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CHAPTER 2 LITERATURE SURVEY -...
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CHAPTER 2
LITERATURE SURVEY
2.1 INTRODUCTION
Air conditioning plays a major role in maintaining the comfortable
condition for human beings in the living space. A very large amount of
electrical energy is consumed for this purpose and sometimes it is found to be
difficulty in satisfying the summer peak electrical demand. Therefore,
increasing the thermal storage capacity of a building can increase human
comfort by decreasing the magnitude of internal air temperature swings. A
thermal storage unit using Phase Change Materials (PCMs) can be
incorporated in the building element to reduce the thermal load and also to
minimize the cost of the conventional cooling system. In this context, the
present chapter reviews the various studies that are carried out related to
natural cooling of building in the recent time. Thus, the focus is on natural
cooling of building using the phase change materials. Section 2.2 deals with
the simulation studies and numerical methods used for analysis of natural
cooling of building spaces. In section 2.3, various experimental and
theoretical studies are reviewed. Studies on various analytical methods that
are used for natural cooling are presented in section 2.4. This chapter ends
with conclusions arrived out of this review and objectives of the present
research work.
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2.2 STUDIES USING SIMULATION TOOLS
Numerical tools are used to analyze the heat transfer and fluid flow
character using the computer simulation programmes.
Peippo et al (1991) have numerically tested the thermal
performance of a PCM wall in the residential application in Madison,
Wisconsin (43°N). The results indicated that a phase change temperature of 1-
3 °C above the average room temperature would yield optimal diurnal heat
storage and found that direct energy savings of 5-20 % could be possible, but
depending on climate. Manuel Ibanez et al (2005) presented and validated a
methodology for the energetic simulation of building elements with PCM,
using the TRNSYS program. This was used to evaluate the influence of walls,
ceiling and floor with PCM in the whole energy balance of a building. The
key parameter in the simulations is the equivalent heat transfer coefficient
which has to be determined for each material.
Na Zhu et al (2010) developed and validated a physical model of
building structures integrated with Shaped-Stabilized Phase Change Material
(SSPCM). The parameters of the simplified model are identified using
Genetic Algorithm (GA) on the basis of the basic physical properties of the
wall and PCM layer. Validation results show that the simplified model can
represent light walls and median walls that are integrated with SSPCM with
good accuracy. Na Zhu et al (2011) have recently conducted simulation
studies in an office building to investigate the impact of SSPCM under two
different weather conditions. Through these conditions, the air-conditioning
system and other configurations of the building remain unchanged. The test
results show that reduction of building electricity costs by 11 % and 20 %
during peak load energy consumption.
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Ghoneim et al (1991) studied the performance of collector storage
walls, using masonry and PCM and the effect of thermal properties of phase
change materials on the performance of collector storage walls. Esam et al
(2011) have very recently tested the thermal effectiveness of a building roof
that consists of a concrete slab with vertical cone frustum holes filled with
PCM. A parametric study is conducted to assess the effects of the cone
frustum geometry, and the same PCM is used. The results have indicated that
the heat flux at the indoor surface of the roof can be reduced up to 39 % for a
certain type of PCM and geometry of PCM cone frustum holes.
Markus Koschenz and Beat Lehmann (2004) developed a
numerical model for computation of the thermal behaviour of wall and ceiling
systems by incorporating PCMs as shown in Figure 2.1. By means of
simulation calculations and laboratory tests conducted, 5 cm layer of
microencapsulated PCM (25 % by weight) and gypsum are sufficient to
maintain a comfortable room temperature in standard office buildings.
Figure 2.1 Thermally activated ceiling panel with PCM (Markus
Koschenz and Beat Lehmann 2004)
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Kousksou and Bruel (2010) numerically examined a storage system
formed by a cylindrical tank, randomly packed with paraffin as phase change
material. The packed bed was tested for various complex input temperature
signals generated by stochastic differential Langevin equation. The results
obtained for a multi-slab configuration indicated that it was possible to
maximise the energy storage by properly selecting and ordering the different
PCMs in the bed. Chan (2011) has just investigated a typical residential flat
modeled with PCM integrated external walls and evaluated the thermal
performance and orientation of the wall by computer simulations. It was
found that west-facing PCM integrated external wall performed better and
interior surface temperature decreased up to a maximum of 4.14 % and annual
energy saving of 2.9 % in air-conditioning system was achieved. But, a long
cost payback period of 91 years makes this model economically infeasible.
Guobing Zhou et al (2009) have investigated the effect of SSPCM
plates as inner linings of walls and the ceiling in a building combined with
night ventilation during summer. The result has shown that the SSPCM plates
could decrease maximum temperature every day by up to 2 ºC due to the cool
storage at night. Guobing Zhou et al (2011 a) have analyzed thermal
performance of hybrid space-cooling system by having thermal storage and
using Shape-Stabilized Phase Change Material (SSPCM) with night
ventilation by using a verified enthalpy model. SSPCM plates are used as the
inner linings of walls and the ceiling of the building. Simulation results have
indicated that it can improve the thermal-comfort level and save day time
cooling energy consumption by 76 %. Guobing Zhou et al (2011 b) have
examined the thermal performance of SSPCM wallboard with periodical heat
flux waves on the outer surface, and have numerically tested and compared
with conventional building materials like brick, foam concrete and expanded
polystyrene. The results have showed that the thermal wave amplitude is
decreased and wave phase is delayed due to the latent heat thermal storage.
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Athienitis et al (1997) conducted an experimental and numerical
study in a full scale outdoor test room with PCM gypsum board as inside wall
lining as shown in Figure 2.2. An explicit finite different model was
developed to simulate the transient heat transfer process in the walls. The
result has shown that PCM gypsum board may reduce the maximum room
temperature by 4 ºC during the day time and also decrease the heating load at
night significantly.
Figure 2.2 Schematic of outdoor test room with PCM gypsum board as
inside wall lining (Athienitis et al 1997)
Dariusz Heim and Clarke (2004) modeled a naturally ventilated
passive solar building by using ESP-r and PCM impregnated gypsum
plasterboard as an internal room lining. The air and surface temperature and
the energy requirement at the beginning and end of the heating season were
estimated and compared with PCM case and Non-PCM case. The results have
shown that the solar energy stored in the PCM–gypsum panels have reduced
the heating energy demand by up to 90 % during the heating season. Dariusz
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Heim (2010) examined the thermal behaviour of isothermal heat storage
composites, using ESP-r simulation tool. Numerical simulations were
conducted for PCM-impregnated gypsum plasterboard as an internal room
lining and also for transparent insulation material (TIM) combined with PCM
in the south oriented wall. For both the cases, air temperature and internal
surface temperature are recorded and latent heat storage effect is then
analyzed.
Yuichi Hamada and Jun Fukai (2005) investigated the effect of
carbon fiber brushes which were inserted to improve the heat transfer rates in
the phase change materials, in an air conditioned building as a space heating
resource. The effect of the brushes on the thermal outputs of the tanks was
investigated by using the corrected model and result has thereby shown that
the brushes contribute to save the space for reducing the cost of the tanks.
Muriset et al (2010) modeled a Minergie house and studied the temperature
differences between a Minergie house connected to a storage device and a
house without such a device and optimal solutions were presented and
simulation results were discussed.
Jo Darkwa (2009) designed a laminated phase change concrete duct
system for cooling applications in buildings and numerically analysed the
thermal performance of the system. It was found that the PCM concrete duct
system could be used as a method for minimizing energy consumption in an
air-conditioned building.
Miroslaw Zukowski (2007) designed a mathematical model for a
ventilation duct filled with encapsulated paraffin wax RII-56 to assess the
thermal performance. The interpolating cubic spline function method was
used for determining the effective specific heat and equations for three-
dimensional transient thermal analysis and solved by the control volume finite
difference method with the fully implicit scheme. The influence of the PCM
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capsules geometry on the thermal performance of the tested storage was
analysed.
Halawa et al (2005) discussed the PCM thermal storage unit (TSU)
of a roof integrated solar heating system consisting of several layers of thin
slabs of PCM in which air flows between the slabs. The melting and freezing
of PCM slabs in an air stream was analysed numerically and air outlet
temperatures and heat transfer rates during the phase change process were
discussed. Halawa and Saman (2011) have recently studied the thermal
performance of an air based TSU for space heating. The numerical analysis
was based on an experimentally validated model. A study has been carried out
including the study on the effects of slab thicknesses, air gaps and the air
outlet temperatures and heat transfer rates of the thermal storage unit.
Carbonari et al (2006) tested and compared numerically and
experimentally the performance of two different kinds of PCM containing
sandwich panels for prefabricated walls. The addition of an air layer between
the PCM and the external metal finishing layer was capable of improving the
performance of PCM containing sandwich panels. Kuznik and Virgone (2009)
investigated the optimal value of the PCM wallboard thickness. To calculate
the optimal value, the in-house numerical code CODYMUR was used and the
results had shown that an optimal value was existent according to daily
external and internal temperature fluctuations.
Jianli Li et al (2009) conducted simulation studies to find the
temperature-regulating and cost-reduction effects of Form-Stable Phase
Change Material (FSPCM) as the Thermal Storage Layer (TSL) of an Electric
Floor Heating System (EFHS). A simulation program based on implicit finite
difference scheme was developed to calculate the hourly temperature field of
a model room with the EFHS. A cost-benefit analysis was also carried out to
evaluate the FSPCM in energy efficient buildings.
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Ming JunHuang (2011) has developed a photovoltaic PV/PCM
numerical simulation model for single PCM application and has modified it to
predict the thermal performance of the multi-PCMs in a triangular cell. A
series of the tests of numerical simulations have been carried out to study the
thermal regulation of the modified PV/PCM system in triangular shaped cells
and the use of a range of different phase transient temperature PCMs under
static state and realistic conditions.
Alawadhi (2008) analysed a two-dimensional model that consisted
of a common building brick with cylindrical holes filled with PCM and solved
using the finite element method. A study was conducted to assess the effect of
different design parameters such as the PCM’s quantity, type, and location in
the brick. The results indicated that the heat gained was significantly reduced
when the PCM was incorporated into the brick. PCM cylinders located at the
centerline of the bricks showed the best performance. Xing Jin and Xiaosong
Zhang (2011) have studied the thermal performance of the radiant floor
heating-cooling system by having two layers of PCM with different melting
temperature. The results show when compared to the floor without PCM, the
energy released by the floor with PCM in peak period will be increased by
41.1 % and 37.9 % during heating and cooling when the heat of fusion of
PCM is 150 kJ/kg.
Berroug et al (2011) have analysed the thermal performance of a
north wall made with CaCl2·6H2O as phase change material (PCM) in
east–west oriented greenhouse. A numerical thermal model was designed for
different components of the greenhouse and calculations were done for the
climate of January. The results show that with an equivalent of 32.4 kg of
PCM per square meter of the greenhouse ground surface area, temperature of
plants and inside air were found to be 6–12 ºC more at night during winter
with less fluctuation.
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Francois Mathieu-Potvin and Louis Gosselin (2009) designed a
numerical model to determine the thermal shielding performance of an
exterior wall containing layers of PCMs and optimized with a genetic
algorithm based on yearly analysis. A result showed that the shielding effect
of PCM was likely to be active in the summer but not in the winter and
genetic algorithm was used to identify the best material composition of a wall.
Maha Ahmad et al (2006) analysed a light wallboard containing PCMs
subject to climatic variation and a comparison was made with a test-cell but
without PCMs. A Vacuum Insulation Panel (VIP) was attached to the PCM
panel. An experimental study revealed that the efficiency of PCM was
significant with a reduction of the indoor temperature amplitude which was
approximately 20.8 ºC in the test-cell. A numerical simulation with the
TRNSYS software was carried out and it coincided with experimental results.
Ismail et al (2001) studied numerically and experimentally about
the thermal efficient windows and found that PCM filled window leads to
filtering of thermal radiation and reduced the heat that would be either gain or
loss. The result showed that the double glass window filled with PCM was
effective when compared to the same window filled with air. The
experimental and simulation study had shown that coloured PCM window
was effective in reducing the heat gain.
2.3 STUDIES USING EXPERIMENTAL WORK
Xiaoming Fang and Zhengguo Zhang (2006) prepared a composite
PCM by blending an organic PCM, RT20 with an organic-modified
montmorillonite. The thermal characteristics of the composite PCM were
close to those of the pure PCM and 1500 times heating–cooling cycles’ test
showed that the composite PCM had good performance stability and it could
increase human comfort and cut down the energy consumption by decreasing
the frequency of internal air temperature swings.
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Shanmuga Sundaram et al (2010) experimentally examined thepassive cooling system for telecom shelters installed in tropical and desertregions by using thermosyphon integrated with PCM based Thermal EnergyStorage (TES) system. The newly developed system was found to be highlyefficient for remote areas where there has been no power supply andmaintenance required would be minimum. Hadjieva et al (2000) investigatedthe heat capacity of composite PCM concrete system using sodiumthiosulphate pentahydrate as PCM. The experimental results obtained for thermophysical and structural behaviours of the PCM composite system specified itslimitations and applicability to phase-change thermal storage wallboard.
Nagano et al (2006) designed a small experimental system byhaving floor supply air conditioning system with the help of a granular PCMto improve building thermal storage. A scaled model was constructed for thesystem as shown in Figure 2.3. Step response tests in which the temperatureof air supplied to the under floor space were reduced so as to investigate theheat response of the granular PCM. Results from measurements in officebuildings indicated that 89 % of daily cooling load could be stored each night,when a 30 mm thick packed bed of the granular PCM was used.
Figure 2.3 Granular phase change material floor supply
air- conditioning system (Nagano et al 2006)
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Karlessi et al (2011) have investigated the development and thermal
performance of infrared reflective cool coatings doped with organic paraffin
Phase Change Materials as shown in Figure 2.4, which can be used in the
external facade of buildings i.e. for roofs, walls, and pavements. Thirty six
coatings of six colours, containing different quantities of PCMs in different
melting points were produced and results demonstrated that all PCM coatings
present lower surface temperatures than other coatings and enhance the
thermal inertia.
Figure 2.4 Maximum temperature differences between PCM, common
and cool coatings (Karlessi et al 2011)
Pasupathy et al (2008) conducted the experimental study on roof made of in-
organic eutectic PCM and ordinary roof. The effect of variation in the
ambient condition for all the months, the variation in heat transfer coefficient
on the outer surface of the roof and the PCM panel thickness were studied.
The experiments were conducted to test the possibility of removing the heat
from the PCM slab and the ceiling by circulating water through the PCM
panel and results showed that the quantity of water required was very large
which was not easily available during the summer season. Pasupathy and
Velraj (2008) analyzed the phase change material system for thermal energy
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management in building as shown in Figure 2.5. A mathematical model has
been developed with finite volume method and validated with the
experimental results. The effect of double layer PCM has been analyzed for
year round thermal management and the performance is compared with single
layer PCM and concluded that the indoor air temperature swing is to reduce to
suit for all seasons and hence a double layer PCM incorporated in the roof is
recommended.
Figure 2.5 Double layer PCM for roof cooling (Pasupathy and Velraj 2008)
Cecilia Castellon et al (2010) demonstrated the feasibility of using
a micro-encapsulated PCM in sandwich panels to increase the thermal inertia
and to reduce the energy demand of building. Three different methods were
used for manufacturing PCM sandwich panels. The results showed that some
samples had the effect of the PCM (higher thermal inertia) and another
sample reacted similar to the conventional sandwich panel.
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Frederic Kuznik et al (2008) investigated experimentally to
enhance the thermal behaviour of light weight building in a summer day. A
numerical modeling was used to test the energy storage. A 5 mm PCM
wallboard improved the thermal inertia of the building and stores double the
energy that could be released during the experiment. Frederic Kuznik et al
(2008) tested the thermal performance of a PCM composite wallboard in a
full scale test room. The comparative thermal performance, with and without
PCM wallboards for three different days: a summer day, a winter day and a
mid-season day was evaluated. The results showed that the air temperature in
the room with PCM lowered up to 4.2 ºC. Frederic Kuznik and Joseph
Virgone (2009) made a comparative study, using cubical test cells with and
without PCM composite. A double test cell, MICROBAT, was used to
measure the temperatures and characterized the phase change effects. The
experimental data were compared with numerical data and the results showed
that the melting process arose higher than the solidification process and
hysteresis phenomenon must be taken into account to predict the PCM
composite thermal behaviour. Frederic Kuznik et al (2011) have done the
assessment for a renovated light weight building room equipped with PCM
wallboard in walls and ceilings and the other room with ordinary wallboard
has been monitored for a year. It was found that the thermal comfort in the
room with PCM wall board is enhanced due to both the air temperature and
the radiative effects of the walls and the non-renovated building has lower
inertia.
Parameshwaran et al (2010) experimentally investigated a new
Variable Air Volume (VAV) chilled water-based air conditioning system
combined with the TES system for summer and winter climatic conditions
under Demand Controlled Ventilation (DCV) and DCV combined with the
Economizer Cycle Ventilation (ECV). The results showed that DCV and
combined DCV–ECV system achieved 28 % and 47 % of average energy
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conservation per day compared to the conventional chilled water-based A/C
system.
Lv Shilei et al (2006 a) conducted thermal cyclic test for phase
change wallboards combined with eutectic mixtures of Capric Acid (CA) and
Lauric Acid (LA) using differential scanning calorimetry and the results
showed that the melting temperature and latent heat of these phase change
wallboards did not vary after 360 thermal cycles, which proved that these
phase change wallboards had better thermal stability. Lv Shilei et al (2006 b)
tested and compared the ordinary wall room and phase change wall room for
the winter climate. The effect on indoor temperature, surface temperature of
wall board and heat flow through the wall was studied. They concluded that
the phase change wallboards could improve the indoor thermal environment.
Li Huang et al (2009) studied the paraffin-water emulsion as a
Phase Change Slurry (PCS) for comfort cooling applications in a temperature
range of 0–20 ºC. The stability of the emulsion was examined during the
storage period and under mechanical–thermal loads. The results indicated that
the paraffin water emulsion containing a paraffin weight fraction of 30–50 wt
% was an attractive candidate for cold storage and distribution applications.
Evers et al (2010) developed and tested the PCM-enhanced cellulose
insulation frame walls. The Peak heat fluxes, the total daily heat flows, the
surface and air temperatures were measured and recorded. Results showed
that it could reduce the average peak heat flux by 9.2 % and average total
daily heat flow by 1.2 %.
Diaconu et al (2010) tested the phase change material slurry based
on microencapsulated Rubitherm RT6 at high concentration (45 % w/w). The
comparative study was carried out to quantify the natural convection heat
transfer occurring from a vertical helically coiled tube immersed in the phase
change material slurry and water. It was found that the values of the heat
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transfer coefficient for the phase change material slurry were higher than
water, under same operating conditions. Diaconu (2010) has proposed a
PCM-enhanced wall system by developing a model of the heat transfer
between the ambient and the heated indoor environment. Four different
occupancy patterns with different values of the set point temperature were
considered. The potential for energy savings was evaluated by calculating the
energy demand for heating in two cases, with and without PCM in the
building envelope. The effect of ventilation was also assessed first ignoring
and then including the ventilation effect in the numerical simulation.
Maha Ahmad et al (2006) studied 3 types of wall board containing
different phase change material namely polycarbonate panel filled with
paraffin granulates, a polycarbonate panel filled with polyethylene glycol
PEG 600. PVC panel filled with PEG 600 coupled to a VIP and thermal
response of these wallboards was determined. PVC panels filled with PEG
600 showed better performances than the other two types as its high heat
storage capacity and properties were not affected even after more than 400
thermal cycles. A numerical study was also carried out and it was found that a
good agreement took place between experimental and theoretical results.
Stritih and Butala (2010) experimentally analysed the cooling of
building using night-time cold accumulation in paraffin which had a melting
point of 22 ºC. The air temperature and the heat flux in the indoor were
observed for different air velocities and inlet temperatures. Entrop et al (2011)
have presented the use of Phase Change Materials in concrete floors, in which
thermal energy from the sun is stored in a mix of concrete and PCMs. The
thermal energy is stored during day time and released during the evening and
early night. The temperatures of four concrete floors were monitored to know
the influence of PCMs and type of insulation in relation to ambient
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temperatures and solar irradiation. The application of PCMs in concrete floors
resulted in a reduction of floor temperatures from 7 ºC ± 3 % to 16ºC ± 2 %.
Castell et al (2010) studied the benefit of using PCM in
conventional and alveolar brick construction. The experimental results
showed that the PCM could reduce the peak temperatures up to 18 ºC and
smoothened out the daily fluctuations. The electrical energy consumption was
reduced about 15 % in the PCM cubicles and results in the reduction of the
CO2 emissions by 1–1.5 kg/year/m2. Yanlai Zhang et al (2011) have
investigated experimentally the heat storage characteristics of PCM
microcapsule slurry under natural convection condition in a horizontal
rectangular enclosure that is heated only at a constant temperature at the
bottom using the electric power input. The experimental results indicate that
the PCM in the slurry has a large effect on heat storage.
Belen Zalba et al (2004) have studied the free-cooling system and
the influencing parameters using the design of experimental strategy. A
viability analysis demonstrates that this kind of system is not only technically
feasible, but also economically advantageous to existing cooling systems.
With the empirical model developed in this work, a real free-cooling system
was designed and economically evaluated. Mohamed Rady (2009 a) made an
experimental study on Granular Phase Change Composites (GPCC) and
determined the phase change temperature, latent heat, and energy storage
capacity by using differential scanning calorimeter and temperature-history
methods. Packed-bed column experiments revealed that the presence of non-
uniform GPCC particles complicated the heat transfer phenomena.
Ruolang Zeng et al (2009) did experimentally and also numerically
to analyze the heat transfer of Microencapsulated Phase Change Material
Slurry (MPCMS) in a circular tube under constant heat flux. Three different
fluids namely pure water, micro-particle slurry and MPCMS were
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numerically investigated to separate the influences of the micro-particle and
phase change. The Nusselt number and the dimensionless wall temperature
were used to describe the degree of heat transfer enhancement.
Medina et al (2008) designed Phase Change Material Structural
Insulated Panel (PCMSIP) and evaluated their thermal performance based on
heat transfer rate reduction, under full weather conditions. The peak heat flux
reductions produced by the PCMSIPs in combination with 10 % and 20 %
PCM were 37 % and 62 % respectively. The average daily heat transfer
reductions across the PCMSIPs were 33 % and 38 % for concentrations of 10
% and 20 % PCM, based on the weight of the interior wallboard. Qureshi et al
(2011) have tested two identical office buildings. One of the office walls and
ceilings is fitted with ordinary gypsum boards while the other office with
PCM impregnated gypsum boards. Controlled heating facility is provided in
both the offices and it was found through observations that the Phase Change
Material (PCM) in building enabled the efficient thermal storage and reduced
the overall electrical energy consumption. The peak load shifting was
achieved for space heating in winter period.
Hawes et al (1993) studied the impregnation of PCM in gypsum
wall board. Different types of PCMs and their characteristics and
manufacturing techniques were described. The performances of gypsum
wallboard and the concrete block which were impregnated with PCMs were
examined and PCM concrete block provided approximately 4 times of energy
storage of wall board.
Xu Xu et al (2005) modeled the thermal performance of shape-
stabilized PCM and various parameters influencing the thermal performance
of PCM like thickness, melting temperature and thermal conductivity were
analysed. The model was verified with the experimental results. Halford and
Boehm (2007) developed a numerical model to investigate the ability of
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encapsulated phase change materials in an RCR configuration to shift the
peak electrical demand. The effects of ambient condition, insulation
thickness, and thermostat set point were investigated. The model was
designed based upon a simple conduction analysis by keeping the geometry of
the problem as general as possible. Comparisons are made to the temporal
variations of the heat flows without the application of the phase change
material to those with the phase change material.
Feldman et al (1991) designed an energy storage gypsum wallboard
by direct incorporation of 21 %-22 % commercial grade butyl stearate (BS).
The properties of the energy storage wallboard comparatively quite well with
values were obtained for standard gypsum board. The capacity of energy
storing board has a ten-fold increase in storage and discharge of heat, when
compared with gypsum wallboard. Ana Lazaro et al (2009) designed an
empirical model for simulating the thermal behaviour in the tested heat
exchanger for different cases. The thermal properties of PCM vary with
temperature, a PCM-heat exchanger works as a transitory system and hence
the design must be based on transitory analysis. One of the criteria for PCM
selection is power demand. The result obtained for the PCM-air heat
exchange can be useful for selecting PCM for other heat exchanger
applications that use the tested geometry.
Griffiths and Eames (2007) analysed a micro encapsulated PCM
slurry with melting - crystallization temperature around 18 ºC in a test
chamber containing a chilled ceiling. The results obtained over four months
testing have proven that a concentration of 40 % microcapsules containing
PCM can be used as the heat transfer fluid in a chilled ceiling application. It
requires a slower fluid flow rate, which reduces pumping requirements,
thereby avoiding increase in panel surface temperature. Darkwa et al (2006)
evaluated the laminated composite PCM drywall in a narrow phase change
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zone, which would be more effective in moderating the night time
temperature in a passively-designed room. The laminated PCM drywall
increased the room temperature at night by about 17 % more than the
randomly mixed type.
Bentz et al (2007) tested the energy storage capacity of PCM-filled
lightweight aggregates in concrete for residential construction with a PCM
transition temperature near room temperature. It was found out that PCM
reduced the temperature rise of a concrete section during adiabatic curing and
also the number or intensity of freeze-thaw cycles experienced by a concrete
exposed to a winter environment. Conrad Voelker et al (2008) studied the
modified gypsum plaster and a salt mixture as two materials for the reduction
of room temperature. Four identical test rooms were erected as light weight
constructions, where measurements were carried out under different
conditions. The experimental findings were finally reproduced by a
mathematical model.
Huang et al (2004) investigated experimentally and numerically the
use of a phase change material to moderate building integrated photovoltaic
temperature rise. Experimental data were used to validate the previously
developed two-dimensional finite volume heat transfer model. A parametric
study of a design application was also reported. Temperatures, velocity fields
and vortex formation within the system were predicted for a variety of
configurations, using the experimentally validated numerical model. Huang et
al (2006) simulated the temperature rise of building integrated photovoltaic
(PV) in a PV/PCM system by using finite volume method and experimentally
validated the results. The thermal energy storage and the temperature control
behaviour of PCM cavity walls using different phase transition temperatures
and operational conditions have been investigated.
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Zhaolin Gu et al (2004) designed and developed a recovery systemusing technical grade paraffin wax as phase change materials to store the
rejected heat from air conditioning system. The volume expansion during thephase change process, the freezing point and the heat of fusion was
investigated for technical grade paraffin wax and the mixtures of paraffin waxwith lauric acid. Adeel Waqas and Kumar (2011) conducted experimental
studies using Phase Change Material (PCM) storage for building ventilationin dry and hot climates to determine its thermal performance. The influence of
air flow rate and the inlet air temperature during charging process anddischarging process were analyzed. Experimental observations showed that
solidification of PCM quickly took place by decreasing the chargingtemperature and increasing the air flow rate.
Ahmet Sari et al (2001) studied experimentally, the thermalperformance and phase change stability of myristic acid. The experimental
results showed that the melting stability of the PCM was better in the radialdirection than the axial direction. The variety of the melting and solidification
parameters of the PCM with the change of inlet water temperature was alsostudied. Saman et al (2005) analysed the thermal performance of a phase
change thermal storage unit used in the roof integrated solar heating systemfor space heating of a house. The study was based on experimental results and
a theoretical two dimensional mathematical model of the PCM employed toanalyse the transient thermal behaviour of the storage unit during the charge
and the discharge periods.
Cabeza et al (2007) studied a new innovative concrete with PhaseChange Materials (PCM) on thermal aspects to achieve energy savings in
buildings. Two real size concrete cubicles were constructed and studiedexperimentally the effect of the inclusion of a PCM with a melting point of
26.8 ºC. The results showed the energy storage in the walls by encapsulatingPCMs and the comparison with conventional concrete without PCMs leading
to an improved thermal inertia as well as lower inner temperatures.
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2.4 STUDIES USING ANALYTICAL METHOD
Chao Chen et al (2008) established a one-dimensional nonlinear
mathematical model for heat conduction of the PCM energy-storing
wallboard (Figure 2.6) by effective heat capacity method. Simulation and
calculation were made using the software MATLAB to analyze and solve the
heat transfer problem of the PCM room. The result indicates that applying
proper PCM to the inner surface of the north wall in the ordinary room
enhances the indoor thermal comfort and also increases the utilization rate of
the solar radiation. So, the heating energy consumption is decreased and
energy saving has been achieved.
Feng Jiang et al (2011) have modeled analytically to get the optimal
phase change temperature and latent heat of the interior PCM for a passive
solar room. The optimized results are compared and agreed to optimize non-
linear thermal mass in an inverse problem. Through simulation, it is proved
that the passive solar room with the estimated optimal PCM can reach indoor
thermal comfort.
Figure 2.6 Schematic diagram of a new PCM energy storing wallboard
(Chao Chen et al 2008)
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Vakilaltojjar and Saman (2001) proposed a phase-change energy
storage system in thin containers consisting of different materials with
different melting temperatures and air was passed through gaps between
them. A semi- analytical model was developed and calculations were carried
out using the finite element method. Results obtained from three models with
different assumptions were compared. The effect of the design parameters
such as PCM slab thickness and fluid passage gap on the storage performance
was also investigated.
Wei Xiao et al (2009) established a simplified theoretical model to
optimize the interior PCM for energy storage in a lightweight passive solar
room. Analytical equations were presented to calculate the optimal phase
change temperature and latent heat capacity to estimate the energy storage.
The analytical optimization was applied to the interior PCM panels in a
direct-gain room with realistic outdoor climatic conditions. The analytical
results agreed to the numerical results.
Alvaro de Gracia et al (2010) developed a Life Cycle Assessment
(LCA) for three cubicles and used hypothetical scenarios such as different
systems to control the temperature different PCM types or different weather
conditions proposed were studied, using LCA process to denote the critical
issues. A parametric analysis of the lifetime of buildings was developed.
Results showed that the addition of PCM in the building decreased the energy
consumption but did not reduce the impact throughout the lifetime of the
building. From the hypothetical scenario, considering summer conditions all
year around and a lifetime of the building of 100 years, the use of PCM
reduces the overall impact by more than 10 %.
Tosun et al (2011) have used Artificial Neural Network (ANN)
technique to design a building and studied five different wall types in four
different climatic regions in Turkey. The ANN was trained and tested by
33
using MATLAB toolbox on a personal computer. The results showed that
ANN model could be used as a reliable modeling method for these studies.
Xichun Wang and Jianlei Niu (2009) proposed a combination of Cooled
Ceiling (CC) and a Microencapsulated Phase Change Material (MPCM)
slurry storage tank for the air-conditioning system. A mathematical model
was used to predict the system performance of an office room under Hong
Kong weather condition using hour-by-hour calculations. A feasibility
analysis for the combined system was also made with computer calculations.
The results indicated that a small MPCM slurry storage tank is capable in
shifting the part of cooling load from day time to night time and saves both
energy and economy.
Huanzhi Zhang and Xiaodong Wang (2009) confirmed that the poly
urea shell materials were successfully fabricated on to the surface of
microencapsulated n-octa decane by using the Fourier transform infrared
spectra and optical phase-contrast microscope. These micro capsules also
exhibited better phase change properties, higher encapsulation efficiency and
better anti- osmosis property than the other.
Mohamed Rady (2009 b) carried out experiments in a packed bed
to characterize the phase change characteristics of two Granular Phase
Change Composites (GPCC) for thermal energy storage. Packed bed column
experiments have been conducted to study the heat transfer. A mathematical
model has been developed for the analysis of charging and discharging
process dynamics. As compared to the use of single GPCC, using composed
mixture of GPCCs with an optimized mixing ratio results in improvement of
storage performance.
Borreguero et al (2011) have recently developed a mathematical
model based on one dimensional Fourier heat conduction equation and
solution is simplified by using an apparent heat capacity depending on
34
temperature. Theoretical curves obtained for gypsum blocks with three
different contents of Phase Change Materials (PCMs) are in agreement with
experimental ones and indicating that this thermal process can be reproduced
theoretically by using the apparent heat capacity. Results indicate that with
increase in PCM content, the energy storage capacity of the wallboard also
increases and lowers the wall temperature variation.
Ming Liu et al (2011) have developed a one-dimensional liquid-
based model for a flat slab phase change thermal storage. The model allows
for varying wall temperatures along the direction of flow and integrates a
convective boundary layer using a previously developed algorithm, which is
employed to iteratively calculate the liquid fraction and the temperature of
each Phase Change Material (PCM) node. The mathematical model is
validated by using two sets of experimental data obtained from tests and a
PCM having a melting point of 26.7 ºC and a liquid glycol based heat transfer
fluid. The numerical result shows a good agreement with the experimental
work.
Jianli Li et al (2009) prepared six polymer based form stable
composite Phase Change Materials (PCMs) by blending and compression
molding method. The Differential Scanning Calorimeter (DSC) results
showed that the melting and freezing temperatures and latent heats of the
form stable PCMs are suitable for energy storage applications. Thermal
cycling test indicated the form - stable PCMs have good thermal stability
when subjected to 100 melt–freeze cycles and thermal conductivity was
increased by 17.7 % by adding 8.8 wt % MMG.
Hui Li et al (2010) prepared a phase change material composite by
adding n-nonadecane in porous network of cement. The thermal properties
and thermal stability were investigated by a Differential Scanning Calorimeter
(DSC) and Thermo Gravimetric Analysis apparatus (TGA). The results
35
indicate that this composite material has the melting heat of 69.12 kJ/kg at
31.86 ºC, and solidifying latent heat of 64.07 kJ/kg at 31.82 ºC.
2.5 CONCLUSIONS FROM THE LITERATURE REVIEW
From the review of literature presented above, the following are the
major conclusions.
i. The use of Phase Change Materials in building components
has been widely studied in the past 20 years.
ii. A wide variety of PCMs has been studied. Some of them
widely taken are paraffins, calcium chloride hexahydrate,
octadecane, glauber salt, butyl stearate, dodecanaol, tetra
decanol, sodium thiosulphate penta hydrate, stearic acid and
palmitic acid.
iii. PCMs are used either directly or micro encapsulated capsules
or as shape stabilized materials.
iv. PCMs are used either outside or inside or in the middle of the
structure.
v. PCMs are used in variety of ways such as for roofs, walls,
window panels, as pipes in the concrete structure, sandwich
type wallboards impregnated with PCMs, and as floors.
vi. PCMs with melting temperatures 16-26.8 ºC are tested.
vii. PCMs are found to reduce the average peak flux by 5-30 %
and average daily heat flow by 3-65 %.
viii. Life and degradation of properties over time of the PCMs are
the major problems with the use of PCMs.
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ix. Efforts are made to develop variety of PCMs suitable for
various climatic conditions. Characterization of their properties
of various PCMs is also attempted.
x. Most of the studies have been carried out with single PCM at a
particular period of the year and only limited studies are
available on year round performance.
xi. A recent study by Pasupathy et al (2008) has pointed out that
PCM suitable for summer climatic conditions do not perform
well in winter and vice - versa. Hence, they proposed a double
layer PCM, one suitable for summer and the other suitable for
winter climatic conditions of the location.
2.6 OBJECTIVES OF THE PRESENT RESEARCH WORK
As most of the studies have heat transfer performance at a given
external climate, it has been decided to carry out a year round performance.
The study of Pasupathy et al (2008) claims that two different PCMs as two
layers are needed for such a year round performance. However, it is felt that if
a single PCM with suitable mass has been used, it can take care of such year
round variation. Numerical studies have shown good agreement with
experiments. Thus, it is decided to carry validated numerical experiments for
analyzing the problem. Among various components, Sun exposed building
roof contributes higher to the building cooling load. Keeping these aspects in
mind, the following are taken as the objectives of the present research work.
i. To develop a numerical procedure with ANSYS FLUENT
software for analysis of transient heat transmission across the
building roof with non - phase change and Phase Change
Materials and the validation with available experimental
results
37
ii. Analysis of heat transfer behaviour of three roof structures
(Reinforced Cement Concrete (RCC) only, Reinforced
Cement Concrete (RCC) plus Weathering Coarse (WC) and
Reinforced Cement Concrete (RCC) plus Hollow Clay Tile
(HCT) filled with PCM) during a typical summer day
iii. Analysis of heat transfer of three roof structures during a
typical winter day
iv. Analysis of year round performance by carrying out
simulation for 365 days
The following chapters will present the progress of research carried
out with the above objectives.