Building systems for_interior designers phần 6 ppt

them. Photovoltaic cells are made from a very pure form of silicon, an abundant element in the earth’s crust that is not very difficult to mine. Photovoltaic cells provide direct electrical current. When enough heat or light strikes a cell connected to a circuit, the difference in voltage causes current to flow. No voltage difference is produced in the dark, so the cell only provides energy when exposed to light. A cell can be connected to a battery, to provide continuous power. Even the best PV cells turn less than a quarter of the solar energy that strikes them into electricity, with the rest given off as heat. Commercially available cells are currently only about 10 to 12 percent efficient. New designs currently being researched are up to 18 percent efficient. Individual PV cells are wired together to produce a PV module, the smallest PV component sold commercially, and these modules range in power output from about 10 to 300 W. Usually, individual modules are mounted onto an existing roof. Some modules can be designed directly into the roof, acting as both a roofing material and an electricity generator. To connect a PV system to a utility grid, one or more PV modules is connected to an inverter that converts the modules’ DC electricity to AC electricity. The AC power is compatible with the electric grid and can be used by lights, appliances, computers, televisions, and many other devices. Some systems include batteries to provide backup power in case the utility suffers a power outage. Small commercial and industrial PV applications include lighting, traffic counters, signaling, and fence charging. Larger systems provide electricity for residential, office, educational, and mobile electrical needs. Systems are not limited to sunny tropical areas. A solar electric system in Boston, Massachusetts, will produce over 90 percent of the energy generated by the same system in Mi- ami, Florida. In areas with low-sun winter seasons, like New England, these systems are frequently paired with a generator or other backup systems for extra power. Photovoltaic energy is a clean, reliable alternative for providing electrical power. It minimizes dependence on fossil fuels and reduces vulnerability to fuel price spikes. Solar energy can decrease utility bills and in- crease the resale value of real estate. When the PV system generates more electricity than is needed at the site, excess energy can be fed directly onto electric lines for use by other electric customers (Fig. 27-3). Through a net-metering agreement with the electric utility, PV system owners are compensated for the excess power they produce. The PV system contractor installs an inverter that ensures that the electricity coming from the PV system is compatible with electricity coming from the power lines. Stand-Alone Photovoltaic Arrays The oldest type of PV system is the stand-alone array. Stand-alone arrays are isolated from the utility electrical grid and designed for a specific job. They are used for sign lighting, railroad crossing lights, unattended pumps and navigational aids, lighthouses, motor homes, sail- boats and yachts, and isolated small residences. When a fuel-powered generator is added for a more reliable supply, the system becomes a hybrid stand-alone. Storage batteries store the excess from peak hours to use during cloudy days and at night. Because the power is DC, some uses require a DC–AC inverter to change to AC power. Fluorescent lighting fixtures are available with inverter ballasts. Some kitchen appliances and power tools may only be available for use with AC, but the number of DC-compatible appliances is increasing. For systems that aren’t attached to the utility grid, PV system batteries help smooth out supply and use patterns. In homes, PV production peaks at noon, while use peaks in the evening. Stores, shops, and cottage in- dustries tend to have usage that coincides more closely with PV production. This reduces drain on the battery and allows less expensive batteries to be used. Batteries must be able to supply most or all of the electrical requirements for a given period, usually three days of cloudy weather. The cost of replacing the backup battery adds to the system cost over time. Commercial Photovoltaic Applications Until the late 1980s, PV systems had very limited applications and were generally not cost effective. In 1982, ARCO started up the first PV central power station in How Electrical Systems Work 219 PV arra y on south-facing roo f d ct oa c inverte r Meter f o r P V energ y Meter for energy used b y hous e House electrical p ane l Electric a l service dro p Figure 27-3 Grid connected PV system. San Bernardino County, California. More recently, fed- erally financed research and development and state and federal legislation have increased the impact of PV systems on commercial electrical power. In 1990, the U.S. Department of Energy (DOE) and 20 private companies initiated the PV manufacturing technology project (PV Mat), and in 1992 the DOE sponsored PV : bonus, a building cost-sharing project. These programs reduced PV module costs by more than half and spurred development of new PV module materials, construction technologies, product forms, and PV module efficiency. Costs for the power produced dropped from around $0.50 to $1 per watt to about half that. Many states are establishing requirements for electricity from renewable sources. By 2003, electricity suppliers in Massachusetts will be required by law to provide electricity generated from renewable sources, such as solar PV systems. Designing Buildings for Photovoltaic Systems PV system arrays are complete connected sets of modules mounted and ready to deliver electricity. Building mounted arrays are stationary and usually consist of flat plates mounted at an angle. Tracking arrays follow the motion of the sun, providing more contact with the solar cells. A building with good access to the sun and a roof that faces south is ideal for installation of a PV system. Roofs that face east or west may also be acceptable. Flat roofs also work well for solar systems, because the PV array can be mounted flat on the roof facing the sky or can be mounted on frames that are tilted toward the south at the optimal angle. All or most of the sun’s path should be clear and not obscured by trees, roof gables, chimneys, buildings, and other features of the building and surrounding landscape. Shade falling over part of the PV array for part of the day can substantially reduce the amount of electricity that the system will produce. The amount of mounting space needed for the solar system is based on the size of the system. Most residential systems require between 4.6 and 19 square meters (50–200 square ft), depending on the type of PV module used and its efficiency. Composition-shingle roofs are the easiest type to work with, and slate roofs are the most difficult. The decision to install a PV system involves several economic considerations. The connection to the electrical grid and the cost of power from the grid are basic criteria. The cost of the system components over the life of the whole installation must be added to the costs of maintenance and financing. The PV system’s battery can double as an emergency source for computers and pe- ripherals to cover grid power interruptions. Photovoltaic panels can substitute for other construction materials, providing a cost savings. New solar electric technology has made possible a number of products that serve another building function while acting as photovoltaic cells. Building integrated PV (BIPV) elements are structures that combine PV modules into roof panels, roofing tiles, wall panels, skylights, and other building materials, replacing traditional building elements. Companies in the United States, Japan, and Europe are actively pursuing new module designs. So- lar roof shingles, structural metal roofing, and architectural metal roofing are now available, along with win- dow glass. These products use flexible, lightweight panels designed to emulate conventional roofing materials in design, construction, function, and installation. Structural metal panels are used for PV-covered parking, charging stations for electric vehicles, park shelters and other covered outdoor spaces, and for commercial buildings. PV shingles can be used in combination with conventional shingles. Custom-color crystalline solar cells, including gold, violet, and green, are becoming available. Other architectural module designs have space between the cells and opaque backings to provide dif- fuse daylighting along with electric production. A single-residence PV system costs about $10 per watt of rated system capacity, including installation and all system components. A 1000-W system that would supply about one-third of the electricity for an energy- efficient home would cost approximately $10,000. With larger systems and projects where costs can be shared, the cost per watt could be reduced significantly. It currently costs from $10,000 to $40,000 to install a full solar system in a home, but rebates for up to one-half of that are currently offered in about 30 states, with more considering doing so. When purchased in quantity by a builder, solar panel systems add about $50 per month to the cost of the house, while saving from $50 to $100 in monthly electric bills. From a long-term perspective, it does not have to cost more to build with solar. The smartest building designs will specify a tight building envelope and high- efficiency lighting and HVAC equipment. The savings from these energy-efficient measures can be used to pay for a solar investment over time. While it is common for builders and architects to focus on current equipment costs, it is critical to approach projects with a focus on the cost of both constructing and operating a building over its lifetime. States offer residential tax 220 ELECTRICITY credits for solar applications, and there are both state and federal tax incentives available for corporations, making commercial solar applications highly attractive. As mentioned previously, the 1978 Public Utility Regulatory Policy Act (PURPA) requires that electric utilities buy electrical power from small suppliers. The price is established at a price equal to the cost the utility avoids by not having to produce that power. This has been interpreted as the cost of the fuel alone, without consideration of the cost of additional plant construction and related expenses. Under PURPA, energy has been purchased at around three cents per kWh by the same utilities that sell energy at eight to fourteen cents per kWh. This policy has discouraged development of grid-connected PV installations. More recently, states have adopted net-metering laws that require the utility to pay PV providers at the same rate at which it sells the electricity during PV gen- erating hours. The energy that the customer generates and uses is credited at the rate the utility would other- wise charge that customer. Only when the customer is producing more energy than he or she uses does the utility pay at the avoided cost rate. This means that small producers get fair credit for the energy they supply them- selves, and are able to sell any excess to the utility, even if at a low rate. When the PV user buys from the utility, they pay at the conventional utility rate. Thirty states offer net-metering as of 2001. Net-metering benefits both the customer and the utility. Some utilities have instituted PV installation programs primarily for residences. The utility installs and maintains the PV system on the customer’s property (usually the roof), and the customer pays a small sur- charge to the utility bill. The result is an environmen- tally beneficial power supply. With the metering systems currently in use and the relatively high initial product costs, PV grid-connected systems can seldom justify the cost of installation on economic grounds only, but this is changing. Some utilities allow the installation of small individual PV modules in existing conventional buildings. These PV modules plug into conventional outlets in the building and supply power to the building. The excess not used in the building is fed back to the utility via a re- versible energy meter. The system can be expanded gradually without centralized installation expenses. Two large PV installations were completed in 2001. The 49-kW system on the Field Museum of Natural His- tory in Chicago is connected to the local utility’s electricity grid, reducing the amount of power from nonre- newable, high-emissions sources during peak periods. The 200-kW system mounted on the Neutrogena Cor- poration headquarters in Los Angeles covers 2230 square meters (24,000 square ft) of roof area and will help reduce the company’s energy consumption by about 20 percent. At the DOE’s headquarters in Washington, DC, a blank south-facing wall presents three-quarters of an acre of poured-in-place concrete to views from the Na- tional Mall. This eyesore is scheduled to become one of the largest solar installations in the world. The DOE, with the National Renewable Energy Laboratory, the American Institute of Architects, and the Architectural Engineering Institute, organized a design competition for a clean, renewable energy design. The winning design, proposed by architects at Solomon Cordwell Buenz & Associates in Chicago and engineers Ove Arup & Part- ners in New York, is an elegant, sweeping wall of ten- sioned cables, struts, and glass. The wall is a light, rigid structure that supports a PV collection system to turn solar energy into electricity, plus a solar thermal system that generates heat. Many small projects are cropping up, such as the renovation of the Porter Square Shopping Center in Cambridge, Massachusetts, where roof-mounted PV panels provide almost all the energy needed for lighting. Another project is the Conde Nast skyscraper in New York City, where PV panels wrap the upper floors. The National Fire Protection Association (NFPA) publishes NFPA 70, Article 690, Solar Photovoltaic Sys- tems, which sets standards for PV systems. If the system is connected to the electrical grid, the local utility will have additional interconnection requirements. The electric utility will also know about the option of offering net-metering. Some homeowners’ associations require residents to gain approval for a solar installation from an architectural committee, which in turn may require a system plan and agreement from neighbors. In most locations, building and/or electrical permits are required from city or county building departments. After the PV system is installed, it must be inspected and ap- proved by the local permitting agency (usually the building or electrical inspector) and often by the electric utility as well. More than 500,000 homes worldwide use PV to supply or supplement their electricity requirements, though all but about 10,000 are rural or remote off- grid applications. Residential and commercial BIPV are the most likely large-scale markets for PV in the developed countries. With participation of architects and building engineers, the technology is taking a progres- sively more sophisticated, elegant, and appropriate role in building design, putting energy-producing buildings within our reach. How Electrical Systems Work 221 Fuel Cells Fuel cell systems are currently being developed and mar- keted for residential and light commercial applications in Europe beginning in mid 2003. The fuel cell units, which operate on natural gas or propane, will be used to generate electricity for backup electrical power or as primary power. Some of the fuel cells will be offered in cogeneration units, using the heat generated by the fuel cell for space heating and domestic hot water. The electricity produced will replace or reduce use of electricity from the electrical grid. The Long Island Power Authority in New York State is connecting 75 fuel cells to its electric grid. The fuel cells are intended to add to the reliability and perfor- mance of the electrical grid system. By connecting the fuel cells directly to the transmission grid, the electricity they create will be distributed through the utility’s electric transmission and distribution system. A new 500-W residential cogeneration fuel cell system is being introduced for the Japanese residential market. The goal is an efficient, cost-effective fuel cell system using compact 1-kW and 500-W fuel cells, well suited to the residential and apartment markets in Japan, where the demand for low-power alternative energy sources is strong. The manufacturer hopes to de- velop a technology base for new products in the United States and Europe as well. ELECTRICAL SYSTEM DESIGN PROCESS Engineers start the process of designing electrical systems by estimating the total building electrical power load. They then plan the spaces required for electrical equipment such as transformer rooms, conduit chases, and electrical closets. The amount of energy a building is permitted to consume is governed by building codes. A building energy consumption analysis determines whether the building design will meet the target electrical energy budget. If not, the engineer must modify the electrical loads and reconsider the projected system criteria. The engineer will incorporate energy conservation devices and techniques and draw up energy use guidelines to be applied when the building is occupied. These techniques depend upon the day-to-day volun- tary actions of the building’s occupants, which are hard to determine during the planning phase. Once the electrical load is estimated, the engineer and the utility determine the point at which the electrical service enters the building and the meter location. They decide on the type of service run, service voltage, and the building utility voltage. With the client, the engineer looks at how all areas of the building will be used and the type and rating of the client’s equipment, including specific electric ratings and service connection requirements. The electrical engineer gets the electrical rating of all the equipment from the HVAC, plumbing, elevator, interior design, and kitchen consultants. This communication is often made at conferences where the electrical consultant makes recommendations to the other specialists regarding the comparative costs and charac- teristics of equipment options. The electrical engineer is responsible for determin- ing the location and estimated size of all required electrical equipment spaces, including switchboard rooms, emergency equipment spaces, and electrical closets. Panel boards are normally located in closets but may be in corridor walls or other locations. The architect must reserve spaces for electrical equipment. The electrical engineer, the architect, the interior designer, and the lighting designer design the lighting for the building. Plans may have to separate the lighting plan from the layouts for receptacles, data, and signal and control systems. Underfloor, under-carpet, over- ceiling wiring and overhead raceways are usually shown together on their own plan. The engineer then prepares a lighting fixture layout. All electrical apparatus is located on a plan, including receptacles, switches, and motors. Data processing and signal apparatus is located. Tele- communications outlets, network connections, phone outlets, speakers and microphones, TV outlets, and fire and smoke detectors are shown. Control wiring and building management system panels are also indicated. Next, all lighting, electrical devices, and power equipment is circuited to appropriate panels. The engineer will detail the number of circuits needed to carry the electrical load, and the types and sizes of electrical cables and materials and electrical equipment, along with their placement throughout the building. Panel schedules are prepared that list all the circuits for each panel, including those for emergency equipment. Panel loads are computed that show how much power is circuited through each panel. The engineer prepares riser diagrams that show how wiring is run vertically, and designs the panels, switchboards, and service equipment. After computing the sizes of wiring sizes and protective equipment ratings, the engineer checks the work. The engineer then coordinates the electrical design with the other consultants and the architectural plans, and continues to make changes as needed. 222 ELECTRICITY Interior designers are also responsible for showing electrical system information on their drawings (Fig. 27-4). The electrical engineer uses the interior design drawings to help design the electrical system. The interior design drawings often indicate all electrical outlets, switches, and lighting fixtures and their type. Large equipment and appliances should be indicated, along with their electrical requirements. Communication system equipment, like public phones, phone outlets, and related equipment, and computer outlets are shown. In new buildings, the location and size of equipment rooms, including switching rooms and electrical closets, should be coordinated with the electrical engineer. The designer should be familiar with the location and size of the electrical panels, and with the building systems that affect the type of wiring used, such as plenum mechanical systems. The interior designer must know the locations of existing or planned receptacles, switches, dedicated outlets, and ground fault circuit in- terrupters (GFCIs). Lighting fixtures, appliances, equipment, and emergency electrical systems affect the interior design. You may need to coordinate the location of equipment rooms. The presence of an uninterrupted power supply or standby power supply is also important to know about. The interior designer does not usually need to be completely familiar with the electrical code requirements, but there are several areas that may affect interior design work. Building codes set limits on the total amount of energy used by the building, including equipment and lighting, so the interior designer should be aware of energy-efficient options. The National Electrical Code (NEC) is also known as NFPA 70. The NEC sets the minimum standard for all electrical design for construction, and is revised every three years. It is the only model electrical code published, and is the basis for electrical codes in almost all jurisdictions. Interior designers rarely use the NEC, as it is the responsibility of the electrical engineer to design the electrical system. On smaller projects, a licensed electrical contractor will know the codes. However, since you will typically specify the location of electrical outlets and fixtures, you need to know basic code requirements. The electrical code includes restrictions on the proximity of electrical components and plumbing, for example. Standards for electrical and communications systems are set by the American National Standards Institute (ANSI), the Na- tional Electrical Manufacturers Association (NEMA), and the Underwriters Laboratories (UL). In addition, the Americans with Disabilities Act (ADA) specifies mounting heights for outlets and fixtures in handi- capped accessible spaces. How Electrical Systems Work 223 Figure 27-4 Electrical power plan. There are two separate electrical systems in most buildings. The electrical power system (Fig. 28-1) distributes electrical energy through the building. The electrical signal or communication system, which we look at later, transmits information via telephone, cable TV wires, or other separate data lines. The electrical power service from the utility line may come into the building either overhead or underground. The length of the service run and type of terrain, as well as the installation costs, affect the decision of which to use. Service voltage requirements and the size and nature of the electrical load also influence the choice. Other considerations include the importance of appearance, local practices and ordi- nances, maintenance and reliability criteria, weather conditions, and whether some type of interbuilding distribution is required. Overhead service costs from 50 to 90 percent less than underground service to install, but the cost of underground service is decreasing. Overhead service is pre- ferred for carrying high voltages over long runs and where the terrain is rocky. Access for maintenance is easier with overhead service. Wires on poles are more prone to problems in bad weather than underground cables. Underground service is barely noticeable, very reliable, and has a long life. All this comes at a higher cost. Underground service is used in dense urban areas. The service cables run in pipe conduits or raceways that allow for future replacement. Direct burial cable may be used for residential service connections. SERVICE ENTRANCE Wires called service conductors extend from the main power line or transformer to the building’s service equipment (Fig. 28-2). The portion of the overhead service conductors leading from the nearest utility pole to the building is called the service drop. In a residence, you may see three cables twisted together, or in older houses, running separated. In underground systems, the portion of the service conductor extending from the main power line or transformer to the building is called the service lateral. The section of the service conductor that extends from the service drop or service lateral to the building’s service equipment is called the service entrance conductor. A grounding rod or electrode is firmly embedded in the earth to establish a ground connection outside the building. The network of wires that carry electrical current through a building stretches out from a single center, the main service panel, which is usually located where the power line enters the building. In a residence, the 28 Chapter Electrical Service Equipment 224 main service panel is usually located in the basement or in a utility room. In larger buildings, this equipment is usually located in a switchgear room near the entrance of the service conductors, and is mounted on a main switchboard. The main service panel is located as close as possible to the service connection to minimize voltage drop and to save wiring. Secondary switches, along with fuses and circuit breakers for controlling and pro- tecting the electrical power supply to a building, are also in the main service panel. To protect firefighters, the main service panel has a main disconnect (or service) switch. The disconnect switch must be in a readily accessible spot near where the service enters the building. Access to the main disconnect switch must not be blocked. In a residential building, the main disconnect is usually the main switch or breaker of the panel board. This may be a lever disconnect, with an external handle controlling contact with two main fuses in a cabinet. When the lever is pulled to the “off” position, the main power supply is shut off. Some residential systems have a pullout block arrangement. In this type of disconnect switch, the main cartridge fuses are mounted on one or two nonmetallic pullout blocks, and pulling firmly on the handgrips re- moves the blocks from the cabinet and disconnects the power. Other systems use a single main circuit breaker, which shuts off all power when switched to the “off” position. Some homes are not required by the National Electrical Code (NEC) to have a single main disconnect, and use a multiple breaker main. All breakers in the main section, up to a maximum of six, must be switched off to disconnect service. It is important to maintain easy access to the main disconnect. When the voltage used by the building is different from the service voltage, a transformer is used to transform alternating current (AC) of one voltage to AC of another voltage. Transformers are not used with direct current (DC), which can only be used at its original voltage. Transformers may be pole or pad mounted outside a building or in a room or vault within the building. Step-down transformers lower voltage, and step-up transformers do the opposite. Typically, a transformer will step down incoming 1460V service to 480V for distribution within the building. Another transformer then steps down 480V to 120V for receptacle circuits. Low or secondary voltages used in buildings include 120, 208, 240, 277, and 480 volts. Electric Meters A watt-hour meter measures and records the quantity of electric power consumed over time. Meters are supplied by the utility, and are always placed ahead of the main disconnect switch so that they can’t be disconnected. Meters are located outside at the service point or inside the building, where they must be kept readily accessible to utility personnel. Manual reading of kilowatt- hour meters of individual consumers is labor intensive. Meters are often inaccessible, and meter readers may face hostile dogs and inclement weather. Remote reading of inside meters is now common. Programmable electro-optical automatic meter-reading systems can be activated locally or from a remote location. Meter data is transferred electrically to a data processing center, where bills and load profiles are prepared, and area load Electrical Service Equipment 225 Tr a nsf o rmer v au lt with switches , transformers , fuse s Main buildin g switch boa r d with switches , circuit breakers, meterin g Distri bu ti o n p anels Lar ge m o t o rs Li g htin g & a pp liance p anel s Br a nc h circ u i t wirin g Li g htin g , receptacles, small motors & c o ntr o ls Figure 28-1 How electricity is distributed through a building. patterns can be studied. Miniature radio transmitters on the meter can be remotely activated to transmit current kilowatt-hour data, which is encoded and recorded automatically. Such meters are more expensive but are replacing conventional units, resulting in a large reduc- tion in labor costs, and better quality and quantity of data. Even with remote readers, the meter must be available for inspection and service. Within the meter, the electricity drives a tiny motor at a speed proportional to the rate at which current passes through the wires. The motor advances pointers on dials by means of gears, and records the quantity of energy consumed in units of kilowatt-hours. In single- occupancy buildings or where the landlord pays for electrical service, there is one meter. For multitenant buildings, banks of meters are installed so that each unit is metered separately. A single meter is not allowed in new multiple dwelling constructions by federal law, as tenants tend to waste energy when they don’t have to pay for it directly. Advanced smart meters are now available that tell you how much electricity really costs right this hour or minute, and how much it would be worth to you, in real money, to conserve. Electricity prices are set largely by what it costs to produce enough electricity for the busiest few hours of the year, with prices rising dramatically when demand threatens to outstrip supply. A considerable portion of what you pay for electricity each month covers the risk of these rare price spikes and the cost of building special power plants like jet turbines and hydroelectric reser- voirs that are used only rarely to cover demand peaks. If enough people had electric meters that said, in effect, you can save 25 cents by waiting until midnight to dry your clothes, demand could be measurably reduced, enough to trim price spikes significantly. Electric utilities already offer this type of service to their largest industrial and institutional customers, giv- ing them bounties to shut down factories or conserve power when shortages and rolling blackouts loom. Util- ities are also initiating Web sites that allow participat- ing businesses to get real-time electric price information, with incentives to cut back use when prices soar. Companies are developing technologies for the small-user market, such as a device that connects home and business electric meters, and conceivably individual appliances, through the Internet to electric utilities. Utilities would be able to collect billing information directly over the Internet, rather than sending out meter readers. Puget Sound Energy in suburban Seattle has outfitted 1 million homes and businesses with advanced meters that take readings every 15 minutes and send them back wirelessly. Eventually, utilities may be able, with customer’s approval, to control things inside the house like thermostats, electric heaters, clothes dryers, and dishwashers. This would allow consumers to save energy and electric costs without having to repeatedly check their electric meters or the utility’s Web site. Other Service Equipment The area where a step-down transformer, meters, controls, buswork, and other equipment are located is called a unit substation or transformer load center. It 226 ELECTRICITY Three lines from power company Service entr a nce he ad w ate r out Service en t r a nce c o n du i t M eter Tw o h o t wire s M a in d isc o nnec t Ne u tr a l wir e Ne u tr a l bu s bar M a i n se rvi ce p ane l Gr ou n d r od o r c o l d -w a ter service t o met a l p i p es under g roun d Groun d in g electr od e c o n du ct or Gr ou n d clam p To sub p ane l H ot bu s ba r s Figure 28-2 Electrical service entrance. may be located outdoors or indoors in a basement with ventilation, with access by authorized personnel only. Transformers produce heat, which must be either ventilated or used. They are usually located on an exterior wall, with a louver with a bird screen. Indoor locations help to avoid vandalism and hide the transformer’s appearance. Transformer rooms may have to be heated in cold climates. Transformer vaults are fire-rated enclo- sures provided in case of rupture of an oil-filled transformer case. Transformer vaults often have to be vented to the outside with flues or ducts. When a transformer is located outdoors, no building space is required, and there is less of a heat or noise problem. Outdoor locations cost less and are easier to maintain or replace. They provide an opportunity to use low-cost, long-life, oil- filled units. ELECTRICAL PANELS The layout of the electrical system starts with the location of the electrical panels (Fig. 28-3). In residences, the service equipment and the building’s panel board are combined in one unit. The panel board is usually located in the garage, a utility room, or the basement. It is located as close to major electrical loads as feasi- ble, and sometimes an additional subpanel is added near kitchen and laundry loads. In apartments, panels are often located in the kitchen or in a corridor imme- diately adjacent to the kitchen, where they are used as the code-required means for disconnecting most fixed appliances. In smaller commercial buildings, electrical panels may be recessed into corridor walls. In small office, re- tail, and other buildings, lighting panels may be mounted in a convenient area to enable the use of circuit breakers for load switching. Buildings six and more stories high use electrical closets for the panels, and risers to connect floors. Larger buildings use strategically located electrical closets to house all electrical supply equipment. A switchboard is the main electrical panel that distributes the electricity from the utility service connection to the rest of the building. A switchboard is a large freestanding assembly of switches, fuses, and/or circuit breakers that provides switching and overcurrent protection to a number of circuits connected to a single source. Switchboards often also include metering and other instrumentation. The switchboard distributes bulk power into smaller packages and provides protection for that process. Modern switchboards are all of a type called “deadfront,” where all live points, circuit breakers, switches, and fuses are completely enclosed in the metal structure. Pushbuttons and handles on the panel front control the equipment. The NEC regulates the size of the room that contains a switchboard. When equipment is located on both sides of the room, access space is required on both sides. If the room contains a transformer also, additional space must be allowed. The room must be ventilated either directly to the outside or with ducts and fans. Smaller distribution switchboards do not require a special room, and are usually located in a wire screen enclosure with “Danger—High Voltage” signs. Switchboard rooms require exits, hallways, and hatches large enough for the installation and removal of equipment. Low-voltage switchboards with large circuit breakers, and all high-voltage (over 600V) equipment are referred to as switchgear. In commercial, industrial, and public buildings, switchgear is usually located in the basement in a separate well-ventilated electrical switchgear room. Switchgear rooms, emergency generator rooms, and transformer vaults must be completely enclosed and must have their own emergency lighting source. Panelboards are similar to switchboards but on a smaller scale. They accept relatively large blocks of power and distribute smaller blocks of electricity to each floor or tenant space. Within the panelboard, main buses, Electrical Service Equipment 227 Circ u it b re a ker s Circ u it director y P a nel boa r d d istri bu tes electricit y to b r a nch circ u it s Service c o n du ct or Figure 28-3 Electrical panel board. fuses, or circuit breakers feed smaller branch circuits that contain lighting, motors, and so forth. This equipment is mounted inside an open metal cabinet called a back- box, with prefabricated knockouts at the top, bottom, and sides for connecting conduits carrying circuit conductors. The panelboard may have a main circuit breaker that disconnects the entire panel in the event of a major fault. Small panels in residential work may be referred to as load centers. One-sided panels are housed in electrical closets or cabinets placed in or against a wall. They are stacked vertically in multistory buildings. Each floor may also have one or more branch panelboards that supply electricity to a particular area or tenant. Additional distribution panels are located as needed by the loads they serve. Self-contained areas, like laboratories, should have their own panels. ELECTRICAL CLOSETS The space allotted for electrical closets varies to fit other architectural considerations. They are vertically stacked with other electrical closets so as not to block horizontal conduits. Outside walls or spaces adjacent to shafts, columns, and stairs are not good locations. Electrical closet spaces should not have other utilities, like piping or ducts, running through them either horizontally or vertically. Each electrical closet has one or more locking doors. Inside is space for current and expansion panels, switches, transformers, telephone cabinets, and communications equipment. Floor slots or sleeves allow conduit and bus risers to pass through from other floors. The electrical closet must have space, lighting, and ventilation for the electrician to work comfortably and safely on installations and repairs. Electrical closets and cabinets must be fire-rated, as they are common places for fires to start, and they should not be located next to stairwells or other main means of egress. The electrical engineer is responsible for locating electrical closets, and their location will have implications for the interior designer’s space plan. ENERGY CONSERVATION AND DEMAND CONTROL In the past, issues of energy conservation and electrical demand limitation were essentially economic de- cisions. Owners balanced the cost of installing control equipment against the potential for savings on electrical bills. Today, legislation mandates energy use limitations, including lighting controls in certain non- residential buildings. The trend toward stricter regu- lations continues. Energy conservation affects the work of the electrical engineer, the architect, the interior designer, and the building’s owner and occupants. Conservation can start with the selection of high-efficiency motors, transformers, and other equipment. Electrical load control equipment is often necessary to meet code requirements for energy budgets. The electrical design should plan to ac- commodate expansion by making it simple to add additional equipment at a later date, rather than by over- sizing the original equipment. We have already looked at a number of ways to conserve electrical energy. In residential buildings with multiple tenants, individual user metering makes the tenant financially responsible for energy use. The exceptions are hotels, dormitories, and transient residences. Electrical heating elements should be avoided, as they use a high- grade resource for a low-grade task. When we discuss lighting design, we look at how remote control switching for blocks of lighting conserves energy. Sophisticated, sensitive electronic equipment is becoming a greater part of the commercial building electric load. Computers, building automation systems, telephone automation systems, printers, fax machines, PC networks, and copiers are commonplace. This high-tech equipment can save energy by limiting space requirements, reducing the need for direct meetings, and replacing the hand delivery of documents, but it uses electricity to do these things. Look for the ENERGY STAR® symbol on computers and home office equipment, es- pecially color monitors and laser printers. Energy may leak from home electronics and small household appliances that require direct current, such as televisions, VCRs, cordless phones, telephone an- swering machines, portable tools, and rechargeable vac- uum cleaners. These implements draw energy when in use and also when the power is apparently off. The average U.S. household leaks 50 W of electricity continu- ously, or around 440 kW-h per year. This adds up to over $3 billion in electricity in the United States per year. Televisions, VCRs, and cable boxes account for half of this, for instant-on, remote control, channel memory, and those light-emitting diode (LED) clocks that always read 12:00. Digital satellite systems also leak an average of 13 W when not in use. Direct current transformers, such as those on electric toothbrushes, draw 2 to 6 W of electric power even when not in use or when the appliance is fully charged. To encourage your client to save 228 ELECTRICITY [...]... shut down Emergency systems for healthcare in most jurisdictions are governed by NFPA 99, Standard for Health Care Facilities Most codes require emergency systems Some also require standby systems for essential water systems, water treatment systems, and a few other uses The emergency system must pick up loads within ten seconds of the power interruption Legally required standby systems must pick up... emergency systems in the means of egress chapters Emergency lighting systems illuminate areas of assembly to permit safe exiting and prevent panic The emergency power system provides power for the fire detection and alarm systems, and for elevators, fire pumps, and public address and communications It allows the orderly shutdown or maintenance of hazardous processes Building codes identify a number of building. .. must be illuminated by emergency lighting Standby power systems are sometimes required by code The National Fire Protection Association’s NFPA 110, Standard for Emergency Light and Power, and NFPA 111, Standard on Stored Electrical Energy Emergency and Standby Power Systems, govern standby systems Standby systems are required for power processes and systems whose stoppage might create a hazard or hamper... circuit per 49 to 60 square meters (530 64 0 square ft) plus an allowance for expansion, with more provided as needed No point on a wall is permitted to be more than 1.8 meters (6 ft) from a 20-A, grounding-type convenience receptacle Any wall 61 cm (2 ft) or more in length, including walls broken by fireplaces, must have a receptacle You must have a receptacle within 1.8 meters (6 ft) of any door or... equipment package ELECTRICAL EMERGENCY SYSTEMS Most buildings are required by code to have emergency energy sources to operate lighting for means of egress, exit signs, automatic door locks, and other equipment in an emergency Emergency systems supply power to equipment that is essential to human life safety on the interruption of the normal supply The NFPA governs emergency systems under several codes The... turned on, alternating current (AC) electricity flows both ways in the loop, changing direction 60 times a second (60 cycles, or 60 hertz) Lines from the power company run either overhead or underground to carry electricity from a transformer through the meter and into the service entrance panel In smaller buildings, service is usually provided at 230 or 240V Most homes have three-wire service, with... offsets the high initial cost of these systems An intelligent panel board simplifies and improves facility operations and reduces maintenance costs and electric bills Other options for energy conservation include systems that conform to an ideal energy use curve automatically Forecasting systems are the most sophisticated, most expensive, and most effective energy control systems for large structures with... like refrigerators do not count toward the 3 .66 -meter (12-ft) spacing requirement Plan for a readily accessible means for disconnecting electric ranges, cooktops, and ovens within sight of these appliances A small kitchen panel recessed into Range and oven outlet boxes wall mounted 36" AFF, flexible connection to units Dishwasher receptacle on wall behind unit, 6" above floor Countertop appliance receptacles... Accessories are available for connection to 120V power outlets Flat cable systems are low cost and offer flexibility for open-plan offices They are often used in new construction and to rework obsolete wiring systems in existing buildings The NEC prohibits the use of flat cables in wet and hazardous areas and in residential, hospital, and school buildings Flat cable layouts are usually shown on a separate electric... Lightweight die cast aluminum panels are supported on a network of adjustable steel or aluminum pedestals The panels are 46 or 91 cm (18 or 36 in.) square, and the floor depth is normally between 31 and 76 cm (12–30 in.) Where air requirements are minimal, the pedestals can be as short as 15 cm (6 in.) The panels are made of steel, aluminum, or a wood core encased in steel or aluminum, or of lightweight reinforced . opposite. Typically, a transformer will step down incoming 1 460 V service to 480V for distribution within the building. Another transformer then steps down 480V to 120V for receptacle circuits needed. 222 ELECTRICITY Interior designers are also responsible for showing electrical system information on their drawings (Fig. 27-4). The electrical engineer uses the interior design drawings. original voltage. Transformers may be pole or pad mounted outside a building or in a room or vault within the building. Step-down transformers lower voltage, and step-up transformers do the opposite.

Định dạng
Số trang	47
Dung lượng	772,67 KB