Seasonal energy efficiency ratio Totally Explained

Everything about Seasonal Energy Efficiency Ratio totally explained

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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 (External Link

) last updated in 2006. 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-hours (W·h) during the same period. ť SEER = BTU / W·h

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 (for example, 8 hours per day for 125 days) would provide an annual total cooling output of:
ť 5000 BTU/h × 1000 h = 5,000,000 Btu

With a SEER of 10, the annual electrical energy usage would be about:
ť 5,000,000 BTU / 10 BTU/W·h = 500,000 W·h

This is equivalent to an average power usage during the cooling season of: ť 500,000 W·h / 1000 h = 500 W

The average power usage may also be calculated more simply by:
ť 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:
ť 0.5 kWh × $0.20/kWh = $0.10/h

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 the 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 (for example, the temperature distribution for the geographical location of the SEER test). Formulas for the approximate conversion between SEER and EER or COP in California are:

SEER = EER ÷ 0.9
SEER = COP x 3.792
EER = COP x 3.413

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.
The relationship between SEER and EER is relative depending on where you live because equipment performance is dependent of air temperatures, humidities, and pressures. The relationship stated above is typical if you live in the lower-elevation portions of California; however, if you live in Georgia it's better approximated by SEER = EER ÷ 0.80 due to the much higher humidities. A similar relationship exists in relating SEER and COP, also depending on where you live.

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 watts per hour.
   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 (for example 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, and an EER of at least 11 for single package equipment and 11.5 for split systems.
   Today, it's 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. Substantial energy savings can be obtained from more efficient systems. For example by upgrading from SEER 9 to SEER 13, the power consumption is reduced by 30% (equal to 1 - 9/13). It is claimed that this can result in an energy savings valued at up to US$300 per year depending on the usage rate and the cost of electricity.
   With existing units that are still functional and when the time value of money is considered, most often retaining existing units rather than proactively replacing them is the most cost effective. Maintenance should be performed regularly to keep their efficiencies as high as possible.
   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, incrementally higher SEER units are justified. Residential split-system ACs of SEER 18 or more are now available, but at substantial cost premiums over the standard SEER 13 units.

Calculating the annual cost of power for an air conditioner

Air conditioner sizes are often given as "tons" of cooling where 1 ton of cooling is defined as being equivalent to 12,000 BTU/h. The annual cost of electric power consumed by a 72,000 BTU/h (6 ton) air conditioning unit operating for 1000 hours per year with a SEER rating of 10 and a power cost of $0.12 per kilowatt-hour (kW·h) may be calculated as follows:
ť unit size, BTU/h × hours per year, h × power cost, $/kW·h ÷ SEER, BTU/W·h ÷ 1000 W/kW

ť (72,000 BTU/h) × (1000 h) × ($0.12/kW·h) ÷ (10 BTU/W·h) ÷ (1000 W/kW) = $864 annual cost

As another example, a 2000 ft² residential unit near Chicago would require a 4 ton air conditioner based on a location-specific rule-of-thumb that 1 ton is required for each 500 ft² for a typical older house: ť (2000 ft²) ÷ (500 ft²/ton) = 4 tons.

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

The estimated cost of electrical power for the 4 ton unit with a SEER rating of 10 and a power cost of $0.10 per kilowatt-hour, using 120 days of 8 hours/day operation, would be: ť (48,000 Btu/h) × (960 h/year) × ($0.10/kW·h) ÷ (10 BTU/W·h) ÷ (1000 W/kW) = $461 annual cost

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