Controller Controllers are essentially small, purpose-built computers with input and output capabilities. These controllers come in a range of sizes and capabilities to control devices commonly found in buildings, and to control sub-networks of controllers. Inputs allow a controller to read temperature, humidity, pressure, current flow, air flow, and other essential factors. The outputs allow the controller to send command and control signals to slave devices, and to other parts of the system. Inputs and outputs can be either digital or analog. Digital outputs are also sometimes called discrete depending on manufacturer. Controllers used for building automation can be grouped in three categories: programmable logic controllers (PLCs), system/network controllers, and terminal unit controllers. However an additional device can also exist in order to integrate third-party systems (e.g. a stand-alone AC system) into a central building automation system. Terminal unit controllers usually are suited for control of lighting and/or simpler devices such as a package rooftop unit, heat pump, VAV box, fan coil, etc. The installer typically selects one of the available pre-programmed personalities best suited to the device to be controlled, and does not have to create new control logic.
Occupancy Occupancy is one of two or more operating modes for a building automation system; unoccupied, morning warmup, and night-time setback are other common modes. Occupancy is usually based on time of day schedules. In occupancy mode, the BAS aims to provides a comfortable climate and adequate lighting, often with zone-based control so that users on one side of a building have a different thermostat (or a different system, or sub system) than users on the opposite side. A temperature sensor in the zone provides feedback to the controller, so it can deliver heating or cooling as needed. If enabled, morning warmup (MWU) mode occurs prior to occupancy. During morning warmup the BAS tries to bring the building to
setpoint just in time for occupancy. The BAS often factors in outdoor conditions and historical experience to optimize MWU. This is also referred to as
optimized start. Some buildings rely on
occupancy sensors to activate lighting or climate conditioning. Given the potential for long lead times before a space becomes sufficiently cool or warm, climate conditioning is not often initiated directly by an occupancy sensor.
Lighting Lighting can be turned on, off, or dimmed with a building automation or
lighting control system based on time of day, or on occupancy sensor, photosensors and timers. One typical example is to turn the lights in a space on for a half-hour since the last motion was sensed. A photocell placed outside a building can sense darkness, and the time of day, and modulate lights in outer offices and the parking lot. Lighting is also a good candidate for
demand response, with many control systems providing the ability to dim (or turn off) lights to take advantage of DR incentives and savings. In newer buildings, the lighting control can be based on the
field bus Digital Addressable Lighting Interface (DALI). Lamps with DALI ballasts are fully dimmable. DALI can also detect lamp and ballast failures on DALI luminaires and signals failures.
Shading and glazing Shading and glazing are essential components in the building system, they affect occupants' visual, acoustical, and
thermal comfort and provide the occupant with a view outdoor. Automated shading and glazing systems are solutions for controlling solar heat gains and glare. It refers to the use of technology to control external or internal shading devices (such as blinds, and shades) or glazing itself. The system has an active and rapid response to various changing outdoor data (such as solar, wind) and to changing interior environment (such as temperature, illuminance, and occupant demands). Building shading and glazing systems can contribute to thermal and lighting improvement from both energy conservation and comfort point of view.
Dynamic shading Dynamic shading devices allow the control of daylight and solar energy to enter into built environment in relation to outdoor conditions, daylighting demands and solar positions. The common products include
venetian blinds,
roller shades,
louvers, and shutters. They are mostly installed on the interior side of the glazing system because of the low maintenance cost, but also can be used on the exterior or a combination of both.
Air handlers Most
air handlers mix return and outside air so less temperature/humidity conditioning is needed. This can save money by using less chilled or heated water (not all AHUs use chilled or hot water circuits). Some external air is needed to keep the building's air healthy. To optimize
energy efficiency while maintaining healthy
indoor air quality (IAQ),
demand control (or controlled) ventilation (DCV) adjusts the amount of outside air based on measured levels of occupancy. Analog or digital temperature sensors may be placed in the space or room, the return and supply
air ducts, and sometimes the external air. Actuators are placed on the hot and chilled water valves, the outside air and return air dampers. The supply fan (and return if applicable) is started and stopped based on either time of day, temperatures, building pressures or a combination.
Alarms and security All modern building automation systems have alarm capabilities. It does little good to detect a potentially hazardous or costly situation if no one who can solve the problem is notified. Notification can be through a computer (email or text message),
pager, cellular phone voice call, audible alarm, or all of these. For insurance and liability purposes all systems keep logs of who was notified, when and how. Alarms may immediately notify someone or only notify when alarms build to some threshold of seriousness or urgency. At sites with several buildings, momentary power failures can cause hundreds or thousands of alarms from equipment that has shut down – these should be suppressed and recognized as symptoms of a larger failure. Some sites are programmed so that critical alarms are automatically re-sent at varying intervals. For example, a repeating critical alarm (of an
uninterruptible power supply in 'bypass') might resound at 10 minutes, 30 minutes, and every 2 to 4 hours thereafter until the alarms are resolved. Security systems can be interlocked to a building automation system. If occupancy sensors are present, they can also be used as burglar alarms. Because security systems are often deliberately sabotaged, at least some detectors or cameras should have battery backup and wireless connectivity and the ability to trigger alarms when disconnected. Modern systems typically use power-over-Ethernet (which can operate a
pan-tilt-zoom camera and other devices up to 30–90 watts) which is capable of charging such batteries and keeps wireless networks free for genuinely wireless applications, such as backup communication in outage.
Fire alarm panels and their related smoke alarm systems are usually hard-wired to override building automation. For example: if the smoke alarm is activated, all the outside air dampers close to prevent air coming into the building, and an exhaust system can isolate the blaze. Similarly,
electrical fault detection systems can turn entire circuits off, regardless of the number of alarms this triggers or persons this distresses.
Fossil fuel combustion devices also tend to have their own over-rides, such as
natural gas feed lines that turn off when slow pressure drops are detected (indicating a leak), or when excess
methane is detected in the building's air supply. ==Buses and protocols==