How to correctly select a terminating element for a room ventilation system – four steps

How to correctly select a terminating element for a room ventilation system - four steps

The ventilation system inside a building or room can be terminated by two types of elements. These are diffusers and ventilation grilles. Their task is to supply and exhaust air in the room. How to correctly choose the element that ends the ventilation system? Just 4 simple steps!

The role of terminating elements for a room ventilation system

Diffusers allow continuous airflow. They play an important role in proper air circulation in rooms. The design of the diffuser is to meet specific comfort conditions, such as air speed in the room, sound level, humidity or temperature.

Grilles are installed in medium and low-pressure ventilation systems as duct-terminating elements.

Both diffusers and grilles serve to supply or exhaust air. They are installed indoors.

How does the wrong selection of elements that complete the ventilation system affect the room?

If the air is not supplied to the room properly, it promotes the accumulation of water vapour and moisture, which in turn leads to the growth of mould and mildew. This means that, due to the poor selection of supply and exhaust elements (i.e. elements of their type and arrangement), a given room’s users can suffer from allergies, asthma, and other respiratory tract diseases. A controlled air supply eliminates these problems and increases users’ comfort.

Ventilation system terminating elements

What should we choose for our investment? Some suggestions are given below!

Grilles are the basic air distribution devices. They are applied in buildings for various purposes, including industrial, residential, and office facilities. Grilles offer a high degree of flexibility in terms of their size and, therefore, flexibility in terms of the airflow they can supply to the room. They are installed in both gravity and mechanical ventilation. They can be categorised by:

Supply diffusers

  • Ceiling diffusers (rectangular or round) – supply or exhaust elements designed for installation in a ceiling. Depending on the type and shape, they make it possible to direct the air flowing out of the diffusers.
  • Vortex diffusers – they are applied in public buildings and office rooms. Their characteristic feature is the generation of whirl-like air movement, often with a high inductance factor. As a result, vortex diffusers ensure intensive mixing of supply air with room air.
  • Slot diffusers – they are often used in open space office rooms. Thanks to their long and narrow slot, the air is evenly distributed within the room, which minimises draughts and ensures users’ comfort.
  • Floor diffusers – a standard solution for swimming pool halls. These diffusers are installed directly in the floor. They ensure even air distribution at a low level, which is particularly beneficial in places where traditional ventilation systems may prove to be insufficient or improper.
  • Long-range nozzles – applied in high-ceiling rooms of large volumes (such as theatres, cinemas or industrial halls). They are characterised by a long range of the supply air stream and low flow resistances.

Four steps for selecting terminating elements for a ventilation system

1. Calculate the amount of air supplied to the room

The airflow supplied to a room is often determined by the following:

  • the number of people in the room. The amount of fresh air per person is considered. It can be, e.g., 30–50 m3/h per person;
  • the exchange rateof fresh air supplies – e.g. 2 exchanges per hour in a doctor’s office.

2. Dobieramy typ elementu nawiewnego w zależności od przeznaczenia pomieszczenia

3. Specify the number of devices

Place the diffusers as evenly as possible in proportion to the gains and losses of heat in the room.

4. Adjust the parameters and size of the selected element

In this context, the following should be considered:

  •  the location of the diffuser (wall, ceiling, floor)
  • pressure loss in the diffuser
  • noise level generated
  • air speed in the area occupied by people – the limit speed is usually 0.2 m/s
  • obstacles in the way of the supplied air – walls can cause disturbances in the air stream, creating a draught This results in user discomfort.
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