Average indoor spending of human beings has increased over ages and an average individual is spending about 80-90% of time indoors. Indoor environment quality is a major determining factor for mental and physical health and life expectancy.
Though the defines scope is vast, air conditioning in many commercial establishments is confined to pure heating and cooling operations. Indoor environment quality assessments are reduced to report making procedures with no sense to the living individuals.
The elements of indoor air pollution can most often be picked from the below list:
- Airborne particles PM2.5
- Tobacco smoke
- Volatile organic compounds (especially from engineered wooden furniture’s, paints etc.)
- Carbon Monoxide
- Nitrogen Dioxide
- Carbon dioxide
- Microbes such as bacteria, virus, fungus
The list is not exhaustive and the impact of each of them to indoor air quality is truly relative depending on the concentration. In order to enhance indoor air quality, it is important to reduce the concentration of such pollutants to doses not harmful to the occupants. While we consider home and office environment, we need to bring down the doses such that even a long-term exposure is not harmful to the occupant.
One effective way is to do source control. That is to say avoid smoking in indoors, use low emissivity paints, select engineered woods with low VOC emissions etc. Reduction in dust generation, keeping floors, surfaces and corners clean to prevent from being reservoirs of dust is also important.
Providing sufficient ventilation rate will help to clean the indoor air. Gaseous pollutants are necessarily to be diluted through ventilation. Ventilation is an expensive process due to high enthalpy levels of outdoor air compared to the conditioned indoor air. Hence selection of ventilation rate is to be balanced with required indoor air quality, energy cost and equipment capacity.
Air filtration is an important solution to reduce the concentration of airborne particles. Airborne particles are major cause of air pollution.
Filtering air to levels of 5 micron and below require higher efficient air filters rated MERV 10 and above. Use of MERV 13 and higher grade of air filtration has to be pre meditated in the HVAC system and fans are to be designed accordingly.
If the option is not available in the existing HVAC system, separate air cycles may be introduced through recirculatory air filtration mechanisms.
Airborne particulates are the “boats” for tiny microbes and filtration of the particulates help reduce the float time of microbes such as virions and bacteria.
Ultra Violet rays of 250 – 270 nm ranges shall be used to disinfect microbes such as virus, bacteria and fungi. Virus are most susceptible to the UVC rays and disinfection of bacteria and fungi need UV energy in increasing order.
The disinfection of microbes is expressed in terms of UV energy required to cause permanent damage to the RNA or DNA of the microbe. UVC is said to cause Thiamine – Thiamine bond and cause error in the genetic code causing damage of the Nucleic Acid.
A study suggested 14mJ/cm2 of UV energy to cause 4log10 reduction of Novel Corona Virus. Keeping this figure in mind, a designer can select the required UV power through air velocity, area, exposure span etc.
Indoor Air Quality is determined by a set of parameters and the process of improving indoor air quality require deeper focus and is specific to case. General assumptions may lead to inefficient solutions though the parameters to be checked shall be general in nature.