Potential of harvesting rainwater from vertical surfaces

Abstract

The water supply chain is under increasing stress as urbanisation and population growth is driving more and more people to move to cities. An increasing amount of city planners are now looking for alternative water resources, rainwater being one of them. There are multiple benefits to on-site water collection, storage and use, as proven by multiple published studies and successful projects around the world; however, rainwater harvesting (RWH) has remained a niche technique, not seen as part of the mainstream. One of the reasons for this is that, traditionally, rainwater has only been collected from rooves and other horizontal surfaces, and then transferred and stored in various subsurface holding tanks. This method of RWH is dated and not very effective. Furthermore, rainwater is one of the purest water sources, but when collected from horizontal surfaces, it gets polluted with particles that have settled on those surfaces. As a result, RWH in this way can be used only for specific purposes. In order to fully utilise this natural resource, to enable the creation of sustainable cities, we must devise a new method for collecting rainwater. One aspect of RWH that has not yet been deeply explored is collecting it from vertical surfaces. Although some abstract studies have already been conducted, concerning water runoff from vertical surfaces, no studies have evaluated the possibility of harvesting and using such water. In this paper, the impacts of different sets of conditions and variables on the performance of RWH systems mounted on vertical surfaces, such as building facades, are compared. In addition, this study aimed to evaluate the potential of such systems to be used in real-world projects around the globe. To accurately measure collected rainwater, an experimental stand was constructed. This stand consisted of a mechanism that allowed the water-collecting surface and its parameters to be changed, whilst also measuring various aspects of the weather and the amount of water that was successfully harvested. The experiments were conducted in both a controlled environment (laboratory) and under real (natural) conditions. The results of this study provide a more accurate evaluation of how vertical RWH systems can be implemented in real-life projects around the globe and show how natural conditions and the surfaces used can change the effectiveness of RWH.

Feasibility of Vertical Rainwater Harvesting via In-situ Measurement of Wind-driven Rain Loads on Building Facades in a Tropical Climate

“…The KUT gauge (Figure 8) was constructed in the Kaunas University of Technology, Lithuania to measure the rainwater collection rate (Dobravalskis et al, 2018). It is composed of two main parts; the RWH stand and the main control unit.…”

“…For buildings in general and residential buildings in particular, one of the most promising alternative water resources is the rainwater (Lade et al, 2015).Traditionally, the majority of researches have concentrated their studies on roof rainwater harvesting (RWH) system (Canavan, 2008;Cho et al, 2020;Dobravalskis et al, 2018). However, in urban areas with new tall buildings, the ratio of facade surface areas is much higher than the ratio of roof surface areas.…”

“…Thus, rain more and mainly falls onto the buildings' facades and usually, rooftop rainwater collection can be considered inadequate (Adriano et al, 2011) or impossible when the roof has been used as a roof garden (SDI, 2003). On the other hand, as Dobravalskis et al (2018) declared, all rain has a horizontal velocity due to wind acting upon rain droplets which is called wind-driven rain (WDR). Due to this characteristic, WDR hits all buildings' facades even those with a completely vertical angle, and it makes buildings' facades as the available potential surfaces for vertical RWH.…”

“…Due to this characteristic, WDR hits all buildings' facades even those with a completely vertical angle, and it makes buildings' facades as the available potential surfaces for vertical RWH. This new approach to water resource management brings along more benefits in comparison with the horizontal RWH such as; harvesting potential cleaner water because it collects rainwater before ground/roof contamination occurs and utilizes without significant treatment for non-potable purposes; facade areas have not only larger surfaces but also are more unused spaces compared to rooftops in modern urban areas (Dobravalskis et al, 2018). Accordingly, new buildings can benefit from integrated vertical RWH from facade areas in order to optimize their water consumption and minimize their impact on the environment (Beorkrem et al, 2018).…”