Principles and Applications of Building Science
Dr. E Rajasekar
Department of Architecture and Planning
Indian Institute of Technology, Roorkee
 Lecture - 01
Solar Geometry
Welcome to the course Principles and Applications
of Building Science.
This is the first module.
Here we will start with Solar Geometry.
(Refer Slide Time: 00:37)
Mainly we will talk about the Earth-Sun relationship,
Sun-path diagrams and what is the consequence
of it on the solar time and local time and
how they are different.
In Solar radiations, specifically we will
look at how to measure and what are its implications.
Finally, we will look at how does that affects
building design, what are the design implications.
To start with, we will look at the Earth-Sun
relationship.
Some of this we already know.
We will relate it more with climatic building
design.
The climate of earth as you know is driven
by the energy input from the sun, sun is a
source of energy.
(Refer Slide Time: 01:14)
There are two essential aspects that person
has to understand; one is the apparent movement
of the sun or you know if you take a geocentric
theory, it is apparent movement of the sun
where the sun’s position is that is the
solar geometry we typically refer as.
And number two is the energy flow from the
sun, be it heat energy be it light energy.
It is energy flow from sun to the earth and
how to handle it, whether you will include
it in the building or exclude it in the building.
So, two primary things; one is the solar geometry,
number two is the energy flows associated
with it.
(Refer Slide Time: 02:05)
Considering heliocentric view, you have sun
in the centre.
The earth is moving around it 365 days, the
axis which is subtended with the equatorial
plane and the sun.
This particular angle, the tilt of earth is
23 and half degrees, this is constant tilt.
As the earth moves around, you will start
getting two typical extremes; one is called
Northern solstice that is when 23 and half
degrees plus that are on June 21st and 22nd.
It happens that is, the day times are maximum
and the night times are minimum in the Northern
hemisphere, typically we call Northern solstice
for countries or locations in Northern hemisphere,
this is called summer solstice and the other
side winter solstice are the Southern solstice
for the earthen hemisphere which occurs on
December 22nd that is minus 23 and half degree
tilt.
Typically, this is referred as Southern solstice,
for locations in Northern hemisphere we refer
to this as winter solstice.
This is where you know you get the shortest
day and longest night typically we get minimum
temperatures in this particular season.
Apart from this, when earth is typically you
know there is a 0 degree tilt, you call it
as equinox.
It occurs twice that is March 3rd week of
March and 3rd week of September.
So, there are four important dates which are
critical, if you have to understand solar
geometry first is Northern solstice or summer
solstice for the Northern hemisphere, next
is two equinoxes which occurs in March and
September and the last one is Winter solstice
or Southern solstice which occurs which typically
is a minimum temperatures associated with
Northern hemisphere.
It is exactly the opposite for Southern hemisphere.
So during northern solstice they have winters
and during southern solstice they have their
summers.
(Refer Slide Time: 03:41)
So we have an equator here, Tropic of Cancer
and Tropic of Capricorn 23 and half degrees
north, 0 degrees and 23 and half degree south.
So, we are talking primarily about India or
Asian part.
Primarily, we will look at what happens around
here and what is the impact of the solar geometry
on this particular over particular location.
(Refer Slide Time: 04:22)
So, if you have to understand more or if you
have to derive some implications of the solar
geometry on our design, we have to start mapping
the sun position.
The first step is to get into a loco centric
theory and get two typical angles to map the
sun’s position on a two dimensional plane,
sun has 3D movement.
So, from that you are deriving two typical
angles from which you can project, it is a
trigonometric projection, first thing is that
the altitude angle, wherever whichever orientation
it is, you just typically take a horizontal
plane and you mark the position of the sun,
the angle which is subtended to the horizontal
plane is called Altitude angle.
Higher the altitude angle, sun is towards
your head, that is 90 degree means sun is
just above your head.
Typically, if you know if you would say east
and west, then you might get very low altitude
angles.
Next is an Azimuth angle which you can take
either north or south as reference.
In many cases, you take north as a reference
and wherever the sun’s position, irrespective
of its altitude angle where it is located,
you typically project it down and take the
angle difference between or the angle subtended
from north.
For example, when sun is right on the eastern
side, you can say it is 90 degree or towards
the west it will be 270 degrees if you are
taking north as a reference point.
(Refer Slide Time: 05:33)
If you have to really calculate altitude angle
and azimuth angle, these are trigonometric
calculations.
So, you need few indicators like declination
which we talked about earlier, you need the
hour angle from solar noon, then you will
need the number of day of year.
So with these things, there are some formulas
which we are not going to work out as a part
of this module, but if somebody is interested,
if you know these 3 to 4 numbers, it is easier
to locate the position of the sun and it is
easy to calculate altitude and azimuth angles.
We will go more with a graphical representation
given the shorten duration of this specific
modules.
(Refer Slide Time: 06:08)
Let us consider two specific examples to get
a better picture of these solar movements.
First let us take a location Srinagar, typically
Northern part of India.
The latitude is 34.1 degree north and the
longitude is 74.8 degree east.
First let us look at what is the impact of
change in latitudes.
So, we will be considering Srinagar first,
followed by Trivandrum which is in the Southern
tip of India, so first.. no.. next we will
look at longitude where we will talk about
the solar time, also how to calculate local
and derive local time from that.so we will
look at that First let us take a look at the
latitude of the place 34 degree north.
There are three images.
This is summer solstice where..you know here
we are referring to the Northern solstice
or summer solstice here.
Sun’s position, it rises somewhere, then
at this point and then it moves traverses,
sets here.
Typically you get sun right above the head,
this is on summer solstice, it never crosses
towards the Northern side, it is slightly
tilted towards south, but still you get sun
from the north east and north western side
during the morning and evening times.
During equinox if you see, sun moves.. you
know the sun rises here, moves along and then
sets in this point.
So, typically you get sun rising exactly in
the east, setting exactly in the west during
equinox, but it traverses.
You know it has a Southern traverse and it
rises in the east, traverses through south
and sets in the west.
Winter solstice, you have further lower altitude
angle, here we are talking about three altitude
angles, this altitude angle is high, slightly
lesser and winter solstice December 21st here
we have typically the least possible altitude
angle.
You do not get sun directly on the east or
west, it is mostly somewhere close to south-east
and south-west and it has a Southern traverse,
this is the case of 34 degree north latitude.
Take a look at Trivandrum.
This is 8.5 degrees north latitude which is
much closer to the equator.
So, when we looked at Srinagar, it is of tropic
of cancer further north of tropic of cancer.
Here, we are talking about a location south
of tropic of cancer much closer to the equator.
If you look at the sun movement, it has you
know the sun rise happens somewhere close
to north-east and sets somewhere close to
north-west.
It traverses not directly through south, it
is somewhat half the center point, that is
it has a slightly Northern traverse during
summer solstice, it is further half.
So, this is a center point, this is south,
this part is north.
So, it has a typical Northern traverse, what
implication this has is if you have a Northern
wall which has large windows typically during
summer especially in latitudes like this say
11 degrees, 10 degrees are even you know 15
degrees, 13 degrees north latitude.
You will have solar incidents on your Northern
facade and Northern windows during summer
months.
The lower you go towards equator like typically
the case of 8 degrees, 8 and half degrees
north latitude, you will have up to 4 and
half months, you will have solar incidence
on your Northern wall.
So, when you are blindly following a code
which says or a text book which says sun traverses
from east to west through south, Northern
wall or Northern facades are you know free
of direct solar radiation.
It might be misleading, you have to closely
look at what latitude it is which decides
because critical months like summers like
May, June and July where solar radiation is
also more, temperatures are also more, you
are going to get direct solar radiation on
your Northern facade here.
During equinox, east and west a slight Southern
traverse is noted, it is slightly half the
center point, slightly traverses towards the
south.
Winter solstice, the altitude angle if you
compare with Srinagar is not as slow as you
looked at Srinagar, you do not get such a
low steep penetration of solar radiation,
it is slightly higher in terms of altitude
angle.
In all the three cases, the altitude angle
is much higher compared to 34 degrees that
is, the location Srinagar which we talked
about.
Now, let us look at something called Sun-path
Diagram which is highly useful if you are
designing a building specifically for shading
devices or locating, orienting your building,
for anything to start with sun path diagram
is a basic requirement.
(Refer Slide Time: 10:58)
It is nothing but a projection, a two dimensional
projection of a 3D movement.
Mostly we refer to stereo graphic projection.
There are other types like orthographic.
We will look at few of them in an example.
Primarily, we are working with a stereo graphic
projection.
There are other things like spherical orthographic
but mainly we are looking at a stereo graphic
projection.
You need two specific angles that is altitude
angle and azimuth angle to locate our map
to the position of the sun.
Now, coming back to our two example cities
Srinagar and Trivandrum, the solar movement
can be mapped like this.
We looked at in the three dimensions, now,
this is what we were talking about, this is
your traverse of sun during your summer solstice,
this is your traverse of sun during winter
solstice, equinox occurs somewhere here.
We will look at the components more in detail,
this is for Trivandrum like I said, this is
a center point and these are month lines.
So, if you see up to four months easily, you
will get direct solar radiation or solar incidence
on Northern façade.
If you have to access a Northern façade,
it will fall somewhere in this center line,
again Southern facade you have to take this
as a center line and see how many months or
how much duration you have solar incidence
on your Southern facade.
So, typically in this case your Northern facade
is going to have solar incidence for more
duration whereas, here it is only for 2-3
months that too slightly in the morning and
evenings which can be prevented or up stretched
to a vertical shading system.
Here, you will also need a horizontal shade
on your Northern wall in order to avoid direct
solar radiation during summer.
(Refer Slide Time: 12:27)
In laboratories, this particular thing is
studied using helloidol, you might have heard
of this name, this is a device where you can
set the solar position, everything is adjustable,
you can set latitude, longitude, solar position
and then I mean typically these are lights
which cause shadows you can put your modal
and you can assess what is a shadow penetration
and what is a solar incidence?
These things can be experimentally assessed.
In this module, we are going to look at 3D
graphic which is generated by a software called
eco tech, we will be primarily using for demonstration,
we will be using the models from eco tech
as well as a associated tool called solar
tool which helps us to graphically represent
a three dimensional sun path.
(Refer Slide Time: 13:14)
So, similar thing which we are going to look
at, this is a solar tool which I was talking
about, here we are talking about the solar
path, this is a stereo graphic projection.
There are different types of projections as
I said Spherical, Equidistance, Stereographic,
Orthographic, Wall drums, you can also look
at tabular mapping of it.
There are key components here, the peripheral
line represents the azimuthal angle which
we talked about and then the concentric line
talks about altitude angle, these are the
date lines, month lines for summer to winter
solstice and these things are the hour lines.
So, knowing this date and hour lines, you
can locate the sun’s position at a particular
point.
Other than this, this particular tool let
us set the date and time, say for example,
if you are setting June 21st then you will
have summer solstice here, for a particular
time you will know where the sun’s position
is.
When you will change it to winter that is
December, sun position changes here.
You can also change the latitude of the place.
Now, it is 34 degrees that is for Srinagar
if I change it to Trivandrum’s location,
the solar path that is the total sun-path
diagram varies, this is during December and
this is during June.
A simple representation of sun movement, we
will look at the shadow and shadow assessments
further in detail.
So far we have been dealing with the latitude
of a location and how it effects the sun’s
movement.
Now, in this section we will talk about the
impact of longitude and primary considerations
which we have to give.
So for this, one major thing you have to understand
is the difference between solar time and the
local time.
The time used in the solar chart is a general
solar time and it coincides with the local
clock time only at a reference longitude for
a particular time zone.
(Refer Slide Time: 14:52)
If you take the case of India, we do not have
different time zones, there is one time zone
across the country though we have a vast extend
from west to the east, we have only single
time zone and the reference longitude for
India is 82.3 degrees east longitude.
If you take a country like U.S, they have
a different time zones as you go from east
to west of united states the time zone varies
for example, they have half an hour to 1 hour
time adjustment every time zone as you move
from east to west.
For a basic understanding, every degree of
longitude you move, it means a time difference
of 4 minutes.
(Refer Slide Time: 15:43)
We will use this in further calculations.
To understand this better, let us consider
two locations, first is Mumbai which is 73
degrees east longitude on the western side
of India, number two is Dibrugarh which is
95 degrees east longitude which is further
east of India.
Mumbai lies west of India’s reference longitude
that is 82 degrees reference line, it lies
west of reference line by 9.5 or 9 degrees
30 minutes whereas Dibrugarh lies on the east
of India’s reference longitude by 12 degrees
and 30 minutes.
Another thing which has to be factored in
the calculation is the equation of time correction
which can be done like I said earlier, it
can be done numerically or I am showing you
a graphic indicator, this simple graph which
tells you how to find out the time correction.
Along the x axis it has a number of days that
is day of the year, starts from 0 goes to
366, then on the y axis we have the equation
of time correction.
This depends on the day of the year considered.
For example, if you take 26th January, it
comes somewhere here 26th day of the year,
the time correction will be minus 13 minutes,
if you take 26th October or 27th October which
is somewhere around the 300th day of the year,
the time correction will be plus 17 minutes.
Using this, what we can do if you take the
same case of Mumbai and Dibrugarh, the calculation
goes like this.
(Refer Slide Time: 17:10)
For example, if I have to establish; what
is a local solar noon, what time the local
noon occurs in Mumbai, noon is 12 o'clock
minus 38 minutes, this 38 comes from this
9 degree 30 minutes, if you multiply that
for every longitude degree, it is 4 minutes.
So, if you multiply you will get 38 minutes
minus 13 because I am calculating it for 26th
January, where is if I am calculating it for
say as a example I stated 26th October or
27th October, the correction will be positive,
it will be plus 17 minutes, here it is minus
13.
So, this comes to 11:09.
Subtract this from 12 then you will get 51
minutes.
So, local solar noon at Mumbai occurs 51 minutes
later than Indian standard time because it
lies to the west of the reference longitude.
In the case of Dibrugarh, in the same way
if we calculate, we find that the local solar
noon occurs 37 minutes earlier than the Indian
standard time.
If India were to have different time zones
from east to west, then the time zone adjustments
will be something like half an hour to 45
minutes for each time zone if one were to
divide the country into three different time
zones.
(Refer Slide Time: 18:29)
We will look little bit more in detail about
solar radiation, two main measures are there,
number one is Irradiance watts per meter square
is most commonly used, it is a instantaneous
flux or energy flow, earlier it used to be
called solar intensity, now it is called irradiance
watts per square meter, it can be horizontal
or vertical.
On Number two is irradiation which means the
energy quantity integrated over a specific
time, it can be per day, per hour or per year,
total hour for a specific season.
It is measured in watt hour per meter square.
Looking little bit more into the details of
the solar radiation itself, the sun’s surface
is around 6000 degrees centigrade, peak of
its radiation emission occurs at 550 nanometer
wave length.
(Refer Slide Time: 19:14)
Now, this is a solar spectrum, we know three
major things one is a visible spectrum, then
you have ultra violet and infrared.
Once the sun’s energy hits earth’s atmosphere,
part of it is reflected back, absorbed and
transmitted, whatever component is observed,
it is re radiated, then after entering the
earth’s atmosphere, the ground absorption
or water bodies observe and reflect part of
it, whatever is absorbed is re-emitted, what
comes in a short wave radiation, once it is
absorbed and then re-radiated, it goes back
as long wave radiation.
These long wave radiations are trapped by
the cloud cover which we generally call green
house effect where this re-radiator long wave
radiation gets trapped in the earth’s atmosphere.
There is a large variation in irradiation
among different locations of the earth.
This is for three main reasons; one is the
angle of incidence.
(Refer Slide Time: 20:01)
We know the cosine law which states that the
steeper the angle of incidence, the difference
will be more, number two is the atmospheric
depletion and again it is a factor of the
angle of incidence.
For example, if it is in the polar region,
the same sun’s radiation has to traverse
a long distance across the atmosphere cutting
through.
So, there is a factor which varies between
0.2 and 0.7 and then number three is the duration
of sunshine.
For example, earlier we said summer solstice
versus winter solstice or the Northern solstice
versus Southern solstice where the sun’s
duration of sunshine considerably varies between
June 21st and December 22nd.
So, this has a considerably impact on the
irradiation.
(Refer Slide Time: 20:55)
Let us come back to the example of Srinagar
which is 34 degrees north and 74.8 degrees
east longitude.
You take the same Southern wall surface, I
have put some windows and some shading systems
here, if you take the solar radiation incidence
on a winter, this is winter solstice you have
a steep Southern sun, this is where the solar
radiation incidence occurs if you see in this
scale, this portion corresponds to somewhere
around 3000 watt hours.
This is for a particular day.
On the instance of December 22nd this is the
solar radiation which occurs on the Southern
surface, this is the total solar radiation.
One more thing we have to remember is this
total solar radiation has two components,
one is a direct radiation and other is a diffuse
radiation.
For example, consider this surface at this
point of time, this is around noon, this particular
surface is not getting any direct solar radiation,
but still the radiation will be there because
of diffuse components.
Diffuse radiation will still have some impact
on these surfaces, total radiation and net
radiation will be minimum.
Consider the case of Trivandrum which is 8
and half degrees north latitude.
(Refer Slide Time: 22:02)
This is again winter solstice.
This Northern sun is not as steep as you found
in Srinagar and it is slightly with a higher
altitude angle.
Carefully look at this numbers, the total
solar radiation incident on a Southern facade
which is somewhere around 6000 watt hours.
So, the solar incidents you receive on the
Southern facade considerably vary between
the Northern parts of India that is a location
like Srinagar versus Trivandrum.
Now, let us not worry about what climate condition
it is, Srinagar has a colder climate versus
Trivandrum has a warm and humid climate.
We are not getting into the climate classification
that is part of a different module, the subsequent
module, but just the solar radiation intensity
considerably varies on a given building façade
and how do we account for this particular
solar radiation in our building related calculation,
the main parameter which is used this Sol-air
temperature which is kind of a inclusive number.
(Refer Slide Time: 23:04)
If you read this equation this is T out is
a outside air temperature in degree centigrade,
this is a drivel temperature of outside air,
sol-air temperature actually includes the
effect of air temperature and adds up a small
component to it which is inclusive of the
main thing global solar irradiance watts per
meter square, absorptivity of a particular
surface as I say imagine the same Southern
facade which I was talking about, if it were
to be bright colored, say a white surface
versus a black surface.
This absorptivity of the surface considerably
varies.
So in that case, this particular factor will
vary.
The 3rd part of this small factor is h naught
or the heat transfer coefficient for radiation
and convection, this is equivalent to the
film coefficient on the outside surface of
the wall.
So, this particular factor is added to the
outside air temperature.
Sol-air temperature typically will be equal
or more than the ambient air temperature in
tropical climates, what happens is say imagine
if you take a western facade somewhere around
4 o'clock in the evening, there will be an
ambient temperature, take a case like Srinagar
in June 21st say the ambient temperature is
30 degrees in the Southern facade which we
looked at.
The solar radiation intensity will be x plus
the absorptivity of a surface, imagine a white
surface, there will be a heat transfer coefficient.
So, a small magnitude say about 4 to 5 degrees
will get added up which becomes the sol-air
temperature.
This is more or less equivalent to the surface
temperature of a particular wall.
(Refer Slide Time: 24:48)
I have done some calculations using the same
equation.
Take this location, this dotted line represents
the outside air temperature which starts from
6 o'clock, this is evening 6, this is a 12
hour graph.
Morning, the temperatures are around 27 degree
and goes up to 35 degree in the evening.
There are two other lines in this graph, this
is time in hours, this is temperature and
there are two other lines, this is sol-air
temperature on the eastern façade, this blue
line versus this purple line, this is a sol-air
temperature on the western façade.
Interestingly, if you notice the eastern façade,
the sol air temperature goes as high as 40
degrees.
Early in the morning only around say 7 to
9 o'clock the peak occurs, then it cools down,
comes back below the ambient air temperature
whereas, on a western façade, this sol-air
temperature rise much lower than the ambient
temperature and then it peaks up in the evening
and then its heat, now it gets heated up and
what is the impact on building design.
For example, if you were to have a wall which
is part of a bedroom, your bedroom wall is
exposed to eastern side.
The sol-air temperature will go as high as
40 degree in the morning and then it will
cool down.
So, when you want to occupy it somewhere around
9 o'clock in the night, the surface temperature
is not that high and including the time lag
which we will discuss later.
The inside temperatures will be relatively
cooler whereas, a west facing wall of a bedroom,
the maximum temperature occurs somewhere around
4 o'clock to 5 o'clock in the evening, then
this will be transmitted in.
So, you will have relatively higher temperature
inside surface temperature as well as heat
gain through that particular wall.
(Refer Slide Time: 26:27)
Here, we did a small calculation as such sol-air
temperature is dependent on two main things,
the one we have earlier saw the absorptivity
of a surface that is represented by a brighter
surface versus a reflective surface versus
a darker surface.
Number two is, it can be modified with the
effect of shading, what happens in the case
of shading, the moment you have a shading
device or a balcony, the direct solar radiation
is cut, but you have to keep in mind the defuse
solar radiation still exist.
So, it is not totally negated, but the direct
component which is quite significant is totally
negated if you have a full cover of shading.
We have calculated the sol-air temperature
ranges for 8 orientations.
There are three cases here, the first case,
this is a dark blue, the absorption, the solar
absorption of dark sun’s of the surface
is 0.4 which corresponds to a normal white
painted or a ivory color painted external
wall.
There is direct solar radiation and it does
not have any shading.
Number two, this light blue where we painted
the surface with a reflective coating.
Today, we will get a lot of reflective commonly
called low e coatings which are done on the
wall, that is low emissive coating, mainly
reflective coating has been done for the second
case and the third, the same wall an additional
shading system was added to the first case
that is the absorptivity remains and there
is no reflective coating, but additionally
a shading system was provided that is the
wall is completely shaded and you can imagine
there is balcony present in front of the wall.
So, what happens in the first incidence is
the sol-air temperature for example, in the
eastern wall goes as high as 47 degrees, for
a west facing wall it goes up to 51 degrees.
This is in a tropical warm humid climate and
goes as high as 51 degrees in a west facing
wall whereas, when you paint it with a reflective
coating it can be brought as low as 41 degree,
you will find 10 degree difference on the
external surface or sol air temperature.
Instead of reflective coating, if you go for
a proper shaded west facing wall, you can
bring it down to as low as 37 degree and you
have to notice that this is more or less equivalent
to a north facing wall.
Imagine you have a balcony which has a west
facing wall and you cannot avoid it, the better
solution in today’s context would be if
you are in a design stage, you can provide
a balcony or a deep over hang.
So, as to shade the complete wall, it becomes
more or less equivalent to a north facing
wall forgetting about the wind and other components
which we are discussing just with solar radiation
and this can be made equivalent to the north
facing wall or if you further do not have
choice, you have crossed the design stage,
then the next best alternate would be to look
for a reflective coating, but this is temporary,
the coating would last for around 2-3 years
after which it loses its reflective property,
it has to be recoated.
There can be a slightly better improvement
with reflective coating, but with permanent
shading system, the whole sol-air temperature
can be brought down.
(Refer Slide Time: 29:31)
Let us discuss about few design implications,
this particular graph, two things, this is
again for Srinagar, this is winter solstice
and this is summer solstice and this is the
same solar radiation, but this is a direct
solar radiation graph.
I have split the whole thing, instead of drawing
a square I have made a cylindrical structure
which is segmented.
So, each of this segment represents a specific
orientation say if you want to take just four
cardinal orientation east, west, north and
south, you can refer watt hour per meter square,
this is radiance at this particular instance
of time, this is during winter solstice in
Srinagar, this is a Southern sun summer solstice,
this is a condition.
(Refer Slide Time: 30:10)
This is for Trivandrum, the numbers get higher
during winter solstice and this is during
summer solstice.
Even Northern surfaces and north eastern surfaces
get more solar radiation.
One important thing which we should not forget
is the use of for example, Northern windows
or north lights as you go down the tropic
of cancer towards equator, Northern surfaces
start receiving solar radiation, it is not
that Northern surfaces are totally divide
of solar radiation and as you get closer to
equator, what happens is suns starts traversing
towards your Northern wall as well.
This is considering a loco centric theory
with sun as a moving body, you are located
here and sun starts moving towards your north.
If your building facade is this, you will
still get solar radiation in your Northern
facade for at least four months for latitudes
south of tropic of cancer.
Further you go towards equator, it gets more.
Especially, on an equator there will be equal
distribution, half of the year sun will be
to the Northern side, half of the year sun
will be to the Southern side.
(Refer Slide Time: 31:17)
To get a better understanding, we have this
graph.
This small box rectangle here represents a
building’s orientation, these lines here,
the red one indicates the solar radiation
during summer which is deputed as overheated
period, the blue one which is shown here indicates
the solar radiation during the under heated
period or the winter season.
This is an interesting graph which shows that
which is a major direction from which higher
solar intensity comes during summer, this
is during winter and the green one is an a
annual average.
Typically it is understood and agreed upon
that, your longer surface of the building,
longer facades of the building should not
be facing east and west without enough solar
protection.
So, it is a better idea to orient it, the
longer surface to orient it towards north
and south, shatter towards east and west it
is understood, but still you can go for minor
directional changes depending on the location
for example, in case of Srinagar the major
solar incidence during summer occurs in this
direction not exactly in the east, but it
occurs slightly away from the east and during
winter it is not directly on the south, but
it is towards little bit towards east it is
not south east, but slightly ahead of east.
(Refer Slide Time: 32:44)
So, in this case the actual right orientation
of the building will be a slight tilt rather
than just on the plane.
Considering the case of Trivandrum, the case
changes the maximum solar radiation intensity
during summer occurs at 70 degrees.
So, this is where you get maximum solar radiation
during summer and during winter you get somewhere
around 160 degrees and this is where the maximum
occurs.
So, a trade of the best orientation would
not be just south, the longer facing not just
facing south, but it is somewhere around 160
degrees that is a perpendicular if you draw,
this should be facing 160 degrees.
(Refer Slide Time: 33:18)
This would be the best case in which the building
can be oriented.
We will close this session here, take a quick
recap.
We studied five important things, first thing
is the Earth-Sun relationship, how it moves
around and we studied about Northern solstice
equinox and Southern solstice, the earth’s
tilt and then we talked about how this earth
movement rather sun movement would be translated
into diagrams for quick reference that is
sun-path diagrams, the stereo graphic projection,
how it is built and how it can be used.
Number 3, we talked about the effect of longitude
and time zones.
We calculated solar time and local time and
then we talked about the impact of solar radiation.
We took specific example of a building facade
and were studying it for two different geo
locations, then we studied about the design
implications; that is how to orient your building
considering the solar radiation before positioning
a building itself.
Thank you.
