Indoor Air Quality, abbreviated as IAQ, is an index which measures the cleanliness of air in the surroundings. Maintaining a standard IAQ is important because not doing so can be disastrous for your health. The rating is affected by dangerous gases, the most common of which is carbon monoxide.
The AQI ranges from 0 to 500. The value is directly proportional to the health concerns of individuals. Lower values are good for the environment and higher values are hazardous. A value of 50 categorizes the air quality as good with no potential effects on health. The standard value which must be maintained is 100. Any value below this is satisfactory and any value above this is harmful.
It is really important to consider indoor air quality control when designing HVAC systems, and it must be evaluated at every stage of designing and constructing. The primary methods employed to improve Indoor Air Quality ratings are filtration, ventilation and source control.
A popular method which maintains adequate indoor air quality control and consumes less energy is the demand controlled ventilation. Carbon dioxide sensors monitor the percentage of gas in the air, emitted by the building occupants, and accordingly change the air replacement rate.
Air filters are used to trap some of the pollutants present in the air. The Minimum Efficiency Reporting Value (MERV) must be at least 13. This standard has been set by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). The filters also limit the quantity of dirt reaching the coils. Unhealthy substances inhibit growth in the presence of dust particles. This also reduces the efficiency of the system.
High humidity serves as an ideal condition for moisture and mold to grow. This causes respiratory problems. The system must be set to supply air at lower temperatures but this increases the power consumption.
In warm regions, air is supplied at higher temperatures to conserve energy. In tropical areas, the outdoor temperatures are moderate and the need for cooling air indoors is eliminated altogether. The air supply is part of the design consideration and it can not be changed once the process is over.
The dew point also plays an important role in maintaining a suitable indoor air quality control index. It is the temperature at which water vapor in the air turns into liquid water. This is effective in reducing humidity.
The recommended values are between 40 簞F to 50 簞F. Gas fired heaters are implemented on desiccant wheels to dry the atmosphere and attain the dew point temperature required. Once the moisture has been condensed, cooling coils are used to lower the room temperature to the set value.
The limiting infiltration technique is often implemented in commercial buildings, and at time residential apartments. This is effective in reducing humidity in the air. The atmospheric air pressure in the building is kept slightly positive when compared to the outside air pressure to reduce infiltration.
Ozone forms many toxic chemicals when combined with common indoor pollutants. If the outdoor ventilation rate is kept higher, the concentration of ozone increases indoors and more reactions take place.
Even if the rate is kept low, the reactions cannot be avoided altogether. The chemicals formed are capable of causing diseases as well as death so ozone must be eliminated during ventilation. This is also achieved by diluting indoor air.
The international environmental and health organizations have set some standards that must be maintained to employ efficient indoor air quality control in order to lower the IAQ value. The outdoor air changes per hour must be 2.5. Carbon dioxide must be limited to 1500 ppm. The ventilation rate must be 3 changes per hour for small gatherings but this varies with the number of individuals.
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