Control Systems in Building Automation
BAS (Building Automation Systems) refer to complex systems governing various subsystems and devices concerning heating, access control, air conditioning, fire protection and many other functions. Formerly the building automation was dedicated to HVAC (heating, ventilation and air conditioning). However, the recent development of circumstances has fostered new objectives of BAS.
The increasing cost of electricity and decreasing costs of instrumentation parts of BAS justify their use. With increasing data storage capacity of devices it is possible to control, analyze and optimize the power consumption of typical building electrical devices. Moreover, the electrical devices number increases and their coordination makes sense.
Furthermore, the bandwidth and feasibility of communication technologies forces vendors to incorporate network interfaces into their products. For example, thermometers with Ethernet interface are not uncommon. Finally, the wireless technologies developments, which mow down the burden of laying cables across neat houses, encourages the spread of building automation even in private houses.
Closed loop control methods intrinsically concentrate on control of linear time invariant system. Control tasks of building automation deals with systems beyond this system basic class. The basic constraining issues have to be noted:
• The systems are non linear. For example, the valves of heating block have non linear characteristic of fluid flow vs. rotary position.
• The times of sample are long. 1s sampling is very common for temperature measurement.
• A/D and D/A converters resolution are poor. 8 bit converters are very common.
• Systems different from SISO often appear. Usually MIMO and MISO systems have to be controlled which is very uncomfortable with classical closed loop control.
Dynamic control in building automation is dedicated predominantly to HVAC systems. Dynamic control in local closed loops is provided by PID algorithms if it is possible. If more control loops start contradicting, or if the control loop does not perform a role of desired, then it is time for more sophisticated algorithms.
Posted by Cartiman Iman