• Energy Research

AbstractThere is a strong link between water and energy in municipal water systems then the Alliance to Save Energy coined the term “Watergy” [1].Each component of the integrated water system contributes differently to the energy balance. With regard to urban water distribution systems (WDS), the pumping energy cost represents the single largest part of the total operational cost, also magnified by every litre of water lost to leaks. Even a small increase in operational efficiency may result in significant cost savings to the water industries.Therefore the inefficient management of water distribution systems results not only into depletion of water resources but also into energy consumption that increase CO2 emissions related also to the treatment of water volumes greater than needed, with use of excessive chemical components and consequent higher environmental global impact.The research outlined in this contribution was born with the aim to develop appropriate methodologies and tools to support the optimization of the WDS performance, in terms of water saving and reduction of energy consumptions and consequently environmental impacts. The integration of advanced WDS hydraulic modelling with a material and energy flow analysis is proposed herein, where the output of the hydraulic simulations permits to get more accurate input for a metabolic analysis of the system. Next phases of this research will test the integrated model under different scenarios, aimed at quantifying the environmental impact of different WDS management solutions by means of selected indicators.

Abstract Pump-as-Turbine (PaT) technology is taking the field in different small-hydro or energy recovery applications. These machines can be installed in water distribution grids to have pressure levels adjustment and electrical energy production. A PaT working in turbine mode has a different best efficiency point due to a variation of the fluid-dynamic operating conditions. In this paper, laboratory tests are performed to investigate its performances in pump and turbine mode. Hydraulic efficiency, torque and mechanical power are evaluated in several load conditions. In conclusion, an energy evaluation is shown considering a test case of a water distribution grid.

Modelling heat load is a crucial challenge for the proper management of heat production and distribution. Several studies have tackled this issue at building and urban levels, however, the current scale of interest is shifting to the district level due to the new paradigm of the smart system. This study presents a stochastic procedure to model district heat load with a different number of buildings aggregation. The proposed method is based on a superimposition approach by analysing the seasonal component using a linear regression model on the outdoor temperature and the intra-daily component through a bi-parametric distribution of different times of the day. Moreover, an empirical relationship, that estimates the demand variation given the average demand together with a user aggregation coefficient, is proposed. To assess the effectiveness of the proposed methodology, the study of a group of residential users connected to the district heating system of Bozen-Bolzano is carried out. In addition, an application on a three-day prevision shows the suitability of this approach. The final purpose is to provide a flexible tool for district heat load characterisation and prevision based on a sample of time series data and summary information about the buildings belonging to the analysed district.

Abstract General guidelines are available for the design of intake structures in river power plants. Nearly all existing criteria are limited in scope to a (rectangular) control section near the trash rack. In this section, a homogeneous flow with negligible wall influence is defined as the ideal condition. 3D numerics can simulate the complete velocity field up to the turbine, and therefore inform investigations of different inflow structure variations. This paper presents a review of six existing criteria and a modification of the Fisher-Franke criterion. All criteria are tested for both theoretical pipe flow conditions and artificial biased velocity distributions, for which different simplified obstacles in front of a turbine are investigated with the help of the 3D numerical software ANSYS-CFX. The best results could be achieved using the evaluation of the kinetic energy flux coefficient as well as the new modified criterion. Both can be recommended for the geometry optimisation of the intake structure.

Abstract Renewable and smart energy systems require district heating and cooling grids able to operate with variable flow rates, to manage different supply temperatures, and to support distributed energy production involving bidirectional flows. Due to these requirements, accurate and effective thermo-hydraulic models are essential to correctly simulate the flow rates, the head drops and the temperature transients for supporting the design, management and optimisation of thermal distribution networks. In this article, an efficient numerical scheme for the simulation of thermal grids based on a thermo-hydraulic model with a quasi-dynamic approach is proposed. Global gradient algorithm of Todini together with a uniformly distributed representation of demand along the pipes is used for steady-state hydraulic simulations of the networks modelled according to the graph theory. The temperature distribution is computed by solving a first order hyperbolic PDE which accounts for heat advection in the flux term and heat dissipation in an algebraic source term. A very efficient second-order Eulerian-Lagrangian finite volume scheme is employed on a staggered mesh, which evolves in time the temperature distribution starting from the velocity distribution given by the hydraulic solver. The usage of a Eulerian-Lagrangian algorithm for the discretisation of the convective terms, allows the proposed model to be unconditionally stable for every time step size. As such, the main advantages of the proposed model are the flexibility due to the admissibility of any spatial-temporal discretisation, the second order accuracy provided by both the demand schematisation and the thermo-hydraulic solver, and the computational efficiency guaranteed by the decoupled modelling approach. The resulting algorithm is extensively validated on four tests consisting of thermal grids of various complexity that have been carefully designed in order to capture different features and behaviours of the model. The accuracy of the results in terms of velocity, pressure and temperature is tested by separately checking the symmetry, the advection term, the heat loss component and, finally, by simulating a complex grid configuration with multiple heat sources. The article aims to present a proof-of-concept concerning a breakthrough numerical scheme for the efficient thermo-hydraulic simulation of pipeline networks, which proves to be suitably implemented in the modelling of district heating and cooling networks.

Abstract Sustainable urban energy planning depends on how renewable and local sources are integrated, how smart systems are implemented, and how synergies between regional and national policies are maximized. This study presents a methodology for the design of 100% renewable energy systems aiming to optimize the use of biomass and energy exchange with the national system while ensuring electricity import and export balance. The proposed procedure combines the robustness of the EnergyPLAN hourly energy system simulation model with the flexibility of multiple-criteria decision analysis. The result is a suitable methodology able to identify the best energy scenario based on a deep multi-parameter analysis from a technical point of view. A test case is proposed aiming at achieving 100% renewable energy for the Alpine city of Bozen-Bolzano in 2050.

This paper examines the complex dependence between peak district heating demand and outdoor temperature. Our aim is to provide the probability law of heat demand given extreme weather conditions, and derive useful implications for the management and production of thermal energy. We propose a copula-based approach and consider the case of the city of Bozen-Bolzano. The analysed data concern daily maxima heat demand observed from January 2014 to November 2017 and the corresponding outdoor temperature. We model the univariate marginal behaviour of the time series of heat demand and temperature with autoregressive integrated moving average models. Next, we investigate the dependence between the residuals’ time series through several copula models. The selected copula exhibits heavy-tailed and symmetric dependence. When taking into account the conditional behaviour of heat demand given extreme climatic events, the latter strongly affects the former, and we find a high probability of thermal energy demand reaching its peak.