NJ GREEN BUILDING MANUAL
EXISTING COMMERCIAL UPDATED 19-MAY -11
Dual-Technology Occupancy Sensors
What are Dual-Technology Occupancy Sensors?
A dual-technology occupancy sensor system uses both passiveinfrared (PIR) and ultrasonic technology. The PIR technology
helps to detect occupants by sensing heat while the ultrasonic
technology can detect motion even when the sensor does not
have a direct “line-of-sight” to occupants. The system consists
of the actual motion sensors, an electronic control unit, and a
controllable switch. Once installed, it serves three basic
functions: 1
Figure 1 – Occupancy
sensor on wall in
1. Automatically turns lights on when a room becomes
Rutgers Visitor Center
occupied
(Source: Rutgers
2. Keeps lights on without interruption while the controlled
University)
space is occupied
3. Turns the lights off within a preset time period after the space has been vacated
Lighting accounts for about 21% of a building’s electricity use and about 17% of total
annual US electricity consumption. 2 Because many building spaces are unoccupied more
than half the time, switching unneeded lights off makes it possible to reduce direct
lighting energy consumption by up to 45%. Reducing lighting electricity usage reduces
energy cost and lessens the negative environmental impacts associated with electricity
generation. 3
Electric lighting is only necessary when people are present in the building and daylight is
inadequate or absent. Both the presence of people and daylight can be detected through
the use of sensors. Most sensors are designed to function independently or in parallel
with other sensors for larger areas. Installing occupancy sensors with both of these
technologies is an effective and relatively inexpensive way to lower energy consumption,
keeping costs down.
1
Whole Building Design Guide Resource Pages. Electric Lighting Controls. 2009.
http://www.wbdg.org/resources/electriclighting.php (accessed January 12, 2010).
2
Energy Use in Commercial Buildings. 2003.
http://tonto.eia.doe.gov/energyexplained/index.cfm?page=us_energy_commercial (accessed February 5,
2010).
3
Whole Building Design Guide. Documents & References. Environmental Library. Green Seal. Green Seal
Reports: Occupancy sensors. http://www.wbdg.org/ccb/GREEN/REPORTS/cgrsens.pdf (accessed January
12, 2010).
NJ GREEN BUILDING MANUAL
EXISTING COMMERCIAL UPDATED 19-MAY -11
How to Install Dual-Technology Occupancy Sensors
1. Conduct a lighting audit
a. Which rooms/spaces are the most frequently used? The least?
b. Which rooms do people tend to leave on lights? Restrooms?
c. Are there rooms that are occupied only during specific times of the day?
2. Survey potential areas for occupancy sensors to be located
a. The best areas are spaces that are not frequently used, have irregular use
patterns, or areas where lights are inadvertently left on.
b. How large/small is this space?
c. How many sensors will be needed?
3. Conduct a cost analysis of the retrofit action.
a. Areas that have incandescent lighting will typically yield reductions that
are more significant and have a faster payback.
4. Implement retrofit activities.
Selecting automatic light controls that come with manual override systems will help
reduce occupant frustration in the case of a sensor malfunctioning or a circumstance that
requires lighting to stay on beyond the parameters programmed into the automatic
controls.4
In addition, commissioning and proper calibration of lighting controls is essential. See
“Section B: Selecting the Appropriate Lighting Controls” from the “Electric Lighting
Controls” article in the Whole Building Design Guide, written by David Nelson, AIA for
information on commissioning and selecting lighting controls.
Additional information on choosing an appropriate system:
http://www.anaheim.net/utilities/ea/PA_10.html#manufacturers
4
Greenyour.com. http://www.greenyour.com/office/office-space/office-lighting/tips/control-officelighting-with-timers-and-motion-sensors (accessed May 17, 2011).
NJ GREEN BUILDING MANUAL
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Examples
Lighting Upgrade: Dual-Technology Occupancy Sensors in NJ Municipal Facility
The following data is based on dual-technology occupancy sensor installation associated
with the NJ BPU commercial audit program for a 10,563 square foot municipal facility in
New Jersey.
Energy Savings Summary:
Installation Cost ($): $750
NJ Smart Start Equipment Incentive ($): ($200)
Maintenance Savings ($): ($0)
Net Installation Cost ($): $550
Total Energy Savings ($ / yr): $262
Simple Payback (yrs): 2.1
Based on calculations for the existing spaces, lighting power density (Watts/ft2 ) was
determined to be 0.68 Watts/SF. Ten percent of this value is the resultant energy savings
due to installation of occupancy sensors:
Savings = 10% x 0.68 Watts/SF x 10,563 SF x 2,080 hrs/yr. = 1,494 kWh x $0.175/kWh
Savings = $262 / yr
Installation cost per dual-technology sensor (Basis: Sensorswitch or equivalent) is
$75/unit including material and labor. The SmartStart Buildings® incentive is $20 per
control which equates to an installed cost of $55/unit. Total number of rooms to be
retrofitted is 10. Total cost to install sensors is $55/unit x 10 units = $550.
Broughton Hall Classrooms at North Carolina State University
In four years, Broughton Hall received a payback on their investment in occupancy
sensors and achieved a cost savings of approximately $800/year.
http://www.energync.net/programs/docs/usi/om/hvac/finalreportdocs/NCSU%20Brought
on%20Hall%20Occupancy%20Sensors.doc
Benefits
o Reduces energy use and greenhouse gas emissions
o Decreases utility bills
NJ GREEN BUILDING MANUAL
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Costs
The cost for occupancy sensors is impacted by factors such as the type of surface on
which the sensors can be mounted, and size of the area to be sensed. 5 Depending on
wattage, type of sensor, and other features, the cost can range from $50 to $150 per unit. 6
There are often incentives available to install dual-technology occupancy sensors (see
Resources).
The following example illustrates how to do a cost analysis.
All estimates based on the following per unit costs:
$0.14/kWh, $10.66/MMBtu, $1.07/therm
Scenario:
A 20,000 square foot building operates for 10 hours a day, 5 days a week, 52 weeks per
year. Consider the following room types in which a total of 400 2-lamp T-8 32 watt
lighting fixtures are used: 1 open office, 12 private offices, 2 bathrooms, 1 cafeteria, 1
auditorium/multi-purpose and 2 conference rooms. 7 If 23 8 occupancy sensors are
installed, approximately 30%9 (approximately 15 hours per week) of electric lighting
usage can be reduced. This calculation is an average and in some cases, reductions of up
to 45% are possible. For more specific reductions based on type of space, see Land-ofSky Regional Council’s fact sheet on Occupancy Sensors:
http://www.energync.net/resources/docs/pubs/occupancy.pdf
Assumptions: 10
Room Sizes
1 open large office = 180 SF
5
Energync.net.
http://www.energync.net/programs/docs/usi/om/hvac/finalreportdocs/NCSU%20Broughton%20Hall%20O
ccupancy%20Sensors.doc (accessed May 17, 2011).
6
CA.gov. Best Practices Manual. Building Maintenance – Lighting and Occupancy Sensors.
http://www.green.ca.gov/EPP/building/sensors.htm#cost (accessed May 17, 2011).
7
Whole Building Design Guide: Space Types - Example Program. June 2009.
http://www.wbdg.org/design/spacetypes.php (accessed February 5, 2010).
8
Green Seal's Sensors Report. http://www.greenseal.org/ (accessed February 5, 2010).
9
CA.gov. Best Practices Manual. Building Maintenance – Lighting and Occupancy Sensors.
http://www.green.ca.gov/EPP/building/sensors.htm (accessed February 5, 2010).
10
Whole Building Design Guide: Space Types - Example Program. June 2009.
http://www.wbdg.org/design/spacetypes.php (accessed February 5, 2010).
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12 private offices = 120 SF ea * 12 = 1,440 SF
2 public toilets = 120 SF ea * 2 = 240 SF
1 cafeteria = 4,000 SF
1 auditorium/multi-purpose = 8,000 SF estimated
2 conference rooms = 760 SF ea. * 2 = 1,520 SF
Subtotal = 15,380 SF
Miscellaneous & circulation space = 4,620 SF
Sensor coverage
Minimum coverage areas for sensor types are applied as followed:
Wall Switches = 300 SF (for smaller areas, i.e. bathrooms, private offices)
1 open large office, 12 private offices, 2 public toilets
= 15 sensors
Ceiling Mount = 1,500 SF (for larger areas, i.e. conference rooms, auditoriums)
1 cafeteria, 1 auditorium, 2 conference rooms
= 8 sensors
Total sensors = 23 sensors
Note: Assumption is that lighting upgrades have been fulfilled; therefore this scenario
uses T-8 lighting fixtures.
Variable
Lifetime of Measure (Years)
Capital Costs to Municipality ($)
Dual-Technology Occupancy Sensors
a) 12 to 15 years11 for occupancy sensors
b) 6 to 10 years for control switches
49.9 kWh/T-8 lighting fixture through use
of occupancy sensors a
19,968 kWh
a) $20 per control (Wall Mounted)
b) $35 per ballast (Remote Mounted) 12
$145/unit (with $20/unit incentive) b
Average Payback
1.2 years (1 year and 3 months)
Annual Electric Savings (kWh)
Annual Peak Load Reductions (kW)
Tax Credits and Incentives ($)
See Notes section for further information on this cost table.
11
Lightsearch.com. Resource Center Light Guide: Occupant Sensors.
http://www.lightsearch.com/resources/lightguides/sensors.html (accessed December 12, 2010).
12
NJ Office of Clean Energy. Lighting Control Prescriptive Incentive.
http://www.njcleanenergy.com/misc/commercial-industrial/lighting-control (accessed February 5, 2010).
NJ GREEN BUILDING MANUAL
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Equations
Conventional scenario:
64 Watts * 1 Fixture = 64 Watts/fixture
64 Watts * 2,600 hours/yr = 166,400 watt hours/yr
166,400 watt hours/yr ÷ 1000 = 166.4 kWh/yr
30% Usage Reduction Scenario:
64 Watts * 1 Fixture = 64 Watts/fixture
64 Watts * 780 hours/yr = 49,920 watt hours/yr
49,920 watt hours/yr ÷ 1000 = 49.9 kWh/yr/lighting fixture
Payback:
[average payback in years] = [average capital cost per unit]*[number of sensors/units] /
[annual cost savings]
years = ($165/unit-$20 BPU incentive)*23 / $2,795.52
years = $3335/$2,795.52
years = 1.19 years, or, 1 year and 3 months
64 Watts * 400 T-8 fixtures (2-lamp 32 W) = 25,600 Watts used total
Annual Electric Savings = 19,968 kWh/yr
19,968 kWh*$0.14/kWh = $2,795.52
Annual Cost Savings = $2,795.52
Resources
Whole Building Design Guide - Electric Lighting Controls
http://www.wbdg.org/resources/electriclighting.php
ENERGY STAR Building Upgrade Manual - Lighting
http://www.energystar.gov/index.cfm?c=business.EPA_BUM_CH6_Lighting#S_6_7
US DOE | EERE – Commercial Building Initiative
http://www1.eere.energy.gov/buildings/commercial_initiative/guides.html
NJ’s Clean Energy Program - Lighting Control Prescriptive Incentive
http://www.njcleanenergy.com/misc/commercial-industrial/lighting-control
NJ GREEN BUILDING MANUAL
EXISTING COMMERCIAL UPDATED 19-MAY -11
National Electrical Manufacturers Association – Energy Efficiency – Commercial
http://www.nema.org/gov/energy/efficiency/industry/
National Electrical Manufacturers Association (NEMA) – Commercial Lighting Tax
Deduction – Occupancy Sensors
http://www.lightingtaxdeduction.org/technologies/occupancy-sensors.html
Energy Design Resources
http://www.energydesignresources.com/resources/publications/technologyoverviews/technology-overview-occupancy-sensors.aspx
Notes
Cost table
a)
Assuming a building operates an average 2,600 hours/year, running 400 T-8 lamps (64
Watts), implementing dual-technology occupancy sensors can reduce electricity usage by
approximately 30% per fixture (1,040 hours per year).
b)
RS Means Cost Works. Occupancy Sensors, infrared, ceiling mounted = $109 (bare
material) + $56 (bare labor) = $165 - $20 BPU incentive = $145