Afghan Islamic International University

Engineering Faculty
Industrial Engineering Department

OPTIMIZATOIN OF HVAC ENERGY DEMAND FOR A

RESEDENTIAL BUILDING ENVELOPE IN KABUL CITY

A THESIS

Submitted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

In Industrial Engineering

By
Abdul Rahman Erfan

Advisor
Dr. Mustafa Akbari

May 2025
In the Name of Great Allah
 This thesis has been approved in partial fulfillment of the requirements for the
Degree of MASTER OF SCIENCE in Industrial Engineering.

Thesis Advisor: Dr.Mohammad Mustafa Akbari

Committee Member: Dr. Iftkhar Hussain

Committee Member: Dr. Haroon Sarwari

Department Chair: Dr. Aref Naimzad

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Abstract

This study evaluates the effect of roof and wall insulation on HVAC energy
consumption in a four-story residential building situated in the semi-arid continental
climate of Kabul. Before assessing the energy savings from upgrades like EPS
insulation (5 cm to 10 cm), double-glazed windows, external shading, and improved
airtightness, the study uses the Hourly Analysis Program (HAP) to simulate baseline
conditions with uninsulated walls and single-glazed windows. According to the results,
7.5–10 cm EPS insulation can cut heating loads by up to 43%. Energy demand can also
be decreased by upgrading windows and reducing infiltration. An approximate 30%
reduction in HVAC energy is the result of the integrated envelope improvements. These
results provide recommendations for energy-efficient design that are appropriate for the
climate and building context of Kabul.

Keywords: EPS insulation, HVAC simulation, energy efficiency, building envelope,

Kabul climate

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Acknowledgements

I would like to express my deepest gratitude to all those who supported me

throughout the course of this research and thesis writing.

First and foremost, I am sincerely thankful to my thesis advisor, [Dr. Mustafa

Akbari], for their invaluable guidance, encouragement, and constructive feedback that

greatly contributed to the successful completion of this study.

I am also grateful to the faculty and staff of [Industrial Department/Afghan

Islamic International University] for providing the necessary resources and a conducive

learning environment. Special thanks to my colleagues and friends who offered support,

shared ideas, and motivated me during challenging times.

My heartfelt appreciation goes to my family for their unwavering love, patience,

and encouragement, which have been my constant source of strength.

Finally, I acknowledge any institutions or organizations that provided data, tools,

or funding that supported this research.

This thesis would not have been possible without the contributions of all these

individuals and groups.

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Table of Contents

List of Figures.................................................................................................................iii

List of Tables...................................................................................................................iv

1 Introduction.................................................................................................................1
1.1 Background and Context.......................................................................................1
1.2 Objectives..............................................................................................................4
1.3 Problem statement..................................................................................................6
1.4 Research questions.................................................................................................7
1.Structure of the Thesis...............................................................................................7

2 Literature review........................................................................................................8

3 Research Methodology.............................................................................................22
3.1 Research Design..................................................................................................22
3.1.1 Key features of the selected building.........................................................22
( Light Destiny Consulting Services & Construction, 2025 )..............................23
3.1.2 Key Variables and Optimization Scenarios................................................23
3.1.3 Research Implementation Steps.................................................................24
3.2 Building Description............................................................................................25
3.2.1 General Characteristics...............................................................................25
3.2.2 Architectural Features................................................................................25
3.2.3 Internal Layout...........................................................................................26
3.2.4 Thermal Properties and Envelope Performance.........................................26
3.2.5 Occupancy and Usage Patterns..................................................................26
3.2.6 Climatic Context.........................................................................................27
3.3 Design Parameters...............................................................................................27
3.3.1 Wall and Roof Insulation...........................................................................27
3.3.2 Window Glazing Type...............................................................................28
 3.3.3 External Shading Devices..........................................................................29
3.3.4 Infiltration Rate and Airtightness...............................................................29
3.3.5 Summary of Design Parameters for Simulation.........................................29
3.4 Simulation Setup..................................................................................................30
3.4.1 Simulation Software...................................................................................30
3.4.2 Weather Data..............................................................................................31
3.4.3 Building Model and Thermal Zoning.........................................................31
3.4.4 Internal Gains and Occupancy...................................................................32
3.4.5 Ventilation and Infiltration.........................................................................32
3.4.6 HVAC System Assumptions......................................................................32
3.4.7 Simulation Scenarios..................................................................................33

4 Results and Discussion..............................................................................................34

4.1 Results..................................................................................................................34
4.2 Discussion............................................................................................................65

5 Conclusion and Recommendations.........................................................................70

5.1 Conclusion...........................................................................................................70
5.2 Recommendations................................................................................................70

References.......................................................................................................................vi

Appendix A....................................................................................................................xii

Appendix B....................................................................................................................xvi

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List of Figures
Figure 1. Kabul city Climatic Chart...................................................................................3

Figure 2 Typical building front view..................................................................................5

Figure 3 Typical Building Floor Plan...............................................................................23

Figure 4. HVAC Load Reduction for 5cm EPS Compare to Baseline by (kw)................40

Figure 5. HVAC Load Reduction for 5cm EPS Compare to Baseline by (%)..................41

Figure 6. HVAC Load Reduction for 7.5cm EPS Compare to Baseline by (kw).............43

Figure 7. HVAC Load Reduction for 7.5cm EPS Compare to Baseline by (%)...............43

Figure 8. HVAC Load Reduction for 10cm EPS Compare to Baseline by (kw)..............45

Figure 9. HVAC Load Reduction for 10cm EPS Compare to Baseline by (%)................46

Figure 10. Heating load Reduction vs EPS thickness (Kw)..............................................47

Figure 11. Heating load Reduction vs EPS thickness (%)................................................48

Figure 12. Cooling load Reduction vs EPS thickness (Kw).............................................49

Figure 13. Cooling load Reduction vs EPS thickness (%)................................................50

Figure 14. HVAC load Reduction for double glass vs single glass by (KW)...................53

Figure 15. HVAC load Reduction for double glass vs single glass by (%).......................54

Figure 16. HVAC load Variation for 1m peak vs no peak by (KW).................................57

Figure 17. HVAC load Variation for 1m peak vs no peak by (%)....................................58

Figure 18. HVAC load Reduction for 0.5ACH vs 1ACH by (KW).................................60

Figure 19. HVAC load Reduction for 0.5ACH vs 1ACH by (%).....................................61

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4

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List of Tables
Table1. Roof and Wall U value for different Insulation Thickness.................................28

Table 2. Summary of Design Parameters.........................................................................30

Table 3. Thermal Properties of Materials.........................................................................35

Table 4. Load Summary of Baseline Model.....................................................................37

Table 5. U-value for EPS Insulation Scenarios................................................................38

Table 6. HVAC Load for 5 cm EPS Insulation................................................................39

Table 7. HVAC Load for 7.5 cm EPS Insulation.............................................................42

Table 8. HVAC Load for 10 cm EPS Insulation..............................................................44

Table 9. Double glass scenario Description......................................................................51

Table 10. HVAC Load for 3mm Double Glass with 6mm air gap...................................52

Table 11. HVAC Load in 1m peak case...........................................................................56

Table 12. HVAC Load in 0.5 ACH case..........................................................................59

Table 13. U-Value and Infiltration rate for each Scenarios..............................................63

Table 14. HVAC load for Combined Optimized case......................................................63

Table 15.Comparison of Baseline vs Combine optimization............................................64

1 Introduction

1.1 Background and Context

HVAC (heating, ventilation, and air conditioning) systems are essential for
preserving indoor air quality and ensuring thermal comfort in buildings. Regardless of
the outside weather, these systems regulate temperature, humidity, and ventilation to
give residents a safe and cozy indoor environment. HVAC systems are essential to the
overall energy use of residential buildings since they frequently account for the largest
portion of energy consumption.

Globally, HVAC systems can account for approximately 40% to 60% of the total
energy consumption in buildings, depending on climate and building type (International
Energy Agency, 2018).

This sizeable portion of energy consumption emphasizes the necessity of

increasing HVAC efficiency and lowering its load, especially in areas with harsh
climates where there is a high demand for heating or cooling. Reducing greenhouse gas
emissions and other environmental effects requires addressing HVAC energy
consumption in sustainable building design.

Globally, the demand for HVAC systems is rising due to urbanization, population
growth, and increased expectations for indoor comfort. However, this growth comes at a
substantial energy cost. HVAC systems are responsible for a significant portion of
energy use in buildings accounting for nearly 50% of energy consumption in residential
and commercial buildings combined (International Energy Agency, 2018).

Particularly in developing nations with expanding middle classes, the need for
cooling systems is increasing as global temperatures rise and heatwaves become more
common as a result of climate change.

The increased use of air conditioners and heaters contributes not only to higher
electricity demand but also to peak energy loads, which place stress on power grids and
lead to infrastructure instability. Moreover, in many regions, electricity is still generated

1
from fossil fuels, meaning the expansion of HVAC use directly contributes to
greenhouse gas emissions, exacerbating the very climate problems that increase cooling
demand ( Santamouris, M., 2016).

The inefficiency of the current building stock exacerbates the energy challenge,
particularly in nations with lax or poorly enforced building codes. HVAC systems have
to work harder to compensate for heat gain in the summer and loss in the winter because
millions of buildings worldwide lack basic thermal insulation. A vicious cycle is
produced by this situation: high energy use raises emissions, which exacerbate climate
change and raise the need for cooling.

Enhancing building energy efficiency through passive design techniques, such as

building envelope optimization, is crucial to reducing these difficulties. By doing this,
HVAC loads can be greatly decreased, and the built environment will become more
resilient and sustainable.

The building envelope refers to the physical barrier between the interior and
exterior of a structure, including components such as walls, roofs, floors, windows, and
doors. It plays a fundamental role in controlling the flow of heat, air, and moisture into
and out of a building, directly affecting the indoor thermal environment and the
performance of HVAC systems ( Attia, S., Evrard, A., & Gratia, E., 2019).

An efficient building envelope minimizes unwanted heat loss during winter and
heat gain during summer, thereby reducing the need for mechanical heating and cooling.
Inadequate insulation, thermal bridging, and air leakage through poorly designed
envelopes can significantly increase HVAC energy loads, leading to higher operating
costs and environmental impact ( Berardi, U., 2015).

Improving the thermal performance of the envelope through insulation materials,

high-performance glazing, airtight construction, and reflective surfaces can result in
energy savings of 20–50% in both heating and cooling, depending on the climate and
building type ( Bhamare, D. K., Rathod, M. K., & Banerjee, J., 2019).

2
 As a result, one of the most economical methods for increasing building energy
efficiency and accomplishing sustainability objectives is the building envelope.

Optimizing envelope components is crucial as part of any HVAC load reduction

strategy because a poorly insulated envelope significantly increases the demand for
heating energy in cold climates like Kabul.

Kabul, the capital of Afghanistan, is situated in a high-altitude valley and

experiences a continental climate characterized by hot, dry summers and cold winters.
Average summer temperatures often exceed 35°C, while winter temperatures can drop
below −7°C, creating a high demand for both cooling and heating systems throughout
the year ( Kakar, M. A., Safi, M. H., & Hossaini, S. M., 2022).

A thorough summary of Kabul City's climate is given in Figure 1, which also

highlights monthly temperature variations and annual weather trends. Given Kabul's hot
summers and frigid winters, this climatic background is essential to comprehending the
heating and cooling requirements of residential buildings in the city.

Figure 1. Kabul city Climatic Chart

( ClimatesToTravel.com, 2023)

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 Kabul experiences severe seasonal temperature swings, as the chart illustrates,
with average summer temperatures rising above 35°C and winter temperatures falling
below -7°C. Since both heating and cooling are necessary for indoor thermal comfort,
this duality poses a serious design challenge for HVAC systems. The significance of
optimizing the building envelope to reduce energy consumption throughout the year is
highlighted by these climatic extremes.

Despite these climatic extremes, most residential buildings in Kabul are

constructed using traditional and uninsulated materials, such as unreinforced masonry,
mud bricks, or bare concrete blocks. These structures generally lack modern thermal
insulation, double-glazed windows, or airtight construction methods. As a result, the
building envelopes are highly inefficient, allowing significant heat loss during the
winter and heat gain during the summer ( Ahmad, B., & Javadi, A. A., 2019).

Moreover, Kabul faces chronic energy supply issues, including power outages
and limited access to modern heating or cooling technologies. This leads many
households to rely on inefficient and polluting heating methods, such as coal, firewood,
or diesel stoves, which not only raise indoor air pollution levels but also pose serious
health and environmental risks ( World Bank, 2020).

These conditions make the optimization of the building envelope a critical

priority in improving energy efficiency and reducing HVAC loads in Kabul’s residential
sector.

1.2 Objectives

This study's main goal is to use HAP software to optimize the HVAC energy
demand of a four-story residential building envelope in Kabul City. The purpose of this
study is to suggest climate-appropriate and energy-efficient design techniques that lower
heating and cooling requirements without sacrificing indoor thermal comfort.

The front view of the four-story residential building chosen for this study is
displayed in Figure 2. The picture serves as the visual reference for the building model

4
used in the HVAC energy optimization simulations and depicts a typical mid-rise
residential building in Kabul City.

Figure 2 Typical building front view

( Light Destiny Consulting Services & Construction, 2025 )

Large window openings, masonry walls, and flat concrete roofing are typical
Kabul architectural features. The image emphasizes the existence of several floors with
identical layouts and few passive design features, highlighting the necessity of better
envelope strategies to improve indoor comfort and energy efficiency.The specific
objectives are:

1. To create a comprehensive HAP model that incorporates actual construction

methods and climatic data for a typical four-story residential building in Kabul
City.
2. To use the current envelope design parameters to calculate baseline HVAC loads.
3. To examine how different envelope elements, including airtightness, shading,
glazing type, roof construction, and wall insulation, affect heating and cooling
loads.

5
 4. To optimize the building envelope by identifying configurations that minimize
HVAC energy consumption and modeling alternative design scenarios.
5. To assess how well the baseline and optimized envelope designs perform in terms
of HVAC load and energy.

6. To suggest economical and energy-efficient building envelope techniques

appropriate for the economic and climatic circumstances of Kabul.

1.3 Problem statement

There is a significant need for space heating and cooling in residential buildings
because Kabul City experiences severe seasonal temperature fluctuations, with hot
summers and severe winters. The bulk of Kabul's housing stock, however, is built with
antiquated methods and materials, including single-glazed windows, uninsulated brick
walls, and thermally inefficient roofs that are not airtight or thermally resistant. This
results in high utility bills, excessive HVAC energy loads, and occupant discomfort.

Kabul continues to struggle with structural inefficiencies as well as the high cost
of heating systems that rely on fossil fuels and an unstable electrical supply. As a result,
many homes turn to dirty, ineffective heating techniques that endanger public health and
indoor air quality. Despite these urgent problems, there is a dearth of research that is
specific to the context and useful design guidelines that deal with energy efficiency in
Kabul's residential sector, especially through envelope optimization techniques that are
climate-appropriate.

Furthermore, the majority of previous research is either based on climates that are
very different from the continental conditions in Kabul or concentrates on isolated
envelope parameters. Assessing the combined effects of passive envelope components
like insulation thickness, glazing types, airtightness, and shading on HVAC energy
demand using accurate local climate data is a crucial research gap.

In order to close that gap, this study models, measures, and optimizes the HVAC
energy performance of a typical Kabul mid-rise residential building using simulation

6
tools. The objective is to find affordable, climate-responsive envelope upgrades that can
be used as workable ways to lower energy use and enhance indoor thermal comfort in
Afghanistan's expanding urban housing market.

1.4 Research questions

1. How do the typical building envelope features of Kabul City's residential

buildings impact HVAC energy loads?
2. Using HAP software, what are the baseline heating and cooling loads of a four-
story Kabul residential building?
3. What effects do modifications to building envelope elements like airtightness,
shading, glazing type, and insulation levels have on HVAC energy loads?
4. In the climate of Kabul, which combination of envelope design techniques
produces the most energy-efficient HVAC performance for residential
buildings?
5. In comparison to the baseline design, how much HVAC energy can be saved by
optimizing the building envelope?
6. What are the most practical and cost-effective building envelope
recommendations for reducing HVAC energy loads in Kabul's residential
sector?

1. Structure of the Thesis

Chapter 1: Introduction

 1.1 Background and Context

 1.2 Objectives
 1.3 Problem statement
 1.4 Research questions

7
2 Literature review

One of the most relevant studies addressing passive energy-saving strategies

through building envelope optimization was conducted by Aljabri and Al-Sallal (2024),
who focused on the hot-arid climate of Al Ain, United Arab Emirates. Their research
aimed to identify and evaluate effective retrofitting measures that can significantly
reduce the cooling energy requirements of residential buildings in similar climatic
contexts. Using DesignBuilder software coupled with the EnergyPlus simulation engine,
the study modeled a typical two-story detached residential building with existing
envelope characteristics and compared it with several retrofitted scenarios. The
researchers considered five main passive retrofit strategies: (1) external wall insulation,
(2) roof insulation, (3) high-performance glazing (double-glazed windows), (4) external
shading devices.

The simulation results demonstrated that applying 50 mm of polyurethane

insulation to the external walls reduced annual cooling energy consumption by
approximately 25% compared to the base case. Similarly, insulating the roof using
extruded polystyrene (XPS) showed a cooling energy reduction of about 18%, and
replacing single-pane windows with double-glazed units provided a further 15%
improvement. When these passive measures were combinedwall and roof insulation,
glazing, and shading the total cooling energy demand dropped by more than 45%,
showcasing the synergistic benefits of integrated retrofitting. The study emphasized that
building envelope enhancements not only reduce operational energy but also improve
thermal comfort and reduce dependency on mechanical HVAC system ( Aljabri, M. A.,
& Al-Sallal, K. A., 2024).

Though Kabul City has a colder winter season than Al Ain, the summer cooling
demands are comparable due to increasing summer temperatures and limited natural
ventilation. This makes the findings highly applicable to the Kabul context. For
instance, the wall and roof insulation materials tested in this study particularly
polyurethane and XPS are suitable for application in Kabul’s continental climate, where
both heating and cooling energy reductions are critical for year-round efficiency.

8
 Furthermore, the use of simulation tools such as DesignBuilder and EnergyPlus
aligns directly with this thesis’s methodology, supporting evidence-based decisions on
optimal envelope materials and configurations. This study reinforces the importance of
envelope focused retrofitting in achieving meaningful HVAC energy reductions in
residential sectors, especially in regions where electricity resources are limited and
building stock is poorly insulated.

One of the most comprehensive reviews of energy-efficient retrofitting strategies

for residential buildings was conducted by Sohani, Zendeboodi, and O’Brien (2022),
who focused on a wide range of building envelope retrofit methods applicable across
various climatic zones. Their study systematically analyzed over 1,000 abstracts and
reviewed nearly 70 full-text research articles to identify effective energy conservation
measures (ECMs) and simulation tools used for evaluating the energy performance of
residential buildings. Particular attention was given to opaque envelope upgrades (such
as wall and roof insulation), glazing improvements, and advanced materials including
phase change materials (PCMs) and aerogels. The study categorized ECMs into
conventional methods such as insulation and airtightness and emerging technologies,
and assessed their effectiveness using tools such as EnergyPlus, BEopt, OpenStudio,
and DesignBuilder.

The findings highlighted that combining ECMs, rather than applying single
measures, produced the highest energy savings. For example, envelope retrofits that
included wall insulation, air-tightening, and high-performance windows resulted in
energy savings ranging from 20% to 50%, depending on the climate and initial
condition of the building. In cold climates, air infiltration control was identified as the
most impactful single measure, reducing heating demand by up to 30%. Window
upgrades contributed up to 15% energy savings through reduced heat loss, while wall
insulation achieved around 20% savings. Roof insulation had a smaller impact unless
the building’s roof-to-wall area ratio was high. The study emphasized that simulation-
based analysis enables designers to assess the cost-effectiveness of various retrofit
packages before implementation, enhancing the feasibility of envelope optimization for

9
large-scale residential energy conservation ( Sohani, M., Zendeboodi, F., & O’Brien,
W., 2022).

While most of the reviewed case studies were focused on North America, the
findings are highly relevant to Kabul City, where heating loads dominate in winter and
cooling is increasingly important during warmer months. The identified ECMs,
particularly wall insulation, window retrofitting, and air sealing, align directly with the
goals of this study to optimize the building envelope for energy efficiency in Kabul’s
continental climate. Moreover, the simulation tools evaluated in the review especially
EnergyPlus and DesignBuilder are also proposed in this research, ensuring
methodological alignment. The study supports the implementation of bundled ECMs
tailored to local climatic conditions, providing a strong foundation for strategic
envelope retrofitting in Kabul’s under-insulated residential sector.

Kreko et al. (2024) presented an in-depth study focused on reducing heat loss due
to thermal bridging at balcony–wall junctions in multi-story residential buildings
through optimized façade insulation strategies. Thermal bridging at balconies is a
critical problem, especially in cold climates, where poorly insulated balconies act as
conduits for heat loss, causing cold spots and increasing overall heating demand. Using
SolidWorks Simulation Xpress 2021, the authors performed a comprehensive thermal
analysis of façade components in frame–brick and monolithic constructions, both
common in many urban residential buildings.

The study evaluated several insulation configurations: traditional full-perimeter

insulation around the balcony slab, versus a more innovative targeted insulation solution
involving the application of 30 mm insulation on the top surface of the balcony slab, 50
mm insulation beneath it, and a 750 mm horizontal extension of insulation into the
adjacent exterior wall. The simulation results demonstrated that this targeted approach
effectively eliminates the cold bridge effect, maintaining interior surface temperatures
above critical thresholds to avoid condensation and mold growth while significantly
reducing heat loss. Compared to full-perimeter insulation, the targeted insulation
required less material, reducing installation costs and complexity while delivering

10
comparable thermal performance. This balance of thermal effectiveness and economic
feasibility highlights the retrofit’s suitability for large-scale application in cost-sensitive
construction environments ( Kreko, M., Petrović, D., Horvat, I., Pavlović, M., &
Shevchenko, Y., 2024).

From a practical standpoint, the authors emphasize that balcony slabs without
thermal breaks serve as dominant sources of heat loss and potential structural damage
due to freeze-thaw cycles. By addressing these junctions specifically, the retrofit
improves the overall energy efficiency of the building envelope, contributing to lower
HVAC loads. For Kabul City, where cold winters drive significant heating demand and
building envelopes are typically under-insulated, this targeted insulation strategy offers
a pragmatic solution to retrofit existing residential buildings economically. The study’s
methodology—using detailed 3D thermal simulations—aligns with the thesis’s
approach of employing simulation tools like ANSYS and EnergyPlus to optimize
building envelope parameters and improve HVAC energy efficiency.

While the focus of the study was primarily on winter thermal performance, the
authors suggest that the approach may also contribute to improved summer thermal
comfort by reducing unwanted heat transfer through balconies. Limitations include the
study’s focus on multi-story apartment buildings, whereas Kabul’s residential
typologies tend to be lower-rise and often more varied in construction. Further research
integrating dynamic climate data and occupant behavior would strengthen the
applicability of the findings. Nevertheless, Kreko et al. (2024) provide a clear
demonstration that carefully designed, targeted insulation interventions at façade
thermal bridges can produce significant energy savings and improve occupant comfort,
making this approach a valuable component of an optimized residential envelope
retrofit strategy.

The most effective approach is to insulate the balcony slab edges by extending
insulation 750 mm into the exterior wall, applying 30 mm on top and 50 mm beneath
the slab, effectively eliminating cold bridging with less material and lower cost

11
compared to full perimeter insulation ( Kreko, M., Petrović, D., Horvat, I., Pavlović, M.,
& Shevchenko, Y., 2024).

Ali et al. (2023) investigated the effectiveness of passive building energy-saving

techniques through envelope retrofitting measures in the hot arid climate of the United
Arab Emirates. This study focused on how improving the building envelope walls,
roofs, and windows can substantially reduce cooling loads, which constitute the
majority of energy consumption in such climates. Using DesignBuilder coupled with
EnergyPlus simulation tools, the authors modeled a typical residential building and
evaluated multiple retrofitting strategies, including enhanced thermal insulation,
reflective roof coatings, high-performance glazing, and shading devices.

The research revealed that improving the thermal resistance (R-value) of walls
and roofs led to notable reductions in indoor temperatures and cooling energy demand.
For example, adding 50 mm of insulation to the external walls decreased annual cooling
energy consumption by approximately 18%. Window retrofits, such as installing
double-glazed low-emissivity (low-e) glass, reduced solar heat gain significantly,
yielding up to 15% cooling load savings. The integration of shading devices further
improved comfort by minimizing direct solar radiation without compromising natural
daylight. Importantly, the study emphasized that the building envelope’s thermal
performance directly correlates with HVAC energy savings, underscoring the value of
comprehensive retrofitting ( Ali, M., 2023).

Moreover, the authors conducted a parametric analysis to optimize envelope

parameters tailored to the local climate, such as selecting insulation thicknesses and
window-to-wall ratios that balance thermal performance with cost. The findings also
highlighted the synergistic effects of combining multiple envelope upgrades, with
bundled measures achieving cooling energy savings exceeding 30%. This supports the
thesis objective of optimizing envelope design parameters to reduce HVAC energy
consumption ( Ali, M., 2023).

While the study focused on hot arid climates, the methodology and simulation
tools used are applicable to other regions, including Kabul, where moderate summers

12
and cold winters require dynamic envelope optimization for both heating and cooling
loads. The use of DesignBuilder and EnergyPlus aligns well with the thesis’s simulation
approach, offering a validated framework for evaluating energy retrofit scenarios. The
study’s results underscore the critical role of thermal insulation, window upgrades, and
shading in achieving energy-efficient residential buildings, thus providing practical
guidance for retrofitting existing stock in climates with extreme seasonal variations.

Improving the thermal performance of building envelope components can reduce

cooling energy consumption by over 30% when multiple retrofitting measures are
combined ( Ali, M., 2023).

Rashid and Khan (2021) conducted a comprehensive study on the impact of

building envelope thermal performance on HVAC energy consumption in residential
buildings located in cold climate zones. Their research focused on improving the
insulation quality of walls, roofs, and windows to optimize heating loads during
prolonged winter conditions. The study employed EnergyPlus simulation software to
model various envelope configurations, analyzing how different insulation materials and
thicknesses influence overall energy demand.

The authors investigated common insulation materials such as expanded

polystyrene (EPS), mineral wool, and polyurethane foam, evaluating their thermal
conductivity, cost, and installation feasibility. Their simulations demonstrated that
increasing wall insulation thickness by 50 mm resulted in a heating energy demand
reduction ranging from 15% to 25%, depending on the base building’s insulation
quality. Roof insulation upgrades contributed similarly to energy savings, especially in
buildings with large roof-to-wall ratios. Additionally, replacing single-glazed windows
with double-glazed low-emissivity windows led to approximately 10% heating energy
reduction by minimizing heat loss and cold air infiltration ( Rashid, A., & Khan, M.,
2021).

A significant finding of the study was the critical role of airtightness in envelope
retrofits. The research showed that sealing air leaks around window frames and wall
joints could reduce heating energy consumption by an additional 10%, highlighting the

13
importance of both material upgrades and construction quality. Furthermore, the study
addressed the cost-benefit aspect, indicating that although higher-performance
insulation materials had greater initial costs, the payback periods were reasonable due to
substantial energy savings over the building lifecycle ( Rashid, A., & Khan, M., 2021).

The simulation-based approach and focus on cold climate envelope optimization

align directly with the objectives of this thesis, which aims to reduce HVAC energy
consumption in Kabul’s cold winters. The study validates the use of EnergyPlus as an
effective tool for evaluating building envelope parameters and their impact on heating
loads. Rashid and Khan’s findings provide empirical evidence supporting increased
insulation thickness, window upgrades, and air-tightness improvements as key strategies
for residential energy efficiency in cold climates.

Enhancing wall and roof insulation, combined with improved airtightness and
double-glazed windows, can reduce heating energy demand by up to 40% in cold
climate residential buildings ( Rashid, A., & Khan, M., 2021).

Li et al. (2022) investigated the optimization of building envelope design for

energy-efficient residential buildings under temperate climatic conditions with distinct
seasonal variations. Their study specifically focused on how various envelope
components—walls, roofs, and windows—affect the overall HVAC energy demand.
Using EnergyPlus simulation software, the authors modeled residential buildings with
different combinations of insulation levels, glazing types, and airtightness rates to
determine the most effective strategies for reducing annual heating and cooling loads.

The study compared conventional insulation materials, such as mineral wool and
foam boards, with advanced solutions including vacuum insulation panels (VIPs) and
phase change materials (PCMs). Results showed that upgrading wall and roof insulation
to high-performance materials could reduce annual HVAC energy consumption by up to
35%. Moreover, the inclusion of triple-glazed windows with low-emissivity coatings
improved thermal comfort and reduced heat loss/gain by 20% compared to double-
glazed alternatives. The research highlighted that the synergy of multiple envelope

14
improvements leads to greater energy savings than isolated measures ( Li, X., Zhang,
Y., & Wang, J., 2022).

Additionally, Li et al. emphasized the importance of airtightness, demonstrating

that reducing air infiltration rates from 10 to 3 air changes per hour could lower HVAC
energy demand by 15%. The study also incorporated sensitivity analyses to identify the
most cost-effective insulation thicknesses for walls and roofs, balancing energy savings
against material and installation costs. This approach provides practical guidance for
optimizing envelope design tailored to specific climatic contexts ( Li, X., Zhang, Y., &
Wang, J., 2022).

The findings of this study are highly relevant to Kabul’s climate, which features
cold winters and moderate summers, as it confirms that a well-optimized envelope
significantly reduces both heating and cooling loads. The use of EnergyPlus simulation
aligns well with the methodological framework of this thesis. Li et al.’s work supports
the thesis objective of employing simulation tools to analyze and optimize building
envelope parameters to achieve energy-efficient residential designs ( Li, X., Zhang, Y.,
& Wang, J., 2022).

Comprehensive envelope optimization, combining advanced insulation, high-

performance glazing, and enhanced airtightness, can reduce HVAC energy consumption
by more than 40% annually ( Li, X., Zhang, Y., & Wang, J., 2022).

Chen et al. (2023) conducted a thorough investigation into the effects of advanced
glazing systems combined with shading devices on the energy consumption of
residential buildings in climates characterized by significant seasonal variations.
Recognizing that windows often represent the weakest thermal link in building
envelopes, the study focused on how improvements in glazing technology and shading
design can optimize indoor thermal comfort while reducing heating and cooling energy
loads.

Using EnergyPlus simulation software, the study modeled a typical residential

building with various glazing types, including double- and triple-glazed windows

15
featuring low-emissivity (low-e) coatings that minimize infrared heat transfer while
allowing visible light transmission. The simulations assessed the thermal performance
across seasons, comparing energy use for HVAC systems with different glazing
configurations. Results showed that upgrading from double to triple glazing with low-e
coatings could reduce winter heating demand by approximately 20%, primarily by
lowering conductive and convective heat losses through the window assembly. In the
summer, the same glazing reduced cooling loads by up to 15% by limiting solar heat
gain without sacrificing daylight ( Chen, L., Zhao, H., & Liu, S., 2023).

A key contribution of this research was the detailed analysis of shading devices
including fixed overhangs, adjustable louvers, and vertical fins designed to control solar
radiation dynamically. By modeling various shading geometries and orientations, Chen
et al. demonstrated that optimized shading can significantly reduce cooling loads by
blocking high-angle summer sun while permitting beneficial low-angle winter sun
penetration. The parametric study revealed that shading could decrease cooling energy
by an additional 10-20%, depending on device type and climate specifics ( Chen, L.,
Zhao, H., & Liu, S., 2023).

The study further explored the window-to-wall ratio (WWR) and its impact on
energy performance. It found an optimal WWR around 30-40%, balancing the benefits
of natural daylight and solar heat gain against increased heat loss through glazing in
winter. This nuanced understanding of WWR provides valuable guidance for residential
envelope design, especially in Kabul’s climate where both heating and cooling needs
exist seasonally ( Chen, L., Zhao, H., & Liu, S., 2023).

Importantly, Chen et al. incorporated daylighting analyses, highlighting that

improved glazing and shading also reduce reliance on artificial lighting, thereby cutting
overall electricity consumption. The integration of thermal and visual comfort
considerations makes this approach comprehensive. The study aligns closely with this
thesis’s goal of optimizing envelope parameters to reduce HVAC energy consumption
using simulation tools like EnergyPlus ( Chen, L., Zhao, H., & Liu, S., 2023).

16
 This research underscores the necessity of combining high-performance glazing
with adaptive shading strategies to achieve substantial energy savings. For Kabul’s
residential buildings, where winters are cold and summers moderately warm, such
integrated solutions can significantly enhance building energy efficiency and occupant
comfort.

Advanced triple-glazed low-e windows combined with properly designed shading

devices can reduce HVAC energy consumption by over 25%, while simultaneously
improving daylight availability and indoor comfort levels ( Chen, L., Zhao, H., & Liu,
S., 2023).

Martinez and Lopez (2022) examined the role of building envelope optimization
in improving thermal comfort and reducing HVAC energy consumption in residential
buildings located in Mediterranean climates, which feature hot summers and mild
winters. Their study focused on the combined effects of insulation thickness, material
selection, and window properties, utilizing DesignBuilder coupled with EnergyPlus for
dynamic thermal simulation. The research aimed to identify optimal design parameters
for walls, roofs, and fenestration to minimize energy use while maintaining occupant
comfort throughout seasonal variations.

The study evaluated several insulation materials including expanded polystyrene

(EPS), polyurethane foam, and natural fiber-based options, analyzing their thermal
resistance and environmental impacts. Results indicated that increasing insulation
thickness on walls and roofs could reduce heating and cooling energy consumption by
20-30%, with diminishing returns observed beyond 100 mm thickness. Furthermore, the
research highlighted the significant impact of glazing type and window placement on
energy efficiency; high-performance double glazing with low-emissivity coatings and
optimized window-to-wall ratios (WWR) provided substantial reductions in heat gain
during summer and heat loss during winter ( Martinez, F., & Lopez, J., 2022).

In addition to insulation and glazing, Martinez and Lopez emphasized the

importance of thermal mass in the building envelope. They demonstrated that
incorporating materials with high thermal inertia, such as concrete or brick, helps

17
moderate indoor temperatures by absorbing heat during the day and releasing it at night,
thereby reducing HVAC loads. This effect was particularly pronounced during shoulder
seasons and contributed to improved occupant comfort ( Martinez, F., & Lopez, J.,
2022).

The authors also conducted a cost-benefit analysis to determine the most

economically viable combinations of insulation thickness and glazing options,
reinforcing the need for a balanced approach that considers both upfront investment and
long-term energy savings. Their findings support the thesis objectives by demonstrating
how simulation tools can be effectively employed to optimize building envelope design
parameters according to local climate characteristics ( Martinez, F., & Lopez, J., 2022)

For Kabul’s climate, which shares similarities with Mediterranean conditions in

terms of moderate summers and cold winters, the results suggest that a combination of
adequate insulation, proper glazing selection, and utilization of thermal mass can lead to
meaningful reductions in HVAC energy consumption while enhancing thermal comfort.

Optimizing insulation thickness and glazing properties, combined with leveraging

thermal mass, can reduce annual HVAC energy consumption by up to 30% while
ensuring stable indoor thermal conditions ( Martinez, F., & Lopez, J., 2022).

Nguyen and Tran (2021) conducted an in-depth study on the impact of building
envelope design on both energy consumption and indoor thermal comfort in residential
buildings situated in subtropical climates, which typically experience hot, humid
summers and mild winters. The study’s primary goal was to identify optimal
combinations of insulation materials, glazing types, and window-to-wall ratios (WWR)
that would minimize HVAC energy usage while ensuring occupant comfort throughout
the year.

Utilizing DesignBuilder integrated with EnergyPlus, the researchers created

dynamic thermal models simulating a variety of building envelope scenarios. They
compared conventional insulation materials such as fiberglass and expanded
polystyrene with innovative eco-friendly alternatives like cellulose and sheep wool.

18
These bio-based insulations not only offered competitive thermal performance with R-
values comparable to traditional materials but also contributed to environmental
sustainability by reducing embodied carbon. The simulations revealed that increasing
insulation thickness on walls and roofs by 50–100 mm could lead to annual HVAC
energy savings of up to 25%, with diminishing returns beyond certain thicknesses
( Nguyen, T., & Tran, H., 2021).

A significant focus of the study was on glazing optimization. Nguyen and Tran
evaluated the effectiveness of double-glazed low-emissivity (low-e) windows, which
minimize infrared heat transfer while maximizing visible light penetration, thereby
reducing solar heat gain and conductive losses. These glazing upgrades resulted in a
reduction of cooling loads by approximately 15%, particularly during peak summer
months when solar radiation is intense. Moreover, the authors highlighted the synergy
between glazing improvements and external shading devices such as fixed overhangs
and adjustable louvers—which further curtailed cooling energy consumption by
blocking direct sunlight while preserving daylight ( Nguyen, T., & Tran, H., 2021).

The analysis of window-to-wall ratio (WWR) provided additional insights,

showing that maintaining a WWR between 30% and 40% offers an optimal balance
between natural daylighting and thermal performance. Larger window areas, while
beneficial for daylight, can increase unwanted heat gains or losses, stressing the HVAC
system. Conversely, smaller window areas reduce daylight and may increase the need
for artificial lighting, thereby indirectly raising energy use ( Nguyen, T., & Tran, H.,
2021).

Beyond energy metrics, Nguyen and Tran assessed indoor thermal comfort using
operative temperature ranges and predicted mean vote (PMV) indices, confirming that
optimized envelope configurations contribute to stable and comfortable indoor
environments across seasons. Sensitivity analyses under varying climate conditions
further strengthened the robustness of their recommendations ( Nguyen, T., & Tran, H.,
2021).

19
 This study’s comprehensive approach covering insulation materials, glazing
technologies, shading solutions, and envelope geometry directly aligns with the
objectives of this thesis. Its findings support the use of simulation tools like EnergyPlus
for detailed building envelope optimization tailored to Kabul’s climate, which features
cold winters requiring heating and moderate summers where cooling is less intensive
but still relevant ( Nguyen, T., & Tran, H., 2021).

Integrating enhanced insulation, high-performance glazing, optimal window-to-

wall ratios, and shading devices can collectively reduce HVAC energy consumption by
up to 30%, while maintaining superior thermal comfort and promoting sustainable
building practices ( Nguyen, T., & Tran, H., 2021).

Singh and Kumar (2023) focused on the optimization of building envelope

components to reduce HVAC energy consumption in cold and temperate climates,
addressing the critical role of insulation, glazing, and airtightness in residential energy
efficiency. Their research utilized ANSYS coupled with EnergyPlus for detailed
thermal simulations, enabling a multi-physics approach that combined heat transfer
analysis with energy modeling to capture realistic building performance under varying
weather conditions.

The study investigated multiple insulation materials, including traditional

fiberglass, polyurethane foam, and advanced aerogel-based composites, evaluating their
thermal resistance, durability, and cost-effectiveness. Results indicated that aerogel
insulation, despite its higher initial cost, provided superior thermal performance with up
to 40% better heat retention compared to conventional materials, leading to significant
reductions in heating energy demand. The researchers emphasized the importance of
optimizing insulation thickness, showing that a 75 mm increase in wall insulation could
lower annual heating loads by approximately 30% ( Singh, R., & Kumar, S., 2023).

In addition to insulation, Singh and Kumar extensively analyzed the impact of

window technologies, comparing single, double, and triple glazing options with low-
emissivity coatings. Their simulations revealed that triple-glazed low-e windows reduce
conductive and radiative heat losses, contributing to a 20% decrease in overall HVAC

20
energy consumption during the heating season. The study also highlighted the
effectiveness of airtightness improvements, demonstrating that reducing infiltration
rates from 10 to 2 air changes per hour (ACH) could cut heating energy use by an
additional 15%, underscoring the need for high-quality construction practices and
sealing techniques ( Singh, R., & Kumar, S., 2023).

The integration of thermal bridging analysis through ANSYS provided further

insight into localized heat loss areas around window frames and wall junctions, enabling
the identification of critical design weaknesses. This approach facilitated the
development of targeted retrofit strategies to minimize thermal bridging, which
accounted for up to 10% of total envelope heat loss in the base models ( Singh, R., &
Kumar, S., 2023).

Singh and Kumar’s comprehensive methodology and findings are highly relevant
to the objectives of this thesis, which seeks to optimize building envelope parameters to
reduce HVAC energy demand in Kabul’s cold winters. The combination of advanced
simulation tools, including ANSYS and EnergyPlus, offers a robust framework for
detailed thermal performance analysis and energy optimization tailored to local climate
conditions ( Singh, R., & Kumar, S., 2023).

Advanced insulation materials, high-performance triple-glazed windows, and

improved airtightness collectively enable a reduction of up to 45% in heating energy
consumption in cold climate residential buildings ( Singh, R., & Kumar, S., 2023).

21
3 Research Methodology

3.1 Research Design

The goal of this study is to optimize the HVAC energy demand of a residential
building envelope in Ahmad Shah Baba Mena, Arzan Qemat, Kabul City, using a
quantitative case study and simulation-based methodology. In order to assess how
important architectural and envelope design factors affect heating and cooling loads in
Kabul's climate, the study makes use of building performance simulation.

Architectural drawings of a four-story residential building with one apartment per

floor served as the basis for the case study. The structure is located in the Ahmad Shah
Baba Mena neighborhood, which is a growing residential area in Kabul's eastern region.
The building's total area is 720 m², with 180 m² per floor.

3.1.1 Key features of the selected building

 Location: Ahmad Shah Baba Mena, Arzan Qemat, Kabul City

 Building Type: Residential (4 stories, one apartment per floor and one
floor for parking)
 Total Building Area: 720 m² (180 m² per floor × 4 floors)
 Construction Type: Brick masonry with reinforced concrete
 Openings: Multiple window types and standard doors

22
 This building type is appropriate for assessing possible HVAC energy
optimizations because it is typical of Kabul's mid-rise housing, which is distinguished
by its simple construction and low insulation.

The case study building, a four-story residential building in Ahmad Shah Baba
Mena, Arzan Qemat, Kabul City, has a typical floor plan layout, as shown in Figure 3.
The energy simulation model's zoning and internal gain assumptions were based on this
arrangement.

Figure 3 Typical Building Floor Plan

( Light Destiny Consulting Services & Construction, 2025 )

The floor plan consists of a living/dining area, two bedrooms, kitchen, bathroom,
and circulation spaces, all arranged in a compact yet functional configuration. This
internal zoning informed the simulation's thermal zones living, sleeping, service, and
circulation which allowed for a more accurate assessment of heating and cooling loads
under real occupancy conditions.

23
3.1.2 Key Variables and Optimization Scenarios

The study systematically explores the effects of several building envelope

parameters, including:

 Wall and Roof Insulation Thickness: To measure decreases in thermal

transmittance (U-values) and their effect on energy demand, three levels
of expanded polystyrene (EPS) insulation five, seven, and ten
centimeters are tested.
 Window Glazing Type: Transition from single-glazed windows (U-
value: 6.975 W/m²K) to double-glazed units with a 3 mm glass and 6
mm air gap (U-value: 4.469 W/m²K).
 External Shading Devices: installation of a horizontal shading peak that
is one meter long and twenty centimeters thick in order to minimize solar
heat gains, especially in the summer.
 Air Infiltration Rate: Comparison between a typical infiltration rate of
1.0 air changes per hour (ACH) and an improved airtightness scenario of
0.5 ACH.

An isolated and comprehensive understanding of each parameter's contribution to

HVAC load reduction is made possible by its analysis both separately and in
combination.

3.1.3 Research Implementation Steps

1. Baseline Model Development

HAP (Hourly Analysis Program) is used to create a baseline HVAC
energy model. Architectural drawings and realistic residential occupancy
patterns are used as the basis for entering the building geometry, material
properties, window types, and usage profiles into HAP. The outdoor
environmental conditions are defined using Kabul's local weather data.
2. Envelope Parameters for Optimization
The following key design variables are selected for testing:

24
  Wall and roof insulation thickness and material type
 Window glazing type (single, double)
 External shading devices (overhangs or fins)
 Airtightness (infiltration rate 1 ACH , 0.5 ACH)
3. Simulation Process in HAP
In HAP, parametric simulations are run. The impact of each variable can
be separately analyzed because each scenario alters one parameter at a
time while maintaining the others constant. Additionally, combined
optimizations are tested. Both winter and summer design conditions are
simulated.
4. Analysis of Results
Each optimized model is compared to the baseline in terms of:
a. Total cooling and heating loads (in kWh)
b. Percentage reduction in HVAC energy demand

3.2 Building Description

A typical mid-rise residential building in Ahmad Shah Baba Mena, Arzan Qemat,
Kabul City a developing urban neighborhood with standard construction practices and
rising demand for energy-efficient housing is the subject of the case study.

3.2.1 General Characteristics

 Building Type: Residential apartment building

 Number of Floors: Four (3 typical conditioned residential floors + 1
parking floor not included in load calculations)
 Conditioned Floor Area: Approximately 118.9 m² per residential floor,
totaling about 356.7 m² for the three conditioned floors
 Building Footprint: 180 m²
 Parking Floor: Ground-level, unconditioned space excluded from
HVAC energy simulation due to lack of thermal loads

25
3.2.2 Architectural Features

 Structural System: Reinforced concrete framing with brick masonry

infill walls
 Wall Construction: Uninsulated brick masonry with cement plaster
finish, typical for local construction; no thermal insulation in the base
case
 Roof: Flat reinforced concrete slab, also uninsulated in the baseline
configuration
 Windows: Aluminum-framed, single-glazed glass units with a U-value
of 6.975 W/m²K in the baseline; window types vary slightly but
primarily conform to this standard
 Doors: Solid wood for both interior and exterior doors, consistent with
local practices

3.2.3 Internal Layout

Each of the three conditioned floors contains one apartment unit comprising:

 Living/Dining Area (Living Zone)

 Two Bedrooms (Sleeping Zone)
 Kitchen and Bathroom (Service Zone)
 Circulation Spaces including corridors and staircases (Circulation Zone)

This zoning is reflected in the HVAC simulation to capture the differing thermal
loads and occupancy patterns of each functional space.

3.2.4 Thermal Properties and Envelope Performance

 Baseline Wall U-Value: 2.4 W/m²K

 Baseline Roof U-Value: 2.9 W/m²K
 Baseline Window U-Value: 6.975 W/m²K

26
  Infiltration Rate: Assumed 1.0 ACH (air changes per hour) for the base
case, consistent with typical airtightness levels in Kabul residential
buildings

3.2.5 Occupancy and Usage Patterns

With a 24-hour schedule that reflects occupants' constant presence, the building is
modeled under the assumption of full-time residential occupancy. The following
ASHRAE residential benchmarks are applied to local usage levels to account for
internal heat gains from people, lighting, and appliances:

Occupancy Density: Based on typical household size and activity levels

 Internal Gains: Sensible and latent heat from occupants, lighting loads
of approximately 10 W/m², and equipment loads averaging 8 W/m²
 Ventilation: Primarily natural ventilation with infiltration rates modeled
at 1.0 ACH for the baseline and 0.5 ACH for optimized scenarios

3.2.6 Climatic Context

Kabul experiences hot summers (maximum temperatures exceeding 35°C) and

cold winters (average lows of -7°C) due to its semi-arid continental climate. Thermal
envelope optimization is essential for energy savings and occupant comfort because of
the considerable seasonal variation in heating and cooling demands caused by this
climate.

3.3 Design Parameters

The main building envelope design parameters chosen for analysis and
optimization in this study are defined in this section. These factors have a big impact on
the residential building's HVAC energy demand and thermal performance. The
guidelines concentrate on practical and pertinent passive design techniques and
construction enhancements for residential buildings given Kabul's economic and
climatic conditions..

27
3.3.1 Wall and Roof Insulation

The main tactic investigated to lessen heat transfer through the building envelope
is thermal insulation. A concrete roof slab and uninsulated brick masonry walls make up
the baseline case, which has a comparatively high thermal transmittance.

 Material: Expanded Polystyrene (EPS) with a density of 20 kg/m³

 Thermal Resistance: 27.7 W·m/kg (thermal conductivity derived
accordingly)
 Thickness Variations: Insulation thicknesses of 5 cm, 7.5 cm, and 10
cm were tested

The computed U-values (thermal transmittance rates) for external walls and roofs
with varying Expanded Polystyrene (EPS) insulation thicknesses are shown in Table 1.
This information is essential for comprehending how better insulation enhances the
building envelope's thermal performance.

Table1. Roof and Wall U value for different Insulation Thickness

Insulation Thickness Wall U-Value (W/m²K) Roof U-Value (W/m²K)
Baseline (0 cm) 2.4 2.9
5 cm 0.555 0.578

7.5 cm 0.401 0.413

10 cm 0.314 0.321

The U-value of both walls and roofs is considerably decreased when insulation
thickness is increased from 0 cm (baseline) to 10 cm, as the table illustrates. The wall
U-value, for instance, decreases from 2.4 W/m²K to 0.314 W/m²K, suggesting a
significant improvement in heat transfer resistance. Insulation is one of the best ways to
maximize HVAC performance because of these enhancements, which directly lower the
energy demand for heating and cooling.

This parameter evaluates how increasing insulation thickness improves envelope

thermal resistance and reduces heating and cooling loads.

28
3.3.2 Window Glazing Type

Windows represent a significant heat transfer pathway due to their typically

higher U-values and solar gains.

 Baseline: Single-glazed aluminum-framed windows with a U-value of

6.975 W/m²K
 Optimized Scenario: Double-glazed windows consisting of two 3 mm
glass panes separated by a 6 mm air gap, reducing the U-value to 4.469
W/m²K

This parameter assesses the impact of improved glazing on thermal losses and
solar heat gains.

3.3.3 External Shading Devices

To mitigate solar heat gain in summer months, external shading devices such as
horizontal peaks are tested.

 Design: 1-meter long overhang (peak) with a thickness of 20 cm

installed on the building façade above windows
 Purpose: To reduce direct solar radiation entering the building during
peak sun angles, thereby lowering cooling loads

3.3.4 Infiltration Rate and Airtightness

Infiltration significantly impacts heating loads, particularly in cold climates.

 Baseline: Air change rate of 1.0 ACH, typical for residential buildings in
Kabul with standard construction quality
 Optimized Case: Reduced infiltration rate of 0.5 ACH, achievable
through enhanced sealing, improved window and door quality, and
construction detailing

29
3.3.5 Summary of Design Parameters for Simulation

The baseline and optimized values for the main building envelope parameters
used in the simulation scenarios are compiled in Table 2. These factors, which have a
big impact on HVAC energy demand, include infiltration rates, window glazing types,
external shading devices, and the amount of insulation on the walls and roof.

Table 2. Summary of Design Parameters

Parameter Baseline Optimized Values

Wall Insulation None (U = 2.4 W/m²K) 5 cm, 7.5 cm, 10 cm EPS

insulation
Roof Insulation None (U = 2.9 W/m²K) 5 cm, 7.5 cm, 10 cm EPS
insulation
Window Glazing Single-glazed (6.975 W/m²K) Double-glazed (4.469 W/m²K)

External Shading None 1 m horizontal peak (20 cm thick)

Infiltration Rate 1.0 ACH 0.5 ACH

The table shows how a more energy-efficient design with EPS insulation, double-
glazed windows, external shading, and better airtightness replaced the baseline
configuration, which was uninsulated, single-glazed, and extremely leaky. The
optimization scenarios examined in later chapters, each of which aims to lower heating
and cooling loads under Kabul's climate, are based on these parameter adjustments.

The simulation scenarios outlined in the following chapter are based on these
design parameters. The study investigates how these factors, both separately and in
combination, affect the building's HVAC energy consumption in the climate of Kabul.

30
 3.4 Simulation Setup
The setup of the energy simulation procedure used to assess the case study
building's HVAC performance under various design scenarios is described in detail in
this section. Carrier Corporation's Hourly Analysis Program (HAP), a commonly used
tool for thorough load calculations and energy modeling in building performance
analysis, was used to run the simulations.

3.4.1 Simulation Software

 Tool: Hourly Analysis Program (HAP), version [4.9]

 Developer: Carrier Corporation
 Capabilities: Hour-by-hour calculations of heating and cooling loads,
energy consumption, zone-level analysis, and HVAC system
performance under varying envelope configurations.

3.4.2 Weather Data

 Location: Kabul City, Afghanistan

 Weather File: prepare according to Ministry of Urban Development and
Housing (MUDH) climatic design data.

Climate Characteristics:

 Semi-arid continental climate

 Cold winters with average minimum temperatures around -7°C
 Warm summers with daily maximum temperatures exceeding
35°C
 Moderate solar radiation levels and relatively low humidity

31
3.4.3 Building Model and Thermal Zoning

The residential building model includes three typical conditioned floors with
identical layouts (floor area 118.9 m² per floor). The parking floor is excluded from
HVAC load calculations as it is unconditioned.

 Thermal Zones per Floor:

 Living Zone (living and dining rooms)
 Sleeping Zone (bedrooms)
 Service Zone (kitchen and bathrooms)
 Circulation Zone (hallways and staircases)

Each zone is modeled independently to capture localized heat gains, solar

exposure, and ventilation effects.

3.4.4 Internal Gains and Occupancy

 Occupancy Type: Residential, full-time use

 Schedule: 24 hours per day, 7 days per week
 Internal Heat Gains:
 Occupants: 120 W sensible and 60 W latent heat per person
 Lighting: 10 W/m², reflecting typical residential lighting usage
 Equipment: 8 W/m², representing appliances such as refrigerators
and TVs

3.4.5 Ventilation and Infiltration

 Natural Ventilation: Modeled based on typical Afghan construction

practices
 Infiltration Rates:
 Baseline: 1.0 air changes per hour (ACH)
 Optimized: Reduced to 0.5 ACH through improved airtightness
and sealing

32
3.4.6 HVAC System Assumptions

 Cooling System: Packaged Direct Expansion (DX) unit

 Heating System: Electric resistance heaters (for simplicity in load
estimation)
 Control: Zoned temperature controls for each thermal zone
 Cooling setpoint: 26°C
 Heating setpoint: 22°C

The system type remains constant across all scenarios to isolate the impact of
envelope changes on HVAC energy performance.

3.4.7 Simulation Scenarios

The study includes a baseline case and multiple optimization scenarios to evaluate
the impact of individual and combined envelope improvements:

 Baseline Case: Original building envelope with no insulation, single-

glazed windows, standard infiltration, and no shading.
 Insulation Thickness: 5 cm, 7.5 cm, and 10 cm EPS insulation applied
to walls and roof.
 Window Glazing: Replacement of single-glazed windows with double-
glazed units (3 mm glass + 6 mm air gap).
 External Shading: Addition of 1-meter long horizontal peaks above
windows.
 Infiltration Rate: Reduced infiltration from 1.0 to 0.5 ACH.

Each scenario is simulated for both winter and summer design conditions to
capture seasonal variations in heating and cooling loads.

33
4 Results and Discussion

4.1 Results

The results of the energy simulation study for the chosen residential building in
Ahmad Shah Baba Mena, Arzan Qemat, Kabul City, using the Hourly Analysis
Program (HAP), are shown in this chapter. In Kabul's semi-arid continental climate, the
main objective is to assess how different building envelope design parameters affect
HVAC energy demand, specifically heating and cooling loads.

Following a baseline model that depicts the current building configuration, the
simulations go through a number of optimization scenarios that alter one or more
envelope features. These scenarios cover improvements like adding external shading
devices, improving window glazing, lowering the infiltration rate, and insulating the
walls and roof.

Each scenario is analyzed based on:

 Annual heating and cooling energy consumption (in kWh)

 Peak heating and cooling loads (in kW)
 Percentage reduction in total HVAC energy demand compared to the
baseline model
 Implications for occupant thermal comfort and energy efficiency

Starting with the baseline simulation and moving on to individual and combined
optimization scenarios, the results are presented in an organized fashion. While

34
discussions interpret the findings' significance in light of Kabul's building practices and
climatic requirements, tables and graphs are used to facilitate comparative analysis.

Baseline Energy Performance

The current construction of a typical mid-rise residential building in Ahmad Shah

Baba Mena, Arzan Qemat, Kabul City, is represented by the baseline energy model.
This arrangement is typical of Kabul construction, with single-glazed aluminum-framed
windows, uninsulated brick masonry walls, a concrete roof slab without thermal
protection, and a comparatively high air infiltration rate of 1.0 air changes per hour
(ACH). In the sections that follow, the baseline simulation offers a performance
standard for assessing the results of different building envelope optimization techniques.

Building Envelope Thermal Characteristics (Baseline)

The envelope materials used in the baseline model result in high thermal
transmittance values, contributing to significant heating and cooling demands.

The thermal transmittance values (U-values) of the external walls, roof, and
windows important envelope elements used in the baseline building model are shown in
Table 3. Prior to the application of any optimization techniques, these values serve as
the initial values.

Table 3. Thermal Properties of Materials

Envelope Construction Type U-Value (W/m²·K)
Component
External Walls Brick masonry with cement 2.4
plaster
Roof Flat reinforced concrete slab 2.9
Windows Single-glazed, aluminum frame 6.975

The table shows that the concrete roof and uninsulated brick masonry walls have
high U-values of 2.9 W/m²·K and 2.4 W/m²·K, respectively, indicating poor thermal
resistance. With a U-value of 6.975 W/m²·K, the windows are particularly inefficient

35
and greatly increase heat gain in the summer and decrease it in the winter. In order to
lower HVAC energy loads, these thermal characteristics support the need for improved
glazing and insulation.

Conditioned Area

Three residential floors and one unconditioned ground-level parking floor make up the
building's four levels. The HVAC simulation only takes into account the residential
floors.

 Conditioned Floor Area (per floor): 118.9 m²

 Number of Conditioned Floors: 3
 Total Conditioned Area: 356.7 m²

Thermal zones living, sleeping, service, and circulation areas—are functionally

separated into each floor. To take into consideration varying internal gains, solar
exposures, and ventilation requirements, these zones were separately modeled in the
simulation.

Peak Heating and Cooling Loads

The Hourly Analysis Program (HAP) was used to simulate the baseline model
using the Kabul climate data from the Ministry of Urban Development and Housing
(MUDH). Under design day conditions, the maximum heating and cooling loads were
computed.

Using the Hourly Analysis Program (HAP), the baseline residential building's
peak heating and cooling loads for each floor are shown in Table 4. These figures are

36
predicated on current building conditions devoid of any improvements to energy
efficiency.

Table 4. Load Summary of Baseline Model

Zone Name Maximum Maximum Zone
Cooling Heating Floor
Sensible Load Area
(kW) (kW) (m²)
First Floor 17.6 25.8 118.9
Second Floor 14.3 19 118.9
Third Floor 20 28.6 118.9
Total load 51.9 73.4 356.7
W/m² 145.5 205.8

According to the table, the three conditioned floors have a combined peak heating
load of 73.4 kW and a peak cooling load of 51.9 kW, which results in high loads per
square meter of 205.8 W/m² and 145.5 W/m², respectively. These high numbers draw
attention to the baseline envelope's inefficiency, which is caused by inadequate
insulation, high infiltration, and inferior glazing. This highlights the necessity of
optimization in order to lower energy consumption and enhance comfort.

The high energy demand is primarily due to:

 Uninsulated walls and roof, leading to high conductive heat losses

 Extremely poor-performing windows (U-value = 6.975 W/m²·K), contributing
heavily to both winter heat loss and summer solar gain

37
  High infiltration rate (1.0 ACH), which increases uncontrolled air exchange with
the outdoor environment
 No external shading, allowing direct solar radiation to heat interior spaces in
summer

These circumstances highlight how urgently building envelope upgrades are

needed to improve thermal comfort and lower HVAC energy usage. The following
sections will assess the ways in which airtightness, shading, window upgrades, and
insulation improve performance results.

Insulation Optimization Results

One of the best passive ways to lower heating and cooling energy use is thermal
insulation. Three insulation thicknesses 5 cm, 7.5 cm, and 10 cm are used in this section
to assess the effects of adding Expanded Polystyrene (EPS) insulation to the building's
exterior walls and roof.

All cases were simulated using the same HVAC system, climate data for Kabul,
internal schedules, and zoning. The insulation is modeled using the following
properties:

 Material: Expanded Polystyrene (EPS)

 Density: 20 kg/m³
 Thermal resistance coefficient: 27.7 W/kg·m
 Thermal conductivity (approx.): 0.035 W/m·K

The purpose is to assess how varying insulation thickness affects building

envelope U-values and corresponding HVAC energy demand.

U-Values for EPS Insulation Scenarios

The computed U-values for external walls and roofs with varying Expanded
Polystyrene (EPS) insulation thicknesses 5 cm, 7.5 cm, and 10 cm are displayed in

38
Table 5. These figures are used to evaluate how the building envelope's thermal
resistance is enhanced by thicker insulation.

Table 5. U-value for EPS Insulation Scenarios

Insulation Thickness Wall U-Value Roof U-Value (W/m²·K)
(W/m²·K)
0 cm (Baseline) 2.4 2.9
5 cm EPS 0.555 0.578
7.5 cm EPS 0.401 0.413
10 cm EPS 0.314 0.321

As the table illustrates, increasing insulation thickness significantly reduces U-

values for both walls and roofs. For instance, with 10 cm of EPS, the wall U-value
decreases from 2.4 W/m²·K (baseline) to 0.314 W/m²·K. It is anticipated that this
enhanced thermal performance will lead to a significant decrease in the energy needed
for heating and cooling, especially in Kabul's frigid winters.

5 cm EPS Insulation

 Wall U-value: 0.555 W/m²·K

 Roof U-value: 0.578 W/m²·K

Expanded Polystyrene (EPS) insulation that was 5 cm thick and installed on the
case study building's walls and roof was used in a simulation scenario to evaluate the
effect of moderate thermal insulation on HVAC energy demand. The resulting heating
and cooling loads for each floor under this insulation condition are shown in this table.
The purpose of the analysis is to show how basic insulation upgrades over the baseline
configuration can result in potential energy savings.

Table 6. HVAC Load for 5 cm EPS Insulation

Zone Name Maximum Maximum Zone
Cooling Heating Floor
Sensible Load Area
(kW) (kW) (m²)
First Floor 14.1 15 118.9
Second Floor 13.8 14.3 118.9
Third Floor 13.7 15.7 118.9

39
 Total load 41.6 45 356.7
W/m² 116.6 126.2

The addition of 5 cm EPS insulation considerably lowers the building's thermal

load, as Table 6 illustrates. The demand for heating and cooling dropped to 126.2 and
116.6 W/m², respectively, in comparison to the baseline scenario. This indicates a
general decrease in heating load of about 39% and cooling load of about 20%. These
findings demonstrate that, in Kabul's climate, even a relatively thin layer of insulation
can significantly improve residential buildings' thermal efficiency, offering an
affordable energy-saving measure.

Figure 4 compares the HVAC loads of the baseline building with the insulated
case across all three conditioned floors to show the impact of 5 cm EPS insulation. In
order to better understand the direct energy benefits of applying moderate insulation,
this figure shows the absolute reductions in both heating and cooling demands (in
kilowatts).

Figure 4. HVAC Load Reduction for 5cm EPS Compare to Baseline by (kw)

It is evident from Figure 4 that installing 5 cm of EPS insulation significantly

reduces the heating and cooling loads on each floor. The reduction is especially
noticeable on the first floor, which had the highest initial heating load.

40
 The numerical results from Table 6 are supported by this graphical comparison,
which also graphically demonstrates how important insulation is for reducing energy
use and improving thermal comfort in Kabul's residential buildings.

Figure 5 shows these reductions in percentage terms, whereas Figure 4 showed

the absolute decrease in HVAC loads brought about by 5 cm EPS insulation. A more
normalized understanding of how insulation affects overall energy performance is made
possible by this percentage-based view, which makes it easier to compare efficiency
gains across floors.

Figure 5. HVAC Load Reduction for 5cm EPS Compare to Baseline by (%)

When compared to the baseline case, Figure 5 shows that the 5 cm EPS insulation
reduces heating demand by about 39% and cooling demand by about 20%. Even in
buildings with otherwise conventional construction, these proportionate reductions
highlight the significant relative impact of adding basic insulation. The figure illustrates
how well this retrofit measure has worked to increase energy efficiency in Kabul's
residential sector.

7.5 cm EPS Insulation

41
  Wall U-value: 0.401 W/m²·K
 Roof U-value: 0.413 W/m²·K

The simulation was expanded to include a 7.5 cm EPS insulation scenario in

order to better assess the impact of insulation thickness on building energy performance.
The resulting heating and cooling loads for every residential floor at this intermediate
insulation level are shown in Table 7. This comparison aids in determining whether
insulation thickness increases beyond the 5 cm case result in proportionate energy
savings.

Table 7. HVAC Load for 7.5 cm EPS Insulation

Zone Name Maximum Maximum Zone
Cooling Heating Floor
Sensible Load Area
(kW) (kW) (m²)
First Floor 13.9 14.4 118.9
Second Floor 13.8 14.1 118.9
Third Floor 13.6 14.8 118.9
Total load 41.3 43.3 356.7
W/m² 115.8 121.4

With 7.5 cm EPS insulation, HVAC performance continues to improve, according

to Table 7. The cooling demand dropped to 115.8 W/m² and the heating demand
dropped to 121.4 W/m², providing marginally better reductions than the 5 cm case. The
comparatively small improvement over the 5 cm scenario implies diminishing returns,
which is a crucial factor to take into account when weighing performance gains against
material cost, even though the energy savings are noteworthy.

Figure 6 shows the HVAC load reductions in kilowatts relative to the baseline
model to better illustrate the energy-saving effect of 7.5 cm EPS insulation. Increased
insulation thickness on each floor results in direct energy savings that can be measured
with the aid of this graphical representation.

42
 Figure 6. HVAC Load Reduction for 7.5cm EPS Compare to Baseline by (kw)

Figure 6 shows that adding 7.5 cm of EPS insulation lowers the heating and
cooling loads on every floor even more. The incremental gain starts to taper,
particularly in cooling performance, even though the reduction is larger than in the 5 cm
case. The need to weigh cost-benefit tradeoffs in residential energy retrofits is further
supported by this figure, which emphasizes the idea of diminishing returns with
insulation thickness.

Figure 7 displays the percentage decrease in heating and cooling loads attained by
7.5 cm EPS insulation, which comes after the absolute load reduction seen in Figure 6.
The efficiency gains in comparison to the baseline condition are better understood
thanks to this comparative view expressed in percentage terms.

43
 Figure 7. HVAC Load Reduction for 7.5cm EPS Compare to Baseline by (%)

In comparison to the uninsulated baseline, the 7.5 cm EPS insulation results in a modest
20% reduction in cooling load and an approximate 41% reduction in heating load, as
shown in Figure 7. Although the incremental gains are smaller, these percentage
reductions demonstrate that insulation thickness increases beyond 5 cm continue to
improve energy performance. This supports the idea that insulation optimization ought
to be predicated on both financial viability and energy efficiency goals.

Thermal losses are further decreased with increased insulation thickness. 41%
reduction in the heating load is demonstrated, which is marginally better than the 5 cm
case. In contrast to the additional material needed, the incremental improvement is
minimal. This implies a declining rate of return on investment.

10 cm EPS Insulation

 Wall U-value: 0.314 W/m²·K

 Roof U-value: 0.321 W/m²·K

44
 third simulation using 10 cm thick EPS insulation on the building's walls and roof
was carried out in order to ascertain the maximum possible energy savings from
insulation in this study. In order to compare the heating and cooling loads for each
residential floor under this high performance insulation scenario with the baseline and
previously tested thickness levels, Table 8 shows the results.

Table 8. HVAC Load for 10 cm EPS Insulation

Zone Name Maximum Maximum Zone
Cooling Heating Floor
Sensible Load Area
(kW) (kW) (m²)
First Floor 13.7 13.8 118.9
Second Floor 13.7 13.7 118.9
Third Floor 13.5 14.1 118.9
Total load 40.9 41.6 356.7
W/m² 114.7 116.6

According to Table 8, out of all the tested scenarios, 10 cm of EPS insulation

results in the lowest HVAC loads, lowering the heating and cooling demands to 116.6
and 114.7 W/m², respectively. Although this configuration provides the greatest energy
savings overall, the performance improvement over the 7.5 cm case is relatively modest.
This implies that 10 cm of insulation only marginally improves efficiency at a
potentially higher cost, underscoring the significance of weighing economic viability in
addition to energy efficiency.

Figure 8 provides a visual representation of the HVAC load reductions achieved with 10
cm EPS insulation compared to the baseline building configuration. Expressed in
kilowatts, this figure illustrates the extent to which increased insulation thickness can
decrease heating and cooling demands across the three residential floors.

45
 Figure 8. HVAC Load Reduction for 10cm EPS Compare to Baseline by (kw)

The most significant reduction in heating and cooling loads is achieved with 10
cm EPS insulation, as illustrated in Figure 8. Nonetheless, there is not much of a
difference in energy savings when compared to the 7.5 cm insulation scenario. While
more insulation increases performance, the benefits taper off, according to this visual
analysis. For this reason, practical applications should balance the marginal gains
against the costs of materials and installation.

To complement the absolute reductions illustrated in the previous figure, Figure 9

depicts the percentage reduction in HVAC loads resulting from the implementation of
10 cm EPS insulation. This percentage-based comparison helps quantify the efficiency
gain relative to the baseline model, highlighting the proportional benefits of increased
insulation thickness.

46
 Figure 9. HVAC Load Reduction for 10cm EPS Compare to Baseline by (%)

In comparison to the baseline case, Figure 9 illustrates that 10 cm of EPS

insulation lowers heating demand by roughly 43% and cooling demand by about 21%.
The incremental percentage gain over the 7.5 cm thickness is limited, even though this
represents the best level of performance among the tested insulation scenarios. These
results support the idea of diminishing returns and imply that, in the context of
residential construction in Kabul, 7.5 cm might provide the most equitable trade-off
between cost and thermal efficiency.

Insulation Performance Comparison

A comparative graph was created in order to visually evaluate the connection

between insulation thickness and the reduction of heating load. As the thickness of
expanded polystyrene (EPS) insulation increases from 0 cm (baseline) to 10 cm, Figure
10 shows the absolute decrease in heating load (in kilowatts). The graph illustrates the
incremental advantages of more insulation by combining the heating performance data
from three simulation cases (5 cm, 7.5 cm, and 10 cm EPS).

47
 Figure 10. Heating load Reduction vs EPS thickness (Kw)

As shown in Figure 10, switching from no insulation to 5 cm EPS results in the largest
marginal gain and the most noticeable decrease in heating load. Additional savings are
possible with subsequent increases to 7.5 cm and 10 cm, but the benefits diminish. This
pattern highlights how crucial it is to choose the ideal insulation thickness that strikes a
balance between material costs and performance improvements. According to this
study, 7.5 cm insulation seems to provide a workable compromise between construction
viability and thermal efficiency given Kabul's climate.

It's crucial to take into account both the absolute decreases in heating load and
the relative efficiency increases that come with thicker insulation. The percentage
decrease in heating load for each EPS insulation scenario in comparison to the baseline
model is shown in Figure 11. This facilitates more economical decision-making by
providing a clearer picture of the proportionate effect of insulation levels on energy
demand.

48
 Figure 11. Heating load Reduction vs EPS thickness (%)

When 5 cm of EPS insulation is installed, Figure 11 shows a significant decrease

in heating demand nearly 39% less. The reduction rises to roughly 41% and 43% with
7.5 cm and 10 cm insulation, respectively. Although thickness increases thermal
performance, the marginal gains lose significance as thickness exceeds 7.5 cm. This
implies that 7.5 cm EPS insulation might provide the best balance between construction
costs and energy savings for Kabul's residential buildings.

Insulation has a major impact on heating load, but in Kabul's hot summer months,
it also has a crucial impact on cooling load. The cooling load (measured in kilowatts)
decreases as EPS insulation thickness rises, as shown in Figure 12. This graph makes it
possible to compare directly how different insulation levels affect summer energy
demand, which is especially important for enhancing indoor comfort and lowering
reliance on mechanical cooling.

49
 Figure 12. Cooling load Reduction vs EPS thickness (Kw)

As illustrated in Figure 12, the cooling load consistently decreases as insulation

thickness increases. With 5 cm EPS, the cooling demand significantly decreases; with
7.5 cm and 10 cm insulation, further reductions are seen. But as insulation thickness
increases, the rate of improvement decreases, much like heating performance.
According to these findings, moderate insulation levels can result in significant summer
energy savings, making them a workable and effective solution for Kabul's climate.

Figure 13 shows the percentage decrease in cooling load for various EPS
insulation thicknesses to help visualize the relative impact of insulation on cooling
performance. In addition to providing insight into the efficiency gains possible through
gradual insulation improvements during the cooling season, this percentage-based view
enhances the absolute values displayed in Figure 12.

50
 Figure 13. Cooling load Reduction vs EPS thickness (%)

The application of 5 cm EPS reduces the cooling load by about 20%, as shown in
Figure 13. Performance is further improved by increasing insulation to 7.5 cm and 10
cm, which result in reductions of about 20% and 21%, respectively. These findings
demonstrate that insulation significantly reduces cooling energy consumption in
addition to reducing heating loads. That 7.5 cm insulation provides a balanced solution
in terms of performance and material efficiency for Kabul's climate conditions is further
supported by the fact that the marginal gains decrease with increased thickness.

This analysis shows that, in Kabul's climate, even modest insulation levels (5–7.5
cm) can result in significant HVAC energy demand reductions. The ideal insulation
thickness is determined by how well cost and energy savings are balanced. Although 10
cm EPS offers the best performance, 7.5 cm seems to be the most sensible compromise,
providing significant energy benefits with little increase in cost.

Window Glazing Optimization Results

This section assesses the impact on HVAC energy performance of replacing the
building's single-pane windows with double-pane windows (3 mm glass with 6 mm air

51
gap). In regions like Kabul that experience hot summers and frigid winters, window
performance is particularly important in controlling heat gain and loss.

With a high U-value of 6.975 W/m²·K, the windows in the baseline case were
modeled as single glazed aluminum frames, which led to significant energy losses
through the transparent envelope.

Scenario Description

The study looks at how improvements in window glazing affect HVAC energy
performance after evaluating wall and roof insulation. One of the main causes of heat
gain in the summer and thermal loss in the winter is poorly insulated windows. In order
to solve this, double-glazed windows with a 6 mm air gap are installed in place of the
standard single-glazed windows. A comparison of the main features of the baseline and
optimized window glazing scenarios used in the simulation is given in Table 9.

Table 9. Double glass scenario Description

Parameter Baseline Window Optimized Window
Glass Type Single Glazed Double Glazed (3 mm + 6 mm
gap)
U-Value 6.975 4.469
(W/m²·K)
Frame Type Aluminum Aluminum (unchanged)
Air Gap — 6 mm

By lowering the U-value from 6.975 W/m²·K to 4.469 W/m²·K, the optimized
double-glazed windows dramatically improve thermal performance, as shown in Table
9. This improved glazing system ensures compatibility with current architectural
designs by reducing conductive heat transfer while preserving the same frame type and
window area. As further examined in the following figures and load summaries, it is
anticipated that the ensuing insulation improvement will reduce both heating and
cooling demand

Reduced convective and conductive heat transfer through the window assembly is
reflected in the optimized case's higher U-value. To isolate the impact of glazing type,
neither the window area nor orientation were altered.

52
 HVAC Load Results Double Glazing Scenario

Double-glazed windows with a 3 mm glass layer and a 6 mm air gap were used in
a simulation to measure the effect of better window glazing on HVAC energy demand.
The resulting heating and cooling loads are contrasted with the standard single-glazed
situation in this section. The simulation results are summarized in Table 10, which also
shows the peak heating and cooling loads for each floor of the residential building with
the optimal window configuration.

Table 10. HVAC Load for 3mm Double Glass with 6mm air gap
Zone Name Maximum Maximum Zone
Cooling Heating Floor
Sensible Load Area
(kW) (kW) (m²)
First Floor 16.3 22.2 118.9
Second Floor 13 15.3 118.9
Third Floor 19.4 25 118.9
Total load 48.7 62.5 356.7
W/m² 136.5 175.2

Table 10 shows that all three conditioned floors experience a discernible decrease
in heating and cooling loads when double-glazed windows are used. The cooling load
dropped from 51.9 kW to 48.7 kW, and the overall heating load decreased from 73.4
kW in the baseline to 62.5 kW. These findings demonstrate how double glazing reduces
heat transfer and enhances indoor comfort. Upgrading window glazing is still a useful
and realistic way to improve energy performance in Kabul's residential buildings, even
though the decrease is not as significant as with wall insulation.

Figure 14 shows a comparison of the total heating and cooling loads (in kilowatts)
between the optimized double-glazed configuration and the baseline single-glazed
window scenario to illustrate the impact of window glazing improvement on HVAC
energy demand. The absolute energy savings attained through improved glazing
performance are depicted in this graphical representation.

53
 Figure 14. HVAC load Reduction for double glass vs single glass by (KW)

Double-glazed windows significantly lower heating and cooling loads, as seen in Figure
14. The air gap and extra glass layer provide better insulation, as evidenced by the
notable decrease in the heating load in particular. Even though it is less noticeable, the
cooling load reduction still improves HVAC efficiency. These findings lend credence to
the use of double glazing as a practical energy-saving strategy, particularly in regions
like Kabul where both summer cooling and winter heating are required.

Figure 15 shows the percentage decrease in HVAC load in comparison to the

baseline single-glazed scenario, which helps to further elucidate the efficacy of the
double-glazed window upgrade. This figure provides a better understanding of the
efficiency gains from the glazing enhancement by highlighting the proportionate
improvement in both heating and cooling energy performance.

54
 Figure 15. HVAC load Reduction for double glass vs single glass by (%)

In comparison to the single-glazed baseline, the optimized double-glazed window

system reduces the heating load by about 15% and the cooling load by about 6%, as
shown in Figure 15. In line with Kabul's higher demand for winter heating, the
improvement in heating performance is substantial even though the relative gain in
cooling efficiency is small. According to this analysis, installing double glazing in
residential buildings is an affordable way to enhance thermal performance and lower
energy usage.

Upgrading to double-glazed windows leads to a significant drop in U-value, from

6.975 to 4.469 W/m²·K, enhancing thermal resistance and reducing unwanted heat
transfer.

 The peak heating load is reduced by 14.9%, indicating better insulation

performance during winter nights and early mornings.
 The peak cooling load is reduced by 6.2%, attributed to reduced solar and
conductive heat gain.

55
 Window upgrades alone have a moderate impact when compared to insulation
upgrades, but they are especially crucial for glare reduction, condensation reduction,
and occupant comfort near window zones.

This finding backs up the suggestion that Kabul's residential buildings should
have at least double-glazed windows, especially when combined with airtightness and
insulation upgrades for optimal effect.

External Shading Optimization Results

One passive design technique to lessen solar heat gain through windows,
particularly in the summer, is external shading. In this case, the building façade is
enhanced with a horizontal shading device (peak):

 Shading projection (depth): 1.0 meter

 Shading thickness: 20 cm
 Material: Standard reinforced concrete (assumed non-insulating)
 Location: Positioned above windows on sun-exposed façades (primarily
south- and west-facing)

This intervention has a major impact on solar radiation exposure, particularly

during the hottest summer months, but it has no effect on wall or window U-values.

1-meter horizontal peak (overhang) placed above windows was used in a

simulation to evaluate how external shading devices affected HVAC performance. The
goal of this passive design approach is to minimize summertime solar heat gain while
preserving sufficient daylighting. The resulting HVAC loads with and without the
shading element are shown in Table 11, making it possible to compare how well it
reduces heating and cooling demands.

Table 11. HVAC Load in 1m peak case

56
 Zone Name Maximum Maximum Zone
Cooling Heating Floor
Sensible Load Area
(kW) (kW) (m²)
First Floor 17.1 26.1 118.9
Second Floor 13.8 19.2 118.9
Third Floor 19 28.9 118.9
Total load 49.9 74.2 356.7
W/m² 139.9 208.0

According to Table 11, adding a 1-meter shading peak lowers cooling loads on
every floor of the house. External shading successfully reduces direct solar radiation
and lowers indoor overheating during the summer months, as evidenced by the fact that
the total cooling load dropped from the baseline value. The shading element is a useful
passive strategy for increasing summer thermal comfort and reducing air conditioning
energy consumption, even though it has a minimal impact on heating loads.

Figure 16 shows the absolute reduction in heating and cooling loads (in kilowatts)
that is accomplished by adding a 1-meter shading peak in comparison to the unshaded
baseline scenario in order to visualize the impact of external shading on HVAC energy
demand. The performance advantages of this passive design feature are illustrated
graphically, especially in the cooling season.

57
 Figure 16. HVAC load Variation for 1m peak vs no peak by (KW)

With little effect on heating loads, the shading device significantly reduces the
cooling load on all conditioned floors, as seen in Figure 16. The 1-meter overhang's
ability to block high-angle summer sunlight while permitting low-angle winter sunlight
to pass through accounts for its effectiveness. This demonstrates the benefits of external
shading as a straightforward but efficient method of lowering the energy demand for
summer cooling in Kabul's climate, particularly when combined with other envelope
upgrades.

Together with the previously mentioned absolute values, Figure 17 shows the
percentage decrease in HVAC loads attained by adding a 1-meter shading peak in
comparison to the baseline without shading. The relative efficacy of the external
shading device, especially in enhancing summer energy efficiency, is better understood
with this percentage-based view.

58
 Figure 17. HVAC load Variation for 1m peak vs no peak by (%)

As can be observed in Figure 17, the shading peak has a negligible effect on
heating load but reduces cooling load by about 4%, depending on floor level. This
demonstrates that, without negatively impacting winter performance, external shading
devices are particularly effective at lowering summertime solar heat gain. The findings
support the idea that passive solar control techniques can improve building energy
efficiency, particularly when combined with other envelope enhancements like glazing
and insulation.

The installation of 1-meter external peaks above the windows yields the following
effects:

 Cooling load decreases by nearly 4%, demonstrating that shading

devices are effective at blocking direct solar radiation during summer
afternoons, reducing indoor heat gain.
 However, the heating load slightly increases by 1.6%, as the shading
devices also block beneficial winter sunlight, reducing passive solar
heating during cold seasons.

59
 This finding suggests that although external shading enhances performance in the
summer, it may marginally reduce energy efficiency in the winter. Therefore, in Kabul's
cold winters and hot summers, climate-adaptive or seasonally adjustable shading (such
as retractable devices or deciduous vegetation) may provide better all-season
performance.

Airtightness and Infiltration Optimization Results

Unwanted heat loss in the winter and heat gain in the summer are primarily
caused by air infiltration through gaps, cracks, and inadequate sealing in the building
envelope, particularly in older or lower-quality buildings. Enhancing airtightness lowers
uncontrolled airflow, which lowers the energy consumption of HVAC systems.

In this scenario, the infiltration rate is reduced from the baseline of 1.0 ACH (Air
Changes per Hour) to 0.5 ACH, simulating improved sealing, better-quality windows
and Paragraph before Table 12 (Introduction):

By decreasing the air infiltration rate from 1.0 air changes per hour (ACH) in the
baseline to 0.5 ACH in the optimized case, a simulation was carried out to assess the
impact of airtightness on HVAC energy demand. This modification reflects improved
sealing techniques and construction quality. Energy savings can be measured by
comparing the resulting heating and cooling loads under the reduced infiltration
scenario with the baseline case, as shown in Table 12.doors as well as more regulated
ventilation.

Table 12. HVAC Load in 0.5 ACH case

Zone Name Maximum Maximum Zone
Cooling Heating Floor
Sensible Load Area
(kW) (kW) (m²)
First Floor 17.2 24.4 118.9
Second Floor 13.9 17.5 118.9
Third Floor 20.1 27.2 118.9
Total load 51.2 69.1 356.7
W/m² 143.5 193.7

60
 Table 12 demonstrates that increasing airtightness by reducing the rate of
infiltration considerably lowers the heating demand on all building floors. There was a
significant increase in thermal efficiency as the total heating load dropped from 73.4
kW in the baseline case to 69.1 kW. Because infiltration contributes more to heating
loss during Kabul's frigid winters, the cooling load changed slightly. The significance of
airtight construction techniques as an economical method of lowering winter HVAC
loads in residential buildings is highlighted by these findings.

In order to show how better airtightness affects HVAC performance, Figure 18

shows the absolute decrease in heating and cooling loads (in kilowatts) that occurs when
the infiltration rate is lowered from 1.0 ACH to 0.5 ACH. This comparison
demonstrates how tighter building envelopes can save energy, especially in the winter.

Figure 18. HVAC load Reduction for 0.5ACH vs 1ACH by (KW)

Lowering the infiltration rate results in a considerable decrease in heating loads

on all floors, with the most pronounced decreases taking place on the upper levels, as
illustrated in Figure 18. This demonstrates that reducing air leakage is a practical way to
reduce energy loss and enhance thermal comfort indoors during the winter. Since air
infiltration is less important during the summer, the change in cooling load is minimal.

61
All things considered, these findings show that improving airtightness in Kabul's
residential buildings can result in significant heating energy savings.

In Figure 19, the percentage decrease in HVAC loads due to improved

airtightness specifically, lowering the infiltration rate from 1.0 ACH to 0.5 ACH is
displayed to supplement the absolute values in the preceding figure. The relative impact
of lowering air leakage on the energy requirements for heating and cooling is depicted
in this figure.

Figure 19. HVAC load Reduction for 0.5ACH vs 1ACH by (%)

As shown in Figure 19, improving airtightness reduces the heating load by about
6%, showing a significant energy-saving effect in the winter. Given Kabul's climate,
which is characterized by a preponderance of winter heating, the cooling load reduction
is modest roughly 1%. These findings support the notion that one of the best and least
expensive ways to increase building energy efficiency in cold climates is to decrease
infiltration.

Reducing the infiltration rate to 0.5 ACH has the following impacts:

62
  Heating demand drops by nearly 6%, reflecting reduced heat loss due to
uncontrolled air exchange.
 Cooling demand drops only slightly (1.3%), since air leakage is less
significant in summer, particularly in dry climates like Kabul where
natural ventilation is common.

Air sealing is a quick and inexpensive fix, especially when done during
construction or retrofitting, even though it doesn't have the same impact as glazing or
insulation upgrades. Additionally, when paired with mechanical ventilation systems,
increasing airtightness improves indoor thermal comfort, lowers dust infiltration, and
aids in maintaining indoor air quality.

Combined Optimization Scenario

This section presents the results of a combined envelope optimization scenario in

which the most effective measures from the previous simulations are apply
simultaneously to the building. These measures include:

 10 cm EPS insulation on walls and roof

 Double-glazed windows (3 mm + 6 mm air gap, U-value = 4.469
W/m²·K)
 1-meter external shading devices
 Improved airtightness (0.5 ACH)

The aim of this combined strategy is to assess the cumulative impact of passive
design measures on HVAC peak loads and overall energy performance under Kabul’s
climate conditions.

After evaluating each envelope improvement individually, it is important to

compare their thermal properties and corresponding infiltration rates to understand their
relative effectiveness. Table 13 provides a consolidated overview of the U-values for
walls, roofs, and windows, along with the infiltration rates used in each simulation

63
scenario. This summary serves as a reference for the performance characteristics of all
tested envelope configurations.

Table 13. U-Value and Infiltration rate for each Scenarios

Component U-Value (W/m²·K)

Wall (10 cm EPS) 0.314

Roof (10 cm EPS) 0.321
Window (Double) 4.469

Infiltration Rate 0.5 ACH

As shown in Table 13, each optimized scenario achieved significant reductions in

U-values and infiltration rates compared to the baseline. EPS insulation markedly
improved the thermal resistance of walls and roofs, while double-glazed windows
reduced window U-values.

To evaluate the cumulative impact of all building envelope improvements, a

combined optimization scenario was simulated. This integrated case includes 10 cm
EPS insulation, double-glazed windows, 1-meter external shading peaks, and reduced
infiltration at 0.5 ACH. Table 14 presents the total heating and cooling loads under this
fully optimized configuration, allowing direct comparison with individual improvement
cases and the original baseline.

Table 14. HVAC load for Combined Optimized case

Load Type Value Units

Peak Heating Load 38.7 kW

Peak Cooling Load 39.4 kW
Heating Load per m² 107.3 W/m²
Cooling Load per m² 109.3 W/m²

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 As shown in Table 14, the combined optimization scenario results in the most
significant reduction in HVAC loads, with total heating and cooling demands
substantially lower than the baseline model. The heating load dropped to 38.7 kW and
the cooling load to 39.4 kW, reflecting overall reductions.

To clearly quantify the overall effectiveness of the building envelope

improvements, Table 15 presents a direct comparison between the baseline case and the
combined optimized scenario. This comparison includes total heating and cooling loads,
as well as percentage reductions in HVAC demand. The purpose is to demonstrate the
cumulative energy savings achieved through the integration of all enhancement
measures.

Conditioned Area: 356.7 m² (3 residential floors × 118.9 m²)

Table 15.Comparison of Baseline vs Combine optimization

Scenario Heating Load Cooling Heating Cooling
(kW) Load (kW) Reduction (%) Reduction (%)
Baseline 73.4 51.9 — —
Combined 38.7 39.4 47.30% 24.10%
Optimized

As illustrated in Table 15, the combined optimization approach results in a 47.3%

reduction in heating load and a 24.1% reduction in cooling load compared to the
baseline case. These figures highlight the substantial improvement in energy efficiency
achievable through holistic building envelope upgrades. The data confirm that when
insulation, glazing, shading, and airtightness measures are applied together, they deliver
synergistic benefits far greater than any single strategy alone making this integrated
approach ideal for reducing HVAC energy consumption in Kabul’s climate.

The combined envelope optimization results in the highest reduction in both

heating and cooling loads:

 Heating demand drops by 47.3%, highlighting the dominant role of

thermal insulation and air sealing in reducing winter energy losses.

65
  Cooling demand decreases by 24.1%, primarily due to shading devices
and low U-value windows that reduce solar heat gains.

This result confirms that envelope design improvements can nearly halve the
HVAC energy load in Kabul’s residential buildings, offering significant energy savings,
cost reduction, and improved occupant comfort.

4.2 Discussion
This research aimed to evaluate and optimize the HVAC energy demand of a
typical mid-rise residential building located in Ahmad Shah Baba Mena, Arzan Qemat,
Kabul City, through various building envelope improvements. The primary focus was
on reducing heating and cooling loads using passive and construction-based strategies
suitable for Kabul’s semi-arid continental climate, which experiences cold winters and
hot summers.

A quantitative methodology was employed using building performance simulation

via the Hourly Analysis Program (HAP). A four-story residential case study building
(three conditioned floors and one unconditioned parking floor) was selected. Each
conditioned floor had an area of 118.9 m², resulting in a total conditioned space of 356.7
m². The simulation model was developed based on actual architectural drawings and
realistic assumptions for occupancy, internal loads, and local climate conditions.

The study followed a structured simulation approach, beginning with the creation
of a baseline model representing the current construction practices in Kabul, which
typically lack insulation and use single-glazed windows. Several parametric scenarios
were then simulated to test the effect of key envelope design variables, including:

 Wall and roof insulation thickness (EPS insulation at 5 cm, 7.5 cm, and 10
cm)
 Window glazing type (upgrade from single to double glazing)
 External shading devices (1-meter horizontal peaks above windows)
 Air infiltration rate reduction (from 1.0 ACH to 0.5 ACH)

66
 Each scenario was analyzed independently to measure its impact on peak heating
and cooling loads, and then a final combined optimization scenario was simulated to
assess the cumulative energy-saving potential.

The simulation results showed that substantial energy savings could be achieved
through targeted envelope enhancements. Thermal insulation and improved window
systems provided the most significant reductions in HVAC loads, while shading and
airtightness offered valuable complementary benefits. The final combined scenario
demonstrated a 47.3% reduction in heating load and a 24.1% reduction in cooling load
compared to the baseline model.

This research provides an evidence-based foundation for improving energy

efficiency in residential buildings in Kabul, highlighting the importance of passive
design and envelope optimization under local climatic and construction conditions.

Key Findings

This section summarizes the most significant findings from the simulation-based
analysis of building envelope optimization for HVAC energy efficiency in the selected
residential building in Kabul.

Impact of Individual Envelope Strategies

The analysis of individual envelope measures provided insight into their relative
effectiveness in reducing HVAC energy demand:

 Wall and Roof Insulation

 Applying 5 cm, 7.5 cm, and 10 cm of EPS insulation progressively

reduced heating and cooling loads
 The 10 cm insulation scenario achieved the greatest reduction in HVAC
demand, lowering heating load by 43.3% and cooling load by 21.2%.
 This demonstrates that thermal insulation is the most impactful single
intervention, particularly for winter energy performance.

67
  Double-Glazed Windows

 Replacing single-glazed windows (U-value: 6.975 W/m²·K) with double-

glazed units (U-value: 4.469 W/m²·K) resulted in a 14.9% reduction in
heating load and 6.2% reduction in cooling load.
 While less impactful than insulation, window upgrades also improve
comfort and reduce solar heat gain.

 External Shading Devices

 Adding 1-meter horizontal concrete peaks above windows led to a 3.9%

decrease in cooling load, but a slight increase of 1.1% in heating load,
due to reduced winter solar gain.
 Shading is effective for summer performance but requires careful
orientation and sizing to avoid negative effects in winter.

 Airtightness Improvement

 Reducing infiltration from 1.0 ACH to 0.5 ACH reduced heating load by
5.9%, with a minor 1.3% reduction in cooling load.
 Airtightness improvements enhance thermal performance with relatively
low cost and can be especially beneficial in poorly sealed buildings

Combined Optimization Benefits

When all envelope improvements were applied simultaneously 10 cm insulation,

double glazing, shading, and 0.5 ACH infiltration the results were significantly
improved:

 Heating load reduced from 73.4 kW (baseline) to 38.7 kW, a total reduction of
47.3%
 Cooling load reduced from 51.9 kW to 39.4 kW, achieving a 24.1% reduction

68
 These results demonstrate the synergistic effect of combining multiple envelope
strategies. While each measure provides some level of energy savings individually, their
collective impact is substantially greater, particularly in a climate like Kabul's where
both winter and summer conditions are extreme.

Limitations of the Study

Despite the structured methodology and comprehensive simulation scenarios employed

in this research, several limitations should be acknowledged:

1. Simulation Simplifications
The study used the Hourly Analysis Program (HAP), which simplifies dynamic
thermal behaviors such as transient heat transfer and airflow patterns. This may
lead to either overestimating or underestimating energy performance outcomes,
especially in climates with large diurnal temperature variations like Kabul.
Thermal inertia of materials such as brick masonry was not dynamically
modeled, which might affect heating and cooling load accuracy.
2. Exclusion of Natural Ventilation
Although the study referenced natural ventilation strategies in the literature
review, these were not integrated into the simulation model due to the
limitations of HAP and the scope of the current analysis.
3. Limited Envelope Parameters
Only a specific set of building envelope features (EPS insulation, double
glazing, external shading, and airtightness) were evaluated. Other parameters
like thermal mass, window-to-wall ratio (WWR), and glazing types such as low-
emissivity (low-E) glass were not explored in depth, which could influence the
energy efficiency results.
4. Static Occupancy and Load Assumptions
The internal loads (lighting, equipment) and occupancy were assumed constant

69
 and based on ASHRAE standards. In reality, residential buildings in Kabul
exhibit varied patterns, which could lead to discrepancies between modeled and
actual performance.
5. Lack of Cost-Benefit Analysis
The study focused on technical performance without evaluating economic
feasibility. Payback periods or lifecycle cost assessments were not conducted,
limiting the practical implementation of the recommended measures.
6. No Validation with Real Buildings or Advanced Software
The results were not validated using alternative dynamic simulation tools (e.g.,
EnergyPlus, DesignBuilder), nor against real-world energy consumption data.
As a result, the reported energy savings might not reflect actual operational
outcomes.

70
5 Conclusion and Recommendations

5.1 Conclusion

This research has systematically evaluated the HVAC energy demand of a typical
mid-rise residential building located in Ahmad Shah Baba Mena, Arzan Qemat, Kabul
City, under Kabul’s semi-arid continental climate. Through simulation using the Hourly
Analysis Program (HAP), the study demonstrated the significant impact of various
passive envelope strategies on reducing heating and cooling loads.

Key findings from the simulation showed that applying EPS thermal insulation to walls
and roofs, upgrading to double-glazed windows, implementing external shading
devices, and improving airtightness each contributed to HVAC energy reduction.
Among these, insulation and glazing improvements were the most effective. When all
strategies were combined in a fully optimized envelope scenario, the heating load was
reduced by 47.3% and the cooling load by 24.1% compared to the baseline model.

The results emphasize the importance of holistic building envelope design in achieving
energy-efficient residential construction in Kabul. The study offers practical, climate-
responsive strategies for reducing energy consumption, lowering operational costs, and
improving indoor comfort through passive design measures.

5.2 Recommendations

To enhance the accuracy of future studies on building envelope optimization in

Kabul, the following recommendations are proposed:

1. Adopt Advanced Simulation Tools like Design Builder and Energy Plus

71
2. Conduct cost-benefit assessments of retrofit measures, including lifecycle costs,
payback periods, and initial investment to support decision-making under
Kabul’s economic constraints.
3. Simulate retractable or climate responsive shading systems to balance summer
cooling with winter solar heat gain

72
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Appendix A
 Baseline Load Calculation Report

xii
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xv
Appendix B
Author Biography

Abdul Rahman Erfan was born in 1993 in Logar Province, Afghanistan. He earned his
Bachelor of Science degree in Mechanical Engineering from the Faculty of Engineering
at Kabul University in 2015. He is currently pursuing a degree in Industrial Engineering
at Afghan Islamic International University, where he has completed his thesis on
building energy efficiency.

Abdul Rahman has several years of professional experience in HVAC system design,
having worked with various organizations on projects involving residential,
commercial, and healthcare facilities. His expertise includes heating and cooling load
calculations, system optimization, and the application of ASHRAE standards in HVAC
planning. His current academic work focuses on the optimization of HVAC energy
demand in residential buildings, particularly under the climatic conditions of Kabul
City.

He is passionate about sustainable engineering solutions and aims to contribute to the

development of energy-efficient infrastructure in Afghanistan.

xvi