Stack Ventilation

BUILDING PHYSICS

GUIDED BY- PROF. B.S. GARGADE

STACK VENTILATION

BY- AR. TULIKA GALANI

M.ARCH I YEAR

WHAT IS VENTILATION?

The process of removing or supplying air by natural or mechanical means to and from a space.

Necessity •To create air movement, so as to remove the vitiated air or its replacement by the fresh air.

•To prevent an undue concentration of body odour, fumes, dust and other industrial products.

•To remove products of combustion, and in some cases, to remove body heat and heat liberated by the operation of electrical and mechanical equipment.

•To create healthy living conditions by preventing the undue accumulation of CO2 and moisture and depletion of the oxygen content of the air.

•To prevent flammable concentrations of gas vapour or dust in case of industrial buildings.

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TYPES OF VENTILATION

There are two types of ventilations: Natural ventilation Mechanical ventilation

Natural ventilation Facilitate outside air to inside of a building through

windows, doors, ventilation or other openings. Openings should not be less than 1/20th of floor area.

The rate of ventilation by natural means depends on : Wind effect Stack effect

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NATURAL VENTILATION

• By means of purpose-provided aperture (such as openable windows, ventilators and shafts) and the natural forces of wind and temperature-difference pressures

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STACK VENTILATION

Stack ventilation is where air is driven through the building by vertical pressure differences.

The warm air inside the building is less dense than cooler air outside, and thus will try to escape from openings high up in the building envelope; cooler denser air will enter openings lower down.

The process will continue if the air entering the building is continuously heated, typically by casual or solar gains.

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WHEN TO USE STACK VENTILATION?

Stack ventilation, can operate when no wind pressure is available. A building can be designed to induce its own ventilation by duplicating the temperature stratifications that are the source of wind itself.

The stack effect can only take place when the average temperature in the stack is greater than the outside air.

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WHAT TO REMEMBER WHEN USING STACK VENTILATION?

For an effective stack effect, openings and ducts must be large, to minimize resistance.

The pressure difference within the stack varies with height resulting in diminishing air flows from spaces opening on to the stack, as their height above ground floor increases.

In tall spaces (multi-room height) the temperature of the air may be hotter in the upper zone. For a given average temperature, this means that there is a cooler zone at the bottom, which is good news if this is the only occupied space. However it means that rooms facing the upper zone may experience unwanted heat gains, as well as reduced stack effect due to their smaller stack height. TULIKA GALANI

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SOURCE- SUN WIND & LIGHT BY G.Z. BROWN

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STRATEGIES

•Natural Stack Ventilation Strategies

1)Apart from the earlier mentioned strategies, there are several stack ventilation techniques inherited from vernacular architecture worldwide which are still in use today. Among the most common techniques are the static type openings on top or upper part of the building like ridge, static and dormer vent, chimney flue, jack roof and roofmonitor which most of them deal with the function to ventilate the trapped hot air underneath the roof,thus reduce the internal heat gain

SOURCE- http://www.arpapress.com/

SOUTH FACING ROOFS OPTIMIZE DIRECT GAIN

AT PHOTO-VOLTAIC PANELS

WINDOWS


2)STACK VENTILATION STRATEGIES could be enhanced by the use of atrium, stack devices and ventilation shafts. An atrium is a space with glazed roofs which is usually incorporated in the middle of a deep-plan building for both daylighting and ventilation purposes.

This architectural feature could enhance thestack ventilation performance by increasing high differential pressure through the use of the glazing elements at the upper part. This element could absorb solar gain and increase the air temperature near the outlet area which in turnmakes the stack flow more effective



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3) IN THE COLD CLIMATE OF UNITED KINGDOM, AIR ENTERS THE BUILDING THROUGH THE LARGE LOUVERED WINDOWS AND FLOWS UP THROUGH THE FLOORING BLOCKS, BEFORE EXITS THROUGH THE KILN-VENT.


stack ventilation towers like a stack device is another architectural feature which is usually associated with stack ventilation strategy and effective to drive ventilation in lower floors of the multi-storey building

The De Montfort University, UK


Frederick Lanchester Library, UK

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ventilation shaft is a space within the building framework with the primary function to collect, transport and distribute ventilation air to another space or outdoor. For the stack ventilation purpose, this shaft element can be applied to collect hot and stale air from the occupied spaces before extract it out to the outdoors via more suitable elements like chimney or wind tower.

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ADVANCED STACK VENTILATION STRATEGIES

solar induced ventilation wind-stack driven ventilation

Main building elements which are based on this concept of ventilation are solar chimney, solar roof and double façade, wind towers

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CHIMNEY EFFECT

A solar chimney uses the sun's heat to provide cooling, using the stack effect. Solar heat gain warms a column of air, which then rises, pulling new outside air through the building. They are also called thermal chimneys.

the solar chimney relies upon the solar radiation and heat absorption to induce a bigger pressure difference between the inlet and the outlet of the element to increase the stack effect

The most effective application of this natural law (stack effect) is a "thermal chimney," a solar-exposed enclosure tall enough to generate maximum air flow and massive enough to retain heat and power the system into the evening hours.

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SOLAR CHIMNEYS

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, UK

SOURCE- SUN WIND & LIGHT BY G.Z. BROWN

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Wind tower, windcatcher and turbine ventilator are very helpful to induce vertical air movement, thus enhancing the stack ventilation significantly.


ACTIVE STACK VENTILATION STRATEGY


WHOLE-HOUSE FAN ATTIC EXTRACTOR FAN

Whole-house fan which is a low velocity fan that mounts in the ceiling is used to promote air exchange by drawing air from windows and exhaust from a central high point to the attic and then to outside with the help of air vent.

Extractor fan, enhance stack ventilation in the apartment buildings. By placing the fan at the top of the stack, and could significantly increase the average air velocity within the residential unit by 47%.The strategy succeeded to induce upward air movement.

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Documents

Stack Ventilation