Cogeneration: Is It Right for Your Building?

BOMA San Francisco Members:

Please click here to review a report produced by the San Francisco Department of the Environment in 2007 regarding Cogeneration.

What is Cogeneration?

Cogeneration, also known as Combined Heat and Power (CHP), is the process of generating electricity and useful heat from the same power station. Modern power generators create electricity through the combustion of a fuel, or the nuclear processing of uranium, and give off large amounts of exhaust heat to the air, earth, or water that surrounds them. The waste of this excess heat is a fundamental inefficiency in these generators and the use of their fuel. Cogeneration systems are identical to these modern power generators, with the exception that they collect the exhaust heat from the electrical generation process and use this heat to perform other work. This heat can be used to heat the air in an office building, provide hot water or steam, drive a dehumidifier, or even drive an absorption chiller to provide refrigeration and cooling. With this large range of uses, a variety of buildings can benefit from the useful heat in a cogeneration system.


Office Buildings - Overview

With regard to office buildings potential for office buildings varies greatly, depending on the overall size, the inclusion of data centers, and operating hours. Electric loads are particularly high during business hours, but drop significantly during the night in most buildings. This operating pattern should not discourage the installation of systems as the savings from peak electrical rates can be significant and can justify a project economically even if the system does not run during non-business hours. Typical thermal loads in office buildings include space and water heating, and absorption chillers for cooling. Generators can be sited on the roof, in basement level equipment rooms, or in parking structures. Typical cogeneration system sizes for office buildings range from 500 kW – 1.5 MW. This market has the largest segment of active systems in San Francisco, with eight distributed around the downtown area. The office building market also has the largest potential for growth in the city, with well over a hundred potential office buildings in the city, capable of producing in excess of 80 MW. The calculation for this estimate, and the following list of potential locations has been compiled with the assistance of the Assessor’s Office. This list has been used to derive a first estimate of the potential for cogeneration installations in the city. Using existing cogeneration systems in office buildings as a guide, a conservative calculation has been estimated as follows:

Not included in this estimate are buildings in the Commercial Retail or Commercial Miscellaneous classes, any of the new buildings being constructed in the city, or any buildings with less than 200,000 square feet of space. These omissions could each contribute multiple megawatts of power to the city.

For more specific information, please review the report.