The secret behind ventilation dilution effect for healthy indoor air

Indoor Air Cartoon Journal, June 2019, Volume 2, #65

Indoor air pollutants cause odour, irritations, and several health and discomfort problems to building occupants. Indoor air pollutants could also compromise work performance. Some of these air pollutants can be identified, and some cannot be identified with the currently available technologies. Irrespective of whether indoor air pollutants can be identified or not, having good ventilation is a safe strategy towards the creation of healthy indoor air. Ventilation uses dilution effect to improve indoor air condition. Ventilation is the exchange of outdoor air with indoor air. The rate at which this exchange occurs is called ventilation rate. Dilution in this context means the reduction air pollutant intensity in the indoor environment through weakening the bonds holding molecules of the air pollutant. The weaken bonds will make it easier for the air capacity to remove the pollutant from the air.

Today’s issue explains the dilution phenomenon and how its effectiveness can be achieved. What does it take for ventilation to be effective as a dilution strategy? The outdoor air that is introduced into the indoor air must be cleaned, i.e., free of pollutants to the extent of not being a threat to the health of indoor occupants. It must not be stagnant, and its flow rate must be adequate to move the air around in indoor environment effectively. It must mix well with indoor air. The outdoor to indoor air exchange must occur rapidly enough to avoid aged air.

Energy consumption and polluted outdoor environment are the main threats to the usage of ventilation in buildings. The reduction of indoor air pollutants concentrations to be diluted through source reduction or elimination, and air filtration and cleaning will reduce the required ventilation rate and subsequent energy consumption. The reduction of outdoor air pollution is a daunting task with climate change challenge and increasing human contribution to outdoor air pollution. The immediate solution to reducing outdoor to indoor transport of air pollution is to use appropriate and high-efficiency filters to clean the polluted outdoor air before being exchange with indoor air. The reduction of outdoor to indoor transport of polluted outdoor air into naturally ventilated buildings remain a challenge.

65. Ventilation_65

Do you want to know more about this topic? Read Godish and Spengler (1996) and Sundell et al. (2011) papers.

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