Investigation of Local Thermal Comfort and Air Quality of Stratum Ventilation

Description

To save energy for summer air conditioning, there is a trend to adopt a higher room temperature worldwide. New values recommended by several governments in East Asia are significantly higher than the old ones. Conventional air distribution methods face challenges to use less energy to satisfy requirements in thermal comfort and indoor air quality (IAQ) under these new conditions. Thus, it is necessary to explore suitable air distribution possibilities. Stratum ventilation, a new method emphasizing local thermal comfort and IAQ at the head-and-chest level (breathing zone), could be one of these solutions to the problem for small-to-medium-sized rooms. Besides the locations of air supplies, the equipment of stratum ventilation is almost the same as the conventional systems. The Gaps between partitions, instead of the ceiling/underfloor voids, are most likely to house the air duct and plenums. The space used by the system is more or less the same. Preliminary experimental and human subject test results since 2005 have been obtained, which shows that the new method is able to address thermal comfort, IAQ and energy saving simultaneously. The results have been reported in several refereed journal articles. In the summary of the Ventilation 2009 conference held recently in Zurich, stratum ventilation was regarded as one of two significant innovative ideas. Nevertheless, there are many issues at the fundamental and practical levels which need to be examined in order to characterize the system, to quantify its effect on thermal comfort and IAQ, and to formulate design guidelines for its use in buildings. This study is to characterize the performance of the system through laboratory studies (to test the temperature, velocity and CO2 concentration profiles and to conduct human subject tests for their perceptions of comfort and air quality) and though CFD simulations.The laboratory study will be conducted in our large environmental chamber which allows the configurations of office, classroom and shop to be conveniently realized. Objective experimental measurements and computer simulations emphasizing local thermal and flow conditions will be conducted. Human subject tests for different configurations will be carried out. A simplified analytical method to predict the performance of stratum ventilation will be developed to provide more information for practicing engineers. Energy and cost analyses of design, installation and operation of the system will be made in comparison to conventional ventilation methods. Finally, a set of design guidelines for the application of stratum ventilation under higher room temperatures will be developed. Architects, system design engineers and suppliers in the field will be contacted for the development of design guidelines. To sum up, the advantages of the new method show in these aspects:IAQ in the breathing zone comparable to or better than the conventional methods;horizontal air movements at the head-and-chest level (the breathing zone) without drafts;desirable temperature pattern for thermal comfort in summer: modest and reversed temperature gradient in the occupied zone ;convenient installation of ducts and air terminals; andenergy efficiency (at least 10% saving based on conventional methods).