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Why ventilation?
IAQ and Comfort
Ventilation is the process of renewing the indoor air to maintain good indoor air quality. Ventilating a building is almost a direct extension of breathing:
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Breath In fresh air to replenish oxygen levels; |
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Breath Out the stale air to evacuate CO2, excess humidity and pollutants in the same process. |
A ventilation system is therefore a two-way flow of air (fresh air in, stale air out) whose key roles are to:
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reduce indoor pollutants concentrations to a healthy level by extracting and diluting stale air with clean air from the outside; |
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reduce excessive air humidity levels by extracting it when and where it is produced in high concentration such as during cooking, showering, etc.; |
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remove carbon dioxide (CO2) produced by breathing and replace it with clean, fresh air full of oxygen; |
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remove unpleasant smells from cooking and other bodily functions. |
In addition, ventilation can perform other functions such as cooling during the summer by removing excess indoor heat, or supply air to combustion appliances.
Key principles for the “right” ventilation strategy
When planning your ventilation strategy, you should aim at achieving the right balance between the following requirements:
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Provide a sufficient air renewal to achieve good indoor air quality; |
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Reduce heat losses associated with the air flow during the heating season (external cold air displaces internal warm air); |
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Preserve thermal comfort against cold air flows and too high air velocity; |
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Reduce capital costs and ongoing operation and maintenance costs; |
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Keep it simple and easy to operate; |
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Avoid discomfort due to noisy fans, whistling ducting, etc. |
In terms of indoor air quality, our building regulations (Part F in the Ireland and the UK, Part K in Northern Ireland) define ventilation standards following a strategy based on three elements:
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Extract ventilation from rooms where most water vapour and/or pollutants are released in order to minimise their dispersal to the rest of the building. Extract can be intermittent e.g. by a cooker hood or continuous e.g. mechanical ventilation with heat recovery. The required extract rate will vary according to the type of room and its function. |
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General or whole building ventilation which provides an ongoing level of air renewal to supply fresh air and disperse water vapour or pollutants released throughout the building and not dealt with by extract ventilation. |
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Purge ventilation throughout the building to aid removal of high concentrations of pollutants or water vapour by occasional activities (painting, decorating, etc.) or accidental (burnt food, water spillage, etc.). Purge ventilation is normally provided for by window or door opening. |
The above strategy can be achieved with natural ventilation, mechanical ventilation or a combination of both (mixed-mode or hybrid ventilation). There is a large variety of ventilation systems available on the market and we will review them in other sections.
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