Ventilation is the
replacement of air in an surrounding by a supply of fresh outdoor air and the
control of the quality of incoming air with regard to its temperature, humidity
and purity with a view to providing a thermal environment that is conformable
and free from risk of infection.
replacement of air in an surrounding by a supply of fresh outdoor air and the
control of the quality of incoming air with regard to its temperature, humidity
and purity with a view to providing a thermal environment that is conformable
and free from risk of infection.
Types of Ventilation
1.) Natural Ventilation
Natural ventilation is the
simplest system of ventilating a small dwellings, schools and offices. In this
method, reliance is placed on certain forces which operate in nature. They are;
simplest system of ventilating a small dwellings, schools and offices. In this
method, reliance is placed on certain forces which operate in nature. They are;
a.) The Wind: The wind is an active force
in ventilation. When it blows through a room, it is called perflation. When
there is an obstruction, it bypasses the room it is called aspiration. Doors
and windows facing each other provide “cross ventilation”.
in ventilation. When it blows through a room, it is called perflation. When
there is an obstruction, it bypasses the room it is called aspiration. Doors
and windows facing each other provide “cross ventilation”.
b.) Diffusion: Air passes through the
smallest openings or spaces by diffusion. This is a slow process and therefore
is not relied upon as the sole means of ventilation.
smallest openings or spaces by diffusion. This is a slow process and therefore
is not relied upon as the sole means of ventilation.
c.) Inequality of Temperature: Air flow from high density
to low density; it rises when slightly heated and escapes from openings
provided high up the room. The outside air which is cooler and denser will
enter the room through inlets placed low. The greater the temperature
difference between the outside and the inside air, the greater the velocity of
incoming air.
to low density; it rises when slightly heated and escapes from openings
provided high up the room. The outside air which is cooler and denser will
enter the room through inlets placed low. The greater the temperature
difference between the outside and the inside air, the greater the velocity of
incoming air.
2.) Mechanical (Artificial) Ventilation
Mechanical or artificial
ventilation may be of the following types
ventilation may be of the following types
a.) Exhaust ventilation
b.) Plenum ventilation
c.) Balanced ventilation
d.) Air conditioning
a.) Exhaust Ventilation: In this system, air is
extracted or exhausted to the outside by exhaust fans usually driven by
electricity. As air is exhausted, a vacuum is created which induces fresh air
to enter the room through windows, doors and other inlets. Exhausted
ventilation is usually provided in large halls and auditoria for removal of
air. The exhaust fans are housed in the external walls high up near the roof
which facilitate removal of the upper layer of the heated air.
extracted or exhausted to the outside by exhaust fans usually driven by
electricity. As air is exhausted, a vacuum is created which induces fresh air
to enter the room through windows, doors and other inlets. Exhausted
ventilation is usually provided in large halls and auditoria for removal of
air. The exhaust fans are housed in the external walls high up near the roof
which facilitate removal of the upper layer of the heated air.
b.) Plenum: In this system, fresh air
is blown into the room by fans so as to create a positive pressure and displace
heat air. Plenum or propulsion system is used for supplying air to
air-conditioned buildings and factories.
is blown into the room by fans so as to create a positive pressure and displace
heat air. Plenum or propulsion system is used for supplying air to
air-conditioned buildings and factories.
3.) Balanced Ventilation
This is a combination of the exhaust and plenum systems of
ventilation. The blowing fan must balance the exhaust fan.
ventilation. The blowing fan must balance the exhaust fan.
4.) Air-Conditioning
Air-conditioning is defined
as the “simultaneous control of all or at least the first three of those
factors affecting the physical and chemical conditions of the atmosphere within
any structure. These factors include temperature, humidity, air movement,
distribution, dust, bacteria, odour and toxic gases most of which affect in
greater or lesser degree human health and comfort”. In air-conditioning, the
air is first filtered and then saturated with water vapour. The excess of
moisture is removed and the air is heated to the desired temperature before it
is supplied.
as the “simultaneous control of all or at least the first three of those
factors affecting the physical and chemical conditions of the atmosphere within
any structure. These factors include temperature, humidity, air movement,
distribution, dust, bacteria, odour and toxic gases most of which affect in
greater or lesser degree human health and comfort”. In air-conditioning, the
air is first filtered and then saturated with water vapour. The excess of
moisture is removed and the air is heated to the desired temperature before it
is supplied.
