Sensing the way to greater energy efficiency
Buildings represent 32% of total final energy consumption. In terms of primary energy
consumption, buildings represent around 40% in most countries affiliated with the
International Energy Agency[1]. This considerable consumption raises a challenge for
building owners and occupants in managing cost and environmental impact.
To meet this challenge, building owners and occupants turn to various ways to increase
energy efficiency, such as retrofitting to more efficient equipment or building design. Equally
crucial is the patterns of energy use within a facility, which may fluctuate over the course of a
day and be difficult to program for optimum energy utility. Here is where the application of
sensors within a building can optimise energy use and prevent unnecessary wastage.
What are building sensors?
Building sensors are electronic devices used to detect the presence, occupancy, or
environmental quality of a space within a building. These sensors are linked to the
equipment to which energy use is to be controlled, such as lighting, ventilation and airconditioning. Sensors can also be part of a larger building control system, which serves to
monitor and control the mechanical, electronics and lighting systems in a building.
Here, various types of sensors and the equipment they control, as well as the energy
savings that can be obtained with their proper application, are elaborated.
Occupancy sensors for lighting control
Occupancy sensors automatically turn off lighting in unoccupied spaces such as classrooms,
conference rooms, washrooms, public
spaces, and offices.
The most common occupancy sensor
types for lighting control are infrared and
ultrasonic, and they typically include a
timer to compensate for when people are
in the room but not moving or in a “dead
zone”.
Infrared
sensors
detect
Figure 1: How occupancy sensors operates by detecting
temperature changes in a room, and
people in a room
works well where the entire room is within
the sensor’s field of view. Ultrasonic
sensors use high frequency sound to detect motion. Dual-technology sensors utilise both
methods, increasing accuracy and flexibility, though at an increased cost.
Occupancy sensors for lighting control are most effective in areas that are often unoccupied,
such as restrooms and corridors. Depending on where they are deployed, occupancy
sensors can reduce energy use by lighting by 50% or more[2].
Light intensity sensors for lighting control
During the day, natural light can be used for illuminating building interior, through windows or
skylights. As natural light intensity varies through the day, depending on the time and
weather, artificial lighting may be needed to ensure sufficient illumination. Light intensity
sensors detect the level of illumination in a room, and relays signals to the lighting control
system to brighten or dim the light fixtures.
Application of this sensor saves energy by keeping lights turned off or dimmed, even when a
room is occupied, as long as adequate natural light is available. Lights zoning may have to
be performed as locations deep in the interior may not get as much natural light as those
nearer to the windows. Different levels of artificial light to suit each zone’s need will be
required.
Occupancy sensors for air-conditioning control
As for lighting control, occupancy sensors can also be applied for controlling air-conditioning
in a room. Similarly, sensors detect the presence of occupants, and the air-conditioning
system turned off when a room is empty. These are ideal for rooms that are sporadically
occupied through the day, such as conference rooms.
More advanced occupancy sensors are able to detect the actual number of occupants in a
room. When coupled with a variable-air-volume air-conditioning system, cooling air-flow rate
can be catered to the exact occupancy and energy consumption optimised.
Carbon dioxide sensors for indoor ventilation control
Figure 2: Integration of carbon dioxide sensors in a building's air handling unit to vary outside air intake according to
concentration of carbon dioxide gas emitted by occupants
Carbon dioxide sensors continuously monitor the concentration of carbon dioxide (CO2) in
an air-conditioned space. As room occupants exhales CO2, its concentration increases and
the room will have to be ventilated with outdoor air to maintain a safe environment. This is
more prevalent in large commercial buildings, where air-conditioning is managed by an airhandling system.
Typically, to conform to air quality standard, the air-handling system extracts fresh outdoor
air at the maximum level whenever a building is occupied, regardless of the occupancy and
activity level in a room. This could lead to over-ventilation which results in higher energy
consumption as energy is required to cool the warmer outdoor air.
With carbon dioxide sensors, fresh air is extracted only when concentration of CO2 goes
beyond a specified level. Less energy is thus needed to cool the lower amount of warm
outdoor air, while maintaining the air quality of the room.
Case studies of carbon dioxide sensors application in the United States have demonstrated
an energy savings of about 10%, and a payback period of about 3 years. The price of CO2
sensors is expected to decrease due to higher market proliferation, giving them a better
return-on-investment[3].
Carbon monoxide sensors for indoor car parks ventilation control
Carbon monoxide sensors are used to monitor the concentration of carbon monoxide (CO)
in an enclosed area, usually indoor or underground car parks such as in commercial or
residential buildings. CO is a colourless and odourless gas emitted from vehicle exhaust that
can be lethal to humans at high concentration. To ensure safety of car park users, indoor air
is constantly ventilated regardless of occupancy or
activity level within the car park, causing significant
energy consumption by the ventilation system.
With carbon monoxide sensors, the ventilation
system will only start when the concentration of CO
has reached a pre-determined level. Unnecessary
energy consumption by the ventilation system is thus
prevented. Up to 80% energy savings is possible
with the application of CO sensors in an indoor car
park[4], with a short payback period.
Figure 3: Carbon monoxide sensors such as this are
installed in car parks to optimise ventilation
Proper application of sensors can produce considerable energy savings for building owners
and occupants. To be more effective, sensors will have to be adopted as part of a
comprehensive building energy management system that allows a high degree of control
over lighting, air-conditioning and ventilation systems. This will lead to a smarter building
capable of optimising energy consumption to be as efficient as possible.
To learn more about the application of sensors in buildings, please visit:
http://www1.eere.energy.gov/buildings/technologies/sensors_controls_research.html
Contributed by H2PC Asia resource team of E2 writers. Please contact byap@h2pcasia.com
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[1]. http://www.iea.org/aboutus/faqs/energyefficiency/
[2].’Occupancy Sensors: Energy Savings – Fact Sheet’
http://wastereductionpartners.org/phocadownload/userupload/Resources/Energy%20Saving%20Fact
%20Sheet%20Occupancy%20Sensor.pdf
[3]. ‘Demand-Controlled Ventilation Using CO2 Sensors’
http://www1.eere.energy.gov/femp/pdfs/fta_co2.pdf
[4]. ‘Carbon Monoxide Detection and Control Systems for Parking Structure: Guidelines for the Design
Engineer’ http://www.inteccontrols.com/pdfs/CO_Parking_Garage_Design_Guidelines.pdf