 x 7 days a week x 52 weeks = usage per year

(Usage per year x .09) + 100 = cost

Cost per 24 – cost per 18 = savings

Calculations:

9 bulbs x 1.73 kWh = 15.57 kWh per 24 hours for the hallway

15.57 kWh x 7 days a week x 52 weeks a year = 5667.5 kWh per year

5667.5 kWh per year x .09 per hour = $510 for one year without motion sensors

9 bulbs x 1.30 kWh = 11.7 kWh per 18 hours

11.7 x 7 x 52 = 4258.8 kWh per year

4258 kWh per year x .09 per hour = $383 for one year with motion sensors

$510 - $383 = $127 savings per year for one hall in Babcock residence hall

Note:

A) The $127 savings does not include the $100 for motions sensor and installation, but that would be a one time cost while the $127 would be saved every year.

B) One thing we did not factor in was the effect of turning the lights on and off. It would have some impact, but not enough to overcome the 127 dollars saved.

In our opinion it would be very beneficial to have motion sensors in the hall way.