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Sustainable ArchitectureProf. Avlokita AgrawalDepartment of Architecture and PlanningIndian Institute of Technology, RoorkeeLecture - 36Energy Efficiency - IGood morning. Welcome to this new week of lectures of this ongoing online course onSustainable Architecture and in this week we will be talking about Energy Efficiency as partof the sustainable buildings. Now energy has become so important in our life and almost allthe functions all the activities in our day to day life are dependent upon availability of energy,we cannot think of our lives going ahead with our lives without energy even for a couple ofhours and we become almost paralyzed, our transportation systems, our communicationsystems, our food production, our life in general everything depends upon energy and itsavailability.And if we look at the global trends, this dependence on energy is increasing. Our lifestyles arechanging in such a manner that we are becoming more and more dependent upon this energyand that is why the entire world is discussing about how to reduce the consumption of thisenergy in various heads wherever it goes. We are talking about architecture, we are talkingabout buildings here and we are also talking about how we can conserve, how we can saveenergy, how we can make our buildings more and more energy efficient in today’s times andwhy at all are we talking about energy.Let us look at these energy consumption trends in buildings. If we look at the energy scenarioof the world we can see that the per capita consumption of energy.(Refer Slide Time: 02:17)If we are looking at in kilo Watt hour per capita the developed nations have very high percapita numbers and our country has very low per capita energy usage, but if we look at theoverall numbers the population and the absolute numbers, we are quite high simply becausewe have a huge population. And if we multiply this kilo Watt hour per capita by ourpopulation, we would see that we are quite high up there when overall energy consumption isconcerned. (Refer Slide Time: 02:57)If we look at this energy scenario of the world since most of the development in nationswhether they are developed nations, developing nations or underdeveloped nations is directlylinked to the energy available in a country. So, every nation pays, focuses their attentiontowards creation of new energy sources or towards conservation of energy when simultaneousdevelopment has to happen.So, large percentage share of GDP is actually going towards the energy resources, creation ofenergy resources. If we look at the energy scenario electricity scenario in India and we look athow and where this electricity is going(Refer Slide Time: 03:51)We can see that a large part of this energy is actually being consumed by industry which isaround 38 percent, the rest of it is largely going towards domestic, commercial, infrastructurewhich is public lighting, transportation and again infrastructure here.Also a substantial part is going towards agriculture which is towards food production, but ifyou look at this infrastructure public works, public water works and sewage pumping, publiclighting, domestic and commercial all of it together comes out to be around 35 percent, that isone third of the total electricity which is consumed in our country goes towards thesefunctions which are directly related to the buildings and built environment. So, either building or our roads or our infrastructure or infrastructure which is required tosupport the buildings. So, one third of this total energy is being consumed in buildings andbuilt environment which is a huge number.And this number overall consumption varies from state to state in some states for example,Punjab large percentage of electricity is actually going towards the agricultural activity, whilein a state like Delhi which is an urban state and a very dense state, large portion of this energyis actually going towards the built environment domestic, commercial and also industrybecause there are a lot of industries being set up here. So, there is a variation in the state wiseper capita electricity consumption.(Refer Slide Time: 05:44)However, if we look at the overall scenario of energy in our country we see that our primaryenergy demand is going to increase, we are anyways, we have a huge energy demand becausewe have a huge population. So, even though the per capita consumption is less the overallconsumption of energy of the world we still have a considerably high amount despite this percapita low energy consumption we still have power deficit, we have energy deficit.So, we have an energy deficit of around 1 percent and peak power deficit of around 16.5percent which is a huge percentage. So, we still have that peak power deficit and that is why alot of our capital investment is going towards creating the supply, creating new sources ofenergy and gradually the focus is shifting from non renewable energy sources to renewableenergy sources like solar, hydro, wind.So, we are gradually shifting our focus to renewable energy sources supply, but on the wholethere has been a huge investment towards the supply creation of energy. So, currently there isapproximately three 29 giga Watts of installed capacity in India and the projected capacity in20 30 has been proposed to be has been estimated to be 800000 mega Watts, which impliesthat for the next 20 years we will have to add a capacity of around 600 mega Watt each week,which is a huge capital investment. And we need that energy if we want to sustain our GDP.We cannot sustain the same growth rate if we have less amount of energy available becauseour industries need energy, our service industry need needs energy, our agriculturalagriculture requires energy. So, the government already is investing a lot towards the supplyside of the energy creating more and more supply of energy; however, that requires hugecapital investment, it requires policy planning, it requires a long term planning from thegovernment side from the top, the other side of it where we are talking about the demandmanagement.So, on one hand yes we are supplying, but on the other hand we have to manage the demandand as we have seen that around 35 percent of this energy is going to be consumed or is beingconsumed in buildings and built environment. We can actually reduce or keep it constant thedemand towards the buildings and built environment. (Refer Slide Time: 09:05)And as per the estimate, as per a study done by USAID ECO-III an estimate of the growth ofcommercial buildings was made. It was forecasted and it was estimated that the currentbuilding stock of commercial buildings is only one third of what it will be in 2030, whichimplies that around 65 percent of building stock is yet to be constructed and besides this theenergy consumption because of installation of air conditioners is going to go up.So, the percentage of electricity, the amount of energy which is currently consumed towardscommercial buildings is going to rise substantially. So, even while we may be adding moreand more of energy resources in our country we will still be facing a deficit if the commercialbuildings continue to grow like this without taking care of the demand side. And we look atsome of these buildings in different parts of our country, they look very similar.(Refer Slide Time: 10:23)So, if I remove these names here if I do not talk about these buildings then more or less lookthe same. This is the kind of commercial buildings which are coming up in India. So, they areextremely energy intensive, they consume a lot of energy not by virtue of the design.We are not even talking about the design some of these buildings may be highly efficient,they might be using the best of the materials, but just by virtue of the functions that arehoused within them these buildings are highly energy intensive, however we can still reduceor contain the amount of energy which is being consumed in these commercial buildings.Now, if we look at the concept of energy efficiency. It is a very simple concept if we haveseen how the energy is produced.(Refer Slide Time: 11:25)So, if around 100 units of primary fuel has been supplied, through the process of electricitygeneration and transmission and distribution finally, when the energy reaches our householdor commercial buildings, whatever buildings.Out of the 100 units of the primary energy only 24 units are supplied, which implies that if wesave 1 unit here at the end user end around 4.2 units will be saved at the power plant end andhere we are not even looking at what goes behind this, Where is this fuel coming from? So,still around 65 percent of the energy in our country is produced from thermal power plantsand the coal for these thermal power plants is sourced largely from far off countries likeAustralia Indonesia.So, even before this we are taking this 100 unit of primary fuel into account, a lot of energyhas already been spent to bring energy to bring the primary fuel to our power plants, powergeneration plants. So, if we calculated further back, probably 1 unit of energy saved at the enduser end will probably become around 10 units of energy saved at the power plant it is a hugenumber.So, while we are talking about adding a lot of energy sources. We should ideally,simultaneously be talking about energy conservation and energy efficiency at the demandside, where for each unit saved we are talking about at least 5 units saved at the power plantend. Hence a very simple proposition and also the investment which is required to manage thedemand side is much lesser than to add more supply to the supply side. It is a low hangingfruit it can be done right away, right now and it does not require a long term planning.It is a short term plan which is required and we can start doing it immediately. That is why wetalk about buildings and conservation of energy at the building level itself. If you look at thesebuildings and we look at the lifecycle cost of a building.(Refer Slide Time: 14:08)We can see that around 75 percent of the lifecycle cost of the building is during the operationand maintenance phase and of this operations and maintenance phase a large part of the costis actually the cost of energy. Besides energy there are other resources which also inflow forexample, water is there, some material is also there. But large part of the cost which goestowards this operation and maintenance is the energy cost.(Refer Slide Time: 14:47)And hence we talk about conserving energy, making our buildings more and more energyefficient. (Refer Slide Time: 14:56)So, I have been using this energy efficiency and energy conservation quite interchangeablythroughout my discussion so far. So, we use, I use energy conservation sometime, I useenergy efficiency both are the means for demand side reduction of energy use; however, theyare not exactly the same things. They are two very similar, but distinct terms and processes.So, when we talk about energy conservation. We are talking about any behavior or a processthat results in the use of less energy. So, for example, turning the lights off when leaving theroom or for example, making more and more of your spaces as naturally ventilated and not airconditioning them at all is an energy conservation practice.While when we talk about energy efficiency it is the use of technology that requires lessenergy to perform the same function. For example, in a room, any room if we have to provide400 lux or 300 lux of artificial lighting, after we have already reduced this demand by addingthe daylight. So, during the light if I have to provide for 300 lux while I have already takeninto account the energy conservation measures. Instead of providing for a CFL or anincandescent lamp, I would actually be using the LED light bulb which will be more energyefficient.So, for the same amount of power output, for the same amount of illuminance I will be usingless amount of electricity and that is what energy efficiency is. So, both energy conservationas well as energy efficiency are needed to reduce the demand for energy in buildings.(Refer Slide Time: 17:08)So, if you talking about energy conservation, we are talking about the design principles, wetalking about how we design our HVAC, how do we design our lighting and electrical units?While when we are talking about energy efficiency we are talking about building un loop. So,what are the thermal, what kind of materials should be used and what should be their thermalproperties, what kind of HVAC systems. So, again we are talking about HVAC system, butbesides a design here we are talking about the efficiencies of this HVAC system.So, maybe we have already reduced the size the tonnage of AC from 500 tons to 300 tons thatis through conservation, adding different types of practices and design strategies, but that 300tonnage of HVAC can also be installed with very high coefficient of performance or veryhigh energy efficiency, same as with selection of lighting fixtures and their controlmechanism the sensor technology and also the electrical power. So, when we are talkingabout the energy demand reduction. We are talking of these two ways simultaneously and notin isolation at all.(Refer Slide Time: 18:25)Now, when we talk about this demand side reduction, we are talking about the fundamentalsof building physics. We should know how the energy is transferred and what are the differentfunctions for which energy is consumed in a building? So, when we look at this energyconsumption pattern in a building there are various functions for which energy is consumed,largely energy in a building is consumed for maintaining thermal comfort for maintainingenvironmental comfort inside the building that is for HVAC Heating Ventilation and Airconditioning.So, our mechanical fans, the air conditioners they consume the maximum amount of energybesides that huge amount of energy is also consumed by lighting fixtures. So, the artificiallighting fixtures which are installed in the buildings, they also consumes substantial amountof energy. So, these two are the major guzzlers of energy besides on these two heads theequipment and tools which are anyways going to be there.And also processes like cooking or in commercial buildings there might be processes like forcomputing, photo copier stationary and several such activities. So, whenever we are talkingabout building energy efficiency and building energy conservation. We are largely focusingon these 2 heads which is for energy consumed, for thermal comfort environmental comfortcreation and for the artificial lighting purpose. Now, when we are talking about the HVAC forthermal comfort creation, we are talking about the heat exchange.So, what happens commonly as a common sense if we have a building which is placed in ahot dry climate, where the outdoor temperatures are quite high it is very hot outside? So, whathappens that a lot of heat is transferred from outside to inside and the temperature indoorsgoes up and we start feeling uncomfortable. So, in order to maintain the comfort cooling hasto be introduced where the heat which is indoors has to be extracted and thrown out.In another season when it is extremely cold and the outdoors are cool the heat transfer takesfrom indoors to outdoors and in order to maintain the comfort we have to heat the indoors. Inall these different scenarios whether it is summers or winters or monsoons or a comfortableperiod the heat exchange is quite critical to reducing the energy consumption in a buildingand heat exchange takes place through the very basic 3 mechanisms and that remains thesame that is the fundamental of building physics.So, there are 3 different modes of heat transfer; one is conduction, convection and the third isradiation. So, when we talking about heat transfer through conduction in buildingsspecifically we are talking about the thermal properties of the materials and the effectivenessof insulation. So, what kind of materials should be selected so that they reduce the heattransfer from indoor to outdoor or outdoor to indoor? And the properties which we have toconsider are the thermal properties of these materials for example, the U value or the R valueof these materials.Next we are talking about the convection. Now, this convection is takes place heat transferthrough convection takes place because of the air movement at this surface and also throughthe fenestration. So, this is how heat transfer is taking place and when we are talking aboutthis heat exchange through convection. We will be talking about the sealing envelope sealingrequirements so as to reduce this convection heat loss through convection.And lastly when we are talking about radiation we are talking about indirect or direct solarradiation and here we will be again talking about the R values of roofs and walls. We will betalking about the S R I value the Albedo values of the materials. So, a couple of theseterminologies that I have used to explain the basic concepts of heat transfer. (Refer Slide Time: 23:34)I will be covering as part of my first lecture and then gradually we will move on to more ofthe compliance approaches and how to select the materials, how to understand the variouscodes related to the energy specification when we are talking about sustainable buildings.So, first property is specific heat all of you who are attending this course are sciencegraduates and you very clearly know what is specific heat is. So, specific heat of a substanceas we clearly understand is the amount of heat which is required to cause a unit temperatureincreases of a unit mass of the substance. Now, what it implies is that higher is the specificheat of the material more will be the amount of heat which it can absorb from either side ofthe building and gradually transfer to the other side. So, if we have a material which has higher specific heat it means that material can store heatfor a longer duration and also more amount of heat can be stored given the volume of thematerial.(Refer Slide Time: 24:57)The next is thermal conductivity, now this thermal conductivity is a property where it relatesit tells us that how much of the heat will be passing through the thickness of the material fromone side to the other side when the difference between the temperature of its one phase to theother phase is 1 unit degree. So, it is expressed in a unit which is Watts per meter per degreeKelvin. So, which is for a unit thickness so for example, 1 meter thickness of a material howmuch heat can be passed from one side to the other if the difference between the two surfacesis 1 degree Kelvin.Now, higher is the thermal conductivity higher is the rate at which heat will be transferredfrom one side to the other side. So, if we look at this stone has a very high conductivity. So,though it also has very high specific heat, it also has a high conductivity which implies that itcan take in more amount of heat, but it will also transfer at a much faster rate.If we look at concrete again high specific heat, but high thermal conductivity, brick also hashigh thermal conductivity, metals have even much higher thermal conductivity we know thatis why most of the materials are good conductors of heat. So, whatever amount is taken fromone surface is almost the entire is passed to the other surface and that is why conductivitythermal conductivity is quite an important property.For example on the other hand a materials such as glass wool has very low conductivitywhich means it makes it a good insulation material, when we talk about conductivity for aunit area of a material irrespective of its thickness then it becomes conductance.(Refer Slide Time: 27:07)So, if we look at its unit it is Watt per meters square per degree Kelvin. So, the amount ofheat which is transferred from 1 unit area of a material of a given thickness to the other sidefor 1 degree temperature change is what conductance is. Conductance is directly dependentupon the thermal conductivity and the thickness of the material.(Refer Slide Time: 27:33)Now, we have the reciprocal values of conductivity and conductance which are called thermalresistivity and thermal resistance. Thermal resistivity is the property of the material to resistthe transfer of heat and it is the reciprocal of the conductivity. So, higher is the resistivitybetter is the insulation property or capacity of the material. Now again resistivity is for a unitthickness of the material for a unit degree change. Thermal resistance is the reciprocal ofconductance and it is the property applicable to the unit area of the material of uniformdensity to resist the transfer of heat.We use R values when we are talking about the insulation properties of the materials wetalked about conductivity and conductance, when we are talking about the hint heat transferproperty of the material. So, if we have to calculate the R value which is the thermalresistance.(Refer Slide Time: 28:43)And if there are multiple layers of these material so, in case instead of this one single materialif we have multiple layers where the thickness is vary from d 1 to d n and their conductivity isalso vary from k 1 to k n, using this formula which is summation of the thickness of thematerial divided by the conductivity of the material and summing it up we get the totalthermal resistance of a material.(Refer Slide Time: 29:22)Now, we have another value which we use as thermal transmittance which is the U value.Now, this is the amount of heat which is passing through a unit area of a given material, ofunit thickness, for unit degree change of temperature from one surface to the other surface.So, the unit is Watt per meter square per Kelvin. So, it has a unit which is similar toconductance, but it takes into account a unit thickness of the material and the unit area.This is a very commonly used property which is what we will quite often come into contactand a lot of our codes talk about the U values of these materials. Now again U value could befor a uniform material which is of uniform density. It could also be for layers of materialswhere we would be talking about a combination of the these materials and the overall thermaltransmittance which is the overall U value for a given assembly. (Refer Slide Time: 30:47)So, assembly U value or the thermal transmittance is the reciprocal of the thermal resistance. (Refer Slide Time: 30:57)If we look at the effect of thickness on the resistance and conductance or transmittance of amaterial, we can clearly see as we reduce the thickness of a material its conductanceincreases. So, instead of a unit material say 1 meter for which the conductivity was 0.036Watt per meter Kelvin, which is also the conductance in this case because the d is 1 thethickness of this material is 1 meter 1 unit.And here the thickness has been reduced. So, the conductance of this material has increasedwhich implies that more amount of heat will be passed if the thickness of the material isreduced keeping all other properties as the same. So, the specific heat remains the same, theconductivity remains the same, but the conductance changes if the thickness is reduced.(Refer Slide Time: 32:03)Couple of other properties, include Albedo, now Albedo is the surface property of a materialwhich is indicative of the absorptive or reflective qualities of the surface of the material. So, itis the quality which implies how much of the heat which is incident on a material is reflectedor absorbed by the material. So, higher is the amount of heat which is reflected higher is theAlbedo of the material.Higher Albedo materials imply they reflect most of the energy which falls on them, while lowAlbedo materials absorb most of the energy which is incident on them. (Refer Slide Time: 32:46)Next we also talk about high SRI external finishes I will not go in detail over this particularproperty here because we have already discussed it in detail when we were discussing aboutthe urban heat island and selection of materials for reducing the urban heat island at the sitelevel.Now, all these properties will be used while selecting the materials for construction ofbuilding envelope or for adding the insulation layers on top of these structural members,structural materials. Here when we are choosing the insulation there are multiple propertieswhich need to be kept in mind.(Refer Slide Time: 33:30)We have already discussed one is the thickness how thick the insulation has to be because wehave seen lesser is the thickness more is the conductance and less will be the resistance, thenits density different materials behave differently.So, some materials have if they have higher density and often higher density materials theytransmit more heat from one side to the other side as compared to the low density materialsporous materials because they have more of cavities often filled with air. Then we also talkedabout the thermal properties, thermal conductivity and thermal resistance or resistivity higheris the thermal resistance better is the insulation material. Another property which is called solar heat gain coefficient and it is the property which isspecific to transparent building materials which can permit transfer of heat from one side heatand light both, but mainly heat from one side to the other side.(Refer Slide Time: 34:41)Now here whenever solar radiation is incident on a material surface from one side part of it isreflected back, part of it is absorbed by the material which is then later reemitted reradiated toboth the sides of the materials depending upon the thickness and depending upon the propertyof the material and some is directly transmitted inside. So, SHGC is the sum total of all that istransferred from outside to the inside or vice versa, so from one side heat gaining side to theheat receiving side.So, the total amount of energy which is percentage of it which is passed from the incidentside and as a percentage of the incident solar radiation to the other side is what solar heat gaincoefficient is higher is the solar heat gain coefficient implies higher is the amount of heatwhich is transferred from the heat gain site where the incident solar radiation is received tothe indoors. Next property is visual light transmittance.(Refer Slide Time: 35:57)This implies what fraction of visible light? So, in SHGC we are talking about the heatcomponent of the solar radiation through visual light transmittance, we are talking about thevisible light fraction of the incident solar radiation which is transmitted through thetransparent material transparent or translucent building material often glazing here.So, this is this varies between 0 to 1, 1 implies 100 percent of the visible light is transmittedthrough the material to the other side. Higher is the VLT implies more will be the amount ofdaylight which will be penetrating indoors and thereby reducing our dependence uponartificial light. So, with this I will stop my lecture here and we will discuss about how all these properties areutilized used in buildings design of energy efficient buildings which is an important propertyof sustainable buildings. So, see you in the next lecture which where we will be discussingabout more on energy conservation and efficiency measures and the practices for sustainablearchitecture, sustainable buildings.Thank you for being with us, see you again.