Post 203 – by Gautam Shah
People spend substantial part of their time in indoor spaces. The indoor spaces include homes, work places (offices, factories, shops), automobiles, buses, trains, air-crafts, metro stations, elevators. Some of these space usage are momentary, but in substantially fouled places due to over crowding, enclosed form, very small volumetric space, deeper location (from exterior locations), high-intensity use by humans and other beings and presence of fouling elements (such as plants, equipments, materials, etc.). Some spaces, though, are considered better and safer when there is a greater foot-print (floor space), volumetric space, lesser intensity of use, frequent exchange with the exterior atmosphere and are formed with non-fouling materials.
There is continuous interaction between the building space and its users. The interaction becomes important when we spend as much as 80% of time in such interior spaces. The interaction is intense because the buildings are increasingly becoming non-exchanging entities with the exterior. This attitude arises mainly from conservation of energy required for cooling or heating loads. And the tools for these approach consists of integrated shell-design of the buildings, sealing all points of micro ventilation (air exchange), and insulation with synthetic foams. The use of architectural form, orientation, natural ventilation systems, etc. find no place in dense urban localities, and spaces that subsist on very exact climate controls (Pharmaceutical-food plants, operation theatres, zero dust process rooms, etc.). The problem becomes huge when spaces become part of large interior-conglomerates such as air ports, multi story atrium, malls, shopping arcades, etc. Here the individual interior space modules have secondary, tertiary or very remote exposure to the exteriors.
Indoor quality of air is usually far more inferior to the exterior surrounding, simply because the external atmosphere is infinite in volume and so has greater capacity of dilution. So if there is greater exchange between the interior to exterior environments, the quality of interior pollution can be diluted. Exterior environment can be poor during a sand-dust storm, or may have high proportion of moisture during heavy rains. Exterior environments could be highly contaminated in industrial estates.
Poor quality of indoor air affects health and productivity. One may recover from short exposure but sustained exposure affects the immune systems of the body. People with weak resistance such as the sick, children and aged persons are more readily affected by such atmospheres.
Buildings with infrequent or very rare occupation also have poor indoor atmosphere. This is due to continuous release of contaminants from some of the materials even at room temperature. Such buildings have moisture addition and condensation from leakages and releases from structural elements. The presence of moisture encourages mould and algae.
There is a false perception that air conditioning takes care of the issues related to indoor atmosphere. Basic function of air conditioning is to reduce the air temperature. In the process it scrubs out the excess moisture, often to an unhealthy level for children and the aged. Few air-conditioners have moisture adding device or and monitoring system for it. Air conditioners supposedly have filters for particulate matter, but poor maintenance can make it ineffective. Air conditioners are supposed to have fresh-air input system to dilute the contaminated interior air, but often to add to cooling efficiency this is closed in window and car units. Split air conditioners are notorious on this count. The split AC system relies on micro ventilation and frequent opening-closing of doors for air change. This rarely happens in bed rooms at night, or even in operation theatres. In the later case the door closing-opening occurs in secondary spaces like lobbies that are even more fouled.
Most window and split systems have a collection unit of condensate water. When the unit is switched off, the condensate from cooling fins drains here. The bacteria proliferate in this water during the switch off period (usually night). Next start of the fan sees the mass of bacteria entering into the interior space.