5.22 Building Automation Systems (BAS)
BAS shall be direct digital control (DDC) for providing lower operating costs and ease of operation. Microprocessor PID controllers monitor and adjust building systems to optimize their performance and the performance with other systems in order to minimize overall power and fuel consumption of the facility, BAS monitor systems such as HVAC and lighting.
The system shall consist of series of direct digital controllers interconnected by a local area network. BAS system shall be accessible through a web browser. System shall have a graphical user interface and must offer trending, scheduling, downloading memory to field devices, real-time “live” graphic programs, parameter changes of properties, set point adjustments, alarm/event information, confirmation of operators, and execution of global commands.
A BAS is not required for every project and should be evaluated based on the size of the building. Buildings of 100,000 gsf. and more shall have a BAS. The size of the building, number of pieces of equipment, expected energy savings and availability of trained staff should all be considered before a decision is made. BAS is required and considered part of the system on large facilities (above 9,300 gross square meters (100,000 gross square feet)), both new facilities and major modernizations.
Level of Integration. Since the advent of micro-computer BAS systems, there has been an attempt to integrate as many systems as possible to reduce hardware requirements.
However, caution is advised when planning BAS systems with a high level of integration. The more integration, the more complex the system becomes and the more training is required for the operating staff. Also, reliability requirements for the different systems may vary.
Lighting control systems shall not be connected to BAS except for monitoring of lighting system.
Fire alarm systems, security systems and elevator systems shall not be controlled by a BAS. These systems should have independent control panels and networks. The BAS system shall monitor the status of these systems only, in order to prompt emergency operating modes of HVAC and lighting systems. See Chapter 7: Fire Protection Engineering, Electrical Requirements, Fire Alarm Systems, and Chapter 8: Security Design.
BAS shall utilize ‘open’ communication protocols, such as BACnet per ASHRAE Standard 135, to minimize the costs of providing integration and to allow interoperability between building systems and control vendors. Other open protocol language systems, such as LonTalk, may also be used, provided there is compatibility with overall regional and/or central monitoring and central strategies. A/E to specify and include functional design manual, hardware manual, software manual, operation manual, and maintenance manual. BAS shall have energy management and monitoring software.
In retrofits with an existing old-proprietary system in place, it is recommended that life cycle cost analysis determine between the complete replacement of the existing system or integrating the existing system with customized gateways. In the long term, with hardware and software costs falling as capabilities increase, energy savings are producing the paybacks required to justify the complete control retrofit.
Energy Conservation. The best targets for energy conservation in building systems are the HVAC system and the lighting system. HVAC control algorithms shall include optimized start/stop for chillers, boilers, air handling units and all associated equipment and feed forward controls based on predicted weather patterns. Lighting control shall be accomplished by use of separate control equipment, which allows BAS monitoring and reporting and control settings. Optimal start/stop calculates the earliest time systems can be shut down prior to the end of occupancy hours and the latest time systems can start up in the morning with the aim of minimizing equipment run time without letting space conditions drift outside comfort set points.Weather prediction programs store historic weather data in the processor memory and use this information to anticipate peaks or part load conditions. Programs also run economizer cycles and heat recovery equipment.
Maintenance Scheduling. The BAS shall include programs for control that switch pumps and compressors from operating equipment to stand-by on a scheduled basis. Also, programs that provide maintenance schedules for equipment in every building system shall be included, complete with information on what parts and tools are needed to perform each task.
System Design Considerations. BAS’s require measurements at key points in the building system to monitor part-load operation and adjust system set points to match system capacity to load demands. Table 5-6 of the previous section outlines the minimum control and monitor points for typical HVAC equipment. Controls cannot correct inadequate source equipment, poorly selected components, or mismatched systems. Energy efficiency requires a design that is optimized by realistic prediction of loads, careful system selection, and full control provisions. System ability must include logs of data created by user selectable features. In new buildings and major renovations, the BAS shall have approximately 20 percent spare capacity for future expansion. The system must provide for stand-alone operation of subordinate components. The primary operator workstation shall have a graphical user interface. Standalone control panels and terminal unit controllers can have text-based user interface panels which are hand-held or fixed.
Energy Measurement Instrumentation. BAS shall have the capability to allow building staff to measure energy consumption and monitor performance which is critical to the overall success of the system. Electrical values, such as V, A, kW, KVAR, KVA, PF, kWh, KVARH, Frequency and Percent THD, shall be measured. See also Chapter 6: Electrical Engineering, Site Distribution, for separate metering of power consumption.
Energy management measurements shall be totalized and trended in both instantaneous and time-based numbers for chillers, boilers, air-handling units and pumps. Energy monitoring data shall be automatically converted to standard database and spreadsheet format and transmitted to a designated PC. Energy points are those points that are monitored to ensure compliance with ASHRAE Standard 90.1.