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  • Periodic Reporting for period 1 - TESSe2b (Thermal Energy Storage Systems for Energy Efficient Buildings. An integrated solution for residential building energy storage by solar and geothermal resources)

TESSe2b Report Summary

Project ID: 680555
Funded under: H2020-EU.

Periodic Reporting for period 1 - TESSe2b (Thermal Energy Storage Systems for Energy Efficient Buildings. An integrated solution for residential building energy storage by solar and geothermal resources)

Reporting period: 2015-10-01 to 2017-03-31

Summary of the context and overall objectives of the project

TESSe2b Project - Thermal Energy Storage Systems for Energy Efficient Buildings is an EC financed H2020 four years project. TESSe2b designs, develops, validates and demonstrates a modular and low cost latent thermal storage technology based on solar collectors and highly efficient geothermal heat pumps for heating, cooling and domestic hot water (DHW) production.
That is achieved by integrating compact Thermal Energy Storage Tanks with Phase Change Materials (PCM TES), using encapsulated PCMs inside the geothermal boreholes and an advanced smart energy management self-learning control system.
Demonstration and on-site monitoring evaluation of small scale TESSe2b solution at a building in three pilot sites (Austria, Spain, Cyprus) conducted with the aim of evaluating the system’s integration into a building’s space, assess the impact of TESSe2b solution in different climates and provide evidence of its overall technical and economic feasibility.
The overall objective is to develop a solution to decrease of net energy consumption by 25- 30% and have a return-on-investment period of 8-9 years. TESSe2b solution will increase the use of renewable green energy reducing the dependence of conventional energy sources and their environmental impact in residential buildings.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

A set of paraffins and hydrated salt PCMs have been selected for the different heat storage tanks application (hot/cold and DHW). The selection was done mainly based on the PCMs latent heat and the solidification/melting temperature. The PCMs should have a high latent heat, to maximize the tanks heat density storage, and a melting/fusion temperature according to the tanks operation temperature. However, the selection process also considered the PCMs price, capacity for being manufactured in large scale, thermal conductivity, phase transition temperature, life time/stability, environmental hazards and safety operation.
Enhanced paraffins through the addition of graphite-based nanoparticles were developed. The results confirmed the possibility of enhancing significantly the paraffins thermal conductivity with little impact on the specific heat capacitance and solidification/melting latent heat.
Encapsulated paraffin solutions have also been studied for geothermal borehole applications.
A survey of the standards to produce unpressured plastic tanks was done, focused of HDPE, PP_H and GRP. In parallel, laboratorial compatibility tests between the HDPE/PP_H and the paraffins were developed. The tests revealed the degradation of both plastics material by the paraffins. To overcome this issue a resin coating solution was investigated. The validations of this solution is ongoing, the primary test results show promising results.
The FEA of the tanks design have started, different geometries of cuboid shape tanks have been simulated. The design of the HEs for the storage tanks has also started. A parametric CFD study (Figure 1) is ongoing to identify the optimum design of the HEs and its performance for different operating conditions. The CFD approach was validated based on experimental data obtained in a small laboratorial rig (Figure 2). The results obtained revealed that the water mass flow is the main parameter that controls the heat transfer rate over the PCMs melting/solidification process.
To protect the HEs from hydrated salts corrosion a protective coating film based on AIN was developed and tested (Figure 3). The results demonstrated that AlN coating provide anodic protection from the hydrated salts corrosion at ambient temperature. Tests at high temperature, to accelerate the corrosion process, are ongoing.
The CFD analysis of the encapsulated PCMs inside the borehole started with the study of different macro PCMs encapsulated solutions, based on HDPE tubes, filled with PCM, placed along the boreholes. The first results showed the enhancement of boreholes performance for small time cycles. Alternatively PCM encapsulated in three agents (powder and particles) were produced and characterized and compatibility tests being developed with grout material and water.
A smart model-based control system to optimize the overall operation of the system is being developed in Matlab/Simulink. The analysis of sensors, logical units and actuators to integrate the control system was done and the most appropriate components were selected. The basic models for simulating the performance of the PCM TES, solar collector and geothermal heat pumps were established. A laboratory test bench is under development to test the smart control system.
A laboratorial experimental setup to test the PCM TES prototypes under real operation mode is being developed. The setup has two water tanks and a PCM tank to perform tests at different temperature levels (Figure 4).

Finally, the dwellings chosen to perform the TESSe2b demonstration were selected and the dynamic energy analyses of the house was done. The data regarding the heating and cooling needs of the buildings along the year were obtained. Based on these results the, optimum performance of the storage tanks were identified and the pre-dimensioning of the overall system was done. The initial data are also used for the economic analysis of TESSe2b solution. A market study is also being developed based on a

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Concerning the impacts on advanced thermal energy storage a solution for the hot and cold tanks has been developed and is being optimized, a DHW solution including PCMs is also being developed.
It has already demonstrated the possibility of increasing the paraffins thermal conductivity more than 30% through the additions of graphite-base nano-platelets. The immersed HEs with adequate performance has already been developed, and can be further optimized.
The developments made in the protective low cost thin film coating it is very close to obtain an effective solution to protect the HEs from the hydrated salts corrosion effects.
Encapsulation solutions are being developed. Further studies will be done to assess their influence in the enhancement of the geothermal heat pump efficiency and in the decrease of the boreholes total length.
The advanced self-learning optimization algorithm is being designed, optimized and parameterized to optimize the coupling of the various subsystems. The optimization of the subsystem interdependency will optimize the overall efficiency by 5%. The adaptive control and management system is being developed in order to additionally increase the utilization degree of the PCM storage of up to 20%.
The PCMs stability is being studied to demonstrate a stable long term performance in multi-cyclic seasonal use for at least 20 years. It was proved that an adequate increase in system efficiency is achieved without exceeding 2.5 m3 total storage volume. The exact value for each demo site will be optimized based on cost efficiency optimization studies.
The work done so far shows that it is possible to reduce a net energy consumption by 25- 30% and have a return-on-investment period of 8-9 years. Further studies on economical evaluation of the TESSe2b solution by cost-benefit criteria will be done to achieve the target proposed.
The preliminary study of TESSe2b system in the three demonstration sites, show an increment of the solar fraction, between 7% and 26%, due to the coupling of the hot PCM tanks and the solar collectors, contributing to the net energy consumption reduction.

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