Putting the system back into building energy management
Kevin Sheldrake of Carlo Gavazzi explains why a joined-up approach to controls for services such as HVAC and lighting results in better long-term building performance.
In the phrase ‘building energy management system’ the last word is sometimes overlooked. But a dictionary definition of the word ‘system’ is ‘a set of things working together as parts of a mechanism or an interconnecting network; a complex whole’. And this points to the importance of thinking about the BEMS as a single network.
This idea that the building and, more importantly, the building services are a ‘complex whole’ is very significant when trying to achieve long-term energy-efficient operation. An holistic approach to designing, installing and operating building services is something that the sector has been striving for over the past two decades.
Unfortunately, far from ‘working together’ the various building-services systems sometimes seem to operate in opposition to one another. Heating and cooling run at the same time and lights can be on at night when other services have switched off. The reality of our buildings is that they are often not systematic at all.
However, controls technology is changing and extending the possibilities of what can be achieved. The technology also means that the building occupant can be the focus of the BEMS, which can save energy while also providing better comfort levels centred on a demand-control based system.
This means that services such as HVAC and lighting are only used when they are required. Parameters for ensuring a steady temperature can be programmed into the BEMS to ensure the building stays within certain performance parameters. But ultimately, the building operates for and in response to the requirements of occupants.
As buildings and building-services equipment become more advanced, the functions of today’s buildings are also becoming more complex. The demand for detailed information on building performance means that collecting and delivering that data is very important; it relies on the communications networks of the BEMS, which in turn rely on good-quality wiring. It may not be something that building managers consider too closely, but smart wiring systems can make all the difference in terms of capital cost and long-term efficiency.
Communications networks are used extensively in building-management systems at the automation and management levels. These are often known as the primary levels of a BEMS network. Devices further down the network, at the device level, such as sensors, and I/O modules, including indicators and actuators, would traditionally require separate wiring runs to link them to primary level.
This means that if a project plan includes a high number of these devices spread over a wide area, wiring costs using the traditional approach could be high. This may result in a compromise to the design of the system, with field devices omitted because it is considered too costly to include them. And so the BEMS cannot offer the functionality that the designer has in mind.
However, the very latest wiring technologies and techniques overcome this problem. For example, a 2-wire bus system (such as Dupline from Carlo Gavazzi) can link field devices together, without the requirement to connect each separate sensor or actuator back to the primary level of the building-management system.
Essentially, this approach creates decentralised sensors and I/O modules, giving much greater flexibility on the distribution of devices without the costs of extra wiring. There are also sensors for CO2, temperature and humidity that can now be powered from the bus — further reducing the need for wiring to power the devices. Also, a 2-wire bus cable can be run from sensor to sensor, collecting all the measured values. Each sensor does not have to be individually wired back to the main controller.
Forward-thinking manufacturers are leading the way on creating more potential for a single-system approach. For example, Carlo Gavazzi now offers a DALI gateway from its Dupline wiring system — making it possible to integrate HVAC with lighting applications.
The current industry approach to contracting means that lighting is specified as ‘electrical’ and HVAC as ‘mechanical’. This creates a false message that the two have to be controlled separately — an expensive and unnecessary approach. By putting the ‘system’ firmly at the heart of building management, designers and installers will deliver all-round better buildings.
Kevin Sheldrake is business development manager with Carlo Gavazzi.