CFD Assessment of Thermal Comfort and Heating Demand in Courtrooms Under Envelope Retrofit Scenarios

Courtrooms are tall, densely occupied rooms in which cold glazing, radiator plumes and stratification shape winter comfort - effects that single-zone energy calculations miss. We combined infrared thermography with steady three-dimensional CFD simulations (OpenFOAM, Boussinesq approximation, k-epsilon model, cross-checked with Ansys Fluent) to assess how window replacement and external wall insulation change the heating demand and the thermal comfort in the occupied zone of three courtrooms in Iasi, Romania, at the design outdoor temperature of -18 C. Thermography identified the glazing as the weakest element of the recent building envelope. In all rooms and scenarios the radiators placed under the windows prevented downdraught in the occupied zone: the mean draught rate was 2-7%, the head-ankle temperature difference 0.9-1.8 K (an upper estimate) and the mean PMV between -0.10 and +0.02 (category A of ISO 7730). With radiators sized for the design transmission loss, the occupied-zone air reached 23-24 C, close to the values measured in winter 2025, which points to an oversupply of heat in milder weather. Window replacement cut the transmission loss by 13-21%, and its combination with wall insulation by 39-75%. After retrofit, the ventilation required by EN 16798-1 becomes the largest heat loss, so demand-controlled ventilation with enthalpy recovery should accompany the envelope measures.