This paper has been accepted for publication
in the journal, Energy and Buildings.
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Abstract
An energy test procedure is the technical foundation for all
energy efficiency standards. It provides manufacturers, regulatory
authorities, and consumers a way of consistently evaluating energy
use. The ideal test procedure reflects actual usage conditions
without compromising reliability and cost-effectiveness. Unfortunately,
because these goals are contradictory, every test procedure is
a compromise. Energy test procedures exist for a wide range of
appliances and often each country has its own unique test procedure.
The procedures for refrigerators, furnaces, air conditioners,
clothes washers, and other appliances are described and compared.
The emergence of microprocessor controls complicates developing
specifications for a single operating schedule and simple comparisons
of energy performance. Energy test procedures will face unprecedented
pressures in the next decade as a consequence of international
economic integration and technical innovations.
Introduction
An energy test procedure is the technical foundation for all energy
efficiency standards, energy labels, and other related programs.
It provides manufacturers, regulatory authorities, and consumers
a way of consistently evaluating energy use and savings across
different appliance models. Test procedures support energy labels,
standards, and efficiency programs. A poor energy test procedure
can undermine the effectiveness of everything built upon it.
The relationship among these components is illustrated in Figure
1.
Energy test procedures are a poorly understood aspect of efficiency
standards and labels given to appliances. The origins of the test
procedures, their validity, and international differences are
rarely discussed. As more countries adopt energy efficiency
standards, however, test procedures are attracting greater scrutiny.
Many appliances (as well as the components within them) are internationally
traded or manufactured by multinational corporations having production
facilities in different countries. Accordingly, it is now recognized
that test procedures may pose a trade barrier. This article describes
the overall goals of energy test procedures and follows with discussions
of some of the major technical issues involved.
What Makes a Good Test Procedure?
An energy test procedure must satisfy several goals. In all cases,
an ideal test procedure should:
Unfortunately, these goals are contradictory. A test that tries
to accurately duplicate actual usage will probably be expensive
and not easily replicated. For example, the Japanese refrigerator
test includes two ambient temperatures (to reflect winter and
summer kitchen temperatures) and requires a complex schedule of
door openings. These specifications reflect the way a refrigerator
is actually used by consumers in their homes, but it is expensive
to perform and results are difficult to reproduce. Another example
is the United States Department of Energy (USDOE) efficiency test
for air conditioners. This test accounts for performance at
part-load conditions because the units typically operate a significant
fraction of the time at part-load. Again, this understandable
attempt to make the test reflect actual operation requires many
more measurements and calculations.
The test must yield easily repeatable results. Most ISO energy
test procedures for appliances specify a tolerance of 15%. The
actual uncertainty is probably much smaller. One study [1] of
the USDOE refrigerator test estimated that, if conditions were
maintained as prescribed, the measurement uncertainty was less
than 2%.
When a test procedure is part of an energy efficiency standard
additional considerations are involved . It must be designed such
that it is difficult for a manufacturer to circumvent the intent
of the test procedure by using technical loopholes. For example,
the U.S. washing machine test procedure specifies that energy
consumption be measured with the machine on its "normal"
setting. One manufacturer of clothes washers created a "normal"
setting on the machine to satisfy the test procedure but advised
consumers to use a more energy-intensive cycle for routine operation.
Clearly, an energy test procedure is a compromise: it does not
fully achieve any of the criteria for an ideal test, but it satisfies
enough of them to discourage excessive complaints. At a minimum,
a ranking of different models by their tested energy use should
correspond reasonably close to a ranking by the models' field
energy use. An additional danger of compromise is that manufacturers
may optimize performance for a test procedure that does not assure
energy savings in actual use.
Administratively, all test procedures are difficult to change;
as a result, the relative importance of certain objectives may
become outdated. In refrigerators, for example, the dominant
heat load is conduction through the walls, and current test procedures
focus on this. As the walls become more insulated, other factors,
such as the energy consumed by automatic defrost, door-opening
losses, and ice makers will become more important.
Administrative Bodies Responsible for
Making Test Procedures
Test procedures are typically created by such groups as manufacturers'
associations, governmental agencies, nongovernmental organizations,
and professional societies. A partial list of the major institutions
responsible for energy test procedures covering appliances is
presented in Table 1. The International Organization for
Standardization (ISO) and the International Electrotechnical Commission
(IEC) rely on an international network of national standards organizations
[2]. In Europe, the European Committee for Standardization (CEN)
has assumed responsibility for EU-wide test procedures. In the
United States, some test procedures were established by the Association
of Home Appliance Manufacturers (AHAM) and the Air-Conditioning
and Refrigeration Institute (ARI). Technical societies, such as
ASHRAE and ASME have also developed test procedures. These associations
continue to maintain and update the test procedures, but pressures
caused by the adoption of appliance standards, charges of monopoly
practices, or international trade negotiations have led to increasing
involvement by governments or groups specifically charged with
developing standards.
The steps to modify a test procedure are typically cumbersome
and time-consuming. (Most standards organizations are inherently
conservative, so there must be strong pressure before a modification
is considered and approved.) These institutions are typically
slow in modifying test procedures to adapt to new technologies
in the appliances. Now, with appliance standards linked to the
test procedures, modifications become more difficult to implement.
Many governments also want to review modifications to ensure
that they conform to the World Trade Organization requirements
in order to prevent the restriction of free trade.
Appliances Covered by Energy Test Procedures
Almost every energy-consuming device is tested for its rated input
and output, voltage, grounding, etc., however, most of these concern
safety and electrical service sizing requirements. Most energy
test procedures, such as those developed by ISO or the Japan Industrial
Standards (JIS), are sections of a much larger document that outlines
specifications and test procedures for all aspects related to
the performance of an appliance. For refrigerators, specifications
include procedures to measure volume, ability to maintain certain
temperatures, chill-down capacity, noise, etc. For washing machines,
the list includes cleaning performance, clothes capacity, water
removal, noise, etc. Table 2 lists the major appliances
covered by energy test procedures. A few countries, such as the
United States and Australia, have separate, "stand-alone,"
energy test procedures.
The following sections present aspects of energy test procedures for several appliances. The goal is not to describe the test procedures in detail but, rather, to discuss the problems commonly encountered in energy tests. Most of the discussions revolve around achieving reasonable compromises among the conflicting goals described earlier.
Refrigerators and Freezers
Refrigerators and freezers were among the first appliances for
which energy test procedures were developed, largely because these
appliances use significant amounts of energy and are reasonably
easy to test. A list of the major test procedures is given in
Table 3.
All of the test procedures involve placing the refrigerator in
a controlled environment for a specified time or number of cycles.
An excellent overview of the different procedures was published
in 1995 by Bansal and Krüger [3]. With the exception of
the Japanese procedure, all specify that doors be closed during
tests. The principal difference among test procedures is the
choice of ambient and compartment temperatures. Even a small
difference is significant because small adjustments in temperature
settings cause large changes in energy use. Further differences
involve dealing with automatic defrost, anti-condensation features,
ambient humidity, and food loading. Achieving precise compartment
temperatures is difficult: most procedures involve performing
the test twice in order to bracket the specified temperature.
The energy use for specified compartment temperatures is then
obtained through interpolation.
Until recently, the Japanese (JIS) test procedure required energy
measurements at two different ambient temperatures (15°C
and 30°C). The reason for this is that, at the time the
procedure was developed, Japanese kitchens were poorly heated
in the winter and not cooled during the summer. The JIS test
also includes a door-opening schedule. Japan recently abandoned
its test procedure in favor of the ISO procedure. As a result,
the labeled energy use of Japanese refrigerators suddenly increased
about 40%.
The ISO test procedure is oriented toward European-style refrigerators
and their features. It is weaker with respect to specifications
regarding automatic defrost, anti-condensation heaters, and special
features than the USDOE and Japanese tests. The ISO test can
be conducted at two different ambient temperatures depending on
the eventual destination of the refrigerator. The temperate zone
test uses 25°C, whereas the tropical zone test uses 32°C.
European and Japanese manufacturers report the 25°C value
because 25°C is specified in the CEN procedure.
The ISO test differentiates refrigerators by their ability to
achieve a certain level of performance., which is designated
by 1-star to 4-star labeling. To qualify for the four-star rating,
the freezer compartment must remain below -18°C. The energy
tests reflect this requirement. In contrast, the USDOE test procedure
differentiates by technology, that is, whether the model
has automatic defrost, partial defrost, or manual defrost. The
USDOE energy test does not include performance-based tests.
Technological innovations and new features are constantly being
offered in new refrigerators. Even though most innovations are
modest, they nonetheless challenge energy test procedures. Some
examples are presented below.
Automatic defrosting is present in virtually all Japanese and
North American refrigerators. The energy devoted to this task
is typically 5 to 15% of total energy consumption. Traditionally,
defrosting was activated by a timer, regardless of need. Recently,
microprocessor-based controls and sensors have been developed
to initiate defrost only when needed. This innovation complicates
test procedures because, if no moisture accumulates during the
test, no defrost occurs. Should the same defrost schedule be
imposed upon all refrigerators, regardless of the controls? The
United States' approach to new technologies, such as microprocessor-based
logic, is to deduct a fixed amount (or percentage) of energy.
This approach treats all sensors and control algorithms as if
they perform identically, and thus penalizes better designed sensors
or control logic.
Some Japanese refrigerators have special compartments for storing
fish at exactly -1°C. Other (mostly Japanese) refrigerators
have more than four separate doors and compartments. (Several
models have six doors.) Should these compartments be maintained
at the ISO-required temperatures during the test even though in
actual use they will be operated at different temperatures?
An increasing number of refrigerators are equipped with automatic
ice makers, chilled water dispensers, and other special features
requiring a water connection. These features can increase field
energy use by up to 20% [4]. Yet, no tests specify that the water
line be connected during the test procedure.
Innovations and features unique to a specific region such as those
described above will need to be addressed by the various standard-setting
organizations in the next decade.
Clothes washers
Clothes washing is a universal activity, and clothes washing machines
are used in every country. All test procedures try to account
for the energy used by the agitator motor and the energy required
to heat the water. However, washing habits and the definitions
of "clean" vary enormously from one country to another
[5] This situation has hindered the development of international
energy test procedures for washing machines. Additional factors,
such as variations in the temperature, amount, and hardness (that
is, mineral content) of the water, types of detergents, and use
of clothes dryers, further complicate defining the energy efficiency
of a clothes washer [6]. In addition, given the rapid advances
in clothes washing technology, nearly all of the test procedures
are being changed. In the United States, for example, there is
a current test procedure, a proposed interim test procedure, and
a future test procedure. The "future" test procedure
will be put into force only if the efficiency standard for washing
machines is approved.
European and American authorities have taken nearly opposite approaches
to energy test procedures for washing machines. The U.S. approach
defines energy efficiency independently of cleaning performance.
The issue of cleaning performance is simply ignored; if a manufacturer
fails to deliver satisfactory performance at a given level of
energy use, then it is assumed that consumers will purchase a
different machine. The European approach is to first define cleaning
performance and then, once this definition is available, to select
standard requirements that manufacturers must meet to assure both
minimum energy use and acceptable cleaning performance.
The United States' approach is already collapsing because of the
incorporation of dirt sensors and other controls. In laboratory
tests, these sensors recognize that clean clothes are loaded
into the washer, so the microprocessor selects the cycle with
the minimum energy use. In other words, the test measures the
washing machine's energy consumption for the cleaning cycle with
the lowest energy consumption.
If the goal of the efficiency standard is to reduce life-cycle
energy costs, then detergent should be an important factor in
the test procedure, because the detergent itself has a significant
energy input and sometimes costs more than the energy used to
heat the water. In Europe, detergent represents over 30% of the
life cycle cost of clothes washing [7]. Detergent technology is
changing, too. Improved chemical formulations have obtained greater
cleaning performance at lower water temperatures. At least two
test procedures specify a detergent for use in the performance
tests. Specifying a "baseline" detergent may be acceptable
for the near future, but will inevitably lead to problems as machines
are optimized according to actual detergents available in the
market.
Water is a third input to clothes washing that needs to be considered
in any good test procedure. Some manufacturers may try to sacrifice
water economy for improved energy performance.
In some countries, consumers own both a clothes washer and clothes
dryer. (In the USA and the UK, over half of the homes have dryers
compared to 20% in Japan and 5% in Portugal) The energy performance
of a clothes washer is linked to the clothes dryer. If the clothes
washer spins the clothes and extracts most of the water, then
only minimal drying is needed from the clothes dryer. Even though
the final spin does not affect the cleanliness of the clothes,
it does consume energy and, naturally, will affect the machine's
apparent efficiency. Thus, a seemingly inefficient clothes washer
may be a highly efficient partner when coupled with a dryer.
To address this disparity, a proposed USDOE standard will give
credit for lower remaining moisture content at the end of the
cycle.
A final complication for evaluating the energy efficiency of clothes
washers is how the water is heated. The energy invested in heating
the wash water is the greatest component of the total energy consumed
by the appliance. Most European clothes washers heat the water
with an electric resistance heater in the machine itself. In
contrast, American and Japanese models rely on heated water from
external water heaters. By excluding the energy consumed by the
external water heater, the United States and Japanese models will
appear more efficient than European models. In addition, many
water heaters, especially in the United States, are gas-fired.
In terms of test procedures, this introduces the problem of combining
the energy contributions from two fuels.
The factors affecting energy test procedures for clothes washers
are probably more challenging than for any other appliance. The
clothes washer will serve as a bellweather for the international
community's ability to reconcile technical, geographical, and
cultural differences. If they can be resolved, and an internationally-recognized
test procedure approved, then one can expect the same approach
to be used with other appliance energy test procedures.
Boilers and Furnaces
Test procedures for furnaces and boilers prior to the mid-1970s
were based on simple steady-state tests where the fuel input and
heat output were measured under one set of standard test conditions.
For most countries, the steady-state measurement of efficiency
remains the sole energy-efficiency test.
Important definitional differences appear even today. German
test procedures (DIN) for fossil-fuel-fired furnaces use the "low"
heating values for fuels. In other words, they ignore the latent
heat carried away in the combustion products. With the advent
of condensing furnaces (which condense the combustion gases and
capture the latent heat), reported furnace efficiencies frequently
exceeded 100%. In contrast, because North American test procedures
are based on the fuel's "high" heating value, efficiencies
never exceed 100%.
The steady-state efficiency test does not necessarily reflect
true annual energy consumption because, as with most heating equipment,
there is significant energy loss and/or inefficiencies during
the start-up and shut-down periods. As a result, the USDOE developed
a procedure that includes both steady-state and cycling tests
coupled with a calculation procedure that accounts for changing
weather conditions throughout the heating season [8].
Although the testing required is simple, the estimation of yearly
performance requires an elaborate calculation procedure. The
developers found that the performance of furnaces and boilers
under part-load, on-off operation could be described by a simple
"time-constant" model. In addition, data required to
determine the time-constant could be obtained after a steady-state
test, during "cool-down" and "warm-up," without
extensive cycling tests.
Based on extensive laboratory measurements, six loss terms (listed
below) were found to be critical to accurately characterizing
a furnace's efficiency and are therefore required to be measured:
1. Latent Heat Loss, from the presence of uncondensed water vapor
in the flue gas
2. On-Period Sensible Heat Loss, from the heating of combustion
products and excess air from room temperature up to the flue gas
temperature
3. On-Period Infiltration Loss, from the heating of relief air
during on-cycle combustion and relief air from the outdoor temperature
up to room temperature if the air is drawn from a conditioned
space
4. Off-Period Sensible Heat Loss, from the heating of the off-cycle
draft air up to a temperature in excess of the indoor air temperature
5. Off-Period Infiltration Loss, from the heating of the off-cycle
draft and relief air from the outdoor up to the indoor air temperature
if the air is drawn from a conditioned space
6. Jacket Heat Loss, to the ambient air if the equipment is not
installed in a conditioned space
These six losses are subtracted from 100 to obtain the value of
the seasonal efficiency. To obtain seasonal performance values,
the loss terms are evaluated during the heating season using average
outdoor air temperatures.
This procedure proved to be as accurate as the more complicated
"bin" analysis where the separate efficiency for calculation
for each "bin" must be separately calculated. In addition,
the manufacturer calculates an annual fuel utilization efficiency
(AFUE) which differs from the seasonal efficiency if there is
consumption of energy by a pilot light operating during the non-heating
season.
Since the publication of the original test procedure, the USDOE
has modified or proposed modifications to accommodate advances
in furnace and boiler technology and changes in control strategy.
These advances have included:
1. Pulse combustion and condensing furnaces [9] where there is
very small draft air flow through the heat exchanger during the
off-period (pulse combustion) or the latent heat loss is reduced
by recovering the latent heat of the water vapor in the flue gas
through a condensing heat exchanger (condensing furnace)
2. Step-modulating and two-stage controls on furnaces and boilers
where furnaces designed with the capability of reduced fuel input
rate are cycled between reduced input rate and OFF when the heating
load is light and modulating the input rate up to the maximum
input when the load is higher (step-modulating)
3. Furnaces with inlet dampers where an electro-mechanical damper
at the combustion air inlet of the burner box is automatically
closed during the off-period to reduce the draft air flow rate
4. Furnaces with long post-purge time where the combustion blower
for power-vented units continue to operate after the burner is
shut off; a longer than necessary post-purge time would increase
the off-period loss
5. Stack dampers with delayed and finite closing time at burner
shut-off which will reduce the effectiveness of the dampers in
reducing the off-period stack loss
"Combination heating appliances," that is, products
that integrate more than one function into a single piece of equipment
or system have become more popular. Typical configurations include
a space heating boiler with a tankless water heating coil, a space
heating boiler with an indirectly heated domestic water storage
tank, or a conventional water heater with additional piping to
a heating coil in an air handling unit for forced-air space heating.
As indicated, combined appliances pose special problems for testing
and comparing with their single-application counterparts.
One industry standard, ANSI/ASHRAE Standard 124-1991 [10], specifies
the methods of testing and rating combined heating appliances.
The standard specifies that two separate tests are to be conducted.
The first is a space heating test that follows the USDOE test
procedure for space heating boilers and is designed to obtain
a steady-state efficiency and a heating seasonal efficiency for
the space heating function; the second is a water heating test
that follows the USDOE test procedure for residential water heaters
and is designed to obtain an energy factor for the water heating
function. The three individual performance parameters (steady-state
and seasonal heating efficiencies and energy factor) are used
to calculate the rating parameters for the combination appliance
by combining them through weighting factors. These weighting
factors are based on the fractions of the space heating load and
water heating load to the total heating seasonal and total annual
space-water heating loads and to the length of the nonheating
(space) season to the length of the heating season. Three rating
parameters for the combination appliance are calculated: the "Combined
Heating Season Efficiency," the "Nonheating Season Efficiency,"
and the "Combined Annual Efficiency."
Heat Pumps and Air Conditioners
Heat pumps and air conditioners provide different services but
operate on the same principle; accordingly, the test procedures
are very similar. The fundamental measure of efficiency for these
devices is the ratio of heat delivered (or extracted) divided
by the electrical input energy. For heating performance, the ratio
is called a Coefficient of Performance (COP), and for cooling
performance the ratio is called an "Energy Efficiency Ratio"
(EER).
Test procedures to evaluate the performance of air conditioners
and heat pumps exist in Europe, Japan, and North America [11-14].
All test procedures measure the appliance's steady-state efficiency,
but they differ in the number of additional measurements and calculations
required. Test procedures are also specified for outdoor conditions
where defrosting of the outdoor coil is periodically required.
Similar tests are now included in an ISO procedure [15] which
specifies one cooling mode performance test and three heating
mode performance tests. For the cooling mode test, however, the
prescribed indoor and outdoor ambient conditions (that is, "cool,"
"moderate," or "hot") depend on the climate
conditions present in the eventual destination of the unit.
Whereas the measurements outlined in ISO procedures are sufficient
to calculate a unit's steady-state COP or EER, further calculations
are needed to estimate seasonal heating or cooling energy consumption.
By comparison, North American standards have made estimating
seasonal energy consumption the primary goal of its test procedures.
In the United States, this goal came about mainly because of
energy legislation passed in the mid 1970s that required test
procedures to provide an estimate of annual operating cost and/or
seasonal efficiency.
As with boilers and furnaces, seasonal performance of air conditioners
and heat pumps does not depend only on steady-state performance.
The unit's performance during the transient periods at the beginning
and end of an on-cycle and the parasitic electrical energy used
during an off-cycle also affect seasonal performance. From its
inception, therefore, the USDOE test procedure for air conditioners
and heat pumps has included a cooling mode cyclic test and a heating
mode cyclic test [16, 17] . For single-speed and two-speed capacity
units, a cycle consisting of a 6 minute on-period followed by
a 24 minute off-period is repeated a few times before data for
one complete on-off interval are collected. A measure of the
degradation associated with cyclic operation is gained by using
the results of these cyclic tests plus the results from the steady-state
tests conducted under the same test conditions. The tandem cyclic
and steady-state (dry coil) cooling mode tests and the one cyclic
heating mode test are optional. Default values for the cyclic
degradation are provided in the test procedure.
Using data from steady-state tests conducted at outdoor temperatures
of 35_C and 27.8_C plus the cyclic degradation coefficient, an
estimate can be determined of the seasonal performance descriptor
for the cooling season, Seasonal Energy Efficiency Ratio (SEER).
Initially, for all air conditioners and heat pumps, the SEER
calculation procedure used the bin method mentioned under Boilers
and Furnaces where performance is weighted by the number of hours
the unit operates in each outdoor temperature range or bin. In
contrast to the AFUE of furnaces and boilers, however, the SEER
for single speed air conditioners and heat pumps was found to
vary minimally for climate conditions typically found within the
continental United States. A very close approximation of the
bin-determined SEER was obtained by using only the results from
testing conducted at 27.8_C.
On the heating side, the Heating Season Performance Factor (HSPF)
is calculated using a bin method. The effects of frosting are
assumed to occur over an outdoor temperature range of -8.3_C to
7.2_C for single-speed and two-speed models when they are operating
at high capacity. The HSPF of a heat pump varies with climate.
Moreover, within a given climatic region, the heat pump, theoretically,
could be applied to homes having very different design building
loads. As a result, the USDOE test procedure contains information
allowing the HSPF to be evaluated for six different climate regions
and for a range of design building loads within each region.
For rating purposes, however, the HSPF corresponding to a single
climate region is reported.
Since the initial publication, the USDOE test procedure has been
modified to cover split-type ductless systems and variable-speed
systems [18]. Also, calculation procedures have been developed
for rating mixed systems, that is, where an indoor and outdoor
unit have not been tested as a system [19, 20].
United States manufacturers of complete systems are required to
test each type of outdoor unit with one indoor unit. The indoor
coil is the one that is most frequently sold with the particular
outdoor unit. All other combinations of indoor and outdoor units
are not required to be tested. In lieu of testing, a manufacturer
(including those that manufacture only indoor coils) uses a USDOE-approved
method for predicting rated cooling capacity, SEER (and, for heat
pumps, rated heat capacity and HSPF). Manufacturers have the
option of submitting their own method or using the methods developed
by USDOE. Often, manufacturers use the USDOE methods but then
incorporate their own company-specific changes. These rating
methods are structured such that the performance of the mixed
system is ultimately derived on the basis of performance of the
indoor/outdoor combination that was tested, which is termed the
"matched" system.
Combined appliances are also appearing with heat pumps and air
conditioners. The most common combination is an air conditioner/domestic
water heater. Heat extracted from the refrigeration system is
used to heat the water in the storage tank, thus reducing the
amount of heating the water heater must do. When operating in
the space cooling mode, for example, all or a portion of the heat
that would normally be rejected to the outdoor air is instead
productively used for heating potable water. These types of combined
appliances come in two basic categories: full condensing units
and units that incorporate desuperheaters. The main difference
between the two is that full condensing units can provide on-demand
water heating by operating in a combined mode and in a water-heating
only (dedicated) mode. Units having a desuperheater only provide
hot water when the unit operates to condition the space.
ASHRAE has recently completed work on a standard method for testing
single-speed, air-source air conditioners and heat pumps that
incorporate a desuperheater [21]. The Air-Conditioning and Refrigeration
Institute (ARI) is developing a standard method for rating both
categories of combined appliances [11]. The USDOE has approved
a method for testing and rating air-source full-condensing units
built by two manufacturers.
Declared Energy Use Versus Test Procedure Values
The discussion above refers to measuring the energy consumption
of a single appliance using the required test procedure. A test
procedure is insufficient, however, if the goal is to demonstrate
compliance with a minimum energy efficiency standard or to provide
a labeled energy use for that appliance. Fluctuations in manufacturing
and testing mean that the test value for a single unit will probably
not be representative of the thousands being produced. For this
reason, most regulatory authorities have established procedures
to test the minimum number of units to ensure a certain level
of statistical confidence. The sampling procedure links the test
procedure to the labeled value and compliance with the standard.
Three sampling procedures, from the United States, the European
Union, and Canada are summarized below. All three procedures
rely on a "declared value" of energy consumption that
satisfies the confidence requirements. The general approach is
the same for each appliance but confidence requirements depend
on the appliance.
The European test procedures, such as the one for refrigerators
and freezers (EN-153),[22] require the manufacturer to test the
energy consumption for one appliance. The declared value is the
tested value plus 15%. Alternatively, the manufacturer can test
three units and declare a value equal to the arithmetic mean.
This second option gives manufacturers with a high degree of
quality control an opportunity to declare a few percent lower
energy use for their models.
The Canadian standards, such as that for electric clothes dryers
[23], specify that the declared value must be based on a sample
of units. The sample size is not specified because the manufacturer
has two optionstaking the simple mean of the sample as the declared
(or "represented") value or, alternatively, demonstrating
(with a 97.5% confidence) that the declared value is 1.05 times
greater than the true mean. Again, manufacturers with a high
degree of quality control can achieve a slightly lower declared
energy consumption because less scatter will narrow the confidence
limits. Most standards (e.g., those for clothes dryers, refrigerators,
etc.) are expressed in terms of maximum allowable energy consumption
but some (those for furnaces and air conditioners) are expressed
in terms of minimum efficiency. In these cases, the adjustment
factor (away from the mean) is 0.95, and the confidence limit
is in the other direction.
The sampling requirements for the United States standards [24]
are essentially the same as for the Canadian standards. For both
countries, the confidence limits and the adjustment factors vary
with the appliance. The confidence limits range from 90% to 99%.
The adjustment factors vary from 1.01 to 1.10 for products for
which the consumer will benefit from a lower value and 0.90 to
0.99 for products for which the consumer will benefit from a higher
value. The number of tests needed to meet these criteria will
obviously vary. In the case of refrigerators, however, typically
4 - 6 units must be tested [25].
Efficiency standards can affect the declared values in other,
less predictable ways. Many refrigerators have electric resistance
heaters around the perimeters of the doors to reduce condensation.
Because these heaters can increase a refrigerator's energy use
by up to 15%, some manufacturers install a switch to turn off
the option when the heaters are not needed. Other manufacturers,
however, wire the heaters to be permanently switched on. The
question, then, should the energy tests for those units with switches
be conducted with the switch on or off? The initial regulatory
compromise required the manufacturers to use the average energy
use in the on and off settings. Later, the USDOE modified the
rules requiring manufacturers to calculate the average of a test
with the heater switched on and another test with the heater switched
as shipped from the factory. Thus, the declared energy
use of many refrigerators simply depended on the manufacturers'
decision regarding the heater setting when packaging and shipping
the refrigerators. These kinds of rules greatly complicate assigning
and understanding the declared values.
Translating Results from One Test Procedure
to Another
Energy tests, whether for standards or labels, are expensive.
An internationally recognized testing laboratory charges roughly
US$2000 to perform the USDOE test procedure on a single refrigerator
and US$6000 for a central air-conditioning unit [25]. The laboratory
tests and administrative work needed to create a European Union
energy label for a clothes-washing machine cost about US$3800
[26]. Accordingly, international manufacturers of appliances
would like to convert results from one test to the values of another.
In spite of the recognized need for conversion formulas, surprisingly
few attempts to develop conversion formulas have been undertaken.
Given the limited published research available, conversion formulas
appear to give only approximate values for other test conditions.
While these conversions will be useful for approximate comparisons,
they will never be reliable enough to satisfy regulators.
Almost all comparisons that have been done deal with refrigerators,
the most extensive study of which was conducted by Bansal and
Krüger [3]. They tested four refrigerators using the ISO,
Japanese, US, Australian-New Zealand, and Chinese test procedures.
Each refrigerator exhibited unexpectedly different relationships
among the test procedures. For example, the ISO test of the four
units was 2-64% less than the United States test values. The
conversion from the Japanese to the ISO standard was not even
consistent in one direction: the ISO values ranged from 0.87-1.33
times the Japanese values. This range may also reflect the diversity
among the units tested. As indicated previously, Japan switched
from the JIS to the ISO test procedure in 1995. During 1994 -95,
both values were listed in the manufacturers' catalogs, and the
ISO values were consistently 35-45% higher than the JIS values
for automatic defrost refrigerator-freezers. In an earlier comparison
of the JIS and USDOE test, Meier [27] found that the ratio varied
with the unit's size and features. Models with similar capacities
and features had reasonably similar (within about 10%) ratios
of JIS/USDOE test values or conformed to a simple linear translation
[28].
Conversion of air conditioner EERs from one test to another should,
in principle, be simpler because there are fewer variables in
the test procedure. However, the US has diverged from most of
the world by developing "seasonal" EERs for central
air conditioners and heat pumps. These SEERs rely on performance
data of the individual machine at three pairs of indoor and outdoor
temperatures, as well as local climate data. Even though there
is no straightforward conversion from DOE to ISO values, it is
possible to make reasonably accurate conversions if the input
data to the DOE value are available. (The steady-state efficiency
is one of the measurements made.) There is also confusion within
the ISO test procedure itself because it allows testing at any
one of three ambient temperatures. If one manufacturer chooses
to test at the lower temperature and another manufacturer at the
higher temperature, then comparisons are impossible. In addition,
manufacturers often fail to clearly note which temperature they
used.
Measurements of efficiencies of fuel (oil, gas, and kerosene)
appliances are generally straightforward, and so is conversion
from one procedure to another. However, none of the tests include
the electricity consumed by associated fans and pumps. As mentioned
before, the electricity consumption of these components is often
significant. Unfortunately, however, there is no agreement on
how to combine the fuel and electrical energy, that is, should
the site electricity be converted to primary energy to reflect
generation and transmission losses? If purely site energy is
considered (e.g., 1 kWh equals 3.6 MJ), then the higher cost of
the electrical energy, in addition to the conversion losses,
is not reflected in the efficiency values.
As international trade in appliances grows, there will be increasing
pressure for a single, global energy test procedure for each appliance.
In fact, harmonized tests already exist for many electronic appliances,
such as televisions and photocopy machines, because these appliances
have been internationally traded almost from their inception.
Additional efforts toward harmonization are discussed by Turiel
[29] and Nadel [30]. Progress is slower where regional differences
have evolved in the services provided by the appliances (such
as refrigerators, washing machines, and air conditioners).
There are obvious trade benefits to harmonized test procedures.
Indeed, since most refrigerators are now produced by large, multinational
corporations, it is difficult to understand why local variations
remain. However, there are also drawbacks to harmonized energy
test procedures. A single procedure cannot address unique local
conditions or cultural preferences. For example, Japan and the
United States, countries where hot, humid weather conditions are
common, are much more concerned than the European Union is about
an air conditioner's ability to remove latent heat. One possible
solution is to develop a harmonized basic test procedure and supplement
it with nation-specific variants. For example, the United States
might require an additional energy test for the air conditioner
at part load, and Japan might want a humid-conditions test. Although
this approach is attractive on the surface, it still fails to
accomplish the goal of one energy test for all countries.
The Impact of Microprocessors on Energy
Test Procedures
Few test procedures adequately address the benefits of microprocessor-based
controls and some actually penalize manufacturers of appliances
that have them. Appliances with microprocessors can exploit special
sensors, fuzzy logic, variable speed, and other innovations to
provide near-infinite adjustments to appliance operation in response
to the specific conditions encountered or desired by the consumer
[31]. Combinations of sensors and "intelligent" controls
were originally applied to simple functions, such as the defrost
cycles in refrigerators, but their use quickly expanded to complex
controls for air conditioners, dishwashers, and washing machines.
Microprocessors are integral elements of many pure electronic
appliances, such as fax machines, computers, and copiers. Traditional
appliances controlled by microprocessors obviously provide additional
convenience to consumers, but they often save energy as well.
These controls save energy by, for example, initiating defrost
cycles in refrigerators and heat pumps only when required, preventing
overfilling of washing machines with hot water, and improving
part-load efficiency of air conditioners.
As useful as this technology has been to consumers, it is much more difficult to devise or modify an energy test procedure when the appliance is specifically designed to intelligently conserve energy. The use of microprocessors in appliances complicates the development of test procedures by:
In other words, the microprocessor, by yielding an unrealistically
low test value or achieving superior field performance to that
predicted by the test procedure, can undermine the value of the
test procedure.
For example, a microprocessor, combined with a variable speed
motor, allows an appliance to adjust its output to the load, which
reduces off-cycle losses and improves efficiency. The benefits
of variable capacity do not appear in steady-state tests but can
lead to significant field energy savings for air conditioners
and heat pumps.
In addition, an intelligent appliance can frustrate a test procedure
by recognizing that it is not performing in a realistic situation.
Dirt sensors in washing machines represent a good example. Recognizing
that the test clothes are clean, the washing machine selects an
energy-saving cycle rather than the normal cycle. Even modern
refrigerators can frustrate the test procedure. The microprocessor's
role in controlling the timing of defrost in refrigerators was
discussed above.
Most older electromechanical appliances were truly "off"
when not operating. This is not the case for new appliances having
electronic components that require a constant supply of low voltage
electricity. The low-voltage transformer and the microprocessor
create a low-level, constant electricity "leak." These
leaks have been documented by Sandberg [32], Rainer et. al.
[33] and Perez [34] . For new, efficient refrigerators, the consumption
of electronics represents 5% of total consumption [33] while ductless
air conditioners typically draw over 10W [35]. Again, the constant
consumption of electricity is generally not included in the calculation
of an appliance's energy use.
The presence of microprocessors in variable-speed air conditioners
and heat pumps may lead to worse performance than indicated by
test procedures. The EER is measured at the rated capacity;
however, variable-speed units can be operated at significantly
above rated capacity. Efficiency drops rapidly above rated capacity.
Certain usage patterns can make this a serious problem for utilities.
In Japan, for example, variable-speed air conditioners were promoted
for their energy efficiency. Unfortunately, their efficiency
during peak cooling periods was actually worse than the single-speed
units that they replaced, and this led to even sharper peaks in
electricity demand.
Almost all energy test procedures will need to undergo major revisions
in the next decade to accommodate the presence of microprocessor
control. In the short run, simple credits or adjustments to the
tested values can be applied to appliances having certain features.
For example, the manufacturer may reduce the tested value for
a dishwasher if the unit has a dirt sensor. Unfortunately, this
strategy does not distinguish between well-designed and poorly-designed
controls. In the long run, the only solution is to develop performance-based
test procedures.
Conclusions
Energy test procedures represent the technical foundation for
all energy efficiency standards and labels. Test procedures provide
a means for manufacturers, regulatory authorities, and consumers
to compare the energy consumption of different models of appliances
in a consistent manner. Given the diverse range of users, it
is no surprise that test procedures are compromises between representing
realistic usage patterns and performing measurements that are
reliable and cost-effective. The direction of the compromise
varies with the appliance; for example, the test appears to favor
realistic usage patterns for clothes washers while favoring economy
for air conditioners. This balance will certainly change as the
relative influence of each stakeholder changes, but the results
of energy tests will still play an important role in many private,
commercial, and public policy decisions.
Energy test procedures will face unusual pressures in the next
decade as a consequence of administrative and technical developments.
As countries work to establish energy efficiency standards, the
details of every test procedure will come under more scrutiny.
Manufacturers will seek to make the testing requirements simple
and inexpensive. Foreign manufacturers will regard complex or
unique test procedures as a trade barrier. In addition, domestic
manufacturers will want to ensure that their products appear as
energy efficient as possible, while consumers will want the test
procedures to reflect as realistic results as possible. Meanwhile,
continuing technological innovations will undermine the ability
of existing procedures to reasonably represent an appliance's
energy efficiency. For example, the incorporation of microprocessors
in appliances means that future test procedures will need to measure
the performance of an appliance's mechanical features and
the software that controls them. Finally, new features appearing
in appliancesfrom automatic ice making in refrigerators to dehumidification
modes in air conditionerswill cause consumers to use appliances
differently, thereby rendering the test procedures obsolete.
Test procedures of all types are generally regarded as obscure,
dry, and highly technical. While the issues are indeed complex,
in the case of energy test procedures, there are also technical,
economic, cultural, and behavioral aspects tugging in every direction
at once. Furthermore, small differences in the details of the
test procedures can have a large impact on energy use, the environment,
and the international economy. There are no simple solutions
to these challenges, but understanding the complexities involved
is fundamental to devising a framework for tackling them.
Acknowledgments
This work was supported by the Assistant Secretary for Energy
Efficiency and Renewable Energy of the U.S. Department of Energy
under Contract No. DE-AC03-76SF00098. The authors thank Brian
Dougherty, Stan Liu, and Jim Kao of the National Institute of
Standards and Technology, Peter Biermayer and Gregory Rosenquist
at Berkeley Lab, and Don Mackay of the Air-Conditioning and Refrigeration
Institute for their assistance in the preparation of this paper."
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35.
Nakagami, H. Jyukankyo Research Institute. Personal
Communication. March 13,1996.
Figure 1. Energy test procedures represent the technical foundation
for all energy efficiency standards and labels. Energy labels
cannot be created without an energy test procedure. Standards
are, from an enforcement standpoint, impossible without labels.
Government or utility incentive programs can be implemented in
conjunction with standards or independently, but labels are still
necessary.
Table 1. Major Institutions Concerned with Energy Test Procedures
| Institution | Country or
Region | Address |
| International Organization for Standardization (ISO) | Global | Case postale 56, CH-1211
Geneve, Switzerland |
| Association of Home Appliance Manufacturers (AHAM) | USA | AHAM, 20 North Wacker Drive
Chicago, IL 60606 USA |
| Australia-New Zealand Standard (ANZS) | Australia,
New Zealand | Standards Australia, P.O. Box 1055, Strathfield-NSW 2135, Australia |
| Japan Industrial Standards Committee (JIS) | Japan | Japan Industrial Standards Committee, c/o Standards Department, Ministry of International Trade and Industry, 1-3-1 Kasumigaseki, Chiyoda-ku, Tokyo 100, Japan |
| China (CSBTS) | China | China State Bureau of Technical Supervision, 4 Zhi Chun Road, Haidian District
P.O. Box 8010, Beijing 100088 |
| Russia (GOST R) | Russia | Committee of the Russian Federation for Standardization, Metrology and Certification, Leninsky Prospekt 9, Moskva 117049 |
| Korea (KBS) | South Korea | Bureau of Standards, Industrial Advancement Administration, 2 Chungang-dong, Kwachon City, Kyonggi-do 427-010, South Korea |
| American National Standards Institute (ANSI) | United States | ANSI, 11 West 42nd Street, 13th Floor
New York, NY 10036 USA |
| Brazil (ABNT) | Brazil | Associaçao Basileira de Normas Técnicas, Av. 13 de Maio, no 13, 27o andar
Caixa Postal 1680 20003-900-Rio de Janiero-RJ, Brazil |
| United States Department of Energy (DOE) | USA | Office of Codes and Standards EE-43, Department of Energy, 1000 Independence Ave. S.W., Washington, D.C. 20585 USA |
| Deutsches Institut für Normung e.V. (DIN) | Germany | DIN, Burggrafenstrasse 6
D-10787 Berlin, Germany |
| European Committee for Standardization (CEN) | European Union | Central Secretariat, rue Bréderode 2, B-1000, Brussels, Belgium |
| Indian Standards Institution (IS) | India | Bureau of Indian Standards, Manak Bhavan, 9 Bahadur Shah Zafar Marg
New Delhi 110002, India |
| American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) | USA | ASHRAE, 1791 Tullie Circle NE
Atlanta, GA 30329, USA |
| European Committee for Electrotechnical Standardization (CENELEC) | European Union | rue de Stassart 36
B-1050 Brussels, Belgium |
| European Committee for Standardization (CEN) | European Union | rue de Stassart 36
B-1050 Brussels, Belgium |
| International Electrotechnical Commision (IEC) | Global | International Electrotechnical Commission (IEC) PO Box 131
1211 Geneva 20, Switzerland. |
| Canadian Standards Association (CSA) | Canada | Canadian Standards Association
178 Rexdale Blvd. Rexdale (Toronto), Ontario M9W 1R3 Canada |
Table 2. Major Appliances with Energy Test Procedures
| Air Conditioners |
| Clothes Dryers |
| Clothes Washers |
| Dehumidifiers |
| Dishwashers |
| Freezers |
| Furnaces |
| Heat Exchangers |
| Heat Pumps |
| Lights |
| Microwave Ovens |
| Ovens |
| Refrigerators |
| Stoves |
| Swimming Pool Heaters |
| Personal Computers |
| Photocopiers |
| Televisions |
| Fax Machines |
| Water Heaters |
Table 3. Major Energy Test Procedures for Refrigerators and
Freezers.
| Institution | Code Number |
| ANSI/AHAM | ANSI/AHAM HRF-1-1988 |
| ISO | ISO 7371-1985 (and Amendment 1-1987) ISO/DIS 8187.3-1991 |
| ANZS | AS1430 -1986 and NZS 6205.2-1989 |
| JIS | JIS 9607 (1986) |
| Indian Standard | IS:1476-1979 |
| Chinese Standard | CNS 2062, CNS9577 |
| European Standard | EN 153:1989 |
| United States Department of Energy
(USDOE) | Uniform Test Method for Measuring Energy Consumption of Electric Refrigerators and Electric Refrigerator-Freezers, Appendix A1 to Subpart B of Part 430, Volume 10 of U.S. Code of Federal Regulations (10 CFR Chap. II). 1990. (1-1-91 Edition), pp 48-54. |