Understanding SEER and SCOP
The energy efficiency of air conditioners and heat pumps is characterized by SEER, which is the seasonal energy efficiency ratio for cooling mode, and SCOP, which is the seasonal coefficient of performance for heating mode. At CEIS, we have been characterizing the energy efficiency of HVAC equipment for more than 25 years, so we know a thing or two about energy performance ratings. In this article we will break down what SEER and SCOP are and why they are important.
Why do we need SEER and SCOP?
A wide range of products are regulated to ensure that they either meet specific efficiency benchmarks or do not exceed a certain energy consumption. From heating and cooling systems to computers and tumble dryers, energy-consuming appliances are rated to help consumers in their purchasing decisions for more efficient products and to encourage competition between manufacturers for the development of more sustainable products.
The first Ecodesign Directive (2005/32/EC) aimed to reduce the environmental impact of energy-related products (ErP). This directive has been repealed by directive 2009/125/EC and has subsequently undergone successive amendments (see directive 2012/27/EU). Products used for room air conditioning must meet minimum energy efficiency requirements.
These requirements are adapted to the nature of each product, occurring that, in the case of air conditioners and heat pumps, the performance of the equipment is highly variable depending on external factors such as the outside ambient temperature or the load condition that is required to the equipment, that is, if you are demanding more or less power for heating or cooling. SEER and SCOP take these and other factors into account. They are obtained through standardized tests under conditions that take into account the temperature changes that occur during a typical year.
As the test conditions are standardized in accordance with current regulations, testing makes it easier for the manufacturer to comply with legislation and provides the user with a simple means of direct comparison of efficiency between different equipment.
What is the Seasonal Energy Efficiency ratio (SEER)?
SEER is the seasonal energy efficiency ratio, and measures how efficient an air conditioner or liquid chiller is at transporting energy from an indoor space to an outdoor space. In other words, how efficient it is while cooling a room. It is an evolution of the Energy Efficiency Ratio (EER), which aims to more adequately reflect the use of a unit over a year. While the EER provides the performance at an outdoor temperature of 35ºC, the SEER takes into account that the cooling demand is not the same throughout the year and, therefore, reproduces the seasonal use of air conditioning equipment.
How is a SEER rating calculated?
To estimate the energy consumption of equipment operating in cooling mode throughout the warm season (normalized from Athens climate statistics), performance tests are performed at four different outdoor temperatures, always maintaining 27ºC in the indoor space. EN 14825 standard defines the test methodology and explains the calculation process that consists of interpolating appliance performance data for all the different outdoor temperatures that most commonly occur during the season from the four performance tests.
These measured and interpolated efficiencies are weighted and combined with some other test results such as idle power consumption or thermostat cut-off, to finally provide a single value for the SEER of the appliance. The four performance tests performed correspond to different outdoor temperatures and to capacity percentages (cooling power provided by the appliance with respect to its nominal) ranging from 100% load of the equipment to 21%, when the outdoor temperature is milder (20ºC).
| Capacity | 100% | 74% | 47% | 21% |
| Outdoor temperature | 35oC | 30oC | 25oC | 20oC |
| Indoor temperature | 27°C | |||
The SEER rating is calculated by dividing the total cooling output in KWh at the different conditions, by the total electric energy used in KWhs.
What is a good SEER rating?
Higher is better.
The higher the SEER value, the higher the efficiency of a piece of the appliance. Thus SEER provides a simple way of rating performance based on a single number. Below is an example SEER rating for air-to-air equipment under 12 kW:
| Energy efficiency class | SEER |
| A+++ | SEER ≥ 8,50 |
| A++ | 6,10 ≤ SEER < 8,50 |
| A+ | 5,60 ≤ SEER < 6,10 |
| A | 5,10 ≤ SEER < 5,60 |
| B | 4,60 ≤ SEER < 5,10 |
| C | 4,10 ≤ SEER < 4,60 |
| D | 3,60 ≤ SEER < 4,10 |
| E | 3,10 ≤ SEER < 3,60 |
| F | 2,60 ≤ SEER < 3,10 |
| G | SEER < 2,60 |
What is the seasonal coefficient of performance (SCOP)?
The SCOP, or Seasonal Coefficient of Performance, is used to measure the heating efficiency of heat pumps. It is an evolution of the Coefficient of Performance (COP), which aims to reflect the performance of a system throughout the cold season. While the COP indicates the efficiency of the heat pump at a given point (at +7°C outside temperature), the SCOP takes into account that the heating needs over the course of a day/year change. The SCOP reproduces its seasonal use and with a single number allows to characterize the efficiency of the heat pump for a whole season.
How is a SCOP rating calculated?
SCOP is calculated in a very similar way to SEER, but with two fundamental differences. The first is that SCOP can be calculated for three different climate zones and based on the climatology of Strasbourg, Helsinki and Athens, which represent the average, cold and warm climate. Since the three climates experience very different winter temperatures, this is helpful in understanding how a heat pump performs in a given environment.
Again, it is EN 14825 standard that defines the test methodology and the calculation process up to the SCOP. Energy efficiency is calculated from measurements at six outdoor temperatures and load conditions for the average climate), seven for cold and five for warm. These measurements are combined with interpolated performance data and measurements of standby power consumption, thermostat cut-off, etc., and a single SCOP value is obtained for a climate zone. In the regulation (EU), it is mandatory to declare the SCOP at least for medium climate zone.
| Capacity | 100% | 88% | 54% | 35% | 15% |
| Outdoor temperature | -10°C | -7oC | 2oC | 7oC | 12oC |
| Indoor temperature | 20oC | ||||
The SCOP is obtained by dividing the total heat demand throughout the cold season in kWh by the electrical energy used by the equipment, also in kWh.
What is a good SCOP rating?
The higher the better.
Like SEER, the higher the SCOP value, the higher the efficiency and the better the energy efficiency rating. SCOP values are not as high as SEER values, because more energy is consumed in heating mode than in cooling mode and the same efficiency is not reached. Therefore, if systems with higher heating demand than cooling demand are required, more weight should be given to the SCOP rating when selecting a system. An example of SCOP rating for air-to-air appliances under 12 kW is given below:
| Energy efficiency class | SCOP |
| A+++ | SCOP ≥ 5,10 |
| A++ | 4,60 ≤ SCOP < 5,10 |
| A+ | 4,00 ≤SCOP < 4,60 |
| A | 3,40 ≤ SCOP < 4,00 |
| B | 3,10 ≤ SCOP < 3,40 |
| C | 2,80 ≤ SCOP < 3,10 |
| D | 2,50 ≤ SCOP < 2,80 |
| E | 2,20 ≤ SCOP < 2,50 |
| F | 1,90 ≤ SCOP < 2,20 |
| G | SCOP < 1,90 |
Will my system achieve the SEER and SCOP stated?
The answer is simple, no, but with nuances. Your system may work the same, better or worse than what the manufacturer indicates.
SEER and SCOP give a good indication of seasonal HVAC energy use over a typical year. However, a key thing to remember is that SEER and SCOP are measurements of a system performing at its peak. It’s highly unlikely any system will be performing optimally 100% of the time.
System performance will depend on:
- Good design and professional installation of the entire system
- Regular maintenance
- The size of the building being conditioned and its energy efficiency
- The size of the system and its air handling capacity
- The amount of time the system is used daily
- The indoor temperature you prefer
- The outdoor air temperature.
Conclusion
In conclusion, SEER and SCOP are key energy efficiency indicators for air conditioning and heat pump systems in the European Union. These coefficients allow consumers to easily compare the performance of different appliance and encourage competition between manufacturers to develop more sustainable products. However, it is crucial to keep in mind that, although the values declared by manufacturers provide a general estimate of performance, the actual operation of a system may vary for better or worse, depending on factors such as the building’s energy rating, installation conditions, proper maintenance, weather and of course, usage. Understanding and considering these aspects is essential to making informed decisions and promoting energy efficiency in practice.
