The growing role of sensors in modern building management systems
Buildings are getting smarter in response to growing user expectations, developers’ desire for greater profitability, and the availability of enabling technologies. The heating, ventilation and air-conditioning (HVAC), security and lighting systems of the past are being updated and augmented by new services designed to make buildings more comfortable, efficient, climate-friendly and profitable.
The key enabler of intelligent buildings is sensing technology that provides the raw data upon which these services rely. The relatively low cost of deploying many sensor types is also encouraging developers to deploy them specifically to enable analytic techniques that can create entirely new insights about the way that their buildings are used. It is these new applications that will make buildings truly intelligent.
Simple sensing
Sensing for intelligent buildings involves measuring both basic parameters, such as temperature or humidity, and combining multiple sensing signals to determine other parameters, such as building occupancy.
For example, simple contact sensors can be used to show whether doors and windows are open or closed. The resultant data forms a useful basis for general building security. But the low cost of contact sensors also enables them to be widely deployed, bringing additional security benefits when, for example, used in places such as laboratories to track access to restricted store cupboards, cabinets, or fridges.
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Thermal sensors have long been used in HVAC systems to measure ambient air temperatures and are now also being used to check the operating temperature of sensitive equipment, such as on-premises data centres, to ensure it can work as efficiently as possible. Continuous temperature monitoring also plays an important role in ensuring that HVAC systems do not harbour dangerous bacteria such as legionella. Temperature-sensing technologies include the old-fashioned thermocouple, temperature-dependent resistors, negative thermal coefficient thermistors, and semiconductor devices.
Humidity sensors measure the amount of water vapour in the air, and are important for keeping people comfortable, ensuring machinery can operate correctly, and for preserving health by avoiding the growth of mould and spores in buildings. Humidity detection can be done by capacitive, resistive, or thermal means.
Water-quality sensors are used to measure chemicals, ions, suspended solids, organic elements, and pH levels, and so are important for ensuring that a building’s potable water is fit for human consumption, suitable for use in any onsite machinery, and, critically, can be used in air-conditioning systems without causing health issues. Pressure or flow sensors can also be deployed to monitor, for example, whether filter screens are becoming clogged and need maintenance.
The pandemic has prompted increasing interest in the quality of the air that we breathe. Common gas sensors can measure oxygen concentrations in room air, carbon monoxide as part of fire-sensing systems, and carbon-dioxide levels to avoid stuffiness in highly insulated buildings. Smoke sensors can measure the level of air-borne particulates, essential for fire safety. And pollen sensors are being developed that can detect, identify, and count pollen, mould, dust, and other particles, such as silicates and microplastics, in real time.
Data from these sensors can be integrated with temperature and humidity readings as part of environmental monitoring schemes in buildings.
Motion sensing
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Motion sensing is becoming increasingly important in intelligent buildings, for security and surveillance purposes, and to ensure that buildings don’t waste energy by heating and lighting empty rooms. There are several forms of motion sensor. One of the simplest is based on flooding an area with ultrasonic waves. The sensor then measures the way those waves are reflected within the environment, and how they are altered by the presence of a person. Passive infrared sensors (PIR) detect the heat people emit by comparing the differing amounts of infrared radiation arriving at two windows in front of the active element of the sensor. When people are static, the amount of radiation arriving at the two windows is the same. When they move, the amount of infrared arriving at each window differs, indicating movement.
These simple sensors have been widely used in domestic burglar alarms, automatic doors, and no-touch hand dryers for years. However, they are now being used to much more sophisticated effect. For example, a simple PIR detector can be mounted under a desk or table, or above a cubicle, to sense whether anyone is occupying that space. Small sensor windows and narrow lenses help the sensors avoid false positives, for example from people walking past a desk. Sensors are mounted in a small battery-powered box, with a low-power wireless connection to a gateway linked to the building management system.
It is also possible to use infrared to check how far people are from a sensor, by measuring how long it takes for an infrared pulse to be reflected off a person and return to the sensor. An infrared sensor array can go one step further, measuring the direction in which people are moving as well.
Other sensor types
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Some intelligent building developers are installing electric current sensors so they can monitor the way that electricity is used in their properties. It seems like a crude approach, but the correct deployment of current sensors (on individual machines, circuits, or zones) can provide data for managing energy efficiency in a building as well as helping to monitor the operation of critical equipment. Once such sensors are in place, it becomes possible to build up a historic profile of normal current consumption for each machine, circuit, or zone, and therefore to automatically recognise anomalies and take action to investigate and rectify them. Some sheltered housing developers are even piloting schemes that track electricity usage in their facilities, so that concerned relatives can keep an eye on whether residents are maintaining their daily routines (boiling a kettle in the morning, making toast at lunchtime) to help monitor their welfare.
Intelligent buildings may use other forms of sensor, including optical sensors for monitoring light, and level sensors to check how much fluid is in reservoirs to sense possible overflows. Parking garages may use specialised gas sensors to check for the build-up of exhaust gases or any fuel spillages in basements. And very tall buildings are increasingly using accelerometers as part of active vibration-damping systems designed to counter the effects of high winds and minor seismic events.
Putting sensor data to work
Each of these sensors is fairly simple but the data they generate can be very powerful when aggregated for analysis within the context of a building management system. This level of data gathering also has privacy implications. For example, a positive application of occupancy monitoring sensors would be to efficiently allocate spaces in a hot-desking environment, but the technology could also be abused by overzealous employers to check on staff presence. Similarly, time-of-flight sensors can be used to monitor the flow of people through a building, which is useful for ensuring safety and security, but abusive if used to track consumer shopping patterns in a supermarket.
Legislation such as Europe’s General Data Protection Regulation must be considered when planning the services that will be derived from sensor deployments in intelligent buildings.
It is increasingly important that the buildings in which we live, work and play protect our health and the health of the planet by providing maximum comfort at minimal environmental cost. A wide variety of sensors is now available to provide the raw data necessary to make this kind of multifactor optimisation possible. These large sensor deployments can also enable new kinds of analysis which, when used responsibly, will make intelligent buildings even smarter.
This article was taken from the latest edition of Focus magazine. Click below to read the magazine in full, or alternatively, if you have a question about sensors for building automation you can get in touch with our team of technical specialists.
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