Enhancing Energy Performance in Hot Climates: A Multi-Criteria Approach Towards Nearly Zero-Energy Buildings

Abstract

Accelerating decarbonization in hot-climate buildings requires integrated retrofit strategies that address energy performance, environmental impact, thermal comfort, and economic feasibility within a unified decision framework. This study develops and validates a simulation-driven multi-criteria approach to evaluate retrofit packages across three representative ASHRAE hot sub-climates (1B, 2B, 2A). An academic building was modeled using DesignBuilder (Stroud, UK) and validated in accordance with ASHRAE Guidelines. The retrofit analysis integrates envelope enhancements (insulation and reflective coatings), glazing-integrated photovoltaics (GIPV), rooftop photovoltaics (RTPV), and a Dedicated Outdoor Air System (DOAS). The performance evaluation incorporates dynamically simulated energy consumption, operational CO₂ emissions, thermal comfort indicators (PMV and DCH), and techno-economic metrics (IRR, ROI, PBP). Weighting factors were derived from a structured stakeholder consultation to reflect context-sensitive sustainability priorities. The results indicate energy reductions of approximately 51–57% and carbon emission reductions of 40–53% across the examined zones, while discomfort hours decreased by roughly 42–46%. This demonstrates significant improvements in thermal comfort under integrated retrofit strategies, particularly with DOAS integration, highlighting the importance of ventilation-driven comfort enhancement. Economic feasibility was climate-dependent; envelope-focused solutions yielded high returns, while integrated strategies delivered balanced environmental and economic performance. The proposed framework enables systematic, climate-specific prioritization of retrofit alternatives and supports scalable, economically viable NZEB transitions in rapidly expanding hot-climate educational infrastructure.

1. Introduction

Climate change threatens the environment, human health, and the economy. Rising sea levels, extreme weather, and resource scarcity are impacting regions globally due to greenhouse gas (GHG) emissions from fossil fuel use. Human activity, especially the burning of fossil fuels, is the main cause of rising CO₂ emissions, a key driver of global warming. Energy use drove CO₂ emissions to a record high [1,2,3,4]. Global energy-related CO₂ emissions are on track to produce the second-sharpest annual rise in history [5]. According to the Energy Information Administration (EIA), during the previous 20 years, primary energy demand has increased by 49% while CO₂ emissions have risen by 43%, with anticipated annual increases of 2% and 1.8%, respectively [6]. With fossil fuels nearing their tertiary phases, several countries are beginning the process of transitioning to alternate energy infrastructure [7,8]. Currently, managing this transition by reducing adverse effects and gradually integrating technological solutions is of the utmost importance. Mitigating climate change requires near-term carbon reduction, fossil fuel sequestration, and a shift to renewables and energy efficiency [8].

Scientists forecast rising global temperatures due to human greenhouse gas emissions, with cities expected to contribute over 80% of these emissions by 2050 [9,10]. Comprising 30–40% of global energy consumption and responsible for nearly 19% of greenhouse gas (GHG) emissions, buildings are the world’s largest electricity consumer [9,11,12,13,14,15,16]. Heating, Ventilation, and Air Conditioning (HVAC) systems are the primary culprit, responsible for about half of this energy demand [11,12]. Rising populations and the pursuit of thermal comfort are key factors behind the ever-increasing energy demands of buildings. Developing nations see particularly high demand, with roughly half the energy dedicated to space conditioning and an additional 20% consumed by electronics, lighting, and other internal processes [17]. In hot regions, HVAC and lighting can comprise over 85% of a building’s total energy use, with HVAC susceptible to oversizing due to design miscalculations, highlighting the challenge of achieving sustainable designs that meet occupant needs while reducing energy use [18,19,20,21]. Developing effective strategies to reduce building energy consumption while maintaining human health, comfort, and sustainability is crucial. Advanced building designs, incorporating improvements in the building envelope, HVAC, lighting, and appliance technologies, can achieve 20–50% reductions in overall energy consumption [22,23,24,25].

Decarbonizing buildings is a new focus, with advanced building science, controls, and simulations forging the path [26]. Retrofitting existing structures and incorporating energy efficiency into new designs offer significant opportunities to cut global carbon emissions. However, assessing building energy use remains complex due to numerous factors [9]. Performance analysis is crucial for both designing efficient new buildings and retrofitting existing ones. Contrary to popular belief, energy-efficient buildings in developing nations can be built at lower costs [23]. Early design stages hold immense potential for optimizing energy use and resource efficiency in buildings. At this stage, cost-effective solutions have the greatest impact. Energy modeling, a valuable tool for high-performance buildings, leverages simulations and data to assess energy use and environmental impact, ensuring both comfort and sustainability [9]. The optimization of passive building design parameters is paramount to minimizing a building’s energy demands. This not only enhances the overall energy efficiency of the structure but also facilitates the optimization of active building systems, such as HVAC, for further energy consumption reduction [24].

In regions facing power outages, energy efficiency is even more critical [27,28]. Energy-efficient buildings reduce energy consumption, lessen strain on the national grid, and minimize disruptions. These buildings also improve occupant well-being and productivity by creating healthier indoor environments. Prioritizing these factors in building design and management leads to better decision-making, improved well-being, and cost savings for building owners.

Accordingly, this study develops a validated simulation model and evaluates integrated retrofit packages across hot-climate subzones using a multi-criteria decision framework. The main contributions of this study are

• Development of a validated energy model based on as-built data and actual operational schedules of an institutional building.
• Comparative evaluation of integrated retrofit packages across three ASHRAE climate zones (1B, 2B, and 2A).
• Simultaneous assessment of energy performance, carbon emissions, thermal comfort (PMV and DCH), economic feasibility (IRR, ROI, PBP), and health-resilient ventilation strategies.
• Integration of Glazing Integrated Photovoltaics (GIPV), reflective paints, insulation, DOAS, and rooftop PV within a unified decision-making framework.
• Climate-specific techno-economic comparison revealing performance trade-offs between the three climatic zones: very hot–arid, hot–arid, and hot–humid.

2. Literature Review

In hot climates, buildings face a complex challenge: balancing growing energy demands for occupant comfort with existing inefficient structures and reliance on fossil fuels [28]. Recent studies on hot-climate building performance focus on achieving decarbonization through a balance of energy efficiency and renewable energy. This sustainable design paradigm emphasizes demand reduction as a prerequisite for renewable integration. Accordingly, this review examines the central role of comprehensive energy management in meeting the long-term sustainability goals.

A study by Mynhardt [29] assessed a new university building’s energy use in Stellenbosch, South Africa. The building used 16.5% more energy than a modelled energy-efficient design. This disqualified it from the Green Star rating due to its exceeding the energy consumption limits. Lighting and air conditioning were major factors in the difference. The modelled building used a more efficient air conditioning system and had a higher lighting density. The study recommends reducing lighting and improving air conditioning to significantly lower the building’s energy use and environmental impact. Financial analysis showed these improvements would be cost-effective. Building energy management (BEM) is crucial in addressing the high energy consumption of buildings, a major contributor to global warming, as highlighted by Iwayemi et al. [30]. BEM solutions aim to optimize energy use and costs while ensuring occupant comfort and productivity. Their study suggests that non-intrusive equipment load monitoring and smart lighting offer significant energy reductions in both residential and commercial buildings. Further research by Attia et al. [31] focused on developing realistic building energy data and models for Egypt’s residential sector. The authors utilized EnergyPlus software to simulate energy consumption in surveyed apartment buildings, highlighting the importance of model verification against actual building characteristics. Their work establishes benchmark models for Alexandria, Cairo, and Asyut, considering factors like air conditioning, lighting, hot water, and appliances. This allows for future assessment of the impacts of new energy standards on energy use and costs. Vakiloroaya et al. [32] delve deeper into optimizing energy use in air-conditioning systems, a key contributor to a building’s energy footprint. Their study utilizes a model-based approach to analyze energy-saving opportunities in central cooling plants. The validated simulation tool incorporates real-world data to demonstrate the potential for significant energy savings and improved comfort through their recommended optimization technique. A study by Fathalian et al. [33] used simulations to evaluate energy-saving strategies for office buildings in Iran. Replacing windows with double-glazed windows, adding wall insulation, and using external shading all significantly reduced energy consumption (13% to 18%). This suggests building envelope improvements can be effective energy-saving techniques. Ghose et al. [34] examined eco-friendly refurbishments in New Zealand and found that prioritizing energy-efficient HVAC systems and reducing window area in large buildings were key measures. William et al. [9] assessed energy performance using dynamic simulation modelling. Focusing on building envelope retrofits, 25 mm XPS insulation was optimized, reducing HVAC energy by 16% and overall energy by 8%, with approximately 2 years of payback. Another study [23] assessed retrofit strategies for institutional buildings using a multi-criteria decision-making approach that evaluated environmental, economic, and thermal comfort implications. The results indicated reflective paints were the most effective measure among certain other insulators. Emphasizing the potential for energy savings in the building sector, Emil and Diab [35] investigated the implementation of energy efficiency measures in an educational facility in Cairo. The researchers used EnergyPlus software to model the impact of building envelope improvements (walls, roof, and windows) and HVAC system upgrades. Their findings revealed that the envelope retrofits led to a significant energy reduction of about 29%, while upgrading the HVAC systems yielded even greater savings of over 50% annually. Different studies explored methods to improve HVAC efficiency in buildings. Adjusting thermostats, airflow, and building features like windows and insulation all showed promise. Highlighting the importance of these findings, the US National Renewable Energy Laboratory (NREL) [36] focused on proper sizing of air conditioning units, especially in hot and humid climates. Oversized units waste energy, cost more, and struggle to remove moisture effectively, leading to comfort issues. NREL recommends considering building characteristics such as insulation and size to determine the correct cooling load for optimal efficiency. Several authors have investigated methods for optimal cooling system design in various contexts. Woradechjumroen et al. [37] specifically addressed the issue of HVAC equipment oversizing in commercial buildings. Their study, which relied on real-world data from retail stores, found that oversizing can be significant, leading to increased energy consumption. Their findings provide valuable insights for designers to improve building load design and avoid oversizing HVAC equipment.

Building upon the critical role of building envelopes in thermal performance, hot-climate design must prioritize strategies that manage both moisture and heat transfer within the envelope assemblies [38]. The building envelope’s insulating properties directly affect energy consumption and peak loads. Deterioration necessitates effective thermal design, which is achieved through high-performance insulation, phase change materials, or adaptive facades [39,40,41]. Several strategies can enhance the building envelope’s thermal resistance and reduce cooling demands. Selecting appropriate insulation materials [39] or incorporating innovative solutions as phase change materials [40] or adaptive facades [41] can significantly improve thermal performance. Studies have shown that implementing thermal insulation [25], double-skin facades [42], or comprehensive Energy Conservation Measures (ECMs) [43] can significantly reduce cooling needs in hot environments. The most common approach involves adding thermal insulation coatings to opaque building facades. This optimization can be achieved through iterative adjustments of single parameters within wall, roof, or glazing assemblies, leveraging simulation models to assess building loads and predict cost-performance benefits [20,44,45]. Driven by rising energy costs and environmental concerns, demand for energy-efficient buildings has soared. Sadineni et al. [46] report substantial energy savings (20–40% in Greece, 35–47% peak cooling in Hong Kong) from envelope improvements, underlining the value of optimized building design. Moujaes and Brickman [47] investigated reflective paint for building envelopes in hot–arid climates. Their simulations showed an 11% summer cooling energy reduction using the paint solely on a southwestern US building’s roof, highlighting the potential of the technology. Bolatturk’s [48] research underscores climate-specific insulation selection and thickness. Thin plaster used in hot climates promotes heat dissipation, while colder climates require thicker walls for insulation. Extruded polystyrene insulation in hot environments should be 3.2–3.8 cm thick for optimal performance. Delgarm et al. [49] used building energy modeling to optimize designs in various Iranian climates. By adjusting building features, the authors achieved significant energy savings (23.8–42.2% annually). This highlights the importance of climate and design decisions on building efficiency, promoting optimization during design. López et al. [50] used simulation to assess building envelope retrofits at the University of Oviedo. While façade insulation alone yielded modest energy savings of 3%, this finding emphasizes the role of targeted retrofits in improving building energy efficiency, particularly when combined with other measures.

PV systems are gaining traction across diverse sectors due to their scalability, longevity, ease of installation, and low environmental impact, with building-integrated, rooftop applications leading the way [51,52,53]. Rooftop PV (RTPV) installations are one of the configurations that offer economic benefits, including cost savings and investment security due to predictable energy pricing over the system’s lifespan. Additionally, RTPV systems can be integrated into smart grids and contribute to mitigating climate change by reducing fossil fuel consumption [54,55,56]. Setyonegoro et al. [57] assessed the impact of high rooftop PV penetration on distribution networks. A Monte Carlo simulation was employed to determine PV hosting capacity for real-world urban and rural feeders. The results indicate a higher PV hosting capacity of 31% full load in urban areas, compared to 18% in rural areas. This research underscores the heterogeneity of PV integration challenges across different network topologies. Xue et al. [58] assessed rooftop PV economics in 21 Guangdong cities, identifying the Pearl River Delta (75% of potential) as top-performing due to urbanization, electricity costs, and self-consumption. Internal Rate of Returns (IRR) ranged from 14.6 to 19.2% (commercial/industrial) and 9.9–15.9% (residential). Less developed cities anticipate IRR growth of 4.9–5.8% (commercial/industrial) and 4.4–5.9% (residential) by 2030, with payback periods decreasing by 5.8–6.7 and 3.4–4.1 years, respectively. Technology drives long-term growth, while socioeconomic factors and policy impact short-term performance. Cuesta-Fernández et al. [59] propose an urban–metropolitan energy exchange framework to expand residential rooftop PV coverage in Valencia from 61% to 79.2% through inter-municipal collaboration, enhancing energy self-sufficiency and equity. Wang et al. [60] optimized rooftop PV systems in Nanning, determining optimal azimuth (245°) and tilt (32.5°) angles for various roof types. Flat roofs benefit from fixed angles, while gable roofs favor east–west orientation. Nanning’s total rooftop PV potential of 19.99 TWh/year can meet 76.1% of city’s electricity demand, a finding that provides insights for tropical regions. Building-Integrated Photovoltaics (BIPV) are another configuration that have garnered increasing attention due to their potential to generate clean energy while simultaneously serving as building envelopes. Ng et al. [61] propose semi-transparent Building-Integrated Photovoltaics (BIPV) for improved energy efficiency in tropical buildings. The results show these panels outperform conventional glazing in Singapore’s climate, making them a promising sustainable option. Sorgato et al. [62] promote sustainable construction in Brazil through building-integrated photovoltaics (BIPV). Their research suggests replacing conventional facades with BIPV systems in commercial buildings across Brazil for cost-effective energy savings and on-site renewable energy generation. Accounting for nearly half of a building’s energy use [7,22,26,28,44,63], HVAC systems in commercial buildings necessitate cost-effective optimization to reduce environmental impact and ensure occupant health. The COVID-19 pandemic highlights the need for stricter ventilation control for airborne disease mitigation [64,65]. Studies suggest proper ventilation and humidity management (40–60% RH) can improve air quality and potentially reduce viral transmission [66,67,68,69]. In this context, Korolija et al. [70] demonstrate that VAV systems outperform CAV systems in UK offices, achieving substantial energy savings of up to 50%, reinforcing the importance of optimal HVAC design for energy efficiency. Mihara et al. [71] report a DOAS-CF system with fans maintained comfort at a warmer 27 °C compared to traditional AC (24 °C), suggesting airflow improves comfort and reduces energy use by 27.7%. This holds promise for energy savings and occupant control in educational buildings. Pan et al. [72] call for optimizing HVAC systems to improve ventilation and reduce airborne contaminants, including COVID-19 transmission. Authors emphasize the importance of adaptable ventilation for future health emergencies and public health in buildings. Guo et al. [73] advocate for maximizing fresh air intake to reduce airborne transmission, recommending strategies like using 100% outdoor air in AHUs. This prioritizes fresh air over filtration for mitigating airborne particles, aligning with international guidelines. William et al. [74] evaluated energy-efficient HVAC solutions for mitigating airborne transmission risks indoors. A dedicated outdoor air system (DOAS) reduced CO₂ emissions by 691 tons, HVAC energy consumption by 37%, and overall building energy consumption by 16%, while simultaneously improving indoor environmental quality. This resulted in a 6% return on investment.

To systematically substantiate the identified research gap,

Table 1. Systematic comparison of representative retrofit studies.

Study	Climate Scope	Envelope + HVAC Integration	Renewable Integration	Comfort Assessment	Economic Evaluation	Health-Resilient Ventilation	Multi-Criteria Framework
Mynhardt [29]	Single (South Africa)	Partial	No	No	Yes	No	No
Iwayemi et al. [30]	General	HVAC-focused	No	No	Yes	No	No
Attia et al. [31]	Single (Egypt–Residential)	Yes	No	Limited	Limited	No	No
Vakiloroaya et al. [32]	Single	HVAC optimization	No	Limited	No	No	No
Fathalian et al. [33]	Single (Iran)	Envelope	No	No	Limited	No	No
Ghose et al. [34]	Single (New Zealand)	Yes	No	No	Yes	No	No
Emil & Diab [35]	Single (Cairo)	Yes	No	No	Yes	No	No
Sadineni et al. [46]	Multi-country	Envelope	No	No	No	No	No
Moujaes & Brickman [47]	Single	Envelope	No	No	Limited	No	No
Delgarm et al. [49]	Single (Iran)	Envelope	No	No	No	No	Optimization only
López et al. [50]	Single (Spain)	Envelope	No	No	Limited	No	No
Ng et al. [61]	Single (Singapore)	Envelope (BIPV)	Yes	Limited	No	No	No
Sorgato et al. [62]	Single (Brazil)	Envelope (BIPV)	Yes	Yes	Yes	No	No
Mihara et al. [71]	Single	HVAC (DOAS)	No	Yes	Limited	Yes	No
Pan et al. [72]	General	HVAC	No	Yes	No	Yes	No
Guo et al. [73]	General	HVAC	No	No	No	Yes	No
William et al. [9]	Single	Envelope	No	Yes	Yes	No	No
William et al. [74]	Single	HVAC (DOAS)	No	Yes	Yes	Yes	No
Present Study	Three sub-climates (1B, 2B, 2A)	Yes	Yes	Yes	Yes	Yes	Yes

summarizes some of the studies cited in this review according to climate scope, integration level, comfort assessment, economic evaluation, health-resilient ventilation consideration, and use of multi-criteria decision frameworks.

As illustrated in Table 1, the majority of previous studies focus on single climatic contexts and typically evaluate isolated retrofit components or partial integration strategies. Although several investigations combine energy, economic, and comfort metrics, very few conduct comparative analyses across distinct hot sub-climates. Moreover, only a limited amount of research integrates health-resilient ventilation strategies within a unified NZEB-oriented decision framework. The present study distinguishes itself by applying a simulation-driven multi-criteria framework consistently across three ASHRAE hot sub-climates, thereby enabling systematic identification of climate-specific performance trade-offs.

3. Methodology

Aligned with the global drive towards Nearly Zero-Energy Buildings (NZEB), this study explores strategies aiming to minimize building energy consumption within diverse hot climate zones. By integrating energy efficiency and renewable energy sources, the study aims to optimize building energy performance while considering thermal comfort, economic, and environmental factors, as illustrated in Figure 1. An academic facility serves as a case study to evaluate the potential of energy-efficient design and renewable energy technologies. Building energy performance is predicted using the hourly heat balance calculations through an EnergyPlus dynamic simulation solver within the DesignBuilder platform [75,76,77,78,79,80]. The simulator dynamically simulates building energy performance by considering both internal characteristics (building envelope, volume, and energy systems) and external environmental conditions (weather data) [81,82].

The analysis commences with a baseline model (B.L) established using ASHRAE standards for design conditions, occupant density, ventilation rates, and internal heat gains [83,84,85]. Model validation was conducted by comparing simulated energy consumption to actual data, adhering to ASHRAE’s prescribed validation criteria [86]. The sensitivity analysis identified critical factors influencing energy consumption. The study evaluated the impacts of different solutions on building performance through modelling and simulation, considering energy consumption, environmental impact, and indoor comfort. To ensure methodological transparency, weighting factors were derived through a structured stakeholder-consultation process. The participants included (30%) academics and HVAC consultants, (33%) industry experts, (13.5%) independent academics, (10%) sustainability experts, and (13.5%) building owners (percentages approximate). Participants allocated relative importance among three evaluation criteria: indoor thermal comfort, economic feasibility, and environmental impact. The results produced weighting ratios of 45% for thermal comfort, 35% for economic performance, and 20% for environmental impact. The prioritization of thermal comfort reflects the educational function of the case study building and the critical influence of thermal conditions on occupant productivity and well-being. This proposed MCDM framework differs methodologically from conventional approaches in several aspects. First, weighting factors were not adopted from predefined standards but were derived directly from a stakeholder-consultation process, ensuring contextual relevance. Second, the decision matrix integrates dynamically simulated outputs, including energy consumption, carbon emissions, and thermal comfort metrics, rather than static performance indicators. Third, the same decision structure is applied consistently across three distinct ASHRAE hot sub-climates (1B, 2B, 2A), enabling comparative climate-sensitive ranking of integrated retrofit packages. Finally, the framework incorporates health-resilient ventilation strategies (DOAS) within the optimization process, extending beyond traditional energy–economic evaluations commonly found in NZEB studies.

4. Case Study Model

This study analyzes a representative academic building to address the sustainable planning needs of Egypt’s expanding higher education sector. Full access to as-built documentation and on-site operational data enabled the precise characterization of geometry, internal activities, and thermal zoning. Such data-driven modeling ensures the resulting NZEB framework is realistic and transferable to upcoming campus developments across the region.

4.1. Model Description

The case study building, depicted in Figure 2, is a six-story educational building with an approximate total area of 11,350 m².

The building is oriented towards the northwest. Operational schedules follow typical university occupancy patterns, with primary building usage occurring between 08:00 and 17:00 on working days. To further clarify internal zoning distribution, Appendix A 

Table A1. Occupied zones percentage to building total area.

Zone	Area (m2)	Area %
Call Center	43	0.5
Classrooms	693	7.9
Corridors	2253	25.8
Dry Lab	407	4.7
GYM	150	1.7
Lecture Halls	707	8.1
Libraries	466	5.3
Lobby	827	9.5
Lounges	453	5.2
Meeting Rooms	276	3.2
Offices	1584	18.2
Receptions	634	7.3
Restaurants	237	2.7
Total	8728	100

presents the percentage of occupied zones relative to the total building floor area.

The building material properties of the envelope components align closely with the typical values observed in most Egyptian non-residential buildings and are detailed in

Table 2. Envelope specifications.

Wall
U-value (W/m2 K)	1.924
Roof
U-value (W/m2 K)	2.27
Glazing
WWR	30%
Glazing	6 mm Double Pane (Blue) + 6 mm Gap (Air)
U-value (W/m2 K)	3.094
SHGF	0.503

.

The baseline envelope configuration represents typical Egyptian non-residential construction practices. To ensure consistent comparative analysis, the same envelope characteristics were maintained across all three climate zones prior to applying retrofit scenarios. This approach isolates climatic influence and allows performance differences to be attributed directly to climate variation rather than envelope construction changes.

4.2. Climatic Classification

To establish a global framework for building energy analysis, this study adopts the widely recognized Köppen–Geiger and ASHRAE climatic classifications. Egypt, classified as BWh and BSh by Köppen–Geiger [87,88,89], is further subdivided into very hot–dry, hot–dry, and hot–humid regions by ASHRAE. Aswan, Cairo, and Alexandria are selected as representative cities for these climate zones, and their recommended design conditions are presented in

Table 3. Recommended design conditions [83,90].

Location	ASHRAE Climate Zone	Dry-Bulb Temperature (°C)	Wet-Bulb Temperature (°C)	Direct Normal Irradiation (kWh/m2)	Wind Speed (m/s)
Aswan	1B	44.1	21.1	2254	4.04
Cairo	2B	38.2	21.2	2036	3.58
Alexandria	2A	33.2	22.4	1955	3.92

[83,90].

4.3. Internal Loads

Internal loads represent the heat generated within the building, encompassing contributions from occupants, ventilation, lighting, equipment, and operational schedules. Occupant density, ventilation rates, lighting, and plug loads were set according to ASHRAE Standards 62.1 and 90.1 [84,85]. The building model was developed based on actual building operation data obtained from the facility management team and as-built documentation. The cooling setpoint temperature was maintained at 24 °C throughout occupied hours, consistent with ASHRAE recommendations and real operational practices. HVAC systems operated according to institutional schedules, with setback during unoccupied hours.

Lighting design followed ASHRAE 90.1 recommendations using the space-by-space Lighting Power Density (LPD) method. The LPD values are listed in

Table A2. LPD for institutional buildings [85].

Zone	LPD (W/m2)
Classroom	13.4
Coffee Stations	7
Computer Lab	18.4
Conference/Meeting	13.3
Corridors	9.9
Laboratories	15.5
Lecture Hall	13.4
Libraries	11.5
Lounge	7.9
Main Entry Lobbies	9.7
Office Spaces	12
Reception Areas	5.9
Restaurants	11.6

. Lighting operation schedules aligned with occupancy schedules, operating during institutional working hours with shutdown during unoccupied periods.

4.4. Model Validation

Model validation, comparing simulated and actual energy consumption (Figure 3), yielded NMBE and CVRMSE values of 6% and 3%, respectively, confirming model reliability [86]. Sensitivity analysis of the validated model indicated that the building envelope contributed to approximately 50% of heat gain, while the HVAC system consumed around 45% of total energy, aligning with energy use in similar climates [63,64,91].

4.5. Sensitivity Analysis

To identify key factors influencing building energy consumption, this study employed sensitivity analysis as shown in Figure 4.

The outcomes align with previous research in hot zones, indicating HVAC systems as the primary energy consumer, accounting for approximately half of total building energy use. Furthermore, building envelopes contribute significantly to heat gain, comprising nearly 50% of the building’s thermal load. Focusing on hot climate zones, this study evaluates the impact of building envelope materials on energy performance. To optimize energy consumption further, the study explores improvements in HVAC systems and the integration of renewable energy sources alongside building envelope enhancements.

5. Results

Building upon previous research, this study evaluates the performance implications of integrating various building envelope and HVAC components within a comprehensive modeling framework. Specifically, the analysis examines insulation, reflective paints, glazing-integrated photovoltaics (GIPV), and rooftop photovoltaic (RTPV) installations. Additionally, it incorporates a Dedicated Outdoor Air System (DOAS) configured to supply 100% treated outdoor air for latent loads, while terminal units manage sensible loads. This system utilizes demand-based ventilation, and humidity control (targeting 40–60% RH) to align with health-oriented standards. Through an enviro-economic assessment, the model quantifies reductions in energy consumption and carbon emissions while simultaneously evaluating improvements in indoor environmental quality, thermal comfort, and economic feasibility

5.1. Building Performance and Carbon Emissions

This section presents a comparative analysis of building performance under various retrofit scenarios across the three selected cities. Simulation results and operational CO₂ emissions, estimated according to Environmental Protection Agency (EPA) [92], are presented and discussed. The data presented in

Table 4. Building performance and carbon emissions.

	Aswan (1B)		Cairo (2B)		Alexandria (2A)
Model	Energy Use (GWh)	Tons CO2	Energy Use (GWh)	Tons CO2	Energy Use (GWh)	Tons CO2
Baseline	1.311	918	1.178	824	1.091	763
B.L + GIPV	1.117	782	1.057	740	0.989	692
Ins + GIPV	0.974	682	0.975	682	0.936	655
R.P + GIPV	0.903	632	0.828	580	0.795	557
R.P + GIPV + DOAS	0.766	537	0.708	496	0.682	477
Proposed Energy Model	0.563	430	0.546	410	0.538	462

outlines the energy consumption and carbon emissions for three locations under varying modelling scenarios.

The results show that the energy needs and environmental impact differ significantly between Aswan (Zone 1B), Cairo (Zone 2B), and Alexandria (Zone 2A). The proposed energy model consistently yields substantial reductions in both energy use and carbon emissions across all locations. Aswan, characterized by its warmer climate, demonstrates the most dramatic improvements, with energy consumption and carbon emissions falling by 57% and 53% approximately. Cairo and Alexandria also ex-perience notable decreases, with energy savings of 54% and 51%, accompanied by carbon reductions of 50% and 40% approximately.

Figure 5 below visually represents the building and HVAC energy consumption and associated CO₂ emissions for each location under the different modelling scenarios. These visual representations provide a clearer understanding of the performance disparities between the different models and the impact of geographical location on energy demand and environmental impact.

5.2. Thermal Comfort Evaluation

Thermal comfort is a critical yet challenging objective for facility managers [23]. By enhancing thermal comfort, it is possible to reduce complaints, operational costs, and energy consumption.

Several indices are now available to correlate indoor microclimatic conditions with users’ thermal perceptions [93,94]. Most of these indices are stationary models based on the thermodynamic equilibrium between the environment and the human body. However, emerging models also incorporate psychological and cultural factors [95,96]. Considering these factors, indoor thermal comfort can be quantified using two methodologies: quantitative and adaptive. Quantitative methodologies assess the heat balance between the body and the environment, accounting for physiological responses to climatic stimuli. These models are well-suited for mechanically conditioned buildings, where user interaction is limited. Adaptive methodologies, on the other hand, include psychological factors and environmental perception. They determine a neutral temperature and are suitable for naturally ventilated buildings with higher levels of user interaction. This study employs two quantitative indices to evaluate the impact of building retrofits on thermal comfort in a mechanically conditioned building.

5.2.1. Predicted Mean Vote (PMV)

While subjective, standards such as ISO 7730 and ASHRAE 55 provide guidelines for optimal indoor conditions [93,94]. The Predicted Mean Vote (PMV) index is widely recognized as a metric for quantifying thermal sensation. It evaluates human thermal comfort on a seven-point scale, ranging from −3 (cold) to +3 (hot). Figure 6 provides a visual representation of PMV values for the various retrofit scenarios examined in this study.

The comparison of Fanger PMV values between the baseline model and the proposed energy-efficient strategies reveals significant improvements in thermal comfort across all three locations (Aswan, Cairo, and Alexandria). In Aswan, the baseline model demonstrates high PMV levels, especially during the peak summer months, indicating substantial thermal discomfort. The retrofits yield noticeable reductions, with the proposed model achieving near-optimal comfort throughout the year. Similarly, in Cairo, a hot–arid climate, the baseline model presents moderate discomfort, which is mitigated effectively through the combination of retrofits, particularly during the transitional seasons. Alexandria’s hot–humid climate presents distinct challenges with baseline PMV values indicating discomfort during both summer and winter. However, the application of advanced energy measures, particularly the inclusion of DOAS, results in substantial improvements, aligning PMV values closer to thermal neutrality. The results highlight the effectiveness of integrating multiple energy strategies in enhancing occupant comfort.

To simplify the evaluation of indoor thermal conditions, DCH were evaluated based on ASHRAE thermal comfort standards. The DCH index quantifies the number of hours when indoor temperature and humidity levels exceed acceptable ranges, providing a clear and easily understandable indicator for non-experts.

5.2.2. Discomfort Hours (DCH)

To complement the PMV assessment, the study also conducted a discomfort hours (DCH) analysis, which evaluates whether indoor temperature and humidity levels fall within the ASHRAE thermal comfort range.

Table 5. Discomfort hours (DCH) for different retrofits.

	Aswan (1B)	Cairo (2B)	Alexandria (2A)
Model	DCH	DCH	DCH
Baseline	304	276	284
B.L + GIPV	304	276	284
Ins + GIPV	229	228	233
R.P + GIPV	242	247	256
R.P + GIPV + DOAS	173	159	154
Proposed Energy Model	173	159	154

shows the DCH associated with different simulated retrofits for the three locations.

Baseline models, exhibiting the DCH values presented in Table 5 for Aswan, Cairo, and Alexandria, served as benchmarks. While GIPV alone did not reduce discomfort hours in any location, combining insulation with GIPV yielded significant improvements. This combination lowered DCH by 24.7% in Aswan, 17.4% in Cairo, and 18.0% in Alexandria.

R.P. paired with GIPV had a lesser impact, reducing DCH by 20.4% in Aswan, 10.5% in Cairo, and 9.9% in Alexandria. The introduction of a DOAS alongside R.P. and GIPV further enhanced comfort, cutting discomfort hours by 43.1% in Aswan, 42.4% in Cairo, and 45.8% in Alexandria.

A proposed energy model that incorporated rooftop photovoltaics mirrored these reductions, confirming the effectiveness of the comprehensive retrofit strategy in improving indoor comfort. These findings highlight the importance of tailoring energy efficiency measures to specific climatic conditions.

5.3. Techno-Economic Evaluation

A techno-economic analysis was conducted to evaluate the financial feasibility of the proposed retrofits [97,98]. Key metrics included the internal rate of return (IRR), return on investment (ROI), and payback period (PBP). The results are summarized in

Table 6. Key performance indicators (KPIs) for building modifications.

	Aswan			Cairo			Alexandria
Model	IRR %	ROI %	PBP (Years)	IRR %	ROI %	PBP (Years)	IRR %	ROI %	PBP (Years)
B.L + GIPV	10%	10%	6.1	0%	6%	9.8	–3%	5%	11.6
Ins + GIPV	20%	15%	4.1	8%	9%	6.8	2%	7%	8.9
R.P + GIPV	26%	18%	3.3	22%	16%	3.9	17%	13%	4.6
R.P + GIPV + DOAS	18%	14%	4.5	7%	9%	7.1	0%	6%	10.0
Proposed Energy Model	21%	15%	3.9	10%	10%	6.2	0%	6%	10.3

. The initial capital investment was disaggregated to enhance transparency. The GIPV investment includes glazing replacement, integrated photovoltaic modules, inverters, and installation works. The DOAS investment accounts for dedicated air handling units, energy recovery components, ductwork modifications, and advanced control systems. It should be emphasized that all reported costs represent incremental retrofit investments relative to the baseline configuration and not full construction costs.

To facilitate future techno-economic replication studies, unit cost indicators are provided. The estimated DOAS installation cost corresponds approximately to

• 12 USD/m² of floor area in the very hot–arid climate (Aswan);
• 22 USD/m² of floor area in the hot–arid climate (Cairo);
• 30 USD/m² of floor area in the hot–humid climate (Alexandria).

The higher cost observed in humid climates reflects increased system sizing due to the higher dehumidification capacity required, addressing the elevated latent loads.

Similarly, the GIPV installation cost was estimated at approximately 110 USD per square meter of glazing area, including integrated photovoltaic glazing modules, inverters, and facade integration works. The unit cost values are reported as practical guidance to assist future researchers and practitioners in estimating retrofit investments for comparable building typologies and climatic conditions.

For Aswan, the results indicate that combining reflective paints and glazing-integrated photovoltaics (R.P + GIPV) yields the highest IRR, 26%, and the shortest PBP, 3.3 years, making it the most cost-effective solution. However, the proposed energy model, which integrates R.P, GIPV, DOAS, and rooftop PV, offers a well-balanced approach with a respectable IRR of 21% and an optimized PBP of 3.9 years. This model is particularly advantageous for addressing both energy efficiency and the need for pandemic-resilient buildings, despite the slightly reduced financial returns due to the investment cost of the DOAS.

In Cairo’s hot arid climate, the R.P + GIPV model again outperforms other configurations, with a notable IRR of 22% and a PBP of 3.9 years. While the inclusion of DOAS in the R.P + GIPV + DOAS model enhances building resilience, the economic performance declines, as reflected by a lower IRR of 7% and an extended PBP of 7.1 years. The proposed energy model strikes a reasonable compromise, with an IRR of 10% and a balanced PBP of 6.2 years, making it a viable choice when pandemic-proofing and energy performance are both priorities.

In Alexandria’s hot–humid climate (Zone 2A), the economic feasibility of integrated HVAC strategies is significantly influenced by high latent cooling loads and dehumidification requirements. The DOAS system, while improving thermal comfort and reducing DCH, imposes substantial capital costs due to increased ventilation air treatment and moisture removal demands. Unlike hot–dry climates, where sensible cooling dominates, humid climates require continuous latent load management, leading to higher equipment sizing, greater electrical consumption for dehumidification, and elevated installation costs. Consequently, although the proposed integrated model achieves improved comfort and carbon reduction, its IRR approaches 0% and the payback period extends beyond 10 years. This outcome highlights a critical climate-specific insight: in humid regions, envelope-focused strategies (R.P + GIPV) offer superior financial performance, while advanced ventilation systems should be justified primarily by health resilience and indoor environmental quality rather than short-term economic return. Therefore, policy incentives or carbon pricing mechanisms may be required to enhance the financial attractiveness of comprehensive NZEB strategies in humid climates.

6. Conclusions

In response to the growing decarbonization imperative in the building sector, this study developed and validated a climate-sensitive, multi-criteria framework to evaluate Nearly Zero-Energy Building (NZEB) retrofit strategies across representative hot-climate subzones. By integrating dynamic energy simulation, environmental impact assessment, techno-economic analysis, and structured decision-making, the research addressed a key gap in the literature: the absence of comparative and holistic evaluation of integrated retrofit packages in distinct hot climates. Specifically, it demonstrated how climate-adapted retrofit solutions can be systematically ranked using unified performance criteria.

The results show that optimized retrofit combinations substantially outperform isolated measures. Enhanced insulation, glazing-integrated photovoltaics (GIPV), and high-efficiency HVAC systems achieved significant reductions in operational energy demand and CO₂ emissions while improving thermal comfort and maintaining economic feasibility. Retrofit effectiveness was strongly climate-dependent, reinforcing the necessity of region-specific NZEB pathways.

The proposed framework provides a scalable decision-support tool for accelerating economically viable decarbonization in hot-climate buildings. Future research should integrate embodied carbon assessment, grid interaction dynamics, post-occupancy validation, and advanced control strategies, including reinforcement learning-based HVAC optimization implemented within building simulation and co-simulation platforms (e.g., BuildingGym), to further enhance adaptive and predictive energy management in hot climates.