Convenience
Switching lights in commercial and institutional buildings
can require features that conventional switches cannot supply.
Some advantages provided by low voltage lighting controls
are:
Switching many circuits from one location. Switching many circuits with one switch. Switching from large distances. Switching automatically. Switching automatically as well as manually.
Save Energy, Save Money
The biggest single energy cost in commercial and institutional
buildings is the lighting load. Significant costs can be saved
by proper management of lighting loads.
Reduce Energy Costs
Energy costs are equal to the watts of electricity used over
a period of time: Costs = Energy used = (WATTS) x (TIME).
There are 2 ways to reduce costs:
Manage the operating time (TIME). Lighting controls reduce the
operating time with time schedules, daylight sensing and occupancy detection. Use more efficient fixtures and lamps (WATTS). High efficiency reflectors, ballasts and
lamps can make a substantial impact on operating costs.
Douglas lighting control products focus on item #1, managing the operating TIME of the lighting load.
To Calculate Energy Sayings
This method of calculation is similar for all types of projects.
First, calculate the hourly operating costs for a group
of lamps.
a) Add up the watts used by all the lamps;
b) Divide by 1000 for the KW value;
c) Multiply by the 1 KW/H rate charged.
Then, calculate how many hours can be saved in a
year.
You must make some assumption about the application and how
lighting controls will be used. This is best described by
examples.
AUTOMATING THE OFF FUNCTION
If regular wall switches can be used, how do lights get switched
OFF and when? If switching lights OFF is a custodian’s duty,
a lighting control system would probably switch the lights
OFF sooner
How much sooner each day? How many days are affected?
If it is from Monday to Friday, the answer is 260 days per
year.
Thus, saving one hour per day with a $0.25
per hour operating cost translates into $65.00 per
year saved.
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To Calculate Energy Savings (continued)
MANUAL OFF, AUTOMATIC ON
Automatic ON (using contactors), has to occur at the earliest
acceptable time.
Manual ON control ensures lights are only switched ON when
the space becomes occupied.
Saving an average of 1/2 hour per working day with Manual
ON controls with an operating cost of $0.25 per hour, would
mean an annual savings of $32.50 for 260
workdays.
AUTOMATIC CONTROLS (THEY NEVER FORGET)
Consider the effect of forgetting to turn OFF the lights.
A weekend from 6pm Friday to 6am Monday is 60 hours long and
a weekday night from 6pm to 6am is 12 hours long.
A $0.25/hr
operating cost translates into a $15 cost per weekend and
a $3 cost per weekday.
If controls are manual, forgetting
will occur: the question is ‘How often?'
Use the preceding examples as a guide to make estimations
of how many hours can be saved over a year. Multiply this
by the hourly operating cost to determine the annual cost.
Multiply by 5 to determine the cost savings over 5 years.
Example: Office Building Calculation
1. Calculate hourly operating cost
eighty 3-tube fluorescents:
32W x 3 = 96W, 96W x 80 = 7680W
7680W/1000 = 7.680 KW
If electrical rate is $0.10 per KWH:
7.680 KWH x $0.10 = $0.77/hour.
2. Calculate annual cost savings
a) AUTOMATIC OFF
Assume that 1.5 hours can be saved every weekday by automatic
controls, since custodians do not make rounds until the office
is vacated.
Thus, annual cost savings are $0.77 x 1.5 x 260 = $300.30.
b) MANUAL ON, AUTOMATIC OFF
Saving an average of 0.5 hours per weekday yields 130 hrs.
per year.
Annual savings: 130 x $0.77 = $100.10.
c) FORGETTING TO TURN LIGHTS OFF
A 60-hour weekend would cost $46.20.
Forgetting to switch lights OFF before weekend twice a year
would results in a cost of 2 x $46.20 = $92.40.
A 12-hour weeknight costs $9.24.
Forgetting to switch lights OFF 8 times a year on a weeknight
results in a cost of 8 x $9.24 = $73.92.
Annual costs of both are: $166.32.
The above scenarios translate into a total annual
saving of $566.72.
Over five years, this translates into a total cost saving of $2833.60
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