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
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