Journal of Engineering, Project, and Production Management

2021, 11(3), 196-206

Energy Performance Analysis of Building Envelopes

Ibrahim Motawa1, Asser Elsheikh2, and Esraa Diab3
1
Professor, Structural Engineering Department, Mansoura University, Elgomhouria St., Mansoura, 35516, Egypt, E-mail:
i_a_motawa@mans.edu.eg
2
Assistant Professor, Department of Civil Engineering, Peoples’ Friendship University of Russia (RUDN), Russia. E-
mail: elsheykh-am@pfur.ru; Structural Engineering Department, Mansoura University, Egypt. E-mail:
assermfee@mans.edu.eg
3
Graduate Student, Building and Construction Engineering Department, Tanta Higher Institute for Engineering and
Technology, Tanta, El-Gharbia, Egypt, E-mail: esraadiab807@yahoo.com (corresponding author).

Engineering Management
Received November 15, 2020; revised December 30, 2020; accepted January 1, 2021
Available online February 2, 2021
_________________________________________________________________________________________

Abstract: The building sector has a high level of energy consumption caused mainly by the buildings heating and cooling
energy demands to satisfy indoor comfort requirements. Reducing both the amount of energy consumed and the life cycle
cost is a main challenge for the construction of buildings. It is evident that sustainable materials have low environmental
impacts and need low consumption of energetic resources in addition to their durability and recyclability. Therefore, this
research aims to test different sustainable materials available in Egypt for the construction of building envelopes that
include local stones “Marble and Limestone” and insulation materials “Polyurethane- expanded and Extruded polystyrene
(XPS) foam” in order to achieve savings in energy and total life cycle cost. The simulation tests were conducted through
Design Builder software. The results aim to provide solutions for building designers to achieve energy-efficiency and cost-
effective design. The proposed alternatives showed a significant reduction in energy consumption by up to 62% and the
total life cycle costs significantly reduced by up to 45.8%.

Keywords: Building energy performance, thermal comfort, initial cost, payback period, life cycle cost.

Copyright © Journal of Engineering, Project, and Production Management (EPPM-Journal).

DOI 10.2478/jeppm-2021-0019
_________________________________________________________________________________________

1. Introduction sustainable materials have low environmental impacts and

need low consumption of energetic resources in addition to
The energy sector across the globe is facing huge their durability and recyclability, many research has been
challenges. For example, Egypt has the largest consumption conducted to use such materials for various building
of oil and natural gas in Africa: about 20% of Africa’s oil elements. This research aims to test different sustainable
consumption and 40% of dry natural gas consumption materials for the construction of building envelopes. As the
(Energy Information Administration, 2015). Additionally, study is conducted in Egypt, local stones and insulation
the population inflated issue increases the demands for new materials “Polyurethane- expanded and Extruded
buildings, which will rapidly increase the energy polystyrene (XPS) foam” are used to modify external walls
consumption rate of the operation stage for these buildings. and roof systems. The study evaluates the impact of using
In this way, the electricity demand is expected to increase these materials on energy consumption and the building life
by 6.8% annually over the next years (Hanna, 2015). For cycle cost. The research uses simulation tests as
this reason, building designers and stakeholders are experimental works are not part of the methodology at this
searching for more effective solutions to restrict building stage. This paper firstly reviews the related literature on
energy consumption. During the building life cycle, the building envelopes, then the proposed sustainable materials
operation stage is responsible for a large amount of energy for cladding and roofing will be described, and then the
consumption, through the HVAC loads: heating, cooling, simulation tests and results will be discussed.
ventilation, lighting, and equipment loads. During this stage,
there are a large amount of energy losses through the 2. Literature Review
building envelope elements: external wall, roof, doors,
windows, which raise the demand for energy to recover the The design of high thermal performance envelope systems
indoor temperature to the thermal comfort region. In order has attracted increasing attention in both academic and
to improve the efficacy of the envelope elements, the heat professional fields (Lin et al., 2016). The exterior surfaces
transmittance value (U-value) must be reduced. As of a building envelope system are exposed to several
environmental factors specific to the local climate, such as:
 Energy Performance Analysis of Building Envelopes 197

dirt, wind, sunlight, snow, and rain. All these environmental Atikol (2017) in order to find an optimum insulation
factors contribute to variations in thermal and moisture thickness. The study used a wall system as shown in Fig. 1-
performance. When the incident solar radiation hits the C that consisted of plaster, brickworks, insulation,
envelope surface, part of the solar radiation is reflected back brickworks, and plaster. The maximum energy saving
and the other part is absorbed by the envelope system. The achieved was at 45.1 cm, while the total wall thickness
absorbed part of solar radiation results in increasing the greatly increased to 96.1 cm.
surface temperature, thereby increasing the cooling energy
loads in summer and decreasing/ increasing the heating Salandin and Soler (2018) analyzed different scenarios
energy loads in winter. Therefore, the studies to improve for material types as well as the thickness of each layer in
the thermal performance of the building envelope try to wall system that consisted of plaster, brickworks, insulation,
minimize the thermal transmittance (U-value) of the air gab, brickworks, and plaster, as shown in Fig. 1-D.
envelope elements in order to reduce the heat gains or losses. Although the study tested the wall system thermal
For this research, the focus will be on improving the performance, the energy-saving percentage was not entirely
thermal performance of the external walls and roof clear for the suggested solution. This makes homeowners
elements. The following sections will review previous not aware of how the suggested solution could save more
works on testing external wall and roof systems using energy than the existing system.
simulation (numerical analysis) methods as well as those 2.2. Testing External Wall Systems using Experimental
systems tested in experimental work. Works
2.1. Testing External Wall Systems using Numerical
Analysis Tejedor et al. (2017) measured the U-value for a modified
wall system that consisted of plaster, insulation, brickworks,
Mayhoub et al. (2019) compared the thermal performance and plaster as shown in Fig. 2-A. The results showed low
of the sustainable material “Autoclaved Aerated Concrete U-value with a reasonable thickness, the construction costs
Blocks” instead of brickworks in a modified wall system and the life cycle costs were unknown in order to evaluate
that consisted of gypsum plaster, concrete block, extruded the suitability of the suggested solution to implement.
polystyrene, and brickwork as shown in Fig. 1-A. The effect
of this replacement led to a slight reduction of energy An advanced wall system that consisted of plaster,
consumption by 0.18% in addition to the great increase of brickworks, insulation material, air gab, and brickworks as
the environmental impacts by 54%. However, it enhanced shown in Fig. 2-B was tested by Guillen et al. (2014). The
thermal comfort conditions by 18.9%. According to these indoor thermal comfort was enhanced by 30%. The annual
results, the proposed sustainable material did not achieve energy consumption for the wall system could not be
the enhancement of all objective functions as targeted, and evaluated by the experimental work, which makes it
it was not enough to convince the costumers toward that difficult for homeowners to understand the advantages of
choice. such an energy-efficient system.

Ingrao et al. (2016) created a wall system that consisted Asdrubali et al. (2014) tested another advanced wall
of plaster, thermal block, thermal insulation, air gab, and system that consisted of plaster, thermal block, insulation,
cement plaster, as shown in Fig. 1-B. The proposed system and thermal block as shown in Fig. 2-C. The study
achieved energy reduction by 13% with usage of recycled recommended that there should be a trade-off between the
materials “polyester fiber” which is characterized by low increase of total thickness and the U-value reduction to
energy demand during the life cycle and is also eco-friendly. meet other social and economic measures. The thermal
Although the proposed system reduced the energy performance of a green wall system was tested by Nadia et
consumption and the environmental impacts, the total al. (2013) which consisted of cement plaster, brickworks,
thickness of this system is great “47.5 cm”. To help the cement plaster, and plant cover layer “Jasmine and
wide adoption of green buildings, the total wall thickness Aristolochia” as shown in Fig. 2-D. The test was conducted
must be reasonable that could be acceptable by designers in the semi-arid regions during the summer period. The
and homeowners. results showed that the plant cover layer minimized the
indoor temperature; however, it increased the relative
The effect of different insulation thicknesses on the humidity.
energy-saving percentage has been tested by Aktemur and

Fig.1. External wall systems tested using numerical analysis

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198 Motawa, I., Elsheikh, A., and Diab, E.

Fig.2. External wall systems tested using experimental works

Fig. 3. Flat roof systems using numerical analysis

2.3. Testing Flat Roof Systems using Numerical changing the material type has a small effect on energy
Analysis saving by 7%, so the study did not provide a convincing
solution to homeowners.
The effect of adding a reflective coating to a roof system on
the building energy consumption was tested by Mohamed Gagliano et al. (2015) tested the thermal performance of
et al. (2016). The proposed system consisted of cement a green roof system that consisted of plant layer, soil,
sealant “reflective coating,” concrete blocks tiles, soil, pavement layer, insulation layer “8 cm”, and reinforced
bitumen, reinforced concrete R.C slab, and gypsum plaster, concrete slab as shown in Fig. 3-D. This system reduced the
as shown in Fig. 3-A. The reflective coating has a great annual energy needs by 85.2% and the thermal discomfort
effect on saving energy consumption by 17.4%. The intensity has been reduced by 96%. This system used a
proposed roof system included some unsustainable massive thickness of “54 cm”. The study did not investigate
materials that worsen the environmental impacts during the the life cycle cost to evaluate the profitability of such a
building life cycle. system.
Saber and Maref (2019) analyzed a roof system which 2.4. Testing Flat Roof Systems using Experimental
consisted of ceramic tile “light color,” mortar, sand screed, Works
insulation layer, waterproofing, sand screed, foam concrete,
and reinforced concrete slab as shown in Fig. 3-B. The The effect of the total evaporation in different plant growth
study focused on maximizing the energy-saving only stages on energy consumption was tested by Bevilacqua et
without specifying the proposed other sustainability goals: al. (2015). The study performed an experimental test in
the environmental impacts and the life cycle costs. Catalonia-Spain,and determined the required depth of the
substrate layer to enhance energy savings. The green roof
The effect of different tile materials on energy saving system consisted of plant layer, substrate layer, insulation
was tested by Radhi et al. (2017). The tile materials tested layer, porous concrete, geotextile felt, air/water layer,
were concrete screed, bituminous felt, light tile ceramic, waterproofing, and geotextile felt, as shown in Fig. 4-A.
and dark tile ceramic. The roof system consisted of tile, The results highlighted that the maximum plant grows that
insulation layer, reinforced concrete slab, air gab, and occurred at the beginning of spring and summer seasons has
gypsum plaster, as shown in Fig. 3-C. It is concluded that a negative impact on energy-saving caused by the lack of

Journal of Engineering, Project, and Production Management, 2021, 11(3), 196-206

 Energy Performance Analysis of Building Envelopes 199

moisture in the substrate layer. Therefore, the substrate over each window. The traditional roof system consisted of
layer depth must set at 8 cm. concrete tile, mortar, sand, insulation board, bituminous
damp insulation, and reinforced concrete slab. The
Zhao et al. (2013) tested the effect of variable green roof modified wall system consisted of a double brickworks
materials which included: seven types of plants and five layer with an air gap in between, as shown in Fig. 5-C and
types of substrates on green roof thermal performance 5-D. The results showed that this system slightly reduced
based on evaluating the roof U-value for a commercial energy consumption by 13%.
building in Chicago. The roof system consisted of a plant
layer, substrate layer, filter layer, waterproof layer, and 2.6. Aim and Objectives of This Research
reinforced concrete slab “R.C” as shown in Fig. 4-B. The
results show that both plant and substrate types could affect From the reviewed literature on building envelope systems
the green roof thermal performance as high as 15%. to minimize energy consumption, researchers have used
different envelope component materials including the
The thermal performance of four roof tile types was addition of insulation layers in order to maximize energy
tested by Ascione et al. (2018) which included: dark saving. Not all research has conducted an economic
bituminous membrane, commercial high reflectivity paint, evaluation for these developments despite its importance to
polished aluminum paint, and acrylic white paint. The roof homeowners (Mayhoub et al., 2019; Ingrao et al., 2016;
system consisted of a mineral fiber panel, steel sheet, Aktemur and Atikol, 2017; Salandin and Soler, 2018;
insulation material, and steel sheet as shown in Fig. 4-C. Tejedor et al., 2017; Guillen et al., 2014; Asdrubali et al.,
The results show that the white roof paints reduced the 2014) and also the use of sustainable materials are not
variation of the inside and outside temperature and also widely adopted. Many works were also conducted to
reduced the cooling loads. However, the heating loads have improve building thermal performance by adding reflective
been increased significantly during the winter season. coating and insulation layers but also without economic
evaluation of these developments (Mohamed et al., 2016;
Tang and Zheng (2019) tested the thermal performance Saber and Maref, 2019; Radhi et al., 2017; Ascione et al.,
of a green roof during sunny summer days. The green roof
2018). On the other hand, adding a plant layer to building
system consisted of a canopy layer, substrate layer, planting envelope systems has been tested which significantly
plate, waterproofing, cement mortar, hollow core slab, and improved building thermal performance during the summer
plaster as shown in Fig. 4-D. The results showed that the season; however, the side effect of these solutions was
green system reduced energy consumption by 14.7%. recorded in the increase of the relative humidity (Nadia et
2.5. Testing Building Envelope Systems in Egyptian al., 2013; Gagliano et al., 2015; Bevilacqua et al., 2015;
Climates Zhao et al., 2013; Tang and Zheng, 2019). In the Egyptian
context, the improvement of thermal performance by using
Khalil et al. (2018) suggested two types of envelope insulation layers and by adding air gab layers to building
systems: a low and a high envelope technology using a envelope systems have been studied. The use of air gap
reflective slats shading system. The low type uses the layers has slightly reduced energy consumption compared
insulation material “straw bale” with 10 cm thickness for to the use of insulation layers, but the initial costs were
walls and roofs. The high type uses polyurethane foam with approved to be significantly higher in case of using
5cm thickness for the walls and roofs. The two systems insulation layers that suggested this solution is not
consist of the same wall and roof layers as shown in Fig. 5- appropriate to the economic situation in Egypt (Khalil et al.,
A and 5-B. The results showed a reduction in the annual 2018; Mahmoud et al., 2019). Furthermore, the use of
energy consumption by 46% and 50% for the low and high sustainable materials for building envelope systems in
technologies, respectively. While the low type is 5 cm Egypt still needs further research. In this regard, the
thicker than the high type, the high type has higher initial research analyzes the performance of different stone
construction costs. cladding “Marble and Limestone” and different insulation
Mahmoud et al. (2019) tested a modified building materials “Polyurethane-expanded and Extruded
envelope located in Cairo, where the system consisted of a polystyrene (XPS) foam” to modify external walls and roof
traditional roof system, modified wall system, and 6 mm systems. The following sections will illustrate the
single reflective glass with reinforced concrete sunshades methodology adopted to achieve these objectives.

Fig. 4. Flat roof systems tested using experimental works

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200 Motawa, I., Elsheikh, A., and Diab, E.

Fig. 5. Building envelope systems tested in Egyptian climates

Fig. 6. A residential building unit layout (Khalil et al., 2018)

3. Material and Methods year calendar is divided as follows: season 1 (1th October :
31st May), season 2 (1st June : 30th August), and season 3
This research aims to test different sustainable materials for (31st August : 30th September). Table 2 summarized
the construction of building envelopes. To achieve the occupancy, artificial lighting, and HVAC system schedules.
study aim, three objectives have been defined:
Khalil et al. (2018) have developed the design of
 To select a reference case building model shown in Fig. 6 where he added an
 To design the proposed wall and roof cross-sections insulation layer of 5cm to the wall and roof systems, and
 To test the designed cross-sections against energy changed the glazing system to double-glazing with blinds
consumption, thermal discomfort, life cycle cost shading system, as detailed in Table 3. The modified model
(LCC), and payback period showed a significant reduction of 48% for the energy
3.1. Selection of a Reference Case consumption and a reduction of 18.7% for the discomfort
hours compared with the base model.
A local existing building model has been chosen to test the
proposed new wall and roof cross-sections and to compare 3.2. Description of the Proposed Stone Cladding
the performance results with its current known results. The Materials for the Wall and Roof Systems
current building energy performance has been measured by This research proposes different alternatives by adding an
Khalil et al. (2018). The building is a residential apartment insulation layer and a stone cladding layer to the external
block located in Alexandria, Egypt. Fig. 6 shows the plan wall system and the roof system in order to improve energy
layout of the building. Table 1 shows the building efficacy. The proposed cross-sections for the external wall
properties and typology components characteristics. The and roof alternatives are shown in Fig. 7.

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 Energy Performance Analysis of Building Envelopes 201

Table 1. Case study building and its typology components (Khalil et al., 2018)
Building Description (Base model)
Shape Rectangular (25 m × 11 m)
Floor height 2.8 m
Occupancy density 5 person
Building features Description of the housing in initial case
2 cm cement plaster + 12.5 cm burned brick + 2 cm cement plaster, U-value = 2.5
External wall components
W/m2.K
2 cm ceramic/porcelain + 2 cm cement plaster + 4 cm sand and gravel + 2 cm
Flat roof components bitumen pure + 7 cm pre-cast concrete + 16 cm reinforced concrete slab, U-value =
1.39 W/m2.K, roof surface absorbance = 0.6
2 cm ceramic/clay tile + 2 cm cement plaster + 6 cm sand and gravel + 5 cm pre-cast
Ground floor slab
concrete + 2 cm bitumen + 20 cm pre-cast concrete , U-value = 1.58 W/m2.K
2 cm ceramic tile + 2 cm mortar + 4 cm sand and gravel + 15 cm reinforced concrete
Typical Floor slab components
slab, U-value = 1.8 W/m2.K
Wall U-value = 1.732 W/m2 K
Partition wall
Wall surface absorbance = 0.7
6 mm single clear pane glass, U-value = 6.25 W/m2.K
Glazing type Solar heat gain coefficient = 0.5
Shading coefficient for glass = 0.70
WWR 0.45 north, 0.35 south facades
Window frame type Wooden frame type
Temperature set point 24 °C - adaptive
Living rooms 17 W/m2
Lighting installation power
Bedrooms 13 W/m2
density
Others 9 W/m2
Plug loads average installation
6 W/m2
power density

Table 2. Occupancy, artificial lighting, and HVAC system schedules (Khalil et al., 2018)
Season 1 2 3
Occupancy Living room 6 a.m. to 11 p.m. 10 a.m. to 11 p.m. 11 a.m. to 11 p.m.
schedules Bed rooms 11 p.m. to 6 a.m. 11 p.m. to 10 a.m. 11 p.m. to 11 a.m.

Artificial lighting Living room 6 to 10 p.m. 7 to 11 p.m. 8 to 11 p.m.

schedules Bed rooms 9 p.m. to 11 p.m. 11 p.m. to midnight 11 p.m. to midnight

HVAC system Living room - 5 to 11 p.m. 3 to 11 p.m.

schedules Bed rooms - 11 p.m. to 5 a.m. 11 p.m. to 5 a.m.

Table 3. Modified typology components (Khalil et al., 2018)

Building features Description of the developed envelope system (Khalil’s model)
2 cm cement plaster + 5 cm polyurethane, foam + 12.5 cm burned brick + 2 cm cement
External wall components
plaster, U-value = 0.4 W/m2.K
2 cm ceramic/porcelain + 2 cm cement plaster + 4 cm sand and gravel + 5 cm
Flat roof components polyurethane, foam + 2 cm bitumen pure + 7 cm pre-cast concrete + 16 cm reinforced
concrete slab, U-value = 0.4 W/m2.K
Double blue glass with 6 mm/13 mm argon, U-value = 2.5 W/m2.K, solar heat gain
Glazing type
coefficient = 0.494, direct solar transmission is 0.373, light transmission is 0.5
WWR 0.45 north, 0.50 south facades
Blind with high reflectivity slats for the external glass layer of south facade, which
Shading system
worked dynamically from 8:00 to 18:00

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202 Motawa, I., Elsheikh, A., and Diab, E.

The study uses two local stone cladding (Marble and construction and to the roof construction as detailed in
Limestone) which are found in Egypt as follows: Table 4. The window to wall ratio is reduced to 20% for all
proposed alternatives. The HVAC system is allowed for
 Marble stone found in the areas of Assiout, Kharga, the mixed mode, so that natural ventilation could be
Zafarana, and East of Sohag (Kandil and Selim, 2006) involved during the determination of HVAC working
 Limestone found in the areas of South of Luxor, Giseh period in order to minimize energy consumption. The
plateau, and Holocene (Klemm and Klemm, 2001) thermo-physical properties of the building construction
These stone cladding materials have been selected for materials are defined according to the materials databases
the following reasons: provided by ASHRAE (ASHRAE Handbook, 2009). The
unit cost of each wall type was determined by the
 Sustainable natural materials have low environmental researcher through a field study conducted in March 2019.
impacts and need low consumption of energetic It is subject to changes based on market prices. The
resources in addition to its durability and recyclability. following sections illustrate the adopted methodology to
 The use of natural stones gives the opportunity to determine energy consumption, discomfort hours, and the
maintain the identity and peculiarity of the construction LCC for case study building.
culture.
 Marble envelopes represent a relatively common 3.3. Testing the Proposed Design Alternatives
architectural solution used in a variety of building A BIM model was first developed to test the building
facades (including historical buildings). It has the ability performance using “Design Builder” that used to evaluate
to reduce solar heat gains, while improving indoor the annual energy consumption and initial cost in this study.
thermal comfort and energy efficiency in the summer All input data (such as zones types assignment, occupancy
time. Limestone also has the ability to enhance the density, occupancy schedules, HVAC type, HVAC
thermal comfort of a house and its sustainability. schedules, lighting systems, economic data, etc.) was then
Based on the base model described above, this research exported for energy simulation using “Energy Plus.”
proposes different alternatives to the external wall

Fig. 7. Proposed stone cladding elements

Table 4. Modified building elements

Building element Element layer Thickness (cm) U-value Cost/m2(LE) Weight (Kg/m2)
Lime stone cladding 2.5
Cement plaster 2
Wall 1 Polyurethane, expanded 8 0.216 600 205.4
Concrete blocks 15
Plaster board 2.5
Marble board 2.5
Cement plaster 2
Wall 2 XPS layer 8 0.285 735 221.75
Concrete blocks 15
Plaster board 2.5
Lime stone 2.5
Cement plaster 2
Roof 1 Polyurethane, expanded 10 0.198 1730 499.85
R.C slab 16
Plasterboard 2.5
Marble tile 2.5
Cement plaster 2
Roof 2 XPS 10 0.274 1915 516.45
R.C slab 16
Plasterboard 2.5

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 Energy Performance Analysis of Building Envelopes 203

Then, the design variables alternatives were created and

a test was conducted for each alternative to evaluate energy
consumption, thermal discomfort, life cycle cost (LCC),
and payback period. The prediction of the annual energy
consumption is based on the heat balance method adopted
by the “Energy Plus” mathematical model and used as a
plug-in for the BIM software (Design Builder) to run
energy simulation.
3.3.1. Discomfort hour calculation
The energy simulation tool (Energy Plus) generates the
annual discomfort hours according to the American Fig. 8. Comparison between different systems to
National Standard ASHRAE 55 (2004). ASHRAE
establishes the ranges of indoor environmental conditions determine the payback period (Khalil et al., 2018)
to achieve acceptable thermal comfort for occupants of 4. Results and Discussion
buildings according to specific parameters that must be
taken into account to examine the thermal comfort in any This section discusses the energy simulation results for the
building. These parameters include environmental suggested alternatives in comparison with the reference
parameters, air temperature, mean radiant temperature, cases. Table 5 shows the results obtained by the simulation
relative humidity, in addition to personal parameters: like and calculation of the annual energy consumption (AEC) in
activity levels and clothing insulation (ASHRAE Standard Kwh/m2, the percentage of reduction in the annual energy
55, 2004). consumption (% AEC), discomfort hours per year (D.H.),
the percentage of reduction in the annual discomfort hours
3.3.2. Life cycle cost and relative payback period (% D.H.), the initial cost in USD (I.C.), the percentage of
calculation reduction in the initial costs (% I.C.), the total life cycle cost
The used simulation tool (Design Builder) provides a (LCC) in USD, the percentage of reduction in the LCC (%
limited lifetime of up to 40 years to determine the LCC LCC), and payback period (P.P.).
(Life Cycle Cost/ Parameters/Design Builder Website, The base model represents the traditional building
2019). Therefore, the life cycle cost will be calculated in properties used in Egypt; therefore, its energy simulation
this research using a mathematical model that formed by the results are set as a benchmark point “base case” for
Federal Energy Management Program (Fuller and Petersen, comparison. In addition, Khalil’s model was also used for
1996) as shown in Eq. (1). For the purpose of comparison, comparison as it was developed based on the same model.
the values of few variables were assumed according to As shown in Table 5, Khalil’s model reduced energy
Khalil et al. (2018). consumption by 48%, and thermal discomfort by 18.7%.
(1+L)n However, the initial costs increased by 20.7%, and also the
P( -1) total life cycle costs were reduced by 32.1%.
(1+r)n
LCC = IC+ (1)
L−r Alternatives wall 1 and wall 2 proposed by this research
Where: I.C.: initial costs, P: annual operating cost significantly reduced the energy consumption by 62% with
which calculated based on Egyptian Electricity Holding slight increase in the initial costs by 5.2% and 8%,
Company Annual Report (Egyptian Electricity Holding respectively. Furthermore, the life cycle costs were reduced
Company Annual Report, 2018), L: annual increase rate in by 45.8% and 44.6%, respectively. However, the thermal
the price of electricity = 16% (Khalil et al., 2018), r: Bank discomfort hours have slightly reduced by 4.4% and 4.3%,
interest rate = 12% (Khalil et al., 2018), n: lifetime = 90 respectively. Alternatives roof 1 and roof 2 have achieved
years (Khalil et al., 2018). a great reduction of the initial costs by 11.4% and 7.3%,
respectively with a significant reduction of energy
The relative payback period between alternatives is consumption by 56% and 55%. The total life cycle costs
calculated by drawing their cash flow lines as shown in Fig. were reduced by 42.4% and 41.1%. However, the
8. The intersection of these lines means that the difference discomfort hours slightly reduced by 3.6% and 3.4%,
between the initial cost value of the two alternatives “base respectively.
model and Khalil’s modified model” has been achieved,
where the relative payback period will be determined from
the line initiation to the intersection point.
Table 5. Results of the simulation tests
%
Model name AEC %AEC DH I.C. %IC LCC %LCC PP
D.H.
Base Base Base Base Base
Base model 22.4 3271.85 37179.5 157228
case case case case case
Khalil’s model 11.54 -48 2659.20 -18.7 44871.8 +20.7 106718 -32.1 12
Alternative wall 1 8.45 -62 3126.10 -4.4 39107.9 +5.2 85209 -45.8 3
Alternative wall 2 8.62 -62 3132.54 -4.3 40136.5 +8.0 87159 -44.6 5
Alternative roof 1 9.81 -56 3154.88 -3.6 32938.1 -11.4 90495 -42.4 0
Alternative roof 2 9.97 -55 3160.58 -3.4 34477.8 -7.3 92657 -41.1 0

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204 Motawa, I., Elsheikh, A., and Diab, E.

total LCC saving percentage of the proposed alternatives

are higher than Khalil’s model. Alternatives roof 1 and roof
2 have lower initial costs than the costs of the base model,
but the initial costs of alternatives wall 1 and wall 2 are
slightly higher than the initial costs of the base model. Both
alternatives wall 1 and wall 2 have lower initial costs
percentage than Khalil’s model.
The relative payback periods of the proposed
alternatives have shown much lower values than Khalil’s
model in comparison with the base model. While the
relative payback period of Khalil’s model is 12 years, the
results show 3 and 5 years for alternatives wall 1 and wall
2, respectively, as shown in Fig. 9-a and 9-b. However,
alternatives roof 1 and roof 2 have initial costs lower than
the base and Khalil’s models, so the relative payback
periods are considered zero for the two alternatives as
shown in Fig. 9-c and 9-d.
The base model used a wall thickness of 16.5 cm where
the wall thickness of Khalil’s model was 21.5 cm. The total
thickness of alternatives wall 1 and 2 is 30 cm, which may
explain the difference in the results of the AEC and the D.H.
While the proposed wall alternatives are thicker but they
still provide less I.C. and LCC. For the roof system, the base
model used a roof thickness of 35 cm where the roof
thickness in Khalil’s model was 38 cm. The total thickness
of alternatives roof 1 and 2 is 33 cm, which still gives lower
values for all measures.
The wall and roof weights of the base model are 257.9
kg/m2 and 718.2 kg/m2 respectively where the wall and roof
weight of Khalil’s model were slightly higher 259.4 kg/m2
and 719.7 kg/m2 respectively. The proposed alternatives
wall and roof have significantly reduced weight 205.4,
221.75, 499.85, and 516.45 kg/m2 respectively, which is a
quite important factor for design and construction purposes
that gives an advantage to the proposed alternatives over the
reference cases.
4.1. Discussion
From the above analysis, all proposed alternatives showed
a significant reduction in energy consumption by up to 62%.
However, for the discomfort hours the alternatives showed
slight reduction by up to 4.4%. The total life cycle costs of
all proposed alternatives were significantly reduced by up
to 45.8%. While the initial costs increased by 5.2%, and 8%
respectively for alternative wall 1 and wall 2, alternatives
roof 1 and roof 2 have shown reduced initial costs by 11.4%
and 7.3%, respectively. Alternative wall 2 has the
maximum payback period of the proposed alternatives “5
years”, followed by alternative wall 1 “3 years”, and
alternatives roof 1 and 2 have payback periods equals to
zero. However, Khalil’s model has the maximum payback
periods “12 years”, so all proposed alternatives
significantly reduced the payback period compared to
Khalil’s model. One of the disadvantages of the proposed
alternatives wall 1 and wall 2 is related to the wall thickness
which is thicker than the reference cases. However, the total
thickness of alternatives roof 1 and roof 2 is reasonable
when compared with the reference cases. A key advantage
Fig. 9. Determination of the relative payback periods of the proposed alternatives over the reference cases was
approved as they are lighter in weight (reduction of 20.4%,
(adopted and modified from Khalil et al. (2018)) 14%, 30.4%, and 28% respectively compared to the
reference case). Although this study was implemented in
All proposed alternatives have higher energy saving
Egypt, the study results could be achieved in different
percentage than Khalil’s model. However, the discomfort
countries by adding such sustainable materials to the
reduction percentage is lower than Khalil’s model. Also, the
building envelope components.

Journal of Engineering, Project, and Production Management, 2021, 11(3), 196-206

 Energy Performance Analysis of Building Envelopes 205

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Journal of Engineering, Project, and Production Management, 2021, 11(3), 196-206

206 Motawa, I., Elsheikh, A., and Diab, E.

Construction, Procedia Engineering, 145, 987–994. Asser Elsheikh is Assistant Professor,

DOI: 10.1016/j.proeng.2016.04.128. Department of Civil Engineering,
Nadia, S., Noureddine, S., Hichem, N., and Djamila, D. Peoples' Friendship University of
(2013). Experimental study of thermal performance Russia (RUDN), Structural
and the contribution of plant-covered walls to the Engineering Department, Mansoura
thermal behavior of building. Energy Procedia, 36, University. In 2015 he achieved his
995–1001. DOI:10.1016/j.egypro.2013.07.113. PhD degree in Moscow State
Radhi, H., Sharples, S., Taleb, H., and Fahmy, M. (2017). University of Civil Engineering, Moscow, Russia. He
Will cool roofs improve the thermal performance of our
received his BSc and MSc in Mansoura University (2000,
built environment? A study assessing roof systems in
2005). He is author of 6 journal publications, and 6 papers
Bahrain. Energy and Buildings, 135, 324-337.
http://dx.doi.org/10.1016/j.enbuild.2016.11.048. in the proceedings of international conferences. He has
Saber, H. H. and Maref, W. (2019). Energy performance research interests of: BIM, cost estimation, building
of cool roofs followed by development of practical materials, and construction project management.
design tool. Frontiers in Energy Research, 7, Article
No.122. DOI: 10.3389/fenrg.2019.00122.
Salandin, A. and Soler, D. (2018). Computing the Esraa Diab is Demonstrator at
minimum construction cost of a building’s external Building and Construction
wall taking into account its energy efficiency. Journal Engineering Department, Tanta
of Computational and Applied Mathematics, 338, 199- Higher Institute for Engineering and
211. https://doi.org/10.1016/j.cam.2018.02.003. Technology, El-Gharbia, Egypt. In
Tang, M. and Zheng, X. (2019). Experimental study of the 2016 she achieved BSc in Civil
thermal performance of an extensive green roof on Engineering Department, Delta
sunny summer days. Applied Energy, 242, 1010-1021. Higher Institute for Engineering and
DOI:10.1016/j.apenergy.2019.03.153. Technology, Mansoura, Egypt. She has research interests
Tejedor, B., Casals, M., Gangolells, M., and Roca, X. of BIM, energy efficiency in building, thermal comfort,
(2017). Quantitative internal infrared thermography for life cycle cost, and building envelope elements design.
determining in-situ thermal behaviour of façades.
Energy and Buildings, 151, 187-197. DOI:
10.1016/j.enbuild.2017.06.040.
Zhao, M., Tabares-Velasco, P. C., Srebric, J., and
Komameni, S. (2013). Comparison of green roof plants
and substrates based on simulated green roof thermal
performance with measured material properties.
Proceedings of 13th Conference of the International
Building Performance Simulation Association, BS,
Chambery, France.

Prof. Ibrahim Motawa is a Professor

of Construction Engineering and
Management, Mansoura University,
Egypt. Prof Motawa obtained his PhD
from the School of Architecture,
Building and Civil Engineering,
Loughborough University, UK. He got
his undergraduate degree in Civil
Engineering and his Master degree in Structural
Engineering. His research work covers the areas of:
Building Information Modelling, Big data in construction,
Construction Simulation and Optimisation, Modelling
Complexity in the Built Environment, Energy Efficient
Construction and Knowledge Management. Prof Motawa
has been the principle investigator of research projects
related to BIM development and energy efficiency in
buildings, and has supervised many PhD students in related
areas.

Journal of Engineering, Project, and Production Management, 2021, 11(3), 196-206

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