Air Quality or the lack of it is a key topic of discussions in all forms of media these days. Rising air pollution levels are being recorded not only across all major cities in the country but also in smaller towns. There is also a greater awareness amongst the population of the ill effects of pollutions and the sources of pollution as well. People are now aware of the impact of Particulate Matter (PM) 10 and 2.5 in the air, a major change from a few years back when air pollution always meant smog. With greater urbanization and rapidly expanding population of cities and towns, the work is moving from outdoors as was the case with people employees in agriculture, to indoors. More and more people are spending more time inside buildings and work spaces than out one the open and hence, the quality of air within these spaces is as important as the air outside in environment.
Ventilation plays a key role in making buildings, work spaces as well as the places we reside inhabitable. Traditional homes had natural ventilation arrangements such as openings near the ceiling to allow hot and stale air to move out as it got displaced by the cooler outside air. Modern buildings which house large numbers of workers can no longer rely on natural ventilation and mechanical ventilation is essential to make the space usable. Thus, ventilation of the work or living space is critical to ensure a healthy atmosphere for the occupants.
Ventilation Systems in Buildings
The ‘V’ in HVAC stands for ‘Ventilation,’ which is an important component of building systems that enable the occupants to work or inhabit the space in a safe and comfortable manner. Ventilation essentially means movement of air or circulation of air in the work space with the aim of transferring heat as well as maintaining a healthy atmosphere for the occupants. The key functions of a ventilation system in a building are:
– Supply of fresh, outside air and removal of the stale air within the work space
– Removal of heat from the space – heat from equipment’s, occupants etc.
– Transfer of cool air to work spaces for comfort air conditioning
– Removal of odours in spaces such as washrooms, kitchens, closets etc.
– Excavation of smoke in emergencies
– Extraction of pollutants in basements from vehicular exhaust system
Supply of air is one of the main functions of the ventilations system in a building. To provide a comfortable work environment, air is cooled and conditioned in the Air Handling Unit (AHU) and directed into the workspace. The heated room air is then drawn into the AHU via the return air ducts where the air loses its heat across the heat exchanger and again sent to the room. The air is essentially recirculated in the room and will end up getting stale or saturated with carbon dioxide that the occupants breathe out. Thus, to maintain the air quality of the recirculated air, a small amount of external ‘fresh’ air is mixed with the return air and sent into the room. The amount of air introduced can vary from as low as 5 – 10% to a full 100% fresh air change, depending upon the application. Typical work space fresh air induction ranges between 5 to 10 %.
Outdoor and Indoor Air Quality
Building air conditioning systems take in small amount of air from the external environment to keep the indoor air healthy. Thus, the quality of air going into the AHU is as important as the quality of air within the work space. The air quality in the environment around the AHU and building is usually not in control of the building manager. The indoor air can be managed better as the building management team has access to a number of equipment and technologies to monitor as well as maintain the air quality. The key pollutants that are found in external and internal air are listed in table 1.
As can be seen from Table 1, while outdoor air pollution is a major cause of worry, the indoor air pollutants are even more important as occupants spend a large part of their day indoors. The exposure to pollutants is thus more in indoors, and hence the health effects are more serious.
Studies have shown that indoor air pollution can be as high as 3 to 5 times the outdoor pollution levels and with people spending around 80 to 90% of their time indoors, the problems related to indoor air quality get amplified.
Managing Indoor Air Quality through Ventilation
ASHRAE Standard 62.1-2013 – Ventilation for Acceptable Indoor Air Quality is the most widely used reference document for ventilation in buildings. The standard defines and lays downs various processes and parameters that ensure the minimum acceptable levels of air quality in the work space.
The standard primarily addresses the design considerations. In addition to adhering to a good design, best practices in operation of the ventilation system as well as workplace hygiene help in improving the air quality. Some of the methods that building managers can adopt to ensure a high level of IAQ are shown in figure 1 above and explained below:
Figure 1: Ventilation for good IAQ…
– Maintenance of AHU filters: Filtration is the first step in preventing pollutants entering the work space. Most modern AHUs have multi-layer filtration systems and the maintenance team needs to carry out filter upkeep as per the manufactures guidelines. While this seems a very basic task, experience shows that filter cleaning is often not carried out due to in accessibility of the filters, lack of staff or time for cleaning the filters or simply lack of awareness of the need to maintained the system.
– Keep the AHU room clean: Most occupants of a building do not ever enter an AHU room and hence do not know what’s inside. Where the building management is not so concerned about IAQ, one would generally find the AHU rooms being used as store rooms or change rooms for the maintenance staff. Cleaning chemicals are often kept in the AHU rooms. Since the return air system takes in air from the AHU room for mixing with the return air, any contaminants due to these unwanted items in the AHU room will impact the IAQ.
– Maintain AC discipline: Any air entering the work space other than from the AHU will be untreated air as it has not passed through a filter. Thus, ingress of untreated air should be minimized by using suitable technologies such as air curtains and air locks. Awareness amongst the occupants on the need to maintain the air conditioned space discipline by keeping doors closed when not in use is also essential to improve IAQ.
– Measure air quality: What cannot be measured cannot be measured is a famous management phrase, and this applies to ventilation as well. Measurement of the air quality in the work space is essential to assess effectiveness of the ventilation system. There are some key parameters that are typically measured in an IAQ test. The test should be done at least once a year. Low cost measurement devices are now available that allow online measurement of a few important parameters such as CO and particulate matter.
– Maintaining outdoor air quality: The air that circulates in a building comes from the surroundings of the buildings, and hence, efforts should be made to keep the environment around the building as healthy as possible. Air intake systems should be free from obstructions and no debris or air pollution causing agents should be allowed near the air inlets.
– Operating AHUs at design points: The air flow rates of AHU’s are designed keeping in mind the occupancy and layout of the office space. The air flow rate depends on the number of people as well as floor area. Thus, any change in the floor occupancy density will require a change in the AHU flow rates. This however does not occur in practice and leads to poor air quality in the work space.
– Air balancing: The occupancy of the floor or the layouts keep on changing in any office environment, due to operational requirements or space constraints. The original ducting of the office is designed for the original layout and aims to provide the right quality of air to the various spaces in the office. When changes occur in the work space (Say, meeting room converted to cubicle seating), or the density of staff increases, the original AHU flow patterns do not work. There is thus a need to reassess the flow whenever such change occurs to ensure that the IAQ is maintained. This may also involve tweaking with the AHU air flow rates.
Humans breathe in about 10,000 – 70,000 liters of air every day, while we eat only about 2 – 3 Kg. Yet, we fuss over that 2- 3 KG food much more than the air we breathe. The rising urbanization and use of fossil fuel is increasing the outdoor pollution levels.
This is in turn impacting the indoor air quality as that same polluted outdoor air enters our homes and buildings.
While governments and individuals are working to reduce the source of the outdoor pollution, ventilation systems can be harnessed to maintain the IAQ within the work spaces and indoors where we spend so much of our time. Effective maintenance and operations of the ventilations system will go a long way to ensure a healthy and productive work force.
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