Equipment used in cooling systems in residential and small commercial buildings often express the cooling system efficiency in terms like

**EER - Energy Efficiency Ratio and/or**

**SEER - Seasonal Energy Efficiency Ratio.**

For central air conditioner systems it is more common to use SEER - Seasonal Energy Efficiency Ratio.

**EER - Energy Efficiency Ratio :-**

EER is a measure of how efficient a cooling system operates in steady state (over time) when the outdoor temperature is at a specific level (outdoor conditions commonly used are

95°F (35°C)).The higher EER - the more energy efficient is the system.

**The EER can be calculated using this equation :-**

- 1 Btu/h = 2.931x10
^{-4}kW = 0.0299 kpm/s = 0.252 kcal/h = 3.986x10^{-4}hk = 3.939x10^{-4}hp = 0.2163 ft lb/s.

**SEER - Seasonal Energy Efficiency Ratio :-**

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:

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.