VENTILATION IN BUILDING

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1) Functions of ventilation

The three main functions of ventilation are for: –

FUNCTIONS OF VENTILATION
  1. The supply of fresh air
  2. Maintain cooling effect for comfort conditions.
  3. Removing heat from the thermal mass in the building structure ( we will concentrate on night time cooling).

2) The supply of fresh air

Fresh air is required in buildings to: –

  1. Provide sufficient oxygen
  2. Dilute odors
  3. Dilute to acceptable levels of carbon dioxide produced by occupants & combustion.

3) Types of ventilation

TYPES OF VENTILATION

4) Heat balance in building

HEAT BALANCE IN BUILDING

5) Nighttime cooling of the building

NIGHT TIME COOLING OF THE BUILDING
  • Night cooling refers to the operation of natural ventilation at night in order to purge excess heat and cool the building fabric.
  • A building with sufficient thermal mass, which can be exposed to night time ventilation:-
  • It can reduce peak daytime temperatures by 2° to 3° using this strategy.

6) Wind & temperature effect

Light or heavyweight structure?

  • Air moves from high pressure to low pressure.
  • Light weight building track external temperatures more closely than heavyweight buildings.
  • Outdoor mean maximum temp. are greater than 34 deg. In july .

Light weight structure is:

  • Well insulated roof
  • No direct solar gain
  • Ventilation path trough the building are effective

i) Wind effect

  • Wind pressure on a building depends on wind direction, speed & the shape of the building.

ii) Temperature effect

Temperature differences between indoors & outdoors causes density differences in the air which in turn causes pressure differences (as hot air rises).

  • Stack pressure can be calculated
  • Ps=0.042XhXT
  • Ps= stack pressure
  • H= Height of stack
  • T= Temperature difference

7) Ventilation

There are four main ways in which buildings are naturally ventilated: –

  1. Single sided ventilation
  2. Cross ventilation
  3. Stack effect
  4. Reverse stack effect

i) Single sided ventilation

  • It occurs when large ventilation openings, such as doors & windows are situated on one external wall only.

ii) Cross ventilation

CROSS VENTILATION
  • It occurs when inflow & outflow openings in external walls have an internal flow path between them.
  • Flow characteristics are determined by the combined effect of wind & temperature differences.

iii) Stack ventilation

STACK VENTILATION

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