A building automation system is a comprehensive system composed of a central computer and various control subsystems. It utilizes sensor technology, computers, and modern communication technology to provide fully automated integrated management of systems including heating, ventilation, elevators, air conditioning, water supply and drainage, power distribution and backup power, automatic fire alarms and fire-fighting linkage, and security. The subsystems are interconnected and can work together to provide building owners, managers, and customers with the most effective information services and a highly efficient, comfortable, convenient, and safe environment.
Building Automation (BA) systems typically employ distributed control and centralized monitoring and management. The key components are sensing technology, interface control technology, and management information systems. So, what kinds of sensors are used in BA systems?
Sensors are the primary devices in automatic control systems, directly interacting with the object being measured. Their function is to sense changes in the measured parameters and emit corresponding signals.
There are generally three requirements when selecting a sensor: high accuracy, high stability, and high sensitivity.
1. Temperature sensor
In building engineering, the main contact-type temperature sensors used, such as resistance temperature detectors (RTDs), thermocouples, and PTC silicon sensors, often exhibit a time lag in measurement because sufficient heat exchange is required between the sensing element and the measured medium. For example, Pt1000 has a resistance of 1000Ω at 0°C, which decreases as the temperature increases. Its sensitivity is typically 3–4Ω/K, and its response speed is generally 15–30.
2. Pressure sensor
Commonly used pressure sensors include electrical pressure sensors, which convert changes in the measured pressure into changes in various electrical quantities such as resistance and inductance, thereby achieving indirect pressure measurement. Common types include differential pressure switches, gauge pressure sensors, and static pressure sensors.
3. Flow sensor
Electromagnetic flowmeters are commonly used. According to Faraday's law of electromagnetic induction, an induced electromotive force is generated in a conductor that moves in a magnetic field and cuts magnetic lines of force. This induced electromotive force has a linear relationship with the volumetric flow rate of the fluid.
4. Humidity sensor
Used to measure indoor air relative humidity.
5. Liquid level sensor
Used to control the upper and lower limits of liquid levels in water tanks, pools, etc.
Actuator:
In the system, it receives control signals from the controller and converts them into linear or angular displacement to change the flow cross-sectional area of the regulating valve, thereby controlling the inflow or outflow of materials or energy into the controlled process, thus achieving automatic control of process parameters.
1. Air Valve Actuator: Used to control air valves installed at fresh air and return air inlets. It can control both opening and closing. The actuator is equipped with a universal clamp that can be directly clamped onto the drive shaft of the air valve. It also has a manual reset button for manual adjustment in case of malfunction. Actuators with different torques can be selected according to the size of the duct cross-section.
2. Water pipe valve actuator: Used in conjunction with valves, there are two types: on/off and regulating. On/off actuators are generally larger in diameter and are used in cooling and heating plants to control the opening and closing of process pipelines in various systems and the switching between various operating conditions. Regulating actuators are mainly used to control flow. In air conditioning units, they control the return water flow and steam humidification flow according to the temperature and humidity setpoints of the controller to maintain the temperature and humidity at the setpoints.
Field Controller (DDC):
A DDC (Distributed Control Center) is a controller used to monitor and control electromechanical equipment in a system. It is a complete controller with the necessary hardware and software, capable of independent operation and unaffected by network or other controller failures. Controllers are provided in quantities and specifications tailored to different types of monitoring points to meet control requirements. Each DDC has a 10-15% capacity expansion or redundancy.
The controller configuration must meet the following requirements:
(1) A programmable DDC with a 32-bit or 16-bit microprocessor;
(2) It has the ability to operate independently or networked, detached from the central control host;
(3) Has a power module
(4) Has a communication module
(5) The DDC has a template LED display showing the real-time status of each digital input and output point. When the external power is interrupted, the DDC's backup battery can ensure that the data in the RAM is not lost for 60 days.
(6) When external power is restored, the DDC can automatically resume normal operation without human intervention.
(7) When the data stored in the DDC is lost abnormally, the user can rewrite the data to the DDC controller through the field standard serial data interface and through network operation.
(8) The operation and application programs of DDC are both written in PPCL high-level language.
(9) The writing and modification of DDC programs can be done on the central station or through a portable computer.
(10) When the external power is interrupted and the backup battery is lost, the DDC can store its program.
(11) The acquisition accuracy of the DDC is matched with the accuracy of the sensor.
(12) Working environment: Temperature 0 to 50 degrees Celsius, relative humidity 0-90%
(13) Power supply: AC220V, 10%, 50HZ.
DDC has the following functions: timed start/stop, adaptive start/stop, automatic amplitude control, demand forecasting control, automatic event control, scanning program control and alarm processing, trend recording, and comprehensive communication capabilities.
Central Monitoring Station: The central management workstation system, consisting of a PC host, a large-screen color monitor, and a printer, is the core of the BAS system and can be directly connected to Ethernet. All monitored electromechanical equipment within the building is centrally managed and displayed here. The built-in software provides operators with drop-down menus, human-machine interfaces, and dynamic graphic displays, offering a user-friendly and easy-to-learn interface. Operation is simple; operators do not require any prior software knowledge and can manage the entire control system using only a mouse and keyboard.
