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Abstract In Hot Summer and Cold Winter Climate Zone, the cooling potential of natural/passive night ventilation is limited during summer due to the insignificant difference between the outdoor and indoor temperatures. Therefore, a novel mechanical ventilation strategy, the wall-mounted attached ventilation (WAV) system, is proposed in the present paper to improve ventilation efficiency of night cooling. The idea is that WAV can produce a downward airflow over the internal wall surface that is somewhat similar to a sidewall jet, so as to achieve enhanced heat transfer in the room. This paper starts with a series of experiments in a test chamber, and continues with thermal analysis of the heat transfer characteristics and heat removal performance of WAV. The performance of night ventilation with WAV is further evaluated in terms of ventilation efficiency index and energy performance index. It is shown that the overall average value of the convective heat transfer coefficient at the internal wall surface with WAV is 10.79 W m−2 °C−1. With WAV, the amount of heat removed from the ventilated wall is about five times that in the natural night ventilation case, and the total amount of heat removed from the whole chamber is twice as much. The average value of the surface cooling effectiveness of WAV is 1.48, and the overall coefficient of performance (COP) of WAV turns out to be 26.8. As a night ventilation strategy, WAV is capable to achieve good cooling performance under hot summer conditions. Highlights • A novel wall-mounted attached ventilation (WAV) night cooling system proposed. • Experiments carried out to understand the temperature decreasing effect of WAV. • Transient heat transfer models established to analyse the thermal performance of WAV. • WAV has much better performance on surface cooling and heat removal than natural ventilation. [ABSTRACT FROM AUTHOR]

The complexity and diversity of airflow in buildings make the accurate definition of convective heat transfer coefficients (CHTCs) difficult. In a full-scale test facility, the convective heat transfer of two cooling systems (active chilled beam and radiant wall) has been investigated under steady-state and dynamic conditions. With the air-based cooling system, a dependency of the convective heat transfer on the air jet trajectory has been observed. New correlations have been developed, introducing a modified Archimedes number to account for the air flow pattern. The accuracy of the new correlations has been evaluated to±15%. Besides the study with an air-based cooling system, the convective heat transfer with a radiant cooling system has also been investigated. The convective flow at the activated surface is mainly driven by natural convection. For other surfaces, the complexity of the flow and the large uncertainty on the CHTCs make the validation of existing correlations difficult. [ABSTRACT FROM PUBLISHER]

Abstract: Night-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 12h of discharge by night-time 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. [Copyright &y& Elsevier]

Radiant cooling is a promising thermal control technology for built environment. Unfortunately, condensation limits the potential of radiant cooling. Recently, numerous technologies have been developed to address the issue of condensation on radiant cooling surfaces. Nevertheless, a special review on the condensation control for radiant cooling is absent. The passive condensation prevention for radiant cooling refers to a technology that could realize the dew-free operation of radiant cooling terminals without additional control strategies or external energy consumption. The methods of creating surperhydrophobic surfaces and adding cover shields to prevent condensation on radiant cooling surfaces are systematically reviewed, involving anti-condensation mechanisms and specific studies. Finally, the limitations of passive methods are critically discussed and perspectives are proposed, attempting to seek suitable solutions and inspire new ideas for future research. In this study, the concept of passive condensation prevention for radiant cooling is proposed for the first time. It is aimed to release the potential of radiant cooling and provide alternative ideas for the design and application of radiant cooling. [ABSTRACT FROM AUTHOR]

Abstract: Due to an overall trend towards less heating and more cooling demands in buildings in many European countries over the last few decades, passive cooling by night-time ventilation is seen as a promising technique, particularly for commercial buildings in the moderate or cold climates of Central, Eastern and Northern Europe. The basic concept involves cooling the building structure overnight in order to provide a heat sink that is available during the occupancy period. In this study, the potential for passive cooling of buildings by night-time ventilation was evaluated by analysing climatic data, without considering any building-specific parameters. An approach for calculating degree–hours based on a variable building temperature – within a standardized range of thermal comfort – is presented and applied to climatic data of 259 stations all over Europe. The results show a high potential for night-time ventilative cooling over the whole of Northern Europe and still significant potential in Central, Eastern and even some regions of Southern Europe. However, due to the inherent stochastic properties of weather patterns, a series of warmer nights can occur at some locations, where passive cooling by night-time ventilation alone might not be sufficient to guarantee thermal comfort. [Copyright &y& Elsevier]

Abstract: Night-time ventilation is seen as a promising approach for energy efficient cooling of buildings. However, uncertainties in the prediction of thermal comfort restrain architects and engineers from applying this technique. One parameter essentially affecting the performance of night-time ventilation is the heat transfer at the internal room surfaces. Increased convection is expected due to high air flow rates and the possibility of a cold air jet flowing along the ceiling, but the magnitude of these effects is hard to predict. In order to improve the predictability, heat transfer during night-time ventilation in case of mixing and displacement ventilation has been investigated in a full scale test room. The results show that for low air flow rates displacement ventilation is more efficient than mixing ventilation. For higher air flow rates the air jet flowing along the ceiling has a significant effect, and mixing ventilation becomes more efficient. A design chart to estimate the performance of night-time cooling during an early stage of building design is proposed. [Copyright &y& Elsevier]