Best Practice Guide

Local Governments

Introduction

Planning an Energy Program

Funding and Approval

Education

Lighting

Central HVAC System

Procurement Policy

Building Envelope

Demand Response

Distributed Generation

Cogeneration

Solar Energy

Water Use

Motors

Food Service

Resources and Appendices

Lessons Learned


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Distributed Generation

Cogeneration

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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.


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.