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The Advantages Of Cogeneration And Trigeneration

December 13, 2003
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Owners of commercial buildings and commercial businesses are increasingly seeking ways to use energy more efficiently. This is a direct result of dramatically increasing electric rates, decreased power reliability (blackouts, brownouts, rolling blackouts, and other power interruptions), as well as competitive and economic pressures to cut expenses, increase air quality, and reduce emissions of air pollutants and greenhouse gases. The Kyoto Protocol, while not ratified in the United States, continues to be a major driver in much of the rest of the world. In the United States, "ecogeneration" is becoming a preferred method to produce a company's or facility's power and energy requirements.

Ecogeneration defines the optimization of economic and ecological benefits in the power generation process. Ecogeneration produces huge savings for our environment through the reduction, or even elimination, of pollution associated with power and energy production. Additionally, ecogeneration appeals to our customers' economic bottom line by providing them with significant fuel and electrical savings.

Energy technologies that fall under ecogeneration include: wind, solar, geothermal, hydrogen fuel, hydrogen fuel cells, soybean diesel fuels, ocean/tidal power, waste to energy/waste to fuel and waste to watts, combined cycle, district energy, cogeneration, trigeneration, and even quadgeneration power plants.

There are two major ecogeneration initiatives and technologies that we will discuss in this article - cogeneration and the newer technology, trigeneration. Trigeneration is one of the most attractive options, and is even more efficient and economically rewarding than its cousin, cogeneration.

Cogeneration, also known as combined heat and power (CHP), is the simultaneous production of electricity and useful heat, usually in the form of either hot water or steam, from one primary fuel, such as natural gas. While not necessarily defined correctly, cogeneration has also been referred to as district energy, total energy, combined cycle, and simply cogen.

Cogeneration has been mostly a technology used in the utilities and industrial marketplace.

Trigeneration, as the name implies, refers to three energies, and is defined as the simultaneous production of heat and power, just like cogeneration, except trigeneration takes cogeneration one step further by also producing chilled water for air conditioning or process use with the addition of absorption or adsorption chillers. Trigeneration, also referred to as CHCP (combined heating, cooling and power), BCHP (building cooling, heating and power) and integrated energy systems, permits even greater operational flexibility at businesses with demand for energy in the form of heating and cooling. Just as a cogeneration power plant captures and makes use of the waste heat, absorption or adsorption chillers capture the waste (or rejected) heat and produce chilled water.

Trigeneration systems are found in commercial applications typically where there is a need for air conditioning or chilled water by the customer.

When a trigeneration power system is installed on-site, that is, where the electrical and thermal energy is needed by the customer so that the electrical energy does not have to be transported hundreds of miles away, and the thermal energy is fully utilized, system efficiencies can reach and surpass 90 percent.

On-site trigeneration plants are much more efficient, economically sound, and environmentally friendly than typical central power plants. Because of this, customers' energy expenses are significantly lower, and the associated pollution is also much less than if the customer had an energy system supplied with electricity from the grid, along with water heaters and boiler systems on-site. Trigeneration's superior efficiencies surpass even the latest state-of-the-art combined cycle cogeneration power plants by up to 50 percent. Coupled with a four-pipe system, hot water/steam and chilled water can be produced simultaneously for circulation throughout the building or campus (which would be referred to as a district energy system).

And size is not an impediment, since trigeneration systems can be installed, for example, in small commercial settings, such as restaurants, hotels, schools, office buildings, and shopping centers, to large applications such as petrochemical plants, refineries, and in a city's downtown area, providing the energy requirements for multiple buildings. And it will still provide system efficiencies of 90 percent.

History Of Cogeneration Technology

Many people know that Thomas Edison built the first commercial power plant. However, most people do not know that Edison's first commercial power plant known as the "Pearl Street Station," built in 1882 in Lower Manhattan, New York, was also a cogeneration power plant!

Because cogeneration and trigeneration continue to be the most efficient method of generating electrical and thermal energy, in terms of energy output, the U.S. Department of Energy (DOE) has called for the doubling of electrical power generated from cogeneration power plants - from the existing 46 GW (one gigawatt = 1,000 MW) to 92 GW by the year 2010. When this goal is reached, cogeneration will represent about 14 percent of the total U.S. generating capacity of electricity. The American Council for an Energy-Efficient Economy (ACEEE) estimates that an additional 95 GW of cogeneration capacity could be added between 2010-2020, resulting in 29 percent of total U.S. electric power generation being produced through cogeneration. Europe is also dramatically increasing the number of cogeneration power plants over the next decade.

And the historical basis and success of cogeneration has been the foundational basis for expanding the efficiencies of cogeneration to trigeneration and even quadgeneration, with each new increase in energies recovered resulting in higher efficiencies and lower fuel/energy costs and fewer related emissions.

President Bush's National Energy Plan

In the United States, President George W. Bush's National Energy Plan recognizes the efficiency of cogeneration technologies - and it plays an important role in meeting national energy objectives and maintaining comfort and safety in commercial and office buildings. Released in May 2001, the president's National Energy Plan states:

A family of technologies known as combined heat and power (CHP) can achieve efficiencies of 80 percent or more. In addition to environmental benefits, cogeneration projects offer efficiency and cost savings in a variety of settings, including industrial boilers, energy systems, and small building scale applications. At industrial facilities alone, there is potential for an additional 124,000 MW of efficient power from gas-fired cogeneration, which could result in annual emissions reductions of 614,000 tons of NOx emissions and 44 million tons of carbon equivalent. Cogeneration is also one of a group of clean, highly reliable, distributed energy technologies that reduce the amount of electricity lost in transmission while eliminating the need to construct expensive power lines to transmit power from large central power plants.

Since the 1930s approximately two-thirds of all the fuel used to make electricity in the U.S. is generally wasted by central power plants in the form of unused thermal energy in the electrical generation process. While there have been impressive energy efficiency gains in other sectors of the economy since the oil price shocks of the 1970s, the average efficiency of power generation in this country has remained around 27 to 35 percent for nearly 70 years. The use of cogeneration and trigeneration can significantly improve that efficiency.

Pollution Associated With Inefficient Power Plants

Currently, power plants in the U.S. have been cited for producing two-thirds of its annual sulphur dioxide emissions, one-quarter of the nitrogen oxide emissions, one-third of mercury emissions, and one-third of carbon dioxide emissions. These resulting pollutants produce serious environmental and health consequences, including:

  • Increased sick days in areas with high urban smog levels.

  • Lung problems in the young and old, including increased rates of asthma and chronic bronchitis.

  • Global climate change.

  • Urban haze and smog.

  • Acid rain.

  • Acidification of lakes, streams, rivers, and oceans.

  • Dead and dying lakes, stream, rivers, and wildlife in and near these areas.

    "Curing" the problems associated with inefficient electrical power generation begins with pollution prevention. The choices are clear - we must stop wasting energy and start increasing the efficiency of power generation facilities. Instead of building inefficient, wasteful, pollution-generating central power plants owned by utility companies, where the thermal energy is wasted, we need to start building efficient, on-site power plants where the heat energy can be utilized. These on-site cogeneration, trigeneration, and quadgeneration power and energy systems are also referred to as "distributed generation" or "distributed energy" technologies. They can be installed easily and affordably, and they operate economically throughout their life cycle.

    The U.S. Environmental Protection Agency (EPA) understands that resolving these problems must start with pollution prevention, which equates to using fewer energy resources to produce goods and services. The National Energy Plan includes four specific recommendations to promote CHP, three of which were directed to EPA for action:

  • Promotion of CHP through flexible environmental permitting.

  • Issuing of guidelines to encourage development of highly efficient and low-emissions CHP.

  • Promotion of the use of CHP at abandoned brownfield industrial and commercial sites.

    As a follow-up to those recommendations, EPA joined with 18 Fortune 500 companies, city and state governments, and nonprofit organizations in February 2002 in Washington, DC, to announce the EPA Combined Heat and Power Partnership (CHPP). The CHPP aims to advance CHP as a more efficient, clean, and reliable alternative to conventional electricity generation. This initiative now boasts nearly 50 partners, including state and local regulators, end users, project developers, and equipment suppliers.

    Clean On-Site Power For Commercial And Industrial Customers

    Distributed generation locates smaller and more efficient power plants where the power and thermal energy is actually needed. These on-site power systems are also called "inside the fence" power systems and are designed and engineered to maximize the customer's power and energy requirements.

    The DOE's Energy Information Administration (EIA) recently sponsored a study to estimate the potential of cogeneration installations in the U.S. According to their study, there are 1,431,805 buildings in the United States that are suitable for on-site cogeneration power systems (most of these are actually better suited for trigeneration) requiring a capacity of 77,281 MW. At an average of $1 million per MW, this translates into a $77,281,000,000 market opportunity. That's over $77 billion in the U.S. alone. Trigeneration would be an even greater market opportunity as this study focused on applications where thermal energy load was in the form of steam or hot water, and does not take into consideration use of thermal technologies, such as absorption/adsorption chillers or desiccant dehumidification, as part of the potential for the building's thermal load.

    When absorption/adsorption chillers are added to a cogeneration system, it is now referred to as a trigeneration system. Therefore, the total market potential in the study could be significantly higher than the 77,281 MW when considering the opportunity for trigeneration applications. The study also estimates the total existing capacity of cogeneration installations in the U.S. to be only about 4,930 MW, and that over 70 percent of the existing facilities are under 1 MW and are powered by small reciprocating engines.

    Even quadgeneration is a possibility, taking trigeneration one further step, producing four energies from one process. By extracting most, if not all, of the available heat from the power/energy generation process, end users obtain the most efficient, optimized energy system. But the efficiency gains are wasted if the recovered waste heat is not put to work or the existing boilers or water heaters displaced, reduced, or eliminate entirely. This is why it is absolutely critical that a thorough and complete feasibility study is done to determine a properly sized on-site energy system, and that conventional systems are either eliminated, compensated for, or integrated into the new energy system.

    It should go without saying, but if the facility that installs a trigeneration system does not replace or reduce other systems, there can be a net loss of efficiency. If the facility does not offset the net efficiency gains of the new trigeneration system by reducing, displacing, or eliminating the existing water heaters/boilers load, then the facility will not have an optimized installation and therefore will not profit to the extent it could have had the feasibility and design studies been properly conducted.

    Trigeneration Takes Lead Over Cogeneration Due To Superior Efficiency

    A trigeneration system consists of a cogeneration plant, and either absorption or adsorption chillers that produce chilled water by making use of some of the waste heat recovered from the cogeneration power plant.

    Figure 1. Schematic presentation of a gas turbine-based trigeneration facility.


    While cooling can be provided by electric-driven compression chillers, low quality heat (i.e., low temperature, low pressure) that is not used by the cogeneration power plant can be used to drive the absorption or adsorption chillers so that the overall primary energy consumption is reduced.

    Trigeneration power plants with absorption and/or adsorption chillers have gained acceptance due to their capability of not only integrating with cogeneration systems but also because they can operate with industrial waste heat streams that can be fairly substantial. The benefit of power generation with absorption or adsorption cooling can be realized through the following example that compares it with a power generation system with conventional electric-driven compression systems.

    Assume in this example a factory needs 1 MW of electricity and 500 refrigeration tons (RT). (Defintion: A refrigeration ton or RT is defined as the transfer of heat at the rate of 3.52 kW, which is roughly the rate of cooling obtained by melting ice at the rate of one ton per day.)

    Let us first consider the gas turbine that generates electricity required for the processes as well as the conventional electric-driven compression chiller. With an electricity demand of 0.65 kW/RT, the compression chiller needs 325 kW of electricity to obtain 500 RT of cooling. Therefore, a total of 1,325 kW of electricity must be provided to this factory. If the gas turbine has an efficiency of 30 percent, primary energy consumption would be 4,417 kW.

    However, a trigeneration system with absorption or adsorption chillers can provide the same energy service (power and cooling) by consuming only 3,333 kW of primary energy.

    In this example, the trigeneration power plant saves about 24.54 percent of the primary energy needed compared to the cogeneration power plant with electric-driven compression chillers. Since many industries and commercial buildings can use combined power and heating/cooling, trigeneration systems have a high potential for industrial and commercial applications. (The above example is courtesy of ASHRAE.)

    Trigeneration, when compared to combined-cycle cogeneration, can be up to 50 percent more efficient, further reducing operating costs, fuel expenses, and environmental pollutants.

    Trigeneration systems for commercial buildings are very profitable investments for building owners. A new trigeneration system can pay for itself in as little as two years, depending on local electric rates, natural gas (or other fuel) costs, and the load profile of the building. Trigeneration systems help not only the building owner, but also benefit society in a number of ways, including:

  • Increased power reliability;

  • Reduced power requirements on the electric grid; and

  • Reduced dependence on foreign oil.

    The on-site trigeneration system can be economically attractive for many types of buildings, including, but not limited to, the following:

  • Hospitals

  • Schools, colleges, and universities

  • Office buildings

  • Shopping centers

  • Government facilities

  • Manufacturing plants

  • Data centers

  • Nursing homes

  • Hotels

  • Supermarkets

  • Refrigerated warehouses

  • Retail stores

  • Restaurants

  • Theatres

  • Ice arenas

  • Airports

  • Golf/country clubs

  • Casinos

  • Resorts

    Facilities with trigeneration systems use them to produce their own electricity, and use the unused excess (waste) heat for water heating, space heating, air conditioning, process steam, and other thermal needs.

    Improved Power Reliability

    Economic losses due to power outages in the U.S. have cost American businesses billions of dollars. The following table shows the economic impact of power outages on some industries.

    Table 1. Economic impact of power outages.


    As we all know, power outages and rolling blackouts are occurring more frequently than ever before. And they are not happening only in California; many other states have experienced similar problems. These problems primarily occur when demand for power exceeds its supply, for example, on hot days when power demand for cooling systems increases significantly. Similar situations occur on very cold days when demand for heating becomes very high. There may also be local areas that are more prone to power outages because the demand for power exceeds the ability of the local distribution line to provide the energy. Other times, weather-related storms knock down power lines and substation transformers.

    Cogeneration and trigeneration systems give commercial and industrial end users their own reliable power supply to keep equipment and facilities operating. Plus, they help reduce the load on the power grid and local area lines and, thus, help improve the local community's power reliability.

    Improved Indoor Environments

    Also of increasing interest is the issue of indoor air quality. In order to prevent the growth of mold, mildew, and bacteria, it is important to keep humidity in the indoor air to below 60 percent. Cogeneration and trigeneration systems for buildings can help improve indoor air quality by supporting the use of a desiccant dehumidification system to dry the air. Desiccant systems use a material that directly removes moisture from the air, then use heat, such as that provided by the exhaust gases of the cogeneration/trigeneration equipment, to regenerate the desiccant. This provides a very energy efficient and cost effective method of dehumidifying indoor air, rather that using an air conditioner to "over cool" the air to remove humidity.

    Summary: Advantages Of On-Site Cogeneration And Trigeneration

  • Cogeneration and trigeneration are accepted as the most energy-efficient means of producing electricity.

  • They now produce almost 10 percent of our nation's electricity and 10 percent of electricity globally.

  • They save customers up to 50 percent on their energy expenses.

  • They provide even greater savings to our environment through significantly reduced emissions associated with power plants.

  • They are backed by environmental organizations such as the Sierra Club and the U.S. Environmental Protection Agency.

  • The U.S. Environmental Protection Agency is promoting the use of more electricity to be produced through cogeneration power plants. The EPA recently formed the CHP/Cogeneration Partnership to foster more cogeneration power plants to meet our nation's electricity demand.

  • Cogeneration is a proven technology that has been around for over 100 years. The world's first power plant designed and built by Thomas Edison in 1882 was a cogeneration plant. Trigeneration just takes cogeneration one step further.

  • Two-thirds of the fuel used to make electricity today in the United States is wasted. While there have been impressive energy efficiency gains in other sectors of the economy since the oil price shocks of the 1970s, the average efficiency of power generation in the United States has stagnated at around 33 percent since 1960. Cogeneration and trigeneration offer significant efficiency improvements.

  • A new trigeneration power plant may pay for itself in as little as 2-3 years.

  • It is important to note that increasing the use of cogeneration and trigeneration systems is, and has been, one of the best technologies available for reducing greenhouse gas emissions and other pollutants created by the typical power plant as well as a means for conserving fuel and reducing our reliance on foreign oil.

  • The Kyoto Protocol, while not being ratified here in the United States, is moving ahead with ratification throughout the rest of the world. Countries throughout much of Europe and Asia view cogeneration and trigeneration as the best energy technologies to meet the stringent emissions requirements of the Kyoto Protocol.

  • Primary fuels commonly used in trigeneration include natural gas, oil, diesel fuel, propane, coal, wood, wood-waste, and bio-mass. These "primary" fuels are used to make electricity that is a "secondary" energy. This is why electricity, when compared on a Btu to Btu basis, is typically three to four times more expensive than primary fuels such natural gas.

    A typical cogeneration power plant consists of an engine, steam turbine, or combustion turbine that drives an electrical generator. A waste heat exchanger recovers waste heat from the engine and/or exhaust gas to produce hot water or steam for a building. In trigeneration power plants, an absorption or adsorption chiller is added to a cogeneration system to also utilize the waste heat to make chilled water for air conditioning.

    Cogeneration produces a given amount of electric power and heat with 20 to 30 percent less fuel than it takes to produce the electricity and heat separately. Trigeneration produces chilled water in addition to electric power and heat with approximately 50 percent less fuel than it takes to produce electricity, heat, and chilled water separately.

    Monty Goodell is the founder and chairman of EcoGeneration Solutions LLC, the parent company of Cogeneration Technologies and Trigeneration Technologies. Goodell has a B.A. in Economics from Texas State University and an M.B.A. from Baylor University. With a background in the natural gas utility industry, he started marketing cogeneration and trigeneration in the mid-1980s. For more information, visit the Cogeneration Technologies website at www.Cogeneration.net or the Trigeneration Technologies website at www.Trigeneration.com, or e-mail info@cogeneration.net.

    Publication date: 12/15/2003

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