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Venting thoughts on IAQ

Lack of adequate and efficient ventilation systems with the right airflow rate is a health hazard. Good IAQ is an essential requirement of modern living, says Gaetan Pierrefeu.

| | Feb 20, 2011 | 6:39 pm
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Lack of adequate and efficient ventilation systems with the right airflow rate is a health hazard. Good IAQ is an essential requirement of modern living, says Gaetan Pierrefeu.

Ventilation is a basic need. It is required to ensure proper Indoor Air Quality (IAQ) and level of comfort, and improve the quality of life for people. A system of continuous air renewal is necessary for health, by the process of elimination of pollutants – CO2, Volatile Organic Components or VOCs – as well as odours, spores or germs. It also reduces the humidity rate, and by extension, the development of moulds and acaroids.

A few of the traditional ventilation solutions, such as wind towers or the barajeel system used earlier in the region, ensured basic comfort for residents through a natural system of cool air renewal inside local dwellings, until the 19th century, as can be exemplified by the Bastakya district in Dubai. The need for ventilation is, therefore, old, basic and vital.

Air conditioning and split-unit technologies came into the region later to cope with high temperatures. But the noise they generate and low thermal comfort they provide are the two main reasons why central AHUs and FCUs have gained popularity in recent times. These systems generally ensure a greater level of cooling due to high cooling loads and lack of proper insulation. This has obviously led to high energy consumption.

The first step in the evolution towards sustainability is, therefore, to work on the envelope of the building to ensure an efficient system of building insulation, air tightness and shade. On the flip side, though these will lead to better energy savings by reducing the cooling load (low heat transfer and low air leakage), they will also increase the need for an efficient ventilation system, bringing outdoor air to cure and improve the IAQ. Indeed, all pollutants and VOCs trapped inside buildings will have to be removed effectively through a continuous ventilation system.

Absence of such an adequate ventilation system with the right airflow rates will increasingly give rise to health issues, especially for the most fragile – children and seniors. In fact, some of the prevailing health disorders can be traced to building-related illnesses.

Indeed, high level of CO2 concentration in a building can often be traced to an occupant’s poor health, a feeling of discomfort and performance degradation. For example, sick-building syndrome reportedly affects the health of employees and reduces work hours. This obviously has a direct bearing on efficiency and productivity. Apart from poor IAQ, the development of new construction and furnishing materials has generated diverse VOCs, which are health hazards.

It is only logical, then, that we direct our collective effort to improving the quality of air inside buildings in which we spend 90% of our time, and where the indoor air is usually two to five times more polluted with formaldehyde, benzene and toluene, than the outdoor air. Here, it must be mentioned that a lot of people are still unaware of the health risks posed by bad indoor air quality.

Many countries in the world have chosen carbon dioxide as an IAQ indicator that reveals the pollution level in the atmosphere, mainly caused due to human activities and materials.

The CO2 threshold value from European standard EN 13779 for non-residential premises is fixed at 800ppm (parts per million) above the outdoor level, which is between 350 and 400 ppm, depending upon the building’s location and the prevailing season. Therefore, in order to ensure the correct level of IAQ, concerned authorities and designers should enforce the common threshold. A daily average air change rate of 0.5-0.6 ach (air change per hour: Vol/hour) for housing is considered sufficient to achieve the CO2 concentration limit of 800ppm above the outdoor level, and a relative humidity of 60% at 18° to 20°C during occupancy.

In the light of this, many types of demand-control ventilation systems have been developed to modulate airflow rates, taking into account the real occupancy inside a building and the working hours. These systems can be timer-controlled. They generally modulate airflow according to optical detection, CO2 or humidity levels, preferably with a minimum airflow for dwellings. Indeed, humidity is also a tracer for a ventilation system, as in every breath cycle, people consume some amount of oxygen and exhale CO2 and H2O in identical quantities.

Other efficient ventilation systems combine the approach of IAQ and demand-control ventilation, with energy-recovery ventilation for further energy consumption control. These systems transfer heat directly to the outdoor air for free pre-cooling, in order to limit cooling from the central AHU or decentralised HRV units, which are used more and more in new designs, especially in schools.

A secondary benefit of good ventilation is that the air can act as an efficient carrier of calories or frigories, naturally present in the outdoor air, which may be warmed by the sun (recovery in the back of a solar cell), or cooled down in the ground (through geothermal ducts), or both, through a heat pump.

As far as countries in the Middle East without any specific ventilation regulations are concerned, in the public interest, it is vital to consider the requirements that define and specify the need for ventilation.

For a healthy IAQ and from the hygiene point of view, dwellings have to benefit from an air renewal and pollutant extraction system, especially from certain areas like the bathroom and kitchen, to avoid health hazards due to high indoor air pollution rates and condensation. As the first step in this direction, CO2 concentrations calculated over one year should not exceed 1,200 ppm for more than two per cent of the year for conventional dwelling occupancy.

It must be remembered that breathing clean air is an inalienable right, as much as the right to drinking water. But, apart from a hygienic environment with high IAQ and low pollutant concentrations, thermal comfort during winter and summer is also a human need.

The writer is Managing Director of Aldes Middle East. He can be contacted at pierrefeu-gaetan@aldes.com


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