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Climatic Considerations and Physiological Objectives of Design

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Climatic Considerations, Physiological Objectives of DesignGood morning, welcome to this new lecture on Climatic Considerations andPhysiological Objectives of Design for the online course on Sustainable Architecture.And, I am your instructor Dr. Avlokita Agarwal, assistant professor at Department ofArchitecture and Planning IIT Roorkee. In the previous lecture, we have seen how toproceed with designing of sustainable buildings and we have seen the fundamentals ofgreen buildings, what are the different components and how do we go about designinggreen buildings or synonymously sustainable buildings.Today, we will be starting with the technical content, where the first step towardsdesigning which we had already identified was to understand the climate of a place, theclimatic context. Today, we will see how to understand how to define the climate of aplace and then through design how do we respond to this climate.(Refer Slide Time: 01:27)So, what is climate responsive design or bio climatic design? We have already seen thedefinitions. We know that these are the designs which employ design strategies that areappropriate for the context of site for the given climatic point of view. It mainly emphasizes on use of technologies that are optimum for energy consumption. We aremainly talking about the passive design strategies which help us reduce the demand andmake the entire structure, the building envelope energy efficient.(Refer Slide Time: 02:04)To start with we have to first identify and understand the climatic zones. Now, this worldclimatic zones are given as per Koeppen’s climatic classification and as per Koeppen’sclimatic classification they are largely divided in 5 climatic zones of which 4 are presentwithin our own country India.So, it is tropical, dry, temperate, cold and polar. Polar climate classification is not thereand we have in India all the 4, though for India as per ECBC we have differentclassification of climatic zones and we largely follow these climatic zones and the designconsiderations accordingly. (Refer Slide Time: 02:43)So, the 5 climatic zones which we take are hot dry which is largely the western partwhich is mainly the desert part and it extends slightly below. Then we have warm humidwhich is largely the coastal region of the country. We have composite which is mainlythe north central region of the country.We have temperate which is present in very limited pockets in the country this region iswhere Bangalore is so, Bangalore qualifies to be falling in the temperate climatic zone.And then we have north which is largely in the northern part of the country. So, these arethe 5 climates which are defined in which our entire country has been divided. (Refer Slide Time: 03:45)Let us look at these climate classifications and how have they been classified to fallunder each of these categories. So, what we are mainly looking at is, we are looking atthe mean temperatures of summers as well as winters and the diurnal variation. Diurnalvariation is the difference between the day and night. The maximum to minimumdifference is the diurnal variation. We are looking at relative humidity which is alsodependent upon precipitation.So, what is the amount of precipitation that the place is receiving impacts how therelative humidity is going to behave, but it is not the only criteria, it is not the onlyreason why relative humidity of a place would vary. It may also vary because of thealtitude, because of the altitude of the terrain. So, very high mountains may also behaving deserts, while they might still be receiving some amount of rain. So, that is whatwe would be looking at and then sky condition which impacts the radiation which isbeing received. (Refer Slide Time: 05:05)So, let us go over each of these climates which are in our country and look at how theseparameters vary for each of these climates. So, first of all we are talking about hot dryclimate. Now, this hot dry climate as we have already seen is found in the western part ofour country which is desert like conditions. So, we are talking about cities like Jaipur,Jaisalmer, we are talking about the region of Kutch falling in hot dry climate. So, largelythe west of Aravalis is what we are seeing as hot dry.Now, in hot dry climate the temperatures summer temperatures are very high. So,summer midday temperatures the highest temperatures are within the range of 40 to 45which is a very high temperature. In summer nights the temperatures fall down and thereis a large diurnal range that we are looking at, but they are still within the range of 20 to30 degree centigrade. So, the diurnal range is very high, we are looking at a diurnal rangeof 15 to 20 degree centigrade.So, in the data in and when the temperatures are around 45 degree, in the night time wemight still have a temperature falling around 25, 27 degree centigrade. So, that is a largediurnal range that, we usually look at in hot dry climates. If you look at winters, themidday temperatures may range from 5 to 25. So, in extreme winters the temperaturesmay fall to very close to 0.So, 5 degrees and in moderate winters they may also go as high up as 25 degreecentigrade. While in winter nights the temperatures may fall, they may come very close to 0. So, they may be varying between 0 to 10 which if you follow the weather news, youwould see that the lowest temperatures in the plains are often in these cities of Churu,Jhunjhunu, Silchar which are predominantly hot dry regions.So, this is what the temperature profile in a typical hot dry climate would look like. Themean relative humidity is very low 25 to 40 percent almost throughout the year. So,throughout the year, we have very low humidity and that is because the precipitation isalso very low the annual precipitation is quite low which is less than 500 mm per yearthat is including the monsoon period.So, which is very low, there is scarcity of water; underground water table is also verylow going to this region. The vegetation is less and overall environment is quite dry. Ifyou look at the sky condition; we see that it is cloudless sky with very high solarradiation which causes a lot of glare. So, there is intense solar radiation and clear sky.So, it makes the condition even worse. So, we have high temperature, low humidity, lowprecipitation and very high radiation; this usually classifies hot dry climate.For the given environmental conditions of the hot dry climate which we have justdiscussed there are certain physiological objectives which can very clearly be identified.So, if you look at this summer temperatures which is very high 40 to 45 degrees. Weautomatically know that the physiological objective of design would be to bring downthe ambient air temperatures, the dry bar temperatures.So, we have to try to reduce this ambient air temperature down to approximately 25 to 30degrees centigrade.centigrade. Now t That is what we have seen when, we were talkingabout thermal comfort in the previous lecture and we were looking at the limits ofthermal comfort, then this temperature needs to be brought down by at the approximately20 degree centigrade. That is the difference that we are looking at.In winters on the other hand we might need to increase this temperature slightly byaround 15 degree centigrade. So, adding heat in winters or reducing. So, both of theseaims can be achieved by reducing the heat transfer during the extreme weathers. So, inextremely hot summers, the heat transfer from outside to inside should be limited andvice versa in winters. And the thermal mass of the building will have a larger role to playin this. The other physiological objective here would be to reduce the amount of directsolar radiation which is received by the building. So, how can we reduce the amount of direct solar radiation becomes a major concern,one of the physiological objectives. Another one, if we can handle it through design iscancan we do something about humidifying the environment. So, the relative humiditywhich is normally low has to be maintained between 40 to 60 percent. So, if we want toincrease the humidity is there a way, is there a design measure through which we canincrease the humidity slightly.(Refer Slide Time: 10:48)Let us look at the warm humid climate, if you look at the warm humid climate thissummer temperatures are between a range of 30 to 35 and summer nights are 25 to 30.Where we can see that the diurnal variation is not very large and the temperatures arealso not very high. They are slightly warm, warmer than the comfortable range, but theyare not extreme as we have seen in case of hot dry climate. In winters also they do notfall too low.So, they are between the comfortable range. So, 25 to 30 and the winter nights would be20 to 25; so, hardly any diurnal variation. Now this is because of their proximity to thewater body which is sea. So, these are all largely the coastal areas which we are talkingabout. So, they remain more or less at the same temperatures, but the problematic thinghere is very high humidity.Now, because of this very high humidity evaporative cooling is not possible. And, we arenot, we cannot look at evaporative cooling as an option, as an alternative. Also the annual precipitation is very- very high, it is more than 1200 mm per year. So, almostthroughout the year there would be a large number of days which would receiveprecipitation. If you look at sky conditions, it is most of the times overcast rangingbetween 40 to 80 percent of cloud cover and that causes extremely unpleasant glare thatalso limits; it also blocks the heat because of the cloud cover.So, this is what the warm humid climate is and at times it becomes very difficult tohandle the one humid climatic conditionscondition much more than the hot dry climaticconditions because of the high humidity. It is easier to humidify than to dehumidify aspace. So, this humidity is a problematic feature here. For the given climatic conditions,if we look at the physiological objective, we might have to slightly reduce thetemperatures by around 5 to 8 degree centigrade not much; not much not more than that,but the prime objective would be to bring down the humidity.So, as to bring the environmental conditions within the comfort range; we would see howwe can do that and if we are looking at the sky conditions, we would still want to shadebecause the temperatures are a little high and this glare, this unpleasant glare is oftenvery tough to handle. So, the objective would be to cut down on the direct solarradiation. Composite climate is a climate which experiences the extremes of both theseasons, both the climates, all three climates rather.(Refer Slide Time: 13:54) So, we have summer, midday high temperatures which range from 32 to 43. So, it isclose to what the hot dry climates experience around 45. So, composite climates will alsohave temperature, summer maximum temperatures similar as hot dry climates and thewinter minimum temperatures very close to what we would see in cold climates. Wewould come to cold climate, but the winter temperature is falling very low.Unlike hot dry climate the humidity is varying, it is in such certain season, it is becomingextremely dry predominantly during the winter seasons and during monsoons it is quitehigh 50 to 95 percent of humidity is also present in composite climate. Along with thatthere is annual precipitation which is varying between 500 to 1300 mm per year,composite climate is a large area if we remember the map of India with climatic zonesshown right in the initial slides of this presentation. So, there is a great variation in theprecipitation which is received in the composite zone.So, during the monsoons the precipitation goes very high. So, composite climate receives3 distinct seasons, summers, monsoons and winters and the conditions vary in each ofthese seasons which is what the problematic causes. And, the sky conditions are againvariable which because it experiences all the 3 seasons. Now, the physiological objectivefor composite climate becomes very difficult. The physiological objectives also varywith season to season in summers it is a hot dry climate, in winters it is a cold climateand in monsoon, during monsoons it is a warm humid climate. So, the physiologicalobjectives for composite climate vary with season to season and they are the same as therespective climates as I have just talked about. So, it is one of the trickiest climates todeal with, when we are talking about composite climate. (Refer Slide Time: 16:06)The temperate or moderate climate is by far the most comfortable climate because thetemperatures range largely within the very close to the comfort range as we can see. So,the summer high temperatures are around 30 to 34 while summer nights are absolutelycomfortable. If we look at winter day temperatures, they also fall within the comfortrange. Now, this comfort range is not as per the ASHRAE 55 as defined by ASHRAE55.This is slightly higher than that, but falls within the comfort range as defined by tropicalsummer index which was developed based upon the responses of Indian subjects. Thewinter night temperatures are also very close to the comfort range, very low diurnalvariation. Now, relative humidity is slightly high on a higher side 60 to 85 percent. Andannual precipitation is higher than 1000 mm per year which is not too high as well.And sky conditions are mainly clear, but in summers it is an overcast sky. Because, ofthis comfortable range of temperatures which we can see in temperate or moderateclimate. The physiological objectives in a moderate climate are not aimed towardsincreasing or decreasing the ambient air temperature. The combination of temperatureand humidity is also such that it remains largely comfortable.So, the physiological objective is to avoid any heat gain or heat loss and maintain theindoors at the same ambient conditions as outdoors for large part of the year, almostthroughout the year; except for few days in the year which are extremely hot or which are extremely hot only that. So, the intent is the physiological objective during some partof the year is to cut down on this direct solar radiation and to reduce the ambient airtemperature indoors.(Refer Slide Time: 18:23)The cold climate is predominantly cold and the summer midday high temperatures fallwithin the comfortable range while the summer night temperatures may also get cold. So,we are looking at around 4 to 11 degrees centigrade which is cold. So, summer nightsmay also become extremely cold and that results in a very high diurnal variation. We areall looking at winter midday high temperatures which may be sub 0 which may be lessthan 0 and we are looking at winter night temperatures which are further low.So, we are looking at an extremely cold climatic conditions, temperature conditions hereand the relative humidity is extremely low. So, these are two types of cold climates weare looking at; we are looking at cold dry and we are looking at cold humid climates. So,there are certain parts of the country. For example, the Leh Ladakh area which is colddry, while if we look at the northeast; if we look at the Arunachal Pradesh or Assam side.So, that is predominantly cold humid. So, a lot of precipitation is received in that area,but it still remains very cold.So, these are two types of climates within cold that we are looking at, when we aretalking about cold climate in our country. So, we have annual precipitation for cold dry,it is very low less than 200 mm per year which is the same as the hot dry. So, hot dry will have same precipitation and humidity while the temperatures go very high and incoldcold, they go very low, in cold humid the annual precipitation is moderate whicharound 1000 mm per year is.So, and the sky conditions are for dry, it is usually a clear sky while for the cold humid itis usually an overcast sky. Now, if you look at the physiological objectives for coldclimate, we can very clearly see that because the temperatures are going so low; theintent is the objective is to bring in a lot of heat. So, increasing the solar radiationexposure, the exposure of the building envelope the solar radiation and bringing in a lotof direct heat, direct sunlight is what the physiological objective of cold climate is.We have to increase the ambient air temperature of the indoors. Now, how do we dothat? We have understood, what a hot dry climate is or what a cold climate is each one ofthese and we have also reasonably understood the climatic conditions. Now, how do weachieve thermal comfort inside the building? So, a lot of research has been carried out onthis and there are a variety of tools which are available to us.One such tool which we have looked at yesterday in the previous lecture was or that ofpsychometric chart. There we would plot the dry bulb temperature, wet bulb temperature,humidity all together and we would see where we are as far as the comfort, thermalcomfort is concerned. We would look at an interactive psychometric chart here.(Refer Slide Time: 21:51) This is an interactive psychometric chart and you can find it at the address which isshown here in the address bar. If you look at this psychometric chart, you can loadwhatever file you want to check. So, load by the file, here I have used the weather datafile of Jaipur to just show you an example, here we are looking at the ASHRAE 55model of comfort.So, this comfort zone which we can see here is, showing us the comfort zone where wehave yesterday seen that it is varying from PMV minus 0.5 to PMV plus 0.5 and this isthe comfort zone. So, and these grids actually show the number of hours as distributed onthe psychometric chart. So, this is the total climate, this is the total weather data of Jaipurwhich is shown on the psychometric chart. Now, if I move this point this is the pointwhich I want to understand.(Refer Slide Time: 23:14)So, suppose I am in a point which has a dry bulb temperature of 25.7 degree centigradeand relative humidity of around 50 percent. I know that I am in the comfort range. (Refer Slide Time: 23:31)If I move this point up, if I go beyond comfort zone and if I am on a slightly higher sidenow, I have a dry bulb temperature of 29 degree centigrade and a relative humidity ofaround 75 percent. I know that I am out of comfort zone, but how do I create acomfortable environment.So, this interactive psychometric chart clearly shows me that, if I cool along withdehumidification. I will be able to bring it down within the comfort zone or if I onlydehumidify then alsoalso, I can bring it down to comfort zone. If I want to just cool thenalsoalso, I can bring it down to comfort zone.Now, if you see how much do, I have to dehumidify; we are looking at a relativehumidity of around 80 percent here 70, 75, 76 percent and if I have to bring it to thecomfort zone, I have to dehumidify by around 30 percent. So, I have to bring it down toaround 50 percent to bring it within the comfort zone. On the other hand, if I go furtherhigh. (Refer Slide Time: 24:44)So, the temperature is further increased at that temperature and humidity of around 70percent, we are looking at 65 percent humidity here. Even after you do dehumidificationonly dehumidification, I might not be able to bring it within the comfort zone. Forbringing it within the comfort zone, I will have to look at the cooling plusdehumidification route here.(Refer Slide Time: 25:15)So, depending upon where this point is what is the environmental condition, we maylook at the different strategies which are available to us. Now from psychometric chart, we can only look at the temperature and humidity changes which is what we can playwith. Here it is also showing us the proposed clothing level and it is also showing us themetabolic rate it is assuming. So, it is assuming a clothing level of one flow clo and ametabolic rate which is for a sedentary activity.(Refer Slide Time: 25:55)Now, if we go back to another tool which is taking it forward from psychometric chart,one we have is bio climatic chart. Now, if we look at this bioy climatic chart, it veryclearly definedefines, it very clearly tells us the comfort zone where on this axis, we havethe temperature, dry bulb temperature and relative humidity. This comfort zone is verysimilar to what ASHRAE 55 defines and as per that what we have seen on psychometricchart. Now, if we are above this comfort zone, where the temperature is increased whichis what we were seeing in psychometric chart just now.There are different strategies which can be employed. Here, we are talking about theneed for wind. So, if we are somewhere between this zone, we may be; we may beneeding wind to bring it to the comfortable zone here. If we are somewhere here, we arequite humid here also we would be needing wind. If we look at a zone which is belowthis, where the temperatures are lower than 20 sunshine is needed. So, we need to addradiation further low we go we need more and more of radiation. Here, we need wind,here we need sun which is what so, the need for sun is increasing as we go here. If we know; if we go towards this side where the relative humidity is less, this is wherewe would slightly need more wind and humidification. This is what comes frombioclimatic chart. Another very interesting tool that, we would find to not just know;what is needed from environmental point of view, but also tells us how to do that throughbuilding design, we can use Mahoney’s table. Mahoney’s table, they are a set ofreference tables which are used in architecture and they help us in designing a climateresponsive building.(Refer Slide Time: 28:21)The parameters that we consider here are air temperature. Humidity, precipitation andwind and using these, we compare the comfort conditions and assess the climate. On thebasis of this the indicators are decided and the climate is assessed as humid or arid and aschematic design recommendation is provided. (Refer Slide Time: 28:49)Let us look at these Mahoney’s table; you might have looked at these Mahoney’s tablesometime during your early courses. For assessing any of the climate, we have to enterthe values for the location, longitude, latitude, altitude. Along with that for airtemperature, we need the monthly mean maximum and monthly mean minimum andfrom that we can calculate the range.(Refer Slide Time: 29:18)Let us look at the climatic data of Jaipur. (Refer Slide Time: 29:27)(Refer Slide Time: 29:28) (Refer Slide Time: 29:32)(Refer Slide Time: 29:35)So, if you look at the climatic data of Jaipur, where the average hourly drivertemperature for each month is given. We can find out the maximum temperatures whichfor January is 22.1 and the minimum is say 11 here. We can enter these values. So,monthly mean maximum was 22.1 and 11 here. So, for each month like that, we fill upthese monthly mean maximum and monthly mean minimum.We would know the monthly range which is the difference of these two. So, we wouldhave 11.1 here which is the monthly mean range. We can have the highest temperatures and the lowest temperatures, the highest of all monthly mean maximums. So, it willcome somewhere in May, June, July and monthly mean low. So, the lowest of all themonthly mean minimums which will be here, we will have an average annual meantemperature which will be the average of the averages of each month. And, there will bean average monthly range which will be the average of all the monthly mean rangeswhich we will get here.This is how we will fill up the data for air temperature. The same thing we do for relativehumidity. So, monthly mean maximum and monthly mean minimum for each month.The average and then on the basis of this average that we get here; so, say for Jaipurwhich we were looking at, we have a humidity which is around 100 percent and 20percent. So, we have a monthly humidity of maximum of around 100 percent andminimum of around 20 percent, the average being 60. So, for this 60 average thehumidity group is 50 to 70 which is the humidity group 3.So, we fill up these two tables, this is the key to fill up the humidity group here.AgainAgain, we have this data for rainfall and the total rainfall, the annual total rainfallprevailing wind which is the primary direction and these secondary directions for each ofthese months. That is table 1 for Mahoney’s table. Once, we have done that there is a keyto start with table 2. Now in table 2, we can write the monthly mean maximum as whatwe have in the table 1. And we can write the monthly mean minimum which we have intable 1 again.Once we have that, we can write for the given humidity group. So, suppose and we alsohave the annual mean temperature. So, suppose the annual mean temperature in case ofJaipur comes out to be say, 24.6 degree centigrade. So, I have an annual meantemperature of 24.6 degrees which we will we can calculate if we have the entire yearsdata. So, looking at the annual mean temperature 24.6 which is above 20 degreecentigrade and we have the humidity group which we identified as group 3 here.So, we can look at the day and night comfort range. So, in January the upper limit wouldbe 29, the lower would be 23 for the day and for night it would be 23 and 17 here. So,from this table, we can actually fill up for each of the month. And, whenell we have tocalculate the thermal stress during the day; what we have to see is, if the mean monthlymaximum which is 22.1, if it is we will compare it with the thermal stress of the day. If it is lying between the comfort limits for the day up between the upper and lower. If it ishigher than that then we write H which is hot heat stress, if it is lower than this then wewrite cold. So, here we see that 22.1 is less than 23 so, we write coldSame we do for monthly mean minimum which is 11 and we compare it with this rangeof night temperatures. So, if it lies between these two, it is O if it is higher than 23 whichis the upper limit it is H and if it is lesser than this it is C. So, we see that for a place ofhot dry climate like Jaipur also the January is actually a cold month. Then, we look at theindicators based upon this key. So, this key has to be used to fill up this one.Now, we are looking at the January data, in January we have thermal stress of C we havehumidity group of 3. So, if we look at this so, we have thermal stress during the day as Cand which implies that, we have the indicator as A3. So, we tick the indicator which isgiven here. So, we have; if we have C it automatically comes to A 3. For other monthsuppose, we have H so, we place the groups. So, we have the rainfall, we have thethermal stress during day and night and we have the humidity group, we also have themonthly mean range. Together, we can find out which indicators are applicable.(Refer Slide Time: 35:34)Once we have done that, we move on and we total up. How many H 1s are there, howmany H 2s are there, H 3 and A 1, A 2 and A 3 and like that we will have these totalnumber of indicators. Once, we have those indicators, we can go about finding out the strategy. So, these are given suppose so, it can be very conveniently read suppose, wehave A1, 3 indicators are there; in case we have 3 indicators, we are looking at this.So, if A 1 is 3 0 or 1, we are looking at large openings of around 40 to 80 percent. This iswhat is the proposed strategy, we are also looking at 0 to 2 for A 1 light walls short timelag is the strategy for walls. So, like that for each one this is I have just filled up thesenumbers, but you would get proper numbers, if you properly fill up the Mahoney’s table.

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