9.4: Air Conditioner Efficiency

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Air conditioners are rated by the number of British Thermal Units (BTU) of heat they can remove per hour. Another common rating term for air conditioning size is the "ton," which is 12,000 BTU per hour.

Each air conditioner has an energy-efficiency rating that lists how many BTUs per hour are removed or “pulled out” for each watt of power it draws.

The efficiency rating for room conditioners is the Energy Efficiency Ratio (EER).
The efficiency rating for central air conditioners, is the Seasonal Energy Efficiency Ratio (SEER).

These ratings are posted on an Energy Guide Label, which must be conspicuously attached to all new air conditioners. Energy Star-labeled appliances mean that they have high EER and SEER ratings.

Energy Guide Label, lists type of appliance, model #, capacity, cost of operation, etc.

Figure 9.4.1. EnergyGuide label, which lists the type of appliance, model number, capacity, cost of operation, etc.

Room Air Conditioners — EER

The Energy Efficient Ratio (EER) measures how efficiently a room air conditioner will operate at a specific outdoor temperature. The higher the EER, the more efficient the system.

The EER can be calculated using the equation

\[ EER = \dfrac{ \tfrac{BTUs}{hr} \, pulled \, out}{Watt} \]

Remember that the EER energy-efficiency rating lists how many BTUs per hour are removed or “pulled out” for each watt of power it draws. Room air conditioners generally range from 5,500 BTU per hour to 14,000 BTU per hour.

National appliance standards require room air conditioners built after January 1, 1990, to have an EER of 8.0 or greater. A room air conditioner with an EER of at least 9.0 is recommended for milder climates, whereas in hotter climates an EER over 10 is preferred.

The Association of Home Appliance Manufacturers reports that the average EER of room air conditioners rose 47 percent from 1972 to 1991. If a 1970s-vintage room air conditioner with an EER of 5 is replaced with a new one with an EER of 10, air conditioning energy costs will be cut by 50 percent.

Central Air Conditioners—SEER

Seasonal Energy Efficiency Ratio (SEER) measures how efficiently a central air conditioner will operate at a specific outdoor temperature. The higher the SEER, the more efficient the system.

The SEER can be calculated using this equation:

\[ SEER = \dfrac{ \tfrac{BTUs}{hr} \, pulled \, out}{Watt} \]

Again, the SEER energy-efficiency rating lists how many BTUs per hour are removed or “pulled out” for each watt of power it draws.

National minimum standards for central air conditioners require a SEER of 9.7 and 10.0, for single-package and split-systems, respectively. But you do not need to settle for the minimum standard—there is a wide selection of units with SEERs reaching nearly 17.

Before 1979, the SEERs of central air conditioners ranged from 4.5 to 8.0. Replacing a 1970s-era central air conditioner with a SEER of 6 with a new unit having a SEER of 12 will cut your air conditioning costs in half. Today's best air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20 to 40 percent of your cooling energy costs by replacing it with a newer, more efficient model.

In general, new air conditioners with higher EERs or SEERs have higher price tags. However, the higher initial cost of an energy-efficient model will be recovered several times during its lifespan. Some utility companies encourage the purchase of a more efficient air conditioner by offering incentives. Buy the most efficient air conditioner you can afford, especially if you use (or think you will use) an air conditioner frequently and/or if your electricity rates are high.