<p dir="ltr">&nbsp; &nbsp; Almost half of the U.S. primary energy is spent on buildings, with most of it spent in the process of achieving thermal comfort by the buildings’ occupants. In addition, individuals spend only 10% of their time outdoors in the summer, and 4% in the winter, with the remaining time being spent indoors. The current COVID-19 pandemic also demonstrates the importance of indoor air quality with various studies showing that while managing indoor air will not stop the spread of the virus by itself, it can help significantly lower the risk of getting infected. Therefore, any energy savings, better thermal comfort and improved air quality, coming even from the most seemingly insignificant component of a given HVAC system, will have an important impact on the well-being, socio-economics and environment of our nation and the world. Maintaining the desired thermal comfort of a room’s occupant(s), and improving the indoor air quality within a room, can only be achieved by thoroughly mixing the air, and this process can be optimized by introducing new air diffuser designs. One such novel design is presented in this work and its performance is analysed using computational fluid dynamics (CFD). The ultimate goal of this investigation is to show how the new diffuser optimizes the above-mentioned mixing process and thus helps achieve better thermal comfort with less energy consumption. A secondary goal is to present a template/process that can be used by investigators to establish the performance of any future air diffusers designs.<br>
&nbsp; &nbsp; &nbsp;The Ansys CFD software was used to investigate the flow behavior of the air supplied to a typical office room through a Coanda enhanced diffuser. The investigation was carried out for both the heating and cooling modes of the HVAC system. The Coanda effect is understood to be "the tendency of a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to entrain fluid from the surroundings so that a region of lower pressure develops." The proposed diffuser promotes the Coanda effect by delivering airflow jets which “hang” longer to the ceiling without the need for additional energy. The advantages of the new design are showcased by comparing its performance with that of an existing diffuser, namely the widely used “multi-cone” design, where the flow is ejected at a predetermined angle. Various performance and ASHRAE Standard 55 thermal comfort factors of building occupants are computed such as: throw and drop, air diffusion performance index (ADPI), vertical temperature difference from human ankle to head (VTAH), ceiling to floor temperature difference, etc. The analysis includes a discussion of the room occupant’s thermal comfort and the approach that was used to evaluate it and its relation to the energy consumption required to achieve the optimal level of thermal comfort.<br>
&nbsp; &nbsp;&nbsp;The results show that the proposed Coanda effect enhanced diffuser presents a distinct advantage, over existing designs, especially in cooling mode where it outperforms the standard multi-cone diffuser by achieving better energy consumption and thermal comfort using the same input parameters. An added advantage of the proposed design, with its simple layout, is that it is expected to be cost effective to produce and install, when compared to other more sophisticated designs.</p>

Investigation of a Coanda-Effect Enhanced Hvac Diffuser Using Cfd Analysis

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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