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This paper aims to investigate the performance of diffuse ceiling ventilation (DCV) in heating mode by a full-scale chamber. Eleven cases combined with different exhaust positions, supply air change rates, internal heat source intensities, and the type and location of contaminant sources were tested. The contaminant removal effectiveness (CRE) and temperature effectiveness (TE) were utilized to evaluate the ventilation effectiveness of DCV. It is found that thermal discomfort due to vertical temperature differences or draught is negligible for all tested cases. The results demonstrate that the effect of exhaust positions on CRE depends on the existence of internal heat source. With the presence of heat source, the room air can reach a good mixing, and the effect of exhaust positions is therefore limited. Nevertheless, when there is no internal heat source, the lower position can force the supply air to enter the occupied zone and improve ventilation performance. Increased air change rates can significantly improve indoor air quality, but have a little influence on ventilation effectiveness. CRE is strongly influenced by the internal heat source intensity and the contaminant source type. With the increase of heat source intensity, CRE increases notably from 0.28 to 0.82. As for different contaminant source types, CRE is about 1.3 under the active source (with heat), but only 0.68 and 0.82 under the passive source (without heat). This study is beneficial to the further design and optimization of DCV for its broader heating application. • The performance of diffuse ceiling ventilation (DCV) in heating mode was studied. • Contaminant removal effectiveness (CRE) and temperature effectiveness (TE) used. • Different parameters impacting the ventilation performance of DCV were discussed. • Exhaust position can affect TE, but its effect on CRE depends on the heat source. • Internal heat source and the type of contaminant source affect CRE significantly. [ABSTRACT FROM AUTHOR]

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. • The heat transfer of night ventilation was investigated by dynamic experiment • The existing correlations did not predict the convective heat transfer coefficient well. • Thermal mass on surfaces greatly affected the convective heat transfer coefficient. • The display of furniture influenced its air distribution and the heat transfer coefficient. • New convective heat transfer coefficient correlations were developed. [ABSTRACT FROM AUTHOR]

The convective heat transfer coefficient (CHTC) is a crucial parameter for night ventilation performance estimation. This paper investigates the heat transfer of night ventilation with diffuse ceiling ventilation (DCV) concept in an office room. A series of dynamic full-scale experiments were conducted with different thermal mass distribution schemes, air change rates per hour (ACH), and supply temperatures. The CHTC at interior surfaces with the inlet and outlet temperatures as the reference and the temperature efficiency of DCV were then derived. In most cases, the experimental CHTCs differed significantly from the CHTCs predicted by existing correlations. The presence of furniture (tables), its location, and the thermal mass installed on the walls had little influence on the CHTC at the floor. However, increasing the thermal mass of one surface can significantly augment its own surface CHTC. New correlations based on experimental CHTCs were developed for potential application in building energy simulation tools. The temperature efficiency of DCV decreased with the increase of ACH, the initial temperature difference between the supply air and indoor air, and the thermal mass level. DCV had higher temperature efficiency than the mixing ventilation and displacement ventilation, except for the case with displacement ventilation at low ACH. • Conduct dynamic experiments for heat transfer of diffuse ceiling ventilation. • Compare the deduced convective heat transfer coefficient with correlations in literatures. • Develop correlations of convective heat transfer coefficient for night cooling. • Study the impact of thermal mass, airflow, and inlet temperature on heat transfer. • Study the temperature efficiency for surface cooling of diffuse ceiling ventilation. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the performance of diffuse ceiling ventilation in a classroom. An experimental study is carried out in a test chamber to examine the impact of diffuse ceiling opening area on the system cooling capacity and thermal comfort. The results indicate that diffuse ceiling ventilation provides a satisfied thermal comfort level in the occupied zone even under a high ventilation rate and a high heat load condition. A design chart method is adopted to compare different diffuse ceiling configurations, and the results indicate that the system with a 18% diffuse ceiling opening area is able to handle the highest heat load without discomfort. On the other hand, a CFD model is built where the diffuse ceiling is simulated with a porous media zone. This model is validated by experimental results and further used to analyze the effect of heat load distribution and room height. The numerical results reveal that even distribution of heat sources gives a lower draught risk environment than centralized distribution. In addition, there is a significant increase on the draught risk with increase of room height. [ABSTRACT FROM AUTHOR]

This paper presents and analyses the performance of an integrated system with diffuse ceiling ventilation and a thermally activated building construction. A full-scale experiment is carried out in a hot box with an office setup. The performance of the integrated system is evaluated under different boundary conditions, considering different weather conditions, internal heat loads, TABS activation modes and with/without diffuse ceiling. The measurement results indicate that the diffuse ceiling plays a beneficial role improving thermal comfort in the occupied zone. However, the diffuse ceiling has the opposite effect on energy performance when TABS is activated in heating or cooling mode. Finally, the air temperature distribution in the plenum and the surface temperature distribution of the diffuse ceiling point out that the air does not perfectly mix in the plenum, the air is not evenly distributed throughout the entire ceiling area and the radiation cooling potential of diffuse ceiling is not sufficient. Thus, a further study should be conducted on optimizing diffuse ceiling and plenum design. [ABSTRACT FROM AUTHOR]