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VILNIUS COLLEGE OF TECHNOLOGIES AND DESİGN

CIVIL ENGINEERİNG FACULTY

Lecture: Building Engineering System

Ventilation System in Building

TEACHER: R. Bilinskienė

2015/2016

Prepared By: Suliman KOHİSTANİ

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Ventilation & Wind Flow

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Index

1- introduction ............................................................................................4

2- ARCHITECTURAL CLIMATOLOGY.....................................................5

3- VENTILATION ...........................................................................................6

4- Process............................................................................................................6

5- Design.............................................................................................................7

6- Ventilation rate standards............................................................................8

7- Standards for residential buildings.............................................................8

8- Ventilation rate procedure...........................................................................9

9-Categories of ventilation................................................................................9

10- Natural ventilation.....................................................................................10

11- Function of natural ventilation ................................................................10

12- Mechanical systems...................................................................................10

13- Fans.............................................................................................................11

14- Supply of fresh air......................................................................................12

15- Stack due to thermal force........................................................................13

16- Air movement through building & around the building.......................15

16- Factors affecting indoor air flow & Around building............................16

17- Wind shadow ..............................................................................................17

18-Conclusion....................................................................................................18

18-References....................................................................................................19

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INTRODUCTION

Climate means a region with a certain condition of temperature, dryness, wind, light, etc..

It is rather an integration in time of physical states of atmospheric environment, characteristics

of geographical location.

Weather is the momentary state of atmospheric environment at a certain location .

Climate can be called the integration of time of weather condition.

Climate has 4 major elements:-

EARTH – soil

WATER – humidity

FIRE – sun and temperature

AIR – wind

Climatology is all about the study of these elements

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ARCHITECTURAL CLIMATOLOGY

Architecture is all about ART and TECHNOLOGY.

It includes public services, water supply and drainage, air conditioning, ventilation,

lighting, etc.

it is the basic science a designer is concerned about.

It involves majorly on:-

climatic elements how they are behaving on us how to be benefited by these climatic elements

how to protect ourselves from the adverse effect of climatic elements

The major steps in architectural climatology are:-

climatology-study of climatic elements

biology-study of human comfort level with respect to climatology

technology-creating of built environment architecture

-the combination of the above and the final product

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VENTILATION

Ventilation is the movement of air within a building and between the building and the outdoors.

Control of ventilation is most subtle yet important concerns in building design. Ventilation is t

Factors needed to be taken into account in designing the ventilation requirement include:

• the nature of the operations or activities

• the toxicity and rate of generation of hazardous substances

• the degree of expected occupancy

• the design of the premises.

Process

The static pressure of air is the pressure in a free-flowing air stream and is depicted by isobars in

weather maps. Differences in static pressure arise from global and microclimate thermal

phenomena and create the air flow we called wind dynamic pressure is the pressure exerted when

the wind comes into contact with an object such as a hill or a building and it is described by the

following equation:

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where (using SI units):

The impact of wind on a building affects the ventilation and infiltration rates through it

and the associated heat losses or heat gains. Wind speed increases with height and is

lower towards the ground due to frictional drag.

The impact of wind on the building form creates areas of positive pressure on

the windward side of a building and negative pressure on the leeward and sides of the

building. Thus building shape and local wind patterns are crucial in creating the wind

pressures that will drive air flow through its apertures. In practical terms wind pressure

will vary considerably creating complex air flows and turbulence by its interaction with

elements of the natural environment (trees, hills) and urban context (buildings,

structures). Vernacular and traditional buildings in different climatic regions rely heavily

on natural ventilation for maintaining thermal comfort conditions in the enclosed spaces.

Design

Design guidelines are offered in building regulations band other related literature and include a

variety of recommendations on many specific areas such as:

Building location and orientation

Building form and dimensions

Indoor partitions and layout

Window typologies, operation, location, and shapes

Other aperture types (doors, chimneys)

Construction methods and detailing (infiltration)

External elements (walls, screens)

Urban planning conditions

The following design guidelines are selected from the Whole Building Design Guide, a program

of the National Institute of Building Sciences Maximize wind-induced ventilation by sitting the

ridge of a building perpendicular to the summer winds

Widths of naturally ventilated zone should be narrow (max 13.7 m [45 feet])

q = dynamic pressure in Pascal's,

= fluid density in kg/m3 (e.g. density of air),

= fluid velocity in m/s.

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Each room should have two separate supply and exhaust openings. Locate exhaust high

above inlet to maximize stack effect. Orient windows across the room and offset from each

other to maximize mixing within the room while minimizing the obstructions to airflow

within the room.

Window openings should be operable by the occupants

Consider the use of clerestories or vented skylights.

Ventilation rate standards

The ventilation rate, for CII buildings, is normally expressed by the volumetric flow rate of

outside air being introduced to the building. The typical units used are cubic feet per minute

(CFM) or liters per second (L/s). The ventilation rate can also be expressed on a per person or

per unit floor area basis, such as CFM/p or CFM/ft², or as air changes per hour (ACH).

Standards for residential buildings

For residential buildings, which mostly rely on infiltration for meeting their ventilation needs, a

common ventilation rate measure is the air change rate (or air changes per hour): the hourly

ventilation rate divided by the volume of the space (I or ACH; units of 1/h). During the winter,

ACH may range from 0.50 to 0.41 in a tightly insulated house to 1.11 to 1.47 in a loosely

insulated house.

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ASHRAE now recommends ventilation rates dependent upon floor area, as a revision to the 62-

2001 standard, in which the minimum ACH was 0.35, but no less than 15 CFM/person (7.1

L/s/person). As of 2003, the standard has been changed to 3 CFM/100 sq. ft. (15 l/s/100 sq. m.)

plus 7.5 CFM/person (3.5 L/s/person)

Ventilation rate procedure

Ventilation Rate Procedure is rate based on standard and prescribes the rate at which ventilation

air must be delivered to a space and various means to condition that air.[8] Air quality is assessed

(through CO2 measurement) and ventilation rates are mathematically derived using constants.

Indoor Air Quality Procedure uses one or more guidelines for the specification of acceptable

concentrations of certain contaminants in indoor air but does not prescribe ventilation rates or air

treatment methods. This addresses both quantitative and subjective evaluations, and is based on

the Ventilation Rate Procedure. It also accounts for potential contaminants that may have no

measured limits, or for which no limits are not set (such as formaldehyde off gassing from carpet

and furniture).

Categories of ventilation

Mechanical ventilation refers to any system that uses mechanical means, such as a fan, to

introduce outside air to a space. This includes positive pressure ventilation, exhaust

ventilation, and balanced systems that use both supply and exhaust ventilation.

Natural ventilation refers to intentionally designed passive methods of introducing outside

to a space without the use of mechanical systems.

Mixed mode ventilation (or hybrid ventilation) systems use both natural and mechanical

processes.

Infiltration is the uncontrolled flow of air from outdoors to indoors through leaks

(unplanned openings) in a building envelope. When a building design relies on

environmentally driven circumstantial infiltration to maintain indoor air quality, this flow as

been referred to as adventitious ventilation.

Natural ventilation

Natural ventilation is the process of supplying air to and removing air from an indoor space

without using mechanical systems. It refers to the flow of external air to an indoor space as a

result of pressure differences arising from natural forces. There are two types of

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natural ventilation occurring in buildings: wind driven ventilation and buoyancy-driven

ventilation. Wind driven ventilation arises from the different pressures created by wind around a

building or structure, and openings being formed on the perimeter which then permit flow

through the building. Buoyancy-driven ventilation occurs as a result of the directional buoyancy

force that results from temperature differences between the interior and exterior.[1] Since the

internal heat gains which create temperature differences between the interior and exterior are

created by natural processes including the heat from people, and wind effects are variable,

naturally ventilated buildings are sometimes called "breathing buildings".

Function of natural ventilation

Ventilation requirements for different workplaces are varied because of different indoor

activities and building designs. The basic methods for control of airborne contaminants are:

• elimination or control of sources

• fresh air supply of contaminants

• proper air distribution

• air filtration (purification)

• removal of contaminated air

Mechanical systems

A more sophisticated system involving the use of mechanical equipment to circulate the air was

developed in the mid 19th century. A basic system of bellows was put in place to

ventilate Newgate Prison and outlying buildings, by the engineer Stephen Hales in the mid-18th

century. The problem with these early devices was that they required constant human labor to

operate. David Boswell Reid was called to testify before a Parliamentary committee on proposed

architectural designs for the new House of Commons, after the old one burned down in a fire in

1834 In January 1840 Reid was appointed by the committee for the House of Lords dealing with

the construction of the replacement for the Houses of Parliament. The post was in the capacity of

ventilation engineer, in effect; and with its creation there began a long series of quarrels between

Reid and Charles Barry, the architect.

He advocated the installation of a very advanced ventilation system in the new House. His design

had air being drawn into an underground chamber, where it would undergo either heating or

cooling. It would then ascend into the chamber through thousands of small holes drilled into the

floor, and would be extracted through the ceiling by a special ventilation fire within a great stack.

Reid's reputation was made by his work in Westminster. He was commissioned for an air

quality survey in 1837 by the Leeds and Selby Railway in their tunnel. The steam vessels built

for the Niger expedition of 1841 were fitted with ventilation systems based on Reid's

Westminster model. Air was dried, filtered and passed over charcoal. Reid's ventilation method

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was also applied more fully to St. George's Hall, Liverpool, where the architect, Harvey

Lonsdale Elmes, requested that Reid should be involved in ventilation design.[43]Reid considered

this the only building in which his system was completely carried out.

Fans

With the advent of practical steam power, fans could finally be used for ventilation. Reid

installed four steam powered fans in the ceiling of St George's Hospital in Liverpool, so that the

pressure produced by the fans would force the incoming air upward and through vents in the

ceiling. Reid's pioneering work provides the basis for ventilation systems to this day. ] He was

remembered as "Dr. Reid the ventilator" in the twenty-first century in discussions of energy

efficiency, by Lord Wade of Charlton

Problems

In hot, humid climates, unconditioned ventilation air will deliver approximately one pound

of water each day for each cfm of outdoor air per day, annual average. This is a great deal of

moisture, and it can create serious indoor moisture and mold problems.

Ventilation efficiency is determined by design and layout, and is dependent upon placement

and proximity of diffusers and return air outlets. If they are located closely together, supply

air may mix with stale air, decreasing efficiency of the HVAC system, and creating air

quality problems.

System imbalances occur when components of the HVAC system are improperly adjusted or

installed, and can create pressure differences (too much circulating air creating a draft or too

little circulating air creating stagnancy).

Cross-contamination occurs when pressure differences arise, forcing potentially

contaminated air from one zone to an uncontaminated zone. This often involves undesired

odors or VOCs.

Re-entry of exhaust air occurs when exhaust outlets and fresh air intakes are either too close,

or prevailing winds change exhaust patterns, or by infiltration between intake and exhaust air

flow.

Supply of fresh air

• Ventilation is a process by which air is removed from and supplied to premises

simultaneously.

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• To supply fresh air to meet the respiratory needs of the occupants.

• To remove airborne contaminants such as dusts, mists, gases, vapour tobacco smoke,

body odors and bacteria which may pose health hazards or nuisance to the occupants.

• To maintain the temperature and humidity within an acceptable range that is appropriate

to the activities on the premises.

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Stack due to thermal force

• All practical steps have been taken by means of collectors, scrubbers, or process changes

to reduce the contaminant discharge rates to of reducing emission rates.

• Wind blowing past a stack aspirates air or flue gas out of the stack. During wind gusts,

there are like surges in outflow from the stack.

• Stacks must be designed and located for satisfactory cooperation during all wind

conditions.

• Wind flow around stacks creates negative zones, eddies, and vortices in the same manner

as around buildings.

Convective cooling

"Convection is the transfer of heat energy by the movement of matter." There are a few points

in that short statement that aren't quite right but it is adequate for most situations.

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Convection is probably the form of heat transfer that we are most familiar with. We heat our

houses with convection (using 'radiators'), we heat our food in convicting saucepans and fan

ovens and we lose most of our excess body heat through convection. Convection may be

familiar, unfortunately it is also fiendishly complicated.

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Air movement through building & around the building

IN BUILDING DESIGN there are many basic criteria that are of doubtful ancestry.

Nevertheless, they seem to be firmly embedded in the minds of the architectural, engineering,

and construction fraternity. Lack of understanding of air flow around buildings and of wind and

rain conditions seems to be the basis for some of this folklore . For example, many texts stress

the need for locating, buildings and their air inlets and outlets to take advantage of the prevailing

winds. Stack caps and ventilation inlets and outlets are frequently designed for nearly vertical

rain.

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Factors affecting indoor air flow & Around building

(1) window openings,

(2) atria and courtyards,

(3) wing walls,

(4) chimney cowls/exhaust cowls,

(5) wind towers,

(6) wind catchers and

(7) wind floor — air inlet system.

(8) solar chimneys and

(9) underground ventilation ducts

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Wind shadow

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Conclusion

By completing of this assignment I learned about Ventilation system of a building and how

important it is in a building. Ventilation system in a buildings is mainly used to control indoor air

quality by diluting and displacing indoor pollutants; it can also be used for purposes of thermal

comfort or dehumidification when the introduction of outside air will help to achieve desired

indoor psychometric conditions.

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References

https://en.wikipedia.org/wiki/Ventilation_(architecture)

https://en.wikipedia.org/wiki/Ventilation_(architecture)#Standards_for_residential_buildings

https://en.wikipedia.org/wiki/Ventilation_(architecture)#Categories_of_ventilation

https://en.wikipedia.org/wiki/Ventilation_(architecture)#Ventilation_rate_standards

https://en.wikipedia.org/wiki/Ventilation_(architecture)#Ventilation_rate_procedure

https://en.wikipedia.org/wiki/Ventilation_(architecture)#Natural_ventilation

https://en.wikipedia.org/wiki/Ventilation_(architecture)#Mechanical_Ventilation_Strategies

http://www.macdonaldarchitects.com/design/green/green_principles/