Building Management System
A BMS or Building Management System in the HVAC (heating, ventilation and air-conditioning) industry is a computerized climate control system installed in a building that controls and monitors the building’s production of heating & cooling and manages the system that distributes this air around the building, and then locally controls the mixture of heating and cooling to achieve the desired room temperature.
Often these systems can be integrated with fire, security and lighting controls into one system. These systems normally use one or more central controllers to send commands and to monitor the remote terminal unit controllers. Typically the BMS or HVAC control systems would communicate with one or more personal computers that are used as the operator interface.
These control systems are most commonly used on large commercial and industrial buildings to allow for central control of one or many HVAC units situated around the buildings. The newest systems use Ethernet cable to communicate between central controllers, allowing remote access from a web browser.
DDC or Direct Digital Control refers to the program control for central and terminal unit controllers that may be customized for the intended use. The programs can include many different features such as time schedules, setpoints, controllers, logic timers, trend logs and alarms. The unit controllers would normally have both analog and digital inputs that allow for measurement of the variables (ie. Temperature, humidity, pressure) and analog and digital outputs for control of the transport medium ( hot/cold water and/or steam). Digital inputs would typically be dry contacts coming from a control device, and analog inputs are usually a voltage or current measurement from a variable sensing device.
Digital outputs are usually relay contacts used to start and stop equipment, and analog outputs are usually voltage or current signals to control the movement of the medium control devices, typically valves, dampers and motors.
BAS or Building Automation Systems refer to more complex HVAC systems, which allow the building owners to exercise more control over the heating and cooling in the building. Owners can monitor the system and respond to alarms generated by the system from either local or remote locations. The system can be scheduled to allow for occupancy or the configuration can be changed from the BAS. Sometimes, the BAS can directly control the HVAC components.