**1. Introduction**

Over the years, human comfort has been a key priority in the process of designing spaces. Before mechanical solutions were available, attempts to achieve this goal were naturally passive. Today, however, even with advancements in mechanical solutions, passive methods remain in favor due to the increasing need for sustainable solutions because of current global environmental concerns. Historically common passive solutions include shading devices, ventilation techniques, and passive cooling and heating techniques. One of the most prevalent cooling and ventilation techniques is the wind tower, also known as a windcatcher. Wind towers are also known as *malqafs* in Egypt, one of the very first countries to implement this feature. Wind towers have become increasingly interesting for researchers due to their potential to create passive cooling and reach target human comfort levels indoors. Wind towers have been in use since the Ancient Egyptian era, primarily used in buildings to facilitate ventilation and indoor cooling. Additionally, windcatchers were used widely during the Egyptian Medieval era and were known as a *malqaf*, literally meaning "catcher".

However, there is a gap in the literature that studied windcatchers in Egypt throughout its history. Most researchers who studied windcatchers in Egypt focused on the medieval

**Citation:** Nessim, M.A.; Elshabshiri, A.; Bassily, V.; Soliman, N.; Tarabieh, K.; Goubran, S. The Rise and Evolution of Wind Tower Designs in Egypt and the Middle East. *Sustainability* **2023**, *15*, 10881. https://doi.org/10.3390/ su151410881

Academic Editors: Lucia Della Spina, Maria Rosa Valluzzi, Antonia Russo, Paola Pellegrini and Angela Viglianisi

Received: 30 April 2023 Revised: 3 June 2023 Accepted: 20 June 2023 Published: 11 July 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

era, especially the Islamic, but none, to our knowledge, thoroughly studied all eras starting from Pharaonic to the modern era going through Coptic and Islamic. In addition, the same gap appeared with research studying windcatchers in the Middle East; it either focused on ancient or modern, but no studies, to our knowledge, went through all eras together. Another new aspect of this current research is analyzing the reason behind the windcatcher form and design, how it differed between regions, and why. Thus, the three primary eras including ancient, medieval, and modern are studied in this research to extract, analyze, and compare windcatchers from different historical periods in Egypt and other Middle Eastern regions. This will contribute to advancing the knowledge of vernacular wind tower designs and bring awareness to their potential as a passive design solution that contributes to sustainability and reduces energy consumption, especially in Egypt. This study offers a timeline for advancing these passive cooling systems, showing how they were incorporated into architecture over centuries. It presents and investigates case studies found in the three eras, explains their main aspects and design differences, including their shapes, number of sides, and orientation, and correlates them to climatic and architectural conditions. This research mainly utilizes the literature and archives to investigate the cases mentioned. Wind roses of each region investigated are then further studied to determine wind towers' correspondence to the prevailing wind directions and the ventilation needs of the connected spaces. The findings also call into question several contemporary windcatcher incorporations that borrow their design from local precedents in terms of efficiency and suitability.

The main purpose of a wind tower is to direct wind toward the desired indoor areas of a building and cool the directed air in the process [1]. Nejat et al. [2] explain, in their research on two-sided wind towers, that wind towers operate on two main forces: wind and buoyancy. The wind force is derived from the difference in wind pressure indoors and outdoors. This feeds into the ventilation function of the wind tower. Buoyancy can be generally understood as the force that pushes objects upward when placed in a fluid [3]. Because hotter air has a lower density than cooler air, it tends to 'float' or rise above the cooler air [4]. Therefore, the force of buoyancy feeds into the cooling function of wind towers [2]. This is because, in buoyancy-driven air shafts, the exhaust vents are placed on the top and connected to a chimney leading them outward, while the inlets are placed lower to allow the cool, dense air to be vented into the space [4]. When the correct number of inlets is provided (such as in multiple-sided wind towers), more wind can be driven into the wind tower to be processed in this way. The number of sides and inlets depends on the prevailing wind directions and wind speed. These operation processes are illustrated in Figure 1.

In short, buoyancy is a force that acts mainly on density [3,4]. This paper's Section 5 will discuss both in more detail.

To provide sufficient ventilation, wind towers are usually built to be tall structures erected on building rooftops [5], enabling them to catch the fast-traveling wind [5] away from the building level below, where the surrounding buildings may obstruct wind movement and slow it down. Moreover, wind towers are directed toward the prevailing wind direction or the direction from which the most significant wind movement occurs [6]. This ensures the highest movement of wind possible, especially on hot summer days when wind movement is typically low. Figure 2 shows a typical Egyptian *Malqaf*.

**Figure 1.** A section showing how windcatchers work (modified by the authors; adapted from [7]).

**Figure 2.** The main components of wind towers (modified by the authors; adapted from [8]).

Before the industrial revolution, people living in hot, dry zones deferred to natural cooling methods. Using easily obtainable materials, inhabitants of the Middle East tried alternative methods to ventilate their homes. Windcatchers were widespread in the Middle East, with significant variance in their construction and design. Despite the various structures, they all served the same purpose: to channel favorable prevailing winds into residential areas [9]. Table 1 below shows how different traditional wind tower designs started to appear in different regions [10].

**Table 1.** Traditional wind tower designs and information (modified by authors; adapted from [10]).


In Section 2, this paper starts by reviewing case studies from Egypt showing examples of wind towers from the Pharaonic, Medieval, and Modern eras. In Section 3, this paper presents case studies from the Middle East, which studied historical and modern towers. In Section 4, this paper compares and contrasts the case studies and examines their characteristics vis-à-vis wind rose of the different locations in which they appear. This analysis reveals that the attributes (e.g., number of sides, height, roof shapes, etc.) of historical wind towers have been highly influenced by the weather and wind characteristics of the location, with the modern towers deviating from this trend. This paper then ends with a discussion and conclusions highlighting the key findings, the main limitations of this study, and the areas requiring further investigation and research.

#### **2. Case Studies from Egypt (Ancient and Modern)**
