05/03/23 1

INTRODUCTION: We have learned how air becomes polluted,

how vitiated air affects the occupant and the reasons for the symptoms produced in him. It has been shown that air movement alone cannot maintain comfortable conditions for long without the introduction of fresh air; no will it remove the danger of spray – borne infections (air – bone infection).

05/03/23 2

In order to maintain comfortable conditions in an occupied room it is necessary to have adequate ventilation. The simplest way of doing this is to replace the warm, humid air by cool, dry fresh air.

05/03/23 3

1. Is the process of replacing foul air by that which is pure, in any enclosed place, as a church, a mine etc.

2. The act of supplying fresh air and get rid of foul air.

3. Ventilation is the movement of air in and out of an enclosed space, including a body.

05/03/23 4

4.The circulation of fresh air through open windows, doors, or other openings, which are in opposite sides of the room or rooms being ventilated.

05/03/23 5

5.Ventilation is the process by which ‘clean’ air (normally outdoor air) is intentionally provided to a space and stale air is removed. This may be accomplished by either natural or mechanical means.

05/03/23 6

5.Ventilation is the intentional movement of air from outside a building to the inside.

05/03/23 7

1.Natural ventilation

2.Mechanical Ventilation

05/03/23 8

1.Natural ventilation Is ventilation that occurs primarily through

open windows and doors and by infiltration through cracks in the building envelope, such as walls, around windows and any penetration through the walls. Natural ventilation is driven by wind or pressure and/or temperature differences between inside and outside a building

05/03/23 9

One of the biggest advantages of natural ventilation is that it does not cost any money to run. Mechanical ventilation and electronic climate control can be quite costly, and may contribute significantly to the overall energy costs involved with running a building. No use of energy also makes natural ventilation an environmentally friendly choice. 05/03/23 10

Natural ventilation systems tend to be easier to maintain, as well, with no parts to break or go wrong, they can't disturb occupants of the building with interruptions in ventilation or add to the operating costs for the ventilation system

05/03/23 11

◦Natural ventilation is generally impractical for large buildings, as they tend to be large, sealed and climate controlled specifically by HVAC systems.

05/03/23 12

Three forms of natural ventilation are:

1.Through ventilation2.Cross ventilation3.Back to back ventilation

05/03/23 13

1. Through ventilation:In this method the windows are opposite to each other, so that a current of air may pass straight through the room.

05/03/23 14

2. Cross ventilation:In this method the windows are so placed that a current of air may pass diagonally across the room.

05/03/23 15

Cross ventilation is obtained by having windows in both sides of the room, causing airflow across the space. Positive pressure on the windward and/or a vacuum on the lee side of the building causes air movement across the room(s) from the windward to the lee side, provided the windows on both sides of the room are open.

05/03/23 16

The windows on the windward side of the building are opened less than the windows on the lee side, in order to obtain an optimal airflow with as little draught as possible.

05/03/23 17

3. Back to back ventilation: Neither through ventilation nor cross

ventilation takes place. It is considered to be unhygienic type of ventilation, since the same air tends to be repeatedly used without being replaced.

05/03/23 18

05/03/23 19

2.Mechanical Ventilation or forced ventilation

Outside air is delivered indoors typically with a fans, which draws air from outside and forces it through ducts to the place where occupants are located. Mechanical ventilation can exacerbate infiltration and/or exfiltration

05/03/23 20

Three forms of artificial/mechanical ventilation are:-

1.Exhaust (extractor/vacuum) system2.Pressure (plenum/propulsion) system3.Balanced system

05/03/23 21

1. Exhaust (extractor/vacuum) system:Fans draw air out of the building in openings high up in the outside walls. The air thus drawn out is replaced by fresh air through windows and other inlets.

05/03/23 22

When it comes to air contaminants, local exhaust ventilation is the capture of those nasties at their source. Local exhaust ventilation is absolutely required when the source have dust, exhaust fumes, solvent vapors, lead fumes, and acid mist, all known as toxic or corrosive contaminants.

05/03/23 23

The fans may be placed directly in windows or outside walls or in ducts which lead the air outside. It is a system that is useful for the removal of dust, smoke and fumes in some factories. But the method has the disadvantage that the flesh-air to replace the foul (vitiated) air must find its own way into the building.

05/03/23 24

2. Pressure (plenum/propulsion) system:

Unlike the exhaust system, this forces the air into a building and therefore control of entering air is possible, the fresh entering air displaces the used up air. The advantage of this method is that the source of air-entry can be controlled and its purity thereby ensured.

05/03/23 25

The air can be filtered, warmed or cooled as required; the method breaks down if insufficient outlets are provided for the foul (vitiated) air or if these are closed or blocked up.

05/03/23 26

3. Balanced system: This is a combination of the exhaust and

plenum system. Air is drawn in through ducts by means of a

centrifugal fan and extracted at suitable points by exhaust fan. When this system of ventilation is employed there should be no natural inlets or outlets.

05/03/23 27

A balanced ventilation system usually has two fans and two duct systems. It facilitates good distribution of fresh air by placing supply and exhaust vents in appropriate places.

05/03/23 28

A typical balanced ventilation system is designed to supply fresh air to bedrooms and common rooms where people spend the most time. It also exhausts air from rooms where moisture and pollutants are most often generated, such as the kitchen, bathrooms, and the laundry room.

05/03/23 29

Balanced ventilation systems are appropriate for all climates; however, because they require two duct and fan systems, they are usually more expensive to install and operate than supply or exhaust systems.

05/03/23 30

Air conditioning is generally employed with this type of ventilation and the temperature and humidity can be controlled. It is suitable for factories where a control of humidity and temperature is necessary to the processes being carried out; as for example in cotton factories. It is also suitable for cinema halls.

05/03/23 31

reasons for ventilation: To keep flammable gases and vapors below

the lower flammable limit (LFL). To keep the air movement at a certain level

so that the hear stress can be reduced. To keep toxic contaminants at or below

certain concentrations To reduce odors To dilute cigarette smoke To control microorganisms, dusts and other

particulates To limit carbon dioxide buildup.

05/03/23 32