Ventilation

ventilation as a component of healthy environment

1. ventilation

2. D ictionary --‘ intentional movement of air from outside a building to inside ’ E xcess of ventilation - discomfort C ontrol of the quality of air - by modifying the temperature, humidity and purity Aim – a. provide an environment, which is thermally controlled and comfortable, b. gives a sense of well-being and c. reduces the risk of transmission of airborne diseases .

3. Ventilation air The air used to provide acceptable indoor air quality It removes the bad odours D elivered either naturally or by means of mechanical ventilation Can change the temperature of air or its moisture content depending on the requirement inside the building. Air exchange rate.

4. Ventilation standards To achieve a sense of freshness in a room and remove body odours. Floor space : the product of the length and breadth optimum floor space requirements per person - 50 to 100 feet. (b) Cubic space of area : Earlier prescriptions - fresh air supply of 3000 cu feet of air per person per hour. beyond 12 feet, not taken into account Current standards - 1000 to 1200 cu feet per person per hour (c) Air change The recommended number of air changes living room - 2 to 3 in an hour, Work rooms and assemblies - 4 to 6 per hour.

5. Types of ventilation

6. Natural forces of nature such as wind, ambient temperature and air pressure Diffusion / infiltration Wind driven Stack driven

7. Diffusion / infiltration T hrough openings, joints and cracks Buildings - kept under slightly positive pressure H elps in moisture management and humidity control inside the rooms

8. Wind driven ventilation P erflation A spiration C ross ventilation . It creates areas of positive pressure on the windward side of the building and negative pressure on the leeward side and the sides of the building . The shape of the building is crucial in creating wind pressures that will drive air flow through its apertures. Simple shapes - improve the ventilation Complex shapes - turbulent air flows Adv - readily available, economic to implement, could be controlled Dis- unpredictability in speed and directions, air quality is not controlled and could introduce pollutants & may create draughts and discomfort

9. Stack driven ventilation The warmer air will have lower density and be more buoyant and thus will rise above the cold air, creating an upward stream. To have optimum ventilation – the inside and outside air temperatures must be different The greater this temperature difference the greater the stack effect. ADV - does not rely on wind , flow is relatively stable with a greater control. DIS - lower magnitude, reliance on temperature differences, restrictions due to building designs & may introduce pollutants. Used in mills, boiler rooms, warehouses and industrial plants.

10. Mechanical ventilation

11. Ceiling fans, table or floor fans Used to circulate air within a room for the purpose of reducing the perceived temperature, because of evaporation of perspiration from the skin of occupants. Do not introduce outside air inside the room Air-coolers are used in hot & dry conditions They comprise of a chamber whose walls are made of straw, which is kept cool by pouring water & evaporation of water . A cool environment is thus created inside the chamber and a fan blows cool air inside the room

12. exhausts The indoor air is extracted out with the help of mechanically driven fans. Used in combination with the doors and windows since exhaustion of air outside the room creates a vacuum and this needs to be replaced by fresh air Exhausts are useful in industries especially where excess heat is generated. In residential areas - for extricating smoke or odours. The exhaust blades should be cleaned & well maintained to ensure Their long life

13. Plenum ventilation Air is blown inside a room by the use of fans and it enters through ducts. Creates a positive air pressure inside the room. Combined with exhaust mechanism it creates ‘balanced ventilation’. Used along with air conditioners, to supply air inside the building such that fresh air is circulated to leave out the odours and pollutants.

14. Air conditioning A s ystem which provides a combination of cooling, ventilation and control of humidity The system has a refrigerant providing cooling through a ‘refrigeration cycle’. This cycle comprises of four elements Compressor , condenser, Evaporator-dehumidifier & fan . Can be stand-alone systems or a part of central air-conditioning systems. Central air-conditioning system should be installed at the time of construction, The split air-conditioning where the fan coils are connected to remoter condenser unit using piping instead of ducts.

15. Demand controlled ventilation Reduces the energy consumption in a building, while maintaining adequate air quality. No fixed air replacement rate C arbon-dioxide sensors control the ventilation rate dynamically based on emissions of actual building occupants.

16. HVAC HVAC stands for ‘Heating, Ventilation and Air- Conditioning’. Important in those places where humidity and temperature must be closely regulated while maintaining healthy and safe conditions inside buildings. To ensure thermal comfort, accessible indoor quality at reasonable installation, operation and maintenance costs . HVAC systems determine the room air distribution i.e. how air is delivered to and removed from room spaces.

17. Ventilation requirements . The factors which determine the difference in ventilation are : ● ● Type of buildings ● ● Size of the buildings and the floor areas. ● ● Type of roof ● ● Locally prevalent wind directions ● ● Number of persons occupying the room ● ● Proximity to commercial or industrial areas ● ● Sanitation of the surrounding area ● ● Nature of work being carried out inside the buildings ● ● Geographical locations such as closeness to sea, large water bodies, hilly areas