climate responsive arch

8/10/2019 Climate Responsive Arch

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MULTI LAYER BODY :


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. Total resistance= sum of the resistance of individuallayers.

R b = R 1 + R 2 + R 3. B1/k1 + b 2/K2 + b 3/k3. Conductance ( C b ) = Reciprocal of resistance. C b = 1/R = .


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In addition to the resistance of a body to the flow of

heat , a bod to the flow of heat, a resistance will beoffered by its surface, where a thin layer of air filmseparates the body from the surrounding air..

Measured- surface or film resistance ( 1/f) m 2 deg C/W. F surface or film conductance (W/m 2 deg C). ur ace con uc ance convec ve + ra an

components of heat exchange.


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AIR TO AIR RESISTANCE R : Sum of the bodys resistance and the surface resistance. R a= 1/f 1+ R b + 1/f 0. f-film conductance. i. e function of surface qualities and of the velocity of air

.


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TRANSMITTANCE: U value Reciprocal of this air- to air resistance is the air- to air

transmittance or U value.

U = 1/R a . . Used : Building heat loss and heat gain calculations.


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Partly absorbed and partly reflected. Proportion of these 2 components ( a ) and reflectance ( r).

a + r = 1. . Light colored, smooth and shiny surfaces higher reflectance

i.e white surface r =1, a = 0. Black bod - r = 0 a= 1. Emittance ( e ) available. e = heat =1.

Absorbance = emittance a=e.


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- : SOL AIR TEMPERATURE CONCEPT :For buildingdesign purposes, it is useful to combine the heatingeffect of radiation incident on a building with the effect of

warm air. T = T x I x a/f . Ts- sol air temperature in deg C T0 outside temperature in deg C. I radiation intensity. a- absorbance of the surface. - 2 .

SOLAR GAIN FACTOR:


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Combined effect- reflective surface + thermal insulation. Reduction : Dark, high absorptive surface with good

u y u v v w

less insulation element . Sol-air tem erature- Ts-T0 = Ix a /f0. Heat flow rate q = I x a/f 0 x U ( W/m 2). Solar gain factor a/I = a x U/f

0(non-dimensional.)


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SOLAR GAIN FACTOR : Heat flow rate through theconstruction due to solar radiation ex ressed as afraction of the incident solar radiation.

Constant value for external surface conductance0 = w m eg .

Solar gain factor a x UFor Warm Humid Climate.

0.04 0.8

Hot dry season

(composite)

0.03 0.6


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FUNCTIONS OF


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1. supply of fresh air 2. convective coo ing 3. physiological cooling

SUPPLY OF FRESH AIR


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Type of occupancy, number and activity of the occupants and y t e nature o any process.

Requirements may be stipulated by building regulations and advisory codes in terms of m 3 /h person, or in number of air c anges per our u ese are app ca e o mec an ca installations.

Natural ventilation: Provision of permanent ventilators i.e of open ngs w c may no e c ose may e compu sory.

These may be grilles or air bricks built into a wall or may be incorporated with windows.

T e s ze o t e opena e w n ows may e st pu ate n relation to the floor area or the volume of the room.

CONVECTIVE COOLING


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The exchange of indoor air with res out oor a r can prov e

cooling.

carrying medium.

PROVISION OF VENTILATION:STACK EFFECT


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Ventilation, i.e., both the supply of fresh air and convective cooling, involves the movement of air at a relatively slow rate.

The motive force can be either thermal or

dynamic (wind). The stack effect relies on thermal forces set up by density difference (caused by temperature difference )between the indoor and out door air.

It can occur through an open window; the warmer and lighter indoor air will flow out at the top and the cooler, denser out door air w ow n a e o om.

The principle is same as wind generation .

WIND EFFECT, STACK EFFECT AND


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VENTILATION SHAFT


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The higher the shaft, the larger the cross sectional area and the grea er e empera ure difference; the greater the motive force therefore, the more air will be moved.

The motive force is the stack pressure multiplied by the cross sectional area.

e s ac pressure can e calculated from the equation: Ps= 0.042 x h x t

Where h =hei ht of the stack (m),

t = temperature difference (deg C)

PROVISION FOR AIR MOVEMENT: WIND EFFECTS


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Thermal forces will rarely be sufficient to create appreciable air movements .

The only natural force that can be

relied on is the dynamic effect of w n s.

Negative control wind is too much, is easy, if windows and

. Wind is generated by pressure

differences so an air flow through

pressure difference between the two sides.

Airalthough light has a mass and as it moves, has a momentum, which is the product of its mass and as it moves, has a vectorial

,


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by another force.

When the moving air strikes an obstacle such as building, this will slow down the air flow but the air flow will exert a pressure on

the obstructing surface . ,

the equation; P w = 0.612 x v 2

= 2

= w ,

This slowing down process effects a roughly wedge shaped mass o a r on e w n war s e o e u ng w c n urn


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diverts the rest of the air flow upwards and sideways.

A se aration la er is formed between the sta nant air and the building on the one hand and the laminar air flow on the

other hand . T e aminar air ow itse may e acce erate at t e o stac e

as the area available for the flow is narrowed down by the obstacle .

At the separation layer due to friction the upper surface of the stagnant air is moved forward , thus a turbulence or

.

Due to its momentum, the laminar air flow tends to maintain

i h h f i h b


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a straight path after it has been diverted, therefore it will take some time to return to the ground surface after the obstacle to occupy all the available cross section.

Thus a stagnant mass of air is also formed on the leeward side, but

this is at a reduced ressure. In fact, this is not quite stagnant, a vortex is formed, the movement is li ht and variable and it is often referred to as wind shadow.

AIR FLOW THROUGH


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Air flow patterns is completely predicted on the basis of empirical rules derived from measurements in actual buildings or in wind tunnel studies.

A wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects . The following factors can be isolated which affect the indoor air flow; Orientation

Cross ventilation Position of openings ze o open ngs

Controls of openings

ORIENTATION

Th g t t th i d d


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The greatest pressure on the windward side of a building is generated when the elevation is at ri ht an les to the wind direction, so it seems to be obvious that

the greatest indoor air velocity will be achieved. A wind incidence of 45 would reduce

the pressure by 50%.

us e es gner ascer a n e prevailing wind direction from wind frequency charts of wind roses and mus or en a e s u ng n suc a

way that the largest opening are facing the wind direction.

Building 45 a greater velocity is created along the windward faces,

ere ore e w n s a ow w e much broader the negative pressure


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much broader, the negative pressure will be increased and an increased

. Optimum solar orientation and

optimum orientation for wind do not .

In equatorial regions, a north south orientation would be preferable for

wind is predominantly easterly.

EXTERNAL FEATURES


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Wind shadows created by ,

avoided in positioning the

building on the site and in positioning the openings in the .

The wind velocity gradient is made steeper by an uneven surface, such as scattered buildings, wall fences, trees.

But even with a moderate velocity gradient such as over smooth and o en round a low buildings can never obtain air

velocities similar to a taller one. For this reason the building is

.

Externa eatures o t e u ng tse can strong y n uence

h b ild


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the pressure build up. o

wall at the downwind end or a projecting wing of an L shaped

building can more than double the positive pressure created. A similar funnelling effect can be created by upward

projecting eaves.

CLASSIFICATION OF


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Climatic zones Tropical climates Warm humid climates Warm humid island climate Hot dry desert climate Hot dry maritime desert climate Composite or monsoon climate Tropical upland climate

Warm Humidclimate

Warm HumidIsland

climate

Hot drydesertclimate

Hot d rymaritimedesert

Composite o r Monsoon

climate

TropicalUplandclimate

Ai r


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Ai r Temperature b/w warmb/w warm

ean ax:Mean Min:

-18-24C

-18-24C

-27-32C 24-30C

humid and hothumid and hotdry climatedry climate

-10-13C

Humidity- - -

20-55%(Dry-

Vapor Pressure:

2500-000N/sq.m

1750-2500N/sq.m

750-1500N/sq.m

500-2500N/sq.m

,55-95%(Wet

Period)1300-1600N/sq.m

800-1600N/sq.m

Precipitation

High High Slight andvariable

Very low Intense andprolonged

Variable

AnnualRainfall

2000-5000mm/annum500mm/month

1250-1800mm/annum200-250mm/month

50-155mm/annum

500-1300mm/annum200-250mm in the

1000mm

month.

SkyConditions

Fai rly cloudy Normallyclear

Normallyclear

Little morecloudy

Monsoon: DullDry season:

Clear andpartly

blue color


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Solar Strong and Strong and Direct and Strong Alternates Direct and.

cause painfulsky glare

warm

humid and Hotdry desertclimates.

Winds Strong windsoccur duringRain squalls

HighervelocitiesOccur during

Local whirlwinds areoftencreated

Local,coastal

windscaused

Monsoonwindsare fairlystrong

Winds arevariabledrasticallydeflected

cyclones by unequalheating andcooling ofland and

and steadybring raincloudsand humid

by localtopography.

surfaces..

Vegetation Grows Less Sparse Sparse Sparse Greenquickly.The red orb l

luxuriant.Soil i s oftend i h

Soils dryquicklyf i

The groundand rocks

b

The soil i sdamp duringh i b i

The soil isdamp duringh i b i


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brown laterite soils.Subsoil

dry with afairly lowwater table

after rainand thesubsoil

are brownor red.

the rains but itdries out

uickl .

the rains but itdries out

uicklwater tableis high

water tableis very

low.S ecial Hi h Tro ical Durin Dust and Dust and sand ThunderCharacteristics

humidityacceleratesmould andalgal

cyclones orhurricaneswith windvelocities

certainmonthsdust andsand

sandstormsmay occur.

storms mayoccur.

storms with afair proportionof electricaldischarges air

,rusting androtting.The thunderstorms are

70 m/swhichconstitute aserious

may befrequent.

.may occur.

accompanied byfrequent airto air

seasonalchanges.

discharges.


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TEXT BOOK1. O.H. Koenigsberger, Manual of Tropical housing and building Climatic Design, Orient Longman, Chennai, 1975.

REFERENCE BOOKS. . , , , , .

2. E.Schild & M.Finbow Environmental Physics in construction & its application in Architectural Design , granadar , london, 1981.3. B.Givoni Man, Climate & Architecture, Applied Science, Essex 1982.4. Donald Watson & Kenneth labs Climatic Design Mcgraw hill NewYork 1983.5. A.Konya Design Primer for Hot Climates, Architectural Press, London, 1980.

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