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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.

13

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)

14

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.

15

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

16

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

17

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

22

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

25

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

26

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

27

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

28

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

29

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.

30

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.

31

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.