Energy flexibility assessment of an educational building: the Geosciences building at the University of Padua

The increasing penetration of renewable energy sources in the energy mix, together with the continuous electrification of end uses including heating, poses growing challenges in terms of power grid regulation. Demand Side Management is going to be an important asset to help System Operators match demand and generation in grids with high shares of non-programmable sources. In this context buildings play a key role, since their massive envelopes and HVAC systems offer a considerable amount of flexibility to shift electrical loads related to space heating and cooling over time. Within this framework, the present work focuses on the energy flexibility that can be offered by non-residential buildings through the modulation of HVAC systems while also evaluating the associated efficiency and the impact on CO2 emissions and thermal comfort, thereby contributing to the understanding of aspects that are still only partially explored in the scientific literature. The selected case study is the building of the Department of Geosciences of the University of Padova, chosen for the diversity of end uses (mainly offices, labs and lecture rooms) within the building and for the availability of both measurements and technical data, which enabled the development of a robust energy model and ensured the reliability of the analysis. The building was modelled using TRNSYS and the model was validated by comparing simulated and measured gas and electricity consumption. The validated baseline configuration represents the reference scenario against which several heating and cooling load modulation strategies were assessed to estimate the effect of Demand Response events. Positive (negative) modulation events aim to increase (reduce) the electrical load compared to the baseline scenario. The starting times of such events were set based on an external Carbon Intensity signal representative of Northern Italy. The duration of all events was fixed to two hours, and the energy flexibility performance was finally quantified primarily through modulation capacity and efficiency, which measure the amount of energy shifted during the event and the building behaviour after the modulation, respectively. Results show that, for both upward and downward modulation events, the highest capacity is achieved through a combined adjustment of temperature and humidity setpoints, acting simultaneously on supply air conditions and zone thermostats. The event with the highest modulation capacity during the heating season is able to shift 25 W/m² of specific electrical power, while in summer, the event with the highest absolute capacity reaches 16 W/m². The heating season value is also characterized by the early activation of the HVAC system, which is not observed in summer due to the different Carbon Intensity levels. Pre-activation plays a key role, as its absence leads to a reduction of about 40% in winter positive modulation capacity, reaching values comparable to summer conditions. Despite these benefits, an increase in thermal discomfort is observed especially for mid-seasons upward events and for summer downward events, although it remains within acceptable limits, with the Percentage of People Dissatisfied always below 22%. The efficiency of positive modulation, however, remains limited, mainly due to the influence of mechanical ventilation and the intermittent usage profile typical of non-residential buildings. Consequently, in the analysed case study, reductions in CO₂ emissions can only be achieved at the expense of a reduction in positive modulation capacity, highlighting the need to find a balance between the energy flexibility that can be offered to the electrical grid and the efficiency of the individual building participating in the Demand Response programs.