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CIVIL & ENVIRONMENTAL ENGINEERING | RESEARCH ARTICLE
The impact of thermal mass on building energy
consumption: A case study in Al Mafraq city in
Jordan
Firas Sharaf
1
*
Abstract: This research discusses the usage of thermal mass of construction materials
to produce comfortable thermal indoor environment and to reduce energy consump-
tion used for cooling and heating. What motivated this research is the disappearance
of traditional construction methods and materials, such as thick stone and clay walls.
Stone is used as a coating material in new buildings, but little attention is given to its
significant thermal properties. These construction methods which are ideal to perform
as thermal masses are becoming extinct in modern buildings. To achieve this aim a test
of thermal mass efficiency is conducted on a case study building which consists two
parts of different thermal mass under same climate condition in Jordan. Indoor
temperatures of two rooms; one with clay walls; and a second room with concrete brick
walls are measured at day and night times in summer and winter. Findings indicate
that in hot and cold climates, the temperature inside the room of clay walls are kept
within the human comfort zone, unlike the temperature in the room with concrete
walls, which was not in the human comfort zone by 5°C. Results are recorded and
analyzed to draw useful insights and recommendations. This research concludes that
construction materials of high thermal mass, such as clay-bricks, significantly keep the
indoor environment within the human thermal comfort zone. Thus, the energy required
for maintaining the thermal comfort of the room is greatly reduced.
Subjects: Environmental; Environmental Health; Heritage Management & Conservation
Keywords: thermal mass; building energy consumption; cooling and heating; green
buildings
Firas Sharaf
ABOUT THE AUTHOR
Firas Sharaf, has a Ph.D. in Architectural
Engineering, and teaches at the University of
Jordan. The thermal mass topic lies within my
research interests and publications in the field of
green and sustainable architecture.
PUBLIC INTEREST STATEMENT
This paper investigates the use of thermal mass
as a construction material to reduce the energy
consumption. The author concludes that thermal
mass is effective in improving comfort tempera-
tures in buildings that experiences high daily
temperature fluctuations. The use of materials of
high thermal mass, such as mud and stone can
play an important role in major reductions to
energy use in heating and cooling systems.
Thermal mass is most advantageous in hot cli-
mates where there is a big difference in outdoor
temperatures from day to night.
Sharaf, Cogent Engineering (2020), 7: 1804092
https://doi.org/10.1080/23311916.2020.1804092
Page 2 of 18
Received: 19 April 2020
Accepted: 27 July 2020
*Corresponding author: Firas Sharaf,
Department of Architecture, The
University of Jordan, Queen Rania Al
Abdullah St 266, Amman, Amman,
Jordan
E-mail: f.sharaf@ju.edu.jo
Reviewing editor:
Paolo Zampieri, Universita Degli
Studi Di Padova, Italy
Additional information is available at
the end of the article
© 2020 The Author(s). This open access article is distributed under a Creative Commons
Attribution (CC-BY) 4.0 license.
This article has been corrected with
minor changes. These changes do not
impact the academic content of the
article.
1. Introduction
Buildings and transportation form the greatest share of energy consumption worldwide as the
total world fuel consumption in 2019 has increased by 2.9% (Jrew et al., 2019). The energy
shortage is evident by increasing prices of fuel. The impact on average citizens takes a form of
unbearable costs for heating, gas, and transportation, food, etc. (Abdalla, 2020). Buildings con-
sume about 40% of global energy, and they emit approximately one-third of greenhouse gas (GHG)
emissions. Heating and cooling of buildings account for more than 50% of energy consumption
(Sharaf, 2018; Sharaf et al., 2016). Population growth, prosperity, and higher urbanization fuel
building and construction activities and increase energy demand and global warming (Wahba
et al., 2018). Residential and commercial buildings consume approximately 60% of the world’s
electricity (Ellabban et al., 2014; Roy & Das, 2018). The Sustainable Development Goals aim at
integrating issues related to the local environment, climate, and economic frameworks (Sharaf &
Al-Salaymeh, 2012). Global efforts to decarbonise and enhance energy efficiency in the world
include buildings that offer great potential for achieving significant energy and GHG emission
reductions, at least cost (UNEP, 2019). Additionally, building sustainably will result in healthier
and more productive environments (Salvia, et al, 2019).
Energy consumption in buildings can be reduced by using a property of the mass of building
known as “thermal mass,” which enables it to store heat providing “inertia” against temperature
fluctuations. For example, a large thermal mass within the insulated portion of a house can serve
to “flatten out” the daily temperature fluctuations, when outside temperatures are fluctuating
throughout the day. Thermal mass absorbs thermal energy when the surroundings are higher in
temperature than the mass, and give thermal energy back when the surroundings are cooler,
without reaching thermal equilibrium (Brambilla et al., 2018)
Building materials and building elements such as walls, ceilings, floors, windows, doors, and
ventilation systems play an important role in the process of equating heat between inside and
outside of the building. Walls and ceilings, for example, together account for 60% of heat leakage
in buildings when they lack good thermal insulation. There are more heat leaks through other
building elements if they are not properly insulated. The lack of control over the heat exchange
process between the building and its external environment leads to energy consumption in the
building, in order to provide indoor temperatures suitable for users (Sadineni et al., 2011).
Energy is used in heating and cooling to compensate for the thermal losses caused by thermal
differences between the inside and outside of the building to reach the level of internal thermal
comfort appropriate for users. The problem arises when designers fail to address the issue of
sustainability and to achieve active and passive thermal solutions in buildings, particularly thermal
mass and thermal insulation (Damirchi Loo & Mahdavinejad, 2018; Lam et al., 2008). Not con-
sidering thermal mass properties of the building construction materials and sufficient thermal
insulation will increases energy consumption in the building (DEFRA, 2016).
Building materials and elements such as walls, ceilings, floors, windows, doors, and ventilation
systems play an important role in the process of equating heat between inside and outside of the
building. For example, walls and ceilings together account for 60% of heat leakage in buildings
when they lack good thermal insulation. There is more heat leakage through other building
elements if not properly insulated. The lack of control over heat exchange process between the
building and its external environment leads to more energy consumption in the building to provide
indoor temperatures suitable for users (Zhang et al., 2019).
This research study the thermal mass performance of the building to achieve a thermal comfort
range, with less cooling and heating loads and energy consumption. The methodology leading this
investigation is presented in the next section.
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2. Methodology
This study aims to evaluate the thermal mass efficiency of construction materials in improving the
thermal performance of buildings to achieve human thermal comfort with less energy consump-
tion. The methodology adopted in this article to study the thermal mass efficiency in buildings is:
a survey of the relevant literature to form a good understanding of the effect of thermal mass in
reducing energy consumption in buildings; Conducting a case study of a building consisting of
different parts with different thermal masses and testing them in the same climatic and thermal
conditions. The location of the case study building was chosen in the city of Al Mafraq, in northern
Jordan, with a semiarid climate suitable for thermal mass testing. The building has an old part
made of clay-brick walls of 40 cm thick and wood rafters ceiling. The other part of the building is
made of concrete brick walls of 10 cm thick and concrete slab with 2 cm cement plaster on the
walls and slab. Architectural drawings of the building and detection of the building materials are
required. A room in each part of the building was determined to conduct measurements of the
daily temperature fluctuations using a thermo meter device. The temperature in the two rooms
was measured in cold weather conditions in November and December and in warm weather
conditions in July and August in 2018. The time of measurements was at the heat rise at 1 pm
and a lower temperature at 9 pm. The temperatures are recorded and documented in both rooms
and a comparison is made between thermal fluctuations of inner and outer air of the building and
with consideration to the human thermal comfort zone Figure 1. The residents of the house are
asked about the indoor environment and heating methods they use. Data is analysed and
presented in charts and tables. Figure 1 shows a diagram explaining the methodology and analysis
chart. The comparison of thermal fluctuations of inner and outer air of the test rooms and
temperature proximity or distance from the human thermal comfort zone is presented in graphs
as Figure 1.
Effect on indoor temperatures in a residential building fluctuations of inner and outer air of two
test rooms in. comparison with thermal comfort zone
Figure 1. Methodology diagram
of the test of thermal mass.
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This paper focuses on thermal mass as an important element of the thermal performance of
a building. Different building materials have different thermal masses and thermal transition
happens through the components of the building. To form a good understanding of how thermal
mass works, it is useful to review the literature on thermal mass characteristics of materials and
heat transfer methods in buildings (Zhai & Previtali, 2010).
3. Thermal mass of building materials
Building materials of high thermal mass capacity and ability to sustain internal suitable climates,
such as clay bricks and masonry have been used widely in hot climate regions (Rapoport, 1969).
Methods to reduce the amount of consumed energy depend on understanding factors that affect
the thermal design of buildings, such as thermal performance of building materials and thermal
insulation. The usefulness of materials for thermal efficiency is based on the relationship between
their thermal properties and the thermal cycle that they are required to moderate. Thermal mass
requires high specific heat capacity, high density, and thermal conductivity that means heat flows
into and out of the material are aligned with the thermal cycle of the occupied space (Yu et al.,
2009). Materials such as concrete and clay brick tend to have a useful thermal mass, whereas
timber is a too slow absorber of heat, and steel has a too high a thermal conductivity. The ability of
a material to absorb and release heat through thermal cycles is described as admittance or
thermal mass and is based on its thermal capacity and conductivity, density, and thickness
(Venkiteswaran et al., 2017). The factors that determine the thermal mass of materials are:
●Thermal capacity: the amount of thermal energy needed to increase the temperature of
a kilogram of material by 1°K.
●Density: depends on the mass (or weight) per unit volume. The relationship between density and
thermal mass is positive; it increases with the increase of thermal mass. Density measurement unit
is kg/m
3
.
●Thermal conductivity: measures the property of material to conduct heat. It is preferable for
thermal conductivity to be moderate in relation to materials with high thermal mass to ease the
process of thermal absorption and releasing it in a way which synchronizes with the cooling and
heating cycle of the building. Thermal conductivity is measured in watts per meter Kelvin (W/mkal).
It is essential to differentiate between thermal mass and thermal insulation. In thermal insulation,
the transmission of heat from inside or outside the building is blocked. The thermal mass main-
tains the heat but retransmits it to either inside or outside the building over a certain period of
time and creates equilibrium of comfort temperatures between day and night (Bansal et al., 1994).
Figure 2. Analysis graph to
compare thermal.
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However, thermal mass works with insulation to reduce thermal transfer, so it requires less
insulation in a thermal mass solution than in a stud wall solution (Sharston & Murray, 2019). For
example, a typical wall R-Value requirement of R-18 might be met by a high-thermal-mass
masonry wall with an R-Value of R-7 (ASHRAE, 90.1 2019).
4. Heat transfer in buildings
Heat transfer is a process of interchange or thermal flow that flows from hot to cold entities. Heat
transfer happens when there is a difference in temperature between two spaces, such as inside
a building and its surrounding. Hot air moves from highest temperatures side to lowest until both
sides acquire the same temperature (Figure 3). Heat transfers in different ways such as conduc-
tion, convection and radiation (Kim & Viskanta, 1984).
Thermal conductivity is a material property that describes ability to conduct heat. Thermal conductiv-
ity can be defined as “the quantity of heat transmitted through a unit thickness of a material in
a direction normal to a surface of unit area due to a unit temperature gradient under steady state
conditions.” Thermal conductivity unit is [W/(m K)] in the SI system (Newell & Tiesinga, 2019). Heat
conduction happens through building materials such as walls, ceilings, and windows. Heat flows from
inside to outside of the building in winter and from outside building to inside in summer. Heat flow
through conduction is affected by wall thickness and temperature differences on both sides of the wall,
the material of the wall and its thermal conductivity coefficient k (Iyengar, 2015). The thermal con-
ductivity coefficient k represents the flow of energy per unit of time. The k value depends on physical
properties of the material, water content, and pressure on the material. It is measured in watts per
meter Kelvin (or degree) (W/mK) (Newell & Tiesinga, 2019. In general, the material with a large k value is
a good heat conductor and with a small k value is a good heat insulator and reduces the amount of heat
transfer between the inside and outside of the building (Zong-Xian; Zhang, 2016). Table 1 shows k value
Table 1. Values of thermal conductivity and density for construction materials Source, (Iyengar,
2015)
Material Heat Transfer Coefficient
k W/(mk)
Density
(kg/m
3
)
Stone 1.7 2300
Solid concrete 1.13 2000
Raw clay brick 0.51 700
Masonry brick 0.7–0.8 500
Cork sheets 0.05 300
Polyester sheets 0.04 20
Wood 0.13 600
Conductive heat transfer q is expressed with Fourier’s Law’s as:
q = (k/s) A dT = heat transfer (W, Btu/h)
q/A = (k/s) dT = heat transfer per unit area (W/m
2
, Btu/(h ft
2
))
k = Thermal Conductivity of material (W/mK or W/m C, Btu/(hr ft °F))
s = material thickness (m, ft)
A = heat transfer area (m
2
, ft
2
)
Figure 3. Heat exchange
mechanism during summer and
winter throughout daytime, to
and from the building.
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of different materials, for example, the k value of raw clay brick is 0.51 W/(mK), this means that raw clay
brick is better thermal insulator that stone which k value is 1.7 W/(mK).
dT = t
1
- t
2
= temperature gradient—difference—over the material (C, F) (Bergman et al., 2019).
If heat transfers through a clay wall of 40 mm thickness and a thermal conductivity of 0.51 W/m,
through 1 m
2
of the wall, and the temperature on one side of the wall is 30°C and on the other side is 20
°C. The conductive heat transfer (q) from this wall is calculated as: q = [(0.51 W/m °C)/(0.40 m)] (1 m
2
)
[(30 °C)—(20 °C)] = 12.7 W, Btu/h (watt, British thermal unit/hour). Likewise, q of a brick wall of a 0.15 m
thickness = 50 W, Btu/h. An inverse relationship is observed between the thermal mass of the material
and the thermal conductivity. If the thermal mass is large, then the thermal conductivity of the
material is low, and if the thermal mass is small, the thermal conductivity increases.
If the air reaches a cold surface, its temperature will decrease, and as a result, its density
increases and moves downward. Likewise, if it reaches a hot surface, its temperature increases and
rises to the top. This phenomenon is called high airflow or heat transfer by convection, which
increases with the increased coefficient of convection. This is related to the speed of the air’s
connection to the wall. The amount of heat transferred through the wall will be greater if the air
attached to the wall is mobile. If a layer of thermal insulation is added to the wall it will damp the
air mobility and will decrease the amount of heat transfer. Also, the amount of heat transferred by
conduction through the insulation material will be less due to its low heat conductivity. On the
other hand, heat transfer by radiation transfers heat between entities without an interface or
materials and heat can be transferred to the building by radiation. An ideal thermal design of
buildings should consider heat transfer methods and the relation with the thermal mass of the
building materials to reach the human thermal comfort range with less energy consumption (Bird
et al., 2007; Rowley & Algren, 1937).
5. Human thermal comfort zone
Human comfort zone is defined as “the sum of thermal conditions surrounding the human, in
which he feels pleased and comfortable, taking into consideration a number of factors, such as the
temperature, humidity and air movement. Thermal comfort ranges maybe calculated for each
climate zone using psychometric charts based on Adaptive Comfort standards (ASHRAE Standard
55, 2010). This enables designers to create indoor climates that occupants find pleasant (Figure 4).
Figure 4. Thermal comfort
range associated with air tem-
perature and relative humidity
(ASHRAE 55, 2010).
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Thermal comfort is attributed with four factors which together create a comfortable environ-
ment; these factors are air temperature, relative humidity, human efficiency and clothing insula-
tion. Humans generally feel comfortable between temperatures of 22°C–27°C and a relative
humidity of 40%–60%. Human body loses extra heat from its surrounding in different ways, such
as sweating. The effort a human body makes to lose extra heat put stress on the body and makes
one feel tired and encounters performance difficulties (Evans, 1980). Suitable thermal comfort
range to improve user performance is achieved through proper interior environmental design to
achieve adaptation between outer environment and building, depending on the energies and
resources of renewable nature. Thermal exchange between a building and external environment
happens through the building envelop which is the walls, roof, doors and windows (ASHRAE
Standard 55, 2017).
6. Thermal mass of the building coat
A building cover provides thermal balance for humans through its design and materials. An
important element of this balance is the thermal mass of the materials making up the building
coat (Klepeis & Nelson, 2001). heavy thermal mass materials enable buildings to resist thermal
fluctuations, also called “thermal flywheel effect.” Materials with high thermal mass can absorb
external heat and store it, then transmit it to areas of lower temperatures. As a result, the thermal
fluctuation and conductivity of the building decrease. This allows for more efficient heating or
cooling in the building and less energy consumption (Granadeiro et al., 2013). Thermal mass is
equivalent to thermal capacitance or heat capacity, which is the ability of a body to store thermal
energy (Slee et al., 2014).It is typically referred to by the symbol C
th
and its SI unit is J/°C or J/K
(which are equivalent). When using thermal mass for buildings the term “heat capacity” is used
instead. The equation relating thermal energy to thermal mass is: Q = C
th
ΔT, where Q is the
thermal energy transferred, C
th
is the thermal mass of the body, and ΔT is the change in
temperature (Halliday et al., 2018).
The increase of heat capacity of materials makes it ideal to use in buildings. Table 2 shows that
solid concrete and adobe have high volumetric heat capacity, which provides ideal thermal
masses suitable for climates with thermal fluctuation, such as desert climate. The way thermal
mass works in buildings ensures the reduction of heating loads during winter and cooling loads
during summer. Passive cooling methods, such as natural ventilation and canopies that protect
the building from direct sun rays also help inner areas of the building to reach thermal comfort
levels with less energy consuming (Figure 5; Givoni, 2011).
Internal temperature is also affected by internal thermal loads, such as lighting units, heat gained
from electrical home appliances, and other appliances (Sharaf & Al-Salaymeh, 2012). During summer,
particularly in hot regions, these factors cause thermal fluctuations. When the temperature reaches
its highest level at afternoon hours, the building coat constructed from materials of high thermal
Table 2. Thermal capacity of different construction materials
Material Heat capacity/unit volume
MJ/m
3
/(Btu/ft
3
)
Gypsum 0.74 (20)
Concrete Hollow Bricks
)Hollow 30 %)
0.74 (20)
Clay bricks (Adobe) 0.93 (25)
Solid Concrete 1.04 (28)
White Oak 1 (27)
Water 2.32 (62)
Stone 1.41 (38)
Source: Bengtson, 2010
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mass absorbs and stores heat. Heat needs time to reach inner areas of the building; this amount of
time depends on the thickness of external walls and their thermal characteristics (Yu et al., 2009). The
time difference between heat gain and release is called “Time lag,” which determines the efficiency of
the thermal mass of the building materials. The longer time difference between storing the heat and
retransmitting it inside the building, the more efficient the thermal mass effect. As a result, internal
temperatures are kept within the human thermal comfort limits, which results in less heating and
cooling loads and less energy consumption (Brown, 1990). Table 3 shows the time Lag of different
construction materials of fixed thickness.
Lechner (2009) the use of materials with thermal mass is most advantageous where there is
a big difference in outdoor temperatures from day to night (or, nighttime temperatures are at least
10 degrees cooler than the thermostat set point). Materials with the ability to enhance a building’s
thermal performance provide one of the best passive design options and result in an integrated
passive design strategy that balances building performance with heating and air conditioning
requirements. Materials with thermal mass such as clay bricks (or Adobe) stone and masonry
provide suitable indoor thermal conditions and pleasant atmosphere during summer and warm
during winter, especially in areas with hot and dry climates (Fathy, 1986; Alaidroos, 2015). In cold
climates, high thermal mass can cause an increase in energy use, which has implications for the
design of buildings in cold climates, and contradicts the commonly-held assumption that high
thermal mass is correlated with low energy use (Reilly & Kinnane, 2017)
7. The Case study house in Al Mafraq city in Jordan
The case study house is located in Mafraq city in the north of Jordan (Figures 6 and 7). The house
has two parts, an old part made of clay bricks and an added part made of concert blocks.
Al Mafraq climate is semi arid, hot, and dry during summer and mild and humid during winter.
January is the coldest month of the year in Mafraq area, as temperatures range from 5 to 10°C.
Figure 5. Thermal mass
mechanism of building materi-
als in walls.
Table 3. Time lag of walls of different building materials
Material (thickness 30 cm) Time lag (hours)
Adobe (clay brick) 10
Red bricks (standard) 10
Bricks (face) 6
Concrete (heavyweight) 8
Wood 20
Stone 12
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Temperatures increase in summer, average temperature range reach up to 33°C (Figure 8).
Extreme hot and cold temperatures in Mafraq city provide good comparison conditions of thermal
performance of building walls made of different construction materials such as stone and rubble
walls and concert bricks. A case study house is selected in Mafraq city which has rooms built of
thick stone walls and rubble and rooms built of concert bricks. The maximum temperature diagram
for Al Mafraq displays how many days per month reach certain temperatures (Figure 8).
There are 26.7 days in July and 27 days in August that have a temperature higher than 30°C
(Figure 8). The sum of days with maximum temperatures exceed 30°C in a year is 120 days (from
April to October).
8. Description of the case study house
The house is located in an old neighborhood in the market area of Al Mafraq city. The old rooms of
the house were built clay bricks in 1938 and the additional rooms were built of concert brick in1961
and 1977 (Figure 9). The house is still inhabited by the owner and his family and consists of four
bedrooms, kitchen, bathroom, a courtyard and outdoor storage room for hay and barley (owner of
the house Mr Makki Al-Maghrebi, 2018).
Figure 7. Location of Al Mafraq
City off the motor way to Syria.
Figure 6. Location of Al Mafraq
City in the north of Jordan.
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The construction materials of the old house are 40 cm clay bricks and ceiling made of wood
rafters, steel beams and wooden shingles. Two rooms and a bathroom were built in 1977 of 15 cm
cement bricks and concrete roof (Figure 10). Concrete was applied to the roof and to the clay walls
to support them and to stop rain water leakage. Cement is applied on the old clay walls to stop
erosion and capability to host insects inside cracks (Figure 11).
Figure 8. The Maximum tem-
peratures in Al-Mafraq city
(www.meteoblue.com, 2020).
Figure 9. Location of the case
study house in Al Mafraq city
and diagram of construction
time of each part.
Figure 10. The case study house
scheme showing thick clay
brick walls in the old and the
added part in 1977 made of
concert brick walls.
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External doors of the house are made of iron; interior doors are made of wood. Windows are single
glazed with wood or iron frames. Doors and windows condition is not efficient as they do not seal
completely to stop air drafting efficiently and support indoor heat insulation (Figures 11 and 12).
Residences of the case study house were asked about difference in room temperature in the
house. Replies indicate that clay rooms are warmer during winter and have nicer climate during
summer than the rooms made of cement blocks.
In order to test the effect of thermal mass performance of clay and concrete materials on internal
temperature under same climate conditions, two rooms in the case study house are selected. One room
is made of clay walls of 40 cm thickness and the second room is made of concrete brick walls of 15 cm
thickness. The ceiling is made of wood shingles in both rooms and both rooms are oriented to South East.
Temperature measurements were conducted in lower outside temperatures in November and December
and higher temperatures in July and August in 2018. Time of measurement was at 1 pm (13:00) and 9 pm
(21:00). The device used to measure temperature is an electronic Thermo Meter (Figure 13).
9. Results and analysis
Figures 14 and 15 show that in lower outside temperatures, in Nov and Dec., temperature inside
the room of clay walls was closer to human thermal comfort range than the concrete room,
especially at night, as it was 5°Chigher than the external temperature in average. Temperature in
the room of concrete blocks was closer to external temperature throughout day and night. The
residence of the case study house in Mafraq said that the rooms of clay walls in their house have
comfortable climate than the concrete block rooms.
Figures 16 and 17 show that in a relatively high temperature atmosphere, in July and Aug.,
temperature inside the clay room during day and night was lower by about 5°C than the concrete
Figure 11. House ceiling made
of wood rafters and shingles on
steel beams.
Figure 12. Iron and wood doors
and windows used in the house.
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wall room, and temperatures in the clay wall room were closer to human thermal comfort range.
This is caused by thermal mass effect as clay walls absorb heat at day time and gradually releasing
it inside the room during night.
Figure 13. The device used to
measure temperature is the
thermo Meter.
Figure 14. Measurements of
room temperature in the clay
and concrete rooms at 1 pm in
Nov. and Dec. 2017.
Figure 15. Room temperature in
the clay and concrete rooms at
9 p.m. in Nov. and Dec. 2017.
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Residents of the case study house said that the rooms made of clay bricks in their house have
a more comfortable climate than the rooms of concrete bricks, especially in the summer. The
residents of the house were asked about the kind of heating they use in winter. They said they use
gas heaters and that the rooms with clay walls consume one gas cylinder (12.5 kg) per week for
heating an average of 6 hours a day. While heating the rooms with concrete brick walls consumes
1.5 cylinders per week. The residence also said there are negative characteristics of clay walls, such
as tendency towards erosion and capability to shelter insects inside cracks.
More elaboration of the results in the discussion to further explore the effect of thermal mass on
room temperature and the proximity to the human thermal comfort zone.
10. Discussion
The mud brick wall of the room (R1) is about three times thicker than the concrete walls in
room R2 which indicates that thickness of construction walls is a significant factor of thermal
Figure 17. Measurements of
room temperature in the clay
and concrete rooms at 9 p.m. in
July and August 2018.
Figure 16. Room temperature in
the clay and concrete rooms at
1 pm in July and August 2018.
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mass effect. Thickness of walls reduces thermal conductivity and enables heat storing, which
give inner spaces more insulation from external heat effects. Heating and cooling loads are
consequently reduced, which in turn reduces energy required for heating or cooling during the
usage of building.
The comparison between the indoor temperature in R1 and R2 in Table 4 indicates that the T
1
day = 21°C is 10°C cooler than the outside temperature (OT) 31°C. T
2
day 25°C is 6°C cooler than
OT. Thus, R1 temperature is 4°C cooler than R2 and in the human comfortable zone which
requires less energy for cooling. At night, R1 is still cooler than R2 by 2.5°C as T
1
-T
2
= 2.5°C.
These result confirm the conclusions that thermal mass works well in hot climates (Section 6,
Alaidroos & Krarti, 2015).
In colder temperatures in Nov. and Dec, the comparison Table 5 show that T
1
d-T
2
d = −3,
which means that indoor temperature of R1 is maintained warmer by 3°C during daytime, and
5°C at colder temperature at night. The results agree with existing literature that high
thermal mass structures are likely to be effective in hot climates; however, in cold climates
the effect is less.
The residents of the house were asked about the kind of heating they use in winter and energy
cost. They said that heating room R1 which is of an area = 12 m
2
by a gas heater for an average of
6 hours a day for a week consumes around one gas cylinder (12.5 kg). The cost of a gas cylinder in
Jordan is 7 dinars = 10 dollars, this is about 40 USD a month. Heating the room R2 consumes 1.5
cylinders/week, which is about 6 cylinders/month, with a total cost = 59. USD Thus, the increase in
heating cost for R2 = 59–40 = 21 USD/month.
This analysis may differ taking into account other factors such as number of occupants, size and
type of heater, insulation, windows and devices. Yet, quantifying cost differences of energy con-
sumption of both rooms for cooling and heating is a way to demonstrate the effect of thermal
mass on energy consumption.
Table 4. Comparison between room temperatures in summer (July and Aug. 2018)
Time Outside
Temperature
OT
R1: Clay brick room
OT T
1
T
1
d = 21°C,
T
1
n = 25.25°C
R2: Concrete brick
room OT—T
2
T
2
d = 25°
C T
2
n = 23.5
T
1
T
2
1 p.m. 31°C 31°C − 21°C = 10°C 31°C − 25°C = 6°C 10–6 = 4°C
9 p.m. 25°C 25°C − 21°C = 4°C 25°C − 23.5°C = 1.5°C 4–1.5 = 2.5°C
Td, Tn: average temperature at day or night
Table 5. Comparison between room temperatures in winter (Nov and Dec. 2018)
Time OT R1 OT T
1
T
1
day = 20
°C T
1
night = 17
R2 OT—T
2
T
2
d
= 17°C T
2
n = 12°C
T
1
T
2
1 p.m. 18.5°C 18. 5 °C − 20°C = −1.5°C 18. 5°C − 17°C = 1.5°C −1.51.5 = −3°C
9 p.m. 12°C 12°C − 17°C = −5°C 12°C − 12°C = 0°C 0–5 = −5°C
Heat transfer (Q) from the concrete brick wall is four times of the mud wall (50 Btu/h ÷ 12.7 Btu/h = 4; sec. 4, pp.4). Heat
transferred to the room R2 requires more energy for cooling than room R1 in summer. The amount of this energy is:
Q
concrete
—Q
clay
= 50Btu/h—12.7 Btu/h = 36.3Btu/h. The Btu power difference for one month, assuming heat transfers for
6 hours a day = 36.3×6×30 = 6534 Btu/month. The power conversion formula of kW to BTU
IT
/hr is: P
(kW)
= P
(BTU/hr)
/3412.142
(www.rapidtables.com). To convert 6534 BTU/hr to kilowatts (kW): P
(kW)
= 6534 BTU/hr/3412.142 = 1.915 kW. The cost of retail
tariff of electricity in Jordan for households of the consumption block (161–300) kWh/month is 72 Fils/kWh = 0.1$/kWh
(NEPCO, 2020). Thus, the cost of 1.915 kW = 0.1$ X 0.1915 kW = 1.951$. The extra 36.3 Btu/h will cost about 2$/month.
Sharaf, Cogent Engineering (2020), 7: 1804092
https://doi.org/10.1080/23311916.2020.1804092
Page 15 of 18
11. Conclusion
Thermal mass is often presented as a desirable feature of buildings and structures. However, the
effects of thermal mass on energy consumption are poorly quantified in the existing literature. The
methodology applied in this paper provides a way to quantify the effects of thermal mass in terms
of energy and costs.
The experimental application shows that the method can provide useful quantitative results and
provides a degree of insight and gives meaningful results when applied to an old structure. In this
respect, the adopted method has significant potential. In terms of analysis, the results for a hot
climate with large diurnal temperature variations show that reductions in energy use are possible; this
is in agreement with accepted results regarding thermal mass. However, for cold climates where
heating rather than cooling is the predominant concern, this analysis shows that thermal mass is not
as efficient, and the drive towards high thermal mass structures in such regions warrants much further
study before it is applied. As the two tested examples show, the thickness of a wall, is important. The
same conclusions apply to both new-build construction and retrofit, and for cold climates, a thermal
mass structural will perform as insulation from the outside temperatures. Further research may
address construction materials of high thermal mass with less thickness.
More generally, for the equivalent overall conductivity, a design goal in hot climates ought to
increase thermal mass, rather than a reduction in it. This study has looked at the heat flows only,
and makes little allowance for the method of heating or cooling. The results presented here do,
however, stretch beyond those of the particular wall types considered.
The authors carried out similar analyses for other locations and wall types, and similar wall types,
with broadly similar results; and the method is applicable, in principle, to any type of construction to
provide a quantitative analysis of the effects of thermal mass on energy consumption.
Funding
The author received no direct funding for this research.
Author details
Firas Sharaf
1
E-mail: f.sharaf@ju.edu.jo
ORCID ID: http://orcid.org/0000-0002-7873-8588
1
Department of Architecture, The University of Jordan,
Amman, Jordan.
Cover Image
Source: Author.
Citation information
Cite this article as: The impact of thermal mass on building
energy consumption: A case study in Al Mafraq city in Jordan,
Firas Sharaf, Cogent Engineering (2020), 7: 1804092.
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