Performance enhancement of a Latent Heat Thermal Energy Storage for Domestic Hot Water production

This study numerically investigates different ways to enhance the discharge performance of a Latent Heat Thermal Energy Storage for Domestic Hot Water production, from a design perspective. The storage is based on the shell-and-tube heat exchanger, comprising 37 finned tubes surrounded by PCM. A dynamic model is used to analyze different ways of enhancing its performance for DHW production. Key parameters studied are fin spacing, PCM selection (especially melting temperature), and tube network arrangement. The Reference Design uses octadecanol as PCM, a 10 mm fin pitch, and a single-pass tube layout. This design permits to store 16.2 kWh between 40°C and 75°C. The useful capacity, defined as the cumulative energy discharged until water outlet temperature falls below 40°C, is 8.9 kWh. This corresponds to 55 % discharge efficiency and a storage useful density of 33 kWh/m 3 . Reducing fin pitch leads to a reduction of the useful capacity, but a rise in discharge efficiency and useful density (for 1 mm fin pitch, discharge efficiency reaches 66 % and useful density 39 kWh/m 3 ). The use of PCMs with higher melting temperature also permits to boost storage performance in discharge. Finally, reconfiguring the tube bundle into a 3-pass layout (instead of a single pass) increases the useful capacity to 12.4 kWh, without changing total stored energy. This corresponds to 77 % efficiency and 47 kWh/m³ density. A High-Performance Design has been defined, by integrating following modifications to the Reference Design: decrease of fin pitch (1 mm instead of 10 mm), use of RT 70 HC instead of octadecanol, and hydraulic arrangement of the tube bundle into a 3-pass pattern. The useful capacity of this Design is 13.1 kWh (+47 % vs Reference Design), permitting to reach a useful density of 65 kWh/m 3 . • Performance in discharge of Latent Heat Thermal Energy Storage for Domestic Hot Water application is studied numerically. • Low fin pitch is recommended to optimize discharge efficiency. • Using a high melting temperature PCM permits to raise storage useful capacity. • Hydraulic configuration is several passes permits to improve storage performance in discharge.