Alan Meier
Lawrence Berkeley National Laboratory
University of California
Berkeley, California USA
AKMeier@lbl.gov
Abstract
An energy test procedure provides a way of consistently evaluating energy use and savings across different models of an appliance. A new technology, microcontrollers, is undermining the credibility of energy test procedures. Microcontrollers are important because more energy savings in the next decade will be achieved by their application than from mechanical improvements. A microcontroller can also be an effective tool to save energy. Many applications will save at least 30%. Current energy tests discourage manufacturers from introducing new, energy-saving technologies. But manufacturers can also use them to circumvent test procedures. In two cases, this has led to legal sanctions. Most of the appliance energy test procedures will need to be revised so as to measure energy performance of both the hardware and the software.
Introduction
An energy test procedure is a standardized way of measuring energy use of a device. For appliances, the energy test procedure is the foundation for energy efficiency standards, energy labels, and other related programs. (Meier and Hill, 1997) It provides manufacturers, regulatory authorities, and consumers a way of consistently evaluating energy use and savings across different appliance models. The relationship among these components is illustrated in Figure 1.
A well-designed test procedure services the needs of its users economically and with an acceptable level of accuracy and correspondence to actual conditions. On the other hand, a poorly-designed energy test procedure can undermine the effectiveness of everything built upon it. For example, many demand-side management programs rely on data from energy test procedures to calculate rebates or to estimate a program’s energy savings.
Figure 1. The relationship between energy test procedures, labels, efficiency standards, and other efficiency programs.
Every energy test procedure is unique, but they do have some common features. All tests consist of placing the appliance in a controlled environment and then measuring its energy consumption. A refrigerator, for example, is placed in a room maintained at 32°C, with its doors closed, for about 24 hours and must include at least one complete defrost cycle. An automobile is placed on a dynamometer and "driven" through a carefully defined driving cycle. These tests capture the thermal resistance of the refrigerator’s walls, the efficiency of the car’s engine, and other mechanical features. The resulting measurement is an energy consumption value, such as kWh/year, or an efficiency, such as SEER or miles/gallon, that eventually appears on energy labels.
This paper describes how a new technology, microcontrollers, is undermining the credibility of energy test procedures. Microcontrollers are important because more energy savings in the next decade will be achieved by their application than from mechanical improvements. But before this can happen, energy test procedures for all appliances — from cars to refrigerators — will need to be revised. The credibility of current energy tests is being undermined by appliances equipped with microcontrollers. At the same time, the existing test procedures discourage the introduction of legitimate, energy-saving technologies relying on microcontroller technology. This situation will require the modification of nearly all energy test procedures in the next decade.
How Microcontrollers Save Energy in Appliances
Appliance manufacturers are increasingly installing microprocessors in their products. These small computers are often called microcontrollers. A microcontroller gives an appliance the ability to collect information, process it, and decide how to operate. These microcontrollers provide new amenities to consumers. Some examples of microcontroller applications are:
A microcontroller can also be an effective tool to save energy. The microcontroller modifies operation in many ways that save energy. Each situation is unique, but there are five common approaches to cutting energy use. These approaches are:
A microcontroller needs sensors to provide it data from which it can make decisions. The real innovation has been combinations of microcontrollers with a range of sensors. Sensors can now measure temperature, pressure, optical properties of dirty water, movement, frost accumulation, humidity, and more. This information helps the microcontroller determine the appropriate response and avoid heavy washing of clean dishes, defrosting when no frost is present, or switching to resistance heat when experience has taught it that heat pump operation will achieve the same goal by the desired time.
There is good reason to believe that a large fraction of energy savings in future appliances will be achieved by the application of microcontrollers rather than with mechanical improvements. However, some of these savings will be fake, that is, they will appear only in the test procedure. The following discussion first explains how manufacturers use the microcontroller to circumvent the test procedure and make the appliance appear more efficient than it actually is.
How Manufacturers Use Microcontrollers To Circumvent Energy Test Procedures
A microcontroller can change an appliance’s behavior during testing so that it uses less energy while actual energy use in common situations is unchanged. In this way, the microcontroller undermines the credibility of the test results. Two examples resulting in criminal prosecution occurred in the motor vehicle industry. These examples pertain to emissions tests rather than energy tests, but the tests are essentially the same and the implications apply to both.
The U.S. Environmental Protection Agency (EPA) emissions and fuel economy tests are conducted on a special dynamometer, in which the car is driven through a carefully-defined sequence of cruising at different speeds. Auxiliary equipment, such as the air conditioner, is switched off. A sensor in the tailpipe measures oxygen concentration in the exhaust and the microcontroller adjusts the fuel-air mixture entering the engine cylinders to minimize engine emissions (and improve fuel economy).
In 1995, General Motors designed certain Cadillacs to go "open loop", that is, switch off the feedback from the tailpipe sensor, when the car exceeded 60 mph. (Cushman, 1995) (This feature gave the cars better acceleration at high speeds.) The microcontrollers were also programmed to go open loop when the air conditioners were switched on. Neither of these programming instructions will be triggered in the emissions test, even though they are both very common situations. The EPA fined Cadillac $46 million and subsequently rewrote the regulations to prohibit all open loop operation.
Evidently the motor vehicle industry found the benefits from microcontroller control too tempting to resist because the diesel engine manufacturers also tried to circumvent the emissions test. (Cushman, 1998) Again, the microcontroller switched the engines to "open loop" for conditions outside those used in the test. The EPA discovered the violations in 1998 and is now prosecuting the manufacturers. In this case, the violation was even more blatant because open loop operation was explicitly prohibited. The fines are expected to be in the hundreds of millions of dollars.
The ways in which a microcontroller circumvents energy test procedures of home appliances is less well documented but rising in importance. Two examples from Japan and the United States may indicate the future.
Most Japanese refrigerators are now equipped with sophisticated microcontrollers. One important new function of these microcontrollers is to recognize when the refrigerator is being tested, that is, being exposed to the test conditions. When these conditions are sensed, the microcontroller modifies operations in ways that reduce energy consumption. This might include switching off auxiliary fans or shortening the defrost cycle. This has enabled some manufacturers to achieve over 25% reduction in tested energy use without significant changes in the units’ mechanical features (that is, thickness of insulation, compressor efficiency, etc.) The same approach has been applied to air conditioners, although the extent of savings are not known.
Recently, the Japanese government created minimum energy efficiency standards for refrigerators. These standards were intended to save consumers money and reduce carbon dioxide emissions. Most of the manufacturers will have reduced the energy consumption of their refrigerators and met the new standard’s requirements simply by adding a few sensors and re-programming the microcontroller. When operated in kitchens, these new units will use about the same amount of energy as the older units.
Consumer Reports tested dishwashers in 1998. (Consumer Reports , 1998) It found that the labeled energy use (that is, the energy consumption determined from the test procedure) was a misleading indicator of the unit’s actual energy use. An energy-saving innovation, the dirt-sensor, was responsible for the discrepancy. Units with dirt sensors (and microcontrollers to control them) could not be tested in the conventional way because clean dishes are used in the Department of Energy (DOE) test. A "smart" dishwasher recognizes that the dishes are clean and greatly reduces the amount of hot water consumed and shortens cycle time. Instead of modifying the test procedure or using soiled dishes (which Consumer Reports does), the DOE test simply measures the smart dishwashers with the sensor turned off and then awards a fixed credit for presence of a soil sensor. The DOE test does not test the sensor’s efficacy. In many cases, Consumer Reports found that the sensor was ineffective, so the credit was not justified.
These examples demonstrate that the use of microcontrollers can have a demonstrable impact on energy use in a wide range of appliances. Furthermore, there are already cases of manufacturers using microcontrollers to make the appliances use less energy in the test procedure than would occur in real situations. Most energy test procedures are vulnerable to this kind of abuse and, for this reason, will soon need revision.
How Microcontrollers Can Save More Energy Than Indicated By the Test Procedure
There are many ways in which an unscrupulous appliance manufacturer can exploit microcontrollers to circumvent or undermine the intent of energy test procedures. Fortunately, there are many more ways in which an innovative manufacturer can save more energy than will be revealed in the test procedure. The generic approaches were described earlier, but some of the specific technologies are discussed below.
Variable-Interval Defrost in refrigerators. The automatic defrost feature in refrigerators can be responsible for as much as 15% of a refrigerator’s total electricity consumption. Most refrigerators use clocks to initiate defrost at a regular interval. The heater is switched on even if no frost has accumulated. The energy test measurement period runs from defrost to defrost so as to capture exactly one energy-intensive defrost cycle. Recently, a manufacturer developed a sensor to detect accumulation of frost in refrigerator-freezers. When a specified level of frost accumulates, the defrost heater is switched on and the frost melts. A refrigerator with this sensor will never defrost during the test because not enough frost accumulates. Other approaches to reducing unneeded defrost (typically called "adaptive defrost") also rely on microcontrollers and other sensors.
Variable-Speed Motors in Air Conditioners, Heat Pumps, and Refrigerators. Variable speed motors in appliances offer many benefits to consumers, including more precise temperature better humidity control, and quieter operation. There are also substantial energy savings when the appliance is operating at part-load. Most appliance energy test procedures, however, measure performance at steady-state. The variable-speed motor performs worse than single-speed alternatives at steady-state because of small losses in the inverter. In practice, savings from variable-speed operation can easily exceed 30% when compared to single-speed units because these units operate for long periods at part-load. These savings will not appear in the tests.
Soil Sensors in Dishwashers and Clothes Washers. The DOE tests do not use dirty dishes or clothes. Several US manufacturers have introduced dishwashers and clothes washers with soil sensors (and they are common in both Japan and Europe). These sensors measure the amount of dirt and the microcontrollers adjust water temperature, amount of water, and dose of detergent to match the needs. Microcontrollers cut washing time, save water and detergent, and avoid needless over-washing. They also save energy through reduced hot water consumption and motor operation. The sensors and logic needed to make successful cleaning selections is complicated but most test procedures ignore the existence of the microcontrollers. No credit is given to superior algorithms or sensors.
Moisture and Temperature Sensors in Clothes Dryers. Clothes dryers waste considerable energy by over-drying clothes. Two strategies have been used to minimize over-drying: temperature sensors and humidity sensors. The DOE test for clothes dryers does not attempt to measure the efficacy of the different approaches; instead it assigns an arbitrary "field use factor" to each sensor. (U.S. Department of Energy, 1997) Both sensors receive a 1.04 factor regardless of their effectiveness.
Replaceable Control Chips for Appliances. The microcontrollers controlling emissions and engine operation in cars have been replaceable for several years. A gray market has developed, allowing consumers to modify their cars’ performance simply by inserting a different chip developed by a third party. Recently, some dishwasher and clothes washer manufacturers plan to offer updated chips with revised programs for new detergents or fabrics. In these examples, the appliances’ energy efficiency may be altered, even though there have been no mechanical changes. For cars, the new chip typically causes lower energy efficiency (but better acceleration) while, for dishwashers, the chip may improve efficiency.
Current energy tests discourage manufacturers from introducing new, energy-saving technologies. Such innovations may have obvious energy-saving benefits during actual use in homes but no measurable savings in the test procedure. Manufacturers have no incentive to use those innovations (unless they provide other non-energy benefits, too). A discrepancy between field and laboratory conditions will always be the case, but it appears that innovations make the discrepancy particularly large now. Essentially all major energy-consuming appliances can benefit from innovations in microcontroller control (including variable-speed drive and use of sensors). The examples above demonstrate that the energy-saving potential is still large.
The Next Generation of Energy Test Procedures
There are two powerful reasons to drastically revise current test procedures. First, current tests are being undermined by microcontrollers, leading to misleading efficiency rankings of appliances. Second, the tests fail to fairly credit many important, energy-saving innovations. Thus both consumers and manufacturers have reasons to support revisions. Since these shortcomings appear in nearly all energy test procedures, from autos to refrigerators, a major administrative undertaking will be required. It will require cooperation among manufacturers, regulators, professional associations, and consumers. Government regulators, such as the EPA and DOE will play an especially important role because their mandatory efficiency standards are based on these test procedures; if the tests change, then the regulations based on them must also be modified.
Revising tests to address these problems will be difficult for administrative, technical, and practical reasons. Every test procedure must be considered individually, although the revisions will address many of the same issues. All future test procedures should have the following goals:
The next-generation test procedures will probably be a combination of hardware and software tests. One approach would be to conduct hardware tests similar to current tests, though perhaps covering more than one set of conditions. (This will permit extrapolation of performance over a range of conditions.) A second set of tests would focus on the microcontroller. These tests would require the interrogation of the microcontroller via a wire connection to another computer in the testing facility. The microcontroller would be presented with thousands of different conditions and its responses recorded. The results of the hardware and software tests would be combined in a specified procedure to determine an overall energy efficiency "score." This scheme has many drawbacks, but does address some of the earlier problems. Other approaches are of course possible. Indeed, different approaches will probably be necessary for different appliances.
International test procedures, such as those established by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC), have the same weaknesses as the US tests and will also need revision. This creates an excellent opportunity for all countries to harmonize their energy test procedures while creating addressing a serious technical shortcoming.
Conclusions
Energy test procedures generally receive very little attention even though they form the basis of many technical and legal activities. It is essential that energy test procedures stay reasonably up-to-date or else they will provide misleading and inconsistent information. An unusual situation has occurred due to the rapid introduction of microcontrollers in all appliances, from air conditioners to cars. As a result, nearly all test procedures are obsolete and cause serious misrepresentations of energy consumption. Many of the changes in operation caused by the microcontrollers are modest, but unscrupulous manufacturers can, under certain conditions, lower the tested energy use by over 30% without a parallel drop in field use. So, in order to maintain the credibility of appliance energy test procedures, a major overhaul will be required.
Just as important, the current test procedures discourage innovation. Microcontroller operation of appliances offers a tremendous opportunity to reduce energy use and could be responsible for most of the energy savings achieved in the next decade. Again, these savings will not be realized unless the tests give credit to software innovations.
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.
References
Consumer Reports. 1998. "Dishing Out Dollars.", March, 37-40.
Cushman, J. H. 1995. GM Agrees to Ante Up $45 Million in Big Recall. The New York Times, December 1.
Cushman, J. H. 1998. Makers of Diesel Truck Engines Are Under Pollution Inquiry. The New York Times, February 11, 1998.
Meier, A. K. and J. E. Hill (1997). "Energy Test Procedures for Appliances." Energy and Buildings 26(1): 22-33.