Building Services Engineering 5th Edition Handbook

272 Lighting
number of lamps =
12.857 × 1000
100
= 129 lamps
Next even number is 130 lamps.
installed power =
electricity cost =
130 × 100
1000
= 13 kW
13 × 4500 × 8
100
= £4680/year
The average annual cost for replacing the lamps can be found by multiplying the number of
installed lamps by the anticipated hours of use, dividing by the lamp manufacturer’s rated average
life hours and then multiplying by the replacement cost for each lamp. In this case,
130 × £1 × 4500
lamp cost =
3000
= £195/year
These tungsten lamps expire within a year, so there will be annual expenditure. A new lighting
system that has lamps providing reliable service for more than a year will not produce replacement
expenditure in the first year or two. The owner needs to budget for the eventual replacement
costs by assessing the average annual cost. A planned maintenance programme will have lamps
replaced, and luminaires cleaned, prior to expiry. This work may be performed out of normal
working hours for the building to avoid disturbance to its normal functions.
Total annual cost = £(4680 + 195) = £4875/year
For the fluorescent lamps
154 286
number of lamps =
5400
= 29 lamps
Next even number is 30 lamps
30 × 65
input power =
1000
= 1.95 kW
1.95 × 4500 × 8
electricity cost =
100
= £702