District energy plants are designed to deliver thermal or electric utilities to multiple buildings on a campus or in a municipality. This approach has been used since the Industrial Revolution. Steam-generating plants and distribution networks were built to produce and deliver steam needed to drive the machinery of large factories and heat the homes of the factory workers. Often, these plants produced electric power first and generated steam as a useful waste product in a combined-heat-and-power (CHP) process. With the invention of air conditioning, district cooling appeared on the scene to meet the cooling needs of large educational and industrial campuses.

Today, large district energy facilities use a variety of fuels to provide cooling, heating, and electric utilities to colleges and universities, health-care campuses, manufacturing facilities, and municipalities in North America, Europe, Asia, and the Middle East.

District energy facilities allow thermal and electric utilities to be generated efficiently and reliably. These systems also allow for the consolidation of maintenance and operations. These reasons alone have justified the significant capital investment required. Today, however, there is a new movement that is changing how these investments are viewed: the sustainable building movement.

In 1993, the U.S. Green Building Council (USGBC), a non-governmental organization with the goal of driving sustainable practices in building design, construction, and operation, met for the first time. Five years later the council introduced its first building-rating system, the Leadership in Energy and Environmental Design (LEED) Building Rating Program. This program allows buildings to receive the “brand”’ of LEED and thus make a statement to their stakeholders about the owning organization’s green values. In a very short period of time, the LEED program has taken off in popularity. Today, more than 1.4 billion sq ft of building space has been certified by the LEED program, and certification is being sought for more than 6 billion sq ft. In addition, countries around the world have adopted variations of the LEED program for local use.

When the USGBC developed the first rating system, however, the impact of district energy was not addressed. For the most part, the rating system only concerned itself with what was occurring on the proposed building's construction site. The assumption was made that building owners had little ability to affect how utilities were generated off site. District energy was treated the same as traditional utilities such as power and gas. The USGBC quickly found that by failing to address district energy within its LEED guidelines created many questions for project designers. In addition, the opportunity to have a positive impact of progressing toward the organization’s sustainability goals was missed.

As a result, the USGBC in 2008 released its first guideline to address applying the LEED program to proposed buildings that would receive district energy, Required Treatment of District Thermal Energy in LEED-NC Version 1. USGBC in 2010 released an update to this guide titled, Treatment of District or Campus Thermal Energy in LEED V2 and LEED 2009 – Design & Construction Version 2 and also released the first version of a separate guide to address district energy under the USGBC’s rating system for existing buildings entitled, Treatment of District or Campus Thermal Energy in LEED for Existing Buildings: Operations and Maintenance Version 1.0. All of these guides are available for free on the USGBC's Website (www.usgbc.org).

There are aspects of district energy systems that align very well with core goals of the USGBC. Understanding these aspects and implementing them in district energy systems creates scenarios in which connecting a proposed building to district energy increases the level of LEED certification that can be achieved. The opportunities—renewable energy, CHP, and thermal energy storage—often are expensive to install and impractical to maintain within a proposed building’s site. However, because of the scale of district energy, these challenges can be overcome when installing them within a district energy system. As such, district energy can be the ideal choice for buildings pursuing LEED certification. This article will review each of these opportunities and their impact on the LEED program.

Renewable Energy
Renewable energy has been around for centuries. Power from wind and water movement and solar thermal were used by ancient civilizations. Today, solar energy, wind, and biomass offer promises of reducing dependency on traditional nonrenewable energy sources, such as coal, oil, and natural gas. The need for renewable energy has never been greater, as the world simultaneously wrestles with climate change, increased demand for fossil fuels in developing countries, and the concept of "peak oil," defined by Wikipedia as "the point in time when the maximum rate of global petroleum extraction is reached, after which the rate of production enters terminal decline."

The problem with traditional renewable energy sources is that they often are cost-prohibitive and difficult to use and maintain. Wind and solar are not in constant supply, and biomass feedstocks often come from immature markets with unreliable supply streams and large price swings—neither of which is conducive to attracting normal sources of private capital investment. The point at which these energy choices can stand on their own economics has been "just around the corner" for decades, but that proverbial corner has yet to be reached.

In concept, renewable energy certainly makes a lot of sense. If we can effectively harness the energy of the sun, wind, or tidal movement or harvest energy from waste streams, our current problems with energy security, supply, pollution, and global warming could—in theory—be solved. As a result, the U.S. government and many state governments encourage the development of renewable-energy markets in the form of tax incentives, grants, regulation, and so on. However, governments are not the only entities trying to encourage the development of renewable-energy markets. The USGBC hopes to accelerate the maturity of renewable-energy markets and technologies through its LEED program. The group will do so by awarding buildings a significant number of points toward the LEED- rating goals of buildings that use renewable energy.

LEED and Renewables
The USGBC recognizes that encouraging the use of renewables helps it achieve its goals. It also recognizes that in order to sufficiently encourage the use of renewables, significant incentives are required within the LEED rating system to overcome first cost, operating cost, and/or long payback periods. As a result, the USGBC gives points for renewable energy in two separate credit categories within the LEED rating system. It is possible, in fact, for qualifying projects to earn many points within each of these categories.

The first way to achieve LEED points with renewables is under Energy & Atmosphere Credit 1 by reducing the total annual energy cost of a building. This credit awards up to 19 points to projects that can demonstrate a percentage of energy savings, measured in terms of a building's total annual energy costs compared with the minimum energy requirements outlined in Appendix G of the ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings.

The LEED rating system, however, assumes that the input fuel costs of all renewables is zero. This certainly is true for solar and wind, but rarely is the case for waste products such as wood chips, oat hulls, poultry waste, and so on. As a result, the assumed "free" cost of renewables increases the amount of points that can be achieved under Credit 1.

Second, under LEED Energy & Atmosphere Credit 2, projects can achieve up to seven points by using renewable energy. To do so, they must consume what the USGBC considers to be renewable (more on that later), and the amount used must reach certain thresholds as defined by the percentage of total annual building energy use. Those percentages, along with their associated assigned points, are shown in Table 1.

The relatively high thresholds make capturing points under Credit 2 with on-site renewables very difficult. For example, the amount of photovoltaics required to achieve just one point would completely cover the exterior of most buildings. In addition, the operational and fuel-handling challenges of burning biomass within a single project building are substantial. On the other hand, the size and scale of district energy often provides good opportunities for burning renewables.

Originally, the USGBC did not include provisions that would allow renewables consumed in district energy systems to be applied to customer buildings. This mandate was changed in the first district-energy guide published for new construction and has been improved in the second version of that guide. As such, district energy often is the best and sometimes the only option for obtaining credit for renewables in the LEED rating system.

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