BUILDING DESIGN, COMMERCIAL

More than 3.3 billion square feet of new commercial buildings were constructed from 1988 to 1998, with 170 percent more expected by the year 2030. Because this new stock is expected to have a lifetime of fifty to one hundred years, this has a dramatic impact on energy consumption not only today, but also for many years to come. This article will discuss the history of commercial building design, how technology has impacted commercial building design, and what impact this has had on building energy use.

HISTORY

The first commercial buildings, built in about 2000 b.c.e., were simple structures that represented the beginnings of architecture—a series of columns, walls, and roofs. Columns represented the upright human stance, walls represented human territoriality, and roofs both kept the rain out and created a crown, or head, for the structure. Walls also represented a separation between the plant and animal world and the human world. The walls of a courtyard formed a human space that became the city. Although the form of buildings has evolved over time, buildings today fundamentally provide these same basic human functions: artistic expression, separation, definition, and shelter.

Modern buildings are fundamentally defined by the mechanical principles that drive their utility. Technology has defined both the form of the buildings and energy use. Electrical lighting, mechanical ventilation, curtain-wall systems, air conditioning, and office equipment all contribute to a modern building's energy consumption. Two of these technologies that have had the most influence on the energy consumed by commercial buildings have been the lightbulb and the air conditioner.

Energy use in buildings has risen dramatically since 1900 because of technologies that enabled the creation of man-made indoor environments. It began with the invention and proliferation of the electric lightbulb in the 1880s. Fluorescent lighting became popular in the late 1930s, and by 1950 had largely replaced incandescent lamps in commercial buildings. However, incandescent lamps still are used in approximately 17 percent of the pre-1970 building stock.

Tasks such as health care, office work, manufacturing, studying, and other tasks requiring visual acuity all benefited from electric lighting. It also meant that workers didn't need access to a window to be productive. Designers could use artificial illumination to light tasks away from windows. Interior spaces that didn't require skylights or cleristories were now possible in commercial buildings.

The next major advance was elevators in the early 1900s followed by air conditioning in 1920s. Air conditioning changed where we lived and the way we lived, worked, and spent our leisure time. Prior to air conditioning, commercial buildings required natural ventilation. This defined the shape of the building, as each office or room required an operable window T-, H-, and L-shaped floor plans, which allowed the maximum number of windows to provide natural light and ventilation, are still visible in New York, Chicago, Boston, and Denver. During the pre-airconditioning era, large cities developed in northern latitudes because workers could remain productive performing office work for most of the year.

The New York Stock Exchange was the first "laboratory" for air conditioning, in 1901. The American public first experienced air conditioning in the Olympia Theater in Miami, Florida, in 1920. Department stores and movie theaters realized the potential for air conditioning to increase their business. And the first high-rise office building to be completely air-conditioned was the Milam Building, built in 1928 in San Antonio, Texas this building demonstrated that office workers were also more productive in a temperature-controlled environment. For manufacturers, air conditioning benefited the manufacturing of textiles, printing, and tobacco by allowing precise temperature, humidity, and filtration controls.

This new technology also allowed greater architectural freedom. Post-World War II construction incorporated sealed aluminum and glass facades, or curtain walls. The United Nations Building was the first major post-World War II project to be designed with a curtain wall system and air conditioning. Larger floor cross sections were possible, and interior offices could be created with man-made environments.

The structure and energy use of post-World War II commercial buildings was re defined as a direct result of air conditioning.

Electrical energy use in buildings rose from the late 1800s through the 1970s while natural gas and fuel oil use declined. Pre-1970 buildings represent 30 billion square feet of floor area, and have an average size of roughly 12,000 square feet. Approximately 70 percent of these buildings are air conditioned and are illuminated with fluorescent lighting. Overall energy intensity declined from about 1910 to 1940, but increased after 1950 as air conditioning became more common. More than 70 percent of the energy used by pre-1970 buildings came from electricity or natural gas.

THE ENERGY CRISIS

In the late 1960s a host of new technologies allowed architects to expand the horizons of their designs. The boundless promise of low-cost energy and a real-estate boom created a certain freedom of expression. This expression also created some of the most energy-intensive buildings ever built, as technology could overcome the shortcomings of a building design that failed to properly shelter occupants from heat, cold, sun, and glare.

The Arab oil embargo and ensuing "energy crisis" in late 1973 began to change the way commercial buildings were designed and operated. The first reaction to the energy crisis was to conserve energy. Conservation of energy means using less energy regardless of the impact that has on the levels of amenities the building provides. This impacted three areas of building comfort; thermal comfort, visual comfort, and ventilation air

The combination of lower thermostat settings, reduced ventilation, and lower lighting levels created environmental quality problems in many buildings. Even today, some building owners associate energy conservation with poor indoor environmental conditions.

Starting in the early 1980s, Energy efficiency gradually replaced energy conservation as the mainstream approach to saving energy. Energy efficiency relies on three key principles:

1. 1. Life-cycle cost analysis. Energy-efficient buildings are typically designed to be cheaper, on a life-cycle basis, than wasteful buildings.
2. 2. Comprehensive design. Often, energy-efficient buildings are cheaper on a first-cost basis as well as on a life-cycle cost basis. This frequently results from approaching the design of all of the energy-consuming systems of a building comprehensively and finding synergies among the various energy efficiency measures. For example, introducing daylight and energy-efficient artificial lighting can reduce the internal heat loads in a building, which reduces the size of the heating, cooling and ventilating ducts. This in turn reduces the floor-to-floor height and the cost of the elevators, building skin, etc., and enables the developer to add more rentable floor space in a given building volume (which is often constrained by zoning restrictions).
3. 3. Environmental quality. In contrast to being dark and cold in the winter and hot in the summer, well-designed, energy-efficient buildings usually are more enjoyable to inhabit. This is particularly true of well-lit buildings, with low glare, balanced luminance, and visual cues from the lighting as to how to most comfortably inhabit the space. Well-designed efficient buildings also allow easy and balanced temperature control, avoiding problems such as some zones being too hot while others are too cold.

The energy crisis also created a rush to develop new technologies and practices to reduce the energy consumption of buildings. One popular technology was solar energy. Commercial building solar technologies focused on harnessing the Sun's energy to cool the building through absorption cooling, provide hot water, or illuminate building interiors.

The Frenchman's Reef Hotel in St. Thomas, U.S. Virgin Islands, was the first large-scale commercial demonstration of solar absorption cooling. Other popular solar applications in the 1970s and early 1980s included swimming pool heating, commercial laundry hot water heating, and the use of natural daylight to offset electrical lighting in buildings.

It took several years before real improvements in commercial building energy efficiency occurred. This was because first-cost decisions drive a large segment of the new construction market. If a construction project begins to run over budget, energy-efficient features may be the first items cut, since they are less visible to the building tenant. In the 1980s, marketplace dynamics helped to change the market for energy efficiency because of the following factors:

• Utilities offered financial incentives to customers to reduce energy consumption because it was less expensive than constructing new power plants to meet the growing demand for electricity.
• Manufacturers incorporated energy-efficient design features into their product lines, making new products and services available to commercial building owners.
• Widespread adoption of building energy codes requiring minimum levels of energy efficiency to be included in new buildings.

The commercial building market began to respond to these dynamics by significantly reducing energy use.

CURRENT COMMERCIAL BUILDING DESIGN

A recent study conducted by California utilities identified the efficiency of buildings constructed in the 1990s with respect to what was required by the state building code. The study showed that most newer buildings use 10 percent to 30 percent less energy than buildings barely meeting the code. This finding is noteworthy in part because California has one of the most stringnet building codes in the country. The technologies and practices that created this result will be discussed in more detail below.

The building envelope in a commercial building plays a very different role than in a residential building. Figure 1 shows the complex interactions of heat flow in a modern commercial building. Energy (Q) enters the building from direct solar gain and heat from people, equipment, and lights. Energy leaves the building through the walls, roof, and windows and by heating ventilation air. An efficient building minimizes energy entering the building and balances that with the energy leaving the building.

The Commercial Building Envelope

The building envelope is one of the keys to both building energy use and thermal comfort. A high-performance building envelope will require a smaller mechanical system, provide natural lighting, and shelter occupants from heat and glare. Building envelopes in a modern building have four key elements that impact energy use. These elements are

• thermal performance
• building orientation
• permeability (air and moisture)
• daylighting.

Envelope construction characteristics for a modern building are shown in Table 1. The predominant stock of buildings is small masonry or metal buildings. The building envelope is an integral part of the way a building is illuminated. Windows and skylights can deliver a significant portion of the lighting needed for building occupants to be productive. Proper daylighting requires that glare and direct sun be minimized while maximizing the use of diffuse light. Architecture and glass property selection accomplish this. Architectural features include aperture areas, overhangs, fins, and light shelves or horizontal surfaces that redirect light entering windows deep into a space. Glass properties include a low solar heat gain coefficient and a high visible light transmittance. When properly designed, daylighting can deliver improved learning rates in schools and higher sales in retail stores.

Mechanical Systems

Building comfort is one of the key elements of a successful commercial building. The thermal comfort of a building is often as compelling as the aesthetics of the design. Modern building mechanical systems have two primary functions: maintain spaces within a predefined comfort range and deliver outdoor air to each space to assure proper ventilation. They have to do this in a quiet and efficient manner.

Heating, ventilating, and air-conditioning (HVAC) systems in modern buildings fall into two general categories: single-zone systems and multiple-zone systems. Both systems use air as the primary transfer mechanism to deliver heating and cooling to a space.

Single-zone systems deliver conditioned air to a single thermal zone. These systems are popular in small buildings (fewer than 10,000 square feet) and in single-story larger buildings. Usually they are vapor compression systems that cool air before it is delivered to a space. Single-zone systems serve 57 percent of post-1980 buildings.

Multiple-zone systems deliver conditioned air to more than one thermal zone. These systems typically have a direct expansion compressor or cold-water chiller to deliver cooling to the system. A central boiler or warm-air furnace at the system level, or electric heating elements at each zone, provide heating capabilities. This collection of components is controlled to maximize comfort and minimize energy use by computer-based controls. Roughly half of these buildings have an energy management control system that is operated by a trained energy manager.

A multiple-zone system must be able to deliver heating to a perimeter thermal zone in the winter while cooling an interior zone to offset internal

gains. To accomplish this, modern multiple-zone systems use a technique called variable air volume (VAV).

A VAV system controls the temperature in a thermal zone by the volume of air delivered to that zone. If a zone thermostat demands heat, the system would first reduce the volume of air to the zone to the minimum required to meet outdoor air ventilation requirements and then begin to heat the air. This helps reduce energy use in two ways: first, the volume of air moving through the system is reduced to a minimum, lowering fan energy use, and second, reheating previously cooled air is minimized. Variable-speed drives are the most efficient method of controlling VAV fans and are used in 8 percent of post-1980 buildings.

The advantages of VAV are that temperature can be controlled while minimizing energy consumption. Also, the system can be smaller because the maximum demand for cooling never occurs simultaneously in all spaces. The disadvantages are the additional space required for the air-handling plants and ductwork.

Another energy-saving feature of modern HVAC systems is the ability to cool the building using outdoor air. This is accomplished through a control and damper arrangement called an outdoor air economizer. An economizer varies the outdoor air supply from the minimum setting to up to 100 percent outdoor air, provided the outside air temperature is less than the supply air temperature required to maintain comfort conditions. Outdoor air economizers are present in 85 percent of post-1980 buildings.

Lighting Systems

Lighting has a significant impact on building occupants, for better or for worse. Lighting also is a significant energy user and is rich with potential energy savings. For some time there has been a good deal of attention and effort invested in mining the energy savings from lighting systems. Preliminary studies into the ancillary benefits of energy-efficient lighting show that quality lighting can have positive effects such as improved productivity, reduced health complaints, and reduced absenteeism.

Figure 2 shows how buildings built after 1980 use energy. Lighting is the most significant energy expenditure in a modern building. The key qualities of an effective lighting system are

• energy efficiency
• room surface brightness
• reduction of glare
• adequate task illumination
• uniform light distribution
• good color lamps
• visual interest
• lighting controls.

Key technologies that are used in modern lighting include electronic ballasts, more efficient tubular fluorescent lamps, compact fluorescent lamps, and lighting controls. Fluorescent lighting is the predominant lighting system installed in post-1980 buildings and is used in 71 percent of floor space. Specialty retail stores use a combination of fluorescent and incandescent, with halogen lights accounting for 2 percent of floor space.

Lighting controls used in post-1980 buildings include automatic shutoff controls through an energy management system (6%) and an occupancy sensor (2%). Daylighting automatically dims artificial lighting in areas where light entering windows and skylights provides adequate illumination. Daylighting, while a promising technology, has not received widespread application.

Office Equipment

All of the advances in modern building design have not dramatically reduced the energy intensity of modern buildings. In fact, they have become more energy-intensive during the 1990s. Buildings constructed from 1990 to 1995 typically used 15 percent more energy per square foot than buildings constructed during the 1980s.

In 1995 an estimated 43 million PCs and computer terminals were used in commercial buildings. More than half of the 4.6 million buildings in the United States had at least one PC or computer terminal. The more PCs and computer terminals used in a given building, the greater the impact on the building's energy consumption. The proliferation of personal computers, printers, copiers, and other types of "plug loads" is the main cause of the rise in energy intensity in recent years.

THE FUTURE OF COMMERCIAL BUILDINGS

The workplace of the future has captured the imagination of researchers and designers internationally and across a wide range of disciplines, from computer science and furniture design to organizational systems. Noticeably missing from these discussions and visions is the energy research community. With more and more businesses operating under tighter and tighter margins, building owners and occupants are going to demand increased attention to the delivery and management of energy in buildings as other changes take place.

Trends in the Workplace

We are moving in a direction in which the information technologies associated with work processes are almost totally decoupled from energy and architectural technologies and systems. Not only is the workplace of the future going to demand more flexibility and rapid reconfiguration of space, it also is increasingly moving toward a radically different use of facilities. In addition, in the interest of meeting shareholder and organizational concerns for increasing profit margins, the workstation footprint is shrinking rapidly. All of these trends have implications for energy.

For example, current trends show telecommuting increasing 20 percent annually. According to one estimate, New York City will have an additional 180 million square feet of empty office space as a direct result of telecommuting. This could shift patterns in energy demand as well as require the development and deployment of new technologies that are suited to renovating facilities rather than for use in new buildings. Furthermore, although many telecommuting advocates see working at home as a way to reduce transportation impacts, there is some indication that the demand for transportation will actually increase. This is because many of the workers who have home offices are independent consultants who spend a good deal of their time in their cars visiting clients and developing work. Further, the introduction of new information technologies is opening up new markets in many areas, which, in turn, are associated with rapid delivery of products, which increase the demand for vehicles.

Many organizations are moving to open-planned, high-communication, team-centered layouts with little understanding of the organizational and performance implications of this fad, and with even less understanding of the implications for the design and delivery of energy where it is needed, when it is needed. Furthermore, the workstation "footprint" is becoming ever smaller as furniture manufacturers reduce the size of the cubicle setting in response to demand from businesses to put more people into smaller areas.

Energy Technology Development Implications

These trends have an impact on both energy use and the technologies that are developed to deliver thermal and visual comfort to the workplace. For example, how does an existing building with a fixed comfort delivery system meet the needs of these new and varying layouts? Current practice suggests that increased airflow is the answer, resulting in higher levels of reheating and recooling of air in a typical office system. Higher occupant density also translates into greater demand for outdoor air ventilation. Higher outdoor air rates can increase total building energy consumption from 20 percent to 28 percent in buildings built prior to 1989. These trends could have the following impacts leading to greater use in the workplace of the future:

• increased air movement to accommodate high occupant densities resulting in increased fan energy consumption;
• individuals bringing in desk lamps, resulting in the use of low-efficacy light sources (i.e., incandescent lamps) in addition to the high, efficacy light sources installed in the buildings;
• electric resistance heaters to warm areas of high air flow (too much cold air) and low air flow (not enough warm air) resulting from high-density loads with controls designed without a high enough degree of zone resolution;
• personal fans to create air movement that is impacted by typical partitions;
• increased ventilation requirements resulting in greater heating and cooling energy demand.

To avoid significantly higher energy consumption, building designers of the future must integrate the knowledge and expertise of the energy-efficiency community. There are several areas of integration, including:

• enhanced personal and team control over ambient conditions, including lighting, temperatures, ventilation, and acoustics;
• greater integration of energy technologies into the design of furnishings;
• glazing materials and window technologies that promote views and natural ventilation while reducing heat gain and glare;
• greater attention to understanding the energy demands that will be required to support the high-technology office of the future;
• development of ways to humanize windowless and underground spaces through features such as sensory variability, borrowed daylight through light tubes, and simulated windows;
• intelligent building systems that can identify and correct potential problems before they become large and more difficult to manage.

Jeffrey A. Johnson William Steven Taber, Jr.

See also:Air Quality, Indoor; Building Design, Energy Codes and; Building Design, Residential; Cool Communities; Economically Efficient Energy Choices; Efficiency of Energy Use; Lighting; Office Equipment; Solar Energy; Windows.