bcl ventilation

8/2/2019 BCL Ventilation

1/28

MODULE III

Ventilation and Dampness control

Functions Factors affecting indoor airflow- airflow aroundbuildings concepts of ventilation- ventilation design.

Causes, effects and prevention of dampness

Driving rainindex. Capacity of drains, DWP and roof gutter


2/28

Ventilation The process by which fresh air is introduced and

contaminated air is removed from an occupied space the intentional movement of air from outside a building

to the inside


3/28

Functions of ventilation To provide a continuous supply ofoxygen necessary for human

existence.

To remove the products ofrespiration and occupation, that is;heat, moisture and carbon dioxide from people

to provide a healthy, refreshing and comfortable environment

To maintain the required air quality inside

To provide adequate air movement

Thermal comfort

to cool the environment in warm humidconditions

To remove foul odours, gases,etc

To remove products of combustion from kitchen, chullahs,chimney, etc.

To remove contaminants or harmful chemicals generated byprocesses


4/28

TERMINOLOGY

Air Change Per Hour-amount of air leakage into

or out of a building or room in terms of thenumber of building volumes or room volumesexchanged.

Indoor Wind Speed - The average of wind speeds

measured at symmetrically distributed points ona horizontal plane in the normally occupied zone(a region lying between 0.6 to 1.2 m above thefloor).


5/28

VENTILATION REQUIREMENTS

for health and for comfort.

To meet the first requirement, the quality of airin buildings is maintained above a certainminimum level by replacing indoor air by freshoutdoor air to maintain certain levels of CO2 andoxygen in air and for control of odours or forremoval of products of combustion duringoccupancy.

Ventilation to meet this requirement isessentially needed under all climatic conditions,

hence it is termed as health ventilation.


6/28

The comfort conditions necessitate ventilation

for providing such thermal environment as to

increase heat loss from the body and prevent

discomfort due to moist skin, and also to cool

the indoor space itself

when the indoor temperature exceeds

outdoor temperature. This type of ventilation

is known as comfort ventilation.


7/28

MINIMUM STANDARDS FOR VENTILATION

Air Change Schedule

Space to be Ventilated Air Changes perHours

*Assembly hall/auditoria 3-6 *Bed rooms/ living rooms 3-6

Bath rooms/ toilets 6-12

*Cafes/ restaurants 12-15

Cinemas/ theatres(non-smoking) 6-9

Class rooms 3-6


8/28

*Factories (medium metal work) 3-6

*Garages 12-15

*Hospital wards 3-6

*Kitchens (common) 6-9

*Kitchens (domestic) 3-6

Laboratoeis 3-6

*Offices 3-6


9/28

A certain minimum desirable wind speed is

needed for achieving thermal comfort at

different temperatures and relative

humidities.

For obtaining values of indoor wind speed

above 2.0 m/s, mechanical means of

ventilation may have to be adopted.


10/28

Classification

Comfort ventilation- necessary only during

certain weather condition to improvethermal comfort

Permanent Ventilation- necessary for all

weather conditions

Natural ventilation- by natural means

Artificial Ventilation- mechanical methods


11/28

Comfort ventilation- for increasing the heat loss /

gain processes to maintain thermal balance of

human body

Permanent ventilation-

-to maintain CO2 content within safe limit and to

provide sufficient O2 content -to control odors

-to remove products of combustion from chullahs,

gas appliances, stove etc.


12/28

Natural Ventilation the intentional flow of outdoor air through an enclosure

under the influence of wind and thermal pressures through

controllable openings. control both temperature and contaminants, particularly in

mild climates.

The arrangement, location, and control of ventilationopenings should combine the driving forces of wind and

temperature dependent on many factors including:

building location with respect to pre-dominant winddirections,

interior layout of offices, corridors, furniture,

other potential airflow obstructions,

sizing of windows and other openings.


13/28

CLASSIFICATION wind driven ventilation and stack ventilation

Wind effect: due to the forces of wind

air enters through openings in the windward walls, andleaves through openings in the leeward wall

The occurrence and change of wind pressures onbuilding surfaces depend on:

-wind speed and wind direction relative to the building; -the location and surrounding environment of the

building; and

-shape of the building.

With large openings on the windward face, the buildingtends to be under positive pressure.

if the openings are smaller than those downstreamvepressure


14/28


15/28


16/28

Stack effect/ chimney effect Air movement due to thermal forces set up by

difference in air density caused by tempdifference between the indoor air and out doorair

the flow of air is in the vertical direction and isalong the path of least resistance throughchimneys, stacks, or other containers,Stairwells, shafts, elevators

increases with

-greater temperature difference - increased height between the higher and

lower apertures


17/28

Stack effect


18/28

+ves & -ves Does not rely on wind: can take place on still, hot

summer days when it is most needed.

Natural occurring force (hot air rises)

Stable air flow (compared to wind)

Greater control in choosing areas of air intake

Sustainable method Lower magnitude compared to wind ventilation

Relies on temperature differences (inside/outside)

Design restrictions (height, location of apertures)

may incur extra costs (ventilator stacks, taller spaces)

The quality of air it introduces in buildings may bepolluted


19/28

During the winter season the following stackeffect occurs:

indoor temperature is higher than outdoortemperature;

the warmer air in building then rises up;

the upward air movement produces negativeindoor pressure at the bottom;

positive indoor pressure is created on the top;

warmer air flows out of the building near the

top; and the air is replaced by colder outside air that

enters the building near its base.


20/28

G id li f l il i


21/28

Guidelines for natural ventilation should be effective regardless of wind direction and there must

be adequate ventilation even when the wind does not blow fromthe prevailing direction;

inlet and outlet openings should not be obstructed by nearbyobjects;

windows should be located in opposing pressure zones since thisusually will increase ventilation rate;

a certain vertical distance should be kept between openings for

temperature to produce stack effect; openings at the same level and near the ceiling should be avoided

since much of the air flow may bypass the occupied zone;

architectural elements like wing walls, parapets and overhangsmay be used to promote air flow into the building;

topography, landscaping, and surrounding buildings should beused to redirect airflow and give maximum exposure to breezes;


22/28

in hot, humid climates, air velocities should bemaximized in the occupied zones for bodily cooling;

to admit wind air flow, the long facade of the buildingand the door and window openings should be orientedwith respect to the prevailing wind direction;

if possible, window openings should be accessible to andoperable by occupants;

vertical shafts and open staircases may be used toincrease and generate stack effect;

openings in the vicinity of the neutral pressure level maybe reduced since they are less effective for thermallyinduced ventilation;

if inlet and outlet openings are of nearly equal areas, abalanced and greater ventilation can be obtained.


23/28

Mechanical Ventilation

Air moved by motor driven fans

Individual systems- fans

Centralized systems-filters ,Ducts , fans


24/28

Indoor airflow

Position and size of window

Wind intensity and direction

Obstructions

Shape of building


25/28

Airflow around buildings

Shape, size of building

Wind direction

Orientation & Spacing of building

Obstructions around


26/28


27/28

Airflow Around Porous and Non-porous

Barriers


28/28

Reduction of Airspeed Upwind and

Downwind of Obstruction

bcl ventilation

Documents