Djamel Ouahrani

An optimal two-bout strategy with phase change material cooling vests to improve comfort in hot environment

Cooling vests incorporating phase change material (PCM) packets are used to improve comfort of workers in hot environments. This work aims to investigate by modeling and experimentation the effect of dividing the working duration into two bouts, where different PCM melting temperatures are used in each bout. An integrated bio-heat and fabric-PCM model predictions of physiological and subjective votes are validated via active human subject testing at hot conditions. A parametric study is performed to select, at two conditions (40°C and 45°C), the optimal PCM melting temperatures of the two bouts that would result with similar thermal comfort and sensation to the optimal single-bout case. The optimal case achieves most reductions in energy use for PCM regeneration, PCM carried weight and material cost. The results of the parametric study showed that heat storage is reduced in the second bout due to wearing the second vest with lower PCM melting temperature, thus thermal comfort and sensation are significantly improved. The optimal case at the 40°C environment uses a vest with 21°C PCMs in the first bout and a vest with 21°C PCMs in the second bout (V21→V21). At 45°C, the optimal case is V18→V10 with significant PCM weight reductions from the reference single bout case by a minimum of 47%. Thus, the issue of extra carried weight that affect metabolism and ease of movement when applying continuous cooling during work have been mitigated by using the two-bout strategy.

Experimental analysis of double and triple glazed façades with different shading devices in Qatar

The design of fully-glazed façades on buildings has become very popular, especially in hot regions where the use of natural ventilation is not recommended. The integration of shading devices to façade surfaces has been extensively studied to mitigate the resulting increase in cooling load due to larger glazed areas. In this paper, the effect of double and triple-glazed façades oriented in the south direction with different types of shading devices is analyzed and experimentally-quantified over the cooling period in Qatar. The façade and shading combinations have been chosen according to actual construction practices in the country. It was found that adding panes to glazed surfaces is more beneficial than shading devices due to the countrys large portion of convective heat gain of the space total cooling load. On the other hand, the benefits of the blinds lie in reducing the transmitted radiation energy with minimal effect on the heat transfer across the façade.