Enhancing energy efficiency in tiny houses: The role of sustainable thermal insulation materials in Faiyum, Egypt

Research problem

Egypt’s housing crisis is a complicated issue that has constantly been a concern for the nation.⁶ Rapid rise in population, urbanisation, deficient infrastructure, and restricted availability of low-cost housing constitutes some of the primary causes of this challenge, which has increased the demand for the launch of tiny houses as an alternative sustainable economic solution.⁷ Furthermore, the daily living and general well-being of Egypt’s citizens are significantly impacted by the lack of thermal comfort. Egypt features extreme temperatures, through which maintaining optimal adequate indoor environment proves challenging under these climatic conditions, especially in the residential housing sector.^8,9

Research aim

With the aim to improve energy efficiency, minimise heat loss or gain, elevate comfort levels, decrease energy usage and expenses, and contribute to a more sustainable lifestyle, this study aims to provide guidance to Egyptian architects and design firms in order to cautiously select the proper materials to be used as insulation for housing. A thorough analysis of tiny housing design approaches and sustainability-related features were carried out in order to strengthen the connection and fill the gap in the requirements for design between architecture and thermal comfort in residential housing. In order to accomplish the aim of the study, a detailed simulation will be performed, evaluating four insulation materials in order to test their effect on indoor thermal comfort.

Literature review

A comprehensive literature analysis will explore the concept of tiny housing, outlining essential design principles and sustainable parameters for tiny house construction. It will examine energy-efficient insulating materials commonly used in Egypt by analyzing previous academic studies to enhance thermal comfort and well-being for residents. The study will specifically test these materials on a 40-square-meter tiny house in Faiyum, Egypt, focusing on the walls and roof, which are most affected by solar heat radiation. The goal is to minimize reliance on air conditioning and reduce overall energy consumption.

Case study

The second part of the study examines a case study involving a proposed 40-square-meter tiny house in Faiyum, Egypt. It simulates the effects of four energy-efficient insulating materials applied solely to the walls and roof. This simulation is conducted using Design Builder software version 7.0.2.006, along with the Energy Plus 9.4 plugin. The research evaluates both the base case and four scenarios utilizing a passive design approach, which includes:

Definition of a tiny house

There is not one, universally recognized definition of a tiny house, however, in broad terms, a tiny house is referred to as a small, effective dwelling that is commonly within the range of 400 square feet, below or above accordingly, allowing its residents to live more sustainably, comfortably, and easily.⁵ As housing, tiny houses are not standard and are difficult to categorize. Shearer and Burton classified them into categories based on four sociological variables (affordability, environmental sustainability, legality, and communal purpose) as well as three structural elements (mobility, size, and design). The term “tiny house” is used to refer to a variety of housing, including those that are fixed, or those who are partially movable (on a temporary foundation).¹⁰ To allow people to maintain simpler lifestyles without as many financial responsibilities, Vail considers tiny houses as an aspect of a movement that seeks to reduce the space occupied. Within context of middle-class housing goals, tiny houses are additionally thought of and potentially presented as a more desirable alternative to conventional forms including caravan parks.¹¹ Small-scale, sustainable living, both are being utilized as an alternate to traditional housing in a growing movement named “tiny house living”. Tiny houses are smaller in size than the typical independent house but still maintain the exact same aesthetic and character as a standard standalone house.¹²

Design principles and parameters while designing a tiny house

The method of designing a tiny house can be challenging since each space must be used effectively. According to Susanka, it’s vital to pay attention to the minor details that can enhance its aesthetic appeal and resident satisfaction while creating a tiny house. Along developing a tiny house, a few principles tend to be kept in mind, including¹³:

For an effective planning layout, additional aspects of tiny housing must be taken into perspective, including the housing area, materials for construction, stairs (assuming that a vertical space has been employed), space organization, smart furniture, colours and lightings, and privacy.¹⁴ Since Arch Daily is the most widely used and reputable website dedicated to architecture, emerging architectural knowledge and inspiration globally, an article published by Yiling Shen entitled “6 Tips for Designing and Building a Tiny House” aims to address the importance to consider the following¹⁵:

Most well-known energy efficient thermal insulation materials in egypt

By limiting heat absorption or transmission through the building envelope, thermal insulation is a good strategy to lower down on the use of energy. Thermal insulation materials are usually applied to insulate the walls, roofing and flooring of a structure, which will improve thermal comfort while preserving the energy generated within.

Since this research is to construct a sustainable, energy-efficient tiny housing design in Egypt, four thermal insulative materials has been selected mainly focusing on the most frequently employed materials in Egypt according to the Egyptian Building Code, Egyptian Environmental Affairs Agency, and reviewing various academic research papers, leading to a conclusion to the choice of materials that has been summarized below in Table 1 including:

These materials could be listed all together and summed up as outlined in Table 1, respectively with their thermal properties to be used further during the simulation process, identifying which one is mostly capable of providing an optimum thermal comfort.

Bioclimatic chart analysis and thermal comfort

The psychrometric chart provides details about the properties of humidity in the air at a particular level of pressure and temperature. A comfort zone is defined in the diagram itself as the characteristics of the air that the majority of people clothed in a certain manner and performing moderate job duties would consider to be comfortable. In the field of architecture, people are starting to forget the value the psychrometric chart, hence it is essential that architecture students and designers understand how useful to understand the environmental conditioning of structures and how significant the chart is in assisting them in discovering the possibility for regulating their facilities.¹⁶

The technique used in Figure 1 involves first analysing the psychrometric chart in order to determine the ideal design approach that’s best for Faiyum’s environment in Egypt. Climate Consultant is a software that has been used for such purpose, including passive design methods and proportions, which provide readers a sense of whether a structure is within the comfort level or not to inhabit depending on its geographical location. Figure 1 shows 16 strategies, if applied to any building design in Faiyum, Egypt, it would reach to a 100% comfort level.

Figure 1. Bioclimatic chart for Faiyum, Egypt, Generated by Climate Consultant Software [By the researchers].

In order to apply only the necessary passive design strategies, Figure 2 below shows the necessary strategies that are highlighted in yellow to achieve optimum passive design. It’s quite notable that the percentage of the year spent in the comfort range failed to exceed 21.6%. The overall number of thermal hours must be raised by roughly 27.8% through maximising the benefits of internal heat gains, mainly during wintertime. More specifically during the summertime, shade from windows might offer an improvement of roughly 21%. Natural ventilation generated 6.1% of the cooling process, and high thermal mass night flushing produced 11.8%.

Figure 2. Bioclimatic chart for Faiyum generated using the Climate Consultant tool using recommended passive design strategies.

Green represents ‘comfortable’ hours by 70%. Red represents ‘not comfortable’ hours by 30% [By the researchers].

Since this study aims to only test the effect of thermal insulation materials in walls in addition to a natural passive design strategy, the Natural Ventilation Cooling percentage 6.1% and the Internal Heat Gain 27.8% will increase the comfort level by approximate a total of 34%, which gives the designer an initial thought about how effective each strategy can affect the comfort level.

However, the previous findings only offered general recommendations for design improvement, given that it was based only on the analysis of the climatic data and did not take into consideration the specificities of any design case. As a consequence, the analysis to come will additionally specify the design variables for the example given. Design Builder v.6.1.0.006 had been the software programme employed as demonstrated in Figure 3, which is a widely used programme for assessing human thermal well-being and energy consumption in buildings. Energy Plus, a whole-building simulation engine created by the US Department of Energy, is used by it for building energy calculations.¹⁷

Figure 3. Three-dimensional model of a tiny house in Fayium, Egypt, constructed with Design Builder v.6.1.0.006 [By the researchers].

Description of the tiny house model

The residential tiny house model designed for this study is a 40 square meters single-storey house (4mx10m), located in Faiyum, Egypt, due to its traditional houses, peaceful, natural surroundings, clean air, and serene envision of the blue lake facing the huge mountains on the other side, through which this location was magnificently chosen. The decision to build a tiny house often stems from personal experiences and a desire for a simpler lifestyle. For many, including those returning from abroad, such as individuals who have lived in crowded cities, a tiny house represents an opportunity to embrace tranquillity and simplicity. The emotional benefits of living in a peaceful environment can significantly enhance overall well-being. Designing a tiny house in Faiyum, Egypt, can be justified by several economic and financial factors that align with the current housing market trends and the specific context of the region as seen in Table 2 below:

It is of a simple proposed primitive design, with one window placed each on the longest two facades to allow for cross ventilation and increase the natural light into the space. The setup was entirely designed to allow for natural ventilation considering the research focused on passive design approaches; neither active heating, cooling, mechanical cooling, or ventilation control were allowed to operate considering not everyone with a tiny house can afford purchasing air conditioning. By using the climatic data together with the latitude and longitude data of the city of Faiyum, and by further examining the variations in indoor temperature values of the tiny house in the Design Builder program, issues such as: the best orientation (presented in Figure 4), building materials (displayed in Table 4) and comfort data simulations, were analysed to help testing the indoor thermal comfort. Table 3 below displays a summary of the project file settings that were loaded into the software including heating, ventilation and air conditioning (HVAC), environment, and activity settings.

Figure 4. Best Orientation through the Weather Data Software [By the researchers].

According to Givoni (1991), variations in the inside temperature related to orientation can be considered minimal if walls and the building envelope are appropriately insulated at the exterior and windows are properly screened. The outcomes of this investigation, however, showed that there is an immediate and significant connection between the building’s orientation and the amount of energy consumed to maintain a pleasant internal temperature. Therefore, the ideal orientation for this tiny housing model to be constructed in Faiyum, Egypt, was determined before further analysis on thermal comfort data.

The optimum orientation for the tiny housing model located in Faiyum, Egypt, is 172.5° North and 7.5° South, according to the calculations based on the longitude and latitude coordinates of Faiyum region. The ideal orientation for the model is shown in Figure 4. Based on this finding, this approach seeks to maximise the opportunity for solar absorption by orienting the building’s longest side towards the sun.

By building the section of the envelope constructed with traditional materials without initially including insulation, the thermal model in the research study was assumed. Following that, the walls and roof are going to have the insulation materials from Table 1 gradually added one at a time to compare the values of discomfort hours, PPD%, assessing the impact of these materials on lowering energy consumption, thereby lowering energy bills and saving money, by narrowing down to the material that has been noticed offering the most notable thermal comfort. Without the addition of any insulation, the following project construction materials assigned in Design Builder as a base case model is represented below as shown in Table 4, as well as the base case Discomfort Hours chart displayed in Figure 8.

Figure 5. Wall Section – Base Case [By the researchers].

Figure 6. Wall Section – Scenario 1 on the left, Scenario 2 on the right [By the researchers].

Figure 7. Wall Section – Scenario 3 on the left, Scenario 4 on the right [By the researchers].

Figure 8. Comfort Graph Extracted from Design Builder Simulation showing 2715 discomfort hours – Base Case Scenario [By the researchers].

The chart of discomfort hours corresponding to the four scenarios in Table 5 applied to the base case can be seen in Figures 9, 10, 11, and 12.

Figure 9. Comfort Graph Extracted from Design Builder Simulation showing 2205 discomfort hours – Scenario 1 applying Fibreglass Insulation – Thickness 300 mm [By the researchers].

Figure 10. Comfort Graph Extracted from Design Builder Simulation showing 2273 discomfort hours – Scenario 2 applying Rockwool Insulation – Thickness 200 mm [By the researchers].

Figure 11. Comfort Graph Extracted from Design Builder Simulation showing 2146.5 discomfort hours – Scenario 3 applying Cellulose Insulation – Thickness 250 mm [By the researchers].

Figure 12. Comfort Graph Extracted from Design Builder Simulation showing 2269.5 discomfort hours – Scenario 4 applying EPS Expanded Polystyrene Insulation – Thickness 300 mm [By the researchers].

Case study simulation results

The simulation period was assigned for the overall year from 1 January to 31 December, within hourly output intervals. Four simulations were conducted, all of which modified scenarios for the same housing aimed at testing the four different insulation materials effect to the walls and roof. Table 5 summarizes the simulation scenarios, with Figures 5, 6, and 7 showing the wall construction cross section.

Discomfort hours refer to the total number of hours in which an individual experiences discomfort, this could be converted into percentage annually, to calculate how much percentage during the year individuals experience discomfort. There are 24 hours in a day and 365 days in a non-leap year. Therefore, the total number of hours in a year is calculated as:

Hence, calculating the percentage of discomfort hours in a year:

According to the discomfort hours method, the base case scenario has showed 27.15 discomfort hours, which represents approximately 30.96% of the total hours in a year feeling dissatisfied. Scenario 1 using Fibre Glass insulation has shown 2205 discomfort hours, which means that 25.13% of the total hours feeling discomfort. Scenario 2 using Rock Wool insulation displayed 2273 discomfort hours, which clarifies that 25.91% of the total hours’ individuals don’t feel comfort. Scenario 3 using Cellulose insulation has shown 2146 discomfort hours, meaning 24.49% of the total hours feeling discomfort. Lastly, Scenario 4 using EPS Expanded Polystyrene insulation showed 2269.5 discomfort hours, which means 25.88% of the total hours feeling discomfort. These calculations show the percentage of discomfort for each insulation scenario based on the discomfort hours provided, highlighting that cellulose insulation has the lowest percentage of discomfort among the scenarios tested.

Discomfort hours is considered a good method for evaluating thermal comfort in indoor environments. The discomfort hours method takes into account the duration of time that occupants experience discomfort, and is based on the concept that thermal comfort is not solely determined by instantaneous conditions but also by the cumulative effect of prolonged exposure to uncomfortable conditions. It considers both the magnitude and duration of discomfort, providing a more comprehensive assessment of thermal comfort. By considering the duration and intensity of discomfort, it provides a more accurate representation of occupants’ experiences over time.

Figure 13 below presents a comparison chart illustrating the discomfort percentages across four scenarios in relation to the base case, demonstrating that cellulose is the most effective insulating material.

Figure 13. Comparison Chart of Discomfort Percentages Across Four Scenarios Compared to the Base Case [By the researchers].

The percentage of reduction in discomfort hours for each insulation scenario compared to the base case can be calculated using the following formula:

Hence, Table 6 and Figure 14 below demonstrates the percentage reduction in discomfort hours for each insulation scenario compared to the base case, highlighting that cellulose insulation offers the highest reduction in discomfort among the options tested.

Figure 14. Percentage Reduction in Discomfort Hours for Four Insulation Scenarios [By the researchers].

The Fanger PPD% has also been analysed for all four scenarios, demonstrating that cellulose insulation exhibits significant improvement, as shown in Table 7 below. The percentage of reduction related to the PPD% compared to the base case scenario has been calculated using the formula below:

Ethics consent

No human participation was involved in this study.