Egypt is confronted with severe housing shortages as a result of rapid population growth, low wages and rising living expenses. The situation is made more difficult by frequent power outages caused by excessive energy consumption. In order to improve energy efficiency in construction, phase change materials (PCM) will be investigated as a wall insulating solution in conjunction with passive design techniques. Additionally, the idea of micro-apartments, which are 40 square meters on average, provides a small-scale and financially feasible housing option though its success in other nations has largely prevented it from being explored in Egypt, this is due to the devaluation of the Egyptian pound currency that has significantly impacted everyday citizens, particularly those in the middle and lower classes, hence, leading to increased prices for essential goods and services where many families are struggling financially, as wage growth has not kept pace with rising costs.

The research aims to investigate two energy-efficient concepts that are not widely commonly used in Egypt: phase change materials (PCM) and micro-apartments. It aims to examine the thermal comfort using the application of RT24HC PCM in walls in the residential sector with the addition of passive design strategies. This promotes innovative housing solutions in Egypt, specifically Alexandria, by increasing awareness among researchers and designers.

The literature review will cover various key topics such as definitions of affordable housing, micro-apartments and phase change materials. It will also address the essential functional needs of micro-apartments and discuss the current state of affordable housing in Egypt, focusing on affordability issues. Following this, the literature will define passive design particularly emphasizing thermal insulation related to Phase Change Materials (PCMs). An overview of PCMs will include the impact of PCMs on building construction with the focus on residential walls and will then finally explore the application of PCMs in Egypt and the specific factors influencing PCM selection in the country.

The second part of the research focuses on a case study of a proposed 40 square meter micro-apartment in Alexandria, Egypt. It simulates the impact of the RT24HC Phase Change Material (PCM) on thermal comfort metrics, Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfaction (PPD%), using Design Builder software. The study tests the base case as well as four scenarios involving PCM and selective passive cooling strategies for the apartment’s walls only which are: 1.

Base Case: A standard wall without insulation.

The research methodology assesses the effectiveness of Phase Change Materials (PCMs) and selective passive design strategies to enhance thermal comfort in micro-apartments in Egypt. Simulations using Design Builder software, version 7.0.2.006 with an Energy Plus 9.4 plugin, will evaluate the Predicted Mean Vote (PMV) and Percentage of People Dissatisfied (PPD%) for a 40 sqm micro-apartment case study in Alexandria, focusing on how these materials and strategies impact the thermal environment.

Micro-apartments are compact living spaces under standard sanitary regulations, typically ranging from 280 to 450 square feet, designed for efficiency and space conservation. ^{6, 7} They generally measure 15-30 m ², accommodating one or two occupants with essential amenities. ⁸ The growing interest in micro-apartments reflects the need for affordable housing solutions in urban areas. ⁹

Features of micro-apartments

Living alone in cities is increasingly common, with one-third of urban residents choosing micro-apartments for one or two occupants. These units prioritize sustainable living through multifunctional furniture and thoughtful design, including high ceilings and large windows to enhance space perception. ^{6, 7} Vertical space is optimized with convertible furniture and storage solutions. ¹⁰ Careful design elements improve comfort while addressing social interaction challenges. ⁸ Micro-apartments, classified as compact living spaces by the British Property Federation, must include essential elements for functionality, as shown in Figure 1. These units are designed for one or two occupants and emphasize efficient use of space through thoughtful design. ¹¹

Egypt’s affordable housing crisis arises from limited access for low-income individuals, high price-to-income ratios, and a mismatch between supply and demand, complicating adequate housing provision. ^{12– 14} Contributing factors include: 1.

Rapid population growth

Table 2 illustrates key affordability issues in Egypt, hence, discussing the research problem to the urge need of implementing micro-apartments. ¹⁵

The potential of phase change materials (PCMs) and thermal energy storage to lower global energy demands is drawing attention. ¹⁸ During phase transitions, PCMs absorb and release thermal energy stabilizing temperatures, enhancing efficiency with passive techniques like natural ventilation. ¹⁹ They absorb heat when melting and release it upon solidification. ²⁰ Figure 2 illustrates this process. PCMs serve as effective latent heat storage materials due to their high heat of fusion, ²¹ whereas Figure 3 shows how PCMs are divided into three groups: eutectic, inorganic, and organic. ^{18, 22}

Impact of PCMs on building wall construction emphasizing on residential buildings

The optimal location for Phase Change Materials in building walls is illustrated in Figure 4, emphasizing their placement on the exterior and middle surfaces in hot climates to absorb external heat before it enters indoors. ²⁵ This arrangement enhances thermal performance and maximizes energy savings.

Application of PCMs in Egypt

Paraffin is the most common Phase Change Material in Mediterranean climates, used 87.5% of the time for its adaptability and high latent heat. ¹⁹ Egypt’s climate is classified as BWh (hot dry desert), indicating intense summer heat and minimal precipitation, hence, Table 3 highlights key factors for applying Phase Change Materials (PCMs) in Egyptian buildings, considering the country’s hot and dry climate:

Previous research on PCMs in Mediterranean cities reveals important guidelines for effectively using PCM and passive strategies in housing design, as shown in Table 4.

This study examines Alexandria’s bioclimatic chart using Climate Consultant v.6.0, generating a psychrometric graph from meteorological data. This graph highlights potential bioclimatic design strategies to improve indoor thermal comfort, as illustrated in Figure 5, showcasing effective passive design methods.

Figure 5, analysed by the researchers, shows that only 20.8% of the year was within Alexandria’s climate comfort zone. The following passive design techniques were assessed in an effort to increase thermal comfort using Climate Consultant v.6.0 software by the researchers: •

Applying internal heat gains might result in a 36.8% increase in pleasant hours, notably in the winter.

However, these conclusions were confined to general recommendations based on climate data analysis. The building case study’s particular design parameters will be further investigated in order to determine the best solutions.

Positioned within latitudes 22°N and 32°N and the longitudes 25°E and 35°E, lies Egypt, with a hot climate. The Housing and Building Research Centre identifies eight climatic regions. Alexandria experiences summer highs of 32°C to 34°C and a transitioning climate from hot desert to semi-arid, with high humidity around 70% due to the Mediterranean Sea. ^{31– 33}

The simulation focuses on a 40 square meter micro-apartment model, the largest size for this prototype space, located in a four-story residential building in Alexandria, Egypt. This unit, positioned directly below the roof, allows for testing under challenging conditions. Essential features include a bed, kitchen, and bathroom to ensure minimal spatial comfort. A basic model plan ³⁴ was taken as a reference to implement the proposed micro-apartment design layout. The design emphasizes flexibility to meet occupants’ specific requirements, highlighting the importance of adaptable layouts to enhance comfort and functionality in compact living spaces.

The micro-apartment floor plan in Figure 6 features four mirrored identical units per floor, each 40 square meters, including a kitchen, living room, bedroom, and bathroom with multipurpose furniture for efficient space use.

The 5m x 8m configuration is optimal for a 40 sqm micro-apartment due to: •

Better use of space: The square shape allows for flexible furniture placement and efficient use of the floor area compared to a long, narrow layout.

The 40 square meter micro-apartment model in Alexandria, Egypt, addresses energy efficiency and thermal comfort challenges posed by its hot, humid Mediterranean climate. Many local housing projects lack proper planning, making this simulation essential for improving residential energy performance.

The Egyptian Construction Law mandates a minimum internal ceiling height of 2.7 meters for the 40 square meter micro-apartment, hence, this research uses 3 meters. ³⁵ The micro-apartment proposed unit to be simulated is shown in Figure 7.

Design Builder 7.0.2.006 with an Energy Plus 9.4 plugin is the software used to simulate energy in this case study. It accurately models the building’s environmental conditions yearly, monthly, daily and hourly, including humidity, lighting, thermal balance, and energy consumption.

Activity

The activity of each space is specified accurately as well as the number of users, occupancy density, metabolic rate as shown in Table 5.

Construction

Construction data, including materials for walls, slabs, and roofs, is crucial for accurate simulation. The U-value and insulation levels significantly affect energy use, as they transfer heat. Table 6 displays the building materials used in the Design Builder program.

Openings

Heat gain and loss through windows significantly impact energy consumption, especially in warm climates where solar heat is a major contributor. Accurate simulation requires precise glazing and shading details, as illustrated in Table 7, particularly relevant for Alexandria, Egypt.

HVAC

Passive design techniques were prioritized due to restrictions on HVAC systems and mechanical ventilation, addressing affordability issues in Alexandria. This approach aims to reduce energy consumption and mitigate power outages. The HVAC settings used in the program are listed in Table 8 below.

The study utilizes RT-category phase change materials (PCMs), specifically RT24HC from Rubitherm, which has an adjustable melting temperature between -10°C and 90°C. ³⁶ This PCM is optimal for Egypt’s high temperatures, enabling effective thermal management and energy savings. ³⁷

The simulation ran from January 1 to December 31, testing four scenarios on PCM material and passive cooling strategies for the micro-apartment unit’s walls, summarized in Table 9. •

Base Case: A baseline by using a standard wall without any insulation layers.

The maximum PCM layer thickness in the simulation used is 30 mm, as greater thicknesses yield diminishing returns and potential drawbacks that were tested by the researchers while conducting the simulations, hence, this indicates that 30 mm PCM thickness is optimal for thermal performance and energy efficiency. Figures 8 to 11 illustrate wall section diagrams for the base case and the other scenarios, including window shading blinds and a local overhang with a 1-meter projection properties.

Table 10 shows variations in results compared to the base case across four scenarios, highlighting PPD% values on the hot scale with fluctuating trends.

A challenge with phase change materials (PCMs) in residential sectors is annual temperature variability, as most systems are optimized for summer or winter. This study analyses PMV and PPD% values during hot months to enhance summer comfort and reduce air conditioning demand. The PMV scalability variables are presented in Table 11. A PMV of -3 represents a cool feeling, while a PMV of 3 implies a hot sensation.

Figure 12 highlights variations from the base case scenario, emphasizing summer months to enhance thermal comfort and reduce dissatisfaction with phase change materials (PCMs). This strategy aims to lower air conditioning reliance and energy consumption, addressing recent power outages in Egypt, particularly Alexandria. Figures 13 to 17 display PMV and PPD Fanger charts from Design Builder for all scenarios.

The analysis of four scenarios for a micro-apartment provides valuable insights into enhancing thermal comfort. The base case without insulation has a Predicted Mean Vote (PMV) of 1.43 and a Percentage of People Dissatisfied (PPD) of 47.08%. Scenario 1, adding two layers of RT24HC phase change material (PCM), improves PMV to 1.39 and reduces PPD to 44.94%. Scenario 2, combining one layer of RT24HC PCM with traditional XPS insulation, achieves a PMV of 1.40 and PPD of 45.28%. Scenario 3 incorporates two layers of RT24HC PCM with high reflectivity slat blinds, yielding a PMV of 1.36 and reducing PPD to 43.42%. The most effective scenario, Scenario 4, combines two layers of RT24HC PCM with a one-meter horizontal overhang, resulting in a PMV of 1.30 and a PPD of 40.41%, marking a significant reduction in discomfort.

The findings highlight the importance of integrating PCM and shading strategies to improve indoor thermal comfort in hot regions like Egypt, with Scenario 4 being the most effective as shown in Table 12 and Figure 12.

This holistic approach enhances indoor comfort and energy efficiency by combining effective insulation and shading strategies, promoting occupant satisfaction and sustainability through a comprehensive passive cooling strategy that reduces energy consumption in residential spaces. The percentage of energy reduction for each scenario compared to the base case is shown in Table 12 and Figure 18 below. This indicates how much energy is reduced in each scenario compared to the base case, with Scenario 4 showing the highest reduction percentage at approximately 14.18%.

No human participation was involved in this study.