Calculating AHU energy class
Eurovent Association has released a comprehensive case study on energy classification for air handling units (AHUs). With a focus on energy consumption by energy class, the case study offers a useful tool for estimating which AHU energy class best suits specific project needs, across different regions. Central to Eurovent’s new case study is the winter and summer energy efficiency class labels calculated by the Eurovent Certified Performance programme for Air Handling Units. Energy class calculations offer a simple and effective way to directly compare the energy efficiency of products.
In this article we explore the case study itself, why we need energy classification, how Eurovent Certification calculates energy class, and the difference between the winter and summer energy labels.
About the case study
The ‘Eurovent energy classification for air handling units’ case study demonstrates typical applications and working conditions for AHUs across various cities in Europe, using summer and winter conditions. By using this method, not only does the case study provide practical guidance on making the right choice in the design and selection of the most suitable product, but it also shows the rough value of savings in energy costs over 17 years; the typical AHU lifetime assumed in the studies of Ecodesign requirements for ventilation units if an A+ class unit is installed instead of a C class unit.
The case study covers three application groups:
- Group 1: School, kindergarten, office buildings
- Group 2: Restaurant, eating place
- Group 3: Multifamily residential building.
Energy calculations are given for several cities in Northern, Eastern and Western Europe (usually subject to the winter label) and Southern Europe (usually subject to the summer label). This enables Eurovent to make a direct comparison of energy consumption by AHU class, depending on the location for the winter or summer label.
Why do AHUs need energy classification?
Good Indoor Air Quality (IAQ) is becoming increasingly important as we strive to ensure indoor spaces contribute to our health and general wellbeing. It’s vital that buildings are properly ventilated, cooled, heated, and that indoor pollutants are minimised. However, the systems used to deliver these services can use large amounts of energy. System designers can find themselves in a battle to balance performance and energy efficiency.
Therefore, those choosing the wrong system could see serious impacts on IAQ and energy consumption. Those specifying, designing and installing systems need access to verified, accurate, comparable, performance data to make good product decisions.
Eurovent explains further, “A key element of a typical ventilation system is the AHU which transports, heats and usually cools the air. These processes, indispensable to provide a high IAQ entail significant energy consumption. Therefore, IAQ must always be considered in conjunction with the energy efficiency of the AHU. Ensuring adequate IAQ with the lowest energy consumption is essential to optimise running costs, as well as minimise the environmental impact of the ventilation system, since energy use typically accounts for 80% of the Global Warming Potential (GWP) emissions generated by the AHU over its lifetime.”
How do you calculate energy class?
AHUs are complex products, that can be built to numerous configurations, with or without different components. Additionally, AHU energy use can vary over different climates. This can make it difficult to easily evaluate and compare the overall energy efficiency of different units. To solve this problem, Eurovent Certification calculates AHU energy efficiency class based on two key factors:
- Thermal energy use
- Fan energy use
AHU energy efficiency is expressed by a label in classes from A+ to E. Only Eurovent certified units may be marketed with this label.
Under the Eurovent Certified Performance programme all products are tested against set reference cities for both summer and winter energy efficiency class. This ensures that AHUs can been compared fairly and accurately, across different regions, by those using certified data.
The difference between the winter and summer label
For both labels thermal energy (for heating and cooling) and electrical energy for fans is considered.
The winter label
This label applies to units in cold climates, where heating energy dominates annual thermal energy consumption and the summer temperatures and humidity are mild, making recovery of latent energy (moisture) unreasonable.
The major influencing factors when calculating thermal energy consumption include:
- Heat Recovery System (HRS) efficiency
- The climate dependency for the thermal energy consumption
- And the difference in primary energy between thermal energy and electrical energy is taken into account to evaluate the impact of the pressure drops across the HRS (factors 1 to 2).
The thermal energy for cooling is not considered because it will have less impact (negligible for most of Europe).
The major influencing factors when calculating fan energy consumption include:
- Velocity
- Heat recovery system pressure drop
- Overall static efficiency of the supply and/or the extract air fan
- And efficiency of the electric motor(s).
The summer label
This label applies to units in warm climates, where cooling energy dominates annual thermal energy consumption, and the summer temperatures and humidity are high so that latent energy recovery significantly reduces cooling demand.
The basis used to assess the energy efficiency class for the summer application is the same as the winter application. Correction factors are applied in the calculation which considers the effect of:
- Humidity Recovery
- Reduction of the pressure drop in the Heat Recovery System (HRS) bypass.
For both labels the methodology for evaluating energy efficiency class rating is given in the AHU programme Technical Certification Rules. The required values for the classes adopted in the calculations are taken from the European Standard EN13053:2019: “Ventilation for buildings – Air handling units – Rating and performance for units, components and sections.”
Download the case study
The case study has been published by Eurovent and prepared in a joint effort by participants of the Product Group ‘Air Handling Units’ (PG-AHU), which represents a vast majority of all manufacturers of these products active on the EMEA market. It is available as a free download from the Eurovent website.
Eurovent certified Performance for AHUs
The Eurovent Certified Performance programme for Air Handling Units is the most recognised AHU certification scheme in the world. The programme attests the conformity of air handling units to European Standards and provides independently verified product performance data via an impartial and vigorous certification process.