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Chapter 15

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  1. Chapter 15 Building Automation Systems & Controllers

  2. Building Automation Systems • A system that uses microprocessors (computer chips) to control the energy using devices in a building • Most common control systems installed in commercial buildings today • Control HVAC equipment, lighting, security, and other essential functions in a building • Can indicate abnormal conditions like alarms and provide information regarding energy consumption and equipment maintenance • BAS include: • Central Supervisory Control System • Central-direct Digital Control Systems • Distributed Direct Digital Control System

  3. Central Supervisory Control System • The earliest BAS • A control system in which the decision-making equipment is located in one place and the system enables/disables local (primary) controllers • Large central pneumatic systems were used before CSCS • All control decisions are made by the CPU which are centrally located in the building • Control decisions are sent over a pair of wires to interface devices • Temperature sensors are wired into the CPU to relay building or system conditions • Require large amounts of wire to connect the devices and equipment • Wire cost was often 40% to 50% of total job cost • Because of the cost they were unavailable to most small to medium size businesses • Wire failure also cause problems • The system fails if the CPU fails • Manual overrides had to be implemented to avoid long time failure do to loss of the CPU • The failure rate of CSCS has caused a lack of confidence in its use • Interfaces are often available to enable communication between CSCS and new BAS

  4. Central Supervisory Control System • Perform a limited number of basic control functions • Control functions • Time clock functions • Enable or disable existing controllers to perform their function (unitary controllers) but does not directly perform control functions • It did enable one technician to change time clock functions for many controllers from a central location • Does not replace existing controllers but determines if they are allowed to operate • Local controllers enabled/disabled by CSCS • Pneumatic receiver controllers • Electric room thermostats • Light switches

  5. Central Supervisory Control System • Disadvantages • Doesn’t correct problems with existing local controls • High failure rate • Expensive • Limited control functions • Obsolete today • Replacement parts are scarce

  6. Central-Direct Digital Control Systems • System in which all decisions are made from one location • Provides closed loop control – feedback occurs between controller, sensor, and the controlled device • BAS controller replaces the thermostat or other controllers in the system • BAS systems have a sensor input and sends an output signal to a valve, damper, or other controlled devices • Came into use in the late 70’s to early 80’s and many are still in use today • Control devices without the need for a local controller • Use twisted shielded pairs of wires for communication • Field Interface devices – an electronic device that follows commands sent to it from the CPU of a CSCS • Cannot perform control on their own • May be referred to as (DGPs) data gathering panels (DAPs) data acquisition panels, slave panels, or submaster panels • Often referred to dumb panels or dumb input/outputs because they have no decision making abilities • May improve failure if CPU is lost

  7. Central-Direct Digital Control Systems • CDDCS reliability • Relies on a communication network to carry commands from the CPU to the field interface devices • The system fails if the CPU fails • Many used for supervisory control instead of closed loop control • Field controllers can be set-up as fail safe enabling them to continue to operate with a CPU failure

  8. Central-Direct Digital Control Systems • CDDCS Functions • Functions include: • Duty cycling • Electrical demand control • Time clock • Closed loop control • Include maintenance management functions such as • Data logging – recording of information such as temperature and equipment ON/OFF status at regular time intervals • Alarms – notification of improper temperature or other conditions existing in a building • Preventive maintenance reporting – the generating of forms to notify maintenance personnel of routine maintenance procedures • CDDCS have greater control capability than CSCS • Wiring cost are lower than CSCS • Biggest disadvantage is the reliability of the system because of CPU failure

  9. Distributed Direct Digital Control Systems • A control system that has multiple CPU’s at the controller level • Building control system currently most installed in commercial buildings today • Decisions are made by each controller • Began replacing CDDCS in the mid 1980’s • Architecture • Each controller has the ability to make its own decisions • The ability of decision making is spread out (distributed) throughout the system • Usually have a master or supervisory controller • The master controller provides communication support, a convenient place to connect a PC or modem for monitoring purposes, and connections for global data (data needed by all controllers in the network, OA & electrical demand) • Stand alone control – ability of a controller to function on its own • Since it is capable of stand alone control it is more reliable and a controller failure doesn’t fail the entire system

  10. Distributed Direct Digital Control Systems • Functions • Duty cycling • Electrical demand control • Time clock functions • Precise closed loop temperature control • Humidity control • Pressure control

  11. Distributed Direct Digital Control Systems Advantages • Improved reliability • Increased capacity • Stand alone features makes it better than previous systems • Are modular and easily expandable

  12. Building Automation System Controllers • Provide comprehensive control and monitoring of HVAC equipment in buildings • Often referred to as control modules, modules, and panels • Controllers include: • Application-specific controllers • Universal input-output controllers • Network communication module

  13. Application-Specific Controller • Designed to control only one type of HVAC system • Most of the time they are the most cost-effective controller • Cost are reduced because most of the software programming is done by the manufacturer, reducing set-up time • Hardware – physical parts that make up a device • Normally consist of: • Circuit board – electronically erasable, programmable, read-only memory chip (EEPROM) • Wiring base plate – normally separate from circuit board so that wiring can be installed and checked before installing circuit board, and it also makes it easier to change out of circuit boards • External Devices • Temperature sensors • Flow switches

  14. Software • Software – the program that enables a controller to function • Specifies the function of the controller • Manufacturers supply controller software that can be loaded on a PC or laptop • The software can be changed or downloaded to a new controller or one that has lost its program • Has the ability to change values, override valves & dampers to check their operation • No battery back up is needed since the software is stored in the EEPROM

  15. Unitary Controllers • Unitary Controllers • Controller designed for basic zone control using standard wall mounted temperature sensors • Used to control • Rooftop units • Heat pumps • Fan coil units • Normally compact in size • Some include air sensing capabilities, flow switches and dirty filter condition switches

  16. Air Handling Unit Controllers • Air Handling Unit Controllers – controller that contains inputs and outputs required to operate large central station air handling units • Control: • Humidification • Static Pressure • Indoor air quality • Many have complex control sequences • Dual ducts and multi-zone AHU’s use because unitary controllers are unable to do the job • Larger and more complex than unitary controllers • Software more complex as well • Used to control single-zone AHU with building space temperature controls

  17. Variable Air Volume Terminal Box Controller Variable Air Volume Terminal Box Controller • A controller that modulates the damper inside a VAV terminal box to maintain a specific building space temperature • Modulate the primary damper inside the VAV terminal box • Used to control pressure-dependent VAV terminal boxes • Also used in pressure independent VAV terminal box with reheat applications

  18. Universal Input-Output Controllers Universal Input-Output Controllers • Controller designed to control most HVAC equipment • Have a fixed number of inputs and outputs usually either 8 or 16 • Most use 24 VAC power supply • Software • Not programmed when shipped from the factory • Custom programmed in field • More difficult to program • More expensive that application specific controllers

  19. Network Communication Modules Network Communication Modules • Coordinates communication from controller to controller on a network and provides a location for operator interface • Most individual controllers do not communicate with each other but with the NCM and communication is passed along • Can have up to 200 controllers • Larger networks may have several NCM and then networked together • Hardware connections • Power supply • Communication network • Operator interfaces • Personal computers • Modems • Use single pair of twisted shielded wire