Energy management of net-zero energy buildings: A two-layer hierarchical approach

Net-zero energy buildings (NZEBs) are increasingly recognized as a key component of bottom-up energy transitions and decarbonization efforts. However, due to the variability in weather conditions driven by climate change, the actual annual performance of an NZEB may deviate from its optimal design targets. To address this challenge, daily energy management can play a crucial role in maintaining the intended energy balance. A major challenge in daily energy management is ensuring compliance with the annual zero-energy constraint. This paper introduces a novel hierarchical approach for NZEB energy management, integrating medium- and short-term energy management models into a two-layer framework. The upper layer allocates monthly energy consumption to individual loads, while the lower layer translates these allocations into daily boundary conditions. Within this framework, daily load scheduling is optimized to minimize energy costs and reduce residents' discomfort. A data-driven approach is employed to model both controllable and uncontrollable loads based on residents' lifestyles and climatic indicators. In particular, thermostatically controllable loads are predicted as a linear function of climatic variables, ensuring adaptive and efficient energy management. The proposed hierarchical approach is implemented in a fully electric, single-family residential NZEB located in Gaithersburg, Maryland, US. The results indicate that a traditional energy management algorithm fails to satisfy the annual zero-energy constraint when annual photovoltaic energy generation decreases to 90% of its current value due to climate change. In contrast, the proposed hierarchical approach successfully maintains the net-zero energy condition even when photovoltaic generation falls below 90% of the current level, while keeping residents' discomfort within acceptable limits.