Optimization through CFD analysis of a Coanda effect enhanced novel HVAC diffuser

Abstract

The need for a convenient environment for humans is the driving cause of coming up with the best thermal comfort conditions possible.

There are major factors influencing room air distribution which requires the knowledge for a proper selection of the best design that will serve the need, taking into account the importance of energy consumption optimization in delivering intended thermal levels.

Modern fluid mechanical problems would be impossible to solve without the use of computational fluid dynamics (CFD). As we have seen, the scope of analytical solutions to fundamental equations of fluid mechanics is very limited and, once a more difficult geometry is encountered, we usually have to choose a given numerical method for obtaining a solution.

In this work CFD analysis software is used to investigate flow behaviour of air used in cooling and heating a room with the use of Coanda effect, which is "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."

Air-conditioning significantly leads to an excessive consumption of energy in buildings. The overall efficiency of air-conditioning systems must be demonstrated and measured to prevent needless energy wastage. This work offers the results of a finished examination to assess the performance of a proposed new design at the end cycle of an air-conditioning system.

The main goal of this work is to determine whether the proposed design will outperform the commercial cone design of diffusers in air distribution, thus; achieving better energy consumption and thermal comfort using the same input parameters. Through introducing a proposed diffuser that delivers airflow horizontally, and placing the design with a commercial design, which is the Multi-cone diffuser, where the flow is ejected at a certain angle a set of parameters and conditions were studied throughout this work, the results of the performance and thermal comfort analysis of the proposed diffuser came out to be interesting and could compete with the Multi-cone diffuser, specifically in cooling situations. These results is presented, and a comparison is made with another design of diffusers, the well known commercial cone diffuser. Room layout and analysis were carried out using ANSYS software.

The Multi-hole diffuser that ejects horizontal jets and promotes Coanda effect (having the jets “hanging” longer to the ceiling) although it is desirable for cooling, it is not an ideal choice for heating since the hot air stays near the ceiling and causes strong stratification. implying that diffusers with large inclination angle towards the ceiling create less efficient mixing in the horizontal direction and should be optimized whether by increasing the airflow velocity of directing the outlet flow to be ejected with a specific angle.

ASHRAE Standard 55's thermal comfort several factors of building occupants were used as the decisive tool for diffusers performance.

An extensive analysis of the new design of the air diffuser that is used to distribute cooling and heating inside an enclosed area will be carried out, the steps of the work will include; designing the diffuser with the use of CAD software, and implementation of a air supply inside a virtual room to work the air distribution through the new diffuser, and the airflow of the diffuser, and whether it will achieve a decent level of thermal comfort in cooling and heating, the work will determine the characteristic of the diffuser through both numerical and experimental work. The analysis will discuss thermal comfort and the different approaches that was made to evaluate it and its relation to the energy consumption that is used to achieve the optimal level of thermal comfort, and how is the design of the diffuser; which is the part that is responsible for distributing the air in the designated medium,affect the energy consumption directly and indirectly.