MICRO VENTILATION in Buildings

Post 588 by Gautam Shah

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Micro ventilation is a very important passive method of adjusting heat and moisture for Hot-arid and Hot-humid climates. It is based on three factors: Air movements due to the differing pressures outside the building, like windward and wind-off sides. Buoyancy forces that results from temperature across the buildings interior and exteriors, and Pattern of circumstantial and designed apertures in the building shell. Micro ventilation relies more on external or macro conditions of the locality, but needs appropriate interior design.

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Micro ventilated Traditional Konkan (Hot-arid) region houses, India Wikipedia image by PP Yoonus

Micro ventilation ensures that AIR enters or leaves a space through cracks, crevices, gaps or apertures, diluting the interior contaminants and adjusting the temperature and moisture. It is one of the easiest and consistent ways of managing comfort in enclosed and semi-open spaces. Micro ventilation systems are of vernacular design and time-tested solutions that have come down from one generation to another.

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Entry and exit of air occur due to Differential Pressures along a point to point paths of air movement. The operative pressure is governed by both, the size and shape of the buildings layout scheme and individual characteristics of the building such as shape, size, height etc. Air movement occurs as a Buoyant Force due to the temperature difference across buildings’ interior and exteriors in general, and across the openings in particular. The air pressure is also affected by temperature of surfaces and surroundings, near the windward and wind-off sides. In a building micro openings are, circumstantial and designed. The micro openings are very much smaller in size in comparison to buildings’ formal openings like doors, windows, gaps etc. Micro openings yet have a characteristic size, shape, passage section, adjunct elements on internal and external faces, and their closeness to the location of need (for ventilation). The circulation or movement of air is affected, by the space profile (section), the task intensive volume and its datum, levels of ventilation (import-export) nodes, the hindrance by elements such as size and shape of external overhangs, the sill depth and its profile shape.

Roof Ventilator

Roof Vents

Micro ventilation operates as outside air has lesser moisture (except during actual raining conditions) then indoor air, so any level of ventilation, dilutes the interior humidity level and adds to the comfort.

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Grass-thatched roof > Wikipedia image by MBAGroup6

Micro openings are circumstantial and designed, as casual parts of the buildings’ structure, components and systems (including openings), or formal or passive elements. But broadly these can be classified by their locations. Movement of air also encourages evaporation and increases cooling in the interior space. In dry arid climates smaller and deep-set openings create a strongly directional air movement allowing dwellers to locate their activities suitably. Deep-set openings also increase absorption of heat in the mass of the built-form or add simple cooling devices such as water wetted grass mats or fountains.

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ROOF RELATED GAPS are such as in the thatched and country tile roofs, loosely laid roofs of slates, stone sheets. Formal devices include vents such as lattices, chutes, hoppers, etc.

GAPS IN UPPER SECTION OF WALLS are such as the unpacked ends of corrugated roofing sheets or terracotta tiles, ends of purlins and trusses when not sealed, and eyelets or oculi like holes in gables.

OTHER GAPS are circumstantial that exist in and around openings such as doors and windows, as loose joinery, leaky fitments, ajar shutters, door bottom space, peepholes, openings without shutters (gaps), latticed constructions such as of woven mats, fabrics, or louvered openings, crack or fissures in building elements, expansion joints, unsealed joints, etc.

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Cadjan House Myanmar > Wikipedia image by Michael Coghlan Adelaide, Australia

Micro ventilation requirements inside a building vary depending on the climate, season of the year, use of the space, tasks, work-schedules, crowding in the space and presence of heat evolving means (hearths, machines, etc.) The ventilation requirements also depend on the amenities used for conducting the tasks.

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Krishnapuram Palace Kerala India > Wikipedia image by Appusviews at ml.wikipedia

In many old buildings the micro ventilation system is almost sufficient for dilution of fouled air. Micro ventilation of the building is further exploited by life style settings attuned to the air flow movement paths, pressure gradients and qualitative variations at different locations and time schedules. Task activities are continually shifted around to match the seasonal and diurnal variations.

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WINDOWS and VENTILATION

Post 280 – by Gautam Shah

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Windows served two main functions for interior spaces: Ventilation and Illumination. To this was added the view out with the advent of glass. The window became part of shop front and it served the purpose of view in.

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For several centuries a window was a minor entity for Illumination of domestic interiors. The door provided enough day time illumination. Domestic finer activities, such as the needle craft were conducted just inside or outside the threshold of the door. In deeper spaces, such as inner rooms, roof holes provided basic illuminance. In early public buildings, illumination was provided through smaller openings covered with parchment or alabaster. The areas of window opening though small, was distributed over a larger surface made available through increased interior heights.

Door as the only opening in the dwelling

In a tropical house admission of light is usually accompanied by heat gain, but the breeze coming through a door balances the interior environment. In tropical climates interiors tend to be darker to reduce the heat gain compared to colder climates where greater illumination is perceived as warmth. Naturally illuminated lit spaces are perceived to be healthier.

Ventilation in extreme climates such as very warm and cold, occurs through the temperature gradient between outside and inside. In hot and humid climates, the temperature gradient is not acute enough to cause natural air movement of a sufficient quantum. The need for large volume air movement is significant for moisture control in hot humid areas.

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Ventilation requirements of an interior space vary depending on the number of occupants, nature of indoor cooking activities, fuels used for indoor heating and cooking, duality of distinct entry and exit points, the structure of the dwelling and scope for micro passive ventilation. To a smaller extent the ventilation needs are governed by the siting of the dwelling, such as the densely populated urban colony. Ventilation also depends on the nature of opening (cracks, crevices, holes), size of opening, number, distribution, location, orientation, and external climatic conditions (snow, rain, windy).

Micro ventilation

Cracks and gaps being unintentional are usually insufficient for heavier needs of ventilation and cooling or heating of spaces such as for toilets, kitchens, production areas and public spaces. Planned openings like windows on external face provide for such needs at the location, elevation, depth and in required quantity (such as a rate of air change -dilution, and the rate of air flow). The effectiveness of windows in achieving desired ventilation depends also on which windows are opened, how far they open, and the nature of shutter fixing.

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Ventilation requirements for a dwelling are regulated by the cooking activity. In hot arid climates cooking is done outside the house, in an attached facility or semi open lean-to shades. Kitchen areas are sited in isolated spaces or corners. Cooking with a centric hearth occurred where it also contributed heat for warming. Moisture dilution is an important factor of ventilation requirements. In hot humid climates water utilities like storage and usage (bathing and washing) are placed in the Chowk like interior courtyards, outside or away from the dwelling. According to cannons of Building design, the Vastu Shastra, place of water is in the North-East side. This orientation provides for exposure to south-west face, the warmest or Sun side in the Northern hemisphere.

Punjab India -Open air – outdoor cooking minimises internal ventilation needs

Ventilation is required to dilute the odours, moisture, carbon dioxide, airborne pollutants such as dust, smoke, volatile organic compounds (VOCs), latent heat from air, objects, etc. and encourage evaporation of body moisture and thereby cause cooling.

Windows provide ventilation, more effectively in rooms with internal doors (that is a door not opening to an exterior face), and especially when the exterior face door is closed for security reasons, such as at night. Movement of air between indoor spaces, and not the outside, is called transfer-air. Transfer-air has very little role in diluting the polluted air.

Windows placed on opposite sides and on same axis are better ventilating devices. The position of window vis a vis the work plane or task is determined whether one wants a draught-breeze over the body and the task, or avoid it. The nature of shutter opening also determines the direction of the internal air movement.

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Windows with shutters opening outward often obstruct the wind path, but double hung sash windows and sliding shutters which open within the frame are better as receptors. Casement window shutters with offset hinges or friction stay which create a small gap on the jamb side help in catching the breeze. Hoppers, awning and jalousie windows direct the breeze due to the angle of opening. The depth of a window and its surround also affects the nature of ventilation. Splayed sides create funnel effect to catch the breeze.

Mumbai Houses -One face for ventilation

Most building codes suggest minimum opening area (including doors, windows, etc.) @4 to 5% of the floor area. But actual ventilation requirements are higher such as during rainy days, moisture content is very high, or when during celebrations and social events lot of people gather in a room. Nominally openings (including doors) @20% of the floor area, are sufficient for the purpose of ventilation, provided some sections of the openings are located within the human height (1.75 mts). Even in unoccupied rooms some ventilation is required to remove fumes and moisture generated by materials, plants and condensation. Minimum volumetric requirements for ventilation are 23 to 25 CMt per person per hour, and 12 to 16 CMt per Kg of fuel burnt. Large sized openings create turbulent air movements, whereas cracks and crevices create a viscous or laminar flow.

Commonly ventilation is measured in terms of entire interior volume of air gets replaced per hour, it is called air changes per hour, ACH, but requirements for air for well being per person are also specified. Minimum 0.35 ACH, but the supplied air must be no less than 15 cfm/person or 7.5 l/s/person. Since 2003, the standards for ventilation have been changed on floor area basis which is from 3 CFM/100 sq. ft. or 15 l/s/100 sq. m. to the 7.5 CFM/person or 3.5 L/s/person. To find the total amount of outside air required, one needs to add 3 cfm/100 sq. ft. or 15 l/s/100 sq. m. to the 7.5 cfm/person or 3.5 l/s/person. Thus, the air change rate requirement will vary by the size of the house and the occupancy.

Ventilation is required for a fire emergency from areas like corridors, stairs, etc. Openings for ventilation are necessary for all climate conditions, but control requirements are very acute in warm and extremely cold climates, due to outward leakage of internal air.

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For adequate ventilation the building must take full advantage of prevailing breezes on the site. This includes consideration of: seasonal and diurnal wind patterns, land contours and other topographical features, shape and form of the building, height of the openings, axial position of the openings, work or task plane, physical state and age of the occupants, etc. Other important conditions are position of the window, the form of the surrounds and projections and design of the window shutter.

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ARCHITECTURAL WINDOWS and the meaning

Post 246 – by Gautam Shah

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Caldarium of the Old Baths at Pompeii

A window in its most primitive form was an unglazed hole in a roof, provisioned mainly for ventilation and illumination. The hole in the roof was ‘windy’ to cause air-change and discomfort. The word for window derives from two separate words ‘vindr = wind‘ and auga = eye, which together literally vindauga‘ mean a ‘wind eye’. It replaced old English eagþyrl, (eye-hole), and eagduru (eye-door). The hole in the roof in its glassed version, was called fenestra (Latin version -in other languages, such as, German Fenster, French fenêtre, Swedish fönster, and English fenester).

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Japanese word for windows, Mado carries similar meaning. Mado consists of two morphemes; ma and do, where the former relates to eye (as well as mi– the root of the verb to see) and the later can mean a place (in sense of place, such as fushi-do (lying or bedroom + place) and kama-do (cauldron or cooking + place). So Mado means a place to see –a window.

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The windows transited from the roof, to upper and then lower sections of the walls, and truly became the auga or eyes, to look out. Doors for many centuries were used to look out, but now windows were an option. There was another divergence in place. Doors were points of entrance, and so placed towards a familiar and negotiable terrain like a known street, a courtyard, a neighbourhood, etc., but windows as an opening, could be placed over a lesser known territory, such as side or back of the building. In a dwelling, a door is absolute necessity for entry, but window for ventilation have been avoided in buildings with loosely tiled or thatched roofs.

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Hagia Sophia Istanbul

Doors need an anthropometric confirmation, but windows remained small apertures. The small size provided security yet a connection to the outside world. Windows had solid plank shutters or heavy tapestry cover, so a closed window was as good as no opening, and an open one, true to its original name, a windy and uncomfortable aperture for many climatic zones. The windy window manifests when there is a chance of cross ventilation or stack effect. Both occurred due to the presence another ventilation system in the room. The door or another window were the cause of former, whereas the later was mainly due to the chimney used for cooking or as fireplace. But in tropical climates, the simultaneity of door and window in space was very desired.

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Windows at lower levels, have been used for strange uses. Romeo preferred a window for surreptitious or secret entry, Adfenestratem or adfenestration, to see Juliet. Some jump out of the window (autocide or suicide or auto-defenester) on not able to do things they would like. Enemies are better defenestrated, thrown out of a window, rather then a door, leaving no doubts of their return. Defenestration is also an act of throwing something out of a window, like garbage and night soil into the backyards, as was a common practice in many medieval cities.

Back yard window to window clothes lines

Windows on familiar territories, such as the front face, tend to be full size. The full size is lintel at head level or more and sill level at belly button height. This size allows reasonable illumination up to 2 to 2.5 meter depth, making the most active work zone. A window seat in a aeroplane, train or bus and worktable near a window are desired places. A window of opportunity will not let anyone jump-out of the window (defenester), but rather persist on trying. Window shopping is compared to a Camel, who can survey every thing but eat (buy) few things. For Window dressing one needs a large glass front and passer-by on a busy street. A launch window is a very narrow or circumstantial opening, only with pre-planning one can push through it.

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Windows provide a sense safety and security to an enclosed space. A person viewing out is able to survey the outside world, but unable to intervene. The windows are elements of frustrations and limitations in jails or palaces. The windows occlude the identity of the person inside, through lattices, structure of the surrounds, curtains, and the comparative darkness of the interiors. Windows frame a view. The masking changes the perception of the view through it. It scale reference helps size objects, and judge their positional depth. Windows frame as a stationary and known object, allows one to note the change or movement occurring in the scene.

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