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Best Practice Guide |
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Commercial Office Buildings |
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Distributed GenerationCogeneration
Cogeneration, also referred to as combined heat and power (CHP), has been around since the beginning days of central power. Thomas Edison used cogeneration as early as 1882 in America's first power plant, selling both electricity and the waste heat produced as a byproduct. Industrial facilities that require process heat or steam have long benefited from cogeneration systems that supply both electrical and thermal energy. More recently, owners and managers of commercial buildings have discovered that cogeneration can be a cost-effective source of reliable energy as well as heating and cooling - the single most expensive operating expense in typical buildings. A cogeneration system consists of an engine, turbine, or fuel cell (prime mover) that generates on-site electricity plus a heat recovery unit that captures waste heat from the generation process. In commercial buildings, cogeneration systems are usually connected to an absorption chiller that provides heating and cooling for the central heating, ventilation, and air conditioning (HVAC) system. The absorption chiller, which is powered by thermal energy, replaces a traditional chiller powered by electricity. Cogeneration systems can also heat domestic water for use in the building.
Common equipment options for on-site electricity generation that are compatible with cogeneration include: reciprocating engines, steam turbines, combustion turbines, and combined cycle combustion turbines. Reciprocating engines are the most common and most efficient prime mover used in commercial cogeneration systems today - technologically the most mature of the distributed energy resources, reciprocating engines are manufactured inexpensively and are widely available. Microturbines, fuel cells, and Stirling engines may be economically viable for cogeneration in the next few years as technology advances.
Absorption chillers, although technically part of the HVAC system, are fueled by low-grade waste heat recovered from on-site electricity generation. Absorption chillers are available in capacities ranging from 100 to 1,500 tons and use environmentally benign refrigerants and absorbents instead of polluting chlorofluorocarbons. Although absorption chillers have a low coefficient of performance compared to electrical chillers, they are extremely cost-effective and efficient when used with a cogeneration system since very little electricity is used to power the chiller. Consider that the cost of cooling is about 22 percent of a building's total electrical expenses - the savings become clear. Business ExamplesArden Realty installed a 600 kW cogeneration plant at a 417,000 sq. ft. office building in Southern California. In addition to supplying energy at peak times, the plant produces 150 tons of chilled water. Annual savings on the electric bill equal about 21 percent of the total bill. Qualcomm Incorporated's two cogeneration systems, collectively generating 7.2 MW, have been especially good investments. Qualcomm saves about $539,720 each year from two 500-ton absorption chillers connected to the cogeneration systems. The absorption chillers run on waste heat, eliminating the expensive operation of electric chillers in the HVAC system. Another $113,880 is saved through a heat recovery unit that supplies industrial hot water. Electricity self-generation reduces demand for utility energy by 14,016,000 kWh per year, saving another $121,920 annually. Total annual savings achieved for the cogeneration systems are about $775,520 each year. Through the operation of small-scale electric and thermal energy generating systems located within its office building, Equity Office Properties can generate energy at twice the efficiency of traditional utility systems. Equity Office is implementing these systems in high energy cost markets, including Chicago, Boston, New York, San Diego, Orange County and San Francisco. Once a building is selected, Equity Office executes the design, engineering, purchasing, construction and installation of the power plant. Equity Office currently has 19 DG systems nationwide. At One Market Plaza in San Francisco, Equity Office installed a 1.5 MW cogeneration system, the first ever in this metropolitan area, and one of the largest ever to be interconnected to a network distribution grid in the United States. Based on the success of this project, Equity Office installed a 750 kW system at the nearby office building located at 201 Mission. Resources Energy and Environmental Analysis report to Oak Ridge Ntnl. Laboratory, Market Potential for Advanced Thermally Activated BCHP in Five National Account Sectors. California Energy Commissiion, Market Assessment of Combined Heat and Power in the State of California. Pacific Region CHP Application Center assists organizations with locating, designing, and implementing CHP projects. RETScreen International, CHP Project Model U.S. Department of Energy, Energy Efficiency and Renewable Energy, Federal Energy Management Program. Combined Heat & Power: A Federal Manager's Resource Guide. |