Efficient ventilation and perception of air quality

In any building where human activity is expected, the environment must be comfortable and beneficial for health. This will largely depend on the proper functioning of an efficient ventilation system.

Due to a change in habits — nowadays, we spend more than three quarters of our time indoors — it is crucial to take care of the indoor air quality of our buildings. If we want to avoid the sick building syndrome, we must ensure a sufficient ventilation flow, depending on the volume of the space and the occupancy, to ensure proper air renewal. Only an efficient ventilation system will generate the necessary sweeping effect to expel stale air while providing fresh, clean air free of contaminants.

Indoor air pollution: origin

The presence of contaminants in indoor environments can be due to various reasons:

• Outdoor air pollution.

• Indoor air pollution due to the presence of radon or formaldehyde.

• Combustion of CO2 as a result of human activity (breathing and sweating).

• Presence of biological contaminating agents (viruses or bacteria).

• Emission of ethers from small appliances.

• An unhealthy relative indoor humidity level.

• An inadequate and insufficient ventilation and air conditioning system.

• Improper maintenance of these facilities and their components (filters, ducts, grilles…).

Indoor air quality

What is air quality? One way to define it is by referring to the level of satisfaction of individuals, in terms of health, comfort, and well-being.

People occupying a building demand that the air they breathe be fresh, clean, odorless, and free of contaminants that could jeopardize their health. A healthy environment will be one that not only offers air free of pollutants (objectively speaking) but that its occupants perceive as such. At this point, it is worth noting that the subjective aspect is also important when assessing air quality since often, the concentrations of contaminating agents may not be excessively high, but the user perceives the environment as “heavy,” “stale,” and “irritating.”

Therefore, human perception is a good measurement method for evaluating the contamination of environments. Thus, the sense of smell (located in the nose) and the chemical sense (located in the mucous membranes) of people can act as reliable indicators to determine how a certain air is perceived.

Olf and decipol: units to determine air quality

In his day, Fanger — an authority in the field of thermal comfort and the appreciation by occupants of indoor environments — thought that a good way to measure indoor air pollution was by comparing it to the smell generated by a well-known source of pollution: the human body. Thus, he introduced olf and decipol, two magnitudes for determining air quality.

The first refers to the rate of bioeffluents emitted by people. The second refers to the environmental pollution produced by those people, considering an air supply of 10 l/s. Therefore, one decipol is the air quality perceived in the presence of one olf ventilated at a rate of 10 l/s with clean air. It is deduced that as the number of decipoles increases, the quality of air decreases (and consequently, the number of dissatisfied individuals increases).

Quality indoor air and efficient ventilation

Studies conducted show that if the building has an efficient ventilation, the contamination perceived by the user does not reach 1 decipol, resulting in almost no dissatisfied individuals with the indoor air. In the case of poorly ventilated spaces, the perception may rise to 10 decipoles, which could exceed 60% dissatisfaction. A controlled mechanical dual flow ventilation system can achieve the objective of creating indoor environments whose air quality approaches the first assumption.