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How Air Conditioners Work

The frst modern air conditioning system was developed in 1902 by a young

electrical engineer named Willis Haviland Carrier. t was designed to solve a

humidity problem at the !ac"ett# Wilhelms $ithographing and %ublishing Company

in &roo"lyn' (.). %aper stoc" at the plant would sometimes absorb moisture *rom the

warm summer air' ma"ing it di+cult to apply the layered in"ing techni,ues o* thetime. 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

stabilied the moisture content o* the paper. /educing the humidity also had the

side beneft o* lowering the air temperature ## and a new technology was born

Carrier realied he-d developed something with *ar#reaching potential' and it wasn-t

long be*ore air#conditioning systems started popping up in theatersand stores'

ma"ing the long' hot summer months much more com*ortable

The actual process air conditioners use to reduce the ambient air temperature in aroom is based on a very simple scientifc principle. The rest is achieved with the

application o* a *ew clever mechanical techni,ues. ctually' an air conditioner is

very similar to another appliance in your home ## the re*rigerator. ir conditioners

don-t have the eterior housing a re*rigerator relies on to insulate its cold bo.

nstead' the walls in your home "eep cold air in and hot air out.

Air-conditioning Basics

ir conditioners use re*rigeration to chill indoor air' ta"ing advantage o* a

remar"able physical law3 When a li,uidconverts to a gas4in a process called phase

conversion5' it absorbs heat. ir conditioners eploit this *eature o* phaseconversion by *orcing special chemical compounds to evaporate and condense over

and over again in a closed system o* coils.

The compounds involved are refrigerantsthat have properties enabling them to

change at relatively low temperatures. ir conditioners also contain *ans that move

warm interior air over these cold' re*rigerant#flled coils. n *act' central air
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conditioners have a whole system o* ducts designed to *unnel air to and *rom these

serpentine' air#chilling coils.

When hot air 6ows over the cold' low#pressure evaporator coils' the re*rigerant

inside absorbs heat as it changes *rom a li,uid to a gaseous state. To "eep cooling

e+ciently' the air conditioner has to convert the re*rigerant gas bac" to a li,uidagain. To do that' a compressor puts the gas under high pressure' a process that

creates unwanted heat. ll the etra heat created by compressing the gas is then

evacuated to the outdoors with the help o* a second set o* coils called condenser

coils' and a second *an. s the gas cools' it changes bac" to a li,uid' and the

process starts all over again. Thin" o* it as an endless' elegant cycle3 li,uid

re*rigerant' phase conversion to a gas7 heat absorption' compression and phase

transition bac" to a li,uid again.

t-s easy to see that there are two distinct things going on in an air conditioner.

/e*rigerant is chilling the indoor air' and the resulting gas is being continually

compressed and cooled *or conversion bac" to a li,uid again. 8n the net page'we-ll loo" at how the dierent parts o* an air conditioner wor" to ma"e all that

possible.

The Parts of an Air Conditioner

$et-s get some house"eeping topics out o* the way be*ore we tac"le the uni,ue

components that ma"e up a standard air conditioner. The biggest :ob an air

conditioner has to do is to cool the indoor air. That-s not all it does' though. ir

conditioners monitor and regulate the air temperature via a thermostat. They also

have an on board flter that removes airborne particulates *rom the circulating air.

ir conditioners *unction as dehumidifers. &ecause temperature is a "ey component
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o* relative humidity' reducing the temperature o* a volume o* humid air causes it to

release a portion o* 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.

!till' the ma:or parts o* an air conditioner manage re*rigerant and move air in twodirections3 indoors and outside3

Evaporator -/eceives the li,uid re*rigerant

Condenser -;acilitates heat trans*er

Expansion valve -regulates re*rigerant 6ow into the evaporator

Compressor - pump that pressuries re*rigerant

The cold side o* an air conditioner contains the evaporator and a *an that blows air

over the chilled coils and into the room. The hot side contains the compressor'condenser and another *an to vent hot air coming o the compressed re*rigerant to

the outdoors. n between the two sets o* coils' there-s an.

expansion valve. t regulates the amount o* compressed li,uid re*rigerant moving

into the evaporator. 8nce in the evaporator' the re*rigerant eperiences a pressure

drop' epands and changes bac" into a gas.

Thecompressoris actually a large electric pump that pressuries the re*rigerant

gas as part o* the process o* turning it bac" into a li,uid. There are some additional

sensors' timers and valves' but the evaporator' compressor' condenser and

epansion valve are the main components o* an air conditioner.

lthough this is a conventional setup *or an air conditioner' there are a couple o*

variations you should "now about. Window air conditioners have all these

components mounted into a relatively small metal bo that installs into a window

opening. The hot air vents *rom the bac" o* the unit' while the condenser coils and a

*an cool and re#circulate indoor air. &igger air conditioners wor" a little dierently3

Central air conditioners share a control thermostat with a home-s heating system'

and the compressor and condenser' the hot side o* the unit' isn-t even in the house.

t-s in a separate all#weather housing outdoors. n very large buildings' li"e hotels

and hospitals' the eterior condensing unit is o*ten mounted somewhere on the roo*.


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Window and Split-sstem AC !nits

window air conditioner unit implements a complete air conditioner in a small

space. The units are made small enough to ft into a standard window *rame. )ou

close the window down on the unit' plug it in and turn it on to get cool air. * you

ta"e the cover o o* an unplugged window unit' you-ll fnd that it contains3

compressor

n epansion valve

hot coil 4on the outside5

chilled coil 4on the inside5

Two *ans

control unit

The *ans blow air over the coils to improve their ability to dissipate heat 4to the

outside air5 and cold 4to the room being cooled5.

When you get into larger air#conditioning applications' its time to start loo"ing at

split#system units. split#system air conditioner splits the hot side *rom the cold

side o* the system' as in the diagram below.


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The cold side' consisting o* the epansion valve and the cold coil' is generally

placed into a *urnaceor some other air handler. The air handler blows air through

the coil and routes the air throughout the building using a series o* ducts. The hot

side' "nown as the condensing unit' lives outside the building.

The unit consists o* a long' spiral coil shaped li"e a cylinder. nside the coil is a *an'to blow air through the coil' along with a weather#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 4at the epense o*

increased noise outside the house5. 8ther than the *act that the hot and cold sides

are split apart and the capacity is higher 4ma"ing the coils and compressor larger5'

there-s no dierence between a split#system and a window air conditioner.

n warehouses' large business o+ces' malls' big department stores and other

sieable buildings' the condensing unit normally lives on the roo* and can be ,uite

massive. lternatively' there may be many smaller units on the roo*' each attached

inside to a small air handler that cools a specifc one in the building.

n larger buildings and particularly in multi#story buildings' the split#system

approach begins to run into problems.


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lthough standard air conditioners are very popular' they can use a lot o* energy

and generate ,uite a bit o* heat. ;or large installations li"e o+ce buildings' air

handling and conditioning is sometimes managed a little dierently.

!ome systems use wateras part o* the cooling process. The two most well#"nown

are chilled water systems and cooling tower air conditioners.

Chilled water sstems -n a chilled#water system' the entire air conditioner

is installed on the roo* or behind the building. t cools water to between =0

and => degrees ;ahrenheit 4=.= and ?.2 degrees Celsius5. The chilled water is

then piped throughout the building and connected to air handlers. This can

be a versatile system where the water pipes wor" li"e the evaporator coils in

a standard air conditioner. * it-s well#insulated' there-s no practical distance

limitation to the length o* a chilled#water pipe.

Cooling tower technolog -n all o* the air conditioning systems we-ve

described so *ar' air is used to dissipate heat *rom the compressor coils. nsome large systems' a cooling tower is used instead. The tower creates a

stream o* cold water that runs through a heat echanger' cooling the hot

condenser coils. The tower blows air through a stream o* water causing some

o* it to evaporate' and the evaporation cools the water stream. 8ne o* the

disadvantages o* this type o* system is that water has to be added regularly

to ma"e up *or li,uid lost through evaporation. The actual amount o* cooling

that an air conditioning system gets *rom a cooling tower depends on the

relative humidity o* the air and the barometric pressure.

&ecause o* rising electricalcosts and environmental concerns' some other air

cooling methods are being eplored' too. 8ne is o#pea" or ice#cooling technology.n o"-peakcooling system uses ice *roen during the evening hours to chill interior

air during the hottest part o* the day. lthough the system does use energy' the

largest energy drain is when community demand *or power is at its lowest. to ?> degrees ;ahrenheit 4?.2

to 2B.A degrees Celsius5. The basic idea behind

#eo-thermal coolingis to use this constant temperature as a heat or cold sourceinstead o* using electricity to generate heat or cold. The most common type o* geo#

thermal unit *or the home is a closed#loop system. %olyethylene pipes flled with a

li,uid miture are buried underground. uring the winter' the 6uid collects heat

*rom the earth and carries it through the system and into the building. uring the

summer' the system reverses itsel* to cool the building by pulling heat through the

pipes to deposit it underground.
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;or real energy e+ciency' solar powered air conditioners are also ma"ing their

debut. There may still be some "in"s to wor" out' but around > percent o* all

electricity consumed in the D.!. is used to power air conditioning o* one type or

another' so there-s a big mar"et *or energy#*riendly air conditioning options.

BT! and EE$

Eost air conditioners have their capacity rated in &ritish thermal units 4&tu5. &tu is

the amount o* heat necessary to raise the temperature o* 1 pound 40.=> "ilograms5

o* water one degree ;ahrenheit 40.>@ degrees Celsius5. 8ne &tu e,uals 1'0>> :oules.

n heating and cooling terms' one ton e,uals 12'000 &tu.

typical window air conditioner might be rated at 10'000 &tu. ;or comparison' a

typical 2'000#s,uare#*oot 41A>.A s,uare meters5 house might have a >#ton 4@0'000#

&tu5 air conditioning system' implying that you might need perhaps B0 &tu per

s,uare *oot. These are rough estimates. To sie an air conditioner accurately *or

your specifc application' you should contact an HFC contractor.

The energy e+ciency rating 4


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&ecause o* the rising costs o* electricityand a growing trend to Kgo green'K more

people are turning to alternative cooling methods to spare their poc"etboo"s and

the environment. &ig businesses are even :umping on board in an eort to improve

their public image and lower their overhead.

ce cooling systems are one way that businesses are combating high electricitycosts during the summer. ce cooling is as simple as it sounds. $arge tan"s o* water

*reee into ice at night' when energy demands are lower. The net day' a system

much li"e a conventional air conditioner pumps the cool air *rom the ice into the

building. ce cooling saves money' cuts pollution' eases the strain on the power grid

and can be used alongside traditional systems. The downside o* ice cooling is that

the systems are epensive to install and re,uire a lot o* space.


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Air conditioning with ice &locks is taking root among some of the world(s

most powerf)l companies* See more pict)res of air conditioners*

HEAT+,# C../+,#

novel method o* conditioning is ta"ing root among some o* the world-s most

power*ul corporations' and it uses the simple power o* ice. Eorgan !tanley and

Credit !uisse now use massive ice bloc"s instead o* traditional air#conditioning

systems in some o* their o+ces. Credit !uisse is considering epanding the system

beyond its 1.9#million#s,uare#*oot Eanhattan o+ce to its other locations around

the world' but they won-t be alone. n estimated B'000 *acilities around the world

use ice#based cooling systems

The system is not only more environmentally *riendly but also saves big companies

li"e Loldman !achs' which put an ice cooling system in its new 6agship o+ce'

millions o* dollars in utility bills. The system wor"s by ma"ing ice at night' when

lower power usage means energy is cheaper and lower temperatures mean less

power is re,uired to *reee water. The larger the dierence between nighttime and

daytime temperatures is' the greater the energy savings. n Credit !uisse-s system'

the ice *orms overnight' and as it melts during the day' *ans blow cold air into thecooling system and throughout the building. t the end o* the day' the >1'200

gallons o* water ## spread across three rooms in @= tan"s ## is ready to be *roen

again. The ice#bloc" system can also be combined with traditional air conditioning'

which is the case in Credit !uisse-s (ew )or" o+ce.

The ice system essentially acts li"e an ultra#e+cient battery' storing energy that-s

gathered cheaply at night and releasing it during the day. ce ma"es a convenient
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and e+cient medium *or the :ob. &y volume' it has up to triple the energy#holding

capacity o* water. The system also has less potential *or brea"down compared to

more traditional systems.

The ice cooling system is intriguing and energy e+cient' but it-s not entirely

original. n the 19th century' a hospital in ;lorida used ice to cool hospital roomsand many a home chemist has used ice to cool himsel* on a hot day. !till' you-re

unli"ely to fnd an ice#based cooling system in someone-s home. The cooling

e,uipment re,uires a lot o* space and a signifcant up*ront investment ## Credit

!uisse paid GB million *or theirs ## though the investment presumably pays *or itsel*

over time.

The state o* (ew )or"' along with other state and municipal governments' is

encouraging companies to ma"e environmentally#*riendly in*rastructure

investments' in some cases oering tabrea"s or grants. The pollutionand waste

caused by s"yscrapers constitutes a ma:or problem *or large systems. ce#cooling

systems do more than save on electricity billsM by using power at night' they easestrain on already overtaed electrical grids ## a process "nown as 0load shifting0##

using energy during non#pea" hours.

Several companies1 s)ch as +ce Energ1 now o"er prod)cts that work with

or in place of traditional air conditioners in order to red)ce energ )se*
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2ore Alternatives to Air Conditioning


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* your home or o+ce already has an air#conditioning system' there are still some

things you can do. ;irst' ma"e sure it-s a modern unit without any oone#

harmingre*rigerants. Close all windows when your air conditioner is running' and

loo" into renewable power sources li"e roo*#mounted solar panels. * you have a

window#mounted air conditioner' seal the area around it and get an energy#e+cient

model 4i* you don-t plan to switch to central air5. ;inally' ma"e sure your home oro+ce central#air conditioner fts the space. * yours is too big' you-ll be constantly

turning it on and o' wasting energy in the process.

#as 3s)&stance4

Las' in physics and chemistry' any substance that epands and spreads indefnitely

when not confned in a container. gas thus has no shape o* its own' but ta"es on

the shape o* its container. The gaseous state is one o* the three basic states' or

*orms' in which all matter eists. 4The two other states are solid and li,uid.5 Lases

and li,uids are both 6uids and have certain properties in common.

gas can be changed into a li,uid or solid by being cooled or compressed' or bothM

a solid or li,uid can be changed into a gas by the application o* heat. substance

that is in the solid or li,uid state at ordinary temperatures is called a vapor when it

is in the gaseous *orm. !team is water vapor at a high temperature.

gas consisting o* one "ind o* chemical element is an elementary gas. t ordinary

temperatures and pressures' there are 12 such gases3 argon' chlorine' 6uorine'

helium' hydrogen' "rypton' neon' nitrogen' oygen' oone' radon' and enon.

gas consisting o* molecules made up o* atoms o* more than one "ind o* element is

a compound gas. mmonia and carbon monoide are common compound gases.

Eolecules or atoms o* gases can be changed into ions 4electrically charged

molecules or atoms5 by being heated. miture o* positively charged gas ions and

electrons is called a plasma.

%roperties o* Lases

Lases vary widely in their physical and chemical characteristics. !ome' such as

oygen' have neither color nor odor. Chlorine' on the other hand' is yellowish#green

and has a distinct odor. !ome gases burn in the presence o* oygen' others do not.

The si inert 4or noble5 gasesPargon' helium' "rypton' neon' radon' and enonP

consist o* single atoms that do not ordinarily combine with other elements to *ormchemical compounds.

espite these variations' gases have certain properties in common. These include

the *ollowing3

Eolecular rrangement
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gas is made up o* molecules or single atoms. 4!ingle gas atoms are regarded as

molecules by chemists and physicists.5 Las molecules are much *arther apart than

are molecules o* solids or o* li,uids and move about at higher speeds. ccording to

vogadro-s $aw' a hypothesis frst stated by the talian physicist and chemist

medeo vogadro in 1A11' e,ual volumes o* dierent gases' under the same

conditions o* temperature and pressure' contain the same number o* molecules.

vogadro-s $aw has been verifed eperimentally. Dnder standard conditions o*

temperature 40Q C.5 and pressure 4?@0 mm o* mercury5' the volume occupied by

one grammolecular weight o* any gas is 22.= liters 4about 0.?9 cubic *oot5. The

number o* molecules contained in this volume has been determined to be about

@.02B R 102B' or @02'B00 *ollowed by 1A more eroes. This fgure is called

vogadro-s number.

iusion and %ressure

&ecause o* the rapid motion o* its molecules' a gas will diuse' or spread uni*ormly.

n diusing' it can mi with another gas or with certain li,uids and solids.

When a gas is confned to a container' the moving gas molecules continually stri"e

the container-s inside walls' eerting pressure. The molecules move in such a way

that the pressure is the same at every point on the inside walls o* the container.

ncreasing the amount o* gas without changing the sie o* the container increases

the pressure. Heating the gas also increases the pressure' because the molecules

move more rapidly as the temperature increases.

Compression and


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!ome gases' such as helium and hydrogen' re,uire etremely low temperatures *or

li,ue*action to occur.

/i5)id

$i,uid' a state o* matter with properties midway between those o* solids and gases.

Water is the most *amiliar li,uid. $i,uid molecules have more cohesion 4mutual

attraction5 than gas molecules but less than solid molecules. Hence' unli"e a gas' a

li,uid has a defnite volumeM but unli"e a solid' it has no fed shape. t is shaped by

its container.

Cohesion accounts *or sur*ace tension. The sur*ace molecules o* a li,uid' drawn to

each other and pulled down by those below' behave li"e a stretched elastic

membrane. !ur*ace tension' combined with adhesion 4the attraction o* molecules

*or other substances5 eplains capillarity' the tendency o* li,uids to rise in narrow

tubes.

$i,uids may evaporate' boil' condense' *reee' and *orm solutions. They are capable

o* diusion and osmosis' and o* trans*erring heat by conduction and convection.

$i,uids 6ow' but they also have viscosity 4resistance to 6owing5. They also possess

buoyant *orce.

How $efrigerators Work

Can o) imagine what life was like &efore the refrigerator came along*

The net time you indulge in an ice cold drin" on a hot day' you have your

re*rigerator 4and onboard *reeer5 to than" *or the re*reshingly chilled beverage. t

wasn-t so long ago that you-d have to be very rich or well connected to score a

chilled drin" with a *ew ice cubes6oating inside. Today' we ta"e re*rigeration *or

granted' but once upon a time' *ortunes were made shipping large bloc"s o* ice

around the world in insulated holds to sell to the rich.
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&e*ore re*rigeration' preserving *ood was a big :ob. )ou could salt *oods' and in

winter' you could bury *ood in a snow dri*t and hope the critters didn-t fnd it. To

stay stoc"ed with the essentials' though' you had to wor" at it ## or be rolling in

money. /e*rigeration is one invention that changed the way we conduct our daily

lives. We can preserve *ood more easily nowadays' so we have much less to worry

about when it comes to *ood#borne illnesses. The *ood supply is more stable' too.That gallon o* mil" can last a couple o* wee"s in the *ridge as opposed to a couple o*

hours on your countertop. That-s huge. t means you don-t need to "eep a cow in

your bac"yard i* you want a regular supply o* mil".

The *undamentals o* re*rigeration are also at wor" in another important household

appliance3 the air conditioner. t-s estimated that around > percent o* all the

electrical energy used in the D.!. is epended to "eep our homes cool. That-s pretty

amaing' especially when you consider the *act that the principle behind most

re*rigeration is simple. Here it is in one sentence3 When a li,uid evaporates' it

absorbs heat in the process. * you want to get rid o* heat' you need to coa a li,uid

to convert to its gaseous state

The P)rpose of $efrigeration

The *undamental reason *or having a re*rigerator is to "eep *ood cold. Cold

temperatures help *ood stay *resh longer. The basic idea behind re*rigeration is to

slow down the activity o* bacteria 4which all *ood contains5 so that it ta"es longer *or

the bacteria to spoil the *ood.

;or eample' bacteria will spoil mil" in two or three hours i* the mil" is le*t out on

the "itchen counter at room temperature. However' by reducing the temperature o*

the mil"' it will stay *resh *or a wee" or two ## the cold temperature inside the

re*rigerator decreases the activity o* the bacteria that much. &y *reeing the mil"

you can stop the bacteria altogether and the mil" can last *or months 4until eects

li"e *reeer burn begin to spoil the mil" in non#bacterial ways5.

/e*rigeration and *reeing are two o* the most common *orms o* *ood preservation

used today. ;or more in*ormation on other ways to preserve *ood'


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Parts of a $efrigerator

* you pour a little rubbing alcoholon your s"in' it-ll *eel cold ## really cold. t isn-t

re*rigerated' so how does this happen Well' alcohol evaporates at room

temperature the way water evaporates at a low temperature in an oven. s it

evaporates' it absorbs the heat on the sur*ace o* your s"in' ma"ing your s"in cooler.

special coolant called a re*rigerant *unctions in a re*rigerator the way alcohol

wor"s on your s"in' ecept in a re*rigerator' the coolant is trapped inside a series o*

coils. s it ma"es a circuit through them' it changes bac" and *orth *rom a li,uid to

a gas.

To pull o this *rosty *eat' a re*rigerator uses fve ma:or components3

Compressor

Heat-exchanging pipes4serpentine or coiled set o* pipes outside the unit5

Expansion valve

Heat-exchanging pipes4serpentine or coiled set o* pipes inside the unit5

$efrigerant4li,uid that evaporates inside the re*rigerator to create the cold

temperatures5

!nderstanding $efrigeration

To understand what-s happening inside a re*rigerator' let-s learn a little more about

how re*rigerants wor". )ou will need3

n oven#sa*e glass bowl flled with water

thermometerthat can measure up to at least =>0 degrees ;ahrenheit

42B2.2 degrees Celsius5
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dd the thermometer to the water flled bowl and place both in the oven. !et the

oven to =00 degrees ;ahrenheit 420=.= degrees Celsius5.

s the oven heats up' the temperature o* the water will rise until it hits 212

;ahrenheit 4100 degrees Celsius5 and it starts boiling. The water temperature will

stay at 212 degrees ;ahrenheit 4100 degrees Celsius5 even though it-s completelysurrounded by the =00 degrees ;ahrenheit environment inside the oven. * you let

all the water boil away' the temperature on the thermometer will shoot up to =00

degrees ;ahrenheit 42B2.2 degrees Celsius5.

$et-s loo" at this eperiment another way3 magine the eistence o* an eotic

creature able to live happily in an oven at =00 degrees ;ahrenheit. $et-s call him

Ea. * Ea is hanging out in a =00 degree ;ahrenheit oven net to a bowl o* water

boiling away at 212 degrees ;ahrenheit 4100 degrees Celsius5' how is he going to

*eel about that water He-s going to thin" the boiling water is really cold. *ter all'

the boiling water is 1AA degrees colder than the =00 degrees ;ahrenheit that he

thin"s is com*ortable. That-s a big temperature dierenceS

This is eactly what happens when humans deal with li,uid nitrogen. We *eel

com*ortable at ?0 degrees ;ahrenheit 421.1 degrees Celsius5' but li,uid nitrogen

boils at #B20 degrees ;ahrenheit 4#19>.> degrees Celsius5. * you had a pot o* li,uid

nitrogen sitting on the "itchen table' its temperature would be boiling away at #B20

degrees ;ahrenheit 4#19>.> degrees Celsius5 ## to you' o* course' it would *eel

incredibly cold 4so cold it would burn youS5.

Eodern re*rigerators use a regenerating cycle to reuse the same re*rigerant over

and over again. )ou can get an idea o* how this wor"s by remembering Ea and his

bowl o* water. He could easily create a regenerating cycle by ta"ing the *ollowingsteps3

1. The bowl o* water in the oven eample boils away' remaining at 212 degrees

;ahrenheit 4100 degrees Celsius5 but producing lots o* =00 degree ;ahrenheit

steam. $et-s say Ea collects this steam in a big bag.

2. 8nce all the water boils o' Ea pressuries the steam into a steel container'

where the temperature rises to A00 degrees ;ahrenheit 4=2@.@ degrees

Celsius5 as the pressure increases. (ow' Ea thin"s the steel container *eels

really KhotK because it contains A00 degree ;ahrenheit 4=2@.@ degrees

Celsius5 steam instead o* =00 degree ;ahrenheit steam.

B. The steel container releases or dissipates its ecess heat to the air in the

oven' and it eventually drops to the oven-s temperature o* =00 degrees

;ahrenheit. n the process' the high#pressure steam in the container

condenses into pressuried water.


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=. t this point' Ea releases the water *rom the steel pressuried container into

a pot' and it immediately begins to boil' its temperature dropping to 212

degrees ;ahrenheit.

&y repeating these *our steps' Ea can reuse the same water over and over again

to provide re*rigeration.

The $efrigeration Ccle

The re*rigerator in your "itchen uses a cycle that is similar to the one described in

the previous section. &ut in your re*rigerator' the cycle is continuous. n the

*ollowing eample' we will assume that the re*rigerant being used is pure ammonia'

which boils at #2? degrees ;. This is what happens to "eep the re*rigerator cool3

1. The compressorcompresses the ammonia gas. The compressed gas heats

up as it is pressuried 4orange5.

2. The coilson the bac" o* the re*rigerator let the hot ammonia gas dissipate itsheat. The ammonia gas condenses into ammonia li,uid 4dar" blue5 at high

pressure.

B. The high#pressure ammonia li,uid 6ows through the expansion valve. )ou

can thin" o* the epansion valve as a small hole. 8n one side o* the hole is

high#pressure ammonia li,uid. 8n the other side o* the hole is a low#pressure

area 4because the compressor is suc"ing gas out o* that side5.

=. The li,uid ammonia immediately boils and vapories 4light blue5' its

temperature dropping to #2? ;. This ma"es the inside o* the re*rigerator cold.

>. The cold ammonia gas is suc"ed up by the compressor' and the cycle

repeats.

&y the way' i* you have ever turned your caro on a hot summer day when you

have had the air conditionerrunning' you may have heard a hissing noise under the

hood. That noise is the sound o* high#pressure li,uid re*rigerant 6owing through the

epansion valve.

%ure ammonia gas is highly toicto people and would pose a threat i* the

re*rigerator were to lea"' so all home re*rigerators don-t use pure ammonia. )ou

may have heard o* re*rigerants "now as C6Cs4chloro6uorocarbons5' originally

developed by u %ont in the 19B0s as a non#toic replacement *or ammonia. C;C#12

4dichlorodi6uoromethane5 has about the same boiling point as ammonia. However'

C;C#12 is not toic to humans' so it is sa*e to use in your "itchen. Eany large

industrial re*rigerators still use ammonia.
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n the 19?0s' it was discovered that the C;Cs then in use are harm*ul to the oone

layer' so as o* the 1990s' all new re*rigerators and air conditioners use re*rigerants

that are less harm*ul to the oone layer.

#as and Propane $efrigerators

* you own an /F' chances are you have a gas# or propane#powered re*rigerator.

These re*rigerators are interesting because they have no moving parts and use gas

or propane as their primary energy source. lso' they use heat to produce the cold

inside the re*rigerator.

gas re*rigerator uses ammoniaas the coolant' and water' ammonia and hydrogen

gas to create a continuous cycle *or the ammonia. The re*rigerator has fve main

parts3

#enerator# creates ammonia gas

Separator# separates the ammonia gas *rom water

Condenser# where hot ammonia gas is cooled and condensed to create

li,uid ammonia

Evaporator# where li,uid ammonia converts to a gas to create cold

temperatures inside the re*rigerator

A&sor&er# absorbs the ammonia gas in water

t wor"s li"e this3

1. Heat is applied to the ammonia and water solution in the generator. 4The heatcomes *rom burning gas' propane or "erosene.5

2. s the miture reaches the boiling point o* ammonia' it 6ows into the

separator.

B. mmonia gas 6ows upward into the condenser' dissipates heat and converts

bac" to a li,uid.

=. The li,uid ammonia ma"es its way to the evaporator where it mies with

hydrogen gas and evaporates' producing cold temperatures inside the

re*rigerator-s cold bo.

>. The ammonia and hydrogen gases 6ow to the absorber where the water

collected in the separator in step (o. 2 mies with the ammonia and

hydrogen gases.

@. The ammonia *orms a solution with the water and releases the hydrogen gas'

which 6ows bac" to the evaporator.
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?. The ammonia#and#water solution 6ows toward the generator to repeat the

cycle.

Electric and Solar Coolers

You won't need a bag of ice to keep your potato saladcold if you have a handy cooler that plugs into your

cigarettelighter. It uses a unique process known as the Peltier effect a ther!oelectric effect to produce

cold te!peratures. It's pretty neat and so!ething we haven't discussed yet.

"a!ed after the #rench $%th century physicist who discovered it you can create the Peltier effect

yourself using a battery two pieces of copper wire and a piece of bis!uth or iron wire. &ttach the copper

wires to the two poles of the battery and then connect the bis!uth or iron wire between the two pieces of

copper wire. (he bis!uth)iron and copper have to be touching ** it's this connection that causes the

Peltier effect.+

(he ,unction where current flows fro! copper to bis!uth will start to get hot and the ,unction where

current flows fro! bis!uth to the copper ,unction will get cold. (he !a-i!u! te!perature drop is about

/ degrees #ahrenheit 00.0 degrees Celsius+ fro! the a!bient te!perature at the hot ,unction.

&s you'd e-pect in an electric cooler the hot ,unction is placed outside the unit and the cold ,unction is

placed inside. (o a!plify the effect coolers contain lots and lots of ,unctions.

Electric coolers aren't the only unique inventions out there designed to chill your lunch. Solar poweredrefrigerators are another option. If you plan to spend ti!e ca!ping or want to start your own hot dog

stand+ you !ay want chilled beverages but not have the electricity to power a standard refrigerator. 1y

now you won't be surprised that a nu!ber of energy solutions can provide power to refrigeration

syste!s. In a solar powered refrigerator a si!ple solar panel does the honors. 2sing the sun's rays to

!ake so!ething cold3 "ow that's ingenious

.

Cold Packs

!pea"ing o* re*rigeration and coldness' have you ever used one o* those Kinstantcold pac"sK that loo"s li"e a plastic bag flled with li,uid. )ou hit it' sha"e it up and it

gets etremely cold. What-s going on here

The li,uid inside the cold pac" is water. n the water is another plastic bag or tube

containing ammoni)m-nitrate fertili7er. When you hit the cold pac"' it brea"s

the tube so that the water mies with the *ertilier. This miture creates
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an endothermicreaction ## it absorbs heat. The temperature o* the solution *alls to

about B> ; *or 10 to 1> minutes.

How Water Heaters Work

A gas heater looks like an electric )nit1 except that it doesn(t contain the

two heating elements* +t has a gas &)rner at the &ottom1 with the chimne

r)nning )p thro)gh the middle of the tank*

The watercoming into your home ma"es a :ourney through a system o* pipes' and

it-s usually cold or cool' depending on the time o* year. To have water warm enough

to ta"e a hot shower or bath' or use your dishwasheror washing machine' you need

a water heater.

Water heaters are *amiliar ftures in most homes. They typically loo" li"e big metal

cylinders' tall drums that are o*ten consigned to a laundry room or basement.

(ewer styles have some interesting *eatures' li"e losing the tan" completely in *avor

o* water#on#demand' but the old' reliable water heater design that-s most widely

used in the D.!. today is really a pretty simple applianceM it-s basically a drum flled

with water and e,uipped with a heating mechanism on the bottom or inside.


22/40

n the net pages' we-ll get into a little hot water and ta"e a closer loo" at what-s

really going on in that big steel can o* a water heater in your basement.

+nside a Water Heater

$et-s ta"e a ,uic" loo" at the components that wor" together in your waterheater to

ma"e your morning shower so satis*ying3

Tank -The inner shell o* a water heater is a heavy metal tan" containing a

water protective liner that holds =0 to @0 gallons 41>1 to 22? liters5 o* hot

water at around >0 to 100 pounds per s,uare inch 4%!5' within the pressure

range o* a typical residential water system. The eterior o* the tan" is

covered in an insulating material li"e polyurethane *oam. 8ver that' there-s a

decorative outer shell and possibly an additional insulating blan"et

8ip t)&e -Water enters the water heater through the dip tube at the top o*

the tan" and travels to the tan" bottom where it-s then heated.

Sh)t-o" valve -The shut#o valve stops water 6ow into the water heater. t-s

a separate component *rom the heater located outside and above the unit.

Heat-o)t pipe -!uspended toward the top o* the tan"-s interior' the heat#out

pipe allows the hot water to eit the water heater.

Thermostat -This is a thermometer# and temperature#control device. !ome

electric water heaters have a separate thermostat *or each element.

Heating mechanism -


23/40

water heater-s thermostatcontrols the temperature o* the water inside the tan".

(ormally' you can set the temperature anywhere between 120 and 1A0 degrees

;ahrenheit 4=9 to A2 degrees Celsius5. The water temperature setting recommended

by most manu*acturers is between 120 to 1=0 degrees ;ahrenheit 4=9 to @0 degrees

Celsius5. This is hot enough to be e+cient *or household use' but not so hot that it

can pose a scalding ris". * there are children living in your home' it-s wise to staycloser to the lower end o* the range.

!etting your water heater to a lower temperature saves energy' too' and i* you

remember to dial bac" the heat when you go on vacation' you-ll eperience even

more energy savings. Dsually' the thermostat is located underneath a protective

cover plate and has a "nob or dial you can turn to set the temperature.

The dip t)&e*eeds cold water *rom your home-s water lines to the bottom o* the

tan"-s interior' where the water starts to warm up. The heating mechanism' either

a burner or an element' stays on until the water reaches temperature. s the water

heats' it rises to the top o* the tan". The heat-o)t pipeis located near the top o*the tan". Water eiting the water heater at the top is always the hottest in the tan"

at any given moment because it-s the nature o* hot water to rise above denser' cold

water.

The secret to a water heater-s design *or separating cold' incoming water *rom hot'

outgoing water is that it relies on the principle that heat rises to do the hard part.

The position o* the heat#out pipe at the top o* the tan" does the rest.

How +cemakers Work

A standard home icemaker that o) install in o)r free7er

8nly a century ago' ice was hard to come by in most parts o* the world. n

hotter climates' you had to buy your ice *rom a delivery service' which imported
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he*ty bloc"s *rom a colder climate or *rom an industrial re*rigeration plant. The price

o* ice was relatively steep' but i* you wanted to "eep your *ood cold' you didn-t have

much choice. n the hottest parts o* the world' ice was a rare luury. n an e,uatorial

country' you might live your whole li*e and never even see a piece o* ice.

This all changed in the early 20th century. Compact' aordable re*rigeratorsbroughtthe means o* *ood preservationand ice production into the home and corner store.

n the 19@0s' new automatic icema"er machines made li*e even easier. These days'

most mericans ta"e ice completely *or granted' even during the hottest days o*

summer.

n this article' we-ll fnd out what-s inside a typical home icema"er' as well as the

larger commercial icema"ers you might fnd at a hotelor grocery store. s we-ll see'

the basic process o* ma"ing ice is very simple ## you :ust *reee water ## but spitting

out per*ectly shaped ice cubes is a *airly elaborate process.

The home icema"er-s predecessor was the plastic ice tray. t-s *airly obvious how

this device wor"s3 )ou pour water into a mold' leave it in the *reeer until it turns to

a solid and then etract the ice cubes. n icema"er does eactly the same thing'

but the process o* pouring water and etracting cubes is *ully automated. home

icema"er is an ice#cube assembly line.

The home icemaker is a miniat)re ice-c)&e assem&l line*

Eost icema"ers use an electric motor' an electrically operated water valve and an

electrical heating unit. To provide power to all these elements' you have to hoo" the

icema"er up to the electrical circuit powering your re*rigerator. )ou also have to

hoo" the icema"er up to the plumbing line in your house' to provide *resh water *or

the ice cubes. The power line and the water#inta"e tube both run through a hole in

the bac" o* the *reeer.
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2aking +ce

When everything is hoo"ed up' the icema"er begins its ccle. The cycle is usually

controlled by a simple electrical circuit and a series o* switches. n the diagram

below' you can see how the icema"er moves through its cycle.

t the beginning o* the cycle' a timed switch in the circuit brie6y sends

current to a solenoid water valve. n most designs' the water valve is

actually positioned behind the re*rigerator' but it is connected to the central

circuit via electrical wires. When the circuit sends current down these wires'

the charge moves a solenoid 4a type o* electromagnet5' which opens the

valve.

The valve is only open *or about seven secondsM it lets in :ust enough water to

fll the ice mold. The ice mold is a plastic well' with several connected

cavities. Typically' these cavities have a curved' hal*#circle shape.


26/40

cycle is interrupted. This "eeps the icema"er *rom flling your entire *reeer

with iceM it will only ma"e more cubes when there is room in the collection

bin.

This system is eective *or ma"ing ice at home' but it doesn-t produce enough ice

*or commercial purposes' such as restaurants and sel*#service hotel ice machines. nthe net section' we-ll loo" at a larger' more power*ul icema"er design.

Commercial +cemakers

There are any numbers o* ways to confgure a large' *ree#standing icema"er ## all

you need is a re*rigeration system' a water supply and some way o* collecting the

ice that *orms.

8ne o* the simplest pro*essional systems uses a large metal ice#cube tray'

positioned vertically. )ou can see how this system wor"s in the diagram below.

n this system' the metal ice tray is connected to a set o* coiled heat-exchangingpipesli"e the ones on the bac" o* your re*rigerator. * you-ve read How

/e*rigerators Wor"' then you "now how these pipes wor". compressor drives a

stream o* re*rigerant 6uid in a continuous cycle o* condensation and epansion.

&asically' the compressor *orces re*rigerant through a narrow tube 4called

the condenser5 to condense it' and then releases it into a wider tube 4called

the evaporator5' where it can epand.

Compressing the re*rigerant raises its pressure' which increases its temperature. s

the re*rigerant passes through the narrow condenser coils' it loses heat to the

cooler air outside' and it condensesinto a li,uid. When the compressed 6uid

passes through the expansion valve' it evaporates ## it epands to become a gas.This evaporation process draws in heat energy *rom the metal pipes and the air

around the re*rigerant. This cools the pipes and the attached metal ice tray.

The icema"er has a water pump' which draws water *rom a collection s)mpand

pours it over the chilled ice tray. s the water 6ows over the tray' it gradually

*reees' building up ice cubes in the well o* the tray. When you *reee water layer by

layer this way' it *orms clear ice. When you *reee it all at once' as in the home

icema"er' you get cloudy ice.

*ter a set amount o* time' the icema"er triggers a solenoid valveconnected to

the heat#echanging coils. !witching this valve changes the path o* the re*rigerant.The compressor stops *orcing the heated gas *rom the compressor into the narrow

condenserM instead' it *orces the gas into a wide &pass t)&e. The hot gas is cycled

bac" to the evaporator without condensing. When you *orce this hot gas through the

evaporator pipes' the pipes and the ice tray heat up rapidly' which loosens the ice

cubes.
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Typically' the individual cube cavities are slantedso the loosened ice will slide out

on their own' into a collection bin below. !ome systems have a clinder

pistonthat gives the tray a little shove' "noc"ing the cubes loose.

This sort o* system is popular in restaurants and hotels because it ma"es ice cubes

with a standard shape and sie. 8ther businesses' such as grocery stores andscientifc research frms' need smaller ice ;akes *or pac"ing perishable items. We-ll

loo" at 6a"e icema"ers net.

6lake +cemakers

n the last section' we loo"ed at a standard cube icema"er design. ;la"e icema"ers

wor" on the same basic principle as cube icema"ers' but they have an additional

component3 the ice cr)sher. )ou can see how a typical 6a"e system wor"s in the

diagram below.

$i"e the cube icema"er design we eamined in the last section' this machine uses a

set o* heat#echanging coils and a stream o* water to build up a layer o* ice. &ut in

this system' the coils are positioned inside a large metal clinder. Water passes

through the cylinder' as well as around its outer edges. The passing water gradually

builds up a large column o* ice surrounding the cylinder *rom the inside and outside.

s with a cube icema"er' a solenoid valve releases hot gas into the cooling pipes

a*ter a set length o* time. This loosens the ice column so it *alls into the ice crusher

below. The ice crusher brea"s the ice cylinder into small pieces' which pass on to a

collection bin.

The sie o* the ice bits depends on the crusher mechanism. !ome crushers grind

the ice into fne 6a"es' while other crushers produce larger' irregularly shaped ice

chun"s.

There are many variations on these designs' but the basic idea in all o* them is the

same. re*rigeration system builds up a layer o* ice' and a harvestingsystem

e:ects the ice into a collection bin. t the most basic level' this is all there is to any

icema"er.

How 6ree7ers Work


28/40

6ree7ers have long &een )sed to preserve food1 &)t how does it work to

keep o)r food from spoiling'

(early every modern merican home has a *reeer' most li"ely attached to a

re*rigerator. &ut why do we *reee *ood To store *or later the *ood we wouldn-t be

able to get to in a couple o* days i* we put it in the re*rigerator. !o that huge pot o*

bee* stew goes into the *reeer' alongside that revolutionary 20th century invention3

the *roen dinner.

&ut the need to store *ood *or later ## or to create ice *or "eeping drin"s cooled ## is

*ar older than le*tovers andTF dinners. t goes bac" about as *ar as civiliation itsel*.

Thousands o* years ago' ancient Eesopotamians discovered that cold *ood rotted

more slowly than *ood le*t outside Isource3 !hepherdJ. !o' they dug big pits into the

ground' insulated them with straw or sand' and then topped them with ice and snow

*rom the nearest mountains. These pits' or ice caves' were used to preserve the

*ood *or two or three wee"s at a time. Eesopotamians understood that warm air

*rom outside could prevent the snow *rom cooling the *ood' so the entrance was

"ept small and narrow to prevent air seepage.

This was how *ood was preserved *or centuries until about the late 1@00s' when


29/40

&y then' science and industry had established the idea o* mechanical re*rigeration'

in which a circulating chemical gas "ept things in a compartment cold. That-s why

today-s mechanically circulated vapor#driven *reeers are a little more complicated

4and e+cient5 than hollowed#out ice caves flled up with mountain snow. Dp net'

we-ll fnd out how several scientifc discoveries led up to the creation o* the modern

*reeer we use today.

8evelopment of the 2odern 6ree7er

&acteria are usually the cause o* *ooddecay' but they can-t grow as well or at all in

*reeing temperatures' which are at B2 degrees ;ahrenheit 40 degrees Celsius5 or

lower. !o' *ood spoils more slowly i* you lower the li,uid inside it ##

the watermolecules ## to *reeing temperatures.

s scientists in the early 1A00s made related discoveries about the nature o*

temperature and the laws o* thermodynamics' it was then that the *ramewor" *or

artifcial temperature regulation *ell into place.

merican inventor Nacob %er"ins built upon the vapor absorption ideas set *orth by

inventor 8liver


30/40

2odern 6ree7ers

!o now you "now that vapor compression is the principle behind the *reeer. &ut

how eactly does it wor" t the core is a *ast#moving stream o* vapori7ed

refrigerant that goes through a cycle inside the *reeer.

To get an idea o* how it wor"s' picture a river as it winds through the mountains and

countryside en route to the ocean. 8nce it empties out' then it-s ta"en up by clouds'

turned into rain' and re#enters that river where it 6ows to the ocean again./e*rigerant 6ows and trans*orms *rom li,uid to gas and bac" in a similar way.

Today' some o* the most commonly used re*rigerants are H;Cs 4hydro

6uorocarbons5. 8ther re*rigerants' such as C;Cs 4chloro6uorocarbons5 and HC;Cs

4hydro chloro6uorocarbons5 are highly regulated ## and banned *rom use in many

products ## in the Dnited !tates since they were contribute to depleting the

atmospheric oone layerIsource3


31/40

condenser coils' it loses the heat but retains its high pressure. t is also converted

into a moderately warm temperature.

The now#li,uid re*rigerant-s inherent pressure pushes it through into the net

component3 the metering t)&e*This small structure regulates the vapor-s pressure

so it can head into the net component.

s the li,uid re*rigerant heads *rom the small metering tube into the

larger evaporator' its pressure drops suddenly' causing it to convert bac" into a

low#pressure vapor. The evaporator also absorbs the heat' which leads to a *reeing

cold vapor that "eeps the unit-s temperature cold enough *or *reeing your *ood.

The vapor then goes bac" to the compressor to begin the process anew.

Tpes of 6ree7ers

n your home' you probably have a re*rigerator7*reeer combination unit. Whether

you have a side#by#side *ridge7*reeer appliance' the "ind with the *reeer on top' or

one with the *reeer on the bottom' the dierences are *ew.


32/40

8pening it too o*ten and allowing too much warm room temperature air in'

which can shut down the *reeer elements that are built to process only cold

air

&loc"ing air 6ow by pushing the *reeer too close to a wall' which ma"es the

condenser coils act less e+ciently

Having a loose rubberseal around the door' which allows that pes"y room

temperature air in

&asically' in each o* these situations' warm air mies with sub#*reeing air. The

result is *rost. Eany newer#model *reeers have an automatic *rost prevention

*eature' which regulates temperatures to "eep the inside temperature consistently

where it needs to be. * you don-t have that *eature' here are some other ways to

prevent *rost3

!et your *reeer-s thermostat to 0 degrees ;ahrenheit ## not too much colder

or warmer Isource3 (CH;%J.

8pen it only when you need to' so as to not wear down the rubber seal

around the door.

* your *reeer has coils on the bac"' ma"e sure you have at least B inches

between the coils and the wall.

* you aren-t able to get rid o* *rost as *ast as it accumulates ## say your rubber seal

is shot' an epensive internal part is overwor"ed' or a coil is *ried ## it might be time

to get a replacement. Dp net' we-ll loo" at what you need to consider when it-s

time to purchase a new *reeer.

How Home Thermostats Work
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A programma&le thermostat is &)t one option for o)r heating and cooling

needs*

* you have specifc heating and cooling needs in order to be com*ortable then

you-ve probably spent a little time loo"ing at and operating your home thermostat.

This handy little device controls the heating and air#conditioningsystems in your

house ## the two pieces o* e,uipment that use the most energy' and the ones that

have the biggest impact on your com*ort and ,uality o* li*e. n these days o* rising

energy prices' you might be interested to see how your thermostat wor"s. &elieve it

or not' it-s surprisingly simple and contains some pretty cool technology.

n this article' we-ll ta"e apart a household thermostat and learn how it wor"s. We-ll

also learn a little about digital thermostats' tal"ing thermostats' telephone

thermostats and system oning.

Eodern thermostats are almost eclusively digital' but be*ore we get to those' let-s

ta"e a trip down memory lane and loo" at the parts o* a non#digital thermostat that

you might still fnd in older homes and motels. $et-s start with the merc)r

switch## a glass vial with a small amount o* actual mercury inside.Eercuryis a

li,uid metal ## it conducts electricityand 6ows li"e water. nside the glass vial are

three wires. 8ne wire goes all the way across the bottom o* the vial' so the mercury

is always in contact with it. 8ne wire ends on the le*t side o* the vial' so when thevial tilts to the le*t' the mercury contacts it ## ma"ing contact between this wire and

the one on the bottom o* the vial. The third wire ends on the right side o* the vial' so

when the vial tilts to the right' the mercury ma"es contact between this wire and

the bottom wire.

There are two thermometersin this "ind o* thermostat. The one in the cover

displays the temperature. The other' in the top layer o* the thermostat' controls the
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heating and cooling systems. These thermometers are nothing more than coiled

bimetallic strips. nd what-s that' you as" We-ll fnd out on the net page.

Thermometers and Switches

&imetallic stripis a piece o* metal made by laminating two dierent types o*

metal together. The metals that ma"e up the strip epand and contract when

they-re heated or cooled.


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s soon as the switch tips to the le*t' current 6ows through the mercury in the

mercury switch. This current energies a relaythat starts the heaterand circulation

*an in your home. s the room gradually heats up' the thermometer coil gradually

unwinds until it tips the mercury switch bac" to the right' brea"ing the circuit and

turning o the heat.

When the mercury switch tips to the right' a relay starts the air conditioner. s the

room cools' the thermometer coil winds up until the mercury switch tips bac" to the

le*t.

Thermostats have another cool device called a heat anticipator. The heat

anticipator shuts o the heater be*ore the air inside the thermostat actually reaches

the set temperature. !ometimes' parts o* a house will reach the set temperature

be*ore the part o* the house containing the thermostat does. n this case' the

anticipator shuts the heater o a little early to give the heat time to reach the

thermostat.

The loop o* wire above is a "ind o* resistor. When the heater is running' the current

that controls the heater travels *rom the mercury switch' through the yellow wire to

the resistive loop. t travels around the loop until it gets to the wiper' and *rom

there it travels through the hub o* the anticipator ring and down to the circuit board

on the bottom layer o* the thermostat. The *arther the wiper is positioned 4moving

cloc"wise5 *rom the yellow wire' the more o* the resistive wire the current has to

pass through. $i"e any resistor' this one generates heat when current passes

through it. The *arther around the loop the wiper is placed' the more heat is

generated by the resistor. This heat warms the thermometer coil' causing it to

unwind and tip the mercury switch to the right so that the heater shuts o.

(et' we-ll ta"e a more detailed loo" at the electricalcircuits in the thermostat.

Wired

This thermostat is designed *or a system with fve wires ## the wire terminations are

mar"ed as *ollows3

$H# This wire comes *rom the 2=FC trans*ormer on the heating system.

$C# This wire comes *rom the 2=FC trans*ormer on the air#conditioning

system.

W# This wire comes *rom the relay that turns on the heating system.

=# This wire comes *rom the relay that turns on the cooling system.

## This wire comes *rom the relay that turns on the *an.
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The two trans*ormers provide the power the thermostat uses to switch on the

various relays. The relays in turn switch on the power to the *an and the air

conditioneror *urnace. $et-s see how this power 6ows through the thermostat when

the air conditioner is running.

%ower *rom the air#conditioning trans*ormer comes into the terminal labeled /C. Theball controlled by the mode switch :umps the current onto a trace that leads to the

terminal in the lower#right corner o* the circuit board.

This terminal connects to the top layer o* the thermostat through a screw. t

connects to the pin" wire' which leads to the bottom wire in the mercury switch. *

the switch is tilted to the right 4as it would be i* the air conditioning were on5' the

current travels through the mercury into the blue wire.

Through a screw' the blue wire 4see above5 connects to a lug in the lower#le*t corner

o* the circuit card.

;rom there' it goes through a trace on the circuit card to the other branch o* the

mode switch. The ball in the mode switch :umps the current onto a trace that

connects to the terminal mar"ed L' which energies the *an' and the terminal

mar"ed )' which energies the air conditioning.

8igital thermostatsuse a simple device called a thermistorto measure

temperature. This is a resistor which allows electricalresistance changes with

temperature. The microcontrollerin a digital thermostat can measure the resistance

and convert that number to an actual temperature reading.

digital thermostat can do a *ew things that a regular mechanical thermostat

cannot. 8ne o* the most use*ul *eatures o* a digital thermostat is programmable

settings. n the winter' you can program it to automatically turn up the heat *or an

hour or two in the morning while you get ready *or wor"' turn down the heat until

you get home' turn up the heat in the evening and then turn down the heat while

you sleep. This is a great money#saving *eature because you can simply turn down

the heat when it isn-t needed.

Sstem >oning

lot o* times' there are rooms in your housethat are always warmer or colder than

others are. There can be many eplanations *or this. ;or one' heat rises' so rooms

on second or third 6oors are o*ten too warm. n turn' basement rooms are typicallytoo cold. /ooms with vaulted ceilings have a di+cult time retaining heat' while

rooms that receive long hours o* sunlightare o*ten di+cult to cool down. These are

:ust a *ew reasons' but regardless o* why a room-s temperature is uncom*ortable'

there-s only one surefre way to even out your house-s temperature3 system oning.

Sstem 7oningis pretty simple. t involves multiple thermostats that are wired to a

control panel' which operates dampers within the ductwor" o* your *orced#air
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system. The thermostats constantly read the temperature o* their specifc one'

then open or close the dampers within the ductwor" according to the thermostat-s

settings. (ot only is system oning help*ul *or houses with inconsistent room

temperatures' but it-s also great *or heating or cooling individual bedrooms based

on the desired temperature setting. * you have a usually empty guest room' :ust

shut the door and close the damper.

* used properly' system oning can help you save money on your energy bills.

ccording to the D.!. epartment o*


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plenum tubing

trans*ormer

fre rated tape

control limit switch

6e dampers

The number o* ones your home needs will aect the way you set up the system. n

a two#one system' with the ones being *airly e,ual in sie' each one-s ductwor"

must be capable o* handling up to ?0 percent o* the total C;E 4cubic *eet per

minute5 o* air produced by your HFC system. n a three#one system' the ones

need to be as close in total area as possible. n this case' each one-s ductwor"

should be able to handle up to >0 percent o* the total C;E. nstalling a *our#one

system re,uires a bit more wor". The ducts need to be enlarged by one inch' and

they re,uire a static pressure relie* damper and high# and low#limit protection. Toavoid ma:or damage' be sure not to completely cut o the air6ow over the heat

echanger or coil o* your HFC system.

Talking Thermostats

Tal"ing thermostats may seem li"e one o* those unnecessary *uturistic inventions

straight out o* an episode o* KThe Netsons'K but they-re actually ,uite practical *or

senior citiens' people who are visually impaired or blind' and other people with

special needs. Tal"ing thermostats announce the time' day' temperature setting and

room temperature' plus they have audio instructions *or setup.


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sent through application-speci9c integrated circ)its' or !C!' and the

thermostat reacts in real time.

&ecause tal"ing thermostats are high#end' cutting#edge accessories to heating and

cooling systems' they come e,uipped with all o* the user#*riendly *unctions that

other ,uality thermostats boast. built#in time#delay *unction "eeps your system*rom immediately starting or stopping i* it-s accidentally ad:usted. !topping and

starting HFC systems puts a lot o* wear and tear on the compressor' which is the

most epensive part o* the system' so the delay *unction is ,uite important. Tal"ing

thermostats are also programmable' which allows you to heat or cool your home

only when it-s necessary.

Telephone Thermostats

)ou-re pretty *ortunate i* you-re able to own a vacation home' but it also means

you-ll be paying to heat and cool two houses. %rogrammable home thermostats can

actually allow you to "eep the heat or air turned o until the day you arrive' but it

re,uires precise planning o* your comings and goings in order to get the desired

result. Telephone thermostats' on the other hand' allow you to heat or cool your

home with a simple phone call.

Telephonethermostats replace your eisting home thermostats. They connect to

both the heating and cooling system and to your phone line. )ou simply have to call

your property and enter a password on a touch#tone phone to access the controls.

Then' you can ad:ust not only the temperature setting but the entire system mode

as well.

Telephone thermostats can handle these *unctions because they use

digital microprocessorsas well as a touch#tone detector and telephone inter*ace

module.


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how compasses work 10 by nafees

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