District heating systems are a relevant solution for reducing CO2 emissions, especially in dense areas with older buildings. However, due to the heavy investment costs, there is a great interest in simulation and software solutions to reduce distribution losses, limit the overuse of peak generators and optimize the use of storage capacities. In this paper, we describe how we designed, validated and used a library of fast, precise and robust components for district heating systems. Among other results, we could reduce the number of equations in some components by a factor of 40 and demonstrate more than 10% reduction in heat losses on a sample application.

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Even though the integration of renewable energies in new buildings is technically easy, the rise of solar thermal systems in the French market of energy renovation is limited by recurring constraints of implementation related to the installation of the storage tank. This is the reason why the Integrated Solar Collector (ISC) constitutes a very promising concept to develop. For both new buildings and renovation of the existing buildings, the ISC gives the opportunity to reduce the cost of installation and operation comparatively to a conventional Solar Domestic Hot Water System, because of their simplicity and passive operating process (without pump, nor controller). This second advantage is extremely important for the development prospects of the solar thermal market which is currently slowed down by the level of investment. The third advantage of our new ISC is the possibility of successful architectural integration, contrary to the currently available solutions with the storage installed on the roof.We developed a new concept of ISC adapted to the energy renovation with a multidisciplinary approach. Its design took into account various aspects: architectural integration (storage bellow the collector), energy performance (solar heat transfer at the bottom of the storage, fully insulated storage) and technological constraints (freezing risk). The project made it possible to study on the one hand its global performance (stratification, solar fraction) and on the other hand the free convective heat transfers inside the storage cavity. The approach used both numerical (architectural draft and design of the prototype, global modelling, and velocity / temperature fields) and experimental tools (test of heat, PIV on a cavity heated at the bottom, test of the prototype). The first prototype of ISC puts forward very satisfactory energy performances. Improvements are possible by enhancing thermal stratification in the storage system. Concerning the heat pipes operation against gravity, the project highlighted the current lack of technological solution adapted to our needs. The study of the building integration showed the architectural opportunities given during the renovation (new volumes) and the technical constraints which were solved (weight, storage insulation, freezing).

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