The Feasibility of Rainwater Harvesting Systems in Buildings with Green Roofs: A Case Study Based on the Köppen Climate Classification

Green roofs (GRs) are becoming a trend in urban areas, favouring thermal performance of buildings, promoting removal of atmospheric pollutants, and acting as possible water collection spots. Rainwater harvesting systems in buildings can also contribute to the management of stormwater runoff reducing flood peaks. These technologies should be enhanced in Mediterranean countries where water scarcity is increasing and the occurrence of extreme events is becoming very significant, as a result of climate change. An extensive pilot GR with three aromatic plant species, Satureja montana, Thymus caespititius and Thymus pseudolanuginosus, designed to study several parameters affecting rainwater runoff, has been in operation for 12 months. Physico-chemical analyses of roof water runoff (turbidity, pH, conductivity, NH4(+), NO3(-), PO4(3-), chemical oxygen demand) have shown that water was of sufficient quality for non-potable uses in buildings, such as toilet flushing. An innovative approach allowed for the development of an expression to predict a 'monthly runoff coefficient' of the GR system. This parameter is essential when planning and designing GRs combined with rainwater harvesting systems in a Mediterranean climate. This study is a contribution to improving the basis for the design of rainwater harvesting systems in buildings with extensive GRs under a Mediterranean climate.

Combining green roofs and rainwater harvesting systems in university buildings under different climate conditions

The focus of the paper is the evaluation of the performance of domestic rainwater harvesting (DRWH) systems in multi-family buildings with one- to three-floor elevations by means of a cost–benefit analysis. The rainwater is here used for both indoor and outdoor non-potable water consumption. The study was carried out with reference to different residential building typologies (flat and condominium) in a specific local climate condition (Ancona). The buildings are characterized by different rooftop areas (100–400 m2), building floor elevations (one to three floors) and inhabitant numbers (3–54 persons). Moreover, in order to highlight the role of the tank capacity on the performance of DRWH, its capacity was changed in the range 50–200%. The combinations of all these parameters led to 276 test cases. The technical performance is evaluated by means of the water saving and retention efficiencies. The economical assessment is provided by comparing the costs and the savings due to the replacement of the water supplied with the rainwater. It is found that the payback periods changed in the range 10–35 years for the site-specific variables such as local rainfall and water service tariff. Cost–benefit analysis can help the design of DRWH systems, with particular attention to the sizing of the tank.

<p>Over the past few years, rapid urbanization, population growth and the projected climate change have contributed to global water scarcity and urban flooding. Thus, the rainwater harvesting system in buildings is getting popular for increasing water efficiency and reducing stormwater runoff. However, it is required to size the rainwater harvesting system adequately for improving its operation. An oversized system increases the capital cost, while an undersized system results in an unreliable water source. Therefore, the storage tank's sizing is the most critical objective for optimizing the overall system in a dense urban location. Rainwater harvesting system and the vegetated roof technology can be particularly promising to address the issue because the vegetated roof and blue roof perform very well as a stormwater management tool by providing reduced stormwater runoff generation. The research identified the factors involved in managing runoff from a complex set of rooftop arrangements, having partially vegetated and non-vegetated areas and developed a set of guidelines to optimize the rainwater harvesting system by utilizing vegetated roofs. The research analyzed four mid-rise buildings of the Ryerson University campus, and the results confirmed that an increase in the total percentage of vegetated area coverage reduces the rainwater storage tank size to a great extent. For a small institutional building, a 40% agricultural roof performs the best for meeting the outside non-potable water demand reducing the annual overflow from the tank. For 60% vegetated area coverage, the municipal service water must supplement the rainwater to meet the total water demand. In terms of substrate depth, 150mm yields the most reasonable benefit. Finally, a blue roof should be combined with a vegetated roof to maximize the stormwater retention and detention onsite. </p>

<p>Over the past few years, rapid urbanization, population growth and the projected climate change have contributed to global water scarcity and urban flooding. Thus, the rainwater harvesting system in buildings is getting popular for increasing water efficiency and reducing stormwater runoff. However, it is required to size the rainwater harvesting system adequately for improving its operation. An oversized system increases the capital cost, while an undersized system results in an unreliable water source. Therefore, the storage tank's sizing is the most critical objective for optimizing the overall system in a dense urban location. Rainwater harvesting system and the vegetated roof technology can be particularly promising to address the issue because the vegetated roof and blue roof perform very well as a stormwater management tool by providing reduced stormwater runoff generation. The research identified the factors involved in managing runoff from a complex set of rooftop arrangements, having partially vegetated and non-vegetated areas and developed a set of guidelines to optimize the rainwater harvesting system by utilizing vegetated roofs. The research analyzed four mid-rise buildings of the Ryerson University campus, and the results confirmed that an increase in the total percentage of vegetated area coverage reduces the rainwater storage tank size to a great extent. For a small institutional building, a 40% agricultural roof performs the best for meeting the outside non-potable water demand reducing the annual overflow from the tank. For 60% vegetated area coverage, the municipal service water must supplement the rainwater to meet the total water demand. In terms of substrate depth, 150mm yields the most reasonable benefit. Finally, a blue roof should be combined with a vegetated roof to maximize the stormwater retention and detention onsite. </p>

Circular economy can be considered not only in relation to building construction materials, but also in relation to resources that are used in the use phase of buildings, such as water, energy or even nutrients. On the other hand, some constructive solutions are becoming increasingly important in the current scenario of climate change, taking into account the need to increase the resilience of the urban environment and the mitigation of emissions. This is the case, for example, of green roofs and living façades, which are an alternative to traditional grey infrastructure, offering many benefits to both citizens and cities. Beyond the ability to improve environmental conditions and quality of life, they can augment the energy efficiency of buildings, reduce flood risks in urban areas and be combined with rainwater harvesting systems. So, taking into account these trends for constructive solutions in the future, this paper analyses the possibilities of a circular use of water in buildings, aiming to create in the future “zero water” buildings. Particular attention is given to the compatibility between new green roofing solutions and rainwater harvesting systems in buildings, but the reuse of grey water and the possibility of nutrient recovery in buildings, such as urine (phosphorus) - which can be used in the building itself on green roofs - living facades or urban agriculture, are also referred to.

A rainwater harvesting system in buildings with green roofs and a rooftop greenhouse in Pyongyang

Rainwater harvesting in buildings involves technology for its proper planning, design, installation, operation, and maintenance. Two major scopes of rainwater harvesting are (1) the use of rainwater for all general purposes and (2) recharging groundwater. In both cases, various functional techniques must be applied. The extent of technological involvement depends primarily on the introduction of various conditioning or treatment technologies in the harvesting system: sedimentation, filtration, and disinfection. Based on the application of these conditioning or treatment technologies, the rainwater-harvesting system in buildings may be classified as (1) a direct-use system, (2) a nonfiltered system, (3) a filtered system, and (4) a complete system. The development process of a rainwater-harvesting system in buildings has four aspects: (1) planning, (2) design, (3) construction, and (4) maintenance. In all aspects of rainwater harvesting‒system development, systematic approaches must be followed to ensure its sustainability. In this chapter, the major scopes of rainwater harvesting are introduced. The extent of technological involvement in the harvesting system is delineated. All aspects of rainwater-harvesting development in buildings and their systematical approaches are discussed. Finally, the problems and prospects of rainwater harvesting in buildings are identified.

The feasibility of installing rainwater harvesting systems in buildings is usually defined based primarily on economic analysis. In this perspective, we reviewed the literature related to water consumption in buildings, rainwater use, and environmental assessment tools to evaluate the impact of rainwater harvesting on the environment. Identifying water end uses in buildings showed a high potential for potable water savings through alternative sources (e.g., rainwater use for non-potable purposes). Most studies reviewed found potential for potable water savings from 20 to 65%. Moreover, the literature reported that rainwater harvesting systems might reduce the runoff volume from 13 to 91%. However, other possible benefits and impacts of the systems on water flow and the environment must be assessed in addition to the potential for rainwater harvesting. Life cycle assessment, life cycle cost assessment, and water balance modelling have been used in urban water management. Most life cycle studies reported that rainwater harvesting systems have better environmental performance than centralised systems. The water balance method may effectively determine the impacts these systems cause on the water cycle. Using life cycle assessment and the water balance method together is essential to evaluating rainwater harvesting systems integrated into the urban environment.

Modular life cycle assessment approach: Environmental impact of rainwater harvesting systems in urban water systems

Energy intensity of rainwater harvesting systems: A review

Green or vegetated roofs are increasingly built in cities to provide multiple environmental and social benefits and are an emerging horticultural industry in Australia. Since 2008, researchers at the University of Melbourne s Burnley Campus have undertaken transdiciplinary research developing and evaluating green roofs for southern Australian conditions which are characterised by hot, dry summers. We have quantified plant performance through experiments on roofs and in controlled environments, using both Australian native and exotic species, to identify plant physiological and morphological traits that will improve green roof performance. We have developed lightweight mineral substrates based on scoria, bottom-ash from coal fired power stations and crushed roof tiles and evaluated water retention additives to improve water holding capacity and plant survival. Hydrology studies have found that 10-cm deep green roofs with scoria substrate can reduce stormwater runoff in Melbourne by 43-88%, depending on season and plant species. We found that a 12.5-cm deep green roof reduces building energy use by 38% in summer. Environmental psychology research demonstrates that people prefer green roofs with flowering meadow like vegetation and that viewing this type of green roof improves concentration and improves work performance. Our results have been embraced by the Australian green roof industry, resulting in construction of green roofs with our best performing substrates and plants and the development of science-based guidelines for future green roof projects.

The Food Waste Atlas: An important tool to track food loss and waste and support the creation of a sustainable global food system

This study presents a life cycle assessment (LCA) of a rainwater harvesting (RWH) system and an air-conditioning condensate harvesting (ACH) system for non-potable water reuse. U.S. commercial buildings were reviewed to design rooftop RWH and ACH systems for one- to multi-story buildings’ non-potable water demand. A life cycle inventory was compiled from the U.S. EPA’s database. Nine scenarios were analyzed, including baseline RWH system, ACH system, and combinations of the two systems adapted to 4-story and 19-story commercial buildings in San Francisco and a 4-story building in Washington, DC. Normalization of 11 life cycle impact assessment categories showed that RWH systems in 4-story buildings at both locations outperformed ACH systems (45–80% of ACH impacts) except equivalent in Evaporative Water Consumption. However, San Francisco’s ACH system in 19-story building outperformed the RWH system (51–83% of RWH impacts) due to the larger volume of ACH collection, except equivalent in Evaporative Water Consumption. For all three buildings, the combined system preformed equivalently to the better-performing option (≤4–8% impact difference compared to the maximum system). Sensitivity analysis of the volume of water supply and building occupancy showed impact-specific results. Local climatic conditions, rainfall, humidity, water collections and demands are important when designing building-scale RWH and ACH systems. LCA models are transferrable to other locations with variable climatic conditions for decision-making when developing and implementing on-site non-potable water systems.

Green roofs are used worldwide to mitigate the impacts of extensive urbanization, bringing benefits on social, economic, and environmental levels. In order to promote and facilitate the construction of green roofs by private investors, many countries have developed specific legislative requirements and incentives. However, there still are countries where the construction of green roofs is not properly addressed in the legislation, and where no incentive mechanisms are developed.  The good practices in three European countries, leaders in regards to the implementation of green roofs – the Netherlands, Belgium, and Germany, are analyzed in this article. A variety of incentives is introduced to accelerate the construction of green roofs. Different requirements are also set to ensure that the roofs will be designed and maintained to provide the desired benefits. The existing local regulations in Bulgaria and North Macedonia were analyzed as well. The only incentive in Bulgaria is the possibility of reducing the legally required green area by compensating it with a green roof. In North Macedonia, no legislative documents or incentives related to green roofs were found. The regulations, applied in the Netherlands, Belgium, Germany, and other countries can be used as good practice examples, modified, and applied from the authorities of countries that still have not developed their own, in order to motivate the investors and facilitate the construction of green roofs.