ASHRAE Journal - November 2009 - B25

Trigeneration Basics Cogeneration uses a generator or other heat engine to produce electricity to power a building. Any excess heat from the generator is used to heat the building when required. Heat from the generator only can be used when the building requires heating, so cogeneration is suitable to cold climates. T rigeneration uses a generator and an absorption chiller, which has the ability to convert waste heat from the generator into cooling energy. The efficiency of a trigeneration plant is potentially much higher than a traditional HVAC plant and cogeneration plant. Trigeneration can reduce the impact of external power outages on building power, heating and cooling. This is especially System significant for large computer installations where cooling of the system is essential. Transmission costs also are reduced. Trigeneration plants reach overall system efficiencies of 90%. Typical central power plants that use boilers for heating and chillers for cooling and do not recover any waste products are about 33% efficient. With the installation of the trigeneration system, the complex has lowered the CO2 emissions by more than 1 million kg per year (1102 ton). This equates to about $163,500 per year saving on energy costs. A gas-fired generator can potentially save up to 2400 L (634 gallons) of water per hour of operation compared to energy produced from coal. Quantity Third-Party Integration Communications Native BACnet Modbus • M-Bus Native BACnet I/O • • • • • • • • • • • • • • • 820 570 355 4973 ing a natural gas-fired generator that produces electricity and heat, and an absorption chiller that uses the waste heat from the electricity generation to chill water. The electricity is used in the Majura Office Park and sold back into the grid; the chilled and heating water is used for heating and cooling in the four office buildings. The BMS engineering and construction departments worked seamlessly throughout the project and information was shared by the entire team, which enabled a comprehensive and open attitude to achieve commercially viable outcomes and to meet the complex technical design brief. The design process was continually developing during the project, which entailed constant design review of the control system requirements. The design change requirements were filtered down to the project team, including team members who were in Germany and China. The main communication backbone is a (10/100) MB fiber optic local-area network (LAN) installed between the buildings within the Canberra International Airport Complex (International Terminal Building, Majura Office Park and Brindabella Business Park) using a virtual LAN (VLAN), creating a large BACnet network, with more than 70 BACnet building controller (B-BC) devices communicating using BACnet/ Ethernet and connected to the LAN via 10Base-T network ports. BACnet MS/ TP (baud rate 76.8 Kbps) is then used to connect to BACnet advanced application controllers (B-AAC) located in the field (such as variable air volume [VAV], fan November 2009 Chillers Cooling Towers Boilers Air-Handling Units Fans Pumps VAV Boxes Fan Coil Units Pump VFDs Gas Flow Meters Magnetic Flow Meters Thermal Energy Meters Gas-Fired Genset Electrical Meters MSSB UPS Total BACnet Objects 4 3 3 11 23 42 84 15 82 4 11 71 1 54 8 4 • Table 1: Systems connected and integrated into the building management system. coil and air-conditioning units, etc.). BACnet MS/TP networks are also used to connect a series of variable-frequency drives (VFD) to these B-BC devices for control and monitoring purposes. Separate M-BUS (baud rate 2400 bps) and MODBUS/RTU (baud rate 9600 bps) LANs are used to monitor a network of thermal energy meters, electrical meters, chillers and generator PLC via an M-BUS gateway and MODBUS-enabled application and system controllers. A dedicated Web server with a 100 Base-T connection serves the Canberra International Airport Complex. Five local operator workstations (OWS) are also installed within plant rooms and facility offices throughout the airport for service and maintenance. The Web server is configured to automatically send critical alarms via SMS text, as well as e-mail to maintenance staff. Remote connectivity is provided via high-speed ADSL connection to access the Web server, as well as directly to BACnet controllers via remote UDP/IP (BACnet/IP) connection. This arrangement allows quick access to the site in the event of failure of major equipment. The total connected I/O of nearly 5,000 points is comprised of approximately 20% native BACnet third-party objects, 20% integration of MODBUS and M-BUS objects via multipurpose controllers with built-in router and gateway functionality. The breakdown of the BMS connected I/O is indicated in Table 1. B A C n e t ® To d a y | A S u p p l e m e n t t o A S H R A E J o u r n a l

ASHRAE Journal - November 2009

Table of Contents for the Digital Edition of ASHRAE Journal - November 2009