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Why do we ventilate?
Expert Commentary
An overview of why CO2 plays a central role concerning Indoor Air Quality (IAQ), the core reasons behind the need to ventilate and essential factors to consider when creating a good indoor climate.
Indoor Air Quality (IAQ) has been gaining traction in recent years. COVID19 has especially underlined the importance of fresh air ventilation, which is critical to achieving good IAQ.
Against this backdrop, carbon dioxide (CO2) concentrations play an important role in conversations surrounding IAQ. Over the years, discussions have centred around
the direct impact of CO2 concentrations on building occupants,
how CO2 concentrations relate to perceived indoor air quality,
indoor CO2 concentrations to control ventilation rates and CO2-based demand control ventilations.
However, it is critical to understand why CO2 plays a central role in these dialogues to gain a deeper appreciation of the reason behind, and importance of, why we ventilate our buildings.
Why is CO2 used as a benchmark?
The relevance of CO2 concentrations to IAQ standards and ventilation, in general, is based primarily on
their direct relation to occupancy and the resulting levels of bio effluents, and
its practically with regard to ventilation rates per person.
CO2 is an excellent indicator of the presence of people, their activity level, and the resulting emissions of bio effluents within a given space. Compared to the over 100 000 compounds that our nose and mucosae are sensitive to, CO2 concentration is relatively easy to measure. In essence, CO2 concentration is a good predictor of the perceived indoor air quality, and a practical and cost-efficient measurement for controlling ventilation rates in demand control ventilation systems.
Nevertheless, CO2 is not the main reason why ventilation is needed.
Many studies have shown associations of elevated CO2 levels with occupant symptoms. Such results can be attributed to lower ventilation rates and elevated concentrations of other contaminants that affect the perception of indoor air quality. Several studies of bio effluent perception in chambers and buildings have also shown correlations between degrees of dissatisfaction, ventilation rate per person, and CO2 levels.
We ventilate because...
Keep this in mind, we must remember the key reasons we ventilate are:
to secure fresh air supply for respiration and combustion processes
to remove emissions deriving from materials and people
to remove dangerous contaminants
to control temperature, and humidity
Replacing stale “used” air with new fresh air is essential to achieving good indoor air quality. Defined indoor air climate parameters can also only be guaranteed with a proper mechanical ventilation system.
For the required thermal and atmospheric indoor environment to be achieved, the ventilation system must be designed with great care. The air handling unit must be equipped with the necessary functions for air handling (e.g., filtration, heat recovery, heating/cooling) with the required capacity. The air distribution system must be designed considering sound levels, air velocities and the air volume requirements in the respective rooms. If a clear focus on energy efficiency is maintained for all design aspects, a balanced mechanical ventilation system with energy recovery will be the most efficient way of achieving an excellent indoor air climate.
IAQ-centric designs
It is also important to remember that the factors for “correct” design will also vary depending on:
building size, category, and type
occupancy
indoor activities
contamination sources and concentrations
building location
climate
For ordinary comfort ventilation, the goal is to achieve a good thermal and atmospheric indoor environment with a “tolerable” percentage of dissatisfied occupants. People vary regarding temperature preferences, activity level, and clothing. Therefore, it is impossible to achieve 100 % satisfaction in any given thermal environment.
Integrating IAQ into Europe’s “Renovation Wave Strategy”
Today, only a fraction of the buildings in Europe have ventilation. The European Commission seeks to promote renovations that lead to higher energy and resource efficiency in its “Renovation Wave Strategy”. With expectations that renovation rates will double in the next ten years, refurbishment efforts must include energy-efficient ventilation solutions, which will enhance the quality of life for people and reduce emissions. At Systemair, we believe that all buildings should be equipped with fresh air ventilation with energy recovery. There is no better way of ensuring a healthy and productive indoor air climate whilst minimising the necessary energy use.
Integrating IAQ into Europe’s “Renovation Wave Strategy”
Today, only a fraction of the buildings in Europe have ventilation. The European Commission seeks to promote renovations that lead to higher energy and resource efficiency in its “Renovation Wave Strategy”.3 With expectations that renovation rates will double in the next ten years, refurbishment efforts must include energy-efficient ventilation solutions, which will enhance the quality of life for people and reduce emissions. At Systemair, we believe that all buildings should be equipped with fresh air ventilation with energy recovery. There is no better way of ensuring a healthy and productive indoor air climate whilst minimising the necessary energy use.