Introduction to the Application of Phase Change Materials under Tropical Climate of Panama

Abstract

Phase change materials (PCM) are materials with the ability to store a large amount of energy (latent heat) during their change from solid to a liquid phase. This takes place at certain melting temperature. Amid the global energy crisis, multiple applications of these materials have been studied at the theoretical, numerical and experimental approach, obtaining promising results in terms of an increase in the efficiency of these systems. However, the application of these materials is being studied since there are no rules or predictions of the feasibility of its application in diverse weather conditions. The tropical climate condition is one of the least studied in this context. In this work, a review of the main findings of recent studies conducted in tropical climate conditions is presented. Additionally, an analysis of the main challenges and opportunities of the application of PCM in the climate of Panama is performed. It was concluded that some applications in passive cooling and solar water heating systems might have the potential for their implementation. However, further studies are required to take into account other applications.

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Introduction to the Application of Phase Change
Materials under Tropical Climate of Panama
Itamar Harris
Department of Mechanical
Engineering
Universidad Tecnológica de
Panama
Panama, Panama
itamar.harris@utp.ac.pa
Maria De Los Á. Ortega Del
Rosario
Department of Mechanical
Engineering
Universidad Tecnológica de
Panama
Panama, Panama
maria.ortega@utp.ac.pa
Arthur James
Department of Mechanical
Engineering
Universidad Tecnológica de
Panama
Panama, Panama
arthur.james@utp.ac.pa
Denis Bruneau
Research Group, comfort of
Environmental, architectural and
urban design
Ecole Nationale Supérieure
d’Architecture et de Paysage de
Bordeaux
Burdeos, Francia
denis.bruneau@bordeaux.archi.fr
Abstract—Phase change materials (PCM) are materials with the
ability to store a large amount of energy (latent heat) during
their change from solid to a liquid phase. This takes place at a
certain melting temperature. Amid the global energy crisis,
multiple applications of these materials have been studied at the
theoretical, numerical and experimental approach, obtaining
promising results in terms of an increase in the efficiency of
these systems. However, the application of these materials is
being studied since there are no rules or predictions of the
feasibility of its application in diverse weather conditions. The
tropical climate condition is one of the least studied in this
context. In this work, a review of the main findings of recent
studies conducted in tropical climate conditions is presented.
Additionally, an analysis of the main challenges and
opportunities of the application of PCM in the climate of
Panama is performed. It was concluded that some applications
in passive cooling and solar water heating systems might have
the potential for their implementation. However, further studies
are required to take into account other applications.
Keywords—phase change materials, tropical climate, PCM
applications
I. INTRODUCTION
The world population and economic activities are
constantly increasing. As a result, the demand for energy has
increased proportionally [1]. The irresponsible use of natural
resources has led to global warming (as a result of greenhouse
gas emissions) and the subsequent climate change [2].
As potential solution to mitigate the effects of climate
change, multiple technologies focused on energy storage have
been proposed in response to the common dissimilarity
between supply and demand of energy resources worldwide.
A potential solution widely explored in recent years is the use
of phase change materials (PCM) for latent heat storage, since
they are capable of store a large amount of residual thermal
energy in periods of low demand [3]. Besides, if compared to
traditional materials, these systems can store this energy in
relatively small volumes.
Essentially, PCM are functional materials that take
advantage of their high density of thermal energy storage in a
small temperature range [4]. They store latent heat while
changing phase, from solid to liquid and from liquid to solid
as the heat transfer occurs, between the PCM and its
surroundings, as shown in Fig. 1. Traditional materials like
rock, sand, gravel, water or masonry, among others, are also
used for thermal energy storage applications. In those cases,
the energy is store as sensible heat. However, PCM can
operate at relatively stable temperatures and store between
five and fourteen times the amount of thermal energy per unit
volume equivalent to the sensible heat stored by materials
other than PCM [5].
Fig.1 Schematic diagram of the phase transition of a PCM [2].
In recent years, the PCM application has grown rapidly in
various industries, such as the space industry [6], the
electronics industry [7], cooling systems and solar air
conditioning [8], solar dryers for agricultural industry [9],
photovoltaic systems [10], food preservation and
pharmaceutical products [11], waste heat recovery systems
and water heating systems for domestic use [12], [13]. PCM
have been implemented in the buildings sector, especially in
applications related to air conditioning [14].
However, there are still limitations in terms of weather
conditions in the application of PCM in buildings and other
fields [4]. Currently, there are no systematic rules or
regulations regarding the application of PCM. However, little
is known about the maximum potential expected when
applying them in different regions. For example, the
application of PCM in buildings in countries with tropical
climate is still uncommon. This could represent a strategy to
minimize the cooling load [15].

The present article contains a literature review oriented to
identify the most significant aspects regarding the use of phase
change materials in the weather conditions of Panama. The
possible challenges and opportunities of the application of
PCM in humid tropical climate conditions were briefly
addressed for energy consumption in buildings.
II. PCM:
ENERGY
STORAGE
MATERIALS
A. Classification of Phase Change Materials
The phase change in PCM can be classified into four
states: solid-solid, solid-liquid, gas-solid and gas-liquid [12].
Only the solid-liquid variety can be used for cooling or heating
buildings since the other varieties have technical limitations
for this purpose [16]. The solid-liquid phase change PCM
usually used can be classified as organic, inorganic and
eutectic, as shown in Fig. 2 [17].
Fig. 2. Different types of phase change materials [17].
a) Organic PCM: Organic PCM have a series of
characteristics that make them useful to store latent heat
in various elements for construction [12]. They are more
chemically stable than inorganic substances. These
materials are non-corrosive, have a high latent heat
storage capacity per unit weight. They are recyclable,
melt congruently, have stable phase change temperatures
without segregation phase and exhibit little or no
subcooling. Oppositely, organic PCM have poor thermal
conductivity and are usually flammable [17].
b) Inorganic PCM: Compared to organic PCM, inorganic
PCM have an appropriate thermal conductivity, higher
heat of fusion per unit mass with lower cost and
flammability [17]. However, these can present a super
cooling phase, segregation, lack of thermal stability,
corrosion and decomposition [18]. This category includes
salt hydrates, saline solutions, and metals. Salt hydrates
are the best-known variety and numerous studies have
implemented them [19].
c) Eutectics: The eutectic PCM consist of a combination of
at least two PCM. During the freezing process, they form
a crystal of the mixture that can consist of
inorganic/inorganic, organic/inorganic and
organic/organic PCM [17].
The eutectic PCM have the advantage of allowing the
adjustment of their melting point by combining different
percentages by weight of their components. This can be
achieved without subcooling or phase segregation that is the
development of concentration gradients inside the material
due to solidification out of equilibrium. These materials can
achieve high thermal conductivities and densities. However,
they usually have low latent heats and specific heats [20].
B. Criteria for Selection of Phase Change Materials
From the economic point of view, the selection of a
suitable PCM is essential to store and release a greater amount
of thermal energy. The main parameters needed to select a
PCM are the melting temperature and the latent heat capacity.
When selecting these materials, their possible disadvantages
must be taken into account according to the expected
operating conditions [8].
TABLE I. C
RITERIA FOR SELECTION OF
PCM
ACCORDING TO THEIR
PROPERTIES
[3].
Criteria for
PCM Selection
Chemical Properties
Non-corrosive
Non-Flammable
Chemical Stability
Non-toxic
Thermal and
Physical properties
High thermal conductivity
High latent heat of fusion
per unit volume
High specific heat and
high density
Small changes in volume
during phase change
Kinetic properties
High nucleation ratio
High crystal growth rate
Then, it is necessary to consider the rest of its thermal,
physical, chemical and kinetic properties, which are presented
in Table I. As of today, no PCM can fully satisfy all the
properties required for optimal long-term performance [21].
Therefore, technical solutions have been suggested:
 To obtain PCM compounds that achieve the desired
temperatures and latent heat storage of phase change
[22].
 To maintain the shape of the PCM through a
encapsulation that has a higher phase change
temperature, non-corrosive, non-reactive with the
PCM and inexpensive [23].
 To improve the thermal conductivity of most non-
metallic PCM by adding high thermal conductivity
materials [24].
Finally, many studies have pointed out that the selection
of a PCM based on a specific phase change temperature in a
climatic region is not necessarily appropriate for other
regions. Some of the important factors that govern the
selection of PCM for building applications include local
climate, type of PCM, design, and orientation [25].
C. Encapsulation Methods of Phase Change Materials
The high PCM leakage potential during the change from
the solid to liquid phase and the possibility of diffusion of
low-density liquids throughout the material. This suggests the
need for encapsulation for the efficient use of PCM [26].
In addition, the PCM encapsulation can increase thermal
conductivity and improve heat transfer between the PCM and
the surrounding environment [27]. In the same way, the
encapsulation can diminish the effect of harmful
Organic
Paraffin
No
paraffin
Inorganic
Salt
hydrates
Metal
Eutectic
Organic -
organic
Inorganic-
inorganic
Organic-
Inorganic

environmental factors, avoid corrosion; as well as allowing
the handling of volume variation during phase changes [28].
The encapsulations can be macro (> 1000 μm), micro (1-
1000 μm) or nanometric (1-1000 nm). Smaller encapsulations
greatly increase the relationship between surface area and
material volume, which improves heat transfer significantly
[29].
D. Common applications of phase change materials
In the literature, it is common to find multiple applications
of PCM, which are mainly related to their fusion [30]. PCM
with medium-low melting temperature (5 °C to 40 °C) are
often used for passive heating and cooling applications for
buildings, air conditioning systems, among others. In
contrast, for solar water heating applications, PCM medium
melting temperature (40 °C to 80 °C) are usually used [3].
Table II presents a review of studies focused on medium-
low and medium melting temperature applications. In all the
studies considered, the results support the technical viability
of the PCM in each of their applications.
TABLE II. M
AIN APPLICATIONS OF MEDIUM
-
LOW AND MEDIUM MELTING
TEMPERATURE
PCM
Melting
temperature
Main
applications
Location of
the PCM
Reference studies
Medium- low Air
conditioning
systems
Absorption
chiller
Khan et al.
[8]
Return pipe Chaiyat y Kiatsiriroat
[31]
Free
cooling
(mechanical
natural
ventilation)
Mettawee et al. [32]
Passive
cooling of
buildings
Ceilings Yoon et al. [33]
Chung et al. [34]
Windows Durakovic et al. [35]
Silva et al. [36]
Block
interior
Lee et al. [30]
PCM plate
on walls
Yao et al. [37]
Kong et al. [38]
Medium Solar
thermal
energy
storage
Water
storage tank
Álvarez- Padiñas et al.
[13]
Mousa et al. [39]
Electronic
devices
Heat sinks Assi et al. [7]
III. APPLICATION
OF
PHASE
CHANGE
MATERIALS
IN
TROPICAL
CLIMATE
Ideally, a PCM must undergo a complete phase change
cycle once a day. However, the lack of guidelines for the
PCM selection for diverse weather conditions is uncertain for
applications in buildings [25]. There is still a need for a
detailed description of the effect that could be expected for
several PCM in various climates.
Particularly for tropical climate, the experimental studies
and simulations available are still very limited [15]. Table III
presents relevant information on projects carried out under
tropical weather conditions. This compendium of research
results emphasizes the strengths, weaknesses and some
relevant observations about the study.
One of the main obstacles to the application of PCM in
the tropical climate is the limited variation of the diurnal
temperature. This implies a high probability of the
incomplete cycle of fusion and freezing of the PCM, which
compromises the heat absorption of the PCM in the next
cycle. It has been shown that the variation in daytime
environmental temperature must exceed 10 K to ensure the
effective thermal storage of PCM as a passive cooling
strategy [40]. It is usually difficult to reach in Panama.
IV. APPLICABILITY
OF
PHASE
CHANGE
MATERIALS
IN
PANAMA
Table III presents studies available for tropical climate.
Panama's climate coincides with five of the subcategories
proposed by Köppen for the tropical climate[41]. These
researches were conducted in conditions of two of the main
climates of Panama: Tropical Savannah (Aw) and humid
tropical (Am). The results of these studies were promising for
the implementation of PCM. This could help to identify
possible challenges for large scale implementations of PCM.
A. Temperature Considerations
It is observed in Table III that the majority of the available
research conducted in tropical climate were focused on
passive cooling. Firstly, this application is considered.
Table IV presents a compendium of the daily average
temperatures, obtained from ETESA [42], of some relevant
locations in Panama. Potential PCM with melting
temperatures that match the Panamanian climate conditions
were analyzed based on their technical data and are
suggested. It is also shown in this table, the possible
temperature to reach when using these PCM as passive
cooling strategy.
ClimSel C24 and hs24 are salt hydrates. The PCM called
Eu1 and Eu2 in table IV, are eutectic PCM. Their chemical
structures are 50% CaCl
2
+ 50% MgCl
2
. 6H
2
O and
66.6 % CaCl
2
.6H
2
O + 33.3% MgCl
2
. 6H
2
O, respectively.
About the suggested PCM, first of all, it was used the
criteria T
max
>T
melting
, T
min
<T
freezing
and
T
freezing
>T
av, env
>T
melting
,where T
av, env
is the average
environmental temperature, in order to discard several PCM.
This criterion was followed since it allows to discard all those
PCM that would not complete a melting-solidification cycle,
just by taking advantage of the daily temperatures as thermal
source.
Then, it was calculated the difference between the average
melting temperatures of the remaining PCM and the average
environmental temperatures of every selected location. These
values resulted on the possible maximum temperature
decrease in a place using the respective PCM.

TABLE III. R
EVIEW OF STRENGTHS
,
WEAKNESSES
,
AND REMARKS OF THE APPLICATION OF
PCM
IN TROPICAL CLIMATE ACCORDING TO PREVIOUS STUDIES
Implementation of PCM in Tropical Climate
Reference PCM Location /
Climate
Strengths Weaknesses Remarks
Pasupathy et al.
[43](2008)
Eutectic
(salt hydrate
and water)
Chennai,
India /
Tropical
Savannah
A double layer of PCM on the
roof of a test house caused an
increase in the upper surface of
the roof with PCM, which implied
a lower air temperature in the
enclosure.
When using a layer of PCM
the increase of the temperature
was variable and, in some
cases, negligible for different
months. A double layer of
PCM was required.
It was concluded that it was not enough
to use the melting temperature as a
selection parameter. It was suggested to
carry out design simulations with PCM
that contemplate this climate, design,
and orientation of the structure.
Guichard et al.
[44](2015)
Paraffin
Wax
(DupontTM
Energain)
Reunion
Island /
Tropical
Humid
A simulation was made
comparing a house with a
traditional roof, and a house with
a roof that included PCM. The
results showed that the indoor air
temperature was lower in the
house including PCM. The
maximum difference was 2.4 °C
when comparing with no use of
PCM. In addition, the use of PCM
delayed the temperature increase.
A difference of ± 1.1 °C was
achieved between theoretical
and experimental results. The
validation criteria were not
favorable. The sensitivity
analysis showed that the
coefficients of heat transfer by
convection should be
corrected.
The experimental tests were performed
under room temperature conditions
between 19 °C and 26 °C and humidity
between 40% and 84%.
Chaiyat y
Kiatsiriroat [31]
(2015)
Paraffin
Wax
Chiang
Mai,
Thailand /
Tropical
Savannah
PCM spheres were placed in the
return duct of an air conditioning
system. This increased the
efficiency of the system and
reduced the refrigeration load.
No effect of other parameters
other than temperatures were
evaluated. Temperatures were
higher than 25 °C during the
day and between 25 °C and 30
°C at night.
It was included an economic analysis
which reflected an electricity saving cost
of 9.10% comparing this system with the
conventional one. The amortization
period was estimated at 4.15 years taking
into account the cost of the PCM.
Sanjani et al.
[45] (2015)
Paraffin
Wax
Kuala
Lumpur,
Malaysia /
Tropical
Humid
Theoretically, a higher thermal
efficiency was obtained from a
solar water heater system with the
inclusion of PCM in certain
conditions, which depends on the
climatic conditions and the flow
rates. The system was more
effective on cloudy and rainy
days.
No specific information was
provided about the weather
conditions in which these tests
were carried out. It was
presented in terms of sunny,
cloudy and rainy weather.
The effect of changing the supply water
flow on the temperature was lower for
the PCM system than for the
conventional system.
Lei et al.
[40](2016)
Derivatives
of paraffin
(n-
Octadecane)
Chennai,
India /
Tropical
Savannah
The cooling load of a building was
reduced by using a 10 mm PCM
layer on the walls. Thus
temperatures between 21 ° C and
32 °C were observed throughout
the year.
The heat gain was reduced by
increasing the amount of
PCM. However, the efficiency
and cost-benefit of PCM also
decreased with increasing
thickness.
It was pointed out that, unlike other
climates, in the tropical climate, it is
possible to take advantage of the PCM
throughout the year. In other regions,
they are only effective in certain seasons.
Thantong y
Chantowong
[46](2017)
Paraffin
Wax
Bangkok,
Thailand /
Tropical
Savannah
The behavior of a solar wall
system with PCM for water
heating and thermal load control
was studied. It reduced the
thermal load of the tested house
by 61.76%.
The velocity of the air in the
solar wall was measured, but
not significant contribution as
identified in the results.
The environmental temperatures of the
tested site varied between 21 °C and 38
°C during the day. The temperature of
the hot water varied between 25 °C and
51.8 °C.
Wonorahardjo
et al. [47]
(2018)
Coconut
Oil
Bandung,
Indonesia /
Tropical
Humid
Coconut oil was promising for
control of internal air temperature
above 20 °C.
The selection of the volume of
the encapsulation for this
PCM was fundamental, given
its low thermal conductivity.
The selection was empirical.
The experimental tests were carried out
with a heat exchanger with direct contact
with ambient air. Diameters of 8 cm, 12
cm and 16 cm were tested.
Memom y
Bigamangetova
[48] (2019)
Paraffin
Wax
(DupontTM
Energain)
Bangalore
y Kolkata
(India) /
Tropical
Savannah
The PCM plates on the walls
caused an energy reduction of
31% in Bangalore and 16% in
Kolkata.
The results were different
between Bangalore and
Kolkata. This can suggest that
the location of the site and the
weather conditions of the site
directly affected the results.
The outer layer of PCM showed better
control of the interior temperature during
sunny days when there was a significant
difference between daytime and
nighttime temperatures.
The possible reached temperatures obtained do not agree
with the comfort temperature of 24 °C suggested by the Air
Conditioning and Ventilation Regulation of Panama [49].
However, the cooling load could decrease considerably,
considering these values, implying the possibility of the use of
PCM as an auxiliary source of cold.
In Table III, another application considered in tropical
climate was the storage of solar thermal energy through hot
water storage tanks with PCM. Therefore, it is important to
consider the research works presented by Sanjani et al. [45]
and Thantong y Chantowong [46], which focused on it. Both
investigations report a better functioning of this type of system
using PCM. Perhaps it is because in this application it is easier

to meet the requirement of temperature variation during the
period of operation [40].
TABLE IV. S
UGGESTED
PCM
AND POSSIBLE REACHED TEMPERATURE IN
SOME LOCATIONS IN
P
ANAMA WHEN APPLYING
PCM
AS A PASSIVE
COOLING OPTION
B. Humidity and Corrosion Considerations
Table III shows that most of the studies available for
tropical climate have not considered humidity as a parameter
of relevance. All them agree to consider the temperatures
variations. It was observed that paraffin wax and coconut oil
were used in most cases. This can be associate to the non-
corrosive properties of these PCM. Salt hydrate was only
used for an application in the Tropical Savanna climate [43].
It could imply that despite having a good potential for passive
cooling in terms of temperature, ClimSel C24 and hs24 (salt
hydrates) could have technical problems in humid tropical
climate of David (see Table IV).
On the other hand, the low conductivity of paraffin wax
can regularly be improved with metallic particles. It is
necessary to evaluate the benefits of increasing the thermal
conductivity concerning the corrosive effects and how to
minimize them, depending on the application.
V. CONCLUSIONS
A review of the characteristics of different types of PCM,
selection criteria and multiple applications has been carried
out. The analysis of previous studies in tropical climate
conditions was emphasized to contemplate the
implementation of PCM in the climate of Panama. However,
these investigations are limited, and concerning Panama,
there is no previous research. Despite the positive results of
these works, some weaknesses were identified and also, the
climates of their locations are not equal to the Panamanian
climate. It is necessary to conduct specific researches in
Panama to identify if these results can be extrapolated.
From the applications found in the literature for the
tropical climate, our analysis focused on the passive cooling
and the storage of solar thermal energy to heat for water
heating with PCM. For passive cooling, our preliminary
results show that PCM could significantly reduce the cooling
load. On solar thermal energy storage, the literature reports
on a better functioning of this type of system using PCM.
Experimental tests and more rigorous studies (numerical and
experimental analysis) should be considered to corroborate
the technical applicability of PCM in the Panamanian
climate. It was not possible to make predictions of the
possible effects of moisture and the incidence of corrosion on
the long-term operation of these systems, since the available
information is limited.
Our preliminary studies did not reflect any organic PCM
as a good option for passive cooling, despite being the most
used in previous research in the tropical climate. Future
research work should consider more types of organic PCM
and an extensive meteorological data to test their potential.
Their use could have positive impact in tropical territories,
since they present attractive properties when considering
corrosive environments.
ACKNOWLEDGMENT
We are grateful to the National Research System of the
Republic of Panama (SNI- acronym in Spanish) for the
economic support to Dr. Arthur James. We also thank the
National Bureau of Research Science and Innovation
(SENACYT- acronym in Spanish) for their support to the
Master of Science program of the Department of Mechanical
Engineering of the Universidad Tecnológica de Panamá.
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Sel
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hs24
[51]
Eu1
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Eu2
[52]
David Am 28,4 25.5 24.5 25 25
Los Santos Aw 29,3 25.5 24.5 25 25
Tocumen Aw 28,3 25.5 24.5 25 25

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