8 12 16 20 24 Time(Hrs) January 2009 Fig.21 Indoor temperature variation in RCC and PCM rooms January 2009 0 4 8 12 16 20 24 Time(Hrs) February 2009 Fig.22 Indoor temperature variation in RCC and PCM rooms February 2009 1) The document discusses the development of novel roof structures for thermal comfort and energy savings in buildings, with a focus on structures with and without phase change materials (PCMs). 2) It outlines the theoretical simulation and modeling analysis conducted

1. Development of novel roof structures
for thermal comfort and energy
savings in buildings with and without
PCM’s

2. Overview
 Development of novel methods for energy
generation, utilization, storage and conservation
has been a matter of concern among researchers
for many years.
 The technologies in the area of energy storage
and conservation in buildings are being gaining
increased attention over the years.
 A technology that can be used to store large
amounts of heat or cold in a definite volume is a
matter of concern among the researchers around
the world.
 Sensible heat storage systems have been
practiced for so many years.

3. Overview
 Energy conservation through energy storage in
buildings has become an exciting and attracting
method for domestic, industrial and commercial
sector applications.
 Reducing the dependency on fossil fuels in view
of the threat of their depletion in another five to
ten decades has really made the researchers to
find the ways and means to develop the
sustainable energy dwellings with the use of
PCM’s.
 In this work it is aimed to attempt on the
development of novel roof structures with and
with out phase change materials(PCM’s) for
building applications.

4. Overview
 In view of the above, the present work is focused
on feasibility of developing novel roof structures
for thermal comfort and energy savings in
buildings with and with out phase change
materials(PCM’s).
 In
India
cooling
of
buildings
consume
considerable amounts of energy due to the
climatic conditions. Sensible heat storage(SHS)
has been used since prehistoric times.
 To overcome some of the inherent problems with
sensible heat storage systems such as excessive
mass and undesirable temperature excursions
during and prolonged periods of high and low
ambient temperatures.

5. Overview
 To overcome the above mentioned problems the
use of phase change materials(PCMs) as latent
heat storage(LHS) medium in buildings began to
receive serious consideration in the last two
decades.
 These materials absorb heat in changing from
the solid to liquid state and release it as they
change in the opposite direction.
 Latent heat storage in a phase change
material(PCM) is very attractive because of its
high-energy storage density and its isothermal
behaviour during the phase change process.

6. Overview
 Thermal storage plays a major role in building
energy conservation which is greatly assisted by
the incorporation of latent heat storage in
building products.
 Increasing the thermal storage capacity of a
building can enhance human comfort by
decreasing the frequency of internal air
temperature swings so that the indoor air
temperature is closer to the desired temperature
for a longer period of time.

7. Aim of the paper
Based on the above background in this paper
1. Attempt is made to study the thermal
performance of the two roof structures i.e., a
simple RCC roof and a PCM integrated roof
and the feasibility of other two proposed roof
structure models.
2. The theoretical simulation results obtained
for RCC and PCM roof using Ansys 10 are
validated by comparing the
experimental
results.

8. Aim of the paper
3. To study the influence of solar flux on the
indoor temperatures, thermal flux, thermal
gradient and the heat flow across the RCC
and PCM roofs.
4. Validating the theoretical results with the
experimental data and to draw the
conclusions and making suggestions and
recommendations based on the findings.

9. Literature review
Literature review

The earlier works done by the researchers
L.E.Bourdeau[1], P.Braousseu et al[2], R.Velraj
et al[3] and A.Pasupathy et al[4] were focussed
on theoretical simulations on the use of
PCMs(small blocks of 50mmx50mm size) for
passive thermal storage for heating and cooling
of buildings.

Most of the works were carried out on
heating applications. In India heating is never a
problem. Some of the works were limited to
provide only the temperature distribution
analysis for the small sample models of PCM
blocks.

10.  In view of the above literature review, in the
present work a computer simulation and
modeling using Ansys 10 software which
provides the complete analysis for the two
modeled roof structures (2mx2m in area).
 The experimental validations made with the
simulation results for the two models is seem to
be promising.
 In this work, an attempt is made to study the
effect of phase change materials(PCMs) on the
indoor room temperatures of a residential
building.

11.  A comparative study on the thermal
performance
of
an
inorganic
PCM(CaCl26H2o) as phase change
material has been carried out both
experimentally
and
through
a
simulation study using Ansys Software
version 10.

12. Theoretical simulation and modeling analysis
using Ansys10
RCC
12 cm
Fig.1 simple RCC roof
Roof Top slab
10 cm
PCM Panel
Concrete Slab (RCC)
2.5 cm
12 cm
Fig.2 PCM integrated roof

13. SUN
Wind
Radiation
Convection
Roof top (brick mixture + lime)
PCM Panel
Concrete Slab
Fig.3 Modeled PCM integrated roof

14. MATERIAL PROPERTY DATA
Material
Density
(kg/m3)
Thermal
conductivity
(W/mK)
Specific Heat
(J/kg K)
Concrete
slab(RCC)
2300
1.279
1130
Roof top slab
(mixture of
brick + lime)
1300
0.25
800
Phase change
material
(PCM)
CaCl26H20
1500
1.01
1440
Latent heat of
PCM(KJ/kg)
188

15. TECHNICAL SPECIFICATIONS OF USED PCM
PCM material
Appearance (color)
Phase change temperature (0C)
Density (kg/m3)
Latent heat of fusion (kJ/kg)
Thermal conductivity (W/mK)
Solid
[0-29 0C]
Liquid
[ 29 – 600C ]
Specific heat (J/kg K)
( 0 – 290C )
( 290C – 300C )
(300C – 600C )
:CaCl26H20
:Grey
: 290C
: 1500
: 188
: 1.09
: 0.54
:1440
:125,000
:1440

16. ASSUMPTIONS MADE
The following assumptions are made in the
analysis.
The heat conduction in the composite wall is one
dimensional and the end effects are neglected.
The thermal conductivity of the concrete slab and
the roof top slab are considered constant and not
varying with respect to temperature.
The PCM is homogenous and isotropic.
The convection effect in the molten PCM is
neglected.
The interfacial resistances are negligible.
The material properties are constant
Radiation heat exchange with in the room is
neglected
 The thermo physical properties of the PCM are
different for the solid and liquid phases but are
independent of temperature.

17. PROBLEM FORMULATION
 The physical system considered is a galvanized
iron panel filled with PCM placed between the roof
top slab and the bottom concrete slab, which form
the roof of the PCM room.

In
each
cycle,
during
the
charging
process(sunshine hours), the PCM in the roof
changes its phase from solid to liquid.
 As melting requires a large quantity of heat at its
phase change temperature, the temperature of the
concrete slab normally will not exceed the PCM
phase change temperature.
 During the discharging process(night hours), the
PCM changes its phase from liquid to
solid(solidification) by rejecting heat to the
ambient and to the air inside the room. This cycle
continues every day.

18.  The composite wall described in the above Fig. is
initially maintained at a uniform temperature.
 The boundary condition on the outer surface of
roof is considered due to the combined effect of
radiation and convection.
 In order to consider the radiation effect, the
average monthly solar radiation heat flux
data(measured values) for every 1-h in
Pulivendula town, A.P, India is used.
 For convection, the heat transfer coefficient(h0)
on the outer surface is calculated based on the
prevailing velocity of wind using Nusselt
correlation[NuL=0.664(ReL)0.5(Pr)0.33] and the inner
surface is considered having natural convection
inside the roof [NuL=0.54(Gr.Pr)0.25]

19.  Using these two correlations the local heat transfer
coefficients are calculated. However, in the
theoretical analysis the heat transfer coefficients
are assumed as 10W/m2 and 5W/m2 at outside and
inside the roofs respectively.
 The boundary condition on the inner surface of the
concrete slab is considered to be natural
convection.
 As the temperature difference between the room
and the wall is very less, most of the earlier
researchers have approximated the bottom wall as
insulated. However, when the temperature
difference becomes appreciable, the effect of heat
flow is considerable and hence this convection
effect is also taken into account in the present work
with
a
suitable
Nusselt
correlation
[NuL=0.54(Gr.Pr)0.25]

20. Ansys 10 software

ANSYS 10 is a general purpose finite element
analysis (FEA) software developed to solve the
problems of both structural and thermal
streams.

It is an user-friendly software that can be
used for modeling the building roof structures
and besides providing the complete thermal
analysis such as variation of temperature
distribution, thermal gradient, thermal flux, heat
flow across the roof etc.,

For comparing the theoretical simulations
obtained using Ansys software, two experimental
identical test rooms have been constructed and
the performance of both have been analysed.

21. MATHEMATICAL EQUATIONS AND METHODS FOR LHTES
The
latent
heat
thermal
energy
storage
systems[LHTES] have been developed for the
applications of cooling and heating of buildings and
for many other applications.
To carryout the theoretical and thermal
performance analysis of such type of systems
invariably require a mathematical model or a
computer simulation software.
The following governing equations and boundary
conditions for one-dimensional
heat transfer
through the two roof models were used.

22. 
In the present research work, a computer
simulation software FEA Ansys version 10.0 is
used to solve the two modeled roof structures.
 Governing Equation used
kmð2 Tm = ρm cpm ð Tm
ð x2
[ 0< x<L] ; m = 1, 2, 3
ðt
where m = 1 for roof top slab
m = 2 for PCM panel
m = 3 for bottom concrete slab.

23. 
The same equation holds good for all the
three material regions by incorporating suitable
k, ρ, cp. In the exterior boundary where the floor is
exposed to solar radiation, the boundary
condition is,
k1 ðT1 / ðx|x=0 = q

rad
+ h0 ( Ta- Tx=0 )
The radiation effect is considered during
sunshine hours. In the bottom layer of the
concrete slab x = L the boundary condition is,
k3 ðT3 / ðx|x=L = hi (Tx=L – T room )

24.  The governing equations may be
either solved by
i) Finite volume method
ii) Finite difference method
(Crank-Nicholson method)
iii) Finite element method
or by using a computer simulation
softwares such as FEA ANSYS, MATLAB

25. TYPES OF ROOFS MODELED AND
PROPOSED

Roof -1(a) RCC Simple RCC roof
(concrete slab) 12 cm thick

Roof -1(b) PCM integrated Roof : PCM Panel
of 2.5 cm thick placed between
RCC (12cm
thick) and Roof top
slab(mixture of broken
bricks + lime
mortar) 10 cm thick.

Roof – 2 A corrugated roof structure with
air gap in the middle and insulated at the
bottom.

Roof – 3 a) A simple RCC b) RCC with WC
c) RCC with Hollow Clay Tile – no air flow
d) RCC with Hollow clay tile with air gap and
free flow of air.

26. Fig.4&5 Mesh generation for RCC(right) and PCM roofs(left)

27. 700
solarflux
Solar flux( W/m2)
600
500
400
300
200
100
0
0
2
4
6
8
10
12
14
16
18
20
22
24
Time (Hrs)
Fig.6 Solar flux for the month of January 2009

28. Fig.7 Two identical Experimental Test rooms(8ftx4ftx4ft) one with out
PCM panel and another with PCM panel
Constructed at JNTU College of Engineering, Pulivendula

29. Fig.8 Digital indicator with thermocouples for the
measurement of temperature across the two roofs

30. Results and discussion
Fig.9 Temperature distribution across the RCC roof at
13hr January 2009

31. Results and discussion
Fig.10 Temperature distribution across the PCM roof at 13hr
January 2009

32. roof top
roof bottom
roof middle
ambient
roof top
50
ambient
16
24
50
Temperature(0C)
Temperature(0C)
roof middle
60
40
30
20
10
40
30
20
10
0
0
0
4
8
12
16
20
24
Time(Hrs)
Fig.11 Temperature Distribution across the RCC
roof January 2009
roof top
roof bottom
0
4
8
12
roof bottom
20
Time(Hrs)
February 2009
January 2009
Fig.12 Temperature Distribution across the RCC
roof February 2009
roof top
ambient
roof bottom
roof middle
ambient
60
60
50
Temperature(0C)
50
Temperature(0C)
roof bottom
40
30
20
40
30
A
20
10
10
0
0
0
4
8
12
16
20
24
Time(Hrs)
March 2009
Fig.13 Temperature Distribution across the RCC
roof March 2009
0
April 2009
4
8
12
16
20
24
Time(Hrs)
Fig.14 Temperature Distribution across the RCC
roof April 2009

33. roof top
roof bottom
roof middle
ambient
roof top
Temperature( 0C )
50
40
0
PCM panel
ambient
60
60
Temperature ( C)
roof bottom
30
20
10
50
40
30
20
10
0
0
0
4
8
12
16
20
0
24
4
8
12
16
20
24
Time(Hrs)
Time(Hrs)
May 2009
January 2009
Fig.15 Temperature Distribution across the RCC
roof May 2009
Fig.16 Temperature Distribution across the PCM
roof January 2009
roof top
roof top
roof bottom
PCM panel
roof bottom
PCM panel
ambient
ambient
70
60
60
Temperature( 0C)
Temperature (0C)
50
40
30
20
10
50
40
30
20
10
0
0
0
4
8
12
16
20
24
0
4
Time (Hrs)
February 2009
Fig.17 Temperature Distribution across the PCM
roof February 2009
March 2009
8
12
16
20
Time(Hrs)
Fig.18 Temperature Distribution across the PCM
roof March 2009
24

34. Results and discussion
roof top
roof bottom
PCM panel
ambient
roof top
PCM panel
ambient
50
Temperature(0C)
60
50
Temperature(0C)
60
roof bottom
40
30
20
40
30
20
10
10
0
0
0
April 2009
4
8
12
16
20
Time(Hrs)
Fig.19 Temperature Distribution across the PCM
roof April 2009
24
0
May 2009
4
8
12
16
20
Time(Hrs)
Fig.20 Temperature Distribution across the PCM
roof May 2009
24

35. Results and discussion
RCC room
PCM room
ambient
RCC room
40
30
35
Temperature(0C)
45
35
ambient
50
40
Temperature(0C)
45
PCM room
25
20
15
10
30
25
20
15
10
5
5
0
0
0
4
8
12
16
20
Time(Hrs)
Fig.21 Experimental Temperature variation in
the ceiling (roof bottom) January 2009
24
0
4
8
12
16
20
Time(Hrs)
Fig.22 Experimental Temperature variation in
the roof top slab January 2009
24

36. Results and discussion
Sim PCM
Exp.Ceilg
Ambient
Sim Ceilg
Exp PCM
42
Temperature(0C)
36
30
24
18
12
0
4
8
12
16
20
Time(Hrs)
January 2009
Fig.23 Comparison of Experimental and Simulated Temperature variations in the
ceiling of RCC and PCM rooms January 2009
24

37. Results and discussion
50
45
0hr
4hr
Temperature ( 0C)
40
6hr
8hr
35
10hr
12hr
30
14hr
16hr
25
18hr
20hr
20
Roof top slab
PCM panel
RCC(Ceiling)
15
0
1
2
3
Fig.24 Temperature variation across the roof of PCM room
January 2009

38. Results and discussion
36
34
0hr
Temperature(0C)
32
4hr
30
6hr
10hr
28
12hr
14hr
26
18hr
24
20hr
22
20
0
0.2
0.4
0.6
0.8
1
RCC slab thickness (Y*)
Fig.25 Temperature variation across the roof of RCC room January 2009

39. Results and discussion
80
0hr
70
4hr
Heat Transfer(W)
60
6hr
8hr
50
10hr
40
12hr
14hr
30
16hr
18hr
20
20hr
10
24hr
0
0
January 2009
0.2
0.4
0.6
0.8
1
Y*
Fig.26 Heat transfer variation across the roof of RCC room
January 2009

40. Results and discussion
60
0hr
Thermal gradient(dT/dx)
50
4hr
6hr
40
8hr
10hr
30
12hr
14hr
16hr
20
18hr
20hr
10
24hr
0
0
January 2009
0.2
0.4
0.6
0.8
1
Y*
Fig.27 Thermal gradient variation across the roof of RCC room January
2009

41. Results and discussion
300
0hr
Thermal gradient(dT/dx)
250
4hr
6hr
200
8hr
10hr
150
12hr
14hr
16hr
100
18hr
20hr
50
24hr
0
0
0.2
January 2009(PCM)
0.4
0.6
0.8
1
Y*
Fig.28 Thermal gradient variation across the roof of PCM room
January 2009

42. Results and discussion
70
0hr
60
4hr
6hr
Heat transfer(W)
50
8hr
10hr
40
12hr
30
14hr
16hr
20
18hr
20hr
10
24hr
0
0
0.2
January 2009(PCM)
0.4
0.6
0.8
1
Y*
Fig.29 Heat transfer variation across across the roof of PCM room
January 2009

43. Results and discussion
105
90
0hr
4hr
Heat Transfer( W )
75
6hr
8hr
60
10hr
12hr
45
14hr
16hr
30
18hr
20hr
15
0
0
March-2009
0.2
0.4
0.6
0.8
1
Y*
Fig.30 Heat transfer variation across the roof of PCM room
March 2009

44. Results and discussion
400
Thermal Gradient ( dT/dx)
350
0hr
300
4hr
6hr
250
8hr
200
10hr
12hr
150
14hr
16hr
100
18hr
20hr
50
0
0
March-2009
0.2
0.4
0.6
0.8
1
Roof top thickness(Y*)
Fig.31 Thermal gradient variation across the roof of PCM room
March 2009

45. Results and discussion
140
Heat flux, W/m2 day
120
100
80
60
40
20
0
RCC
PCM
Fig.32 Comparison of Heat flux entering the RCC and PCM
rooms January 2009

46. Results and discussion
Heat Flux entering the room
350
Heat flux W/m2- day
300
250
200
150
100
50
0
RCC room
PCM room
Fig.33 Comparison of Heat flux entering the RCC and PCM
rooms March 2009

47. Effect of various parameters on the
performance of the PCM roof
Wind Speed m/s
h value W/m2 K
50
Temperature( 0C)
7
6
5
4
3
2
40
Ambient
PCM panel
30
roof top
20
ceiling
10
1
0
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
0
Fig.34 Variation of heat transfer coefficient with
wind speed
0
4
8
12
16
20
24
Time (Hrs)
Fig.35 Effect of PCM Panel thickness for 3cm and
3.5cm

48. 90
80
70
60
50
40
30
20
10
0
r=20mm
r=25mm
r=30mm
r=40mm
r=50mm
r=60mm
60
180 300 420 540
Melting time(min)
Fig.36 Melt fraction of the capsule for various
capsule radii
% Solid fraction
% Melt fraction
Effect of various parameters on the
performance of the PCM roof
90
80
70
60
50
40
30
20
10
0
r=20mm
r=25mm
r=30mm
r=40mm
r=50mm
r=60mm
60
180
300
420
540
Time(min)
Fig.37 Solid fraction of PCM for various radii

49. Effect of various parameters on the
performance of the PCM roof
solar flux w ith reflective coatings
solar flux w ith out reflective coatings
700
Solar flux W/m
2
600
500
400
300
200
100
0
1
2
3
4
5
6
7
8
9
10
Time (Hrs)
Fig.38 Effect of reflective coatings on incident solar flux
11

50. Effect of various parameters on the
Proposed Roof Structure-II
performance of the PCM roof
Solar Reflective
surface coatings
PCM
Air gap
Insulation
Figure.Corrugative PCM integrated roof with air
gap at the middle and insulation at the bottom
Fig.39 A Corrugative PCM integrated roof with air gap at the
middle and insulation at the bottom

51. Proposed Roof Structure-III
Fig. 40. Roof structures for investigation (uniform width of 75 mm) (material: 1-RCC, 2-WC, 3-HCT, 4-air).

52. Conclusions
 Several promising developments are taking place in
the field of thermal storage for thermal comfort and
energy savings using PCMs in buildings.
 In the present work investigations have been carried
out experimentally to study and analyze the thermal
performance of the roof of a building incorporating
PCM for thermal comfort and energy savings in a
residential building. The other two models were
presented as proposed roof structures.
 Two models were used and the theoretical
performance of both is compared by considering one
as the reference case. Several simulation runs were
made using this model for the average ambient
conditions that prevail at Pulivendula town, A.P

53. 
The various parameters that affect the
performance of PCM integrated roof are wind
speed, PCM panel thickness, capsule size,
reflective roof coatings.

A PCM integrated roof has the potential to
maintain a fairly constant temperature inside the
room due to its large heat absorbing and storing
capacity in a passive manner.

Where as the ceiling temperatures always
fluctuate in a Non-PCM room(RCC room)
throughout the day.

It is observed from the analysis that the
ceiling temperatures in the Non-PCM room
fluctuate between 210C and 360C(simulated), 210C
and 350C (experimental).

54. 
The heat flux entering the Non-PCM room is
observed to be 312W/m2 . On the other hand,
in the PCM room the ceiling temperatures are
maintained
at
a
constant
value
of
280C(simulated) throughout the day and
28 (+/_) 30C(experimental).

The heat flux entering the PCM room is
estimated as 84W/m2 . The roof integrated with
PCM is noticed to be better than the RCC roof
in terms of less transfer of heat into the room
due to the incident solar heat flux during the
day time.

The roof installed with PCM can reduce the
heat entering the room about more than twothirds as compared to that of RCC laid roof.

55. 
A reduction of 73.1% of heat transmission is
observed with the PCM roof as compared to the
RCC roof.

It is quite evident from the preceding studies
that the thermal improvements in a building due
to the inclusion of PCMs depend on the ceiling
temperature of the PCM, large latent heat
storage capacity and thermo-physical properties
of the PCM.

The reduction in heat transmission in to the
room
is
directly
proportional
to
the
corresponding reduction in the cooling load in
case of an air-conditioned building or reduction
in the fluctuation of inside room temperatures in
case of a non air-conditioned building.

56. 
Therefore it is observed that a reduction in
power consumption required to maintain the
room at any desired temperature with in the
human comfort temperature limits.
 For the latent heat thermal storage(LHTS)
systems are to be commercialized, it is
necessary to go for experimentation.
 Careful design and development is needed for
use in residential buildings in the near future to
replace conventional A/C systems completely
with an exception of maintaining required levels
of R.H(Relative Humidity).
 The thermal storage systems with PCM will be
useful for those regions of India where the
temperatures exceed 400C in summer.

57.  It is concluded that for the purpose of
narrowing indoor air temperature swing a
PCM incorporated in the roof of a building is
suggested and recommended.
 The other two proposed roof structure
models may be developed in near future for
thermal comfort and energy savings in
buildings with simulations followed by
experimentations.