Types of air diffusion Terminals for air diffusion in a room can be classified according to two main criteria:
Generated diffusion type:
- By mixing
- By displacement
Installation position:
- Wall-mounted
- Ceiling-mounted
- Floor-mounted
Diffusion by mixing is the most common type. Under ideal conditions, this system involves the supply air mixing homogeneously with the entire air mass present in the room. The objective is twofold: on one hand, to avoid the creation of areas with high concentrations of pollutants or with non-uniform temperatures; on the other, to ensure comfort in the occupied zone by controlling the average air velocity and its turbulence.
The operation of diffusers designed for mixing systems is influenced by several factors:
- Their geometric characteristics.
- The way they are installed in the environment (ceiling-mounted, wall-mounted, height, proximity to obstacles, etc.).
- The air supply velocity.
- The temperature differential between the supply air and the ambient air.
All diffusers in this category operate based on the principle of induction. The air, exiting the terminal at a certain velocity, generates a surrounding low-pressure area that draws in and entrains the air already present in the room, thus achieving an effective mixing.
To obtain particularly high air quality within the occupied zone, one can opt for displacement systems. These systems are characterized by an air supply that typically occurs from below.
Diffusion by displacement is achieved by supplying air at low velocity at floor level, at a temperature slightly lower than the ambient one. The colder, denser air spreads across the floor, pushing the warmer air already present upwards, but without mixing with it. This fresh air feeds the upward convective currents generated by heat sources (such as people or equipment) from below. This creates a stratification:
- A lower zone with stratified flow, where the temperature increases with height.
- An upper mixing zone, where the temperature stabilizes at a higher and constant value.
Air Diffusion Devices
- What is the purpose of an air diffusion terminal?
- How is it chosen correctly?
These components constitute the point of contact between the air conditioning system and the environment to be served; consequently:
- they are not solely a decorative component,
- they do not simply serve to close an opening,
- they are not an optional accessory or something to be placed where it is out of the way.
Their function is to introduce the supply air into the room in such a way that:
- the air distribution is optimal,
- “dead zones” or undesired stratification phenomena are prevented,
- excessive air velocities in the conventionally occupied volume, which could cause unpleasant drafts, are prevented.
Wall Air Diffusion
The use of wall-mounted diffusers generally represents the solution adopted when a false ceiling is not available or when the space within it is insufficient for the installation of the more common ceiling diffusers.
For situations where it is required to cover large horizontal distances, long-throw diffusers are used. These represent an effective choice, and at times the only possible one, for large-sized venues such as cinemas, sports halls, exhibition halls, convention centers, and television studios. Their use is also necessary when architectural or structural constraints (for example, the presence of beams or columns) prevent the use of traditional wall grilles, due to their limited airflow rate and the difficulty in effectively directing the air jet.
Ceiling Air Diffusion
Diffusion systems with ceiling-mounted terminals are typically employed when the space available in the false ceiling is adequate for the installation of their corresponding plenums.
When it is necessary to cover significant vertical distances, as in very high and large-sized environments, diffusers for high ceilings are used, which often constitute the only viable solution. For special applications, such as the need to make air flow along large vertical glass walls, long-throw nozzles oriented for a vertical throw can be employed.
Floor Air Diffusion
Floor diffusion terminals are specifically designed to create a microclimate that ensures a high level of comfort in the area immediately surrounding people.
While maintaining the same thermo-hygrometric conditions and the same degree of air filtration, a floor diffusion system offers superior comfort compared to a traditional mixing system.
This type of system utilizes the raised floor as a large plenum for air distribution, eliminates the need for a false ceiling, and provides for air return from above. The diffuser is therefore designed to work with natural convection currents, keeping the residual air velocity and the temperature differential (Δt) at levels compatible with the comfort of people performing sedentary activities.
The main advantage of this approach is that the conditions above the occupied zone do not affect comfort. Consequently, the volume to be conditioned is reduced to only the occupied zone (the area of the room up to a height of about 1.8 – 2 meters). For the same thermal load, this allows for operation with lower airflow rates compared to a mixing system, resulting in a reduction in the size of the air handling units, ductwork, and necessary technical spaces.
