Activating thermal mass in historic brick buildings: In situ monitoring and calibrated summer performance

Historic massive masonry buildings are often assumed to provide favourable summer thermal performance, but thermal mass only mitigates overheating when stored heat can be discharged under suitable boundary conditions. This study develops an integrated experimental and numerical methodology to assess the summer thermal behaviour of a massive brick wall in a historic educational building in Valladolid, Spain. Heat-flux sensors and surface-temperature probes were installed on both sides of a 63 cm thick brick wall, consisting of 60 cm of massive brick masonry with an approximately 3 cm internal gypsum plaster finish, and the data were used to characterise its dynamic storage–release behaviour and calibrate an EnergyPlus model. Under free-running summer conditions, outdoor air temperature varied approximately between 18 and 37 °C, whereas indoor air temperature remained within 26.8–28.4 °C. Heat-flux measurements revealed recurrent daily inversions, with the external wall surface absorbing heat from outdoors for about 10–11 h per day. Regression analysis identified 00:00–08:00 h as the most favourable interval for passive heat discharge. Simulated internal gains of 15 W/m 2 increased indoor air temperature to about 29–31 °C, while an intensive 11 ACH night-purge strategy reduced early-morning indoor temperature by 4–6 °C and limited daytime peaks by about 2–3 °C. None of the simulated scenarios exceeded the Category II upper adaptive comfort limit during occupied hours. Night ventilation nevertheless substantially reduced indoor temperatures, highlighting the cooling potential of thermal mass when coupled with favourable nocturnal temperature gradients and sufficient air renewal. The proposed methodology provides a transferable framework for diagnosing and activating passive cooling potential in historic and public buildings with high thermal inertia.