Experimental investigation of convective heat transfer for night ventilation in case of mixing ventilation

The purpose of night ventilation (NV) is to improve building energy and thermal comfort performance. The key to accurately predicting NV performance is selecting the appropriate convective heat transfer coefficient (CHTC) at different surfaces of the built environment. The current CHTC correlations used in building energy simulation tools are limited and prevent accurate modeling of NV strategies. The building thermal mass activation is also an important factor to influence the efficiency of NV. A series of dynamic full-scale experiments with ten thermal mass distribution schemes, four air change rates per hour (ACH), and two inlet air temperatures was conducted to derive the CHTCs at test room surfaces during NV in case of mixing ventilation. The results show that the existing correlations did not accurately predict the CHTC for most cases. Therefore, the new surface-averaged CHTC correlations with inlet temperature as reference were developed for different thermal mass distribution schemes and ACH. Installing the thermal mass on one surface can significantly enhance its CHTC and affect the CHTC at other surfaces. The mean CHTC of the test room was independent of the inlet air temperature but increased together with ACH and thermal mass level of interior surfaces. Finally, the presence and locations of tables had limited influence on the CHTC at interior surfaces but reduced the mean CHTC.