Mike Murphy

It is time to take a serious look at the testing methodology for determining Seasonal Energy Efficiency Ratio (SEER). If the automotive industry is any indication, HVAC test procedures are probably overdue for some changes.

The automotive industry has recently embraced new test procedures that effectively show decreases in miles per gallon (mpg) estimates. After 23 years, the U.S. Environmental Protection Agency (EPA) has overhauled its fuel mileage testing procedures for all cars manufactured after Sept. 1, 2007. The good news is that the new EPA estimates are much closer to what new-car buyers can expect to achieve in the real world because the new testing more closely resembles how people actually drive. The bad news is that in most cases, mileage estimates on window stickers have dropped an average of 12 percent.

Consider the popular Toyota Prius. For models made before Sept. 1, the EPA sticker estimated that drivers could expect to get 60 mpg in the city, 51 on the highway, and 55 combined. For models made after Sept. 1, the new numbers are 48 city/45 highway, and 46 combined.

Nothing about the Prius changed to make the numbers drop. The only change was in how the EPA arrives at the numbers.

The new test procedures acknowledge that people don’t actually drive in the summertime with the air conditioner off; nor do they only drive when it is 75°F outside, nor do they drive at an average speed of only 48 mph. For the first time, the new EPA fuel economy estimates will use tests designed to replicate three real-world conditions: high-speed/rapid-acceleration driving, use of air conditioning, and cold temperature operation.


The efficiency of air conditioners and heat pumps are rated by the SEER as defined by the Air-Conditioning and Refrigeration Institute in its Standard 210/240 Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment last updated in July 2006. There have been proposals to make some minor changes to the test procedures, however, not enough has been done to create a more real-world test.

When a manufacturer sends equipment to a laboratory to establish its SEER rating, you can bet the equipment is set to perform its best under the test conditions. However, that is not usually the same as the environment an HVAC contractor must work within while trying to make a piece of equipment perform up to its capabilities.

Advanced Energy of Raleigh, N.C., refers to these as the “field adjustment factors.” Using an automotive analogy, these might be called real-world conditions. For example, using a duct system that doesn’t meet industry standards or the specifications of a controlled test environment can cause an air conditioner to deliver far less than the laboratory SEER rating. A laboratory duct system might be consistent from one test to another; however, when is the last time you saw two duct systems in homes that were the same?

Seven out of 10 systems have an inadequate refrigerant charge. I wonder if the lab guys run both under- and overcharged test conditions when determining SEER? Field studies show that central air conditioning systems are, on average, oversized from 24 percent to 100 percent. Oversizing has a bad effect on energy use; however, builders and contractors all do it.

All three of these examples are certainly not ideal for the operation of an air conditioning system. However, it is the real world. The indoor and outdoor SEER test conditions as determined by the Department of Energy (DOE) are not reflective of the real world.

There are additional strong arguments for other modifications such as the external static pressure allowed for testing. Aside from static problems with improper ducts, there are ever-increasing static demands of high efficiency filtration systems. The DOE-approved test procedures allow the creation of artificially high SEER ratings - efficiencies that are not usually obtained in the field.

SEER testing serves a very useful and admirable purpose. Because each piece of cooling equipment is evaluated using the exact same conditions, the SEER rating can be used to compare the performance of equipment from different manufacturers. But after decades of changes in the way air conditioning systems are being applied, it’s time that SEER testing got a facelift. The test procedures need to be more accurate in reflecting the actual operating conditions.

The Auto Alliance, a trade association that includes nine major automotive manufacturing companies, said “ … we want consumers to have accurate estimates of their fuel economy. We support the new (mpg estimate) labels.”

The HVAC industry should have the capability of providing accurate estimates of energy efficiency as measured by SEER.

Sources: Article by Tom Jensen, for Wheelbase Communications; www.advancedenergy.org.

Publication date:12/03/2007