EN 1886

EN 1886 – European standard for Air Handling Units (AHU) mechanical performance

The EN 1886 standard is part of numerous standards related to Air Handling Units (AHU), designed for ventilation and air conditioning of building intended for human occupancy. It is the European standard that specifies the mechanical performance of an AHU as a whole, detailing test methods and requirements in order to qualify the performance following EN1886 classification. More specifically, “mechanical performance” means testing:

  • Mechanical strength of the casing;
  • Casing air leakages (or external air leakages);
  • Filter bypass leakages;
  • Thermal transmittance of the casing;
  • Thermal bridging of the casing;
  • Acoustic insulation of the casing.

Mechanical strength of the casing

This criteria is use to qualify the structural construction of the casing. The AHU is put in overpressure/underpressure in order to measure the deflection of the panels and frames of the unit without permanent deformation. The classification is based on the maximum deflection measured as follows:

Casing Strength
Class Maximum relative deflection (mm x m -1)
D3 exceeding 10
D2 10
D1 4

EN 1886 – casing strength classification.

Casing air leakages

Here, it is the amount of air that can pass through the AHU casing, under defined pressure conditions, that is measured. That parameter is quite important from an indoor air quality point of view but for the fan energy consumption as well.

To determine the casing air leakage rate, the tests are performed at an internal negative pressure of 400 Pa for unit working in under pressure only. For part of the unit working in overpressure, the test is made with an internal positive pressure of 700 Pa.

Depending on the results, the unit is classified as follows:

Casign Air Leakage @ – 400 Pa
Leakage Class Maximum leakage rate (f 400) (l x s-1 x m-2) Filter class (EN 779)
L3 1,32 G1 to F7
L2 0,44 F8 to F9
L1 0,15 supérior to F9

EN 1886 – casing air leakages classification at negative pressure.

Casign Air Leakage @ – 700 Pa
Leakage Class Maximum leakage rate (f 700) (l x s-1 x m-2) Filter class (EN 779)
L3 1,9 G1 to F7
L2 0,63 F8 to F9
L1 0,22 supérior to F9

EN 1886 – casing air leakages classification at positive pressure.

Filter bypass leakages

This information make sure that you know the amount of air that is not actually filtered, which is crucial for building with high indoor air quality requirements.

Test conditions is internal pressure of 400 Pa. Classification is:

Filter Bypass Leakage
Filter Class G1 to F5 F6 F7 F8 F9
Max. filter bypass leakage rate k (in %) 6 4 2 1 0,5

EN 1886 – filter bypass leakages classification.

Thermal transmittance

The thermal transmittance U (W/m².K) give you an idea about how good the thermal insulation of the AHU’s casing can be.

Practically this value represents how much energy is transmitted through 1 m² of casing and for an indoor-outdoor temperature difference of 1 K.

For this parameter, tests must be performed on a model box that closely reproduced the real unit casing construction. An indoor-outdoor temperature difference of 20 K must be ensured for the thermal transmittance calculation.

Thermal Transmittance
Class Thermal transmittance (U) (W x m-2 x K-1
T1 U < 0,5
T2 0,5 < =< 1
T3 1 < U =< 1,4
T4 1,4 < U =< 2
T5 No requirements

EN 1886 – Thermal Transmittance Classifications.

Thermal bridging of the casing

This test helps you understand how important can be the thermal losses between inside and outside the casing through critical locations (between structural profiles and doors, casing corners,…).

It is performed on the model box and for an inside-outside temperature difference of 20 K as well. The highest temperature point on the outer surface is measured and compared to the inside temperature. The ratio between this comparison and the inside-outside temperature difference determines the thermal bridging factor.

Thermal bridging
Class Thermal bridging factor (kb)
TB1 0,75 < Kb < 1
TB2 0,6 < Kb =< 0,75
TB3 0,45 < Kb =< 0,6
TB4 0,3 < Kb =< 0,45
TB5 No requirements

EN 1886 – Thermal Bridging factor Classifications.

Sound insertion loss

The sound insertion loss test determines the acoustic insulation performance of the AHU’s casing.

Sound pressure level from a sound source located in the model box are measured at 2 positions. Then, similar measurements are made on the sound source but now without the casing. The values from the two situations are compared and the difference between them gives the sound insertion loss for each octave band.

Find our EN1886 certificates on each product page.


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EN 1886 – HRflat
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