NOTICEThis report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.
AcknowledgmentsThe author thanks Ren Anderson for his guidance and for his valuable contributions to this report.iv
Executive SummaryEffective mixing of conditioned air with room air is an essential factor for providing uniform comfort in homes. The higher the supply air flow rates, the easier it is to reach good mixing within the space. In high performance homes, however, the flow rates required to meet the small remaining thermal loads may not be large enough to maintain uniform mixing in the space.The objective of this study is to evaluate operating conditions required to maintain uniform mixing, within high performance homes, under both heating and cooling conditions. This can be achieved by creating proper combination of temperature and air motion in the occupied zone of the conditioned space. Lack of uniform conditions in the space or excessive fluctuation of conditions produces discomfort. Discomfort can be caused by excessive air motion (draft), excessive room air temperature variations, or failure to deliver or distribute air according to load requirements.To address this question we used computational fluid dynamics modeling to evaluate the performance of high sidewall air supply for residential applications in heating and cooling modes. Parameters that were varied in the study include the supply velocity, supply temperature, and inlet dimensions. The model provided high resolution velocity and temperature distributions in the room, which were used to determine the effective draft temperature. The latter is then used to calculate the Air Diffusion Performance Index (ADPI). This parameter was used to evaluate the air distribution and thermal comfort in the occupied zone. ADPI is the percentage of locations where the effective draft temperature and air speed meet comfort specifications. The higher the ADPI value is, the more comfortable the space will be for most occupants.The results provide information to guide the selection of high sidewall air supply inlets to maintain proper room mixing for heating and cooling of high performance homes. It is demonstrated that these systems can achieve good mixing and provide acceptable comfort levels....