Energy-Efficient Building

Summary

Energy-efficient building practices involve the construction of buildings using as little energy as possible and with minimal environmental impact, beginning with construction techniques and materials and continuing with the ongoing, energy-efficient operation and maintenance of a building.

Definition and Basic Principles

Energy-efficient building is a construction methodology designed and regulated to minimize the energy consumed in building, operating, and maintaining a given structure. The basic principle of minimizing the energy required for the operation of the building is simplicity itself. The practice of energy-efficient building is at the beginning of its development, however, and a great deal of future research will conceptualize and test materials and structures to minimize the cost and maximize the effectiveness of the technology.

The most basic principle of energy-efficient building is the capture of solar thermal or geothermal energy (or both) that can be stored in some mass of material, such as water or concrete. The energy is then released into the building in a controlled manner to maintain environmental conditions within the building.

A second main principle of energy-efficient building is the prevention of thermal transfer through the use of insulation and insulating structures. This works to prevent heat loss in winter and heat gain in summer. The third principle ensures that the daily operation and maintenance of a building is to consume as little energy as possible.

Background and History

Builders have long known how to construct buildings to make full use of the natural environment for heating, cooling, and ventilation. With the Industrial Revolution of the eighteenth century, and particularly since the establishment of electrical grids, artificial heating, cooling, ventilating, and lighting systems have rapidly developed. They now represent one of the largest general uses of energy throughout the world. As the human population continues to grow, traditional methods of energy production have not been able to meet demand, leading to the necessary development of new materials and more efficient methods of using energy.

Central to this movement are methods that utilize natural heat and light sources to reduce the demand for electrical energy and combustible fuels, and methods to reduce or eliminate energy losses from structures. Initially a fringe philosophy of the 1950s and 1960s, passive solar heating and other methods, for example, have become a rapidly developing part of mainstream building techniques in the twenty-first century.

French engineer Felix Trombe (1906-1985) invented what came to be called the Trombe wall structure in the late 1950s. The photoelectric effect that makes solar cells function was first explained by Albert Einstein in 1905, but it was not until the transistor revolutionized electronics in the mid-twentieth century that silicon became a sufficiently viable commodity to produce solar cells on a large scale. The physical principles that drive these different applications now form the foundation of the energy-efficiency movement.

How It Works

The basic concept of energy-efficient building is to construct buildings with as little energy consumption and environmental impact as possible, beginning with construction techniques and materials to the ongoing operation and maintenance of the completed building. Traditional building techniques and materials remain fundamental components of construction practice, although a significant outcome of the move to higher energy efficiency is the development and application of new materials and methods.

Applied physics provides the theoretical framework for energy-efficient building. Scientists have long understood convection currents and how they arise, but applying this knowledge in modern building practices is a relatively new development. The principle of convection states that warm air, having a lower density than cooler air, rises to float on top of the cooler air, setting up a circulatory movement of air within a room. Passive solar heating extensively uses this principle, and building designers consider the fluid dynamics of air movement to maximize solar heating efficiency. Mechanical devices such as fans to assist convection are often integral to building design. Structures such as a Trombe wall capture and store heat energy. Openings at the top and bottom of the inner wall facilitate convection, while the massive structure radiates heat into the interior of the building.

Foundations represent a significant heat exchange mechanism between the interior and exterior of a building, often producing undesirable moisture-related side effects. Traditional methods rely on sealing the exterior of the foundation wall and either lining the interior of the wall with Styrofoam or creating a dead space with furring strips and paneling. Concrete blocks containing dead air space help in insulating foundation walls, but their strength is limited. Poured concrete is a far more effective and structurally versatile construction method, but concrete is a poor thermal barrier. For energy-efficient buildings, poured concrete has been rethought so that insulated concrete forms are now used in many applications to provide a more efficient thermal barrier.

Above-ground construction, particularly of residential buildings, traditionally utilizes stud-frame construction, in which an insulating material is inserted between the vertical studs of wall structures. The studs themselves serve as thermal conductors connecting the interior and exterior of the building, especially if steel studs are used in place of wooden studs. The use of structural insulated panels, or SIPs, in exterior wall construction provides an uninterrupted layer of insulation throughout the entire wall, with wall strength that meets or exceeds the requirements of a standard stud wall, and an insulating factor between R-45 and R-48 compared with the typical R-20 to R-25 rating for standard stud walls.

Standard-glazed windows have very low insulation ratings, generally no more than R-10. A thermal mass window system, however, functions as a solar energy collector by using the mass of a 7.5-centimeter thick layer of water sandwiched between inner and outer glass plates to capture passive solar heat. Such windows are able to maintain a temperature of between 65 degrees and 115 degrees Fahrenheit, radiating heat into a building, even when the exterior temperature is as low as 34 degrees Fahrenheit.

The heating and cooling of buildings traditionally represent high energy consumption, either through the combustion of fuels or through the use of electricity to provide heat or to power cooling systems. Concerns about the long-term availability of fuels and electrical energy demand that more efficient means be utilized. Geothermal heating and cooling systems, coupled with specialized materials that permit facile heat exchange and capture at relatively low temperatures, have thus become more and more important and are rapidly becoming the standard systems for new constructions.

An energy-efficient building quickly ceases to be so if its ongoing operation and maintenance turn to the use of materials and mechanisms that consume more energy. For example, replacing compact fluorescent light bulbs with standard incandescent light bulbs increases energy consumption. Building maintenance may also specify the use of certain cleaning materials based on the energy consumed in their manufacture or transportation requirements.

Applications and Products

LEED Certification. LEED (Leadership in Energy and Environmental Design) is an accreditation program of the Green Building Certification Institute, with several designated areas of specialization and three levels of achievement for accreditation. The basic level of accreditation, LEED Green Associate, demonstrates fundamental knowledge of green construction practices, design principles, and operations. In this context, “green” indicates that the process is effective at reducing energy consumption and conserving resources. Essentially, it serves to assure others that the completed building is in accord with green construction policies and standards. To qualify for Green Associate Accreditation, a candidate must be able to provide evidence of having been associated with a LEED-registered project, show evidence of employment in a sustainable field, or prove completion of a program of education incorporating green construction principles. The candidate must also successfully complete an examination within specified constraints.

The second tier of LEED certification is accredited professional, and the third is accredited professional fellow. Each level represents a significantly higher degree of experience and training in LEED practices. LEED provides accreditations in new construction, existing buildings' operation and maintenance, commercial interiors, core and shell, schools, retail, health care, homes, and neighborhood development. Operations and maintenance provide standards by which services can be measured to maximize operational efficiency and minimize environmental impact and energy consumption. LEED for homes provides a consensus-based, voluntary rating system that is also third-party verified to ensure that homes meet the applicable standards. The new construction protocol ensures that LEED standards and green principles are included in every aspect of building design.

LEED for commercial interiors is geared to ensuring that the interior environments of buildings are healthy and productive workspaces with reduced operating and maintenance costs and reduced environmental impacts. It also provides the direction for tenants and interior designers to make sustainable choices for their own inhabited spaces. LEED certification enables a better understanding of decisions made in project design and construction. Certification better ensures that the work conforms to the spirit of the design and to the design drawings.

Building Materials. Reconsideration of the performance of materials has resulted in numerous modifications to those materials and the structures in which they are used. Energy-efficient modifications are incorporated into the building structure even before the foundation is formed. Foundations themselves are historically responsible for unregulated heat transfer into and out of buildings in the underground levels. Heated basements tend to lose much of their heat to conductive basement walls, while the coolness of those same walls in warm weather contributes to moisture, mildew, and mold problems.

Energy-efficient building design using insulated concrete forms minimizes unregulated heat transfer across basement walls. Primarily made from reinforced Styrofoam or a proprietary wood fiber and concrete mixture called Durisol, insulated forms are stacked like bricks inside a retaining form and then filled with concrete in the usual way. Once the concrete has set, a well-sealed, insulated wall remains.

Structural insulated panels (SIPs) are thick foam panels that have been bonded on both sides to oriented strand board or to plywood. SIP construction replaces the standard stud-wall structure of a building, locking together in such a way that studs are not required for the formation of a straight, strong wall and an airtight building envelope. The energy requirements of a house built using SIP construction can be as much as 50 percent lower with no further modifications.

Thermal mass (TM) windows are designed to use the heat-storing capacity of a mass of material to absorb solar thermal energy and radiate the stored heat into the interior. Their construction is no more complex than two sheets of thick glass enclosing a mass of water. TM window systems may contain nearly 1,500 kilograms of water and can capture and store tens of thousands of British thermal units (BTUs) of energy. Other designs incorporate aerogel insulation with water or use phase-changing materials to capture thermal energy.

Trombe walls also use the principle of thermal mass. A Trombe wall consists of a thick solid wall of concrete or other dense material, open at the top and bottom to allow convective air circulation. A second outer wall of glass windows adjacent to the solid wall acts as the solar thermal collector.

Geothermal and In-Floor Heating Systems. The constant underground temperature provides a ready means of heating and cooling through the use of geothermal loop systems. A circulating carrier fluid can be used to transfer heat into the building in winter or to remove excess heat from the building in summer. Though geothermal systems can be used to retrofit an existing building, they are more commonly used in new construction to incorporate an in-floor radiant heating system. The circulating fluid, usually just water, moves through an array of piping built into the floor of the structure to heat the floor itself, which then radiates heat upward to warm the interior of the building. The system also can be used to cool floors in the heat of summer.

Passive Solar Heating. This is the original method of solar heating used to reduce the energy requirements of a building. It is based on the capture of solar thermal energy to directly heat the interior of a building, just as a glass greenhouse captures thermal energy. The method heats air that then circulates by convection, requiring that the building be oriented appropriately when built to maximize the effect.

Heat recovery ventilation. Heat recovery ventilation systems capture heat from the exhaust air of various systems in a house, such as the kitchen or bathroom, and use it to regulate the ambient air temperature in the building. The system can be centralized or decentralized and is used to recover heat from the exhaust air and pre-process the ambient air. Multiple sensors are provided to detect various indoor environment parameters, such as moisture, temperature, etc. Based on these parameters, the system maintains the desired environmental conditions inside the building while achieving increased energy efficiency.

Other Methods of Energy Consumption. Energy-efficient buildings, by definition, consume less energy than other buildings. Part of the reduction in energy consumption, defined in standards, includes using low-energy lighting like compact fluorescent light bulbs, insulated flooring, and windows that reflect away excess thermal energy to reduce or eliminate the need for air conditioning.

Social Context and Future Prospects

Access to the energy required to power an ever-growing society has become a major concern in the twenty-first century. Accordingly, developing the means to minimize energy use and maximize energy production has also become important.

Electrical energy is the mainstay of modern industry, while electricity and combustible fuels are the primary means of temperature control in buildings. Traditional electrical energy production methods include hydroelectric generation, coal- and gas-fired plants, and nuclear-powered stations. These methods are aging, and the technologies are becoming outdated. Still, significant efforts continue to augment or replace their capabilities with renewable sources such as solar- and wind-generated electricity. Additionally, efforts are expanding to reduce the energy requirements of buildings and infrastructure. At the forefront of this movement are energy-efficient building design and construction methods.

Zero-energy housing, called nearly Zero Energy Building (nZEB), is a specialty or niche market in energy-efficient building methods that requires little energy input to maintain. The cost of constructing nZEBs is somewhat higher than that of a traditionally built home, but considering long-term energy savings using newly emerging technology, some owners break even after several years. As secure access to energy becomes increasingly complex, the demand and market for zero-energy buildings and construction methods will likely follow an exponential growth curve.

The U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) offers consumers information on home energy efficiency and assessments. They also sponsor clean energy research and development. Some tips offer homeowners simple solutions to reduce energy consumption without undertaking major building renovations, including programable thermostats, Energy Star-approved appliances, heat pumps, air sealing, ventilation placement, lighting, and more. More extensive projects in the twenty-first century include installing cool or green roofs that utilize nature to naturally reduce urban development's environmental impact.

Sustainable architecture is increasingly in demand. Architects specializing in this area provide the foundation for energy-efficient buildings by creating plans using sustainable or recycled materials, installing sustainable energy sources like passive daytime radiative cooling, wind power, or solar heating, and considering the building's placement.

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