Understanding Building Functions: Safety, Comfort, and Environmental Interaction

so good morning everybody this is lecture one first its is related to functions of the building so what are the functions of buildings as you can see this first thing is it must provide a safe shelter structurally safe all right and desired spatial environment within

the space right for any human activity for example this is a classroom so this is what is called teaching of readings you know teaching of readings so it must have good acoustics so that you can hear must have good visual environments so that you can write right and

of course comfortable from thermal point of view its one of the most important thing right thermal point of view so for that human activity here is teaching teaching of reading right which means teaching learning interaction ok so thats what it is

so building must therefore provide safe and comfortable environment internal environment against existing external and unwanted internal conditions for a given human activity now what is external condition for example high temperature outside lot of humidity relative

humidity high so i must have i must have a comfortable environment against such kind of external perturbation similarly noise outside or noise generated within so it should be comfortable against such a thing but obviously safety is most important and building must

accomplish all this economically we would normally one would be talking about lifecycle cost in this context but anyway cost is not eno[ugh]- you know issue in our approval rate right so first to talk about safety which you have learned through an undergraduate

programs it is safe against all kind of natural forces right safe against natural forces such as gravity load first of all gravity you know like if you have to stand somewhere they your own weight would be there so gravity load small load so many of them are vertical load

wind rain etcetera wind and earthquake they also contribute to horizontal loading into the building impacts and so on right because of human actions load can also be there so if i show it schematically there are many of them are gravity loads most of them are

gravity load and there could be horizontal load as well because of earthquake and wind and it must be safe against all these forces so thats what we are saying so thats the safety and we are not discussing this in this course safety is not already you have so much of

elaborate understanding of the same so we will not discussed this so building interacts with surrounding environment earth thats what we are looking here and you have humidity air motion as you can see noise lightning pollution rain and snowfall precipitation

as we call it sunlight air temperature solar radiation and all that so as you can see these are the arms as you see building is at the center it interacts with all those environmental factor outside so to start with we will discuss this environmental factors how we account

for them how do we quantify them how do we quantify them any measurable item how do we measure them because in technologies science and engineering you know basically technology science based engineering right not empiricity would like to reduce so i would like to model

ah effect of air motion on to the building we are looking at the comfort not the loading part of it right similarly effect of you know temperature outside heat transfer into the building and so on so therefore in order to do that we must quantify them we generally

mathematically generalized physical system models when we talk about mathematical modeling we generalize it basically its a mathematical generalization so thats what we like to do and therefore we must look into each of this one how they we measure them and how do you

quantify them right in physical or terms of maths and physics lets see so comfortable a moment convert it must be comfortable against external temperature relative humidity moisture and gas condensation etcetera right and must be comfortable against man made external and

internal you know external as well as internal red colored so it must be comfortable against man made external and internal agency causing discomfort for example noise besides micro climatic changes are i will tell you what is micro climatic

changes for example you change the you know your activity human activity lot of building they will change the thermal conditions surrounding the building so we will talk about that later on so examples if i say external temperature humidity solar radiation occasional perturbations

such as heavy storm rain gust these are external manmade internal external noise accidental initiation of fire which i am not discussing again in this course generation of wastes odour fumes and gases etcetera so these are manmade thing they can cause discomfort right

ok then desirable internal environment may require provision of adequate visual condition through proper lighting so these are desirable condition and desirable internal also may require reliable proper circulation of human movement and materials you know space this

is an architectural issue again we are not discussing here circulation space comfortable ergonomics even you know space between two rows minimum distance between two rows so we are not talking of this in this class except for in case of auditorium design we

will talk a little bit related to this so thats kind of ah you know interaction what we will have now as i was telling you that we look into the environmental features which we like to quantify and in terms of some measurable items so temperature is one of them first

is the temperature so we are looking at the thermal aspects so thermal environment temperature is one of them now temperature how do you measure we will come to that next one would be relative humidity air motion air velocity speed and directions is an important solar

radiation these are all related to thermal comfort then precipitation or rainfall because ah thats thats what causes relative humidity change significantly and sunshine hours how many hours sunshine is there then sky brightness is related to day lighting

skry sky brightness is related to day lighting so these are the features of environment and based on this kind of features we actually classify climate so climate is you know climate classifying or group the whole globe into several climatic zones and then zones in a

given ah region also we will talk about that a little bit later so these are the features based on we define them lets see how do you measure temperature if you want to measure air temperature is is measured in what is called stevenson screen now do i have a diagram

of this if i dont have i will just draw it for you no problem its like a box its simply like a box you might have seen and it will have louvers right so its a closed box so that direct sunlight doesnt come in wind doesnt affect their air motion there is no air velocity

significant air velocity inside it remains dry there is no rain coming into it protected from the rain ands you measure what you call dry bulb temperature inside so what you measure is a dry bulb for example if it is a thermometer well there are better varieties of measuring

devices ah liquid thermometers are well known mercury thermometers where expansion of market mercury you know because it has got a linear expansion or expansion doesnt vary with the temperature itself rate of expansion so temperature change

volume change per unit temperature will remain constant over a very large range thats why mercurys use some cases alcohols are used then there are other things like ah what we call ah platinum resistance thermometer because resistance has changes with temperature i

am not discussing them you have a you if you i I believe some of you might take a course on lab so in laboratory class they might discuss this thermocouple is very popular what is the thermocouple you have a hot junction and a cold junction and if you put this you know

two dissimilar metal when you connect them together there is a potential difference that would exist or alloys you can understand that you know for example different metal will have different tendency to lose electron so if alloys will have similar sort of things

so if you connect two dissimilar of them momentarily there will be as current flow because there will be a potential difference existing between the two but if one of the end is at high temperature and another another is at lower temperature so there is a potential difference generated

between these two now this potential difference is a function of the difference in temperature between hot and cold junction so since thermocouple works in this principle but then again voltage emf generated part degree centigrade must be constant so every type of thermocouple

will have its own range of measurements for example copper constantan chromel alumel platinum and platinum rhodium thermocouples so these are these are used basically for measuring temperature ah thermistors there are several other measurement devices we are not going

in details into this so the unit is of course degree centigrade is not degree kelvin its kelvin simply kelvin written you know absolute scale of temperature so this is one thing this is all measure of temperature now relative humidity what is

relative humidity ok lets first define relative humidity i think i will come to the algebra part of it later on but i think i have not defined yeah you see the air is nothing but a mixture of let me go back to this and write it here straight away here essentially is

a mixture of nitrogen oxygen carbon dioxide little bit of argon right i think it is a a r argon not ag ag silver so a little bit of argon and obviously moisture vapour right now this is around seventy eight percent as you know twenty one percent or whatever it

is i am not really interested in this but i am interested in this part now it forms a kind of gaseous phase solution so this is the vapour moisture vapour and this moisture vapour has got an importance related to thermal comfort as usual see later on the body would

like to maintain a fixed temperature right you know deep body temperature has to be constant so if outside surrounding atmosphere is warm warm under the deep body temperature it would actually ah you know heat flow to occur from outside to inside but then what you would

like to reject it we will discuss this mechanism sometime later on but one of the mechanism is losing by evaporative cooling so for example in the skin moisture the skin if it evaporates latent heat of evaporation will be taken from the skin itself and it will cool down the

body itself it will cool down so therefore relative humidity or moisture content in the surrounding environment is important because if it is dry it can absorb a lot of moisture if it is already saturated because its a kind of a solution as i said so there is a air

has got a capacity to you know absorb moisture vapour and this is a function of temperature itself higher the temperature it can absorb more moisture vapour so relative humidity is related to that relative humidity is a kind of measure its the capacity

for the surrounding environment to absorb moisture so we talk in terms of you know we talk in terms of relative humidity we talk in terms of moisture content that is if i denote it by phi it will be moisture content g sometime we denote it by g moisture content

we denote by g as we shall be doing in this class divided by g s saturated moisture content at that particular temperature thats how we define so relative humidity we define this now how do you define partial vapour pressure or partial pressure of two gases supposing

i have two gas and i you know individually it occupies a volume v gas one the pressure is p one and second gas which occupies the same volume its pressure is p two right now when i mix them together same mass of the two and mix them together and put in the

same volume the total pressure will be sum total of this one you can understand from basically ah connect theory of gases because pressure is nothing but molecule hitting the boundary of the vessel when i pack them together two gases obviously they will exert more pressure

so partial pressure is the pressure of the gas in a mixture which is the pressure when it occupies the same volume as the mixture itself so p is p one plus p two partial pressure so in case of air partial pressure of air for partial pressure of vapour is a total

pressure right now if i if if relative you know if if the g is more moisture content is higher this will be also higher so i can relate this to partial pressure vapour pressure as we call it to the relative humidity all right let

us see how do you do it let us see how do it so partial pressure will be written like this and we treat them as ideal gases so pa lets say its only the dry air va is equals to the mass of the air there divided by molecular mass of air rt similarly for vaporize i can

write in the same manner and both of them are occupying same volume by definition so g is mass of the vapour divided by mass of the dry air thats how we define the moisture content this will be simply from this one it follows right so g is mass so this divided

by this and therefore it would be this divided pv mv divided by pa ma right v will cancel out from both the sides this will also cancel out because temperatures are same right and this universal gas constant because already we have taken end into account

so this value molecular mass of water is eighteen point zero two and molecular mass of air is twenty eight point nine six now what does it come because nitrogen we know is twenty eight point seven eight multiplied by nitrogen molecular weight of nitrogen because it occupies

seventy eight percent is a ah seventy eight percent is a nitrogen oxygen we know twenty one percent or whatever it is so when we sum them up i get twenty eight point nine six so this therefore pv by p a comes in and pa is nothing but atmospheric pressure minus

vapour pressure so you can see that moisture content is a function of vapour pressure and point six two two so its its actually can be related to the vapour pressure of air right ok now there are some empirical so relative humidity

is g by gs saturated moisture content at saturation for the same temperature so there are some empirical formulae maybe i will solve a problem sometime but there are other ways of finding this out also phi g etcetera its through psychrometric chart i will come back to this sometime later

on this is called a psychrometric chart a psychrometric chart is one where in this direction here you have got dry bulb temperature dvt you know you may not be able to see this very clearly there could be difficulties but my intention is not to show here or read it here

but you might be familiar with it because you can refer to this in sp forty one or any book of the reference that i have given marcus and morris kenneth berger and so on so forth i hv guideline x ray hand book and so on many places you will find it

ah now now this axis is dbt and this from minus ten to i think it is plus sixty so what this range this particular graph is i mean it is there for various ranges some will have up to thirty or whatever it is so this dbt is along this direction this direction is

a moisture content in kg per kg you know absolute moisture content kg per kg now this is the saturation line this is a saturation line this is the saturation line this is the saturation line so if you know dbt if you know moisture content relative humidity lines are you know

relative humidity lines of this saturation line there is ninety eighty etcetera etcetera so these are relative humidity line so you can actually if you know the moisture content relative humidity value we can find it out from there also there is something

called wet bulb temperature how do you measure relative humidity then it will come now this curves can be fitted into an empirical equation as i said and you have vapour pressure is given a saturated vapour pressure minus some constant into atmospheric pressure t minus

tw is called wet bulb temperature i will just define what is called wet bulb temperature and some again as i said empirical formula is given psb and ps at any any any any temperature what is the saturation pressure those are those are values are empirically obtained

maybe i will solve a problem some time that will be clear i will come back to this later on but let me now define what is wet bulb temperature lets see if it is there ok before the mathematics comes in ah wet bulb temperature is supposing

i have got a thermometer i have got a thermometer right something like this supposing i put a wet cotton here its a thermometer that thermometric bulb you know its a thermometric bulb thermoelectric bulb and i put cotton here wet cotton here another case i have just the bulb and no cotton

or anything of that kind right so i will have the unit could be mercury simply so this is dry bulb temperature now where will the supposing i have got relative immunity hundred percent right where will be this height or reading of this thermometer

it will be same because this is wet and nothing can evaporate right but supposing the relative humidity is low then what will happen moisture from here from the bulb which is covered with a wet cotton or jute will evaporate and this will result in depression of this mercury

here which we call wet bulb depression right so this would be somewhat lower do you get it if i have some jute or wet cotton around wet it has to be wet so they used to have something called wheeling hygrometer where they will have you know a wrapped around a

jute wet jute draped around textile means very important you know many other other places temperatures relative memory is very important so they will go on or in a room where you want to control humidity they will go on moving around this and then measure the depression

of the wet bulb temperature or reading of the wet bulb temperature the difference between these two is a function of relative humidity it will be maximum when when it will be maximum when it is zero zero you know it is totally dry environment it will be maximum and there

will be no depression when the environment is saturated saturated environment is saturated so dbt and wvt wet bulb temperature so relative humidity you know relative humidity can be measured

through wet bulb temperature there are other techniques like hygrometer you might have seen a hygrometer willing hygrometer i was saying hygrometer measures relative mobility earlier days they would use horses tail you know horses hair basically fibers are very

sensitive to relative humidity their dimension changes occur swell or shrink so they would use horses tail long one which will expand or contract depending upon the relative humidity and this movement can be converted into you know some kind of analog movement analog scale

and all that so we used to have one in the lab of the similar kind anyway so wet bulb temperatures can be measured through hygrometer and one way is to measure the wet bulb temperature and dry bulb temperature both right so thats what it is so thats how we measure

relative humidity ok if i have to go to this a little bit lets go to a little bit of physical chemistry or you know you might have heard of osmosis if i have a semi permeable permeable membrane and i have a concentrated

solution on one side and you have simply the solvent on the other side after some time concentration concentration becomes same on both the sides now this can happen in air also right why does it happen because the molecules the solute

will have brownian movement and if they collide with the concentration is same on both the sides they collide with each other and come back to their original so concentrations are doesnt change now ah dont have much of a relevance here but still i will just quickly tell you

but supposing i have two columns one has got the solvent other has got the solution and i have a semipermeable membrane in between i am not drawing the diagram but just trying to explain you quickly and if i put a pressure on the pure solvent side i find that concentration

doesnt change you know so thats osmotic pressure so concentration gradient can cause movement same thing with vapour concentration gradient so vapour concentration you know if there is concentration of the water molecule where moisture vapour molecule is less at one place

inside so there will be a movement so this is given by fixed diffusion equation diffusion law so this dc is the concentration dc dx rate of mass flow can be written as some diffusion coefficient into dc dx and c is nothing but concentration is mass per unit

volume volume volume so you know if i have rho v c concentration can be written in this manner you know if you have if you if you remember we had p v

v v was equals to m v divided by m v into rt so concentration will be given by v v divided by you know mv divided by vv concentration is nothing but m v by c is equals to m v by vv mass per unit volume and therefore it follows from here pv mv divided by rt right pv mv

divided by rt right so thats what it is so m dot now i can replace this pv i mean i can write it like this you know diffusion coefficient m dot you know combine this equation dc dt so you differentiate this with with respect to x this is constant this is constant right

and lets say temperature is constant then this will be function of simply vapour pressure gradient so mass flow is the function of vapour pressure gradient right mass flow as a function of vapour pressure gradient so the amount of

moisture that can evaporate from your body is a function of that vapour pressure gradient as well so you know and this i can add to a frictional coefficient this is if there is no kind of a resistance but there is a frictional resistance then i will just put

this mu as a frictional resistance term and thats how i can write this mu dot and you know its convective so convective heat or movement as usual see we will see that the rate can be proportional to this so i think we will ah stop here