Experimental investigation of convective heat transfer during night cooling with different ventilation systems and surface emissivities

Abstract

a b s t r a c tNight-time ventilation is a promising approach to reduce the energy needed for cooling buildings without reducing thermal comfort. Nevertheless actual building simulation tools have showed their limits in predicting accurately the efficiency of night-time ventilation, mainly due to inappropriate models for convection. In a full-scale test room, the heat transfer was investigated during 12 h of discharge by nighttime ventilation. A total of 34 experiments have been performed, with different ventilation types (mixing and displacement), air change rates, temperature differences between the inlet air and the room, and floor emissivities. This extensive experimental study enabled a detailed analysis of the convective and radiative flow at the different surfaces of the room. The experimentally derived convective heat transfer coefficients (CHTC) have been compared to existing correlations. For mixing ventilation, existing correlations did not predict accurately the convective heat transfer at the ceiling due to differences in the experimental conditions. But the use of local parameters of the air flow showed interesting results to obtain more adaptive CHTC correlations. For displacement ventilation, the convective heat transfer was well predicted by existing correlations. Nevertheless the change of floor emissivity influenced the CHTC at the surface of interest.

Review of phase change heat storage and night ventilation technology of buildings

“…亓晓琳等人 [34,35] [36] 搭建了一个全尺寸实验房间用以对比研究置换通风 和混合通风两种夜间通风模式, 开发了一种可以应 用于建筑设计初期估算夜间通风制冷性能的图表. Dréau等人 [37] 在此基础上进行了多种工况的实验, 对 [40] . 同时, 基于相关研究, 刘加平等人 [41] [42] .…”

Effects of Night Ventilation on Indoor Air Quality in Educational Buildings—A Field Study

“…Chao and Hu [16] discussed that classroom occupants can be exposed to harmful concentrations because emissions may accumulate without proper ventilation during the unoccupied periods. Earlier research shows that night ventilation has been typically used to enhance indoor thermal conditions [17][18][19][20][21][22]. Even though many standards and guidelines have been provided for health-based ventilation [10,23,24], different night ventilation methods have been relatively rarely studied regarding organic pollutant levels in the mornings at the beginning of space use.…”

Numerical assessment of night ventilation impact on the thermal comfort of vernacular buildings

“…The results showed that the higher the cooling demand of the building, the higher the potential contribution of night ventilation under specific boundary conditions. In Le Dréau et al [17], heat transfer during 12 h of discharge by nighttime ventilation in a full scale test room was investigated. Different ventilation types, air change rates, temperature differences between the inlet air and the room, and floor emissivity were examined.…”