What is Indoor Air Comfort?

Transcript of video

What is Indoor Air Comfort

Air is vital

We can live 30 days without eating, 3 days without drinking…

...but only 3 minutes without breathing.

Throughout the ages, air quality in buildings has been recognised as a source of wellbeing and essential to good health, for instance in preventing the spread of diseases.

The quality of air has dramatically changed over the last couple of centuries.

As pollution levels have risen, attention has been given to the threats of outdoor air pollution on human health and the environment.

It is only in the last few decades that attention has been paid to indoor air quality.

The sources of indoor pollution can be divided into 4 categories:

  1. Outdoor sources
  2. Occupant-related activities and products
  3. Building materials and furnishings
  4. Poorly maintained ventilation systems.

In sufficient concentration, pollutants can have a direct effect on health. Their effects on our wellbeing can be less easily quantifiable.

ODOURS originate from various sources.

They are generated by volatile molecules that the human nose can detect at very low levels of concentration.

Some volatile molecules can also cause SENSORY IRRITATIONS. Generally, the threshold for sensory irritation is higher than for odour perception.

The sensation of STUFFINESS results from the overall pollution load and lack of fresh air. Different pollutants at very low concentrations but combined can affect our wellbeing.

Good air quality is defined by the absence of health threatening pollutants, bad smells, sensory irritations and stuffiness.

THE PHYSIOLOGICAL aspect of indoor air comfort

We inhale and exhale an average of 12,000 litres of air per day. Our ability to assess the quality of this air involves 2 senses.


The olfactory nerve in the nose detects molecules.

The information is sent to be interpreted as a smell in several parts of the brain: the cortex, where conscious perception is formed, and the limbic system, which controls mood and emotions.


This is the ability to sense irritants. The process is fairly similar, but involves different nerves.

THE PHYSICAL aspect of indoor air comfort

Air is a gas mainly composed of oxygen (21%) and nitrogen (78%).

The remaining 1% can concentrate a number of pollutants.

The different indoor pollutants can be classified into 2 main categories:

  1. PHYSICO-CHEMICAL pollutants
  2. BIOLOGICAL pollutants

Exposure to pollutants is influenced by environmental parameters such as ventilation rate, air velocity, temperature, relative humidity, the activities taking place and the

frequency and duration of exposure.

THE SOCIO PSYCHOLOGICAL aspect of indoor air comfort

The quality of air has a profound effect on our conscious and subconscious mind.

Odours are deeply linked to our emotional state, motivation and memory.

If unpleasant, they can cause mental distraction and have a negative impact on mood and stress levels.

The presence of pollutants in buildings is shown to decrease efficiency. For instance, high concentration of CO2 impairs our ability to take decisions.

This is why we are usually more creative, alert and efficient in well-ventilated schools or offices.

Designing for indoor air comfort

To improve indoor air quality, 3 factors have to be considered:

1. REMOVING or minimising emissions of pollutants at source.

However, it is not always economic, practical or even possible.


The appropriate extraction and replacement of air depends on levels of occupancy, activity, etc…

3. PURIFYING the air by filtering incoming air and indoor air.

However, these filters need to be maintained to prevent the ventilation system itself from becoming a source of pollution.

Mechanical ventilation can be very efficient (when used appropriately)…

but we should not forget the benefits of natural ventilation, particularly in terms of health and cost.

User control and contact with the outside world are key to making us feel comfortable.

However, the benefits of natural ventilation depend on what this outside world consists of.

Ventilation can be a source of noise or thermal discomfort. A balance is to be found to reach the optimum solution.

An idea gaining ground is for hybrid ventilation: natural ventilation in mid-season and mechanical in winter and summer.


Our indoor air quality needs will probably remain the same.

However, our understanding of indoor chemistry will surely evolve, allowing us to better detect and interpret the thousands of indoor air pollutants.

In order to improve energy efficiency, the use of mechanical ventilation systems is likely to change.

New means of renewing air efficiently while maintaining a comfortable thermal environment will have to be developed.