A HVAC control system is a computerized control system for climate control in buildings. A control system is a device or set of devices to manage command direct or regulate the behavior of other devices or systems A control system is a device or set of devices to manage command direct or regulate the behavior of other devices or systems Stand alone control devices may be pneumatic or electronic. Some may have microprocessors, but to be considered a "control system" for the context of this article, computerized and networked are expected requirements. HVAC stands for heating, ventilation, air-conditioning. HVAC (pronounced either "H-V-A-C" or occasionally " H-vak " is an Initialism or Acronym that stands for " Heating Ventilation is the intentional movement of Air from outside a building to the inside The term air conditioning refers to the cooling and dehumidification of indoor air for Thermal comfort. Often, these integrate fire, security, and lighting controls into one system. These systems typically use one or more central controllers to command and monitor the remote terminal unit controllers, and they communicate with one or more personal computers that are used as the operator interface. These control systems are typically used on large commercial and industrial buildings to allow central control of many HVAC units around the building(s). The latest systems use ethernet for communications between central controllers--allowing remote access from a web browser. Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs A web browser is a software application which enables a user to display and interact with text images videos music games and other information typically located on a
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Direct digital control
Central controllers and most terminal unit controllers are programmable, meaning the direct digital control program code may be customized for the intended use. The program features include time schedules, setpoints, controllers, logic, timers, trend logs, and alarms. Setpoint is the target value that an automatic control system for example PID controller, will aim to reach The unit controllers typically have analog and digital inputs that allow measurement of the variable (temperature, humidity, or pressure) and analog and digital outputs for control of the transport medium (hot/cold water and/or steam). An analog or analogue signal is any continuous signal for which the time varying feature (variable of the signal is a representation of some other A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for Digital inputs are typically (dry) contacts from a control device, and analog inputs are typically a voltage or current measurement from a variable (temperature, humidity, velocity, or pressure) sensing device. Digital outputs are typically relay contacts used to start and stop equipment, and analog outputs are typically voltage or current signals to control the movement of the medium (air/water/steam) control devices. (Valves/dampers/motor speed)
History
It was only natural that the first HVAC controllers would be pneumatic, as the engineers probably understood fluid control. Pneumatics, Pressurized gas to affect mechanical motion Pneumatic power is used in Industry, where it is common to have factory units plumbed for Compressed Thus mechanical engineers could use their experience with the properties of steam and air to control the flow of heated or cooled air. Mechanical Engineering is an Engineering discipline that involves the application of principles of physics for analysis Design, Manufacturing There are still pneumatic HVAC systems in operation in some buildings, such as schools and offices, which can be a century old.
After the control of air flow and temperature was standardized, the use of electromechanical relays in ladder logic, to switch dampers became standardized. Ladder logic is a philosophy of drawing electrical logic schematics A damper is a valve or plate that stops or regulates the flow of air inside a duct, Chimney, VAV box, Air handler, or other air handling equipment Eventually, the relays became electronic switches, as transistors eventually could handle greater current loads. In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals By 1985, pneumatic control could no longer compete with this new technology. Year 1985 ( MCMLXXXV) was a Common year starting on Tuesday (link displays 1985 Gregorian calendar)
By the year 2000, computerized controllers were common. 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. Today, some of these controllers can even be accessed by web browsers, which need no longer be in the same building as the HVAC equipment. This allows some economies of scale, as single operations center can easily monitor thousands of buildings.
See also
External links
- ASHRAE - The American Society of Heating, Refrigerating and Air-Conditioning Engineers
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