The Latent Heat Thermal Storage installed at the Politecnico di Torino Energy Center building


The Energy Center is a building owned and managed by Politecnico di Torino which hosts firms, academic staff and public administration. These entities jointly develop research activities in energy sustainability and the transition towards decarbonized societies. This building will validate the RE-cognition framework by interacting the already existing and newly-developed energy technologies with the RE-cognition platform. The existing energy technologies are a PV field on the rooftop, several PV panels integrated on the hall windows, a geothermal heat pump, a district heating substation and two small experimental wind turbines. The newly-developed technologies will complement the RE-Cognition project: the Latent Heat Thermal Storage (LHTS), the Hybrid Solar Cooling (HSC), the micro-CHP turbine, the EV charger and the i-Gateway, which will enable the exchange of data and information with the intelligent project platform. In December 2021, the installation of the LHTS was completed, while the remaining technologies are on their way to the pilot site.

What is a Latent Heat Thermal Storage? In general, it is a device that can accumulate a relevant quantity of thermal energy to use when heating is needed. In this way, it is possible to store the extra energy produced by renewable sources and use it later. And that’s the aim of the LHTS in the RE-cognition project: helping maximizing the share of the renewable energy consumption in the building. Through the suggestions of the intelligent platform, the LHTS will be optimally deployed according to the pilot’s needs. The core of this technology is the Phase Change Material (PCM), which allows storing and releasing heat, changing its status from solid to liquid and vice versa. Specifically, the LHTS developed in this project appears as a tank filled with an appropriate PCM crossed by several pipes where the water of the heating system is flowing. To enhance the rate of the heat exchange between the water and the PCM, extensions made of high conductive material are added to the pipes, thus facilitating the charging and discharging processes.

How does the LHTS work? The working principle of this technology is relatively simple, as there are only two operational modes. When heat is stored, hot water is supplied through the pipes, and the initially solid PCM melts gradually. This is referred to as the charging phase due to the analogy with the most common batteries. On the contrary, cold water is supplied through the same pipes and the initially liquid PCM solidifies when heat is released.

Similarly, this is known as the discharging phase. The energy required for these transformations is very high since the molecular structure of the PCM is modified. Hence, a large amount of heat can be accumulated in a relatively small volume, up to 5 times lower than a traditional water tank.

What are the features of RE-cognition LHTS? Two tanks were manufactured, and they can store up to 40 kWh of thermal energy each. They contain the same quantity and type of PCM, bio-based paraffin whose melting point is 74 °C. However, the internal pipes extensions (known as fins) are different. Following a topological optimization approach in the design phase, the same quantity of high conductive material was arranged differently around the tubes to increase the LHTS performance. Therefore, the two storage tanks are expected to release most of their energy content in less than one hour. Experimental tests are currently in progress, and they will reveal the real potential of this technology by this spring.

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