CH-99-06-5 -- A CFD Study for Cold Air Distribution Systems PDF

This paper presents a computational fluid dynamics (CFD) study of the indoor environment provided by a cold air distribution system using three alternative types of diffusers, i.e., a square multi-cone type, a wall-mounted nozzle type, and a ceiling nozzle type. The surface condensation risk on the diffusers is also discussed using the CFD results and a simple condensation model. An innovative proposal to prevent surface condensation and cold air dumping when using multi-cone circular diffusers with cold air is presented. The results show no significant variation in temperature distribution, airflow patterns, mean age of air, and mean carbon dioxide concentration at the occupied zone using a conventional chilled air system compared with a cold air distribution system. The ceiling nozzle type diffusers are suitable for cold air distribution systems. The wall-mounted nozzle type diffusers lose their jet momentum very fast because of reversed flow, and, therefore, they have a very limited range of cooling areas. The risk of surface condensation on the diffuser increases as the supply flow rate increases. The influence of the multi-cone diffuser lips on airflow diffusion is very significant.

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