Toggleswitchesare actuated by a lever angled in oneoftwo or more positions. The common light switch used in household wiring is an exampleofa toggle switch. Most toggleswitcheswill come to rest in anyoftheir lever positions, while others have an internal spring mechanism returning the lever to a certainnormalposition, allowing for what is called "momentary" operation.

Pushbuttonswitchesare two-position devices actuated with a button that is pressed and released. Most pushbuttonswitcheshave an internal spring mechanism returning the button to its "out," or "unpressed," position, for momentary operation. Some pushbuttonswitcheswill latch alternately on or off with every pushofthe button. Other pushbuttonswitcheswill stay in their "in," or "pressed," position until the button is pulled back out. This last typeofpushbuttonswitchesusually have a mushroom-shaped button for easy push-pull action.

Selectorswitchesare actuated with a rotary knob or leverofsome sort to select oneoftwo or more positions. Like the toggle switch, selectorswitchescan either rest in anyoftheir positions or contain spring-return mechanisms for momentary operation.

A joystick switch is actuated by a lever free to move in more than one axisofmotion. One or moreofseveral switch contact mechanisms are actuated depending on which way the lever is pushed, and sometimes by howfarit is pushed. The circle-and-dot notation on the switch symbol represents the directionofjoystick lever motion required to actuate the contact. Joystick handswitchesare commonly used for crane and robot control.Someswitchesare specifically designed to be operated by the motionofa machine rather than by the handofa human operator. These motion-operatedswitchesare commonly calledlimitswitches, because they are often used to limit the motionofa machine by turning off the actuating power to a component if it moves too far. As with handswitches, limitswitchescome in several varieties:

These limitswitchesclosely resemble rugged toggle or selector handswitchesfitted with a lever pushed by the machine part. Often, the levers are tipped with a small roller bearing, preventing the lever from being worn off by repeated contact with the machine part.

Proximityswitchessense the approachofa metallic machine part either by a magnetic or high-frequency electromagnetic field. Simple proximityswitchesuse a permanent magnet to actuate a sealed switch mechanism whenever the machine part gets close (typically 1 inch or less). More complex proximityswitcheswork like a metal detector, energizing a coilofwire with a high-frequency current, and electronically monitoring the magnitudeofthat current. If a metallic part (not necessarily magnetic) gets close enough to the coil, the current will increase, and trip the monitoring circuit. The symbol shown here for the proximity switch isofthe electronic variety, as indicated by the diamond-shaped box surrounding the switch. A non-electronic proximity switch would use the same symbol as the lever-actuated limit switch.Another formofproximity switch is the optical switch, comprisedofa light source and photocell. Machine position is detected by either the interruption or reflectionofa light beam. Opticalswitchesare also useful in safety applications, where beamsoflight can be used to detect personnel entry into a dangerous area.In many industrial processes, it is necessary to monitor various physical quantities withswitches. Suchswitchescan be used to sound alarms, indicating that a process variable has exceeded normal parameters, or they can be used to shut down processes or equipment if those variables have reached dangerous or destructive levels. There are many different typesofprocessswitches:

Theseswitchessense the rotary speedofa shaft either by a centrifugal weight mechanism mounted on the shaft, or by some kindofnon-contact detectionofshaft motion such as optical or magnetic.

Gas or liquid pressure can be used to actuate a switch mechanism if that pressure is applied to a piston, diaphragm, or bellows, which converts pressure to mechanical force.

An inexpensive temperature-sensing mechanism is the "bimetallic strip:" a thin stripoftwo metals, joined back-to-back, each metal having a different rateofthermal expansion. When the strip heats or cools, differing ratesofthermal expansion between the two metals causes it to bend. The bendingofthe strip can then be used to actuate a switch contact mechanism. Other temperatureswitchesuse a brass bulb filled with either a liquid or gas, with a tiny tube connecting the bulb to a pressure-sensing switch. As the bulb is heated, the gas or liquid expands, generating a pressure increase which then actuates the switch mechanism.

A floating object can be used to actuate a switch mechanism when the liquid level in an tank rises past a certain point. If the liquid is electrically conductive, the liquid itself can be used as a conductor to bridge between two metal probes inserted into the tank at the required depth. The conductivity technique is usually implemented with a special designofrelay triggered by a small amountofcurrent through the conductive liquid. In most cases it is impractical and dangerous to switch the full load currentofthe circuit through a liquid.Levelswitchescan also be designed to detect the levelofsolid materials such as wood chips, grain, coal, or animal feed in a storage silo, bin, or hopper. A common design for this application is a small paddle wheel, inserted into the bin at the desired height, which is slowly turned by a small electric motor. When the solid material fills the bin to that height, the material prevents the paddle wheel from turning. The torque responseofthe small motor than trips the switch mechanism. Another design uses a "tuning fork" shaped metal prong, inserted into the bin from the outside at the desired height. The fork is vibrated at its resonant frequency by an electronic circuit and magnet/electromagnet coil assembly. When the bin fills to that height, the solid material dampens the vibrationofthe fork, the change in vibration amplitude and/or frequency detected by the electronic circuit.

Inserted into a pipe, a flow switch will detect any gas or liquid flow rate in excessofa certain threshold, usually with a small paddle or vane which is pushed by the flow. Other flowswitchesare constructed as differential pressureswitches, measuring the pressure drop across a restriction built into the pipe.Another typeoflevel switch, suitable for liquid or solid material detection, is the nuclear switch. Composedofa radioactive source material and a radiation detector, the two are mounted across the diameterofa storage vessel for either solid or liquid material. Any heightofmaterial beyond the levelofthe source/detector arrangement will attenuate the strengthofradiation reaching the detector. This decrease in radiation at the detector can be used to trigger a relay mechanism to provide a switch contact for measurement, alarm point, or even controlofthe vessel level.

Both source and detector are outsideofthe vessel, with no intrusion at all except the radiation flux itself. The radioactive sources used are fairly weak and pose no immediate health threat to operations or maintenance personnel.As usual, there is usually more than one way to implement a switch to monitor a physical process or serve as an operator control. There is usually no single "perfect" switch for any application, although some obviously exhibit certain advantages over others.Switchesmust be intelligently matched to the task for efficient and reliable operation. REVIEW: Aswitchis an electrical device, usually electromechanical, used to control continuity between two points. Handswitchesare actuated by human touch. Limitswitchesare actuated by machine motion. Processswitchesare actuated by changes in some physical process (temperature, level, flow, etc.)

Electrical Faceplate Types and DimensionsElectrical faceplates, also called wall plates or cover plates, come in an infinite array of combinations, sizes, and shapes. However, there are some standard sizes for basic faceplates. First, we will discuss the openings in the face plates.Accommodated DevicesThere is a wide array of devices that can be accommodated by an electrical faceplate including: outlets, switches, motion sensors, telephone jacks, data jacks, dimmers, etc. Some of the more common devices are shown below.Electrical OutletsOpenings: 1-11/32" W x 1-1/8" HToggle or SwitchOpening: 13/32" W x 15/16" H

Decorative or RockerOpening: 1-1/4" W x 2-1/2" HTelephone or DataOpening: Varies

GangsGangs refer to the number of vertical groups of openings that are accommodated. The devices can change between gangs. For instance, in a 4 gang electrical box, one could have any combination of devices (1 toggle switch and 3 duplex outlets; or 2 toggle switches and 2 duplex outlets; or 1 toggle switch, 2 duplex outlets, and 1 tele/data; etc).Electrical faceplates come in 1-gang up to 10-gang. Shown below are 1-gang through 4-gang1-GangShown: Single Duplex2-GangShown: Double Duplex

3-GangShown: Triple Toggle4-GangShown: Quadruple Duplex

Standard Size Electrical FaceplatesAll standard size faceplates are 4-1/2" in height.Widths are listed below. Please note that these sizes are standard; however, your faceplates may not match.GangsWidthGangsWidth

1-Gang2-3/4"2-Gang4-1/2"

3-Gang6-3/8"4-Gang8-3/16"

5-Gang10"6-Gang11-13/16"

7-Gang13-5/8"8-Gang15-7/16"

9-Gang17-1/4"10-Gang19-1/16"

2004 CSI Masterspec DivisionMedium-Voltage Electrical Distribution: 26 10 00Low-Voltage Electrical Distribution: 26 20 00

Light Fixture (Luminaire) ComponentsThe diagram below identifies the components of a light fixture, also known as a luminaire. The diagram shows a recessed can fixture, but the components apply to all light fixtures. Keep in mind that some of the components are optional and will not be found on every luminaire. Descriptions of the components can be found below the diagram.

WiringElectrical wiring, which provides power to the luminaire. Depicted here is flexible conduit, but it can also be hard piped based on electrical codes.Junction BoxThe junction box provides a location to connect the wiring that comes from the power source with the internal wiring for the light fixture. Shown is a box attached to the top of the fixture; however, this is sometimes a separate box and sometimes the connection is made inside the fixture.Lamp HolderThe lamp holder or light socket is the receptacle that the lamp screws into.LampThe lamp, often referred to as the light bulb, emits light when connected to a power source. The lamp is often sold separately from the fixture. It is important to use lamps in a wattage that are recommended for the fixture to prevent damage or possible fire.ReflectorThe reflector provides a reflective surface to direct or spread the light from the lamp out into the space. Parabolic reflectors focus light toward a point, while elliptical reflectors spread light.LensThe lens is a transparent or translucent material used to direct or diffuse light. In addition, the lens protects the lamp; however, it can also trap heat, which can be problematic.TrimThe trim or flange is a decorative element that is detachable. This piece is installed after the finished wall or ceiling material is installed. Since ceiling materials require a space between the fixture and the material, the trim piece is used to cover this space and provide a clean finish.2004 CSI Masterspec DivisionInterior Lighting Fixtures, Lamps, And Ballasts: 26 51 13Light Distribution CurvesLuminaire and lamp manufacturers provide candlepower (or luminous intensity) distribution curves for their fixtures. The curves provide the designer with important information about the way light is distributed from the fixture and also how that light falls upon a surface.Candlepower Distribution Curve

The image above is a candle power distribution curve, which provides information on how light is emitted from a lamp or light fixture. The diagram represents a section cut through the fixture and shows the intensity of light emitted in each direction. The portion of the graph above the horizontal 90-270 line indicates light that shines above the fixture (indirect), while the portion of the graph below represents light shining down (direct). The straight lines radiating from the center point identify the angle of the light emitted while the circles represent the intensity. For instance, point A above shows that the intensity of light at 80 is approximately 110 candlepower. Point B shows that at 30 you will get about 225 candlepower.Isochart

To the left is a diagram that provides information on the distribution of light in plan. The isochart (or iso-lux/iso-candlepower) is useful for determining how much area a light fixture can cover. For instance, in a parking lot, the diagram at left indicates that there will be about 1/2 of a foot-candle of light at about 18-20 feet from center. If 1/2 foot-candle is acceptable, then the fixtures can be placed about 36-40 feet apart.

Photometric Data FilesInformation about a fixture's light distribution is also generally available in a file format that can be loaded into an analysis or rendering program and used to help better understand the lighting within a space. There are a number of different file types, the most popular of which are listed below.IESis the international standard file type for providing luminaire light distribution information. The standard was developed by the Illuminating Engineering Society of North America (IESNA), which has simply become the Illuminating Engineering Society. IES files have a .ies file extension.EULUMDATis the main format used in Europe. The standard was originally developed in Germany, but there is currently no official documentation on the format. EULUMDAT files have an .ldt file extension.CIBSEis a format used primarily in Great Britain and is published by the Chartered Institute of Building Service Engineers. CIBSE files have a .cibse file extension.LTLIis a format occasionally used with Autodesk products such as 3ds Max. LTLI was developed by the Danish Illuminating Laboratory and is the standard used in Scandinavian countries. LTLI files have an .ltli file extension.Wire Size (Gauge)Wire thickness is measured in gauge. The table below provides conversion to inches.AWGGaugeConductorDiameter

0000.46

000.4096

00.3648

0.3249

1.2893

2.2576

3.2294

4.2043

5.1819

6.1620

7.1443

8.1285

9.1144

10.1019

11.0907

12.0808

13.0720

14.0641

15.0571

16.0508

17.0453

18.0403

19.0359

20.0320

21.0285

22.0253

23.0226

24.0201

25.0179

26.0159

27.0142

28.0126

29.0113

30.0100

Ground Up or Ground Down?There is an age-old debate about whether an electrical outlet should be mounted with the ground pin up or down. Unfortunately, there is not a fully accepted answer. However, it is commonly accepted that the National Electrical Code (NEC) of the United States, or NFPA 70, does not provide any specific direction for the orientation of the outlet.

Some theories about the orientation of an outlet: The outlet should be oriented with theground pin upbecause if the plug comes slightly loose and a metal object were to fall from above, the ground plug, which usually does not carry current, would deflect the object so that it would not hit is live prongs. It is accepted that this idea began in health care facilities where many tools used for patient care are metal. The story goes that hospitals were wired by union electricians and as the unions grew the practice spread to other types of buildings. The outlet should be oriented with theground pin upbecause this pin is longer and the plastic around the plug is meatier, so it will help to keep the plug inserted in the outlet. The outlet should be oriented with theground pin downbecause a person grabbing the outlet will have their index finger at the bottom side of the plug and the index finger sticks out further than the thumb. Having the ground down will keep a person's index finger from touching the live pins. The outlet should be oriented with theground pin downbecause many common household items such as nightlights, timers, and battery chargers are oriented with the ground pin down. In addition, GFCI outlets, which have text on the reset and test buttons, are oriented with the ground pin down (and the text readable).A quick internet search provides comments that easily debunk any of these theories. The most basic final answer is that it truly doesn't matter which way your outlets are oriented. Select the strategy that best works for you.Laminar Flow vs Turbulent FlowLaminar flow is a phenomenon where air, gas, or a liquid flows in parallel layers and there is no mixing of layers. It is the opposite of turbulent flow, where the molecules are constantly mixing and moving in varied ways across a space. Relative to HVAC systems, laminar flow provides a way to maintain the clean nature of air within a space and also prevents mixing of air, which can cause contamination. Laminar flow HVAC systems are often used in surgery suites, laboratories, or other clean rooms.Turbulent FlowThe diagram below shows a typical room with a supply diffuser and return grille, both of which are in the ceiling. In this case, the air moves in an unpredictable manner as dictated by pressure and temperature differences. Air molecules are constantly colliding and can create contamination of the air as particles are transported around the room before eventually leaving via the return grille.

Laminar FlowIn a laminar flow situation, as seen in the diagram below, the air move predictably and in parallel layers from the supply diffusers in the ceiling. Since the return grilles are located low, the air is forced down and toward the returns without having to move back through clean air to ceiling returns. This prevents contamination since any unwanted particles are transported in a straight line out of the room.

Laminar Flow ApplicationsWhile the examples above assume that the space is a room and the air is supplied by ducts, the space can also be a desktop device used within a laboratory. No matter the application, the goal is the same: to prevent contamination of the air by providing airflow in parallel layers that do not mix.Duct Shaft LayoutWhen sizing duct shafts, architects must account for steel supports, duct take-offs, dampers, and insulation. The following diagrams provide general clearances, but consult with an HVAC engineer for the needs of a particular system.General LayoutProvide 9" from the sheet metal to the inside face of a shaft.Provide 12" from the sheet metal to the inside face of a shaft on sides where there is a duct take-off. See the note below for information about dampers, which can require up to 24" of clear space.Provide 9" between ducts (sheet metal to sheet metal).

Relative to StructureThe above diagram addressed the distance from the face of the duct to the inside face of the shaft; however, the designer must also consider structure or deck/slab edges.While maintaining the above dimensions, also provide a minimum of 6" from the face of the duct/slab to the deck edge. The section diagram below shows these clearances.

DampersConsult with the damper manufacturer for dimensional requirements. Fire dampers generally require 15" between the duct face and the inside face of the shaft wall. Combination Fire and Smoke dampers can require up to 24" of clear space between the duct face and the inside face of the shaft wall. In addition, the damper must be accessible so that the unit can be reset after it has been closed.Air ConditionerHow Products Are Made |1998 |CopyrightAir ConditionerBackgroundResidential and commercial space-cooling demands are increasing steadily throughout the world as what once was considered a luxury is now seemingly a necessity. Air-conditioning manufacturers have played a big part in making units more affordable by increasing their efficiency and improving components and technology. The competitiveness of the industry has increased with demand, and there are many companies providing air conditioning units and systems.Air conditioning systems vary considerably in size and derive their energy from many different sources. Popularity of residential air conditioners has increased dramatically with the advent of central air, a strategy that utilizes the ducting in a home for both heating and cooling. Commercial air conditioners, almost mandatory in new construction, have changed a lot in the past few years as energy costs rise and power sources change and improve. The use of natural gas-powered industrial chillers has grown considerably, and they are used for commercial air conditioning in many applications.Raw MaterialsAir conditioners are made of different types of metal. Frequently, plastic and other nontraditional materials are used to reduce weight and cost. Copper or aluminum tubing, critical ingredients in many air conditioner components, provide superior thermal properties and a positive influence on system efficiency. Various components in an air conditioner will differ with the application, but usually they are comprised of stainless steel and other corrosion-resistant metals.Self-contained units that house the refrigeration system will usually be encased in sheet metal that is protected from environmental conditions by a paint or powder coating.The working fluid, the fluid that circulates through the air-conditioning system, is typically a liquid with strong thermodynamic characteristics like freon, hydrocarbons, ammonia, or water.DesignAll air conditioners have four basic components: a pump, an evaporator, a condenser, and an expansion valve. All have a working fluid and an opposing fluid medium as well.Two air conditioners may look entirely dissimilar in both size, shape, and configuration, yet both function in basically the same way. This is due to the wide variety of applications and energy sources available. Most air conditioners derive their power from an electrically-driven motor and pump combination to circulate the refrigerant fluid. Some natural gas-driven chillers couple the pump with a gas engine in order to give off significantly more torque.As the working fluid or refrigerant circulates through the air-conditioning system at high pressure via the pump, it will enter an evaporator where it changes into a gas state, taking heat from the opposing fluid medium and operating just like a heat exchanger. The working fluid then moves to the condenser, where it gives off heat to the atmosphere by condensing back into a liquid. After passing through an expansion valve, the working fluid returns to a low pressure state. When the cooling medium (either a fluid or air) passes near the evaporator, heat is drawn to the evaporator. This process effectively cools the opposing medium, providing localized cooling where needed in the building. Early air conditioners used freon as the working fluid, but because of the hazardous effects freon has on the environment, it has been phased out. Recent designs have met strict challenges to improve the efficiency of a unit, while using an inferior substitute for freon.The ManufacturingProcessCreating encasement parts from galvanized sheet metal and structural steel 1 Most air conditioners start out as raw material, in the form of structural steel shapes and sheet steel. As the sheet metal is processed into fabrication cells or work cells, it is cut, formed, punched, drilled, sheared, and/or bent into a useful shape or form. The encasements or wrappers, the metal that envelopes most outdoor residential units, is made of galvanized sheet metal that uses a zinc coating to provide protection against corrosion. Galvanized sheet metal is also used to form the bottom pan, face plates, and various support brackets throughout an air conditioner. This sheet metal is sheared on a shear press in a fabrication cell soon after arriving from storage or inventory. Structural steel shapes are cut and mitered on a band saw to form useful brackets and supports.Punch pressing the sheet metal forms 2 From the shear press, the sheet metal is loaded on a CNC (Computer Numerical Control) punch press. The punch press has the option of receiving its computer program from a drafting CAD/CAM (Computer Aided Drafting/Computer Aided Manufacturing) program or from an independently written CNC program. The CAD/CAM program will transform a drafted or modeled part on the computer into a file that can be read by the punch press, telling it where to punch holes in the sheet metal. Dies and other punching instruments are stored in the machine and mechanically brought to the punching arm, where it can be used to drive through the sheet. The NC (Numerically Controlled) press brakes bend the sheet into its final form, using a computer file to program itself. Different bending dies are used for different shapes and configurations and may be changed for each component. 3 Some brackets, fins, and sheet components are outsourced to other facilities or companies to produce large quantities. They are brought to the assembly plant only when needed for assembly. Many of the brackets are produced on a hydraulic or mechanical press, where brackets of different shapes and configurations can be produced from a coiled sheet and unrolled continuously into the machine. High volumes of parts can be produced because the press can often produce a complex shape with one hit.Cleaning the parts 4 All parts must be completely clean and free of dirt, oil, grease, and lubricants before they are powder coated. Various cleaning methods are used to accomplish this necessary task. Large solution tanks filled with a cleaning solvent agitate and knock off the oil when parts are submersed. Spray wash systems use pressurized cleaning solutions to knock off dirt and grease. Vapor degreasing, suspending the parts above a harsh cleansing vapor, uses an acid solution and will leave the parts free of petroleum products. Most outsourced parts that arrive from a vendor have already been degreased and cleaned. For additional corrosion protection, many parts will be primed in a phosphate primer bath before entering a drying oven to prepare them for the application of the powder coating.Powder coating 5 Before brackets, pans, and wrappers are assembled together, they are fed through a powder coating operation. The powder coating system sprays a paint-like dry powder onto the parts as they are fed through a booth on an overhead conveyor. This can be done by robotic sprayers that are programmed where to spray as each part feeds through the booth on the conveyor. The parts are statically charged to attract the powder to adhere to deep crevices and bends within each part. The powder-coated parts are then fed through an oven, usually with the same conveyor system, where the powder is permanently baked onto the metal. The process takes less than 10 minutes.Bending the tubing for the condenser and evaporator 6 The condenser and evaporator both act as a heat exchanger in air conditioning systems and are made of copper or aluminum tubing bent around in coil form to maximize the distance through which the working fluid travels. The opposing fluid, or cooling fluid, passes around the tubes as the working fluid draws away its heat in the evaporator. This is accomplished by taking many small diameter copper tubes bent in the same shape and anchoring them with guide rods and aluminum plates. The working fluid or refrigerant flows through the copper tubes and the opposing fluid flows around them in between the aluminum plates. The tubes will often end up with hairpin bends performed by NC benders, using the same principle as the NC press brake. Each bend is identical to the next. The benders use previously straightened tubing to bend around a fixed die with a mandrel fed through the inner diameter to keep it from collapsing during the bend. The mandrel is raked back through the inside of the tube when the bend has been accomplished. 7 Tubing supplied to the manufacturer in a coil form goes through an uncoiler and straightener before being fed through the bender. Some tubing will be cut into desired lengths on an abrasive saw that will cut several small tubes in one stroke. The aluminum plates are punched out on a punch press and formed on a mechanical press to place divots or waves in the plate. These waves maximize the thermodynamic heat transfer between the working fluid and the opposing medium. When the copper tubes are finished in the bending cell, they are transported by automatic guided vehicle (AGV) to the assembly cell, where they are stacked on the guide rods and fed through the plates or fins.Joining the copper tubing with the aluminum plates 8 A major part of the assembly is the joining of the copper tubing with the aluminum plates. This assembly becomes the evaporator and is accomplished by taking the stacked copper tubing in their hairpin configuration and mechanically fusing them to the aluminum plates. The fusing occurs by taking a bullet, or mandrel, and feeding it through the copper tubing to expand it and push it against the inner part of the hole of the plate. This provides a thrifty, yet useful bond between the tubing and plate, allowing for heat transfer. 9 The condenser is manufactured in a similar manner, except that the opposing medium is usually air, which cools off the copper or aluminum condenser coils without the plates. They are held by brackets which support the coiled tubing, and are connected to the evaporator with fittings or couplings. The condenser is usually just one tube that may be bent around in a number of hairpin bends. The expansion valve, a complete component, is purchased from a vendor and installed in the piping after the condenser. It allows the pressure of the working fluid to decrease and re-enter the pump.Installing the pump 10 The pump is also purchased complete I h from an outside supplier. Designed to increase system pressure and circulate the working fluid, the pump is connected with fittings to the system and anchored in place by support brackets and a base. It is bolted together with the other structural members of the air conditioner and covered by the wrapper or sheet metal encasement. The encasement is either riveted or bolted together to provide adequate protection for the inner components.Quality ControlQuality of the individual components is always checked at various stages of the manufacturing process. Outsourced parts must pass an incoming dimensional inspection from a quality assurance representative before being approved for use in the final product. Usually, each fabrication cell will have a quality control plan to verify dimensional integrity of each part. The unit will undergo a performance test when assembly is complete to assure the customer that each unit operates efficiently.The FutureAir conditioner manufacturers face the challenge of improving efficiency and lowering costs. Because of the environmental concerns, working fluids now consist typically of ammonia or water. New research is under way to design new working fluids and better system components to keep up with rapidly expanding markets and applications. The competitiveness of the industry should remain strong, driving more innovations in manufacturing and design.The first modern air conditioning system was developed in 1902 by a young electrical engineer named Willis Haviland Carrier. It was designed to solve a humidity problem at the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, N.Y. Paper stock at the plant would sometimes absorb moisture from the warm summer air, making it difficult to apply the layered inking techniques of the time. Carrier treated the air inside the building by blowing it across chilled pipes. The air cooled as it passed across the cold pipes, and since cool air can't carry as much moisture as warm air, the process reduced the humidity in the plant and stabilized the moisture content of the paper. Reducing the humidity also had the side benefit of lowering the air temperature -- and a new technology was born.Carrier realized he'd developed something with far-reaching potential, and it wasn't long before air-conditioning systems started popping up intheatersand stores, making the long, hot summer months much more comfortable [source:Time].The actual process air conditioners use to reduce the ambient air temperature in a room is based on a very simple scientific principle. The rest is achieved with the application of a few clever mechanical techniques. Actually, an air conditioner is very similar to another appliance in your home -- therefrigerator. Air conditioners don't have the exterior housing a refrigerator relies on to insulate its cold box. Instead, the walls in your home keep cold air in and hot air out.Let's move on to the next page where we'll discover what happens to all that hot air when you use your airAir-conditioning BasicsAir conditioners use refrigeration to chill indoor air, taking advantage of a remarkable physical law: When aliquidconverts to agas(in a process calledphase conversion), it absorbs heat. Air conditioners exploit this feature of phase conversion by forcing special chemical compounds to evaporate and condense over and over again in a closed system of coils.The compounds involved arerefrigerantsthat have properties enabling them to change at relatively low temperatures. Air conditioners also contain fans that move warm interior air over these cold, refrigerant-filled coils. In fact, central air conditioners have a whole system of ducts designed to funnel air to and from these serpentine, air-chilling coils.When hot air flows over the cold, low-pressureevaporator coils, the refrigerant inside absorbs heat as it changes from a liquid to a gaseous state. To keep cooling efficiently, the air conditioner has to convert the refrigerant gas back to a liquid again. To do that, a compressor puts the gas under high pressure, a process that creates unwanted heat. All the extra heat created by compressing the gas is then evacuated to the outdoors with the help of a second set of coils calledcondenser coils, and a second fan. As the gas cools, it changes back to a liquid, and the process starts all over again. Think of it as an endless, elegant cycle: liquid refrigerant, phase conversion to a gas/ heat absorption, compression and phase transition back to a liquid again.It's easy to see that there are two distinct things going on in an air conditioner. Refrigerant is chilling the indoor air, and the resulting gas is being continually compressed and cooled for conversion back to a liquid again. On the next page, we'll look at how the different parts of an air conditioner work to make all that Page 1 2 3 4

HowStuffWorksThe Parts of an Air ConditionerLet's get some housekeeping topics out of the way before we tackle the unique components that make up a standard air conditioner. The biggest job an air conditioner has to do is to cool the indoor air. That's not all it does, though. Air conditioners monitor and regulate the air temperature via athermostat. They also have an onboard filter that removes airborne particulates from the circulating air. Air conditioners function asdehumidifiers. Because temperature is a key component of relative humidity, reducing the temperature of a volume of humid air causes it to release a portion of its moisture. That's why there are drains and moisture-collecting pans near or attached to air conditioners, and why air conditioners discharge water when they operate on humid days.Still, the major parts of an air conditioner manage refrigerant and move air in two directions: indoors and outside: Evaporator -Receives the liquid refrigerant Condenser -Facilitates heat transfer Expansion valve -regulates refrigerant flow into the evaporator Compressor -A pump that pressurizes refrigerantThe cold side of an air conditioner contains the evaporator and a fan that blows air over the chilled coils and into the room. The hot side contains the compressor, condenser and another fan to vent hot air coming off the compressed refrigerant to the outdoors. In between the two sets of coils, there's anexpansion valve. It regulates the amount of compressed liquid refrigerant moving into the evaporator. Once in the evaporator, the refrigerant experiences a pressure drop, expands and changes back into a gas. Thecompressoris actually a large electric pump that pressurizes the refrigerant gas as part of the process of turning it back into a liquid. There are some additional sensors, timers and valves, but the evaporator, compressor, condenser and expansion valve are the main components of an air conditioner.Although this is a conventional setup for an air conditioner, there are a couple of variations you should know about. Window air conditioners have all these components mounted into a relatively small metal box that installs into a window opening. The hot air vents from the back of the unit, while the condenser coils and a fan cool and re-circulate indoor air. Bigger air conditioners work a little differently: Central air conditioners share a control thermostat with a home's heating system, and the compressor and condenser, the hot side of the unit, isn't even in the house. It's in a separate all-weather housing outdoors. In very large buildings, like hotels and hospitals, the exterior condensing unit is often mounted somewhere on the roof.Window and Split-system AC UnitsA window air conditioner unit implements a complete air conditioner in a small space. The units are made small enough to fit into a standard window frame. You close the window down on the unit, plug it in and turn it on to get cool air. If you take the cover off of an unplugged window unit, you'll find that it contains: A compressor An expansion valve A hot coil (on the outside) A chilled coil (on the inside) Two fans A control unitThe fans blow air over the coils to improve their ability to dissipate heat (to the outside air) and cold (to the room being cooled).When you get into larger air-conditioning applications, its time to start looking at split-system units. A split-system air conditioner splits the hot side from the cold side of the system, as in the diagram below.The cold side, consisting of the expansion valve and the cold coil, is generally placed into afurnaceor some other air handler. The air handler blows air through the coil and routes the air throughout the building using a series of ducts. The hot side, known as the condensing unit, lives outside the building.The unit consists of a long, spiral coil shaped like a cylinder. Inside the coil is a fan, to blow air through the coil, along with aweather-resistant compressor and some control logic. This approach has evolved over the years because it's low-cost, and also because it normally results in reduced noise inside the house (at the expense of increased noise outside the house). Other than the fact that the hot and cold sides are split apart and the capacity is higher (making the coils and compressor larger), there's no difference between a split-system and a window air conditioner.In warehouses, large business offices, malls, big department stores and other sizeable buildings, the condensing unit normally lives on the roof and can be quite massive. Alternatively, there may be many smaller units on the roof, each attached inside to a small air handler that cools a specific zone in the building.In larger buildings and particularly in multi-story buildings, the split-system approach begins to run into problems. Either running the pipe between the condenser and the air handler exceeds distance limitations (runs that are too long start to cause lubrication difficulties in the compressor), or the amount of duct work and the length of ducts becomes unmanageable. At this point, it's time to think about a chilled-water system.

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HowStuffWorksChilled-water and Cooling-tower AC UnitsAlthough standard air conditioners are very popular, they can use a lot of energy and generate quite a bit of heat. For large installations like office buildings, air handling and conditioning is sometimes managed a little differently.Some systems usewateras part of the cooling process. The two most well-known are chilled water systems and cooling tower air conditioners. Chilled water systems -In a chilled-water system, the entire air conditioner is installed on the roof or behind the building. It cools water to between 40 and 45 degrees Fahrenheit (4.4 and 7.2 degrees Celsius). The chilled water is then piped throughout the building and connected to air handlers. This can be a versatile system where the water pipes work like the evaporator coils in a standard air conditioner. If it's well-insulated, there's no practical distance limitation to the length of a chilled-water pipe. Cooling tower technology -In all of the air conditioning systems we've described so far, air is used to dissipate heat from the compressor coils. In some large systems, a cooling tower is used instead. The tower creates a stream of cold water that runs through a heat exchanger, cooling the hot condenser coils. The tower blows air through a stream of water causing some of it to evaporate, and the evaporation cools the water stream. One of the disadvantages of this type of system is that water has to be added regularly to make up for liquid lost through evaporation. The actual amount of cooling that an air conditioning system gets from a cooling tower depends on the relative humidity of the air and the barometric pressure.Because of risingelectricalcosts and environmental concerns, some other air cooling methods are being explored, too. One is off-peak or ice-cooling technology. Anoff-peakcooling system uses ice frozen during the evening hours to chill interior air during the hottest part of the day. Although the system does use energy, the largest energy drain is when community demand for power is at its lowest. Energy is less expensive during off-peak hours, and the lowered consumption during peak times eases the demand on the power grid.Another option is geo-thermal heating. It varies, but at around 6 feet (1.8 meters) underground, the earth's temperature ranges from 45 to 75 degrees Fahrenheit (7.2 to 23.8 degrees Celsius). The basic idea behindgeo-thermal coolingis to use this constant temperature as a heat or cold source instead of using electricity to generate heat or cold. The most common type of geo-thermal unit for the home is a closed-loop system. Polyethylene pipes filled with a liquid mixture are buried underground. During the winter, the fluid collects heat from the earth and carries it through the system and into the building. During the summer, the system reverses itself to cool the building by pulling heat through the pipes to deposit it underground [source:Geo Heating].For real energy efficiency, solar powered air conditioners are also making their debut. There may still be some kinks to work out, but around 5 percent of all electricity consumed in the U.S. is used to power air conditioning of one type or another, so there's a big market for energy-friendly air conditioning options [source:ACEEE].BTU and EERMost air conditioners have their capacity rated in British thermal units (Btu). A Btu is the amount of heat necessary to raise the temperature of 1 pound (0.45 kilograms) of water one degree Fahrenheit (0.56 degrees Celsius). One Btu equals 1,055 joules. In heating and cooling terms, one ton equals 12,000 Btu.A typical window air conditioner might be rated at 10,000 Btu. For comparison, a typical 2,000-square-foot (185.8 square meters) house might have a 5-ton (60,000-Btu) air conditioning system, implying that you might need perhaps 30 Btu per square foot. These are rough estimates. To size an air conditioner accurately for your specific application, you should contact an HVACcontractor.The energy efficiency rating (EER) of an air conditioner is its Btu rating over itswattage. As an example, if a 10,000-Btu air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 Btu/1,200 watts). Obviously, you would like the EER to be as high as possible, but normally a higher EER is accompanied by a higher price.Let's say you have a choice between two 10,000-Btu units. One has an EER of 8.3 and consumes 1,200 watts, and the other has an EER of 10 and consumes 1,000 watts. Let's also say that the price difference is $100. To determine the payback period on the more expensive unit, you need to know approximately how many hours per year you will be operating the air conditioner and how much a kilowatt-hour (kWh) costs in your area.Assuming you plan to use the air conditioner six hours a day for four months of the year, at a cost of $0.10/kWh. The difference in energy consumption between the two units is 200 watts. This means that every five hours the less expensive unit will consume one additional kWh (or $0.10) more than the more expensive unit.Let's do the math: With roughly 30 days in a month, you're operating the air conditioner:4 months x 30 days per month x 6 hours per day = 720 hours[(720 hours x 200 watts) / (1000 watts/kilowatt)] x $0.10/kilowatt hours = $14.40The more expensive air conditioning unit costs $100 more to purchase but less money to operate. In our example, it'll take seven years for the higher priced unit to break even.Energy Efficient Cooling SystemsBecause of the rising costs ofelectricityand a growing trend to "go green," more people are turning to alternative cooling methods to spare their pocketbooks and the environment. Big businesses are even jumping on board in an effort to improve their public image and lower their overhead.Ice cooling systems are one way that businesses are combating high electricity costs during the summer. Ice cooling is as simple as it sounds. Large tanks of water freeze into ice at night, when energy demands are lower. The next day, a system much like a conventional air conditioner pumps the cool air from the ice into the building. Ice cooling saves money, cuts pollution, eases the strain on the power grid and can be used alongside traditional systems. The downside of ice cooling is that the systems are expensive to install and require a lot of space. Even with the high startup costs, more than 3,000 systems are in use worldwide [source:CNN]. You can read more about ice cooling inAre Ice Blocks Better than Air Conditioning?An ice cooling system is a great way to save money and conserve energy, but its price tag and space requirements limit it to large buildings. One way that homeowners can save on energy costs is by installing geo-thermal heating and cooling systems, also known as ground source heat pumps (GSHP). The Environmental Protection Agency recently named geo-thermal units "the most energy-efficient and environmentally sensitive of all space conditioning systems" [source:EPA].Although it varies, at six feet underground the Earth's temperatures range from 45 to 75 degrees Fahrenheit. The basic principle behind geo-thermal cooling is to use this constant temperature as a heat source instead of generating heat with electricity.The most common type of geo-thermal unit for homes is the closed-loop system. Polyethylene pipes are buried under the ground, either vertically like a well or horizontally in three- to six-foot trenches. They can also be buried under ponds. Water or an anti-freeze/water mixture is pumped through the pipes. During the winter, the fluid collects heat from the earth and carries it through the system and into the building. During the summer, the system reverses itself to cool the building by pulling heat from the building, carrying it through the system and placing it in the ground [source:Geo Heating].Homeowners can save 30 to 50 percent on their cooling bills by replacing their traditional HVAC systems with ground source heat pumps. The initial costs can be up to 30 percent more, but that money can be recouped in three to five years, and most states offer financial purchase incentives. Another benefit is that the system lasts longer than traditional units because it's protected from the elements and immune to theft [source:Geo Exchange].

Schematic diagram of elevator work and part on high rise buildings is to find the parts in an elevator. By knowing the parts or labor scheme of an elevator (lift) is anarchitectwill easily find out their placement and design, especially in high-risebuilding design.Here is a schematic diagram of the work and parts ofelevatorsin high-rise building

Diagram Parts of Elevator for High Rise Buildings1. Counterweight Guide Rail2. Linear Induction Motor Secondary3. Brakes4. Counterweight Frame5. Linear Induction Motor Primary6. Idler Sheaves7. Guide Rail8. Cab (lift)Machines for moving the e Elevators byChris Woodford.Last updated: February 14, 2012.Hit the top button on the elevator and prepare yourself for a long ride: in just a few days you'll be waving back from space! Elevators that can zoom up beyond Earth have certainly captured people's imagination in the decade or so since space scientists first proposed themand it's no wonder. But in their time ordinary office elevators probably seemed almost as radical. It wasn't just brilliantbuildingmaterials such assteelandconcretethat allowed modern skyscrapers to soar to the clouds: it was the invention, in 1861, of the safe, reliable elevator by a man named Elisha Graves Otis of Yonkers, New York. Otis literally changed the face of the Earth by developing a machine he humbly called an "improvement in hoisting apparatus," which allowed cities to expand vertically as well as horizontally. That's why his invention can rightly be described as one of the most important machines of all time. Let's take a closer look at elevators and find out how they work!Photo: How far will the top button take you? All the way to space? NASA is already working on an elevator that could carry materials from the surface of Earth up to geostationary Earth orbit, 35,786km (22,241 miles) up. Illustration by artist Pat Rawling courtesy ofNASA Marshall Space Flight Center (NASA-MSFC).What is an elevator?

Photo: A typical, modern, electronically controlled elevator. If you wait for the cars to move out of the way, you can often see some of the workings and figure out which bits do what.The annoying thing about elevators (if you're trying to understand them) is that their working parts are usually covered up! From the viewpoint of someone traveling from the lobby to the 18th floor, an elevator is simply a metal box with doors that close on one floor and then open again on another. For those of us who are more curious, the key parts of an elevator are: One or more cars (metal boxes) that rise up and down. Counterweights that balance the cars. Anelectric motorthat hoists the cars up and down, including abrakingsystem. A system of strong metal cables andpulleysrunning between the cars and the motors. Various safety systems to protect the passengers if a cable breaks. In large buildings, anelectroniccontrol system that directs the cars to the correct floors using a so-called "elevator algorithm" (a sophisticated kind of mathematical logic) to ensure large numbers of people are moved up and down in the quickest, most efficient way (particularly important in huge, busy skyscrapers at rush hour). Intelligent systems are programmed to carry many more people upward than downward at the beginning of the day and the reverse at the end of the day.How elevators use energyScientifically, elevators are all aboutenergy. To get from the ground to the 18th floor walking up stairs you have to move the weight of your body against the downward-pulling force of gravity. The energy you expend in the process is (mostly) converted intopotential energy, so climbing stairs gives an increase in your potential energy (going up) or a decrease in your potential energy (going down). This is an example of thelaw of conservation of energyin action. You really do have more potential energy at the top of a building than at the bottom, even if it doesn't feel any different.To a scientist, an elevator is simply a device that increases or decreases a person's potential energy without them needing to supply that energy themselves: the elevator gives you potential energy when you're going up and it takes potential energy from you when you're coming down. In theory, that sounds easy enough: the elevator won't need to use much energy at all because it will always be getting back as much (when it goes down) as it gives out (when it goes up). Unfortunately, it's not quite that simple. If all the elevator had were a simple hoist with a cage passing over a pulley, it would use considerable amounts of energy lifting people up but it would have no way of getting that energy back: the energy would simply be lost to friction in the cables andbrakes(disappearing into the air as wasteheat) when the people came back down.levator located in the engine elevator room which is usually just above the glide rail space.The counterweight

In practice, elevators work in a slightly different way from simple hoists. The elevator car is balanced by a heavy counterweight that weighs roughly the same amount as the car when it's loaded half-full. When the elevator goes up, the counterweight goes downand vice-versa, which helps us in four ways:1. The counterweight makes it easier for the motor to raise and lower the carjust as sitting on a see-saw makes it much easier to lift someone's weight compared to lifting them in your arms. Thanks to the counterweight, the motor needs to use much less force to move the car either up or down. Assuming the car and its contents weigh more than the counterweight, all the motor has to lift is the difference in weight between the two and supply a bit of extra force to overcome friction in the pulleys and so on.2. Since less force is involved, there's less strain on the cableswhich makes the elevator a little bit safer.3. The counterweight reduces the amount of energy the motor needs to use. This is intuitively obvious to anyone who's ever sat on a see-saw: assuming the see-saw is properly balanced, you can bob up and down any number of times without ever really getting tiredquite different from lifting someone in your arms, which tires you very quickly. This point also follows from the first one: if the motor is using less force to move the car the same distance, it's doing less work against the force of gravity.4. The counterweight reduces the amount of braking the elevator needs to use. Imagine if there were no counterweight: a heavily loaded elevator car would be really hard to pull upwards but, on the return journey, would tend to race to the ground all by itself if there weren't some sort of sturdy brake to stop it. The counterweight makes it much easier to control the elevator car.In a different design, known as aduplex counterweightless elevator, two cars are connected to opposite ends of the same cable and effectively balance each other, doing away with the need for a counterweight.Photo: The counterweight rides up and down on wheels that follow guide tracks on the side of the elevator shaft. The elevator car is at the top of this shaft (out of sight) so the counterweight is at the bottom. When the car moves down the shaft, the counterweight moves upand vice versa. Each car has its own counterweight so the cars can operate independently of one another. On this picture, you can also see the doors on each floor that open and close only when the elevator car is aligned with them.The safety brakeEveryone who's ever traveled in an escalator has had the same thought: what if the cable holding this thing suddenly snaps? Rest assured, there's nothing to worry about. If the cable snaps, a variety of safety systems prevent an elevator car from crashing to the floor. This was the great innovation that Elisha Graves Otis made back in the 1860s. His elevators weren't simply supported by ropes: they also had aratchetsystem as a backup. Each car ran between two vertical guide rails with sturdy metal teeth embedded all the way up them. At the top of each car, there was aspring-loaded mechanism with hooks attached. If the cable broke, the hooks sprung outward and jammed into the metal teeth in the guide rails, locking the car safely in position.How the original Otis elevator workedThanks to the wonders of the Internet, it's really easy to look at original patent documents and find out exactly what inventors were thinking. Here's one of the drawings Elisha Graves Otis submitted with his "Hoisting Apparatus" patent dated January 15, 1861. I've colored it in a little bit so it's easier to understand:

Greatly simplified, here's how it works:1. The elevator compartment (1, green) is raised and lowered by a hoist andpulleysystem (2) and a moving counterweight (not visible in this picture). You can see how the elevator is moving smoothly between vertical guide bars: it doesn't just dangle stupidly from the rope!2. The cable that does all the lifting (3, red) wraps around several pulleys and the main winding drum. Don't forget this elevator was invented before anyone was really usingelectricity: it was raised and lowered by hand!3. At the top of the elevator car, there's a simple mechanism made up of spring-loaded arms and pivots (4). If the main cable (3) breaks, the springs push out two sturdy bars called "pawls" (5) so they lock into vertical racks of upward-pointing teeth (6) on either side. This ratchet-like device clamps the elevator safely in place.

According to Otis, the key part of the invention was: "having the pawls and the teeth of the racks hook formed, essentially as shown, so that the weight of the platform will, in case of the breaking of the rope, cause the pawls and teeth to lock together and prevent the contingency of a separation of the same."If you'd like a more detailed explanation, nip over to theUS Patent and Trademark Officeand search for patent number #31,128 (Otis, 1861). (If you prefer, you can go directly to it here:Google Patents: US Patent #31,128.) The Otis patent also explains more fully how the winch and pulleys work with the counterweight.Photo: A modern elevator has much in common with the original Otis design. Here you can see the little wheels at the edges of an elevator car that help it move smoothly up and down its guide bars.Did Otis invent the elevator?No! He invented thesafety elevator: he noted how ordinary elevators could fail and came up with a better design that made them safer. The Otis elevator dates from the middle of the 19th century, but ordinary elevators date back much furtheras far as Greek and Roman times. We can trace them back to more general kinds of lifting equipment such as cranes,windlasses, andcapstans; ancient water-raising devices such as theshaduf(sometimes spelled shadoof), based on a kind of swinging see-saw design, may well have inspired the use of counterweights in early elevators and hoists.Other safety systems

Modern elevators have multiple safety systems. Like the cables on a suspensionbridge, the cable in an elevator is made from many metal cables twisted together so a small failure of one part of the cable isn't, initially at least, going to cause any problems. Some elevators also have multiple, separate cables so the complete failure of one cable leaves others functioning in its place. Elevators also have a safety braking system similar to the one Otis originally designed with spring-loaded arms locking the car into (or onto) vertical guide rails. Even if all the cables brake, this system will still hold the car in place or at least reduce its descent to a safe and slow speed. Finally, if you've ever looked at a transparent glass elevator, you'll have noticed a gianthydraulicorgas springbuffer at the bottom to cushion against an impact if the safety brake should somehow brake. Thanks to Elisha Graves Otis, and the many talented engineers who've followed in his footsteps, you're much safer inside an elevator than you are in a car!Photo: Elevators don't just hang from a single cable: there are several strong cables supporting the car in case one breaks. If the worst does happen, you'll find there's often an emergencyintercomtelephone you can use inside an elevator car to call for assistance.

Escalatorn escalator is a power-driven, continuous moving stairway designed to transport passengers up and down short vertical distances. Escalators are used around the world to move pedestrian traffic in places where elevators would be impractical. Principal areas of usage include shopping centers, airports, transit systems, trade centers, hotels, and public buildings. The benefits of escalators are many. They have the capacity to move large numbers of people, and they can be placed in the same physical space as stairs would be. They have no waiting interval, except during very heavy traffic; they can be used to guide people towards main exits or special exhibits; and they may be weather-proofed for outdoor use. It is estimated that there are over 30,000 escalators in the United States, and that there are 90 billion riders traveling on escalators each year. Escalators and their cousins, moving walkways, are powered by constant speed alternating current motors and move at approximately 1-2 ft (0.3-0.6 m) per second. The maximum angle of inclination of an escalator to the horizontal is 30 degrees with a standard rise up to about 60 ft (18 m).The invention of the escalator is generally credited to Charles D. Seeberger who, as an employee of the Otis Elevator Company, produced the first step-type escalator manufactured for use by the general public. His creation was installed at the Paris Exhibition of 1900, where it won first prize. Seeberger also coined the term escalator by joiningscala,which is Latin for steps, with a diminutive form of "elevator." In 1910 Seeberger sold the original patent rights for his invention to the Otis Elevator Company. Although numerous improvements have been made, Seeberger's basic design remains in use today. It consists of top and bottom landing platforms connected by a metal truss. The truss contains two tracks, which pull a collapsible staircase through an endless loop. The truss also supports two handrails, which are coordinated to move at the same speed as the step treads.ComponentsTop and bottom landing platformsThese two platforms house the curved sections of the tracks, as well as the gears and motors that drive the stairs. The top platform contains the motor assembly and the main drive gear, while the bottom holds the step return idler sprockets. These sections also anchor the ends of the escalator truss. In addition, the platforms contain a floor plate and a comb plate. The floor plate provides a place for the passengers to stand before they step onto the moving stairs. This plate is flush with the finished floor and is either hinged or removable to allow easy access to the machinery below. The comb plate is the piece between the stationary floor plate and the moving step. It is so named because its edge has a series of cleats that resemble the teeth of a comb. These teeth mesh with matching cleats on the edges of the steps. This design is necessary to minimize the gap between the stair and the landing, which helps prevent objects from getting caught in the gap.The trussThe truss is a hollow metal structure that bridges the lower and upper landings. It is composed of two side sections joined together with cross braces across the bottom and just below the top. The ends of the truss are attached to the top and bottom landing platforms via steel or concrete supports. The truss carries all the straight track sections connecting the upper and lower sections.The tracksThe track system is built into the truss to guide the step chain, which continuously pulls the steps from the bottom platform and back to the top in an endless loop. There are actually two tracks: one for the front wheels of the steps (called the step-wheel track) and one for the back wheels of the steps (called the trailer-wheel track). The relative positions of these tracks cause the steps to form a staircase as they move out from under the comb plate. Along the straight section of the truss the tracks are at their maximum distance apart. This configuration forces the back of one step to be at a 90-degree angle relative to the step behind it. This right angle bends the steps into a stair shape. At the top and bottom of the escalator, the two tracks converge so that the front and back wheels of the steps are almost in a straight line. This causes the stairs to lay in a flat sheet-like arrangement, one after another, so they can easily travel around the bend in the curved section of track. The tracks carry the steps down along the underside of the truss until they reach the bottom landing, where they pass through another curved section of track before exiting the bottom landing. At this point the tracks separate and the steps once again assume a stair case configuration. This cycle is repeated continually as the steps are pulled from bottom to top and back to the bottom again.The stepsThe steps themselves are solid, one-piece, die-cast aluminum. Rubber mats may be affixed to their surface to reduce slippage, and yellow demarcation lines may be added to clearly indicate their edges. The leading and trailing edges of each step are cleated with comb-like protrusions that mesh with the comb plates on the top and bottom platforms. The steps are linked by a continuous metal chain so they form a closed loop with each step able to bend in relation to its neighbors. The front and back edges of the steps are each connected to two wheels. The rear wheels are set further apart to fit into the back track and the front wheels have shorter axles to fit into the narrower front track. As described above, the position of the tracks controls the orientation of the steps.The railingThe railing provides a convenient handhold for passengers while they are riding the escalator. It is constructed of four distinct sections. At the center of the railing is a "slider," also known as a "glider ply," which is a layer of a cotton or synthetic textile. The purpose of the slider layer is to allow the railing to move smoothly along its track. The next layer, known as the tension member, consists of either steel cable or flat steel tape. It provides the handrail with the necessary tensile strength and flexibility. On top of tension member are the inner construction components, which are made of chemically treated rubber designed to prevent the layers from separating. Finally, the outer layer, the only part that passengers actually see, is the rubber cover, which is a blend of synthetic polymers and rubber. This cover is designed to resist degradation from environmental conditions, mechanical wear and tear, and human vandalism. The railing is constructed by feeding rubber through a computer controlled extrusion machine to produce layers of the required size and type in order to match specific orders. The component layers of fabric, rubber, and steel are shaped by skilled workers before being fed into the presses, where they are fused together. When installed, the finished railing is pulled along its track by a chain that is connected to the main drive gear by a series of pulleys.DesignA number of factors affect escalator design, including physical requirements, location, traffic patterns, safety considerations, and aesthetic preferences. Foremost, physical factors like the vertical and horizontal distance to be spanned must be considered. These factors will determine the pitch of the escalator and its actual length. The ability of the building infrastructure to support the heavy components is also a critical physical concern. Location is important because escalators should be situated where they can be easily seen by the general public. In department stores, customers should be able to view the merchandise easily. Furthermore, up and down escalator traffic should be physically separated and should not lead into confined spaces.Traffic patterns must also be anticipated in escalator design. In some buildings the objective is simply to move people from one floor to another, but in others there may be a more specific requirement, such as funneling visitors towards a main exit or exhibit. The number of passengers is important because escalators are designed to carry a certain maximum number of people. For example, a single width escalator traveling at about 1.5 feet (0.45 m) per second can move an estimated 170 persons per five-minute period. Wider models traveling at up to 2 feet (0.6 m) per second can handle as many as 450 people in the same time period. The carrying capacity of an escalator must match the expected peak traffic demand. This is crucial for applications in which there are sudden increases in the number of passengers. For example, escalators used in train stations must be designed to cater for the peak traffic flow discharged from a train, without causing excessive bunching at the escalator entrance.Of course, safety is also major concern in escalator design. Fire protection of an escalator floor-opening may be provided by adding automatic sprinklers or fireproof shutters to the opening, or by installing the escalator in an enclosed fire-protected hall. To limit the danger of overheating, adequate ventilation for the spaces that contain the motors and gears must be provided. It is preferred that a traditional staircase be located adjacent to the escalator if the escalator is the primary means of transport between floors. It may also be necessary to provide an elevator lift adjacent to an escalator for wheelchairs and disabled persons. Finally, consideration should be given to the aesthetics of the escalator. The architects and designers can choose from a wide range of styles and colors for the handrails and tinted side panels.The ManufacturingProcess1. The first stage of escalator construction is to establish the design, as described above. The escalator manufacturer uses this information to construct the appropriately customized equipment. There are two types of companies that supply escalators, primary manufacturers who actually build the equipment, and secondary suppliers that design and install the equipment. In most cases, the secondary suppliers obtain the necessary equipment from the primary manufacturers and make necessary modifications for installation. Therefore, most escalators are actually assembled at the primary manufacturer. The tracks, step chains, stair assembly, and motorized gears and pulleys are all bolted into place on the truss before shipping.2. Prior to installation, the landing areas must be prepared to connect to the escalator. For example, concrete fittings must be poured, and the steel framework that will hold the truss in place must be attached. After the escalator is delivered, the entire assembly is uncrated and jockeyed into position between the top and bottom landing holes. There are a variety of methods for lifting the truss assembly into place, one of which is a scissors lift apparatus mounted on a wheeled support platform. The scissors lift is outfitted with a locator assembly to aid in vertical and angular alignment of the escalator. With such a device, the upper end of the truss can be easily aligned with and then supported by a support wall associated with the upper landing. The lower end of the truss can be subsequently lowered into a pit associated with the floor of the lower landing. In some cases, the railings may be shipped separately from the rest of the equipment. In such a situation, they are carefully coiled and packed for shipping. They are then connected to the appropriate chains after the escalator is installed.3. Make final connections for the power source and check to ensure all tracks and chains are properly aligned.4. Verify all motorized elements are functioning properly, that the belts and chains

An escalator is a continuously moving staircase. Each stair has a pair of wheels on each side, one at the front of the step and one at the rear. The wheels run on two rails. At the top and bottom of the escalator, the inner rail dips beneath the outer rail, so that the bottom of the stair flattens, making it easier for riders to get on and off.move smoothly and at the correct speed, and that the emergency braking system is activated. The step treads must be far enough apart that they do not pinch or rub against each other. However, they should be positioned such that no large gaps are present, which could increase the chance of injury.Quality ControlThe Code of Federal Regulation (CFR) contains guidelines for escalator quality control and establishes minimum inspection standards. As stated in the code, "elevators and escalators shall be thoroughly inspected at intervals not exceeding one year. Additional monthly inspections for satisfactory operation shall be conducted by designated persons." Records of the annual inspections are to be posted near the escalator or be available at the terminal. In addition, the code specifies that the escalator's maximum load limits shall be posted and not exceeded. Additional safety standards can also be found in American Society of Mechanical Engineers Handbook.The FutureSeveral innovations in escalator manufacture have been made in recent years. For example, one company recently developed a spiral staircase escalator. Another has developed an escalator suitable for transporting wheelchairs. Such advances are likely to continue as the industry expands to meet the changing needs of the marketplace. In addition, the industry is expecting a growth spurt as untapped markets such as China and Hungary begin to recognize the benefits of escalator technology.