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OEM Update
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Indoor Air Quality: What and How?

November 25, 2015 3:29 pm

A way of quantitatively ensuring the IAQ is by the frequency of effective turnover of inside air by replacing it with outside air
  Indoor Air Quality(IAQ) or Indoor Air Pollution  refers to the air quality within and around buildings and premises used for residential, commercial or factory premises and its surroundings especially as it relates to the health and comfort of its occupants. IAQ can be affected by gases (including carbon monoxide, carbon dioxide, radon, volatile organic compounds that include but are not limited from sources such as smoke, toxic gases, kerosene fumes, unvented and malfunctioning furnaces and stoves, building materials such as paint, furnishings, pollen, varnish etc. personal care products), particulates, microbial contaminants (mould formed due to humidity, bacteria), or any mass or energy stressor that can induce adverse health conditions. Ventilation, filtration and control of source are the primary ways to dilute contaminants for improvement of IAQ in most occupied premises. Residential units can further improve indoor air quality by routine cleaning of carpets and area rugs. Cleaning based on traffic, number of household members, pets, children and smokers usually help create framework guidance for IAQ improvement. Carpets and rugs act like an air filter and must be cleaned. Determination of IAQ involves the collection of air samples, monitoring human exposure to pollutants, collection of samples on building surfaces, and computer modelling of air flow inside buildings.
IAQ is part of indoor environmental quality (IEQ), which includes IAQ as well as other psychological and physical aspects of life indoors (e.g., lighting, visual quality, acoustics, and thermal comfort).
Indoor air pollution in developing nations is the most deadly risk globally. A major source of indoor air pollution in developing countries is the burning of wood, charcoal, dung, or crop residue for heating and cooking. Estimates indicate approximately 2.2 – 2.5 million deaths occurring annually as a resultant to such high levels of exposure to particulate matter. The majority of deaths occur in the developing nations.
A way of quantitatively ensuring the IAQ is by the frequency of effective turnover of inside air by replacing it with outside air. In the UK, for example, classrooms are required to have 2.5 outdoor air changes per hour. In gymnasiums, physiotherapy spaces and restaurants and dining areas, the ventilation should be sufficient to limit carbon dioxide to 1,500 ppm. In the US, and according to ASHRAE Standards, ventilation in classrooms is based on the amount of outdoor air per occupant plus the amount of outdoor air per unit of floor area, not air changes per hour. Since carbon dioxide indoors comes from occupants and outdoor air, the adequacy of ventilation per occupant is indicated by the concentration indoors minus the concentration outdoors. The value of 615 ppm above the outdoor concentration indicates approximately 15 cubic feet per minute of outdoor air per adult occupant doing sedentary office work where outdoor air contains 385 ppm, the current global average atmospheric CO2 concentration. In classrooms, the requirements in the ASHRAE standard 62.1, Ventilation for Acceptable IAQ, would typically result in about 3 air changes per hour, depending on the occupant density. Here as we now know the occupants aren’t the only source of pollutants, so outdoor air ventilation may need to be higher when unusual or strong sources of pollution exists indoors. When outdoor air is polluted, then bringing in more outdoor air can actually worsen the overall quality of the indoor air and exacerbate some occupant symptoms related to outdoor air pollution. Generally, outdoor country air is better than indoor city air. Exhaust gas leakages can occur from furnace metal exhaust pipes that lead to the chimney when there are leaks in the pipe and the pipe gas flow area diameter has been reduced.                                                                             Moisture management and humidity control requires operating HVAC systems as designed. Moisture management and humidity control may conflict with efforts to try to optimise the operation to conserve energy. For example, Moisture management and humidity control requires systems to be set to supply Make Up Air at lower temperatures (design levels), instead of the higher temperatures sometimes used to conserve energy in cooling-dominated climate conditions. However, for most of the places where during the majority of hours of the year, outdoor air temperatures are cool enough that the air does not need further cooling to provide thermal comfort indoors. However, high humidity outdoors creates the need for careful attention to humidity levels indoors. High humidities give rise to mold growth and moisture indoors is associated with a higher prevalence of occupant respiratory problems.
The “dew point temperature” is an absolute measure of the moisture in air. Some facilities are being designed with the design dew points in the lower 10 C, and some in the upper and lower 4.5 C. Some facilities are being designed using desiccant wheels with gas fired heater to dry out the wheel enough to get the required dew points. On those systems, after the moisture is removed from the make up air, a cooling coil is used to lower the temperature to the desired level.

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