EN 12238 Ventilation for Buildings - Air Terminal Devices - Aerodynamic Testing and Rating for Mixed Flow Application

The European standard "EN 12238 Ventilation for buildings - Air terminal devices - Aerodynamic testing and rating for mixed flow applications" describes methods for laboratory aerodynamic testing and rating of air terminal devices for mixed flow applications, including the specification of suitable test facilities and measurement techniques. This standard only includes tests for the evaluation of the characteristics of air terminal devices under isothermal conditions. EN 12239 is applicable for the testing of low velocity air terminal devices.

For the purposes of this standard, the following definitions apply in addition to the terms and definitions given in the CR 12792 standard:

The abbreviation ATD is used to indicate an air terminal device.
Functional characteristics of air terminal devices, the nominal size of an air terminal device refers to the nominal value of the dimensions of the duct in which the air terminal device will be installed. For an air diffuser, the nominal size is generally known as the neck size.
The core of an air terminal device is the part of the air terminal device that is located within a convex closed surface of minimum area, where all openings through which air can pass are located.
The free area of an air terminal device is the sum of the smallest cross-sectional areas of all openings of the air terminal device.
The core of a grid is the part of a grid that is contained within a convex closed plane curve of minimum contour length and contains all the apertures of the grid.
The core area of a grid is the area bounded by the plane curve defined above.
The free area of a grill is the sum of the minimum measured areas of each opening through which air can pass.
The free area ratio of a grid is the ratio of the free area to the core area.
The effective area of an air terminal device is the portion that is the result of the measured airflow rate and the measured air velocity determined as specified by the particular device.

In short, this standard specifies test and rating methods for air terminal devices used in heating, ventilation and air conditioning (HVAC) systems. These devices typically control the direction, flow and sometimes temperature of air entering a space. This standard also defines standard test procedures for measuring airflow rate, pressure loss and air diffusion performance.

This standard primarily applies to mixed flow applications, i.e. systems where supply air is mixed with room air. It covers devices such as diffusers, grilles and nozzles used for air distribution.

Performance data derived from this standard helps designers and engineers select the right air terminal devices for energy-efficient and comfortable indoor environments.

When performing tests, the air terminal device (diffuser, grille and similar equipment) is installed in a test duct or a test ceiling, depending on its design. Standard ambient conditions (temperature, pressure) are maintained. Measurements are taken with controlled air supply rates.

The measurements taken are:

Air flow rate: The volume of air passing through the device, usually measured in cubic meters per hour (m³/h) or liters per second (l/s).
Static pressure drop: It is the pressure difference before and after the device. This value shows how much resistance the device has.
Air diffusion performance,
- Throw length: The distance the air travels before its speed drops to a certain level (e.g. 0,25 m/s).
- Induction ratio: The ratio between the total room air moved and the supply air. The higher the better for a good mix.
Sound levels: Noise produced by the air flow passing through the device. Optionally determined according to the EN ISO 5135 standard.

The test methods are:

Speed measurements at various distances from the device
Temperature measurements (if simulating heating or cooling applications)
Use of tracers or smoke to visualize airflow (for qualitative testing)

The manufacturer must report the following:

Air flow and pressure drop curves
Shooting distances at various air speeds
Sound power levels if measured
Installation conditions (e.g. ceiling mounted, wall mounted)

In short, the EN 12238 standard ensures that when looking at the technical data sheet of a diffuser, the performance values are reliable, comparable and based on standard tests.

Aerodynamic testing is performed to measure how air moves through and around a device and how much resistance, directional change, or noise it creates. This testing focuses on how the air flows (how easily and how far it flows) and how it mixes with the room air, not just how much it flows.

Simply put, an aerodynamic test checks:

How much pressure is lost (pressure drop) when air passes through the device.
How far the air can travel into the chamber before slowing down (throw).
How well the supply air mixes with the room air (induction/mixing ratio).
How even the airflow is (is it spread out nicely or is it only thrown in one direction)
How loud the airflow is (optional, but often tested)

Aerodynamic testing is considered important for designing efficient HVAC systems (providing low energy use), making indoor spaces comfortable, and comparing products fairly.

Rating for mixed flow application according to EN 12238 means testing and providing performance data for air devices designed to mix supply air with room air. This standard tells manufacturers how to scientifically measure and report how well their diffusers or grilles work in air mixing systems.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the "EN 12238 Ventilation for buildings - Air terminal devices - Aerodynamic testing and rating for mixed flow application" standard are also provided to businesses.