Empirical exploration of zone-by-zone energy flexibility: A non-intrusive load disaggregation approach for commercial buildings

Building energy flexibility has been increasingly demonstrated as a cost-effective solution to respond to the needs of energy networks, including electric grids and district cooling and heating systems, improving the integration of intermittent renewable energy sources. Adjusting zonal temperature set-points is one of the most promising measures to unlock the energy flexibility potential of central air conditioning systems in complex commercial buildings. However, most existing studies focused on quantifying the energy flexibility on the building level since only building-level energy consumption is normally metered in today's commercial buildings. By better understanding zone-level energy flexibility, building managers can design more targeted energy flexibility strategies, balancing overall flexibility potential with costs to occupants. This study aims to investigate the impacts of temperature set-point adjustment strategies on zone-level thermal and energy performance by developing a non-intrusive data-driven load disaggregation method (i.e., a 'virtual' zonal power meter). Three university buildings in Northern California (containing 136, 217, and 142 zones) were selected to test the proposed load disaggregation method. Zonal temperature set-point adjustment strategies were previously tested in these buildings. We found that heterogeneities of energy use and energy flexibility existed across not only buildings but also air handling units (AHUs) and zones. Moreover, a small number of zones accounted for a large amount of energy use and energy flexibility; and the most energy-intensive zones are not necessarily the most energy-flexible zones. For the three tested buildings, the top 30% most energy-intensive zones accounted for around 60% of the total energy use; and the top 30% most energy-flexible zones provided around 80% of the total energy flexibility. We also found the effects of temperature set-point adjustment on indoor air temperature were limited and heterogeneous. The proposed virtual zonal power meter enables the electric grid or district energy system operators to regard the controlled energy-flexible entities as a fleet of AHUs or zones instead of a fleet of buildings and helps unlock the possibility for targeted demand flexibility strategies that balance zone-by-zone energy reduction with zone-by-zone costs to occupants.