Thermal behavior of a solar-assisted latent heat thermal energy storage unit on the heating season under variable weather conditions

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Due to the fossil-fuel-related climatic problems which got worse in recent decades, the worldwide share of renewable energy has significantly increased. Even though solar energy is one of the most accessible renewables, it has an intermittent nature throughout the day. Different energy storage techniques are implemented to resolve the intermittency problem and make solar-aided energy accessible when it is needed. Energy use in buildings has a huge share of total energy demand, and heating/cooling demands are responsible for most energy consumption in buildings. In this study, the performance of a solar-assisted latent heat thermal energy storage (LHTES) unit integrated with a heat pump is investigated during the heating season under variable weather conditions. Phase change materials (PCMs) with different melting temperatures (Tm) and latent heat of fusions (hsf) are studied, and parametric simulations are conducted to examine the proposed systems' economic advantage and payback duration. Variable weather conditions are defined in simulations, and seven consecutive day analyses are conducted to ensure that results are not dependent on the initial conditions. Results revealed that the PCM with Tm = 35°C and hsf = 240 kJ/kg has a better thermal performance than the other alternatives, i.e., Tm = 31°C and 40°C. The integration of the solar-aided LHTES unit with the heat pump increases the COP of the heat pump, and the increment varies from 35% to 80% for heating months in Izmir. Such an improvement in COP reduces the operating costs related to the electricity consumption of the heating device significantly, and the simple payback period of the combined system is determined to be approximately 13 years in Izmir.