District energy network potentials in a city territory

Following the Covid crisis and the war in Ukraine, the rise of fossil fuels prices demonstrates the insecurity of the supply in addition to the adverse impact it has on the environment. These crises could lead to a global shift in the strategy of building heating. Renewable systems are promising alternatives to fossil fuel heating system. One of them is the District Heating Network that has the advantages of recovering the waste heat from the industry. In the context of a neutral carbon objective set by the aluminium factory Novelis, the city of Sierre is interested in investigating the possibility of develop- ing a District Heating Network (DHN). This study develops a method to design a network between a heat source and a city, based only on open data building’s inventory. The method, applied to the case study of Sierre, shows that, coupled with heat pumps, the DHN could reduce the heating emissions of the connected buildings, between 88% and 96 % and that 50% of the Novelis’ heat is recovered when half of the city is connected to the network. In addition to that, using new generation of DHN, like CO2 based network makes possible to supply cold with the same infrastructure.

Key Energy and Technological Aspects of Three Innovative Concepts of District Energy Networks

Patrick Chatelan, Daniel Favrat, Samuel Henchoz, François Maréchal

Energy needs in urban areas are heterogeneous by their nature, spatial distribution and temperature level required. Three concepts of district energy networks that could provide the energy services efficiently to a city centre are compared. The focus is on the energy and technological aspects. These networks are characterized by similar temperature levels; between 9.5 °C and 18 °C, rely on free cooling for most of the cooling services and use a combination of centralized and decentralized heat pumps to provide the heating services. Two of these concepts exploit the latent heat of evaporation/condensation of CO2 and of the refrigerant R1234yf to store and transfer heat. The third concept is more conventional and uses the sensible heat of liquid water, however with a small temperature spread. The proposed networks allow the waste heat emitted by the users requiring cooling to be transferred and valourised by the users requiring heating, thus reducing the load on the central plant. For the area considered, where the annual heating and cooling demand are 53.1 GWh and 49.4 GWh respectively, the annual electricity required to supply the thermal services amounts to 10.87 GWh for CO2, 10.52 GWh for water and 9.60 GWh for R1234yf. © 2016 Elsevier Ltd. All rights reserved.

2016

Enthalpy and exergy analysis in the framework of a district scale energy balance

Cédric Lambiel

This report presents a study of an enthalpy and exergy analysis in the framework of a district scale energy balance. Energy demand (heating, cooling and lighting) for buildings represents more than 30 % of the total worlds energy use. Main eﬀorts have been made on increasing performances of new building envelop and on the use of low temperature processes in order to increase the exergy eﬃciency. On a district scale, diﬀerent temperature and energy ﬂow levels are present, meaning a great potential to make use of synergetic eﬀects by rationally managing energy ﬂow interactions between buildings as synergies by enhanced energy management and the usability of waste heat source. An optimisation of exergy ﬂows for the heating systems allows to identify the temperatures levels according to the energy demand, which helps to implement the best choice of available technologies. A number of connection cases will be described and studied to show the potential gain in terms of thermal and economical performances, where the thermal performances are deﬁned by both the energy and the exergy eﬃciency. This study shows an improvement of the thermal performances of connection cases where in all scenarios the heat losses are lower than the waste heat recovery. These gains on thermal performances may increase further by the integration of appropriate technologies such as heat pumps. The use of primary resource like gas can also be decreased.

2012

SCCER-FURIES - Report on the role of multi-carrier, multi-services, multi-grids integrated energy conversion systems and their possible role in the Swiss energy 2050 - Deliverable D1.5.3

Luc Girardin, François Maréchal, Paul Michael Stadler

The optimisation of distributed and renewable energy systems in buildings has shown that zero energy systems, using existing technologies, is within reach in the household sector where the thermal and the systems can support each other to increase renewable energy harvesting, co-generation and waste heat recovery. Smart and sustainable systems can be deployed rapidly using solar collectors, heat pumps, energy storages and smart power grid driven by a Smart Energy Management strategy (SEM), based on Model Predictive Control (MPC). Targeting energy autonomous systems will indeed require a step further in the development of the infrastructure. In line with the design of future 100% renewable energy systems and autonomous cities, advanced concepts of multi-service energy systems have been proposed. These concepts of multi-carrier, multi-services and multi-grids systems (electricity, gas, heat distribution and mobility) are built around a "smart thermal grid" connecting buildings, centralised plants and distributed heating and cooling producing units, including individual contributions from the connected buildings and Power to Gas storage (P2G). It has been demonstrated that reasonable investments in advanced heat distribution system could lead to substantial benefits for both the economy and individual consumers, with a break-even time shorter than 6 year.

2017