PASSIVE VENTILATION in Buildings

Post 648 -Gautam Shah

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Passive ventilation sustains good quality of air in interior spaces. It works on circulation or movement of air without the use of power utilities. It relies on principals of source management and dilution, rather than any filtration. Passive ventilation is substantially based on the quality of built-form and to a smaller extent on immediate surroundings. It is a very important method of adjusting heat and moisture in Hot-arid and Hot-humid climates. The quality of air is determined by temperature, moisture content, presence and proportion of ‘other’ gases and airborne particulate matter. The quality of air has important bearing on our body. A body may endure or adopt to certain abnormal conditions for a period of time but there may occur side effects. The side effects may be realized in a different form and at a different time.

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Passive ventilation relies, as much on external or macro conditions, as the interior spatial lay. It is based on three factors:

  1. Air movements due to the differing pressures and temperatures and the buoyancy forces that result across a building and its surroundings,
  2. Location of tasks and activities that support or hinder such patterns of air movements, circumstantial and designed apertures in the building shell.
  3. Factors that define the ventilation in a building are, space-profile (section), base levels of inward-outward nodes of ventilation, nature of surroundings and neighbourhood, sill level, depth and its profile-shape, task-intensive operative plane and its volume, and constraints enforced by elements such as size and shape of external overhangs.

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Passive ventilation occurs with Two major operants.

Differential air pressures are formed by wind movements in the immediacy of the building, the pattern and size of the buildings scheme and individual components of the building. Air movement also occur as a buoyancy effect caused by the temperatures of surfaces and surroundings near the wind-ward and wind-off sides. Air pressure difference occurs, across buildings’ interiors and exteriors, across the openings and temperature of surfaces and surroundings, near the windward and wind-off sides. Entry and exit point for air, though continually shift around due to the changes in pressures.

Desert City Oasis Town Ait Ben Haddou Oasis

Temperature differential depends on the direction and inclination of sun, climate, seasons of the year, local massing of the shadows, surface materials, vegetation, water bodies, and presence of heat evolving entities. Dark surfaces and thin body objects warm up very fast and begin to radiate the heat, creating local heat related buoyancy in air.

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Ventilation requirements vary depending on whether one wants to gain or lose heat, add or subtract moisture, dilute or remove ‘other’ gases and airborne particulate matter contaminants. Ventilation needs change depending on, distance of space occupation from the inlet-outlet for air, functional use of space, types of tasks, work-schedules, crowding in the space and presence of heat evolving means (hearths, machines, etc.). One important aspect is the feeling of air movement near-over the body. It depends on several factors such as air velocity, fluctuations in air velocity, temperature of air, and personal factors like overall thermal sensation and activity level. Even for the same person, sensitivity to air movement may change from day to day.

635px-Wall_Decoration_at_Kesava_Temple_in_Somanathapura_retouchedDraughts (Draft) are very low velocity air movements. These are not always perceptible, as they do not cause any sensation of pain or pressure on skin. Draughts are more felt due to air pressure thresholds near cracks and such leakage points in small and enclosed spaces. Draughts, however, help in convective heat exchange, evaporation and dilution of pollutants in air. Draughts cause localized cooling or heating of sensitive organs of our body.

Breeze or low to medium velocity air movements generally affect only local areas. Breeze does not let airborne particulate matter to settle down. Skin sensation can be avoided by appropriate screening and deflection of the breeze. Since breeze causes effective pressure on skin, with very immediate and very perceptible change sensation.

Winds are high air velocity movements of air affecting larger regions. Winds raise particulate matter in the air, cause rapid change in level of humidity and often cause discomfort due to high pressure sensation on the skin.

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In hot and cold both types of climates people often close all the openings to reduce the air movements and thereby control the convective heat gain or loss. Turbulent air velocity is less comfortable than a Laminar air velocity. Turbulent air movement achieves a better mix of air whereas laminar helps in greater displacement of air mass. This is the reason why in hot arid climates small size openings are used to create turbulence or a viscous flow, and in hot humid climates the body level openings of horizontal nature create a laminar flow to displace the humidity.

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Passive ventilation occurs through macro and micro openings. Macro or formal openings (doors, windows, gaps etc.) are designed with a characteristic size, shape, passage section, adjunct elements on internal and external faces, and occur close to the location of need (for ventilation). Micro openings are circumstantial, and are much smaller in size like cracks, crevices, gaps or apertures. Micro openings offer a passive and consistent ways of managing comfort in enclosed and semi-open spaces. These manifest as intentional gaps, unplanned crevices and cracks of structural stresses. Both, macro and micro openings can be broadly be classified by their locations.

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  • Roof level openings are such as in the thatched and country tile roofs, loosely laid roof slates, stone sheets, or intentionally placed micro passive vents such as lattices, chutes, hoppers, etc.
  • Upper section openings in walls are such as the unpacked ends of corrugated sheets or roofing tiles, ends of purlins and truss and eyelets or oculi like holes and lites in gables.
  • Other openings manifest as doors, windows, cut-outs, chowks, in joinery, leaky fitments, ajar shutters, door bottom space, peep-holes, latticed constructions such as of woven mats or fabrics, louvered openings, crack or fissures in building elements, expansion joints, unsealed joints, etc.

Movement of air through openings encourages evaporation and increases cooling in the interior space. In dry arid climates dwellers locate their activities in the strongly directional air movement formed by small and deep-set openings. Deep-set openings also increase absorption of heat in the mass of the structure. Simple passive cooling devices such as water wetted grass mats or fountains help cooling. Outside air has lesser moisture (except during raining conditions) then indoor air, so any level of ventilation, dilutes the interior humidity level and adds to the comfort.

620px-AlfedPalmersmokestacksAir borne particulates arrive from outside sources like heavy vehicular traffic, polluting industry (mines, thermal power plants, mineral grinding plants, in the vicinity, or sand storms, and internal sources like cooking or craft fuels, and processing materials (grinding, spinning-weaving). Outside particulate can be controlled by changing the ventilation gaps to different location or elevation. Filtration screens occupy more then 60% of opening area, and much lesser due to frequent choking. Dynamic screening like water bodies or sprays can be useful, but costly and perhaps beyond the concept of a passive device. Non turbulent wind flow helps in keeping the particulate matter to lower sections.

Moisture control in interior space occurs by dilution, greater air movement and siting management of moisture generating amenities. Isolation of cooking, washing, bathing areas in dwelling is a common practice in hot-humid climates.

Quality of indoor air mainly depends on the external circumstances. The ‘feel-good aspect’ in a tropical climate (hot-arid or hot-humid) zone is not only regulated by the obvious temperature, rates of movement (pressure) and the moisture content, but also by the level of fouling of air. Some experts have claimed that air quality of a room is chiefly determined by its CO2 concentration. In tropical buildings concentration of CO2 and other gases is not a critical factor, as numerous openings and micro gaps remain substantially open. Location of cooking area is a segregated entity or an outdoor activity, and like cold climates no interior fire places.

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CLIMATE and our BODY

Post 618 –by Gautam Shah

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A climate affects our body system very profoundly. The effects are warmth-cold, pressure and moisture, all sensed by the skin. Five types of sensations are involved with the skin such as, Touch-Pressure (mechanic-o receptors), Cold-Warmth feeling (thermo receptors), Pain and Itch. Cold is a consequence of contraction of blood vessels, and warmth is felt due to dilation of blood vessels, both felt by the same receptors.

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Cold Comforter > Wikipedia image ART by Henri de Toulouse-Lautrec (1864-1901)

Our body functions as a thermal equilibrium system. The thermal bearing capacity has upper and lower limits. The pain occurs at the upper limit of 52°C /126°F, and has a lower limit of 3°C/37°F. The optimum or the comfort level temperature depends on the level of acclimatization. In certain acute work conditions like mines, metal smelting plants, textile plants, cold storage, the efficiency or productivity depends on the endurance level and adaptability of the body. A body may endure or adopt to certain abnormal conditions for a period of time, but there may be side effects. The side effects may be realized in a different form and at a different time.

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Day time sleepers > Image on Wikipedia by Julio Rojas + Flickr as Day_Sleepers

Our body, gains heat from the atmosphere, and also dissipates excess heat to it, to maintain thermal equilibrium. The human body maintains itself at an average temperature of 98.4°F / 37°C. There are many minor variations in body temperature, which are considered normal. Body temperature is highest in the evening and lowest in the morning, within a range of 1.5°F / 1°C. Infants have a very imperfect mechanism for regulation of body temperature. A fit of crying may elevate and a cold wash may lower the body temperature. Aged persons have a low metabolism and so maintain a lower body temperature. It takes much longer for an aged person to gain or dissipate body heat. Female body temperature is slightly lower than male.

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Homeostasis temperature regulation > Wikipedia image

The type of food one takes affect the body temperature. High protein foods increase the body temperature. The act of ingestion and food digestion raise the body temperature. Exercise increases the body temperature, because only 25% of muscular energy is converted into mechanical work, rest comes out as body heat. Atmospheric conditions like, atmospheric temperature, humidity and movement of air, affect the efficiency of heat exchange from the body, and so the body temperature.

There are THREE types of heat generating processes in the human body. Conversion of food matter into useful energy is a continuous heat generating process. Muscular activities, like even sedentary work or sleeping, are heat generating processes. Lastly, certain infections and dysfunctions within the body, elevate or lower the body temperature by extra ordinary rate of heat generation, or weakened heat dissipation mechanisms. Of all the energy produced in the body only 20% is utilized, rest 80% is surplus heat.

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Hindu bathing ceremony > Wikipedia image by Balaram Mahalder

Normal skin temperature is between 31° and 34°C. As the air temperature approaches the skin temperature heat loss from the body gradually decreases, vasomotor regulation will increase the body temperature to 34°C to maintain the heat loss, but if air temperature is higher, the convective heat loss may not work.

As long as temperature of the opposite surface or object (sun, fire, radiator) is below skin temperature, the body can lose heat by radiation. But once it reaches the equilibrium occurs, body will rather gain heat by radiation.

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Hot arid climate Cooking > Wikipedia image by User: (WT-shared) Shivya at wts wikivoyage

When the convective process is inoperative and radiation heat gain is positive, the body can maintain the thermal balance by evaporation. Evaporation can occur if air has velocity and appropriate humidity (low). Even in case of very high humidity conditions a high velocity air can remove the humidity.

A person exposed to a constant high rate of sweating and permanent vaso-dilation can have a lot of physical strain with loss of work efficiency.

The body must not only release all the excess heat that is generated from within the body, but all the excess heat as gained from the environment. Heat is lost from the body by radiation (60%), evaporation (25%), by convection and conduction (15%).

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Beach Hammock > Wikipedia image > Photo taken by flickr user ReubenInStt

Heat is lost through radiation, if there is a difference in temperatures of opposing surfaces. Evaporation heat loss is controlled by the level of humidity in the air (dryer the air, faster the evaporation), temperature of the air, body and rate of air movement. Body dissipates heat through evaporation by perspiration, sweat and exhalation of air. Convection occurs when the air in the vicinity of skin becomes hot, expands, decreases in density, and elevates to allow cooler air in its place. Rate of heat convection from body depends on the difference in temperatures (skin & surrounding air) and rate of air movement. Conduction depends on the difference between the body temperature and the contact object.

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Working in very Hot conditions > Wikipedia image ART by Peder Severin Kroyer (1851-1909) from Fra Burnmeister og Wain’s Iron foundry

The body continues to accelerate or decelerate the heat loss till it reaches equilibrium. Heat loss is accelerated by several body functions like perspiration, high transfer of heat to the skin by increased blood circulation (vaso-dilatation). When these prove to be insufficient, sweating occurs. In hot climates the heat loss rate is lower due to unfavourable atmospheric conditions. But by lowering of the body heat generation (lower metabolic and muscular activity), the net amount of heat to be dissipated can be reduced. But this requires some time to take effect. On immediate basis when the heat loss is not balanced with heat gain, the `heat stroke’ occurs. In cold climates the heat loss is higher, so heat balance is achieved by conservation of heat and by appropriate heat gain. Heat production is raised by certain reflex secretions (adrenaline, thyroxine), higher intakes of food (increased metabolic activity) by reflex shivering (muscular exercise) and by sufficient insulative protection. The body may control the heat loss by vaso-constriction (lower blood supply), and depressed sweating.

Many physical, chemical and bacterial agents disturb the heat regulation mechanism and cause fever. These may be due to increased heat production or reduced heat loss, or both.

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Cold-Blood creatures or Reptiles > Wikipedia image Attribution: Postdlf from w

In a reptiles and amphibia heat regulation mechanism is absent. Their body temperature rises or falls with the atmospheric temperature. Hence they are called cold blood animals. In abnormal temperature conditions they regulate the body temperature by suitable habitat. In winter they go deep into burrows or in hibernation (minimize the metabolic heat generation). Mammals and birds are known as hot blood creatures, because the heat regulation mechanism is well developed, and they are able to maintain a level of body temperature.

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Hot blood animals > Wikipedia image derivative work: Mariomassone

Comfort of an occupant in an environment also depends on subjective variables or individual factors:

1 Acclimatization: exposed to new conditions a person shortly (approx. 30 days) acclimatizes own-self.

2 Age and sex of a person: Older persons take much longer to adjust to temperature change, and as a result slightly higher temperature. Women also have slower metabolic rate than men so prefer a little higher temperature.

3 States of health: Activity / heat output in watts

  • Sleeping   70
  • Sitting, typing    130/160
  • Standing, working at a bench   160/190
  • Walking   220/290
  • Digging   440/580
  • Sustained hard work   580/700

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HUMIDITY MANAGEMENT in BUILDINGS

Post 556  by Gautam Shah

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There are few obvious factors that affect the humidity in buildings. The most important ones are, location of the building and season of the year in consideration. Other factors include, ventilation system, heat input in the interior spaces, location of humidity generating sections within a built space, inter-space air exchanges, and the nature-duration-zoning of activities.

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wikipedia image by NepGrower-commonswiki

The humidity management in buildings has two extremes of high and low humid conditions of external environment. The external humidity affects the interior climate of the building by way of air exchange. The air exchange, adds to the humidity content and also dilutes the interior humidity. Adding humidity to space is comparatively easier than subtracting or scrubbing the excess moisture. Low moisture conditions can occur in hot arid areas and occasionally in cold climate zones. High humid conditions are associated with rains, sea coast areas, forested and tropical locations. Within a built space, toilets, kitchens and washing areas are prolific generators of humidity. Internal humidity is high in areas with high occupation such as meeting rooms, gymnasiums, cinema halls, industrial process areas such as quenching, etc. and in spaces with insufficient air-change or ventilation. External humidity is highest during a rain-shower and a little while after that. The same condition begins to occur, soon after, in interior spaces. But the external environment has greater scope of natural dilution of humidity compared to internal spaces.

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Smaller openings in hot arid zone for viscous air flow at Gurna mosque Luxor Egypt by Hasan Fathy

Level of humidity is the amount of vapour held by air at a particular temperature. If there is a rise in temperature, the air expands, and as a result more vapour can be accommodated in the same volume of air. Inversely when temperature drops, the air density increases, and its capacity to hold the vapour decreases. Many people cannot sense the fluctuations of relative humidity in the range of 25% to 60%, except through the side effects on the body over a longer period.

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Human body cannot cope up with rapid rates of moisture removal, as it has limited amounts of water available within it. Low level of humidity can remove even the moisture that helps skin to remain soft and supple. In cold arid climates the body has, neither excessive amounts of heat nor moisture and so even minute perspiration will evaporate readily. In contrast to this in hot and humid climates the perspiration does not evaporate readily, causing a heat buildup within the body. This is coped up in several manners such as shifting out to low humidity zones, being in the dominant air movement sections, reducing the metabolic activity of the body by resting and quality of food and adopting appropriate clothing. Air with high percentage of humidity is comparatively deficient in oxygen and may cause problems to people with TB or asthma.

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Low and High levels of humidity, directly affect health and buildings, and ‘sick buildings’ further affect the well being. For both humidity level extremities, the common solution lies in air exchange management between sections within the building and with the outside. Condensation and its consequence effects can be prevented by improving thermal resistance of buildings shell. Humidity generation can be managed by adding or isolating high humidity sections of the dwelling or processing plants, by including or avoiding water bodies in the surroundings.

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Desert cooler or evaporative cooler Wikipedia image by Billy Hathorn

Low relative humidity can lead to discomfort, shrinkage of building components mainly of wood and static electricity discharges. Dry conditions discourage growth of mould, bacteria, and viruses, but dehydrate the protective mucus linings of the respiratory system.  In hot arid climates, low level of humidity and movement of air cause rapid evaporation. The rate of evaporation governs the perspiration and sweating, the prime mechanisms to dissipate the body heat.

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High level of humidity will not allow adequate evaporation of the perspiration, resulting in the rise of body temperatures, and one has to resort to other methods of heat dissipation. High level humidity allows condensation of water over colder surfaces. Inner faces of exterior walls and window glasses are vulnerable to condensation. Such surfaces, if porous or textured, allow mould growth, encourage corrosion dust mite infestation and mildew in fabrics and furnishings.

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A laminar flow through low level openings for Hot humid climate Wikipedia image by Arayilpdas

Air movements within and around a building shell are very effective for humidity management, in all types of climates. In colder climates inter-room air exchange helps in dilution of humidity without major change in a heat profile of the body. Conversely direct ventilation of toilets, kitchens and such other zones removes humidity from acute areas. In warmer climates high speed air movement -the ‘winds’, help in heat and humidity exchange. Winds have turbulent or laminar air flow properties. A laminar air is more comfortable than turbulent air. The later one creates greater displacement of air mass, but the former one achieves a better mix of air. This is the reason why in hot arid climates small size opening is used to create turbulence or a viscous flow, and in hot humid climates a laminar flow is generated through body level openings to displace the humidity.

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BUILDING CLIMATE

Post 539  by Gautam Shah

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A building is affected by various aspects of the climate, which are, mainly external to it. A building as a shell modulates the climate, and creates an improvised climatic (interior environment) not only within it, but over the vicinity. Modern buildings have systems that consume energy to provide lighting, ventilation, cooling, heating, conveyance, and various types of kinetic power. Operations of such systems affect the environmental conditions of the building and the surroundings. Occupants of the building are also active energy processors, and leave their imprint in the place of inhabitation.

Gangtok Author Thebrowniris

Building level climate is formed by following factors:

            1.         Climate of the region

            2.         Climate at the location

            3.         Building structure or shell

Ideally a building design should begin with the climate of the region and its location related variant. A building shell is formed of many materials and form-compositions. The materials due to their constitution and forms of composition offer a complex but unique set of interactions with the various climatic aspects.

Kerala courtyard with planter Wikipedia image by Author User: Soumyavn

As a design, the tasks are scheduled and located through appropriate orientation, and so are expected to benefit from the climate. Specific activities are spatially designated and timed in the sections of the building for their density of occupancy in terms of humans, facilities and amenities. These activities, however, often stretch beyond their nominally defined space, overrun the schedules, and have varied levels of occupancy. The adequacy of a building for the climate and possible environmental comfort is thus an averaged experience.

Wikipedia image by Author Baycrest (“CC-BY-SA-2.5”)

In dense urban localities the site size, shape and the predefined exposure due to the surroundings, all constrain perfectly oriented planning. The interrelationship between sections and linkages add to the contradictions. From a climate point of view, a building shell behaves like a biological entity, that is in a continuous process of achieving equilibrium. But the permanency of the site size, shape and predefined exposure, limit the climatic adjustments. There are two sets variable factors that require climatic management: the externally, the unpredictability of climate, and internally changing task profiles, related space occupancy, and time scheduling. The variable factors cannot always be managed in the size, shape and form of the building form, however, amenities, and facilities mitigate the situation.

Wikipedia image by Author Ildar Sagdejev (Specious)

At an extreme level, with the use of ‘universal services’ (central air conditioning, auto ventilation, etc.) environmentally consistency is achieved for the entire building shell. In another approach, relocatable amenities and facilities, help time+space shifting of tasks. Designers also use materials and techniques of composition to make energy exchange favourable. The techniques include architectonic features such as parapets, barricades, curbs, chowks, cutouts, ventilators, ducts, chimneys, shafts projections, chhajjas, balconies, galleries, canopies, and textured surfaces. Landscape features like slopes, hills, mounds, gorges, valleys, water bodies, shrubs, plants, shrubs, hedges, groves etc. are used for the same purpose. The success of a climatic design depends on how the active and passive means can hasten, delay, curtail or terminate some of the environmental processes.

Indian Library Calcutta India, Wikipedia image by Author njanam92

Some of the problems that designers face while designing with the climate are:

1 Building is often required to be located in a climate region that is essentially inappropriate for the intended activity. A dehydration plant to be located in tropical rain forest area.

2 A building consists of several sub units (limbs), some of which will have either inferior or superior climatic orientation. Placement of parking on a west side of a building / bedroom on a windward side.

3 Environmental requirements are often so exact or acute that traditional climate modulation techniques like building shape, materials, orientation etc. is inadequate.

4 Activities within a building cannot be located permanently, because there are many hourly, daily and seasonal variations in a climate.

5 An activity though accurately located in a building, may last longer than the affective duration of the particular type of climate in that section.

6 Activities often require specific climate conditions, but whose occurrence is not easily predictable.

7 Some activities cannot be relocated to new areas to suit the hourly or seasonal changes in a climate, because the amenities with which they flourish are fixed.

17th-century qasbah in the Skoura palm grove in Morocco is built with the traditional pisé, also known as pisé de terre, or rammed earth. Flickr image by Maureen (https://www.flickr.com/photos/amerune/)

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UNDERSTANDING SOLAR ENERGY for BUILDING DESIGN – Part-1

Post 536  by Gautam Shah

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SUN > Wikipedia image from NASA by Author NASA/SDO

Sun is a powerful source of energy as a result of its internal fusion reactions. Part of this energy is transmitted to the Earth, through space by electromagnetic radiation. The strength of solar radiation at the outer edge of the Earth’s atmosphere (the solar constant), is 1.37 kW per sqm. The intensity of energy actually available at the Earth’s surface is less than the solar constant. This is due to shielding effect of the Earth’s atmosphere, and also for the absorption and scattering of radiant energy.

Wikipedia image by Author Christian Thiergan

The process, climate starts with the arrival of radiant energy (radiation) from the Sun, to our planet. Energy enters into the precinct of Earth from many sources and in different forms. Earth receives electromagnetic energy from other bodies in space, and it also experiences gravitational energy associated with their masses. However the most significant of all, is the energy received from Sun.

Smog cutting off the Sun in Peking Wikipedia image by Author Berserkerus

During its passage through the space, the solar radiation loses little energy, but on entering the atmosphere it encounters molecules of gases, liquids and solids, Ozone and water vapour. These absorb radiation, but are affected by different sections of the solar spectrum. Ozone absorbs ultraviolet radiation, having a profound effect on the development of life. Water vapour absorbs an infrared sector. Gases and suspended matter disperse the incident solar radiation, into multi-directional radiation, some of which passes back to the space. In the visible spectrum the blue light is scattered to a greater extent than other wave lengths, resulting in predominantly blue sky. Scattering by suspended materials is termed as diffused selection. The amount of scattering that takes place depends on the size of the particles, particle density in the air and the distance radiation travels in the atmospheric layer containing particles. Sahara dust storms can reduce the solar radiation transmission by 30% and causing a fall of 6.0 C.

Earth energy budget diagram Wikipedia image by NASA

Atmosphere absorbs approximately 17 units of the total 100 units of the solar radiation. This small absorbed component (17 units) contributes to an increase in the internal energy store of the atmosphere. Of the remaining 83 parts, roughly 29 units are lost to the space by reflection, of which 6 units are lost by scattering and 23 units are lost by cloud reflection. The other 54 units are transmitted to the Earth’s surface, of which 36 units arrive as direct radiation, and 18 units by diffuse radiation through the scattering.

Wikipedia image by Author neuro + copyright holder of this image, Christopher Down

  • Energy sources and energy stores:                             Energy x 1020 J
  • Total annual receipt of solar energy by the Earth         54385
  • Energy released in Chinese Earth quake in 1976          5006
  • Combustive energy stored in Earth’s coal reserves       1952
  • Combustive energy stored in Earth’s oil reserves            179
  • Combustive energy stored in Earth’s gas reserves          179
  • Annual consumption of energy in USA                                 3
  • Heat flux from Earth’s interior                                               0.027
  • Total radiation from the Moon                                              0.006

Earth receives only 0.002% of the total radiation emitted by the sun, and, yet the Sun is the main energy provider for Earth. The solar radiation consists of, on average 7% ultraviolet (short wavelengths), 50% of visible wave bands, and 43% of infrared (long wavelengths) radiation. The radiation that penetrates the surface, is absorbed and heats up the surface. It evaporates the water, thaws the snow, drives the air currents, and causes a variety of chemical reactions. Earth’s atmosphere, oceans, and plant life are major collectors of solar energy.

solar radiation spectrum for direct light at both the top of the Earth’s atmosphere and at sea level wikipedia image by Author Nick84

The Earth receives varied amounts of solar energy. At macro level this is due to diurnal exposure, solar flares and solar spots, inclination or tilt of the Earth’s axis of movement, and elliptical orbit around the Sun. Regions beyond 23 N and 23 S, are exposed to Sun only for a part of the year.

Wikipedia image by Author Muhammad Mahdi Karim

The upper surface of cloud is a good reflector of solar radiation. The amount of reflection depends on the degree of cloud cover, type and thickness. A dense cloud may reflect 50% whereas a heavy storm cloud may reflect 90% of the radiation. If there is persistent cloud cover, as exists in some equatorial regions, substantial part of the incident solar radiation is reflected back to space. Water surfaces have low reflectivity (4-10℅) and so are very efficient in absorbing. Snow surfaces, on the other hand, have high reflectivity (40-80℅) and are poor in absorption. High-altitude desert regions absorb more solar radiation because of the reduced effect of the atmosphere above them.

….to continue in next part …..

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CLIMATE and BUILT-FORM

Post 465 by Gautam Shah

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Changes that we experience in things around us generally happen because of various effects of the climate. It affects all beings and things in small measures. A climate is the most pervasive, consistently variable and largely indeterminable phenomena. Climate conditions, our comfort and survival. It builds up all our experiences. It provides the dynamism that is Nature.

Weathering Tafoni at Salt Point, Sonoma Coast, California.

Rocks weather, sea beds get silted, salty water evaporates to provide clean water as rain, etc. are manifestations of a climate. A farmer plants seeds, squirrel collects nuts, or a bird builds a nest, all expecting a certain pattern of the climate. All living beings have an inherent capacity to adjust continuously to various levels of climatic conditions. And more often than not, organisms manage to survive even in unpredictable climates. When climatic changes are very sudden, different or very intense in time scale, complete annihilation of live form may occur. But most climatic effects set in over a long period, and new living forms are evolved through such adaptions.

House on River Kwai SE Asia

Climate manifests, with determinate and indeterminate aspects. With determinate aspects, we plan our actions and for indeterminate aspects, we discipline ourselves for unusual eventualities. Climate conditions our living. We, through our instincts and intuitions find ways not only to survive, but carry on all functions in a manner that is easier than ever before. Unlike other living beings, humans have the capacity to think and plan their actions, and, so achieve a greater degree of adaptability for climate.

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Human beings generally become acclimatized to the normal climate of the area where they live and work. They also have some built in resilience for minor variations. Most societies adopt the climate, through physiological changes, material usage techniques, housing patterns, etc.

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Built-form and climate, are inseparable issues. Through a continuous process of selection and elimination societies develop for themselves a lifestyle and this seems almost intuitive or natural for the particular environment. These lifestyles pass on from one generation to another, and consequently problems of climatic adaption do not occur, or are not so severe.

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In stable societies few people move, and fewer house forms are transmitted from their original environment. Migrants usually try to transmit the original house form, to the place of their migration. Today large number of people migrate from one place to another. However young migrants, who have had no opportunity to imbibe the accumulated knowledge of climate adoption from the place of their origin, find it difficult to establish in an alien situation.

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Builders, Architects or Interior Designers face the problems of climates at many different levels: These are:

1 Comfort,

2 Adaptability,

3 Setting a Life-style (food, clothes, time schedules, tasks handling, etc.),

4 Designing – creating – acquiring built-forms, architectonic elements – interior amenities.

Extreme hot-arid climate of Punjab India

Comfort: Over a period of time our needs and perceptions for comfort change. For example. People age, Social and Economic conditions change Preferences and means of life styles get recast. Technological innovations offer new options.

Adaptability: Problems of climatic adaptability are not acute, for static populations, but arise for migrants. Short term migrants are self motivated, or forced through political or calamity conditions. Long term shifting occurs due to shortage of local resources or major environmental changes. Adaptability of built-form also arises when mixed lot population (caste, religion, cultures) are allotted ‘standard design dwellings’. The new residents find that new house patterns and building materials are not conducive to continue their habitual climate-tested life styles. Similarly certain housing patterns, which were possible in old type of housing colonies, may not be physically or economically viable in the new housing setup.

Image-w-cred-cap_-1200w_-Proenneke-Cabin-page_-Proenneke-in-doorway_2

Setting a Lifestyle (food, clothes, time schedules, tasks handling, etc.). Migrants have many acute problems that require immediate attention, and acquisition of a new life style to suit the changed built-form and its climatic responses are not of immediate priority. Migrants carry varied images of the built-form from places of their origin. The time-tested life style of their original living quarters was based on certain context like group, communal or neighbourhood living, which may not be available now.

Mae La refugee camp

Designing-creating-acquiring built-forms, architectonic elements-interior amenities. New or changed built-forms are required when there are major changes in the family profile, such as division of families divide, addition to families due to marriage, birth etc., death and migration of some members. The new members (parents, newly wedded couples etc.), either have very rigid concepts or may not have imbibed the traditional values that help a natural climatic adaption. Separating members have strong aspirations for a different life style (perceived from other sources), so disregard instinctive or natural climatic adaption processes. New members also have greater resources and better knowledge about how manage climatic related issues through modern devices.

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TEMPERATURE MANAGEMENT by HUMAN BODY

TEMPERATURE MANAGEMENT by HUMAN BODY

Post 382 ⇒   by Gautam Shah 

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Understanding the human body temperature management is very important for Interior Designers. It tells how space and human body interact and in the immediate term regulate the comfort and productivity. The persistent equation between the space and human body also decides the well being of a person.

Climate affects our body system very profoundly. The climatic effects are primarily sensed by the skin. Five types of sensations are involved with the skin: The Touch-Pressure (mechanic-o receptors), Cold-Warmth feeling (thermo receptors), Pain and Itch. Cold is a consequence of contraction of blood vessels and warmth is felt due to dilation of blood vessels; both are felt by the same receptors.

amphibians have poor or no temperature control mechanisms

Our body functions as a thermo equilibrium system. It continues to strive a state of balance, by many different body mechanisms and spatial-environmental interventions. In the shorter period human body may endure or adopt to certain abnormal conditions. Frequent such shocks cause side effects which may be realized in a different form and at a different time. The Optimum or Comfort level temperature depends on the level of acclimatization.

Snow Monkeys Nagano Japan

The thermal bearing capacity has upper and lower limits. The pain occurs at the upper limit of 52° C /126° F, and has a lower limit of 3° C / 37° F. In certain acute work conditions like mines, metal smelting plants, cotton spinning-weaving plants, cold storage, the efficiency or productivity depends on the endurance level, adaptability and duration of exposure of the body.

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Human body generates heat through basic three processes.

  1. Conversion of food matter into useful energy is a continuous heat generating process.
  2. Muscular activities like even sedentary work or sleeping, are heat generating processes.
  3. Certain infections and dysfunctions within the body, elevate or lower the body temperature by extra ordinary rate of heat generation, or weakened heat- dissipation, mechanism.

Human body utilizes only 20 % of all energy being generated by the nominal body processes, and the rest 80 % is surplus heat. The body however gains or loses heat with environmental interactions. All the surplus heat generated within the body and the excess heat gained from the environment must be adequately managed.

Human body gains heat from the atmosphere, and also dissipate excess heat to it, to maintain thermo equilibrium. Heat loss is accelerated by several body functions like perspiration, high transfer of heat to the skin by increased blood circulation (vaso-dilatation). When these prove to be insufficient, sweating occurs. In hot climates the heat loss rate is lower due to unfavourable atmospheric conditions.

Body can manage to lower the heat by lowering the metabolic and by reducing the muscular activity. But both of these require some time to take effect. On immediate basis when the heat loss is not balanced with heat gain, the `heat stroke‘ occurs. In cold climates the heat loss is higher, so heat balance is achieved by conservation of heat and by appropriate heat gain. Heat production is raised by certain reflex secretions (adrenaline, thyroxine), higher intakes of food (increased metabolic activity). Reflex shivering (muscular exercise) and with sufficient insulative protection the heat loss can be controlled. The body may control the heat loss by vaso-constriction (lower blood supply) and depressed sweating. A person exposed to a constant high rate of sweating and permanent vaso-dilation can have lots of physical strain with loss of work efficiency.

High heat environment -long term exposure

The human body maintains an average temperature of 98.4° F / 37° C (ranges between 31° and 34°C). There are many minor variations in body temperature, which are considered normal. Body temperature is lowest in the morning, and highest in the evening, within a range of 1.5° F / 1° C. Infants have a very imperfect mechanism for regulation of body temperature. A fit of crying may elevate and a cold wash may lower the body temperature. Aged persons have a low metabolism and so maintain a lower body temperature. It takes much longer for an aged person to gain or dissipate body heat. Female body temperature is slightly lower than Male.

The type food one takes affect the body temperature. High protein foods increase the body temperature. The act of ingestion and food digestion, both raise the body temperature. Exercise increases the body temperature, because only 25 % of muscular energy is converted into mechanical work, rest comes out as body heat. Many physical, chemical and bacterial agents disturb the heat regulation mechanism and cause fever. These may be due to increased heat production or reduced heat loss, or both.

Colder climate Bed paraphernalia

In reptiles and amphibians a heat regulation mechanism is absent. Their body temperature rises or falls with the atmospheric temperature. Hence they are called cold-blooded animals. In abnormal temperature conditions they regulate the body temperature by suitable habitat. In winter they go deep into burrows or in hibernation (minimize the metabolic heat generation). Mammals and birds are known as hot blooded creatures, because the heat regulation mechanism is well developed, and they are able to maintain a level of body temperature.

Warm climate dwelling

Our life styles reflect culture of the place, which in turn is our response to the environment. The heat management of our body is effected by the type of food, frequency of intake, volume, proportion of liquids, the rest (siesta) periods, the daily work-rest cycles, clothing, form of our habitat, types of furniture and furnishings.

Very warm exposure

Heat management occurs through Four routes:

1 Radiation: Radiation mainly occurs when there is a difference in temperature on opposing surfaces. As long as temperature of the opposite surface or object (sun, fire, radiators) is below skin temperature, the body can lose heat by radiation. But once it reaches equilibrium occurs, body will rather gain heat by radiation.

2 Evaporation is controlled by the level of humidity in the air. Level of humidity is in turn affected by temperature of the air and air movement. It is also depends on the existing proportion of humidity. Body dissipates heat through evaporation by perspiration, sweat and exhalation of air. Dryer air encourages faster evaporation. Evaporation can occur if air has velocity and appropriate humidity (low). Even in case of very high humidity conditions a high velocity air can remove the humidity.

3 Convection occurs when the air in the vicinity of skin becomes hot, expands, decreases in density, and elevates to allow cooler air in its place. The rate of heat convection from body depends on the difference in temperatures (skin & surrounding air) and rate of air movement. When the convective process is inoperative and radiation heat gain is positive, the body can maintain the thermal balance by evaporation.

4 Conduction depends on the difference between the body temperature, duration and extent of the contact.

Average heat exchange between Human body and Environment are of following order.

  • Radiation (60 %),
  • Evaporation (25 %),
  • Convection and Conduction (15 %).
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