Indoor Air Quality (IAQ) - The importance of Mechanical Ventilation

Indoor Air Quality (IAQ) refers to the air quality in a building or structure, breathed in every day by the building’s occupants.

Poor indoor air quality has been linked to sick building syndrome, ill health, reduced well-being and productivity, impaired learning in schools, and delayed recovery in hospitals.

Polluted air is responsible for as many as 36,000 deaths a year in the UK, according to Public Health England (PHE).

In the UK, people usually spend around 90% of their time indoors, however, indoor air quality can be up to five times worse than outdoor air.

Unfortunately, the solution is not as simple as just opening a window, especially for city centre buildings where outdoor air can also be highly polluted.

This is why it is extremely important to take measures to ensure the occupants of a building can always benefit from clean indoor air.

The role of mechanical ventilation

Possibly the most effective way to improve indoor air quality is by mechanical ventilation.

Ventilation is the process of introducing clean and fresh outdoor air into a building and removing contaminated indoor air.

This can be achieved through two methods: natural ventilation and mechanical ventilation (which is usually the most efficient and effective).

Mechanical ventilation systems introduce filtered air from outdoors and simultaneously extract internal air…diluting or even removing the possible presence of bacteria, viruses, CO2, and other contaminants.

At the same time, mechanical ventilation systems can also ensure energy savings through heat recovery. This is where heat and moisture from the airflow being extracted from the building are transferred to the airflow being introduced.

These systems, besides being extremely effective in replacing exhaust air and ensuring high indoor air quality levels, also guarantee optimum thermal control by minimising or eradicating thermal dissipation, which then makes the whole building more energy efficient.

Other aspects that can be addressed with mechanical ventilation to make indoor environments healthier are:

  • air processing, to filter out allergens and odours that can be harmful to human health
  • humidification, to control humidity levels within a building. This is very important as high humidity levels lead to the growth of mould and other harmful microorganisms, which can have severely negative impacts on human health.

Mechanical ventilation system design: things to consider

It is important to choose the right type of mechanical ventilation system for the building.

When designing mechanical ventilation systems, no matter the building type (hospitals, universities, offices or commercial buildings), meeting the cooling and heating demand of the facility, in the most energy-efficient way possible, is very important. Air filtration and air exchange is equally important.

To ensure a comfortable and healthy environment in buildings of all sizes and types, ventilation systems need to be properly sized, so the right airflow and adequate air-exchange rate can be ensured.

There is a close correlation between ventilation rate and indoor air cleanliness. The higher the ventilation rate per hour in a room, the lower the concentration of pollutants. The air exchange topic has been repeatedly brought up during the COVID-19 pandemic, when mechanical ventilation systems have been an important solution to ensure the health and safety of people.

Another relevant aspect, not to be overlooked, is the level of air filtration the ventilation system can provide, cleaning the outdoor airflow of pollutants and contaminants before it is introduced into an indoor environment.


Besides design, there is also maintenance to consider, which is crucial to ensure that the system operates effectively and efficiently. It is necessary to properly schedule cleaning and maintenance activities to ensure correct operations and reliability of the whole system. Regular cleaning and filter replacement can help to ensure that the system is able to effectively remove pollutants and control humidity levels.