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DOE/GO-10099-379FS 206

June 1999ENERGYEFFICIENCY Energy-Efficient

AND

RENEWABLE Air Conditioning C L E A R I N

G H O U S E

ENERGYAre you considering buying a new air

conditioner? Or, are you dissatisfied withthe operation of your current air conditioner? Are you unsure whether to fix orreplace it? Are you concerned about highsummer utility bills? If you answered yesto any of these questions, this publicationcan help. With it, you can learn aboutvarious types of air conditioning systemsand how to maintain your air conditioner,hire professional air conditioning services,select a new air conditioner, and ensurethat your new air conditioner is properlyinstalled.

Understanding Air Conditioners

Many people buy or use air conditioners

without understanding their designs,

components, and operating principles.

Proper sizing, selection, installation,

maintenance, and correct use are keys to

cost-effective operation and lower overall

costs.

This publication discusses both central

and room air conditioners. Heat pumps,which provide both home cooling and

heating, are not covered in this publica

tion. Contact the Energy Efficiency and

Renewable Energy Clearinghouse

(EREC–see Source List below) for more

information about heat pumps of all kinds.

How Air Conditioners Work

Air conditioners employ the same operating principles and basic components asyour home refrigerator. An air conditioner

cools your home with a cold indoor coilcalled the evaporator. The condenser, a hotoutdoor coil, releases the collected heatoutside. The evaporator and condensercoils are serpentine tubing surrounded byaluminum fins. This tubing is usuallymade of copper. A pump, called thecompressor, moves a heat transfer fluid(or refrigerant) between the evaporatorand the condenser. The pump forces the

H O T A I R

C O O L A I R

Air Conditioning

Evaporator coil

Condenser coil

Compressor

The fluid that collects heat at the evaporator and releases it at the condenser is called refrigerantA pump, called the compressor, forces the refrigerant through the circuit of tubing and fins inthe coils. Air moves through the tiny spaces between the fins and is cooled by the refrigerant inthe coils.

T O F E N E R G Y

D E P A R T M

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S T A T S O F A

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This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory.

The document was produced by the Information Services Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiency

and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on

information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC.

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

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refrigerant through the circuit of tubingand fins in the coils. The liquid refrigerantevaporates in the indoor evaporator coil,pulling heat out of indoor air and therebycooling the home. The hot refrigerant gasis pumped outdoors into the condenserwhere it reverts back to a liquid giving upits heat to the air flowing over the

condenser’s metal tubing and fins.

Types of Air Conditioners

The basic types of air conditioners areroom air conditioners, split-system centralair conditioners, and packaged central airconditioners.

Room Air Conditioners

Room air conditioners cool rooms ratherthan the entire home. If they provide cooling only where they're needed, room air

conditioners are less expensive to operatethan central units, even though theirefficiency is generally lower than that ofcentral air conditioners.

Smaller room air conditioners (i.e., thosedrawing less than 7.5 amps of electricity)can be plugged into any 15- or 20-amp,115-volt household circuit that is notshared with any other major appliances.Larger room air conditioners (i.e., thosedrawing more than 7.5 amps) need theirown dedicated 115-volt circuit. Thelargest models require a dedicated230-volt circuit.

Room air conditioners are installed directly in windows or walls, which meansthey have no ductwork. The evaporator ’s fan faces indoors, while the condenser’sfan faces outdoors.

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Room Air Conditioner

Cabinet cover

Condenser

Filter

Condenser fan

Evaporator fan

Evaporator

Central Air Conditioners

Central air conditioners circulate cool airthrough a system of supply and returnducts. Supply ducts and registers (i.e.,openings in the walls, floors, or ceilingscovered by grills) carry cooled air from theair conditioner to the home. This cooledair becomes warmer as it circulatesthrough the home; then it flows backto the central air conditioner throughreturn ducts and registers. A central airconditioner is either a split-system unit ora packaged unit.

In a split-system central air conditioner,an outdoor metal cabinet contains thecondenser and compressor, and an indoorcabinet contains the evaporator. In manysplit-system air conditioners, this indoorcabinet also contains a furnace or the

indoor part of a heat pump. The airconditioner’s evaporator coil is installedin the cabinet or main supply duct of thisfurnace or heat pump. If your homealready has a furnace but no airconditioner, a split-system is the mosteconomical central air conditioner to install

In a packaged central air conditioner, theevaporator, condenser, and compressorare all located in one cabinet, whichusually is placed on a roof or on a concreteslab next to the house’s foundation. This

type of air conditioner also is used insmall commercial buildings. Air supplyand return ducts come from indoorsthrough the home’s exterior wall or roof toconnect with the packaged air conditioner,which is usually located outdoors. Packaged air conditioners often include electricheating coils or a natural gas furnace. Thiscombination of air conditioner and centralheater eliminates the need for a separatefurnace indoors.

Maintaining ExistingAir Conditioners

Older air conditioners may still be able tooffer years of relatively efficient use.However, making your older air conditioner last requires you to perform properoperation and maintenance.

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R E T U R N A I R

A I R

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g e r

Packaged Air Conditioner

Condenser

Evaporator

Air Conditioning Problems

One of the most common air conditioningproblems is improper operation. If your airconditioner is on, be sure to close yourhome’s windows and outside doors.

Other common problems with existing airconditioners result from faulty installation,poor service procedures, and inadequatemaintenance. Improper installation of yourair conditioner can result in leaky ductsand low air flow. Many times, the refrigerant charge (the amount of refrigerant in thesystem) does not match the manufacturer’sspecifications. If proper refrigerant chargingis not performed during installation, theperformance and efficiency of the unit isimpaired. Service technicians often fail tofind refrigerant charging problems or evenworsen existing problems by adding refrig

erant to a system that is already full. Airconditioner manufacturers generally makerugged, high quality products. If your air

A packaged air conditioner sits outside the house next to the foundation or on the conditioner fails, it is usually for one of theroof. Its cabinet contains the evaporator, condenser, compressor, and all other parts common reasons listed below:of the air conditioner. Supply and return ducts connect to this outdoor cabinet.

• refrigerant leaks. If your air conditioner

Evaporative Coolers

An evaporative cooler (also called a “swamp cooler”) is a completely differenttype of air conditioner that works well in hot, dry climates.

These units cool outdoor air by evaporation and blow it inside the building,causing a cooling effect much like the process when evaporating perspirationcools your body on a hot (but not overly humid) day. When operating anevaporative cooler, windows are opened part way to allow warm indoor airto escape as it is replaced by cooled air.

Evaporative coolers cost about one-half as much to install as central air conditioners and use about one-quarter as much energy. However, they requiremore frequent maintenance than refrigerated air conditioners and they’resuitable only for areas with low humidity.

Evaporative coolers cost about half as much as central air conditioners and

use about 25% less energy.

Evaporative Cooler

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is low on refrigerant, either it wasundercharged at installation, or it leaks.If it leaks, simply adding refrigerant isnot a solution. A trained technicianshould fix any leak, test the repair, andthen charge the system with the correct

amount of refrigerant. Remember thatthe performance and efficiency of yourair conditioner is greatest when therefrigerant charge exactly matches themanufacturer’s specification, and isneither undercharged nor overcharged.

• inadequate maintenance. If you allowfilters and air conditioning coils to become dirty, the air conditioner willnot work properly, and the compressoror fans are likely to fail prematurely.

• electric control failure. The compressorand fan controls can wear out, especially

when the air conditioner turns on andoff frequently, as is common when asystem is oversized. Because corrosionof wire and terminals is also a problemin many systems, electrical connectionsand contacts should be checked duringa professional service call.

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The most important

maintenance task

that will ensure the

efficiency of your air

conditioner is to

routinely replace or

clean its filters.

Regular Maintenance

An air conditioner’s filters, coils, and finsrequire regular maintenance for the unit tofunction effectively and efficientlythroughout its years of service. Neglectingnecessary maintenance ensures a steadydecline in air conditioning performance

while energy use steadily increases.

Air Conditioner Filters

The most important maintenance task thatwill ensure the efficiency of your air conditioner is to routinely replace or clean itsfilters. Clogged, dirty filters block normalair flow and reduce a system’s efficiencysignificantly. With normal air flow obstructed,air that bypasses the filter may carry dirtdirectly into the evaporator coil andimpair the coil’s heat-absorbing capacity.Filters are located somewhere along the

return duct’s length. Common filterlocations are in walls, ceilings, furnaces, orin the air conditioner itself.

Some types of filters are reusable; othersmust be replaced. They are available in avariety of types and efficiencies. Clean orreplace your air conditioning system’s filteror filters every month or two during thecooling season. Filters may need morefrequent attention if the air conditioner isin constant use, is subjected to dusty

conditions, or you have fur-bearing petsin the house.

Air Conditioner Coils

The air conditioner’s evaporator coil andcondenser coil collect dirt over theirmonths and years of service. A clean filterprevents the evaporator coil from soilingquickly. In time, however, the evaporatorcoil will still collect dirt. This dirt reducesair flow and insulates the coil which

reduces its ability to absorb heat.Therefore, your evaporator coil should bechecked every year and cleaned asnecessary.

Outdoor condenser coils can also becomevery dirty if the outdoor environment isdusty or if there is foliage nearby. You can

easily see the condenser coil and notice ifdirt is collecting on its fins.

You should minimize dirt and debris nearthe condenser unit. Your dryer vents,falling leaves, and lawn mower are allpotential sources of dirt and debris.Cleaning the area around the coil, removingany debris, and trimming foliage back atleast 2 feet (0.6 meters) allow for adequateair flow around the condenser.

Coil Fins

The aluminum fins on evaporator andcondenser coils are easily bent and can block air flow through the coil. Airconditioning wholesalers sell a tool calleda “fin comb” that will comb these fins back into nearly original condition.

Sealing and Insulating Air Ducts

An enormous waste of energy occurswhen cooled air escapes from supplyducts or when hot attic air leaks into

return ducts. Recent studies indicate that10% to 30% of the conditioned air in anaverage central air conditioning systemescapes from the ducts.

For central air conditioning to be efficient,ducts must be airtight. Hiring a competentprofessional service technician to detectand correct duct leaks is a good investment,since leaky ducts may be difficult to findwithout experience and test equipment.

Duct Leakage at Seams and Registers

Leakage at registers

Leakage at seams

Air from hot attics can leak into the home around registers of the duct system. Air in the ductscan leak out through holes and seams.

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Ducts must be sealed with duct “mastic.”The old standby of duct tape is ineffectivefor sealing ducts.

Obstructions can impair the efficiency of aduct system almost as much as leaks. Youshould be careful not to obstruct the flowof air from supply or return registers with

furniture, drapes, or tightly fitted interiordoors. Dirty filters and clogged evaporatorcoils can also be major obstructions to airflow.

The large temperature difference betweenattics and ducts makes heat conductionthrough ducts almost as big a problem asair leakage and obstructions. Ducts inattics should be insulated heavily inaddition to being made airtight.

Using Your Air ConditionerAn air conditioner will cool the air in your home fairly quickly. For economicaloperation, turn it on only when your home is occupied. You may considerinstalling a programmable thermostat. These allow you to set the time whenthe air conditioner will turn on, such as 30 minutes before you arrive homefrom work on a hot day. Contact EREC (see Source List) for the fact sheet

Automatic and Programmable Thermostats. During the day, keep the drapes or blinds closed on windows that face east, south, and west. This will help reducesolar heat gain into your home.

Buying New Air Conditioners

Today’s best air conditioners use 30% to 50%

less energy to produce the same amountof cooling as air conditioners made in themid 1970s. Even if your air conditioner isonly 10 years old, you may save 20% to 40%of your cooling energy costs by replacingit with a newer, more efficient model.

Sizing Air Conditioners

Air conditioners are rated by the numberof British Thermal Units (Btu) of heat theycan remove per hour. Another commonrating term for air conditioning size is the“ton,” which is 12,000 Btu per hour.

How big should your air conditioner be?The size of an air conditioner depends on:

• how large your home is and how manywindows it has;

• how much shade is on your home’swindows, walls, and roof;

• how much insulation is in your home’sceiling and walls;

• how much air leaks into your homefrom the outside; and

• how much heat the occupants andappliances in your home generate.

An air conditioner’s efficiency, performance,durability, and initial cost depend onmatching its size to the above factors.

Make sure you buy the correct size of airconditioner. Two groups—the Air Conditioning Contractors of America (ACCA)and the American Society of Heating,Refrigerating, and Air ConditioningEngineers (ASHRAE)—publish calculationprocedures for sizing central air conditioners. Reputable air conditioning contractorswill use one of these procedures, oftenperformed with the aid of a computer, tosize your new central air conditioner.

Be aware that a large air conditioner willnot provide the best cooling. Buying anoversized air conditioner penalizes you inthe following ways.

• It costs more to buy a larger airconditioner than you need.

• The larger-than-necessary air conditioner cycles on and off more frequently,reducing its efficiency. Frequent cyclingmakes indoor temperatures fluctuatemore and results in a less comfortable

environment. Frequent cycling alsoinhibits moisture removal. In humidclimates, removing moisture is essentialfor acceptable comfort. In addition, thiscycling wears out the compressor andelectrical parts more rapidly.

• A larger air conditioner uses moreelectricity and creates added demandson electrical generation and deliverysystems.

Air Conditioner Efficiency

Each air conditioner has an energy-efficiency rating that lists how many Btuper hour are removed for each watt ofpower it draws. For room air conditioners,this efficiency rating is the EnergyEfficiency Ratio, or EER. For central airconditioners, it is the Seasonal EnergyEfficiency Ratio, or SEER. These ratingsare posted on an Energy Guide Label,which must be conspicuously attached toall new air conditioners. Many air conditioner manufacturers are participants in

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The higher

initial cost of an

energy-efficient

model will be repaid

to you several times

during its life span.

the voluntary EnergyStar® labelingprogram (see Source List in this publication).EnergyStar-labeled appliances mean thatthey have high EER and SEER ratings.

In general, new air conditioners withhigher EERs or SEERs sport higher pricetags. However, the higher initial cost of an

energy-efficient model will be repaid toyou several times during its life span.Your utility company may encourage thepurchase of a more efficient air conditioner by rebating some or all of the pricedifference. Buy the most efficient airconditioner you can afford, especially ifyou use (or think you will use) an airconditioner frequently and/or if yourelectricity rates are high.

Room Air Conditioners—EER

Room air conditioners generally rangefrom 5,500 Btu per hour to 14,000 Btu perhour. National appliance standardsrequire room air conditioners built after January 1, 1990, to have an EER of 8.0 orgreater. Select a room air conditioner withan EER of at least 9.0 if you live in a mildclimate. If you live in a hot climate, selectone with an EER over 10.

The Association of Home ApplianceManufacturers reports that the averageEER of room air conditioners rose 47%

from 1972 to 1991. If you own a 1970svintage room air conditioner with anEER of 5 and you replace it with a newone with an EER of 10, you will cut yourair conditioning energy costs in half.

Central Air Conditioners—SEER

National minimum standards for centralair conditioners require a SEER of 9.7 and10.0, for single-package and split-systems,respectively. But you do not need to settlefor the minimum standard—there is a wideselection of units with SEERs reachingnearly 17.

Before 1979, the SEERs of central air conditioners ranged from 4.5 to 8.0. Replacinga 1970s-era central air conditioner witha SEER of 6 with a new unit having aSEER of 12 will cut your air conditioningcosts in half.

Hiring Professional Service

When your air conditioner needs morethan the regular maintenance describedpreviously, hire a professional servicetechnician. A well-trained technician willfind and fix problems in your air conditioning system. However, not all service

technicians are competent. Incompetentservice technicians forsake properdiagnosis and perform only minimal stopgap measures. Insist that the technician:

• check for correct amount of refrigerant;• test for refrigerant leaks using a leak

detector;• capture any refrigerant that must be

evacuated from the system, instead ofillegally releasing it to the atmosphere;

• check for and seal duct leakage incentral systems;

• measure air flow through the evaporatorcoil;

• verify the correct electric controlsequence and make sure that the heatingsystem and cooling system cannotoperate simultaneously;

• inspect electric terminals, clean andtighten connections, and apply a nonconductive coating if necessary;

• oil motors and check belts for tightnessand wear; and

• check the accuracy of the thermostat.

Choosing a Contractor

Choosing a contractor may be the mostimportant and difficult task in buying anew central air conditioning system. Askprospective contractors for recent referencesIf you are replacing your central airconditioner, tell your contractor what youliked and did not like about the oldsystem. If the system failed, ask thecontractor to find out why. The best timeto fix existing problems is when a newsystem is being installed.

When designing your new air conditioningsystem, the contractor you choose should:

• use a computer program or writtencalculation procedure to size the airconditioner;

• provide a written contract listing themain points of your installation thatincludes the results of the cooling loadcalculation;

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• give you a written warranty on equipment and workmanship; and

• allow you to hold the final paymentuntil you are satisfied with the newsystem.

Avoid making your decision solely onthe basis of price. The quality of the

installation should be your highestpriority, because quality will determineenergy cost, comfort, and durability.

Installation and Location ofAir Conditioners

If your air conditioner is installedcorrectly, or if major installation problemsare found and fixed, it will performefficiently for years with only minorroutine maintenance. However, manyair conditioners are not installed correctly.

As an unfortunate result, modern energy-efficient air conditioners can performalmost as poorly as older inefficient models.

Be sure that your contractor performs thefollowing procedures when installing anew central air conditioning system:

• allows adequate indoor space for theinstallation, maintenance, and repair ofthe new system, and installs an accessdoor in the furnace or duct to provide away to clean the evaporator coil.

• uses a duct-sizing methodology such asthe Air Conditioning Contractors ofAmerica (ACCA) Manual D.

• ensures there are enough supplyregisters to deliver cool air and enoughreturn air registers to carry warm houseair back to the air conditioner.

• installs duct work within the conditionedspace, not in the attic, wherever possible.

• seals all ducts with duct mastic andheavily insulates attic ducts.

• locates the condensing unit where itsnoise will not keep you or yourneighbors awake at night, if possible.

• places the condensing unit in a shadyspot, if possible, which can reduce yourair conditioning costs by 1% to 2%.

• verifies that the newly installed airconditioner has the exact refrigerantcharge and air flow rate specified by themanufacturer.

• locates the thermostat away from heatsources, such as windows, or supplyregisters.

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Insulating Ducts

All ducts should be insulated when they arelocated in attics or crawl spaces.

DUCT SEALANT

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Sealing Ducts

Reputable contractors seal all joints in bothnew and existing ducts with duct mastic.

If you are replacing an older or failed splitsystem, be sure that the evaporator coil isreplaced with a new one that exactlymatches the condenser coil in the newcondensing unit. (The air conditioner’s

efficiency will likely not improve if theexisting evaporator coil is left in place;in fact, the old coil could cause the newcompressor to fail prematurely.)

If you install a new room air conditioner,try to:

• locate the air conditioner in a windowor wall area near the center of the roomand on the shadiest side of the house.

• minimize air leakage by fitting the roomair conditioner snugly into its opening

and sealing gaps with a foam weatherstripping material.

Paying attention to your air conditioningsystem saves you money and reducesenvironmental pollution. Notice whetheryour existing system is running properly,and maintain it regularly. Or, if you needto purchase a new air conditioner, be sureit is sized and installed correctly and has agood EER or SEER rating.

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Source List Florida Solar Energy Center (FSEC)1679 Clear Lake Road

There are many groups offering information on air conditioning. Cocoa, FL 32922The following groups are just a few that can assist you in (407) 638-1000increasing your air conditioning efficiency. Some of these Fax: (407) 638-1010organizations provide only materials appropriate for www.fsec.ucf.eduprofessionals in the air conditioning industry.

FSEC provides information on building in hot, humidAir Conditioning and Refrigeration Institute (ARI)

climates.4301 N. Fairfax Drive, Suite 425Arlington, VA 22203

For more information about cooling and air conditioning, as(703) 524-8800Fax: (703) 528-3816 well as on a wealth of other energy-efficiency topics, contact:

www.ari.org The Energy Efficiency and Renewable EnergyARI represents manufacturers of air conditioning, Clearinghouse (EREC)refrigeration, and heating equipment and has consumer P.O. Box 3048 brochures on a variety of topics. Merrifield, VA 22116

(800) 363-3732 (800-DOE-EREC)Fax: (703) 893-0400

American Society of Heating, Refrigeration, and E-mail: [email protected] Conditioning Engineers (ASHRAE) www.eren.doe.gov/consumerinfo

1791 Tullie Circle, N.E.EREC provides free general and technical information toAtlanta, GA 30329the public on many topics and technologies pertaining(404) 636-8400to energy efficiency and renewable energy.Fax: (404) 321-5478

www.ashrae.org/

ASHRAE is organized solely for the purpose of Reading Listadvancing the arts and science of heating, ventilation,

The following publications provide more information onair conditioning, and refrigeration for the public’sair conditioning. The list does not cover all the available books, benefit through research, standards writing, continuingreports, and articles on air conditioning, nor is the mention ofeducation, and publications.any publication a recommendation or endorsement.

Air Conditioning Contractors of America (ACCA) ASHRAE Journal, American Society of Heating, Refrigerating1513 16th Street NWand Air Conditioning Engineers (ASHRAE),Washington, DC 200361791 Tullie Circle N.E., Atlanta, GA 30329-2305, monthly

(202) 483-9370 trade magazine.Fax: (202) 234-4721www.acca.org Consumer Guide to Home Energy Savings , A. Wilson and

J. Morrill, American Council for an Energy-EfficientThe Air Conditioning Contractors of America is the most

Economy, 1001 Connecticut Ave. NW, Suite 801,active and widely recognized organization representing

Washington, DC 20036, 1998.contractors in the heating, ventilation, air conditioning,and refrigeration (HVACR) industry. Home Energy, The Magazine of Residential Energy

Conservation, 2124 Kitteredge, #95, Berkeley, CA 94704,monthly trade magazine. For example, the May/June 1995

EnergyStar® Program issue had an article about properly sizing air conditioning1-888-STAR-YES systems.e-mail: [email protected] Consumer Reports, The Consumers Union of the Unitedwww.energystar.gov States, Inc., 101 Truman Avenue, Yonkers, NY 10703,ENERGY STAR®-labeled products, including heating (800) 234-1645 (subscriptions and back issues).

and cooling equipment, use less energy than other “Chill Out: A Guide to Air Conditioning,” (63:6)products and save you money on utility bills. These pp. 36-42, June 1998.products are made by all major manufacturers and areavailable at stores everywhere. “Cool It (Room/Window Air Conditioners)” (64:6)

pp. 35-37, June 1999.

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