Understanding Building Functions: Safety, Comfort, and Environmental Interaction

[Music] so good morning everybody this is lecture 1 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 special 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 environment so that you can write write

and of course comfortable from thermal point of view it's one of the most important things right thermal point of

view so for that human activity here is teaching teaching of reading right which means teaching learning interaction ok

so that's 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 economical we would normally want to be talking about lifecycle cost in this

context but anyway cost is not enough you know issuing 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 rights Africans natural

forces such as gravity load first of all gravity you know like if you have to stand somewhere your own weight would be

there so gravity load small load so many of them are vertical Road wind rain it's a track wind an 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 won't be safe against all these forces so that's

what we are saying so that's 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 he's not discussed this so building interacts with surrounding

environment earth that's 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 empirically would like to

reduce so I would like to model 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 it's a

mathematical generalization so that's 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 let's see so comfortable a

moment convert it must be comfortable against external temperature relative humidity moisture and gas condensation

etc 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 son I'll tell you what is micro climatic changes

for example you change the you know your activity human activity lot of building they've change the thermal conditions

surrounding the building so we'll 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 waste order of fumes and gases etc so these are man-made thing they can cause discomfort right okay

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'll talk a little bit related to this

so that's kind of you know interaction what we'll 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'll come to that next one would be relative humidity here

motion air velocity speed and directions is an important solar radiation these are all related to thermal comfort then

precipitation or rainfall because if that's that's what causes relative humidity change significantly and

sometime hours how many hours sunshine is there then sky brightness is related to day lighting describe 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 region also we'll talk about that a little bit later so these are the features based on

we define them let's see how do you measure temperature if you want to measure air temperature is measured in

what is called Stevenson screen now do I have a diagram of this if I don't have I'll just draw it for you no problem

it's like a box it's simply like a box you might have seen and it will have louvers right so it's a closed box so

that direct sunlight doesn't come in wind doesn't affect their air motion there's no air velocity significant air

velocity inside it remains dry there's no rain coming into it protected from the rain and you measure what you call

dry bulb temperature inside so what you measure the driver for example if eating a

thermometer well there are better varieties of measuring devices liquid thermometers are well known mercury

thermometers where expansion of market mercury you know because it has got a linear expansion or expansion doesn't

vary with the temperature itself rate of expansion so temperature change volume change per unit temperature will remain

constant over a very large range that's why Mercury's use some cases alcohols are used then there are other things

like what we call platinum resistance thermometer because resistance has changes with temperature I am NOT

discussing them you have a you if you 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's 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's 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 thermistors there are several other

measurement devices yeah we're not going in details into this so the unit is of course degree centigrate 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 okay let's first define relative humidity I think

I'll come to the algebra part of it later on but I think I have not defined yet 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 AR hard on not AG AG silver so a little bit of

argon and obviously moisture vapor right now this is around 78% as you know 21% 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

vapor moisture vapor and this moisture vapor has got an importance related to thermal comfort as you'll see later on

the body would like to maintain a fixed temperature right deep body temperature has to be constant so if outside

surrounding atmosphere is warm warm under the deep body temperature it would actually you know heat flow to occur

from outside to inside but then what you would like to reject it we'll 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 or

liquid down so therefore relative humidity or moisture content in the surrounding and

vomit is important because if it is dry it can absorb a lot of moisture if it is already saturated because it's a kind of

a solution as I said so there's a air has got a capacity to you know absorb moisture vapor and this is a function of

temperature itself higher the temperature it can absorb more moisture vapor so relative humidity is related to

that relative humidity is a kind of measure it's 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 sometimes we denote it by G moisture content we denote by G

as we shall be doing in this class / GS saturated moisture content at that particular temperature that's how we

define so relative humidity we define this now how do you define partial vapor pressure or partial pressure of two

gases supposing I have to guess and I you know individually it occupies a volume V gas one the pressure is p1 and

second gas which occupies the same volume as pressure is p2 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 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'll 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 1 plus P 2 partial pressure so in case of air partial pressure of air for partial pressure of

vapor is a total pressure right now if I if if relative you know if the G is more moisture content is higher this will be

also higher so I can relate this to partial pressure vapor 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 let's say it's only the dry air VA is equals to the mass of the idea 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 vapor divided by mass of the dry air that's 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 PB MB divided by PA ma right we 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 or does it come nitrogen we know is 28.7 8 multiplied by nitrogen molecular weight of nitrogen

because it occupies 78% is a 78 percentage of nitrogen oxygen we know 21% or whatever it is so when we sum

them up I get 28 point 9 6 so this therefore PB by p a comes in and PA is nothing but atmospheric pressure minus

the pressure so you can see that moisture content is a function of vapor pressure and 0.66 2 so it's actually can

be related to the vapor pressure off yeah right okay now there are some empirical so relative humidities G by GS

saturated moisture content at saturation for the same temperature so there are some empirical formula maybe I'd solve a

problem sometime but there are other ways of finding this out also phi g etcetera it's through psychrometric

chart i'll 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 you here or

read it here but you might be familiar with it because you can refer to this in SP 41 or any book of the reference that

I have given Marcus and Morris Kenneth Berger and so on so forth i hv guideline SI and book and so on many places you

will find it now now this axis is DBT and this from minus 10 to I think it is plus 60 so what this range this

particular graph is I mean it is there for various ranges some will have up to 30 or whatever it is

so this DBT is along this direction this direction is a moisture content in kg per kg you know absolute most chekalin

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's something called wet bulb temperature how do you measure relative humidity

then it'll come now this cars can be fitted into an empirical equation as I said and you

have vapor pressure is given a saturated vapor pressure minus some constant into atmospheric pressure t minus TW is

called wet bulb temperature I'll just define what is called wet bulb temperature and some again as I said

empirical formula is given PSB and PS at any any in any temperature what is the saturation pressure those are those are

values are empirically obtained maybe I'll solve a problem some time that will be clear I'll come back to this later

but let me now define what is what well temperature let's see if it is there okay before the mathematics comes in wet

bulb temperature is supposing I have got a thermometer I've got a thermometer right something like this supposing I

put a wet cotton here it's a thermometer that thermometric bulb you know it's 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'll have the unit to be mercury simply so this is dry bulb temperature now

where will the supposing I have got relative immunity 100% right where will be this height or reading of this

thermometer it will be same because this is where 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'll have you know a wrapped around a jute wet you to draped

around textile means very important you know many other other places temperatures relative which is very

important so they'll 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 ball 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'll be no depression when the environment is 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 iGrow meter I was saying hygrometer measures relative mobility earlier days they would use hot

sustain you know what says here basically fibers are very sensitive to relative humidity

their dimension changes occur swell or shrink so they would use horse's 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 ball temperatures can be measured through micrometer and one way is to measure the wet bulb temperature

and dry bulb temperature both right so that's what it is so that's not how we measure relative humidity okay if I have

to go to this a little bit let's go to a little bit of physical chemistry or you know you might have heard of osmosis if

I have a semi 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 becomes same on both the sides now this can happen in the 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

and energy now don't 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'm

not drawing the drag Ram but just trying to explain it quickly and if I put a pressure on the pure solvent side I find

that concentration does not change you know so that's osmotic pressure so concentration gradient can cause

movement same thing with vapour concentration gradient so vapour concentration

you know if there's concentration of the water molecule where moisture vapor molecule is

yes at one place inside so there's a movement so this is given by fixed diffusion equation diffusion law so this

DC is the concentration DC DX the 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 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 mb / vb concentration is nothing but M V by C is

equals to M V by V be mass per unit volume and therefore it follows from here PV MB divided by RT right PB MB

divided by RT right so that's what it is so m dot now I can replace this PB 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 which has proved is

with respect to X this is constant this is constant right and let's the temperature is constant then this will

be function of simply vapor pressure gradient so mass flow is the function of vapor pressure gradient right mass flow

as a function of vapor pressure gradient so the amount of moisture that can evaporate from your body is a function

of that vapor 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'll just put this mu as a frictional resistance

and that's how I can write this mu dot and you know it's convective so convective

heat or movement as we shall see we will see that the rate can be proportional to this so I think we'll stop here

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