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Building automation is the auto centralized control of a building's heating, ventilation and air conditioning, lighting and other systems through a building management system or building automation system BAS. The goals of building automation are improved occupant comfort, economical operation of building systems, and reduction in energy intake and operating costs, and improved life cycle of utilities.
Building automation is an example of a circulated control system the computer networking of electronic devices intended to monitor and control the mechanical, security, fire and flood safety, lighting particularly emergency lighting, HVAC and humidity control and ventilation systems in a building.
BAS core functionality keeps building weather inside a particular range, gives light to rooms depending on an occupancy schedule in the lack of overt switches to the opposite, monitors performance and device failures in all systems, and gives malfunction alarms to building maintenance staff. A BAS should decrease building energy and maintenance costs in comparison to a non controlled building. Most commercial, institutional, and industrial buildings built after 2000 include a BAS. Many older buildings have been retrofitted with a new BAS, usually financed through energy and insurance savings, and other savings related with pre emptive maintenance and fault detection.

A building controlled by a BAS is frequently called an intelligent building, "smart building", or if a residence a "smart home". Commercial and industrial buildings have historically relied on robust proven protocols like BACnet while proprietary protocols like X-10 were used in homes. Recent IEEE standards notably IEEE 802.15.4, IEEE 1901 and IEEE 1905.1, IEEE 802.21, IEEE 802.11ac, IEEE 802.3at and consortia efforts like nVoy which verifies IEEE 1905.1 compliance or QIVICON provided a standards based foundation for heterogeneous networking of many devices on many physical networks for diverse reasons, and quality of service and failover guarantees proper to support human health and safety. therefore, commercial, industrial, military and other institutional users now use systems that differ from home systems usually in scale. See home automation for more on entry level systems, nVoy, 1905.1, and the big proprietary vendors who implement or resist this trend to standards integration.
Nearly all multi story green buildings are intended to accommodate a BAS for the energy, air and water conservation characteristics. Electrical device demand answer is a common function of a BAS, as is the more sophisticated ventilation and humidity monitoring obliged of "tight" insulated buildings. Most green buildings also use as many low power DC devices as possible, usually integrated with power over Ethernet wiring, so by meaning generally available to a BAS through the Ethernet connectivity. a passivhaus design meant to consume no net energy whatsoever will usually require a BAS to manage heat catch, shading and venting, and scheduling device use. Most building automation networks comprise of a main and secondary bus which connect high level controllers usually specific for building automation, but can be generic programmable logic controllers with lower level controllers, input/output devices and a user interface aka a human interface device. ASHRAE's open protocol BACnet or the open protocol LonTalk identify how most such devices interoperate. Modern systems use SNMP to track events, building on decades of history with SNMP based protocols in the computer networking world. Physical connectivity between devices was historically offered by dedicated optical fiber, ethernet, ARCNET, RS-232, RS-485 or a low bandwidth special function wireless network. Modern systems rely on standards based multi protocol heterogeneous networking like that particular in the IEEE 1905.1 standard and verified by the nVoy auditing mark. These accommodate usually only IP based networking but can make use of any present wiring, and also integrate powerline networking over AC circuits, power over Ethernet low power DC circuits, high bandwidth wireless networks like LTE and IEEE 802.11n and IEEE 802.11ac and frequently integrate these using the building specific wireless mesh open standard ZigBee. Proprietary hardware leads the controller market. Each company has controllers for particular applications. Some are intended with restricted controls and no interoperability, like simple packaged roof top units for HVAC. Software will usually not integrate well with packages from other vendors. Cooperation is at the Zigbee/BACnet/LonTalk level only. Current systems supply interoperability at the application level, allowing users to mix and match devices from different manufacturers, and to offer integration with other matched building control systems. These usually rely on SNMP, long used for this same function to integrate diverse computer networking devices into one coherent network. Controllers are generally small, purpose built computers with input and output potential. These controllers come in a range of sizes and potential to control devices usually found in buildings, and to control sub networks of controllers.
Inputs let a controller to read temperature, humidity, pressure, current flow, air flow, and other essential factors. The outputs let the controller to send command and control signals to slave devices, and to other parts of the system. Inputs and outputs may be either digital or analog. Digital outputs are on occasion called discrete based on maker. Controllers used for building automation may be grouped in three categories: programmable logic controllers PLCs, system/network controllers, and terminal unit controllers. but an extra device may also exist to integrate third party systems e.G. A stand alone AC system into a central building automation system. Terminal unit controllers typically are suited for control of lighting or simpler devices like a package rooftop unit, heat pump, VAV box, fan coil, etc. The installer usually selects one of the available pre programmed personalities best suited to the device to be controlled, and doesn't have to create new control logic.
Lighting may be turned on, off, or dimmed with a building automation or lighting control system depending on time, or on occupancy sensor, photosensors and timers. One common example is to turn the lights in a space on for a half hour since the last motion has been sensed. A photocell placed outside a building can sense darkness, and the time, and modulate lights in outer offices and the parking lot. Lighting is a good candidate for demand answer, with many control systems the capability to dim or turn off lights to take benefit of DR incentives and savings. In newer buildings, the lighting control may be depending on the field bus Digital Addressable Lighting Interface DALI. Lamps with DALI ballasts are completely dimmable. DALI may also detect lamp and ballast failures on DALI luminaires and signals failures.