Simulation and optimization of night cooling with diffuse ceiling ventilation and mixing ventilation in a cold climate

Accurate convective heat transfer coefficient (CHTC) is crucial to assess the night ventilation performance accurately. Previous experimental studies proposed CHTC correlations tailored for night cooling with diffuse ceiling ventilation (DCV) and mixing ventilation (MV). A holistic approach integrating the building energy simulation and optimization method was put forward to validate the experimentally proposed correlations, simulate and optimize the performance of night cooling with DCV and MV. The validation results demonstrated that the proposed correlations predicted the surface temperatures accurately with a maximum mean absolute error of 1.9 °C. For a typical air-conditioned office room, night cooling with DCV saved about 0.2 kWh/m2 total cooling energy per unit floor area (TCEC) more and provided a lower average predicted percentage of dissatisfied during the working hours (aPPD) by up to 3.1% than that with MV. Compared with the validated correlations, the empirical ceiling diffuser convection algorithm overestimated the night energy-saving potential by up to 0.5 kWh/m2 (13.8%) and yielded a maximum difference in the aPPD of 1.5%. Optimization significantly saved TCEC by 1.1 kWh/m2 (29.0%) for DCV and 0.9 kWh/m2 (25.7%) for MV while maintaining the aPPD within 10%, compared to respective base cases.