Keywords

1 Introduction

Water scarcity is the consequence of many interrelated factors. First, the changing of human habits is enhancing climate change, which provokes an alteration on water cycle, so the spread of desertification and unpredictable rain events. In addition, the shift to a more meat base diet is modifying land use, therefore local ecosystems. Furthermore, trade globalization and increasing industrial production contribute to an economic shift towards more resource-intensive consumption patterns. Moreover, during last centuries earth faced a great grown in global population. The presented factors reflect their footprint on global freshwater consumption and availability; water is becoming a scarce resource. In fact, freshwater for agricultural, industrial and domestic use has increased nearly six-fold since 1900 (Ritchie and Roser 2017). The global use of water is divided in three sectors that are Agriculture, Industry and Municipality. In this scenario of water demand increase and supply decrease, fog stands as an alternative source of water. Fog water has been documented to be an efficient source in many territories that are affected by fog phenomenon (Klemm et al. 2012). Fog harvesting projects are usually developed in rural areas for agricultural purpose; instead, fog collectors’ potentiality should be explored to integrate water supply also in industrial and domestic sector. The aim is identifying chances of improvement and possibility of generating a positive impact on urban water resource management. For the mentioned purpose, the device’s structure should be elaborated, to develop it for urban environment and integrate it in building design. At first, the fog harvesting project requirements should be analysed, and therefore, the design criteria should be individuated. Fog water by itself probably cannot fulfil the water demand, but it could release the stress upon conventional overexploited freshwater resources.

2 Water Scarcity

Even though water covers almost 3/4 of the earth's surface, the 97.4% is saline water, while the amount of freshwater available for human consumption corresponds just to 2.5% (Gleick 1993). Moreover, water is not equally present around the planet; this is due to natural climatic conditions, and to overexploitation for anthropic use (Pereira et al. 2009). However, it is not even equally distributed; in fact, in many cases the hydric issues are caused by bad water management. The main sources of freshwater are surface waters and underground basins. To use this water, it should be extracted and, after being treated, it requires a distribution system, which functioning depends on energy supply. Furthermore, the consumption is not uniform; water availability directly determines per capita consumption. In fact, although WSI index states about 100 m3 of water per capita a year (m3/c/year) as optimum standard of living (Falkenmark 1986), Greece's water withdrawal per capita in 2018 was 962 m3/c/year, while Israel's was 132.7 m3/c/year (OECD 2022). Moreover, the sources are often contaminated (Vörösmarty et al. 2005). Although water is considered a renewable resource, the consumption is not adequate. In addition to the current water constraint, the world population is predicted to grow; for this reason water demand is forecasted to rise by 55% according to UNESCO (United Nations World Water Assessment Programme Secretariat (WWAP) 2016).

3 Fog Harvesting

Fog is a meteorological phenomenon that consists of water droplets suspended in the air. From a physical point of view, when a saturated mass of air, reaches its dew point, fog is generated. Fog can be classified on its forming process; it can be by radiative heat loss, by the mixing of two parcels of saturated air initially at two different temperatures, and by an ascend and resultant cooling of an air parcel (Roach 1994). Many territories worldwide are affected by the fog phenomenon; many of them are in arid areas, while others in territories that will face the hydric crisis in the upcoming years. Since ancient time, in arid fog oasis, the populations adapted to those extreme conditions; here some sort of fog collector have been developed. Some of fog harvesting projects have been mapped, in Fig. 65.1 (Klemm et al. 2012). Usually, those projects are realized in undeveloped areas of rural environment for agricultural purpose (Morichi et al. 2018). Nevertheless, some urban environments are affected by fog phenomenon, and they should take advantage of this alternative resource.

Fig. 65.1
A world map highlights the regions for the fog harvesting project. It highlights the regions in the northern part of Africa, the Southern part of Asia, and Australia.

Fog harvesting projects map, elaboration of the authors based on Klemm et al. (2012) and Schemenauer and Cereceda (1994)

Full size image

3.1 Fog Collector

Fog water is obtained through the fog collector; it is a passive system, made of textile structure. Those collectors must be orientated towards the main wind direction, to optimize the collection; in fact, wind is one of the determining factors for the process.

Therefore, when fog is pushed by the wind towards the mesh, the water droplets get deposited on the mesh’s filaments and when they reach a certain weight and dimension they flow down, where they are collected by a gutter and then stored in tanks (de Dios Rivera 2011). During last century many types of fog collector have been developed, they are generally classified on the type of structure, which can be two or three dimensional. The model most used worldwide, is the Large Fog Collector (LFC); it’s a bidimensional structure (Holmes et al. 2015), designed by Schemenauer and Joe (1989). It is composed by a mesh, two poles and tensors; its collection panel is of 40 m2, made by a double layer of Raschel mesh. Generally, for these experiments the Standard Fog Collector (SFC) is used, it consists of a rigid metal frame that measures 1 m × 1 m; this frame is supported by two poles at 2 m above ground level, to reach stronger winds (Schemenauer and Cereceda 1994). The three-dimensional collectors are still not widely explored. Moreover, a three-dimensional device can provide more collection rate for the same soil occupation, but the additional mesh layers permit to collect the fog droplets that already passed through the first mesh. The three-dimensional structures can differ in shape; they can be cylindrical as in Warka Water project, or parallelepiped as in Nieblagua’s case (Fig. 65.2).

Fig. 65.2
A photograph exhibits 2 fog collector setups. The structures comprise metallic frames covered with some netted fabrics.

Source Photo by the Author

Nieblagua structure—three-dimensional parallelepiped fog collector.

Full size image

4 Novel Fog Harvesting System

4.1 Fog Harvesting Project

In order to develop a fog harvesting project, firstly the climatic conditions of the site should be analysed; in fact, wind speed, wind direction, mean humidity, temperature and Liquid Water Content (LWC) (Holmes et al. 2015) are determining factors for the fog collector disposition and dimensioning. In fact, the collectors should be oriented perpendicularly towards the main wind direction, and generally more wind speed imply more water collection (Schemenauer and Cereceda 1994). Moreover, due to the vertical development and the lightness of the traditional fog collector, the possibility to integrate this device into a smart membrane façade is under consider (Caldas et al. 2018). To do so, the structure of the fog collector must be conceived to integrate it on a building. Furthermore, the novel fog collector should be dimensioned referring to the water demand of such building. The first step to take, to analyse the fog water potentiality of the selected area, is the development of a test campaign. At least a Standard Fog Collector (SFC) (Schemenauer and Cereceda 1994) should be installed for a period, preferably a year or more, to have a mean collection for each season. Several for harvesting projects have been developed which resulted in different collection rates, for example in Cerro Moreno the amount is 8.26 l/m2/d, while in Falda Verde is 1.43 l/m2/d, the amounts refer to the year average (Larrain et al. 2002; Bitonto et al. 2020). Once, the collection property has been stated, depending on the water demand of the building, the smart façade should be dimensioned. The main wind direction could vary during the year, for this reason the façade should be adaptable to any condition. Therefore, flexibility should be one of the main aspect of the smart membrane façade development. Depending on the quantity of water collected on each season, it can be used for domestic purposes, when fog events are abundant, or for watering a green roof or garden in other seasons. The quantity of fog water collection varies from site to site, depends also on the season, and on the structure and mesh used for the fog collector.

4.2 Application Field: Built Environment

The construction sector is one of the most impacting for the environment, and its footprint is progressively increasing in carbon dioxide emissions, causing rise in air temperatures, and consuming a large amount of water (European Parliament, Council of the European Union 2010). For this reason, the European commission has stated some guidelines to reach the goal of Near Zero Energy Buildings (NZEB) by 2020 (European Parliament, Council of the European Union 2010). Moreover, in 2015, also the United Nations stated 17 Sustainable Development Goals (SDGs) (General Assembly 2015). Some of these goals can be reached through the application of a novel smart envelope on buildings. The proposed experimental envelope is composed by a double façade, where the first layer is the main closure of the building, while the external one is the smart mesh. This multipurpose textile façade is a passive and ‘Km 0’ system, because it doesn’t require energy to collect or distribute water, and is located where the users are, unlike the traditional hydric systems. Furthermore, since the external skin is composed by a mesh, it can provide shading. In fact, shading a window during summer can reduce the demand of cooling system, which implies notable energy consumption, and related emissions. If the envelope is combined also with vegetation, the façade can also provide purification of the air, given both by the filter mesh and the absorption properties of the plants. It is important to underline that, depending on the location’s characteristics, fog is not always present along the year. The proposed device refers to the Mediterranean condition, where water can be collected mostly during winter nights and early mornings, while the shading effect is required just during summer days (Fig. 65.3); moreover, each part of the envelope is more suitable for specific functions (Fig. 65.4).

Fig. 65.3
A line graph represents the data for weather conditions and envelope functions. The lines denote the trend for humidity, temperature, and wind speed. The graph also denotes the data for water collection and shading.

Source Graphic by the Author

Weather conditions and envelope functions—relation between the weather conditions and the respective envelope functions along the day in a typical year.

Full size image
Fig. 65.4
A graph with different color gradients represents the data of water collection, shading effect, and vegetation in the roof, facade, and basement areas.

Source Graphic by the Author

Envelope requirements—water collection, shading and vegetation are arranged on a specific part of the envelope, due to users’ comfort but also to functional aspects.

Full size image

Nevertheless, this device is a model that can be applied and adapted to any fog oasis referring to external conditions and users’ needs. In particular, the design methodology of this smart façade is based both on the requirements of the fog collector previously stated, together with requirements of building envelopes. Therefore, it should be composed by modules that can be oriented towards winds direction, for fog harvesting, and towards sun radius for shading (Fig. 65.5).

Fig. 65.5
An illustration of a fog harvesting project. It indicates the position and dimensions of the fog harvesting panel, green grid, and storage system from the top view and side view angles.

Source Graphic by the Author

Façade concept—example of fog harvesting project development in building sector.

Full size image

Today, there are many examples of architectural projects that have worked with adaptive facade systems regarding daylight conditions by implementation of smart systems (Al-Obaidi et al. 2017; Pirouz et al. 2020). Depending on the amount and use of water, the size and placement of the storage must be planned; it can be on the basement or on the roof. In case the amount of water collected is only sufficient for irrigation purposes such as gardening, it can be an autonomous system. Thus, when the amount collected is sufficient for domestic use, it can be connected to the plumbing distribution for utilizing on WC flushes and washing machines after filtration and disinfection processes (Fig. 65.6).

Fig. 65.6
An illustration of the plumbing system highlights the paths for fog water collection, fog water distribution, municipal water, gray water, black water, and sewer.

Source Graphic by the Author

Plumbing system of fog water for domestic use.

Full size image

As regarding the maintenance, weakest point of the LFC is the mesh, in fact it often gets broken because of the high velocity of the wind, generally more than 17 m/s (Holmes et al. 2015). Smaller size for the mesh can reduce the risk of damage as stated by Holmes (Holmes et al. 2015). In the urban environment, the wind speed is usually lower, and the proposed façade is composed of reduced fog collecting modules. Therefore, the maintenance of the proposed façade only regards the gutter cleaning; the lifespan of the fog collector depends on the one of the selected mesh. Since a new application field has been proposed, the potentiality of a fog harvesting façade should be explored with some test campaign both in the field, in a fog oasis, and in the lab, in order to understand the behaviour of a mesh placed in front a solid in varying wind velocities and façade dimensions. In order to develop this kind of façade a parametric design is required to shape it, considering all the variables, so the specific characteristics of the location, the building and the water collection purpose.

5 Conclusions

Considered the actual circumstances of traditional resources crisis, due to inadequate management, and the sustainability goals state for many sectors, including construction, a novel architectonical device is essential to enhance the building performance. The smart textile façade proposed can make the building water self-sufficient lowering the ecological footprint and energy demand. The design depends on many factors that refers to the local climatic conditions, to the building features on which it can be attached and on the water demand and use. In order develop the design some parametric tools are needed together with an experimental campaign. In fact, the efficiency of fog collection has been proven in many areas worldwide; however, the innovative solution must be verified and adjusted on the requirement. Extending the system to a bigger scale, the smart textile can cover billboards, construction sites or can be used as a fence in metropolitan cities, collecting water for public use. Depending on the application site, even the fog water collected may not be sufficient for the complete domestic use along the year, it can be stored and used as a support supply for gardening.