Environmental Protection Agency (EPA) indicate that human beings spend approximately 87% of their living time indoors and another 6% in vehicles. This implies that we spend less than 7% of our life outdoors which is less than half a day or 12 hours per week. 

Indoors could imply residential, commercial, or Industrial spaces. In the US alone, commercial, and residential buildings accounted for 40% of the total national energy consumed. Throughout history, the concept of buildings has changed depending on the need to address social needs. With the advent of the technology of steel framing and other structural innovations, the idea of real estate exploded into the third dimension allowing extraordinary growth while maintaining a limited earthly footprint. However, the added complexity posed new challenges in the engineering systems required to maintain such a space at an adequate level of comfort for its occupants. 

Indoor Air Quality is one of the major factors that are most important in indicating the comfort level, general healthiness, and well-being of the occupants of the building. Indoor Air Quality includes the temperature of the air, levels of moisture in the air, and its composition which is an indicator of the level of pollutants, contaminants, and gases, all of which, play a significant impact on the well-being of the occupants of the building.

“Indoor Air Quality” as the name suggests refers to the quality of the air in a space. “Atmospheric Air” as we know it constitutes of the following gases in its elemental form: Nitrogen at 78%, Oxygen at 21%, Argon at 0.93%, Carbon Dioxide at 0.04% and the remainder being trace amounts of neon, helium, methane, krypton, hydrogen and water vapour which all exist in equilibrium with each other. Why is this important? These relative percentages of constituents are essential to the sustenance of life on this planet. A slight change in these factors can lead to a significant disruption of life itself on this planet.

All life on this planet is sustained through the mechanism of breath. Breathing is a natural process by which lungs absorbs the required amount of oxygen from the air in the atmosphere and exhales by products of ingested air back into the atmosphere. The typical lung respiratory volume for an average adult human male is 6 liters of air. This can be further subdivided into “tidal volume” which is the amount of air inhaled or exhaled during one respiratory cycle which is in the order of 500 – 750 ml, “inspiratory reserve volume” which is in the order of 3 liters, “expiratory reserve volume” which is typically 1.5 liters, and residual volume which is typically about 1 liter. The fresh air introduced into a HVAC system must account for the lung aspiration rate to offset the generation of CO2 in the space. This depends on the occupancy rating of the space. Demand Control Ventilation is a methodology employed in HVAC systems where in economizers are used to control the intake of fresh air based on the number of occupants in the space and CO2 generated because of this.

The pressure of air at sea level or 0’ ASL (above sea level) is 14.696 (psi) pounds per square inches. As the elevation changes or increases, the pressure of air reduces. At 10 000 ft ASL (3 KM), the air pressure is as low as 10 psi resulting in less oxygen to breathe. Ever felt a pain in your inner ear drum when you take off or land in an airplane. The effect is called “Barotrauma”. It is caused by the sudden change in air pressure resulting in a vacuum in the middle ear which can pull the ear drum inward. In severe cases, the middle ear can fill with fluid as the body tries to equalize pressure on both sides. At relatively high altitudes, air pressures become a quality of air that has significant impact on the comfort level of the occupants.  HVAC systems for airplane cabins typically must account for this factor in determining the amounts of recirculated air. HEPA Filters are used to decontaminate the air typically to ensure the recirculated air is free of pathogens and pollutants. Fresh Air is usually taken from the fuel system.

The temperature of the air is a quality of air that we are all familiar with. When it gets too warm, we go over to the thermostat and reduce the room temperature levels and when it gets cold, we try the opposite. Temperature is an intensive property of the air that affects its quality and the well being of the occupants.

Have you ever checked your “Humid-Stat”? This is the device that controls and regulates the relative humidity of your space. It is usually set between 40 to 50 % to ensure the well being of the building occupants. If you have felt a tinge of static electricity coursing through your fingers every time you touch your doorknob, it is an indicator that the relative humidity in your space is lower than 30%. Moisture being a good conductor of electricity helps the dissipation of electric charge freely through the air. Lower humidity levels that 30% can result in electric discharges between dissimilarly charged bodies due to a buildup of pockets of electrostatic discharge. Humidity levels more than 55% to 60% can facilitate and speed the growth of mold and mildew in buildings.

Older buildings typically have toxic asbestos fibers in its construction include ceiling tiles, walls, insulation, ducts, pipes, wall boards, wall seals and duct tapes. In the era of do it yourself home renovations, people might be unknowingly breathing contaminated air containing asbestos fibers It is essential to mitigate his hazard in the initial stages as it asbestos is a carcinogen causing unprecedented changes to the body.

Indoor Concentrations of Pollutants have increased in recent times due to increased use of synthetic materials in buildings, lack of adequate air exchanges, lack of required outdoor air rates, ineffective filtration mechanisms, specialized building usage which negates a “modular, one size fits all” approach to HVAC systems and calls for more individualized attention to HVAC systems required for the special use. The pollutants could include but are not limited to the following listed below

• Environmental Tobacco Smoke, Particulate Matter, Carbon Monoxide, NOX
• Dust and Fur from animals
• Naturally occurring Radon, Mold
• Pesticides, Lead and Asbestos
• Ozone from Air purifiers
• VOC (Volatile Organic Compounds) from cleaning products, paints, thinners, insecticides and other products and materials
• Airborne Pathogens, Viruses, Bacteria

The sources of these pollutants can be indoor or outdoor which can enter through open doors, open windows, ventilation systems and infiltration cracks in structures. Radon is an example of a pollutant that forms within the ground as uranium within rock and soil decays and can enter the structure through cracks and gaps in the foundation of the building. The water supply to a building can be a source of contaminants and chemicals into the building. Dust and Soil can enter the building through people entering the building through clothing and shoes.

Indoor Air Quality can be influenced by multiple factors including air exchanges achieved, outdoor weather conditions and occupant behavior. Air exchange rate and outdoor air rate can be the most important factor in controlling level of outdoor air pollutants and concentrations thereof. Without adequate levels of air exchanges through recirculated, fresh and infiltration air, indoor contaminants can grow at an unprecedented rate unless the source of the contaminant is dealt with.

The consequences of poor indoor air quality can be deleterious and detrimental. Lack of adequate fresh air can result in many undesirable health effects including headaches, dizziness, and fatigue. Those at risk, are those who have prior conditions related to migraine, cluster headaches, sinus sensitivities and are extremely susceptible to indoor air conditions. Indoor air pollutants in sufficient concentrations can cause irritation of eyes, nose and throat, respiratory disorders, including lung disorders, bronchial asthma, bronchitis, cancer amongst numerous others, Environmental tobacco smoke, radon, carbon monoxide, carbon dioxide, NOX, dust, mites, mold, pet fur, pet dander, particulates, particulates and allergens through insect migrants, particulate matter can be triggers in sufficient concentrations for most people include those most sensitive to it like asthma patients.

“Sick Building Syndrome:” is a name given to a condition that occurs in the occupants of a space if the environmental conditions are unsuitable for these occupants. Obviously, the building HVAC system cannot cater to everyone specific needs, however time and research have produced a body and range of data that details the ideal environmental conditions for a large subset of the population. Indoor Air quality is an ever-growing field of study that accounts for these factors and helps make improvements to the quality of our life.