Seasonal energy efficiency ratio

In the United States, the efficiency of air conditioners is often rated by the seasonal energy efficiency ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute, a trade association, in its 2008 standard AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment. A similar standard is the European seasonal energy efficiency ratio (ESEER).

The SEER rating of a unit is the cooling output during a typical cooling-season divided by the total electric energy input during the same period. The higher the unit's SEER rating the more energy efficient it is. In the U.S., the SEER is the ratio of cooling in British thermal units (BTUs) to the energy consumed in watt-hours.

Example

For example, consider a 5000 BTU/h (1465-watt cooling capacity) air-conditioning unit, with a SEER of 10 BTU/(W·h), operating for a total of 1000 hours during an annual cooling season (e.g., 8 hours per day for 125 days).

The annual total cooling output would be:

<math display="block"> \frac{\mathrm{5000~BTU{\mathrm{1~\cancel{h} \times \frac{\mathrm{8~\cancel{h}{\mathrm{1~\cancel{day} \times \frac{\mathrm{125~\cancel{day}{\mathrm{1~year = \mathrm{5,000,000~\frac{BTU}{year. </math>

With a SEER of 10 BTU/(W·h), the annual electrical energy usage would be about:

:5,000,000 BTU/year ÷ 10 BTU/(W·h) = 500,000 W·h/year

The average power usage may also be calculated more simply by:

:Average power = (BTU/h) ÷ (SEER) = 5000 ÷ 10 = 500 W = 0.5 kW

If the electricity cost is $0.20/(kW·h), then the cost per operating hour is:

:0.5 kW × $0.20/(kW·h) = $0.10/h

Relationship of SEER to EER and COP

The energy efficiency ratio (EER) of a particular cooling device is the ratio of output cooling energy (in BTUs) to input electrical energy (in watt-hours) at a given operating point. EER is generally calculated using a outside temperature and an inside (actually return-air) temperature of and 50% relative humidity.

The EER is related to the coefficient of performance (COP) commonly used in thermodynamics with both ratios expressing efficiency in terms of energy/energy. This means both are unit-less in the sense of dimensional analysis. As the EER uses mixed energy units — and COP does not — the conversion factor from watt-hours to BTU (1 W·h = 3.41214 BTU) is multiplied with the COP to obtain the EER as follows: EER = COP × 3.41214 BTU/W·h

The seasonal energy efficiency ratio (SEER) is also the COP (or EER) expressed in BTU/watt-hour, but instead of being evaluated at a single operating condition, it represents the expected overall performance for a typical year's weather in a given location. The SEER is thus calculated with the same indoor temperature, but over a range of outside temperatures from to , with a certain specified percentage of time in each of 8 bins spanning 5 °F (2.8 °C). There is no allowance for different climates in this rating, which is intended to give an indication of how the EER is affected by a range of outside temperatures over the course of a cooling season.

Typical EER for residential central cooling units = 0.875 × SEER. SEER is a higher value than EER for the same equipment. Note that this method is used for benchmark modeling only and is not appropriate for all climate conditions.

But when either replacing equipment, or specifying new installations, a variety of SEERs are available. For most applications, the minimum or near-minimum SEER units are most cost effective, but the longer the cooling seasons, the higher the electricity costs, and the longer the purchasers will own the systems, the more that incrementally higher SEER units are justified. Residential split-system AC units of SEER 20 or more are now available. The higher SEER units typically have larger coils and multiple compressors, with some also having variable refrigerant flow and variable supply air flow.

1992

In 1987 legislation taking effect in 1992 was passed requiring a minimum SEER rating of 10. It is rare to see systems rated below SEER 9 in the United States because aging, existing units are being replaced with new, higher efficiency units.

2006

Beginning in January 2006 a minimum SEER 13 was required. The United States requires that residential systems manufactured after 2005 have a minimum SEER rating of 13. ENERGY STAR qualified Central Air Conditioners must have a SEER of at least 14.5. Window units are exempt from this law so their SEERs are still around 10.

2015

In 2011 the US Department of Energy (DOE) revised energy conservation rules to impose elevated minimum standards and regional standards for residential HVAC systems. The regional approach recognizes the differences in cost-optimization resulting from regional climate differences. For example, there is little cost benefit in having a very high SEER air conditioning unit in Maine, a state in the northeast US.

Starting January 1, 2015, split-system central air conditioners installed in the Southeastern Region of the United States of America must be at least 14 SEER. The Southeastern Region includes Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Virginia. Similarly, split-system central air conditioners installed in the Southwestern Region must be a minimum 14 SEER and 12.2 EER beginning on January 1, 2015. The Southwestern Region consists of Arizona, California, Nevada, and New Mexico. Split-system central air conditioners installed in all other states outside the Southeastern and Southwestern regions must continue to be a minimum of 13 SEER, which is the current national requirement. is designed to better reflect current field conditions. DOE increases systems' external static pressure from current SEER (0.1 in. of water) to SEER2 (0.5 in. of water). These pressure conditions were devised to consider ducted systems that would be seen in the field. With this change, new nomenclature will be used to denote M1 ratings (including EER2 and HSPF2).

{| class="wikitable"

|+New Minimum with M1 Ratings

! rowspan="2" |Split System

! colspan="3" |Region

!North

!Southwest

!Southeast

|AC < 45000 BTU/h

| rowspan="2" |13.4 SEER2

|14.3 SEER2 / 11.7 EER2

|14.3 SEER2

|AC ≥ 45000 BTU/h

|13.8 SEER2 / 11.2 EER2

|13.8 SEER2

Calculating the annual cost of electric energy for an air conditioner

Electric power is usually measured in kilowatts (kW). Electric energy is usually measured in kilowatt-hours (kW·h). For example, if an electric load that draws 1.5 kW of electric power is operated for 8 hours, it uses 12 kW·h of electric energy. In the United States, a residential electric customer is charged based on the amount of electric energy used. On the customer bill, the electric utility states the amount of electric energy, in kilowatt-hours (kW·h), that the customer used since the last bill, and the cost of the energy per kilowatt-hour (kW·h).

Air-conditioner sizes are often given as "tons" of cooling, where 1 ton of cooling equals . 1 ton of cooling equals the amount of power that needs to be applied continuously over a 24-hour period to melt 1 ton of ice.

The annual cost of electric energy consumed by an air conditioner may be calculated as follows:

: (Cost, $/year) = (unit size, BTU/h) × (hours per year, h) × (energy cost, $/kW·h) ÷ (SEER, BTU/W·h) ÷ (1000, W/kW)

Example 1:

An air-conditioning unit rated at (6 tons), with a SEER rating of 10, operates 1000 hours per year at an electric energy cost of $0.12 per kilowatt-hour (kW·h). What is the annual cost of the electric energy it uses?

: (72,000 BTU/h) × (1000 h/year) × ($0.12/kW·h) ÷ (10 BTU/W·h) ÷ (1000 W/kW) = $860/year

Example 2.

A residence near Chicago has an air conditioner with a cooling capacity of 4 tons and an SEER rating of 10. The unit is operated 120 days each year for 8 hours per day (960 hours per year), and the electric energy cost is $0.10 per kilowatt-hour. What is its annual cost of operation in terms of electric energy? First, we convert tons of cooling to BTU/h:

: (4 tons) × (12,000 (BTU/h)/ton) = 48,000 BTU/h.

The annual cost of the electric energy is:

: (48,000 BTU/h) × (960 h/year) × ($0.10/kW·h) ÷ (10 BTU/W·h) ÷ (1000 W/kW) = $460/year

Maximum SEER ratings

Today there are mini-split (ductless) air conditioner units available with SEER ratings up to 42. During the 2014 AHR Expo, Mitsubishi unveiled a new mini-split ductless AC unit with a SEER rating of 30.5. GREE also released a 30.5 SEER rating mini split in 2015 as well. Carrier launched a 42 SEER ductless air conditioner during 2018 Consumer electronic Show (CES), held in Las Vegas. Traditional AC systems with ducts have maximum SEER ratings slightly below these levels. Also, practically, central systems will have an achieved energy efficiency ratio 10–20% lower than the nameplate rating due to the duct-related losses.

Additionally, there are ground-source residential AC units with SEER ratings up to 75. However, ground-source heat pump effective efficiency is reliant on the temperature of the ground or water source used. Hot climates have a much higher ground or surface water temperature than cold climates and therefore will not be able to achieve such efficiencies. Moreover, the ARI rating scheme for ground-source heat pumps allows them to largely ignore required pump power in their ratings, making the achievable SEER values often practically lower than the highest efficiency air-source equipment—particularly for air cooling. There are a variety of technologies that will allow SEER and EER ratings to increase further in the near future. Some of these technologies include rotary compressors, inverters, DC brushless motors, variable-speed drives, and integrated systems such as those found in solar-powered air conditioning.

Lower temperatures may cause a heat pump to operate below the efficiency of a resistance heater, so conventional heat pumps often include heater coils or auxiliary heating from LP or natural gas to prevent low efficiency operation of the refrigeration cycle. "Cold climate" heat pumps are designed to optimize efficiency below . As of 2023 heat pumps are marketed that will extract heat from outdoor temperatures as low as . In the case of cold climates, water or ground-source heat pumps are often the most efficient solution. They use the relatively constant temperature of ground water or of water in a large buried loop to moderate the temperature differences in summer and winter and improve performance year round. The heat pump cycle is reversed in the summer to act as an air conditioner.

References

External links

A new measure for the energy efficiency of heating and cooling devices – Information from Daikin on seasonal efficiency
Climate Impacts on Heating Seasonal Performance Factor (HSPF) and Seasonal Energy Efficiency Ratio (SEER) for Air Source Heat Pumps