How to work out your energy efficiency ratio (EER)
First, you must work out the energy efficiency ratio (EER), which measures how efficiently your cooling system operates when the outdoor temperature is at a particular level.
EER looks at the cooling capacity of an air conditioning unit (in British thermal units, BTU per hour) compared to the power input of the unit (watts) to measure how much heat energy the unit can remove. It’s a ratio usually used for indoor room air conditioners, like split system air conditioning units.
Essentially, the higher an air-con unit’s EER rating, the more efficient it is by having a higher cooling capacity per watt of power.
Calculating your energy efficiency ratio
If EER is not provided when shopping for air conditioning, you can easily calculate it yourself. All you need is the unit’s wattage and BTU values which you can usually get from the manufacturer or supplier.
EER = (output cooling energy in BTU/input electrical energy in Watt)
Although EER is a reliable and valuable way to determine the overall efficiency of an air conditioner, you should be aware that the actual efficiency can vary due to various external factors like weather and humidity. The bigger the difference in temperature between indoors and outdoors, the harder your unit will have to work and the less efficient it will be able to run.
The seasonal energy efficiency ratio (SEER)
In countries where the climate changes drastically between seasons (like in the UK), many manufacturers and suppliers will also use seasonal energy efficiency ratios (SEER). SEER works like EER but considers seasonal factors and air conditioning usage rather than rating a unit’s efficiency all year round.
SEER is more specific and granular by calculating the cooling capacity (BTU per hour) and power input (watts) but only throughout the crucial cooling period as opposed to all year. For example, in the UK this would mean summertime.
Calculating your seasonal energy efficiency ratio (SEER)
- Find the BTUs per hour of your air conditioner. This value is found either on the air conditioner or in the owner’s manual.
- Find the number of watts used per hour for your air conditioner. This value is also located either on the air conditioner itself or in the owner’s manual.
- Calculate the number of BTUs used in the summer months. Use 1,000 hours, which equates to about 125 days or four months, to represent the late spring and summer months when air conditioners are used. Multiply the number from step one by 1,000 to get the number of BTUs used in the summer months.
- Calculate the number of watts-hours used in the summer months by multiplying the number from step two by 1,000.
- Divide the BTUs used in the summer months (the result of step three) by the number of watts-hours consumed in the summer months (the result of step three) to arrive at the SEER rating.
At part load conditions, working out your SEER provides a realistic overall system efficiency rate on a seasonal basis.
The seasonal coefficient of performance (SCOP)
As with SEER, the seasonal coefficient of performance (SCOP) measures a heat pump’s energy consumption based on its energy efficiency over a year. It considers temperature fluctuations and standby periods to provide clear indications of energy efficiency.
To work out your coefficient of performance (COP), divide the total power input by the total power output. The higher the number, the more efficient the system will be.
Working out your SCOP will depend on the average climate. For the correct calculation of SCOP, the heat pump is tested at a series of temperatures.
Efficiency factors
The new seasonal energy efficiency ratio (SEER) and seasonal coefficient of performance (SCOP), determine multiple factors to provide a much more realistic view of energy efficiency in real-life conditions, including:
- Energy performance in different climate zones
- Efficiency at partial load capacity as well as a full load
- Energy consumption in auxiliary and standby modes
- Different load requirements through the seasons
Seasonally efficient products
Seasonal efficiency calculations give consumers a reliable performance rating they can easily understand when buying a heating or cooling device. The new energy label includes multiple classifications from A+++ to G reflected in colour shadings ranging from dark green (most energy efficient) to red (least efficient).
Information on the new label includes not only the new seasonal efficiency ratings for heating (SCOP) and cooling (SEER), but also annual energy consumption and sound levels.
Label requirements
The energy label can be found in the box of the outdoor unit. The SEER/SCOP rating and the energy label must be displayed on product literature, data sheets and websites. Any dealer or wholesaler displaying the outdoor unit must also display the label.
