Exploiting the full potential of a building-management system
There are major benefits to be gained by using a single building-management system to control all systems in a building rather than having separate systems for, say, heating, ventilation and lighting. Ian Ellis explains.
A building management system can be a key tool for any business. It can provide a comfortable working environment for building occupants — enhancing productivity and contribute significantly to saving energy costs and a reduced carbon footprint if used correctly. All too often the capabilities of the BMS itself are not fully utilised, and the potential benefits are lost.
To fully realise this potential the system should be used as the true building manager linking together as many of the different systems that use energy within the building as possible. Users have been put off doing this in the past because of concerns about the potential complexity of the system and the possible increase in initial costs for the system. These issues are now easier to overcome, and an integrated building management system such as the Desigo BMS from Siemens will bring many benefits to the building owner or user.
The key to achieving these benefits is the interaction between devices.
A practical example is the control of a meeting room. When the room is unoccupied it is appropriate to reduce the heating temperature setpoints, increase those for the cooling and turn the lighting off. This can all be done via a signal from an occupancy or CO2 sensor to both the lighting- and temperature-control systems.
In most cases however this does not happen; the two systems are not integrated, and energy-saving potential is lost.
This is a shame as this type of demand-based control is relatively easy to implement, and the payback period for any additional work can be fairly short. The EN 15232 European standard for energy efficiency in buildings states that savings of 30% can be achieved using this type of control.
The ventilation system can also be controlled based on the same demand information. Again this can be linked into the overall system so fans controlled by variable-speed drives can be turned down to save energy and help prolong the life of the plant equipment. The fact that this can all be done automatically increases the energy-saving potential because the system is not relying on users to remember to turn systems down or off.
Other benefits are available. The BMS head end can be used as a single point of information for the whole building if all the building-services data are linked to it. This means information from multiple systems can be displayed on a single page to help give a clearer picture of how the building is performing. Data from meters can also be integrated into the BMS allowing it to become both the monitoring and control system. This makes analysis of different parts of the building or even multiple buildings more straightforward. Energy usage from the different sub-systems in the building such as the lighting and heating systems can be displayed together. One of the main advantages of having a single system is that training effort is reduced as operatives only need to learn one way of how to interface all their building services information.
The last few years has seen a huge growth in the number of building-services products using open communication protocols such as BACnet, LON, KNX, Modbus, M-Bus and others — including chillers, pumps and variable-speed drives, as well as some fire and security systems. This has made integration more straightforward and helped reduce the cost and complexity of such projects. It also allows for more ‘low-level’ integrations at a local level to help reduce complexity in the system.
The key to a successful integrated system is to ensure proper planning takes place. End users must be clear what they want to achieve from their systems and this needs to be understood by everyone involved in a project. Make sure each piece of information that is integrated is necessary and gives a clear benefit in either operational or energy-saving terms. Integrating unnecessary information adds to the engineering time and costs and introduces unnecessary complexity to the system.
The final factor that needs to be taken into account is the cost analysis of an integrated system. On average, 20% of total life-cycle costs arise during planning and construction of a building, with the remaining 80% during its usage — assuming an average building lifecycle of 50 years. The payback of such an integrated system is quite short, so its energy-saving benefits will be enjoyed for a long time and continue to benefit the user.
Ian Ellis is marketing manager with Siemens Building Technologies.