Indoor Air

Indoor Air Quality (IAQ) is an important side of natural ventilation application in buildings. In general, natural ventilation improves IAQ through three mechanisms. It is important to note that little ventilation may result in a poor IAQ, while excessive ventilation may cause undesired draughts. Ultimately, the ventilation rate should be sufficient to maintain both IAQ and thermal comfort requirements. In summer, we get sufficient oxygen through windows. In winter, background ventilation is required in a minimum rate of 400 mm2/ m2 of multi-cell building floor area. This can be achieved by using trickle ventilation. In addition, natural ventilation protects the environment from harmful gases. One of the most common gaseous pollutants is Carbon Dioxide (CO2). The effect of CO2 concentration on human being varies from deep respiration to immediate death. Thus, it is important to predict the expected CO2 concentration due to building occupants, equipment’s, external sources, etc., and ensure that the upper allowed limit is not exceeded. The amount of CO2 in the air is usually expressed in per cent, or in parts per million (ppm). There are various alternatives introduced to control this concentration like CO2 concentration sensors. On reaching the predefined level, these sensors automatically operate natural ventilation by opening windows or roof vents to replace the stale air with a fresh one. Natural ventilation, which is again a passive cooling strategy, is used to cool down indoor air, building structure, and building occupants. The role of natural ventilation in passive cooling is subject to changes in the local climatic conditions. For example: During summer: if the outdoor air temperature is less than the indoor one, airflow through a building removes internal heat gains and increase human thermal comfort. If the outdoor air temperature is higher than the indoor one, it is possible to reduce air temperature by some techniques such as night-time ventilation and underground cooling. In hot arid regions, natural ventilation works effectively with the help of an evaporative cooling method. If the outdoor and indoor air temperatures remain the same, the natural ventilation will provide fresh air and help in increasing the occupant’s comfort. In winter, minimum ventilation, or infiltration, the rate is required to maintain acceptable indoor air quality.

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