“If you cannot measure it, you cannot manage it”
(Narris, 2017). Therefore, to monitor and manage a building, there is a need for
equipment such as sensors and meters (Narris, 2017). “Sensor is a device that
responds to a physical stimulus (such as heat, light, sound, pressure,
magnetism, or a particular motion) and transmits a resulting impulse (as for
measurement or operating a control)” (Merriam-Webster, 2017). Wilson (2005)
stated that different physical properties such as light intensity, temperature,
pressure, force, flow, etc., can be measured using various sensors. Therefore,
sensors are classified according to the measured parameters (Engineersgarage,
2017). This part of the final essay reviews several common types of sensor such
as temperature, flow, electrical power and occupancy sensors which are applied to
energy monitoring in buildings.
Temperature is an important measurement in buildings
(Narris, 2017). Thermocouples, resistance temperature devices, thermistors, etc.,
are temperature sensors (Juliantrubin, 2017). Thermocouples are used often due
to their low cost, the wide range of temperatures they can monitor (200 to 2600oC),
robustness and simplicity (Axmad et al., 2016). However, this type of
temperature sensor also has certain disadvantages such as being prone to
corrosion and being difficult to calibrate (Sciencing, 2017). Being difficult
to calibrate of thermocouples is likely due to their large range of temperature
that they can measure.
Compared to thermocouples, resistance temperature
devices (RTD) have high accuracy and stability (Axmad et al., 2016).
Additionally, they are easy to replace and install. However, RTDs are expensive
(Polytechnic Hub, 2017).
Axmad et al., (2016) stated that “thermistors are the most accurate and
sensitive type of sensors for temperature reading”. This means they have the
ability to determine insignificant changes in temperature very quickly; they
can ensure fast responses in seconds (Get Revising, 2014). Their response times
are shorter than those of RTDs, but this is the same with thermocouples (Axmad et al., 2016). However,
this type of temperature sensor work on batteries (Get Revising, 2014). Clearly
this is a disadvantage because batteries need to be changed periodically.
Air and liquid flows are measured via flow sensors
(Wilson, 2005). Flow sensors have various measurement equipment such as
magnetic flow sensors, positive displacement flow sensors, vortex shedding
sensors, ultrasonic flow sensors and turbine-based flow sensors. Among them,
ultrasonic flow meters demonstrate excellent results in terms of
non-intrusiveness and accuracy (Axmad et al., 2016). However, this type of flow
sensor demands a significant investment for its installation (Flowmetrics Inc,
sensors are used to determine the presence of occupants via their movements;
the light will switch on when a sensor determines that there are people in the
room and will switch off when the room is unoccupied (Axmad et al., 2016). Also, Axmad et al., (2016) stated that “although many studies have demonstrated the importance
of occupancy information for whole building climate control, occupancy sensors
in buildings are currently mainly used for lighting control purposes”. Indeed, “use of occupancy sensors can save up to 30% electrical energy used for
lighting” (Garg and Bansal, 2000). A motion detector is one of the main kinds
of occupancy sensors, which use infrared detectors,
ultrasonic detectors, etc. (Sustaining Our World, 2015).
Infrared detectors are not able to determine differences in objects if
those objects have similar temperatures. Therefore, data received from infrared
detectors can be inaccurate in many case (Online Science, 2017). This is one of
the main disadvantages of infrared detectors.
Ultrasound sensors need to be calibrated carefully to avoid incorrect or
false commands. For example, small movements of the ventilation system can
contribute to enabling switches (Sustaining Our World, 2015).
These sensors can be used with two communication technologies such as
wired and wireless. Wireless technology is cheap and has low cost of operation
and installation (Axmad et al., 2016). This type of communication technology is used often due to its
simplicity and flexibility (Abubakar et al., 2017). In turn, the wired
technology is reliable (Axmad et al., 2016).