How do we ventilate?

Ventilation moves outdoor air into a building or a room, and distributes the air within the building or room.

We need air

We need ventilation in buildings and it must satisfy several different criteria.

It must be reliable, flexible and well-functioning, adaptable, and responsive to different needs and unusual events.

Ventilation needs to be provided for both people and buildings.

Natural or mechanical?

The air exchange from outside to inside of buildings happens in these ways - naturally or mechanically:

  • Unintentional via air leakages from windows, doors, and various holes such as joints and cracks in the building envelope.
  • Intentional via natural ventilation, through opening windows/doors and air vents for deliberate venting by people and for people.
  • Proper mechanical/hybrid ventilation, to add additional and controllable airflow within buildings to provide a good indoor environment.

Basic principles of natural ventilation

Natural ventilation uses pressure difference that is caused by:

  • difference between densities of interior and exterior air given by temperature difference
  • wind velocity providing on windward façade positive pressure and on leeward negative pressure

Did you know?

Natural ventilation is also influenced by wind turbulance and flow pattern around a building (affected by neighbouring buildings, building exposure and building orientation).

Building shape also influences the natural ventilation, i.e. flow direction throughout the building and ventilation intesity.

Typical ways of natural ventilation

Aeration - air supply and exhaust is caused through inlets with proper high difference, i.e. inlet at the ground via openings and outlet via skylights in roofs. Typically used for industrial halls or stables. The ventilation is regulated by inlets and outlets openings.

Shaft ventilation - a combination of inlets via typically controlled window openings and shafts as outlets, creating a stack effect and using pressure difference in different heights. Typically used for multi-floor apartment buildings.

Other points to know about natural ventilation

Controls for natural ventilation can be based on sensors for indoor air quality, meteorological weather data and smart control/management systems.

Natural ventilation is often used for passive cooling at nights, where heat accumulated in the buildings throughout the day is vented out at night to avoid the building overheating.

Do you know?

Do you know that natural ventilation is historically the most widely used ventiation in residential and other types of buildings?

Today, buildings have modern windows that are airtight and efficient, so natural ventilation (via infiltration) is limited to only small amounts of air exchange and natural ventilation (via airing/windows opening) often takes too much effort for building occupants.

Therefore, today it is difficult to keep ventilation requirements using just natural ventilation.

How ventilation works?

Ventilation requires air flowing between interior and exterior. Thus it is necessary to start and maintain air flow according to requirements in a ventilated space. Basically pressure difference is a force starting an airflow.

Fundamentals of mechanical ventilation

Mechanical ventilation is one of the systems that keeps a habitable environment.

Purpose of mechanical ventilation:

  • To heat or cool the incoming air
  • To circulate/move the air in a room
  • To supply/exhaust the required air amount in the room

Basic information about mechanical ventilation:

  • Ventilation is operable independent on exterior conditions
  • Requires precise operation control
  • Provides temperature and humidity (and other sources) control

Mechanical ventilation is based on pressure difference and caused by dynamic pressure of a mechanical device - fan/blower.

Ventilation consists of 3 main parts:

  • Ventilation rate – the amount and quality of the outdoor air
  • Airflow direction – the flow of air within a building, from “clean” to “dirty” areas
  • Air distribution – the delivery of outside air and removal of pollutants

Basic principles of mechanical ventilation:

  • Overpressure ventilation
  • Balanced ventilation
  • Underpressure ventilation

Mechanical ventilation consists of several parts, i.e. air handling unit (AHU), ducts, air supply/exhaust devices, dampers, fan coils, heating/cooling unit,  etc.

Important terminology used in mechanical ventilation

Under the principle of the human right to health, everyone has the right to breathe healthy indoor air.
The Right to Healthy Air, World Health Organisation, 2000