An Elementary Approach to Evaluating the Thermal Self-Sufficiency of Residential Buildings With Thermal Energy Storage

Thermal energy storage (TES) plays a pivotal role in integrating renewable energy. Nevertheless, there are major challenges in the diffusion of TES such as selection of the optimum system size, system integration, and optimization. A key target for using TES is to increase the thermal self-sufficiency of a building or an entire district. Thermal self-sufficiency, unlike total energy self-sufficiency, concerns space heating and domestic hot water exclusively. Thus, it measures the ability of a system to meet its heating demand from local renewable energy sources. Thermal self-sufficiency is an important metric for practitioners and researchers in the design, optimization, and evaluation of energy systems, especially when considering TES. Unfortunately, no comprehensive method exists in the literature for determining thermal self-sufficiency with TES. Energy profiles and simulations are required to determine it. This article aims to close this gap and presents a new method for evaluating thermal self-sufficiency for a building with a TES. Using this approach, the upper and lower limits of the building thermal self-sufficiency are derived for various heat storage capacities and annual heat demands, demonstrating the impact of a TES on the system. A mathematical model applied to a case study of a single-family house illustrates the effect of different TES capacities on the thermal self-sufficiency: small TES significantly improves the thermal self-sufficiency, with a 20-kWh TES reaching 50% thermal self-sufficiency, while higher thermal self-sufficiency values require exponentially larger storage capacities.