ESEER Explained: European Seasonal Energy Efficiency Ratio

ESEER is one of the most accurate metrics for determining the energy efficiency of air conditioners. In HVAC, we already have a lot of these ratings; you might be familiar with EER and SEER ratings, some may even have heard of CEER and IEER rating.

Example: A portable air conditioner can have an EER rating of 11.0, a SEER rating of 14.3, an IEER rating of 15.6, and an ESEER rating of 15.4. Having so many energy efficiency ratings is quite confusing.

That’s why we will look into what ESSER is and why it might become a predominant energy efficiency ratio in Europe.

ESEER stands for European Seasonal Energy Efficiency Ratio. It is used to adequately estimate the real-climate energy efficiency of air conditioning units. Here is how the ESEER rating is calculated (we will look into this equation further on):

eseer equation

Now, there is a lot of confusion about what ESEER is and how it is measured/calculated. Let’s clear some things out:

Most of us know what EER or Energy Efficiency Ratio means (it’s a ratio between the cooling output of AC unit at 100% power input or wattage, more about EER rating here). SEER or Seasonal Energy Efficiency Ratio is a step further; we measure EER rating at part loads (EER25%, EER50%, and EER75%) and at full load (EER100%) and calculate the SEER rating using weighted averages.

If you compare ESEER to EER and SEER rating, you might think that ESEER is just the European version of a SEER rating. This is one of the most common mistakes most of us make.

Yes, ESEER is a European rating. It was introduced in April 2006 in Frankfurt and presented in the paper by Eurovent Certification Company titled “Effect of the Certification on Chillers Energy Efficiency”.

eseer or european seasonal energy efficiency ratio
Europe has a goal to give directives on how energy efficient different HVAC appliances are (to reduce carbon footprint and conserve electricity). ESEER is a rating used to determine the real-climate efficiency of air conditioning systems.

But ESEER is not just the European version of SEER more commonly used in the US. ESEER, in fact, estimates energy efficiency much more thoroughly because it integrates both partial loads as well as different test conditions (namely, ESSER is measured at 35°C, 30°C, 25°C, and 20°C). In that regard, it is closer to the IEER or Integrated Energy Efficiency Ratio used in the US.

Here’s the general deal:

All these AC energy efficiency ratings want to estimate how energy efficient an air conditioner actually is in real-climate conditions. Real-climate conditions are the key here. We would like to know exactly how much are the running costs of a certain air conditioner.

To fully understand what the ESEER rating means, we have to look at how it is calculated:

How To Calculate ESEER Rating (Part Loads + Different Test Conditions)

EER rating is calculated only at only 1 ideal condition and at 100% capacity. We denote this rating as EER100%. SEER rating still uses that 1 ideal condition but takes into account loads at 25%, 50%, and 75% in addition to the 100% load.

When calculating the ESEER rating, however, we include two very important factors:

  1. Different loads (the same as SEER rating). These are loads at 25%, 50%, 75%, and 100% air conditioner cooling capacity.
  2. Different test conditions (not only ideal 35°C outdoor temperature condition). For measuring ESEER, we make measurements are 4 different conditioners. Namely, we measure the performance of an air conditioner not only at 35°C, but also at 30°C, 25°C, and 20°C.

This mixture of different loads and different test conditions that the ESEER rating is based on is vital. This is the best way how to truly evaluate the real-life energy efficiency of air conditioners.

Here is the formula for calculating the ESEER rating:

ESEER = (EER100% × 0.03) + (EER75% × 0.33) + (EER50% × 0.41) + (EEER25% × 0.23)

This is how all 4 components of the ESEER rating are measured and how much of an input each of them has into the total ESEER rating:

  1. EER100% is measured at 100% cooling output and at 35°C. It accounts for 3% of the total ESEER rating.
  2. EER75% is measured at 75% cooling output and at 30°C. It accounts for 33% of the total ESEER rating.
  3. EER50% is measured at 50% cooling output and at 25°C. It accounts for 41% of the total ESEER rating.
  4. EER25% is measured at 25% cooling output and at 20°C. It accounts for 25% of the total ESEER rating.

The ESEER equation is a basic weighted average of these different measurements.

Basically, to capture the real-life conditions as best as possible, the ESEER rating presumes that we run the air conditioner the most on 50% capacity, followed by running it on 75% and 25%. It also presumes that we run an air conditioner on 100% capacity only 3% of the time.

How does this ESEER rating compare to the EER and SEER ratings?

Converting ESEER To EER And SEER (Is It Even Possible?)

Whenever we are looking at EER vs ESEER or SEER vs ESEER ratings, we want to get a general idea of how energy efficient this let’s say 15 ESEER rated air conditioner is.

That means that we want to convert ESEER to EER or to convert ESEER to SEER because we are more familiar with EER and SEER.

However, it is important to understand that it is impossible to directly convert ESEER rating to either EER or SEER.

This is because EER and SEER are only measured at 1 ideal condition. In contrast, ESEER is measured at 4 different test conditions (35°C, 30°C, 25°C, 20°C). Comparing EER or SEER to ESEER is like comparing apples and oranges.

That means that the ESEER rating is a stand-alone energy efficiency metric for air conditioners. We will have to get into a habit of comparing different air conditioners based on ESEER. Or is this even the case?

The IEER rating is comparable to the ESEER rating. IEER is slowly but steadily replacing the older EER rating and even the newer SEER rating.

However, we don’t see ESEER replacing the EER and SEER in Europe to the same extent.

Only time will tell what AC energy efficiency metric we are going to predominantly use in the future. Despite ESEER because the most thorough and accurate metric for real-climate energy efficiency of AC units, it currently doesn’t really appear on specification sheets of modern air conditioners.

Hopefully, you now have a better understanding of what the ESSER rating means and to what extent it estimates the energy efficiency of various air conditioning systems.

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