Energy-Efficient Air Conditioning. Energy Efficiency And .

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Energy-EfficientAir ConditioningAre you considering buying a new airconditioner? Or, are you dissatisfied withthe operation of your current air condi tioner? 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 ConditionersMany people buy or use air conditionerswithout understanding their designs,components, and operating principles.Proper sizing, selection, installation,maintenance, and correct use are keys tocost-effective operation and lower overallcosts.This publication discusses both centraland room air conditioners. Heat pumps,which provide both home cooling andheating, are not covered in this publica tion. Contact the Energy Efficiency andRenewable Energy Clearinghouse(EREC–see Source List below) for moreinformation about heat pumps of all kinds.How Air Conditioners WorkAir conditioners employ the same operat ing principles and basic components asyour home refrigerator. An air conditionercools 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 theAir EWABLEENERGYDOE/GO-10099-379FS 206June 1999Evaporator coilCondenser coilNT OFMEENRTEREDThis 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 Efficiencyand Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based oninformation 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.MU N ITICAGYERDEPAThe fluid that collects heat at the evaporator and releases it at the condenser is called refrigerant.A 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.STAAT E S OFPrinted with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer wasteJohn KriggerHOTAIRCOOLCompressor

Central Air Conditionersrefrigerant 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 thecondenser’s metal tubing and fins.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.Types of Air ConditionersThe basic types of air conditioners areroom air conditioners, split-system centralair conditioners, and packaged central airconditioners.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 theindoor 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.Room Air ConditionersRoom air conditioners cool rooms ratherthan the entire home. If they provide cool ing only where they're needed, room airconditioners 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.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. Thistype 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. Pack aged air conditioners often include electricheating coils or a natural gas furnace. Thiscombination of air conditioner and centralheater eliminates the need for a separatefurnace indoors.Condenser fanEvaporator fanFilterMaintaining ExistingAir ConditionersCabinet coverCondenserJohn KriggerEvaporatorRoom Air ConditionerRoom 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.2Older air conditioners may still be able tooffer years of relatively efficient use.However, making your older air condi tioner last requires you to perform properoperation and maintenance.

Air Conditioning ProblemsOne of the most common air conditioningproblems is improper operation. If your airconditioner is on, be sure to close yourhome’s windows and outside doors.AIRRETURNAIROUTPUTPackaged Air ConditionerJohn KriggerEvaporatorCondenserA packaged air conditioner sits outside the house next to the foundation or on theroof. Its cabinet contains the evaporator, condenser, compressor, and all other partsof the air conditioner. Supply and return ducts connect to this outdoor cabinet.Evaporative CoolersAn evaporative cooler (also called a “swamp cooler”) is a completely differenttype of air conditioner that works well in hot, dry climates.John KriggerEvaporative CoolerEvaporative coolers cost about half as much as central air conditioners anduse about 25% less energy.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 condi tioners 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.3Other 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 refriger ant 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 airconditioner fails, it is usually for one of thecommon reasons listed below: refrigerant leaks. If your air conditioneris 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 correctamount 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 tobecome 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, especiallywhen 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.

Regular MaintenanceAn 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 performancewhile energy use steadily increases.maintenance taskthat will ensure theefficiency of your airconditioner is toroutinely replace orclean its filters.Air Conditioner FiltersThe most important maintenance task thatwill ensure the efficiency of your air con ditioner 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 thereturn 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 dustyconditions, or you have fur-bearing petsin the house.Outdoor condenser coils can also becomevery dirty if the outdoor environment isdusty or if there is foliage nearby. You caneasily 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 FinsThe aluminum fins on evaporator andcondenser coils are easily bent and canblock air flow through the coil. Airconditioning wholesalers sell a tool calleda “fin comb” that will comb these finsback into nearly original condition.Sealing and Insulating Air DuctsAir Conditioner CoilsAn enormous waste of energy occurswhen cooled air escapes from supplyducts or when hot attic air leaks intoreturn ducts. Recent studies indicate that10% to 30% of the conditioned air in anaverage central air conditioning systemescapes from the ducts.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 whichFor 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 RegistersLeakage at seamsLeakage at registersAir from hot attics can leak into the home around registers of the duct system. Air in the ductscan leak out through holes and seams.4John KriggerThe most importantreduces its ability to absorb heat.Therefore, your evaporator coil should bechecked every year and cleaned asnecessary.

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 withfurniture, 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 sheetAutomatic and Programmable Thermostats. During the day, keep the drapes orblinds closed on windows that face east, south, and west. This will help reducesolar heat gain into your home.Buying New Air ConditionersToday’s best air conditioners use 30% to 50%less energy to produce the sam

decline in air conditioning performance while energy use steadily increases. Air Conditioner Filters . The most important maintenance task that will ensure the efficiency of your air con ditioner is to routinely replace or clean its filters. Clogged, dirty filters block normal air flow and reduce a system’s efficiency significantly. With normal air flow obstructed, air that bypasses the .