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.
Page 3 4 5 6
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.