Seasonal energy efficiency ratio
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The efficiency of air conditioners is often rated by the Seasonal Energy Efficiency Ratio (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
The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is the Btu of cooling output during a typical cooling-season divided by the total electric energy input in [[watt|watt-hours during the same period.
For example, a 5000 Btu/h air-conditioning unit, with a SEER of 10, operating for a total of 1000 hours during an annual cooling season (e.g., 8 hours per day for 125 days) would provide an annual total cooling output of:
- 5000 BTU/h × 1000 h = 5,000,000 Btu
With a SEER of 10, the annual electrical energy usage would be about:
- 5,000,000 BTU / 10 BTU/W·h = 500,000 W·h
The average power usage may also be calculated more simply by:
- Average power = (Btu/h) / (SEER, Btu/W·h) = 5000 ÷ 10 = 500 W
If your electricity cost is $0.20/kWh, then your operating cost is:
- 0.5 kW × $0.20/kWh = $0.10/h
[edit] Relationship of SEER to EER and COP
SEER is related to the Energy Efficiency Ratio (EER) which is the ratio of cooling capacity in Btu/Hr and the input power in watts W at a given operating point and also to the coefficient of performance (COP) commonly used in thermodynamics. COP is a unitless measure of efficiency. The COP of a heat pump is determined by dividing the energy output of the heat pump in watts W by the electrical energy in watts W needed to run the heat pump. The higher the COP, the more efficient the heat pump. For example resistive heat has a COP = 1. The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures. EER is related to COP by converting the cooling capacity from watts W to Btu/Hr by multiplying by 3.413 Btu/Hr/W.
The SEER is calculated over a range of expected external temperatures (i.e., the temperature distribution for the geographical location of the SEER test).
From equation (2) above, a SEER of 13 is approximately equivalent to a COP of 3.43, which means that 3.43 units of heat energy are removed from indoors per unit of work energy used to run the heat pump.
[edit] US Government SEER Standards
SEER, Seasonal Energy Efficiency Ratio, is most commonly used to measure the efficiency of a central air conditioner. It measures how efficiently a cooling system will operate over an entire season. The higher the SEER, the more efficient the air conditioner. Technically speaking, SEER is the ratio of the cooling output in Btu divided by the power consumption in watt-hours.
Energy Efficiency Ratio (EER) is a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (95oF). In technical terms, EER is the steady-state rate of heat energy removal (i.e. cooling capacity) by the product measured in Btuh divided by the steady-state rate of energy input to the product measured in watts. This ratio is expressed in Btuh/watt. The higher the EER, the more efficient the air conditioner.
SEER rating more accurately reflects overall system efficiency on a seasonal basis and EER reflects the system’s energy efficiency at peak day operations. Both ratings are important when choosing products.
As of January 2006, all air conditioners sold in the United States must have a SEER of at least 13. ENERGY STAR qualified Central Air Conditioners must have a SEER of at least 14,
Today, 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. The United States now requires that residential systems manufactured after 2005 have a minimum SEER rating of 13, although window units are exempt from this law so their SEERs are still around 10.[1]
