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8 

 

 

 

Article 

Evaluating zero-energy strategies in mixed-use 

buildings: a case study 
Mahmood Abdoos, Mohammad Mahdi Mobaraki, Hossein Yousefi*, Younes Noroollahi 

School of Energy Engineering and Sustainable Resources, College of Interdisciplinary Science and Technology, University 

of Tehran, Tehran, Iran 

A R T I C L E   I N F O 
 

Article history: 
Received 19 October 2024  
Received in revised form 
24 November 2024 
Accepted 04 December 2024 
 
Keywords: 
Zero energy building, Mixed-use development, 
Energy efficiency, Thermal insulation,  
Sustainable design, HVAC systems 
 
*Corresponding author 
Email address:  
hosseinyousefi@ut.ac.ir 
  
 
DOI: 10.55670/fpll.fuen.4.1.2 

A B S T R A C T 
 

The building sector is responsible for over 40% of global energy consumption, 
necessitating innovative strategies to minimize energy usage in both 
commercial and residential buildings, ultimately striving for zero-energy status. 
This study addresses the relatively overlooked area of zero-energy buildings 
within the context of a combined commercial-residential structure, utilizing 
Carrier (HAP) software for precise thermal and cooling load calculations. The 
research introduces a multifaceted approach, examining various scenarios that 
influence energy demand reduction, including wall color modifications, the 
application of noble gases for window insulation, shading effects, and technical 
innovations in window dimensions. Notably, this study emphasizes insulation 
as a cost-effective strategy for achieving zero-energy objectives, revealing that 
the optimal scenario incorporating krypton insulation, color adjustments, and 
effective shading achieves a significant 21.36% reduction in energy 
consumption. This research not only contributes novel insights into mixed-use 
building design but also provides a practical framework for future energy-
efficient building projects. 
 

 
1. Introduction  

In numerous countries across the globe, residential 

buildings account for approximately 40% of the energy 

demand in residential areas, with an impressive 60% of the 

total energy consumption specifically allocated towards 

maintaining optimal heating conditions within living spaces 

[1, 2]. Moreover, it is worth noting that a predominant portion 

of this energy is consumed by air conditioning systems [3]. 

However, implementing thermal insulating materials in 

buildings yields a substantial reduction in energy load. 

Furthermore, there has been a notable surge in the adoption 

of innovative technologies within the realm of building 

construction in recent years. This technical advancement has 

consistently resulted in improved building management 

practices and has paved the way for the successful 

administration of building systems [4]. Implementing 

fundamental measures to conserve energy can result in a 

significant economic boost for the country. Within this arena, 

design and construction play crucial roles, as energy 

consumption can be substantially reduced by applying 

innovative design and construction techniques [5]. The global 

concerns of energy scarcity and environmental pollution 

invoke apprehension, and it is widely acknowledged that 

curtailing energy demand in buildings presents an efficacious 

solution to address this pressing issue [6, 7]. Researchers 

worldwide exhibit unwavering dedication in their endeavors 

to optimize the design and functionality of both buildings and 

energy systems [8-10]. Accurate thermal-cooling load 

assessments are fundamental for designing efficient HVAC 

systems. Studies utilizing advanced software tools have 

demonstrated that proper load analysis can lead to 

reductions in energy consumption by up to 20% in office 

buildings, emphasizing the importance of integrating 

technology into building design processes [11, 12]. Ramesh, G 

et al. [13] assert that buildings contribute to approximately 

thirty-eight percent of greenhouse gas emissions, with twenty 

percent attributed to residential buildings and eighteen 

percent to commercial structures, thereby placing them as 

significant contributors to global warming [14]. 

Implementing effective insulation strategies is crucial for 

reducing energy consumption in buildings. A study assessing 

various insulation scenarios found that buildings could 

achieve up to 30% reduction in heating and cooling loads 

when combined with renewable energy systems (e.g., solar 

photovoltaic panels). This synergy is vital for reaching net-

zero targets, as highlighted in multiple building performance 

analyses [15, 16]. Consequently, research conducted by 

Felimban et al. [17] and colleagues posits that the demand for 

 

 

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M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

9 

 

electricity in the residential sector of Saudi Arabia is projected 

to double by 2025, in comparison to the statistics recorded in 

2009. In their research, Boemi et al. [18] contend that a 

pivotal advancement lies in the realm of sustainable design 

for residential and commercial buildings, coupled with the 

resilience of existing structures, all geared towards achieving 

reduced and optimized energy consumption. As elucidated by 

Baetens. in their research, harnessing renewable energy 

sources to meet the energy demands of buildings constitutes 

a noteworthy means of curbing energy consumption [19, 20]. 

Integrating solar panels in commercial properties has 

emerged as a transformative approach to achieving energy 

efficiency. A report noted that less than 3% of commercial 

buildings currently utilize solar panels; however, with over 8 

billion square meters of suitable rooftops in the U.S., there is 

potential to generate approximately 1,400 terawatt-hours of 

electricity annually, nearly 40% of total utility sales. This 

transition from cost centers to profit centers underscores the 

financial viability of solar investments in commercial real 

estate [21, 22]. A comprehensive bibliometric analysis of 

renewable energy integration in zero-energy carbon 

buildings reveals critical gaps in research methodologies and 

implementation strategies. Machine learning techniques are 

increasingly being applied to forecast energy needs and 

optimize the integration of renewable technologies, which is 

essential for enhancing building performance and achieving 

sustainability goals [23]. Expounding on building energy 

modeling, Robertson J. J. and colleagues propose various 

approaches to enhance energy efficiency, including the 

optimization of passive resilience [24], refinement of building 

position geometry [25], optimization of cooling tower exergy 

[26], and optimization of control systems for variable 

refrigerant flow [27]. 

Using phase change materials has been shown to 

significantly enhance thermal comfort while reducing energy 

demands. Research indicates that buildings employing PCM 

can reduce cooling energy consumption by up to 25%, 

particularly in climates with high-temperature variability. 

This innovative approach allows buildings to maintain 

comfortable indoor conditions with minimal reliance on 

mechanical cooling systems [28, 29]. The innovation of this 

research is distinguished by its comprehensive analysis of a 

large-scale mixed-use building, integrating both commercial 

and residential elements to achieve zero-energy status. 

Unlike previous studies focusing on smaller, single-use 

structures, this research addresses the complexities 

associated with a 4072 square-meter facility, which presents 

unique thermal characteristics and energy management 

challenges. This study innovatively employs Carrier (HAP) 

software to model various scenarios that consider the impact 

of building colors, the use of noble gases like krypton for 

window insulation, and shading effects on energy 

consumption. By pioneering a comparative analysis between 

noble gases and traditional air insulation methods, this 

research provides valuable insights into enhancing energy 

efficiency in large buildings. Furthermore, it incorporates an 

economic perspective by evaluating cost-effective insulation 

strategies while ensuring that the commercial integrity of the 

building is maintained. It fills a critical gap in the literature 

regarding mixed-use developments and sets a precedent for 

future studies to optimize energy performance in large-scale 

buildings. The findings underscore the viability of achieving 

zero-energy status through innovative insulation techniques 

and strategic design modifications, reinforcing the 

importance of such approaches in sustainable urban 

development. 

2. Mathematical expression 

Building walls commonly comprise multiple layers 

composed of different materials, thereby transforming the 

wall into a composite structure. Consequently, the thermal 

resistance exhibited by a composite wall can be determined 

by summing the resistances of its constituent layers. The 

composite thermal resistance of the wall is expressed in 

equation (1): 

Thermal resistance composite wall: R1 + R2 +
X1

K1
+

X2

K2
+ ⋯                                                                                                            

       (1) 

During the heat transfer process between the indoor and 

outdoor air of a building, a thin layer of air forms along the 

surface of the building wall, creating a thermal resistance that 

hinders the flow of heat. This layer, commonly referred to as 

the air film, exhibits a unit thermal coefficient denoted as F. 

The resistance of this air film, analogous to the resistance of 

the surrounding air, is represented by 1/f, where f is the value 

determined by the speed of the airflow. 

U =
1

1

fi
+R1+R2+⋯+

1

fo

                                                                              (2)  

U=The overall coefficient of thermal conductivity 

1/Fi=Inner air film resistance 
R1, R2=Thermal resistance of layers 

1/Fo=Outdoor air film resistance 

The calculation of heat transfer through various building 

components, including walls, ceilings, floors, windows, and 

glass, can be determined using the following equation (3): 

𝑄 = 𝐴𝑈(𝑡1 − 𝑡2)                                         (3) 

Q=Heat transferred from the wall BTU/hr. 
A=wall area ft2 

T1=Temperature on the warmer side ) F) 

T2=Temperature on the cooler side) F) 

Every building has certain rooms or spaces that we 

intentionally do not desire to be heated or cooled to the same 

extent. If there exists an unheated room adjacent to the space 

where we are assessing the thermal load, and this adjacent 

room does not undergo cooling. The temperature of the 

adjacent uncooled room is expressed in equation (4): 

Adjacent uncooled room temperature = ti + (to − ti) ∗

0.667                                                                                                     (4) 

3. Methodology 

3.1 Software  

Hap software exemplifies the amalgamation of two 

formidable tools, offering a comprehensive package that 

encompasses the design of HVAC systems for commercial 

buildings, as well as robust energy analysis capabilities to 

ascertain energy consumption and operational costs for 

various design typologies. The fusion of these two tools yields 

substantial time savings, as input data and calculations from 

the System Design Calculation can seamlessly transition into 

energy studies, obviating the need for redundant input. 



M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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Furthermore, the carrier (HAP) hourly analysis software, an 

esteemed component of the Carrier (HAP) HVAC design 

software family, holds the distinction of being one of the 

oldest and most all-encompassing software solutions 

available for accurately computing the cold and heat load of 

buildings across diverse applications [30]. 

3.2  Case study 

The average rainfall in Tehran varies from 230 mm to 

500 mm annually. Tehran is one of the most climatic cities and 

four seasons in Iran . Precipitation is usually high in winter. 

The cold season starts in March but a little earlier in the 

mountains. Cold seasons last three or four months. In 

February, the cold decreases gradually, and in late February, 

the weather warms up more quickly, and in early May, the 

weather is relatively warm. The climate of Tehran province is 

warm and dry in the desert and South, in the cold and semi-

humid basin areas, and in the cold Highlands with long 

winters. The warmest month of the Spring year is reported 

with an average maximum temperature of 37 ° C, and the 

coldest month of the year with an average minimum 

temperature of zero ° C. The temperature in Tehran is slightly 

cold in the mild winter and warm in the summer. For these 

reasons, this site was chosen over several other potential 

locations. The selection was primarily driven by two key 

factors. First, the site allows for the implementation and 

comparison of various scenarios, enabling the identification 

of the optimal option. Second, the region's unique climate 

contributes significantly to the natural cooling and heating of 

the building, which is crucial for sustainable design. 

Additionally, the study's scope is intentionally focused on 

facilitating the practical application of the best scenario. 

The project is situated within Tehran, serving as a 

tangible real-world case study. It encompasses both 

commercial and residential functionalities, comprising six 

floors dedicated to residential use, four floors designated for 

parking, and an additional commercial floor supplemented by 

a half-floor extension. Spanning an area of 4072 m2, this 

project represents a unique example not previously explored 

in the literature concerning the integration of commercial and 

residential spaces. Particularly noteworthy are the numerous 

thermal waste spaces inherent in the design, offering 

opportunities for mitigation through the implementation of 

existing strategies.  

Given the considerable size of the project, the imperative 

of energy reduction is underscored. Table 1 provides insight 

into the climatic characteristics of the city, as elucidated 

within the carrier (HAP) software, further informing the 

project's development. In this modeling endeavor, the 

selection of air conditioning systems emerges as a pivotal 

consideration, given the thermal demands inherent in both 

the commercial and residential sectors. The convergence of 

energy supply and coordination poses a significant challenge 

in this context. The ventilation system adopted for the 

modeled building comprises a fan coil system supplemented 

with fresh air intake. Notably, the introduction of fresh air in 

the commercial sector plays a crucial role in alleviating 

thermal stress. Furthermore, the heating system chosen for 

this mixed-use project is a packaged system. 

 

Table 1. Weather conditions in Tehran city 

Region Middle east 
Iran 

Tehran 
location 
City 

latitude 35.5 deg 

longitude 51.4 deg 
elevation 5418 ft 

Summer design DB 104 F 

Summer coincident WB 75 F 

Summer daily range 25 F 

Winter design DB 25 F 

Winter coincident WB 18 F 

Soil conductivity 1 Btu/hr/ft/F 

 

The selection of air conditioning units is meticulously 

aligned with the climatic nuances of Tehran, where both 

cooling and heating functionalities are requisite owing to the 

climatic fluctuations. In this regard, neither system holds 

superiority over the other, and thus, they are not prioritized 

based on singular efficiency metrics. Instead, the choice of air 

conditioning systems is calibrated to ensure optimal 

performance under diverse climatic conditions prevalent in 

Tehran. 

3.3 Scenarios used in modeling 

3.3.1 Walls 

Examining walls and their efficacy in mitigating energy 

consumption is a viable avenue for addressing energy and 

environmental concerns. According to Table 2, it is stated that 

according to previous research, choosing the most 

appropriate color can significantly reduce energy 

consumption throughout the year. This reduction manifests 

in a cooling effect of approximately 1.5 degrees Celsius during 

warm seasons and a corresponding increase in temperature 

of approximately one degree Celsius during colder periods. 

The analysis reveals that the wall's design is crucial in 

minimizing heat transfer between the interior and exterior 

environments. The high absorptivity (0.900) of the dark 

exterior surface color suggests that while it may absorb more 

heat from sunlight, effective insulation strategies can mitigate 

excessive heat gain during warmer months. The total R-value 

indicates how well the wall resists heat flow; higher values 

correlate with better-insulating properties, essential for 

achieving zero-energy goals. The U-value reflects the rate at 

which heat is transferred through the wall assembly; lower U-

values are desirable as they signify reduced heat loss or gain. 

Incorporating advanced insulation techniques and 

understanding the thermal dynamics of building materials is 

vital for achieving zero-energy buildings. This analysis not 

only underscores the importance of selecting appropriate 

materials but also advocates for innovative design 

considerations—such as wall color and layered construction, 

that can lead to substantial energy savings. By focusing on 

these elements within a mixed-use context, this research 

provides valuable insights for future developments to 



M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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enhance energy efficiency in large-scale buildings, thus 

contributing to sustainable urban development goals. 

Analysis of Table 3, The enhanced thermal performance of 

Wall Type Number 2 illustrates the importance of selecting 

appropriate materials and configurations for achieving zero-

energy buildings. The higher R-value signifies better 

insulation against heat transfer, critical for maintaining 

comfortable indoor temperatures while minimizing energy 

consumption. The significantly lower U-value suggests that 

this wall type will reduce heating and cooling loads, 

contributing to overall energy savings and supporting zero-

energy objectives. Including R-7 board insulation represents 

a strategic advancement in building design to enhance energy 

efficiency. 

The shift to a lighter exterior color demonstrates an 

understanding of passive solar design principles, which can 

further optimize energy performance. In summary, the 

comparison between Wall Type Number 1 and Wall Type 

Number 2 underscores the critical role that material selection 

and design choices play in achieving zero-energy buildings. 

The advancements seen in Wall Type Number 2, particularly 

through integrating high-performance insulation and 

strategic color selection, demonstrate a clear pathway toward 

enhanced energy efficiency in mixed-use developments. 

These findings reinforce the necessity for continued 

exploration and implementation of innovative building 

strategies that align with sustainability goals in the 

construction industry. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

According to Table 4, Wall 1's high absorption coefficient 

(0.9) implies it will absorb more solar heat, potentially 

leading to higher cooling loads in the summer months. In 

contrast, Walls 2 and 3 have lower absorption coefficients 

(0.45), making them more favorable for energy conservation 

as they reduce the heat gained from solar radiation. The U-

value is a critical measure of thermal performance; Wall 1 has 

the highest U-value (0.225), indicating poorer insulation and 

greater heat loss or gain compared to Walls 2 and 3, which 

both have a much lower U-value (0.096). This substantial 

difference highlights the superior insulating properties of 

Walls 2 and 3. The choice of color significantly affects energy 

performance; the dark color of Wall 1 results in higher heat 

absorption and, consequently, increased cooling 

requirements. Walls 2 and 3 utilize a dark and light color, 

respectively, both contributing to lower energy consumption 

due to their reflective properties and reduced heat gain. In 

summary, the analysis of Table 4 reveals that Walls 2 and 3 

are more advantageous for achieving energy efficiency in 

building designs aimed at zero-energy goals when compared 

to Wall 1. These walls' lower absorption coefficients and U-

values indicate better thermal performance and reduced 

energy demands for heating and cooling. This analysis 

underscores the importance of material selection and color 

choice in optimizing building envelopes for enhanced energy 

efficiency, particularly in mixed-use developments where 

diverse thermal characteristics must be managed effectively. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 2. Details of wall type number 1 

Outside surface color dark absorptivity 0.900 

Layers: inside to 
outside 

thickness density Specific .HT. R-Value Weight 
in lb/ft3 BTU/lb/F HR-ft2-F/BTU Lb/ft2 

Inside surface 
resistance 

0 0 0 0.68500 0 

Gypsum board 0.625 50 0.26 0.56000 2.6 

Air space 0.000 0.0 0.00 0.91000 0.0 
LW concrete block 4.000 38.0 0.20 1.51500 12.7 

Face brick 4.000 125.0 0.22 0.43300 41.7 

Outside surface 
resistance 

0.000 0.0 0.00 0.33300 0.0 

Total 8.625   4.44 56.9 
   Overall U-value 0.225 BTU/hr/ft2/F 

 

Table 3. Details of wall type number 2 

Outside surface color Light Absorptivity 0.450 

Layers: inside to 
outside 

thickness density Specific.HT. R-Value Weight 
in lb/ft3 BTU/lb/F HR-ft2-F/BTU Lb/ft2 

Inside surface 
resistance 

0 0 0 0.68500 0 

5/8 -in gypsem 
board 

0.625 50 0.26 0.56004 2.6 

R-7 board insulation 1.000 2.0 0.22 6.94445 0.2 

4-in LW concrete 
block 

4.000 38.0 0.20 1.51515 12.7 

Face brick 4.000 125.0 0.22 0.43300 41.7 
Outside surface 

resistance 
0.000 0.0 0.00 0.33300 0.0 

Total 9.625   10.47 57.1 

   Overall U-value 0.096 BTU/hr/ft2/F 

 



M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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Table 4. Technical specifications of walls defined in different 

scenarios 

 

3.3.2 Windows 

The window plays a crucial role in reducing energy 

consumption as an integral component of a building. Widely 

regarded as a vital element in construction, the window 

serves multiple functions essential to the built environment. 

Among these functions, providing ventilation, natural light, 

and illumination to the interior space is paramount. 

Additionally, windows serve as filters, regulating the influx of 

sunlight and controlling the airflow to prevent excessive 

entry into the designated environment. When utilized 

effectively within a building, windows contribute significantly 

to enhancing the interior environment, thereby optimizing 

their impact on energy efficiency and overall comfort. 

According to Table 5, Window type number 1 features 

dimensions of 6.00 feet in height and 10.00 feet in width, 

constructed from aluminum without thermal breaks. This 

design choice may result in higher heat transfer compared to 

windows with thermal breaks, potentially leading to 

increased energy costs for heating and cooling. The overall U-

value of 0.779 BTU/hr/ft²/°F indicates a moderate level of 

thermal performance, suggesting that this window may allow 

more heat loss compared to more efficient alternatives. 

Furthermore, the overall shade coefficient of 0.827 signifies 

that the window provides a reasonable level of solar control, 

which can help mitigate excessive heat gain from sunlight. 

The absence of internal shading may enhance natural light 

entry but also necessitates careful temperature regulation 

within the space. In summary, while this window offers ample 

daylighting opportunities, its thermal performance may limit 

its effectiveness in energy-efficient building designs. 

The properties outlined in Table 6 are critical for 

understanding how Window Type Number 1 will perform in 

various thermal scenarios. The high transmissivity coupled 

with low reflectivity means this window type will allow 

substantial solar heat gain. While this can be beneficial in 

colder months for passive heating, it may pose challenges 

during warmer months when cooling demands increase. The 

relatively low absorptivity indicates that only a minor amount 

of solar energy is retained by the glass, which helps mitigate 

excessive heat buildup within the window assembly.  

 

 

 

 

 

 

Table 5. Details of window type number 1 

 

However, in combination with high transmissivity, it 

suggests that careful consideration must be given to shading 

strategies to manage heat gain effectively. When comparing 

Window Type Number 1 with other potential window 

configurations (not detailed here), several factors should be 

considered. Unlike more advanced window types that may 

utilize multiple glazing layers or low-emissivity coatings to 

enhance thermal performance, Window Type Number 1's 

simplicity may limit its effectiveness in extreme climates or 

high-performance applications. The gap type (¼-inch air 

space) provides some insulation; however, it may not be 

sufficient compared to windows employing argon or krypton 

gas fills or thicker air spaces that significantly improve 

thermal resistance. In practical terms, the characteristics of 

Window Type Number 1 suggest several applications and 

considerations for building design. Passive Solar Design: 

Given its high transmissivity, this window type could be 

effectively utilized in passive solar design strategies where 

maximizing natural light and heat gain during winter months 

is desired. Shading and Control Mechanisms: To counteract 

potential overheating during summer months, integrating 

external shading devices or using interior shading solutions 

will be essential to maintain comfort levels and reduce 

reliance on mechanical cooling systems. In summary, Table 6 

highlights the fundamental thermal characteristics of 

Window Type Number 1, emphasizing its role in influencing 

energy efficiency within mixed-use buildings aimed at 

achieving zero-energy status. The balance between 

transmissivity, reflectivity, and absorptivity underscores the 

need for strategic design choices that optimize natural light 

while managing heat gain effectively. As part of a 

comprehensive energy strategy, this window type can 

contribute positively to overall building performance when 

integrated with appropriate shading and insulation 

techniques. According to Table 7, Window type number 2, 

with dimensions of 6.00 feet in height and 4.00 feet in width, 

is constructed from aluminum with thermal breaks, which 

aids in reducing heat transfer. This feature enhances energy 

efficiency and lowers heating and cooling costs. With an 

overall U-value of 0.557 BTU/hr/ft²/°F, this window 

demonstrates relatively good performance in preventing heat 

loss.  

 

 

 

 

 

 

 

 

 

Absorption 
coefficient 

U-value Color Different 
types of walls 

0.9 0.225 dark Wall 1 

0.45 0.096 dark Wall2 

0.45 0.096 light Wall3 

Height 6.00 ft 

Width 10.00ft 

Frame type Aluminum without thermal 
breaks 

Internal shade type None 

Overall u-value 0.779 btu/hr/ft2/f 

Overall shade coefficient 0.827 

Table 6. Details of window type number 1 

Glazing Glass type Transmissivity Reflectivity Absorptivity  

Outer glazing 1/8” clear 0.841 0.078 0.081 

Glazing#2 1/8” clear 0.841 0.078 0.081 

Glazing #3 Not used  

Gap type ¼” air space 

 



M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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Table 7. Details of window type number 2 

 

Additionally, the overall shade coefficient of 0.796 

indicates that this window effectively controls solar radiation, 

helping to maintain indoor temperatures within a 

comfortable range. The absence of internal shading may 

contribute to increased natural light; however, it also raises 

the need for temperature management. Overall, this window 

presents a suitable option for spaces that require both natural 

light and energy efficiency. 

The properties outlined in Table 8 are critical for 

understanding how Window Type Number 2 will perform in 

various thermal scenarios. The high transmissivity coupled 

with low reflectivity means that this window type will allow 

substantial solar heat gain. While beneficial for passive 

heating during colder months, effective shading strategies 

may be necessary during warmer months to mitigate 

excessive heat gain.  The relatively low absorptivity indicates 

that only a minor amount of solar energy is retained by the 

glass itself, which helps mitigate excessive heat buildup 

within the window assembly. However, combined with high 

transmissivity, it suggests that careful consideration must be 

given to shading strategies to manage heat gain effectively. 

The introduction of a ½-inch krypton gap is significant as 

krypton gas has a lower thermal conductivity compared to air. 

This enhances the overall insulation performance of the 

window assembly, reducing heat transfer through conduction 

and improving energy efficiency. When comparing Window 

Type Number 2 with Window Type Number 1 (previously 

analyzed), several key differences and improvements can be 

observed. While both window types utilize clear glass with 

similar transmissivity and reflectivity values, Window Type 

Number 2 benefits from using krypton gas in its gap, offering 

superior insulation properties compared to the air-filled gap 

in Window Type Number 1. Using krypton gas significantly 

lowers the U-value for Window Type Number 2 compared to 

Window Type Number 1. This reduces heat transfer rates and 

enhances thermal resistance, making it more effective in 

maintaining indoor temperatures and reducing energy 

consumption. Combining high transmissivity and improved 

insulation through krypton gas positions Window Type 

Number 2 as a more energy-efficient option than Window 

Type Number 1. This improvement is particularly relevant for 

buildings aiming for zero-energy status where minimizing 

energy loss is critical. Combining high transmissivity and 

improved insulation through krypton gas positions Window 

Type Number 2 as a more energy-efficient option than 

Window Type Number 1. This improvement is particularly 

relevant for buildings aiming for zero-energy status where 

minimizing energy loss is critical. In practical terms, the 

characteristics of Window Type Number 2 suggest several 

applications and considerations for building design. Given its 

high transmissivity, this window type could be effectively 

utilized in passive solar design strategies where maximizing 

natural light and heat gain during winter months is desired 

while ensuring adequate measures are in place to control heat 

gain during summer months. 

To counteract potential overheating during summer 

months, integrating external shading devices or using interior 

shading solutions will be essential to maintain comfort levels 

and reduce reliance on mechanical cooling systems. In 

summary, Table 8 highlights the fundamental thermal 

characteristics of Window Type Number 2, emphasizing its 

role in influencing energy efficiency within mixed-use 

buildings aimed at achieving zero-energy status. The balance 

between transmissivity, reflectivity, absorptivity, and 

enhanced insulation through krypton gas underscores the 

need for strategic design choices that optimize natural light 

while managing heat gain effectively. As part of a 

comprehensive energy strategy, this window type can 

contribute positively to overall building performance when 

integrated with appropriate shading and insulation 

techniques. 

According to Table 9, Window 1 has a higher U-value 

(0.779), indicating less insulation effectiveness compared to 

Windows 2 and 3 (both at 0.551). This suggests that Windows 

2 and 3 will provide better energy efficiency by minimizing 

heat transfer. The use of krypton gas in Windows 2 and 3 

enhances their thermal performance significantly compared 

to the air insulation used in Window 1. Krypton provides 

superior insulation properties due to its lower thermal 

conductivity. While all three windows have comparable Sh-

coefficients, Windows 2 and 3 maintain a balance between 

solar heat gain reduction and thermal resistance, making 

them more suitable for energy-efficient designs in varying 

climates. The combination of lower U-values and effective 

solar heat gain management in Windows 2 and 3 positions 

them as favorable options for achieving zero-energy building 

goals, whereas Window 1 may require additional strategies to 

enhance its energy performance. 

3.3.3 Roofs  

The walls of a building serve as its outermost shell, 

exposed to direct air and temperature fluctuations, thus 

playing a pivotal role in heat exchange and energy regulation. 

Among these walls, the roof wall holds particular significance 

due to its expansive horizontal surface area. This orientation 

exposes it to prolonged periods of sunlight and other 

atmospheric elements, leading to heightened heat exchange 

compared to other walls of the building. Consequently, the 

heat exchange dynamics of the roof wall are accentuated, 

rendering it a critical focal point in building design and energy 

management considerations. This recognition underscores its 

importance as a key scenario warranting thorough analysis 

and optimization strategies. According to Table 10, The 

provided table details the specifications of Roof Type Number 

1, including the outside surface color, thermal absorptivity, 

and characteristics of various roof layers. The dark outside 

surface color, with an absorptivity of 0.900, indicates a high 

capacity for heat absorption. The layers of the roof consist of 

inside surface resistance, steel deck, board insulation, and 

built-up roofing, each with specific thicknesses, densities, and 

thermal properties. The total thickness of the layers is 1.410 

inches, with an R-value of 8.29 HR-ft²-F/BTU, indicating 

effective insulation performance. 

Height 6.00 ft 
Width 4.00ft 

Frame type Aluminum with thermal 
breaks 

Internal shade type None 
Overall u-value 0.557 btu/hr/ft2/F 

Overall shade coefficient 0.796 



M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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Finally, the overall U-value of the roof is calculated to be 

0.121 BTU/hr/ft²/F, reflecting its adequate thermal efficiency 

and contributing to reduced heat transfer. These 

characteristics enhance energy efficiency and improve 

comfort within the building. Table 11 presents the 

specifications for Roof Type Number 2, characterized by a 

light outside surface color and a thermal absorptivity of 0.450, 

indicating a lower capacity for heat absorption compared to 

darker roofs. The roof layers include inside surface resistance, 

steel deck, board insulation, and built-up roofing, each with 

defined thicknesses, densities, and thermal properties. The 

total thickness of the roof assembly is 1.410 inches, with an R-

value of 8.29 HR-ft²-F/BTU, demonstrating effective 

insulation capabilities. The overall U-value is calculated at 

0.121 BTU/hr/ft²/F, suggesting efficient thermal 

performance and minimal heat transfer. These attributes 

contribute positively to energy efficiency and occupant 

comfort within the building structure. Table 12 analyzes roof 

types in the context of net zero energy buildings and reveals 

significant differences in thermal performance based on their 

absorptivity and color. Roof Type 1, characterized by a dark 

color and an absorptivity of 0.900, is likely to absorb a 

substantial amount of solar heat, which can benefit colder 

climates but may lead to increased cooling demands in 

warmer conditions.  In contrast, Roof Type 2 features a light 

color with an absorptivity of 0.450, indicating a reduced 

capacity for heat absorption, which can enhance energy 

efficiency by minimizing cooling loads during hot weather.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Roof Type 3, also light in color with an absorptivity of 

0.90, presents a unique case where, despite its light 

appearance, it retains a high absorptive capacity similar to 

Roof Type 1. These variations highlight the importance of 

selecting appropriate roofing materials and colors in the 

design of net zero energy buildings, as they directly influence 

energy consumption patterns and overall building 

performance. Effective roof design can significantly 

contribute to achieving the energy efficiency goals essential 

for net zero energy status, particularly by optimizing thermal 

comfort and reducing reliance on mechanical heating and 

cooling systems. 

3.3.4 Shade 

Another scenario involves the strategic deployment of 

shading to minimize sunlight penetration and optimize 

energy consumption within the building space. Harnessing 

sunlight and energy efficiently in buildings constitutes a 

fundamental principle for energy optimization, with shades in 

architecture serving as a viable solution. Awnings, in 

particular, represent an effective means of harnessing energy 

resources judiciously. The judicious utilization of solar energy 

within buildings plays a pivotal role in examining the impact 

of shading on reducing energy consumption. According to 

Figure 1, shading is exclusively implemented in Scenario 3, 

aimed at influencing the necessity for shading and its role in 

diminishing energy consumption. The introduction of shading 

in the form of a canopy has resulted in decreased energy 

usage attributable to the creation of a form of insulation and 

thermal barrier.  

Table 8. Details of window type number 2 

Glazing Glass type Transmissivity Reflectivity Absorptivity  
Outer glazing 1/8” clear 0.841 0.078 0.081 

Glazing#2 1/8” clear 0.841 0.078 0.081 
Glazing #3 Not used  
Gap type 1/2” krypton 

 

Table 9. Technical specifications of windows defined in different scenarios 

Sh-coefficient U-value Insulation type Types of windows 

0.827 0.779 air Window1 

0.796 0.551 krypton Window2 

0.796 0.551 krypton Window3 

 

Table10. Details of roof type number 1 

Outside surface 
color 

Dark Absorptivity 0.900 

Layers: inside to 
outside 

Thickness Density Specific.HT. R-Value Weight 
in lb/ft3 BTU/lb/F HR-ft2-F/BTU lb/ft2 

Inside surface 
resistance 

0 0 0 0.68500 0 

Steel deck 0.034 489.0 0.12 0.00011 1.4 
Board insulation 1.000 2.0 0.22 6.94400 0.2 
Built up roofing 0.376 70.0 0.35 0.33200 2.2 
Outside surface 

resistance 
0.000 0.0 0.00 0.33300 0.0 

Total 1.410   8.29 3.7 
   Overall U-value 0.121 BTU/hr/ft2/F 

 



M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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Table 12. Specifications of technical ceilings defined in different 

scenarios 

 

The selection of an appropriate canopy is contingent 

upon factors such as location, climate, and the sun's angle, 

which fluctuates throughout the day. In a building, windows 

represent areas susceptible to high levels of light and heat 

ingress. Employing awnings for windows serves to deter the 

entry of heat and sunlight. Since glass has a greater 

propensity for heat absorption compared to walls, the 

strategic use of various types of canopies holds promise for 

reducing energy consumption and maintaining interior 

coolness. Shading windows or glass walls effectively curtails 

interior heat buildup, diminishing the reliance on cooling 

systems and reducing overall energy consumption. 

4. Results and discussion 

According to Table 13, in the Normal mode, the building 

spans an area of 4072 square meters. The walls are 

constructed using standard materials, while the glass features 

regular insulation with an air layer. The walls and ceiling are 

also dark in color, with an absorption coefficient of 0.9.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1. Details of shade type number 1 

 

 

 

 

 

 

 

 

 

 

Notably, no shading elements are incorporated into the 

building design. In this Normal mode configuration, the 

thermal load of the building amounts to 1090681 BTU/hr. 

According to Table 14, the output from the Carrier (HAP) 

software for Scenario 2 is obtained under specific conditions. 

The wall incorporates R7 insulation, while the color of the 

wall remains dark. However, the ceiling color is light in this 

scenario. The absorption coefficient is maintained at 0.45.  

The space between the double-glazed window is filled with 

krypton gas for enhanced insulation compared to air. Notably, 

no shading elements are present. Additionally, the thermal 

load of the building has been recalculated to 916152 BTU per 

hour after implementing the specified scenarios. Based on 

Table 15, in this scenario, the color of the wall is lightened, 

and the absorption coefficient remains at 0.45. The 

specifications for the roof and window are consistent with 

those of Scenario 2. Additionally, all windows are equipped 

with shades. This configuration represents the optimal 

scenario, resulting in a thermal load calculated at 857610 BTU 

/hr. 
1090681𝐵𝑇𝑈/ℎ𝑟−916152𝐵𝑇𝑈/ℎ𝑟

1090681𝐵𝑇𝑈/ℎ𝑟
∗ 100 = 16%    

 

1090681𝐵𝑇𝑈/ℎ𝑟−857610𝐵𝑇𝑈/ℎ𝑟

1090681𝐵𝑇𝑈/ℎ𝑟
∗ 100 = 21.36 %  

 

916152𝐵𝑇𝑈/ℎ𝑟−857610𝐵𝑇𝑈/ℎ𝑟

916152
∗ 100 = 6.38 %  

 

 

 

 

 

 

 

 

 

 

 

Absorptivity The color of the 
modeled ceilings 

Types of 
roofs 

0.900 dark roof1 

0.450 light roof2 

0.90 light roof3 

Table 11. Details of roof type number 2 

Outside surface 
color 

Light Absorptivity 0.450 

Layers: inside to 
outside 

Thickness Density Specific.HT. R-Value Weight 
in lb/ft3 BTU/lb/F HR-ft2-F/BTU lb/ft2 

Inside surface 
resistance 

0 0 0 0.68500 0 

Steel deck 0.034 489.0 0.12 0.00011 1.4 
Board insulation 1.000 2.0 0.22 6.94400 0.2 
Built up roofing 0.376 70.0 0.35 0.33200 2.2 
Outside surface 

resistance 
0.000 0.0 0.00 0.33300 0.0 

Total 1.410   8.29 3.7 
   Overall U-value 0.121 BTU/hr/ft2/F 

 

 



M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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Table 13. Implementation of base scenario 

 

Table 14. Implementation of the most balanced scenario 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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Table 15. Implementation of the best scenario 

 

 

5. Conclusion 

The significance of zero-energy buildings (ZEBs) is 

increasingly recognized as a crucial strategy in addressing the 

building sector's substantial contribution to global energy 

consumption, which exceeds 40%. This study highlights the 

potential of ZEBs in mixed-use developments, particularly 

focusing on a unique case involving a large-scale commercial 

residential structure. By employing advanced modeling 

techniques with Carrier (HAP)software, this research not 

only identifies effective energy-saving strategies but also 

emphasizes the need for innovative approaches tailored to 

complex building types. The findings reveal that 

implementing a combination of advanced insulation methods, 

such as krypton gas for window treatments, alongside 

strategic design modifications like wall color optimization 

and shading techniques, can lead to significant reductions in 

energy consumption up to 21.36% in the most effective 

scenario. The exploration of diverse thermal characteristics 

and the integration of commercial and residential 

functionalities present new challenges and opportunities that 

have been insufficiently addressed in prior studies. As such, 

this article serves as a vital contribution to the field, 

advocating for the adoption of zero-energy principles in large 

mixed-use buildings. Future efforts should focus on refining 

these strategies across various climates and building types, 

reinforcing the role of ZEBs as a cornerstone in sustainable 

urban development and energy management practices. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Ethical issue 
The authors are aware of and comply with best practices in 
publication ethics, specifically concerning authorship 
(avoidance of guest authorship), dual submission, 
manipulation of figures, competing interests, and compliance 
with policies on research ethics. The authors adhere to 
publication requirements that the submitted work is original 
and has not been published elsewhere in any language. 

Data availability statement 
The manuscript contains all the data. However, more data will 

be available upon request from the corresponding author. 

Conflict of interest 

The authors declare no potential conflict of interest. 

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M. Abdoos et al. /Future Energy                                                                                               February 2025| Volume 04 | Issue 01| Pages 08-18 

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