Improving Central Air Conditioner Performance Ratings: A Review of Seasonal Energy Efficiency Ratings (SEER)
Report Number	A071
Author Info	Harvey M. Sachs, ACEEE; Hugh Henderson, CDH Energy Corp.; Don Shirey, III, Florida Solar Energy Center; and Steven Nadel, ACEEE
Details	Executive Summary U.S. law requires that the energy efficiency of residential air conditioners (and heat pumps in the cooling mode) be measured by the Seasonal Energy Efficiency Ratio (SEER). SEER is intended to provide a representative ranking or measure of seasonal efficiency, so it is based on average U.S. climate conditions. SEER has been a good-faith effort to develop a seasonal efficiency indicator that would be easy for consumers to use, and would provide reliable comparative information. It was originally intended to provide a single metric to rank or compare equipment, not an absolute measure of energy consumption. Since its initial development in 1979, SEER is now a quarter century old. The next round of standard-setting will not take place for several years. In this context, our work attempts to review what the manufacturers and the efficiency community have learned about the relationship between the SEER rating method and field performance, to suggest alternatives that might work better, to examine the implications of the most promising alternatives, and to make recommendations for new approaches, if warranted. Needs have evolved since the SEER was first developed and then implemented in 1979. For example, energy efficiency and consumption was the original focus. Today, in many regions the electric utilities have grave concerns about ability to meet peak (high temperature) summer demands. If, as expected, time-of-day pricing becomes important in the residential market, peak performance will also matter greatly to consumers. In many cases, SEER does not effectively help consumers select equipment that will minimize their operating costs. As an ad hoc measure, California litigation compelled manufacturers to list the Energy Efficiency Ratio (EER), a steady-state measure of performance at 95ºF. In many U.S. regions — including the one represented by the weather data used in the SEER bin calculations — the total hours with temperatures at 95ºF and above are only a few percent of all the hours when air conditioning is required. SEER provides a good representation of seasonal efficiency in these climates. However, in regions such as the Southwest, there are many hours in the cooling season above 95°F, so EER can be a better predictor of seasonal energy use than SEER. Our analysis used weather data for several Southwestern cities in the SEER calculation procedures and showed that bin-calculated SEERs in hot, dry climates are 4–7% lower than the nominal SEER. To remedy this effect, we propose a new metric, referred to as the “SEER-hot-dry” (SEERHD). This can be calculated from the same laboratory test data using bin temperature data for a representative hot, dry climate (e.g., Fresno). This new metric (SEERHD) would meet the needs of consumers in hot, dry climates while the traditional metric (SEER) would be retained for average climates. The SEERHD could also account for the higher costs of electrical energy at high temperatures using the concept of “time-dependent valuation” (TDV) from California. The state is using TDV to evaluate efficiency and demand-side measures for Title 24 (buildings energy code) analysis. As an additional metric to represent extreme performance, we recommend that the EER115 be required as an additional test condition to represent the impact that air conditioners have on the utility grid. This metric will be useful to utility planners and ultimately consumers, who are expected to shoulder more and more of the cost of meeting peak electric demands. As residential construction methods have improved, humidity has become a more significant issue for consumers and the building industry in many areas of the country — especially the Southeast. High humidity negatively affects thermal comfort and increases the potential for mold growth. Special consideration is necessary for hot, humid climates. While efficiency for these regions is reasonably well represented by SEER, other metrics are necessary to confirm air conditioner equipment can address high humidity concerns. To this end, we recommend that the Sensible Heat Ratio at 82ºF (SHR82), at the lowest capacity stage, become a certified rating condition. This would provide customers and contractors a way to understand the tradeoffs between capacity and efficiency. It would also discourage manufacturers from designing equipment that improves efficiency at the cost of marginal dehumidification performance. Finally, we recommend that test conditions in the current procedure be changed to reflect actual conditions and to encourage better designs. The current rating method assumes very low flow resistance of the air distribution system, that is, low “ESP” (external static pressure). The values in the test, 0.1–0.2 inches of water column (IWC), are half to one-third of values typically measured in the field. This challenges manufacturers to design equipment that will do well at these unrealistic laboratory test conditions while also meeting customer expectations in the field. Incorporating more realistic test conditions will allow manufacturers to fully focus on designing equipment to meet customer needs. Customers also need a means to compare the fan performance of different units. To meet this need, we recommend that manufacturers provide a Watt per cfm rating for their units that corresponds to the SEER test conditions. It is important to develop better ways to measure and rate the energy performance of air conditioners. For example, a good test procedure should reasonably reflect typical field operating conditions while also allowing manufacturers to differentiate models that control humidity well or are particularly efficient in very hot climates. Such metrics should also give consumers an indication of seasonal operating costs for their region and even factor in time-of-day and seasonal variations in electric costs. A secondary goal would be to provide electric utilities with measures of high temperature performance so they can understand the impact of demand-side efficiency measures as a means to moderate peak load on the electric grid. We believe that the steps we outline could contribute towards meeting these needs. Finally, changing the system of measuring air conditioner performance is serious business, with large potential impacts on manufacturers and U.S. energy use. We hope these changes can be advanced through a consensus process with all interested parties participating. Development of a consensus would make it much easier for the U.S. Department of Energy (DOE) to make the necessary changes in regulations. Moreover, it is possible that changes along the lines discussed in this report will require changes to the underlying federal legislation. Consensus would make such changes much easier to secure.
Other Info	29 pp., October 2007, A071 This report is Tasks 1.1 and 1.4 of Closing the Gap: Getting Full Performance from Residential Central Air Conditioners View report for free as a PDF.
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