Solar architecture new ppt

Solar Architecture
Solar Architecture is utilizing solar energy is the most effective way to
maintain thermal and cooing comfort. Solar architecture is an architectural
approach that takes in account the Sun to harness clean and renewable solar
power. It is related to the fields of optics, thermics, electronics and materials
science.
This can be done in following ways:
• Active Space conditioning: using solar energy to run the machinery of Air-
conditioner
• Passive space conditioning: Control/remove the heat from space
Solar Energy Nature
Intermittent: In the absence of an energy storage system, solar does not produce power at
night or in bad weather and varies between summer and winter.
Dilute:

Solar Radiation Estimation
The beam radiation on the horizontal surface can be measured by:
cos
b N z
I I 
 0.9 9.4sin
R
T
N ext
I I e 

 
 

 

Where
Iext = Extraterrestrial radiation
TR = Turbidity factor
The attenuation of solar radiation through a real atmosphere versus that through a clean dry
atmosphere gives an indication of the atmospheric turbidity.
Month 1 2 3 4 5 6 7 8 9 10 11 12
Mountain 1.8 1.9 2.1 2.2 2.4 2.7 2.7 2.7 2.5 2.1 1.9 1.8
Flat Land 2.2 2.2 2.5 2.9 3.2 3.4 3.5 3.3 2.9 2.6 2.3 2.2
City 3.1 3.2 3.5 3.9 4.1 4.2 4.3 4.2 3.9 3.6 3.3 3.1
G. N. Tiwari, 2008 Solar Energy Narosa Publications, New Delhi and Polo et al., Solar Energy, 83(8), 1177-1185, 2009.
Turbidity factor for different locations
For Cloudy condition: TR = 10 2

Diffuse radiation on a horizontal surface can be estimated by:
 
1
cos
3
d ext N z
I I I 
 
Total radiation on any given surface can be estimated by:
 
T b b d d r b d
I I R I R R I I

   
Where
R = Geometric or tilt factor and it is defined as the ratio between the radiation incident on the
inclined surface to the horizontal surface.
ρ = reflection coefficient of the ground and it is considered as 0.2 for normal ground surface
and 0.6 for snow covered ground.
r = reflected rays. The reflected rays comes mainly from ground and the surrounding objects.
3

Tilt factor for beam radiation is given by:
'
cos
cos
b N i
b
b N z
I I
R
I I


 
Tilt factor for diffuse radiation depends on the diffuse radiation falling on the inclined
surface. Based on the radiation view factor following correlation is considered to calculate
the Rd & Rr
1 cos
2
d
R



1 cos
2
r
R



The ratio of solar energy incident on a surface to horizontal surface is given by:
' b b d d
T
r
b d b d
I R I R
I
R R
I I I I


  
 
4

Estimation of Average Solar Radiation
Estimation of monthly average daily radiation is important for
designing of solar system.
The ratio of monthly average daily radiation to clear sky radiation for
a given location is given by (Angstrom Correlation):
' '
c
H n
a b
H N
 
Where aʹ, bʹ = Empirical constants depends on the location
c = clear sky
𝑛 = monthly average daily hours of bright sunshine
𝑁 = monthly average of maximum possible daily hours of bright sunshine (day length of
average day of month)
Hourly radiation : I
Daily radiation : H
Monthly average daily solar
radiation: 𝐻
Monthly average daily radiation based on the extraterrestrial radiation is given by:
o
H n
a b
H N
 
It is also called as monthly average clearness index.
5

Estimation of Clear Sky Solar Radiation
 The solar radiation varies due to the effect of atmosphere scattering and absorption.
 The clear sky solar beam radiation may be calculated using atmospheric transmittance and it
is given by:
cnb ext b
I I 

The clear sky solar beam radiation on horizontal surface is given by:
cos
cb ext b z
I I  

0 1 exp
cos
b
z
k
a a


 

   
 
Where τb = atmospheric transmittance for beam radiation and it may be written as:
Where a0, a1 and k are constants for the standard atmosphere with 23 km visibility.
6

 Energy efficient Solar building
• Heating , cooling and lighting load can be reduces.
• Use of Renewable Energy for Artificial lighting and hot water supply
I = Reflectivity (R)+Absorbity (A)+Transitivity (T)
1 =
𝑅
𝐼
+
𝐴
𝐼
+
𝑇
𝐼
= α+ρ+τ
ρ – can be increased by colouring of the surface (say up to 0.8 to 0.95)

Introduction to Building SolarArchitecture:
Outline
 Introduction
 Purpose of Buildings
 Thermal Performance of Buildings
 Visual Performance of Buildings
4
» Thermal Comfort
» Psychrometric Chart
» Optimizing energy use for thermal
comfort
» Climate
» Internal loads
» Building Heat Transfer
» Mass Transfer
» Passive Strategies
» Active Strategies
» Light basics
» Visual Comfort
» Optimizing energy use for
visual comfort
» Climate
» Passive Strategies
» Active Strategies

 Building Solar Architecture
 Analysis of the state and operation of the building envelope
 Hygrothermal, acoustical and light related properties of building components
(roofs, facades, windows, partition walls, etc.), rooms, buildings and
building assemblies
 Essential for designing, constructing and operating high-performance
buildings
5
 Advantages of Building Solar Architecture
 No external energy is used
 No electricity is used to operate any

 Purpose of Buildings
PhysicalProcesses
• Heat Transfer
• Moisture Transfer
• Air (mass) Transfer
• Light Transfer
Occupant Comfort
Thermal comfort
Visual comfort
Acoustic comfort
Air quality
BuildingEnvelope
• Walls
• Roofs
• Fenestration
• Foundations
6

 Main Approaches to Solar Architecture Buildings
 Natural base building as collection cum storage
 Passive heating and cooling concept
 Natural day light
 Solar PV and solar hot water supplies
 Choice of the building materials
 Building envelope
Roof
Walls
Window/Doors
Floor

 Passive Solar Buildings
 Passive Solar Design
Passive solar design refers to the use of the sun’s energy for the heating and cooling
of living spaces by exposure to the sun. When sunlight strikes a building, the building
materials can reflect, transmit, or absorb the solar radiation.
In addition, the heat produced by the sun causes air movement that can be
predictable in designed spaces. These basic responses to solar heat lead to design
elements, material choices and placements that can provide heating and cooling
effects in a home.
Unlike active solar heating systems, passive systems are simple and do not involve
substantial use of mechanical and electrical devices, such as pumps, fans, or
electrical controls to move the solar energy.

 Passive Solar Heating
• The goal of passive solar heating systems is to capture the sun’s heat within the
building’s elements and to release that heat during periods when the sun is absent, while
also maintaining a comfortable room temperature.
• The two primary elements of passive solar heating are south facing glass and thermal
mass to absorb, store, and distribute heat. There are several different approaches to
implementing those elements.
 Passive Solar Cooling
• Passive solar cooling systems work by reducing unwanted heat gain during the day,
producing non-mechanical ventilation, exchanging warm interior air for cooler exterior
air when possible, and storing the coolness of the night to moderate warm daytime
temperatures.
• At their simplest, passive solar cooling systems include overhangs or shades on south
facing windows, shade trees, thermal mass and cross ventilation.

In passive solar building design, windows, walls, and floors are made to collect,
store, reflect, and distribute solar energy in the form of heat in the winter and reject
solar heat in the summer. This is called passive solar design because, unlike
active solar heating systems, it does not involve the use of mechanical and electrical
devices.

 Elements of Passive Solar Heating

 Non-Air Conditioned Building
• Investigation of the thermal behaviour of a non-air conditioned building with
walls/roof being exposed to periodic solar radiation and atmospheric air while
the inside air temperature is controlled by an isothermal mass, window and door
in the walls of the room.
• The thermal design of a building for efficient heating/cooling embraces a large
number of factors that affect the energy balance and hence the energy
consumption.
• Since the role of various design and climatological parameters in predicting the
thermal behaviour of a building is too intricate to be assessed independently, it is
desirable to develop comprehensive models which include all the important
factors and enable one to indicate the effect of different factors over the building
performance.
• So the solar thermal modelling of buildings has attracted a great deal of attention
from scientists and engineers all over the world.

• Accurate prediction and estimation of the heating/cooling load of a building
exposed to solar radiation and atmospheric air is a problem of practical interest
in the thermal design of buildings and minimizing the capacity (and hence capital
cost) of the associated air conditioning plant.
• The classical way of evaluating the thermal behaviour of a building is based on
the assumption of static (equilibrium) conditions, viz. neglecting the periodicity
of solar radiation, ambient air temperature, wind speed and the air humidity.
• Here the TIME DEPENDENT PERIODIC HEAT TRANSFER model for predicting the
thermal performance of a non-air conditioned building for evaluating the overall
heat flux entering from the walls and roof into the room, and the inside air
temperature.
• The outer surfaces of the walls/roof are assumed to be exposed to periodic
variations of solar intensity and ambient air temperature while the inner surfaces
in contact with the variable room air temperature.

 PERIODIC HEAT TRANSFER ANALYSIS
The heat balance of a non-air
conditioned building is influenced by
• (i) climatological factors, i.e. the
environmental variables like solar
radiation and ambient air
temperature, etc. which may be
assumed to be periodic functions of
time on a daily cycle; and
• (ii) design factors which are under
human control and can be used to
maximize energy conservation and
thermal comfort inside the building.
Consider a building room of rectangular shape based on
the ground and having an ordinary glass window on the
south facing wall of the room .

•For the sake of simplicity in the analysis the following
reasonable assumptions are made:
(i) All the four vertical walls are of identical material and the same thickness.
(ii) Heat flow in the walls/roof is always transverse to their surface area.
(iii) The thermo physical properties of the walls/roof are constant and homogeneous.
(iv) The inside air temperature is uniform in space throughout the room as a whole.
(v) The heat given off by human beings, electric appliances and any other mechanical
sources is negligible.
(vi) As time needed for the window to reach equilibrium is short compared to any
other time scale in the problem, a steady state is assumed for the heat transfer
through the window.

(vii) All furnishings are assumed to be equivalent to an isothermal mass
inside the room.
(viii) Since the solar radiation, ambient air temperature and hence the sol-
air temperature are periodic functions of time on a daily cycle, the
temperature distribution in the wall/roof, ground, isothermal mass and
inside air temperatures can also be assumed to be periodic functions of time.
(ix) It is also assumed that due to the air leakage, opening of the
door/window and other air losses a fixed number of air changes per hour
would occur.
(x) The outside air temperature for all the walls/roof is same which is fairly
true for a building of moderate height.

• The temperature distribution in the walls/roof is characterized by the one dimensional
Fourier heat conduction equation
(1)
A. Periodic heat flux through walls/roof
• where αj( = Kj/ρjCj) is the thermal diffusivity of the jth wall/roof material. Assuming
the periodic variation for Tj( x,t ).
and m is an integer.

B. Heat balance for the inside air
• The heat balance for the internal air is composed of various components, viz. heat flux
coming into the room through walls and roof, isothermal mass, heat conduction in the
basement ground, air infiltration and ventilation, difference in relative humidity
between inside and outside and direct decomposition of solar radiation through
windows, etc.
The equation for the temperature of the inside air is given by
(7)
• where the L.H.S, of the equation represents the change in the heat content of the inside
air, Ma is the total mass and Cair is the specific heat capacity of the dry air at constant
pressure, and the R.H.S. represents the balance of various heat transfer rates to or from
the inside air to the walls/roof (QT), window (Qw), outside air via ventilation and
infiltration (Qv) isothermal mass (Qs) and ground (QG), respectively which are given as
follows:

(c) Heat transfer through window: It is not easy to examine the actual heat transfer through
windows. For the sake of simplicity, it is assumed that the heat capacity and absorptivity of the
window glass is negligible and hence a steady state heat transfer approach can be used for the
present purposes.
The energy transfer rate through the closed glass window can be written as
where the first term represents the direct absorption of solar radiation transmitted through
the south-facing window and the second term is 'the net convection-radiation heat transfer
loss through the window. It must be mentioned here that in the absence of a window Qw=O
and equation (15) is applicable only to a closed window. In the case of an open window the
first term remains as such with T~ = 1.0 and the second term vanishes.

Furthermore, the opening of the window increases the number of air changes per hour which
has been included in the air ventilation and infiltration term.
(d) Heat loss due to air ventilation and infiltration: The effect of the air ventilation and
infiltration (including the moisture and air volume changes) is given by
where η is the number of air changes per hour due to the door ventilation and ηo is the
number of air changes occurring due to the opening of the window, ∆H is the latent heat
due to the difference in relative humidity and dry bulb temperature of the outside and
inside air and given by the numerical expression.
AH = ARH(2463)+ 1*88Tair(t)-TA(t) (16b)
(16a)

Therefore, the net heat balance for the internal air of the room is
The solar intensity and ambient air temperature are periodic in nature and hence
can be represented as

and i represents the site of the window.
Similarly, the temperatures of the inside air and the isothermal mass have been assumed to
be periodic in the following manner

• Substituting equations (2), (4) and (18) in the boundary conditions (3) and (5), we
get
and

Therefore, the solutions of above equations yield the co-efficients bo and bm, of inside air
temperature and do and dm, of isothermal mass temperature as below:

Thus the periodic heat flux entering the room from the jth surface may be written as:

Solar architecture new ppt

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