EFFICIENCY RATINGS

UNDERSTANDING AND EXPLAINING ENERGY EFFICIENCY COMPARISONS

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OVERVIEW

Well before department of Energy (DOE)standards were established, heating and cooling efficiency ratings became an important issue. As manufacturers have competed for industry leadership, consumershave become more demanding in their expectations of energy-efficient products. Asthese consumers request more and more comparison information, the manufacturerswho conduct ratings tests and HVAC contractors who install the equipment are ultimately held responsible for ensuring thatthe information is accurate.

Unfortunately, cases have been reportedwhich have the manufacturers and/or contractors have misinterpreted ratings information, calling into question the integrity of the industry as a whole. Thisintegrity is critical for developing the long-term, trusting relationships that result inongoing success. Our goal is to help you

protect those relationships by giving you theinformation necessary to correctly interpretand explain HVAC efficiency ratings.

In this paper, we will take a look at someof the most common rating procedures forHVAC products. Specifically, we will considerheating efficiency for gas furnaces (AFUE)and heat pumps (COP and HSPF); and cooling efficiency for split systems (EER andSEER). In addition, there is informationabout other efficiency issues relating to add-on products such as air cleaners,zoning controls andheat/energy recoveryventilators. Below arethe definitions for eachrating to be discussedfurther in the sectionsthat follow.

HVAC efficiency ratingshelp consumers makeinformed decisions.That’s why it’s importantfor the heating andcooling dealer tounderstand the ratingsand explain them correctly.

RATINGS AT A GLANCE*

Annual Fuel UtilizationEfficiency (AFUE)

Combustion Efficiency

Heating Seasonal PerformanceFactor (HSPF)

Coefficient Of Performance(COP)

Seasonal Energy Efficiency Ratio(SEER)

Energy Efficiency Ratio (EER)

Does not factor in electrical use; does include steady-state operation, cyclic operation, infiltration losses and seasonal heating days in the calculation.Heating output (Btu) annually ÷ Gas fuel input (Btu) annually.

Does not account for infiltration losses; strictly a steady-state ratio of heat output vs. fuelinput. This measure is no longer used due to its incomplete nature.

Factors in seasonal use, temperature bin data, cyclic operation, frost/defrost degradation andsupplemental heating; a measure of energy efficiency during heating mode.Total seasonal heating requirement (Btu) ÷ {Heat pump watts + Electric heat watts overentire season}.

Does not include seasonal use or supplemental heating; strictly a measure of watts out vs.watts in for heat pump primary heating mode at steady-state conditions.Heat output (watts) ÷ Electricity input (watts).

Includes seasonal use, cyclic operation and part-load factors.Seasonal cooling output (Btu) ÷ Seasonal electrical input (watts).

Considers operation only at steady-state, maximum load conditions; does not consider part-load or seasonal variations.Cooling output (Btu) ÷ Electrical input (watts).

GAS FURNACE RATINGS

SPLIT SYSTEM RATINGS

*All ratings are based on a hypothetical home and geographical location. 3

The most important thing to realize is that nomatter what the rating, each measurement mustbe conducted in strict accordance with pub-lished test procedures.The definitions of AFUE,SEER, HSPF and others are not open to interpre-tation and should not be taken out of context.Each rating is prescribed by industry-recognizedregulatory agencies based on very specific test con-ditions (ambient temperature, design heating fac-tor, heating degree days, regional temperature bindata, etc.), and to state a rating based on any devi-ation from this strict set of conditions is unac-

ceptable. For example, the certified and pub-lished HSPF for a split-system heat pump includescalculations based on Region 4 (Pittsburgh) cli-mate data. Ratings based on other regions areonly comparable to calculations based on thesame climate data. In other words, a Region 3HSPF rating is not an accurate or fair comparisonto a Region 4 rating. Ideally, comparisons shouldbe made based on weather data for your area andload calculations for the target structure. If thisdata is not available, use the standard publishedratings for Region 4.

THE MOST IMPORTANT THING TO KNOW

-3 7 17 27 37 47 57 67 77 87 97

400

0

800

1600

2000

2400

1200

Bin

Hour

s

Bin Temperature (Fº)

65º

Weather Data: Indianapolis, Indiana

400

0

800

1600

2000

2400

1200

Bin

Hour

s

65º

-3 7 17 27 37 47 57 67 77 87 97

Bin Temperature (Fº)

Weather Data: Los Angeles, California

As these chartsillustrate, climatedata in one regioncan be drasticallydifferent than climate data foranother. Make comparisons usingcertified ratingsbased on thesame regional climate datawhen possible.Otherwise, refer to the standardpublished ratingsfor Region 4.

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Annual Fuel Utilization Efficiency (AFUE)ratings are used to compare gas furnaces on howmuch fuel gas is used in a year to generate a specific amount of heat. Tests and calculations arebased on DOE rating procedures and are verifiedby the Gas Appliance Manufacturers Association(GAMA). The test standard encompasses morethan 70 pages of test procedures and conditionsthat must be met throughout the rating process.These “rules” take into account everything fromthe grade of fuel used to jacket loss to the type ofburners and draft equipment used. Specific temperatures and pressures must be maintainedevery step of the way, and measurements must beaccurate within the most exacting tolerances.

All in all, nearly 140 different factors must becalculated and computed in complex mathematical formulas to arrive at an AFUE rating. However, for our purposes, in its simplestform, AFUE equals:

Heating output (Btu) annually ÷ fuel gas input(Btu) annually.

Among others, calculations used to arrive atthese final two values incorporate the following:

• On and off cycling as well as steady-state operation

• A specified number of heating degree days

• Input and output under well-defined load conditions

• Efficiencies at high and low speeds when variable-speed blower motors are used

In other words, by its very definition, AFUEis an average efficiency based on all factors thataffect furnace performance throughoutan entire year. If the furnace providesmulti-speed operation, the AFUE iscalculated with weighting fac-tors for operation at differentspeeds.

Consumers are mostly interested in energyefficiency as it translates to their monthly utilitycosts. Therefore, they need to understand that afurnace requires electricity as well as gas, and it is acombination of both energy sources that deter-mines operating costs. Currently, there is no certified rating that allows a consumer to compareoverall combined energy usage in the same waythat he or she can compare one AFUE rating toanother. However, in actual operation, this is themost meaningful comparison for consumers.Consumers don’t understand that a fixed-speedcondensing furnace may have a higher AFUEthan a variable-speed model, but may cost moreto operate because of the electrical expense.

The difficulty in producing an accurate,meaningful energy cost rating stems from thewidely varying fuel costs across the country. Whileit is possible to inform your customer of howmuch electrical input a particular unit requires,this only has meaning when added tohow much gas is required. Adding the two togeth-er requires that we come up with a com-

mon denominator–operating costs. This can bedone from the worksheet in the front of theGAMA directory, but you must factor in local fuelcosts. While it is possible to use national aver-ages for fuel costs to come up with an arbitrary standard, if your customer is served byan electric utility whose rates are exceptionallyhigh, the national average for electricity will mislead them in their decision-making.

You can get a copy of the GAMA Directoryat www.gamanet.org.

GAS HEATING EFFICIENCY: AFUE

ANOTHER MEASURE OF GAS FURNACE EFFICIENCY: ELECTRICAL POWER CONSUMPTION

Annual heatingoutput (Btu)

Annual fuelgas input (Btu)

AFUE =

Annual Gas Usagex Local Cost

+Annual Electricity Usage

x Local Cost_______________________

Total Annual Operating Cost

CONSUMERS' DIRECTORY OF CERTIFIED EFFICIENCY RATINGSfor l

Residential Heating and lWater Heating Equipment

Gas Appliance Manufacturers Association

The complex mathused to calculateAFUE ratings canbe summarizedwith this simpleequation:

Total operatingcost includes bothgas and electricityusage. The com-plete formula canbe found in theGAMA directory

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HEAT PUMP HEATING EFFICIENCY: HSPF

COOLING EFFICIENCY: EER AND SEER RATINGS

The ASHRAE/DOE test procedures to deter-mine heating efficiency for heat pumps are usedby the Air Conditioning & Refrigeration Institute(ARI). Much like those for determining AFUE,these test procedures are very extensive and specif-ic. Heating Seasonal Performance Factor, HSPF, isbasically a ratio of the total seasonal heat-ing requirements (Btu), including supplementalelectric heat, during its annual usage period forheating, divided by the total electric power con-sumption in watts during the same period. Thecalculations used to arrive at this number incorpo-rate:

• Performance variations due to on-off cycling

• Lost heat from defrost operation

• Average annual fractional hours in temperature bins for regional climates

• Variations in capacity and electrical use that occur at these temperatures when the system operates at multiple speeds

Just as it is for furnaces, it is impossible todevelop an HSPF rating for a multi-speed unitbased solely on one of its speeds. By its very definition, HSPF includes weighted factors foroperation at its various speeds. While a ratingcould be approximated at a specific speed, thenumber would be meaningless for efficiency comparisons, since in “real life,” the heat pumpwill not operate continuously at any single, givenspeed.

Some manufacturers and contractors alsoseem to be confusing matters by statingCoefficient of Performance (COP) ratings. Bytheir very nature, COPs seem impressive, as theyare always greater than 1.0. This implies that aheat pump is putting out a lot more heatingcapacity than it is using in electricity. Unlike electric resistance heat–which produces one wattof heat output for each watt of electricity purchased from the electric utility–a heat pumpuses a watt of electricity during the compressioncycle, absorbing heat from the outside air andpumping it into the structure. So, while electricresistance heat achieves a COP of 1 (1 watt output divided by 1 watt input), a heat pumpmay furnish 3 watts of usable heat per 1 watt ofelectricity used, so it is 300% efficient, or has aCOP of 3.

However, a high COP only occurs duringhigher outdoor temperatures. As the outdoor tem-perature falls, the COP falls, because there is lessheat to pull from the outside air. Most important,a COP rating does not factor in supplementalheat. While even at 0˚F, the typical heat pumpwill achieve COPs between 1 and 1.5, it does notkeep the homeowners warm without the use ofback-up heat. The HSPF takes into account theuse of back-up heat to create a realistic rating thatprovides an accurate comparison considering theunit’s use of supplemental heat in conditions at orbelow the balance point. Higher capacities mayreduce the supplemental heat requirements, butthis will be reflected only in the unit’s HSPF, notin its COP.

For both heat pumps and air conditioners,published cooling ratings are Seasonal EnergyEfficiency Ratios (SEER’s). SEERs use data basedon a full cooling season, whereas an EER (EnergyEfficiency Ratio) uses only one specific set of condi-tions (operation at 95ºF outside temperature).Like HSPF, SEER also factors in operation at multiple operating speeds when applicable. ASEER rating includes factors for:

• Steady-state operation

• Cyclic operation

• Changes in input and/or output that occurduring normal operation if the unitprovides multi-speed operation

• Load conditions

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OTHER SYSTEM INFLUENCES

As a wider array of products become marketed by HVAC companies, other ratings arealso becoming important. A few of these aredescribed briefly in the sections that follow.

Airf low

Though the old “rule of thumb” tells us that400 CFM per ton of capacity is necessary toachieve optimum heating or cooling performance,this rule of thumb no longer holds true. Thisnumber originally came about as a way to compensate for installation variables such as ductsizing and configuration (which affects static pres-sure), as well as the floor plan. It allowed a “fudgefactor” to ensure that the rooms furthest from theunit’s fan received adequate heating or cooling.Today, however, our new FK fan coils and vari-able-speed gas furnaces can achieve optimumheating and cooling at airflows below 400 CFMper ton. This is possible because of ECM variablespeed motor technology. By monitoring blowermotor torque and speed at a given airflow, themotor automatically compensates for static pres-sure, using built-in software. Though you mayrarely need to know this to explain to your cus-tomers it does become important as you evaluateHVAC equipment yourself. In some cases, these“smart” motors may help you be more competitive.Since you no longer have to oversize a unit toensure latent performance, you may be able toquote a unit with nominal capacity that will still

provide optimum heating and cooling–even if thehome has work or airflow restriction problems.Carrier’s exclusive Thermidistat™ Control andComfortZone II systems enhance the comfort ofheating and cooling systems by actively controlling humidity year round. Plus, by working with the variable speed blowers to removeexcess humidity in the cooling season, consumerscan be more comfortable at higher temperaturesettings. According to the U.S. Department ofEnergy, setting your thermostat higher during thesummer saves energy.

Air Cleaners

The most troublesome part of air cleaner ratings is the understanding how particle sizeaffects efficiency. Sometimes the benefits of an aircleaner are also misunderstood because a homeowner either assumes or is informed that anair cleaner can eliminate odors, too. While remov-ing particles can sometimes reduce odors, as in thecase of cigarette smoke or cooking grease (becausethere are particles suspended in the air), an aircleaner cannot eliminate odors caused by gases orthe gases themselves.

Mechanical air cleaners trap particles in somesort of mesh. The size of the “holes” in the meshdetermine the size of particles that can be cap-tured. While most mechanical filters do an ade-quate job on dust and pollen, because they are

An electronic aircleaner can removethe most troublesomecontaminants–parti-cles too small to beeffectively removedby mechanical aircleaners or furnacefilters.

100 10 5 2 1 0.5 0.1 0.01 0.001Particle Sizein Microns

Organisms

StandardFilter

GoodMechanical Filter

Full-Size Electronic Air Cleaner

BACTERIA

VIRUSESPOLLEN

PLANT SPORES

COOKING SMOKE & GREASE

TOBACCO SMOKE

HOUSEHOLD DUST

COAL DUST

ANIMAL DANDER

LINT

INSECTICIDE DUST

Smoke

Minerals

Air Cleaner Performance

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larger, most do not work efficiently on viruses orbacteria, which are much smaller. These can onlybe removed efficiently with an electronic air cleaner. An electronic air cleaner will filter out larg-er particles using a mesh filter, and smaller ones byapplying an electrical charge to the air. This “mag-netizes” particles, and they adhere to a metal collec-tor plate. Refer to the chart on page 7 to under-stand how effectively different particle types are fil-tered by various air cleaner types.

Heat Recovery Ventilatorsand Energy Recovery Ventilators

Recent concerns over radon and carbonmonoxide levels in homes has prompted a growingdemand for HRVs and ERVs. Be sure to explain toyour customers that ef ficiency ratings for theseunits are based on how well they capture andreuse heat in the circulated air–not how wellthey “filter” gases.Though most ERVs andHRVs incorporate some type of filtering system toeliminate particles from outside air, their primarypurpose is to eliminate gases by exchanging insideair that contains these gases for outside air inwhich these gases are either non-existent or presentin much lower concentrations. In the process, heatis transferred (remember, heat is transferred even incooling). How well the heating energy is trans-ferred determines the recovery efficiency.

Zoning Systems

To date, there is no published or certified rat-ing system for zoning. Zoning controls have noefficiency of their own, beyond how accurately

they can measure room temperature and setpoint.Yet, zoning systems do increase overall energy effi-ciency of the system, by controlling operation timesand heated/cooled areas. Explain to your customerthat zoning enhances energy savings like a photoelectric sensor reduces electrical costs on adusk-to-dawn lighting system. If you have an outdoor security light, it requires a bulb. If thatbulb is a 60-watt bulb, it will require 60 watts ofelectricity for every hour of operation. The sensordoesn’t make the bulb more efficient. It still uses60 watts per hour whenever it is on. What it doesdo is change the amount of time that a bulb is on.Zoning can also save energy by playing a role simular to individual room light switches. When aroom is in use, zoning will control how much heating or cooling needs to be added to suit a customer’s preferences and usage patterns. Whenthe room is in use, heating or cooling can be shutoff or reduced to that area the way a light switchlets a person turn off the lights in an unused room.

System Efficiency

Much like zoning, other parts of a total systemaffect overall performance. While these things arenearly impossible to compare because of how eachpart affects the others, system efficiency can be veryimportant to a consumer. Regardless of rat-ings, these factors do affect their monthly heat-ing and cooling costs. Proper coil matching andsupplemental heat are just two examples of howoverall system efficiency can be affected by theinteraction among components.Programmable

Thermostats and zoningenhance energy savingsin home comfort systemsmuch like a photoelectricsensor reduces electricalcosts on a dusk-to-dawnlighting system.

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Coil Matching

To achieve optimum cooling capacity, theindoor coil must be properly matched to the outdoor unit. If a new heat pump is matched withan old existing coil, the coil would most likely betoo small. This can result in overcharging the coilin the summer to maintain correct system pressure. The coil may not be able to absorb theheat necessary to keep suction pressures up, so coilfreeze-up could occur. In the winter, the tendencywould be to undercharge the system due to highpressures. This can cause excessive temperature riseand head pressures, which can negatively affectcompressor reliability. It may also reduce efficiencyas the high-pressure switch is repeatedly tripped orthe thermal overload shuts the system down onmilder days.

Heat Pump Supplemental Heat

In many areas of the country, supplementalheat must be available to keep homeowners comfortable when outdoor temperatures drop toaround or below the balance point. Because electric resistance heat requires one watt of electrical input for each watt of heating output, aheat pump system that relies on a great deal of sup-plemental heat will be much less efficient. (This

makes proper sizing for low temperature condi-tions critical, since it will reduce the need for sup-plemental heat.)

While the ratio of output to input will alwaysbe equal for any supplemental heating resistanceheat system, some supplemental heating systemsrequire less power because they can be activated instages (produce less output and more even temperatures) according to heating demand. Refer to our literature on Smart Heat for more information.

Optimum cooling capacity is achievedwhen the indoor coil isproperly matched to theoutdoor unit.

CONCLUSION

The issues that surround HVAC equipmentperformance ratings are increasing everyday.Though pressure from competition may make ittempting to brush over an explanation or totake a rating out of its intended context, ourbest choice is to provide real answers. In doing

so, we position ourselves as knowledgeable lead-ers of the industry and give consumers morereason to trust us. Ultimately, that trust will payoff in lifetime customers that come to count onyou as the authority for all of their home com-fort needs.

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© Carrier Corporation 2001 838-779

Manufacturer reserves the right to discontinue, or change at any time, specifications or designs without notice orwithout incur ring obligations.

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