In recent years, the use of turbines or Pumps operating As Turbines (PATs) has been proven to be a sustainable alternative for managing Water Distribution Networks (WDNs), by coupling pressure ...control and leakage reduction with hydropower generation.
Pumps running in reverse mode can be an effective alternative to using turbines for energy production in WDNs. Many commercial models are readily available on the market and a number of economic and technical advantages for installation, operation and maintenance can be found. Theoretical and experimental criteria for predicting pump performance in turbine mode and for the optimal installation of a PAT in WDNs can be found in the literature. Nevertheless, the prediction of PAT characteristic curves is still an unresolved issue, because of the lack of information provided by manufacturers and the few laboratory campaigns that focus on the topic.
For this purpose, the laboratory results in the present study aim to assess the performance of pumps operating in reverse mode. Two centrifugal pumps were investigated: a centrifugal horizontal single-stage pump and a vertical multi-stage pump. Experiments were compared with theoretical models available in the literature, in order to assess their reliability in predicting PAT performance when data are lacking.
•Pumps As Turbines (PATs) are effective for energy recovery in Water Networks.•Literature is fairly lacking in predicting PAT performance curves.•Experiments were carried out to assess the validity of existing relationships.•Data allowed to obtain more general relationships than existing ones.
The current significant increase in energy consumption has resulted in the need to develop and implement effective approaches for defining alternative and sustainable solutions to couple primary ...resources with supporting methods of energy generation. In the field of effective water distribution network (WDN) management, the suitability of combining pressure regulation with small-scale hydropower generation is attracting even more interest, given that it can possibly reduce water leakages, as well as produce attractive rates of renewable energy. Specifically, pumps as turbines (PATs) are widely considered a viable solution because they combine hydraulic benefits with affordable investment and management costs. Nevertheless, despite several approaches available in the literature for the optimal selection and management of PATs, choosing the most suitable device to be installed in the network is still a challenge, especially when electrical regulation is arranged to modulate the PAT rotational speed and optimize the produced energy. Several approaches in the literature provide interesting solutions for assessing the effectiveness of electrical regulation when a PAT is installed within a water network. However, most of them require specific knowledge of the PAT mechanical features or huge computational efforts and do not support swift PAT selection. To overcome this lack of tools, in this work, an operative framework for the preliminary assessment of the main features (the head drop and the produced power at the best efficiency point (BEP), the impeller diameter and the rotational speed) of a PAT is proposed, aimed at both maximizing the daily produced energy and performing challenging economic selection. Then, it is assessed by estimations of the corresponding payback period (PP) and the net present value (NPV).
Assessing the impact of climate change on water demand is a challenging task. This paper proposes a novel methodology that quantifies this impact by establishing a link between water demand and ...weather based on climate change scenarios, via Coupled General Circulation Models. These models simulate the response of the global climate system to increasing greenhouse gas concentrations by reproducing atmospheric and ocean processes. In order to establish the link between water demand and weather, Random Forest models based on weather variables were used. This methodology was applied to a district metered area in Naples (Italy). Results demonstrate that the total district water demand may increase by 9–10% during the weeks with the highest temperatures. Furthermore, results show that the increase in water demand changes depending on the social characteristics of the users. The water demand of employed users with high education may increase by 13–15% when the highest temperatures occur. These increases can seriously affect the capacity and operation of existing water systems.
Flood risk maps for the built environment can be obtained by integrating geo-spatial information on hazard, vulnerability and exposure. They provide precious support for strategic urban planning and ...decision-making. These maps, generated in a probabilistic framework, can consider various sources of uncertainty in the flood risk assessment such as the occurrence of extreme flooding events, future land use and land cover, characteristics of the buildings, and exposure to flooding. This paper investigates how these maps can be used in complicated urban context such as developing countries, where engineers are forced to work with scarce or little data. Specifically, a detailed investigation on the city of Addis Ababa, Ethiopia, has been conducted. Although the city of Addis Ababa is undergoing extensive formal housing development, it is most likely that the informal settlements will continue to constitute a significant portion of urban housing landscape in the years to come. Recent research findings and field work from a large project (FP7-CLUVA) are employed in order to provide a quantified basis for decision-making between alternative adaptation strategies for informal buildings in Addis Ababa. Risk maps, obtained by up-scaling more accurate risk assessment results at neighborhood level, are adopted for risk zoning of the urban residential texture within the city. This provides risk-based criteria for both identifying suitable flood adaptation strategies and prioritizing between viable risk mitigation measures.
This laboratory study aimed at investigating the mean and turbulent characteristics of a densely vegetated flow by testing four different submergence ratios. The channel bed was covered by a uniform ...array of aligned metallic cylinders modeling rigid submerged vegetation. Instantaneous velocities, acquired with a three-component acoustic Doppler velocimeter (ADV), were used to analyze the mean and turbulent flow structure. The heterogeneity of the flow field was described by the distributions of mean velocities, turbulent intensities, skewness, kurtosis, Reynolds stresses, and Eulerian integral scales. The exchange processes at the flow–vegetation interface were explored by applying the turbulence triangle technique, a far less common technique for vegetated flows based on the invariant maps of the anisotropic Reynolds stress tensor.
The larger anthropic pressure on the Water Supply Systems (WSS) and the increasing concern for the sustainability of the large energy use for water supply, transportation, distribution, drainage and ...treatment are determining a new perspective in the management of water systems ...
Optimizing pump operation in water networks can effectively reduce the cost of energy. To this end, the literature provides many methodologies, generally based on an optimization problem, that ...provide the optimal operation of the pumps. However, a persistent shortcoming in the literature is the lack of further analysis to assess if the obtained solutions are feasible from the technical point of view. This paper first showed that some of these available methodologies identify solutions that are technically unfeasible because they induce tank overflow or continuous pump switching, and consequently, proposed a novel approach to avoiding such unfeasible solutions. This consisted in comparing the number of time-steps performed by the hydraulic simulator with the predicted value, calculated as the ratio between the simulation duration and the hydraulic time-step. Finally, we developed a new model which couples Epanet 2.0 with Pikaia Genetic Algorithm using the energy cost as an objective function. The proposed method, being easily exportable into existing methodologies to overcome the limitations thereof, thus represents a substantial contribution to the field of pump scheduling for optimal operation of water distribution networks. The new method, tested on two case studies in the literature, proved its reliability in both cases, returning technically feasible solutions.
Changes in the hydrologic cycle due to increase in greenhouse gases cause variations in intensity, duration, and frequency of precipitation events. Quantifying the potential effects of climate change ...and adapting to them is one way to reduce urban vulnerability. Since rainfall characteristics are often used to design water structures, reviewing and updating rainfall characteristics (i.e., Intensity–Duration–Frequency (IDF) curves) for future climate scenarios is necessary (Reg Environ Change 13(1 Supplement):25-33, 2013).
The present study regards the evaluation of the IDF curves for three case studies: Addis Ababa (Ethiopia), Dar Es Salaam (Tanzania) and Douala (Cameroon). Starting from daily rainfall observed data, to define the IDF curves and the extreme values in a smaller time window (10′, 30′, 1 h, 3 h, 6 h, 12 h), disaggregation techniques of the collected data have been used, in order to generate a synthetic sequence of rainfall, with statistical properties similar to the recorded data. Then, the rainfall pattern of the three test cities was analyzed and IDF curves were evaluated.
In order to estimate the contingent influence of climate change on the IDF curves, the described procedure was applied to the climate (rainfall) simulations over the time period 2010–2050, provided by CMCC (Centro Euro-Mediterraneo sui Cambiamenti Climatici). The evaluation of the IDF curves allowed to frame the rainfall evolution of the three case studies, considering initially only historical data, then taking into account the climate projections, in order to verify the changes in rainfall patterns. The same set of data and projections was also used for evaluating the Probable Maximum Precipitation (PMP).
One of the main issues arising during the rapid filling of a pipeline is the pressure transient which originates after the entrapped air has been expelled at the air release valve. Because of the ...difference in density between water and air, a pressure transient originates at the impact of the water column. Many authors have analyzed the problem, both from the theoretical and the experimental standpoint. Nevertheless, mainly vertical or horizontal pipelines have been analyzed, whereas in real field applications, the pipe profile is a sequence of ascending and descending pipes, with air release/vacuum valves at high points. To overcome lack of knowledge regarding this latter case, laboratory experiments were carried out to simulate the filling of an undulating pipeline, initially empty at atmospheric pressure. The pipe profile has a high point where an orifice is installed for air venting, so as to simulate the air release valve at intermediate high point of a supply pipeline. In the experiments, the diameter of the orifice and the opening degree of both upstream and downstream valves were varied, in order to analyze their effect on the pressure transient. The experiments were also carried out with a longer descending pipe, in order to assess the effects on the pressure surge of the air volume downstream of the orifice.
This paper presents a comparison between two procedures for the generation of water demand time series at both single user and nodal scales, a top-down and a bottom-up procedure respectively. Both ...procedures are made up of two phases. The top-down procedure adopted includes a non-parametric disaggregation based on the K-nearest neighbours approach. Therefore, once the temporal aggregated water demand patterns have been defined (first phase), the disaggregation is used to generate water demand time series at lower levels of spatial aggregation (second phase). In the bottom-up procedure adopted, demand time series for each user and for each time step are generated applying a beta probability distribution with tunable bounds or a gamma distribution with shift parameter (first phase). Then, a Copula based re-sort is applied to the demand time series generated to impose existing rank cross-correlations between users and at all temporal lags (second phase). For the sake of comparison, two case studies were considered, both of which are related to a smart water network in Naples (Italy). The results obtained show that the bottom-up procedure performs significantly better than the top-down procedure in terms of rank-cross correlations at fine scale. However, the top-down procedure showed a better performance in terms of skewness and rank cross-correlation when the aggregated demands were considered. Finally, the level of aggregation in nodes was found to affect the performance of both the procedures considered.
PDF
