elements of climate.1ppt
TRANSCRIPT
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CLIMATE RESPONSIVE
ARCHITECTURE
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THE ELEMENTS OF CLIMATE
Temperature: data
Humidity: data
Precipitation Climatic information
Temperature:measurement
Driving rain Sky conditions
Solar radiation:measurement
Solar radiation: data
Wind: measurement
Wind : data Special characteristics
Vegetation
Graphic representation
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CLIMATIC INFORMATION
The designer is interested in thoseaspects of climate which affecthuman comfort and the use ofbuildings.
They include averages, changesand extremes of temperature, the
temperature differences betweenday and night, humidity, skyconditions, incoming and outgoingradiation, rainfall and itsdistribution, air movements andspecial features such as tradewinds, thunderstorms, duststorms and hurricanes.
Climatic records as gathered atairports and meterological stationsare not primarily intended for theuse of designers.
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TEMPERATURE MEASUREMENT The temperature of the air is
measured in degree celsiusmost often with mercurythermometer.
Readings taken at specifiedtimes of the day, or if amaximum minimumthermometeris used one
reading daily can give themomentary temperatureaswell as the maximum andminimum temperaturesreached in the past 24 hours.
The dry bulb or true
air temperatureis a
value taken in the
shade, the inside a
louvered wooden box,
known as the
Stevenson screen ata height of 1.20 to 1.80
thermometer being
mounted m above the
ground
Thermographcan be used,which is based on abimetallic thermometerandgives a continuous graphicrecording of temperature
variations.
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TEMPERATURE DATA
Monthly mean temperaturescan be given for each of the 12months.
The averageis taken betweeneach days maximum andminimumand then the averageof the 30 daysaverage isfound.
To give an diurnal variationsthis can be supplemented bymonthly mean maxima andminima.
These will establish themonthly mean range of
temperatures. It will be useful to indicate the
highest and lowesttemperaturesever recorded foreach month, i.e., the monthlyextreme maxima and minima
to establish the monthly meanrange of temperatures. Locations of climate stations with meantemperature data.
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HUMIDITY MEASUREMENT
The humidity of aircan bedescribed as absolute humidityi.e., the amount of moistureactually present in unit mass orunit volume of air, in terms ofgramme per kilogramme.
The relative humidityishowever a much more usefulform of expression, as it givesa direct indicationofevaporation potential.
The amount of moisture the air
can hold depends o n itstemperature.
Relative humidityis the ratio ofthe actual amount of moisturepresent to the amount ofmoisture the air could hold at
the given temperature. RH=AH/SHX100 %
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Humidityis usually measuredwith the wet and dry bulbhygrometer.
This consists of two ordinarymercury thermometers
mounted side by side. The first one measures the air
temperature. The bulb of thesecond one is covered with agauze or wick and is kept wet.
Moisture evaporatinggives a
cooling effect, thus the readingof wet bulb temperature will beless than the dry bulbtemperature.
As in dry air the evaporation isfaster, the cooling is more
pronouncedand the differencebetween the two readingsisgreater in case of 100%RH thetwo readingswill be identical,as there is no evaporation.
Having made the two readingsthe corresponding RH can befound from the psychometricchart.
wet and dry bulb hygrometer
Psychometric chart.
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HUMIDITY DATA
To give an indication of prevailing humidity conditions, it is sufficient
to establish the monthly mean the maximum and monthly mean
minimum relative humidity values for each of the 12 months.
This is only possible where continuous hygrographrecordings are
available. Where these are notavailablereadings are made just before
sunrise,e.g at 6.00 hours (maximum value) and at 15.00
hours(minimum value)
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VAPOUR PRESSURE
Another indication or
expression of atmospherichumIdity is the vapourpressure . i.e the partialpressure of water vaporpresent in the air.
The atmospheric pressureisthe sum of the partial pressureof dry air and partial vapourpressure.
P=Pa+Pv
The air is saturated when thevapour pressure(pv) is equal tothe pressure of the saturatedvapour of the sametemperature(pvs).
Relative humiditycan also beexpressed as the ratio ofactual vapour pressure to thesaturation point vapour
pressure. RH=AH/SHX100=Pv/Pvsx100%
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PRECIPITATION
Precipitation is the collective
term used for rain, snow, hail,dew and frost that is for allforms of water deposited fromthe atmosphere.
It is measured by raingauges,i.e. calibrated receptacles, andexpressed in millimeter per atime unit.
Rain gauge
Th i i f ll f
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The maximum rainfall for any24 hour periodis a usefulguide for the predication offlooding and for the design ofsurface drainage( roofs, pavedareas, gutters and downpipes)
the maximum hourly rainfallintensity should be known.
Values indicating the totalprecipitation for each month of the
year would show the pattern of dry
and wet seasons.
Ever recorded maxima and
minima would give an indication of
the reliability of rains.
Roof drainage
Ground drainage
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DRIVING RAIN
The building designer maywant to know whether intense
rains are associated with
strong winds, in other words
what is the likelihood of driving
rain.
The driving rain index
characterisesagiven location
and express the degree of
exposure.
It is the product of annual
rainfall and annual average
wind velocity.
Actual rain penetrationwill
depend instantaneous rain on
the intensity and the
simultaneous wind velocity.
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SKY CONDITIONS Sky conditions are usually
described in terms of presence
or absence of clouds. On average, two observations
are made per day, when theproportion of sky covered bycloudis expressed as apercentage.Few records exist of
night time sky conditions. It would be useful for the
designer to know the time of dayand frequency of observations.
A single average figuregiving
the sky conditionsfor a typicalday of a given month mayconceal significant differences,e.g. between morning andafternoon conditions, which mayaffect the design of roofs,
overhangs and shading devices.
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SOLAR RADIATION MEASUREMENT
A simple sunshine recorderwillregister the duration ofsunshine, which can beexpressed in number of hoursper day, as an average for
each month. A variety of more
sophisticated instruments(solarimeter, heliometer,actinometer and pyranometer)are used for the quantitative
recording of solar radiation, butreliable and comparable datais few and far between.
Pyranometer
solarimeter
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SOLAR RADIATION DATA
Average daily amounts of solarradiation for each month of theyear would give a fair indication ofclimatic conditions, includingseasonal variations.
This could be supplemented by
the highest and lowest dailytotalsfor each month, to setthe limits of variationswhichcan be expected.for thepurpose of detailed design,hourly totals or rather hourlyaverage intensities must be
known for typical day of eachmonth-or atleast for a typicallyhigh and a typically lowradiation day of the year.
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WIND MEASUREMENT
Wind velocityis measured by acup-type or propeller anemometer,or by a pilot tybe and its directionis measured by a wind vane.
An anemographcan producecontinuous recordingsof wind
velocityand directional changes.
Measurements in urban areas aretaken at a height of between 10 to20m to avoid obstructions.
Velocities near the groundare agood deallower than the free wind
speed.a wind forcescaledeveloped by beaufort in 1806,based on visual observation, isstill in use in spite of its completelyunscientific nature.
Anemometer
Anemograph
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WIND DATA
The designer must try todetermine whether there is aprevailing direction of winds,whether predictable daily orseasonal shifts occurand
whether there is arecognizable pattern of daily orseasonal velocities.
It is also important to note thecalm periodsin each month.allobservatories record the
occurrence of storms,hurricanes, typhoons, ortornadoes.
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SPECIAL CHARACTERISTICS
Most regions experienceconditions which areparticularly unfavourable suchas hail and thunder storms,line or arched squalls,earthquakes,tornadoes,hurricanes and duststorms.
Although such events must berare it is important to extractfrom meteorological data theirfrequency, likely duration andnature.
The designer must classifyrare events into those whichaffect human comfort andthose which may endanger thesafety of buildings and thelives of inhabitants.
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VEGETATION
The picture of climate is
incomplete without some noteson the character andabundance of plant life.
Although generally regardedas a function of climate,vegetation can in its turn
influence the local or siteclimate.
it is an important in the designof out door spaces providingsun shading and protectionfrom glare.
This section of the climaticsurvey may range from a fewnotes about local species ofplant life to a lengthycompendium of the majornative plants and trees- theirshape and colour, also their
preferred orientation andsituation
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