CFD SIMULATION OF COLD AIR SYSTEM IN ENCLOSED SPACES
Ahmed Ali Youssef Abo Ashour;
Abstract
Cold air systems have proven to offer economical and environmental benefits, and are found suitable for many applications. However, these systems did not spread because of the fear from cold draft formation leading to unaccepted indoor air conditions. The current study aims to evaluate the performance of cold air systems when used in enclosed spaces using Computational Fluid Dynamics (CFD).
A brief introduction is presented explaining theory, advantages, and disadvantages of cold air systems. Also, different factors and design considerations affecting human comfort are explained. A brief literature review of previous work in the field of cold air distribution systems and indoor flow simulations is presented as well.
The basic theory and governing equations of CFD are explained, and different turbulence modeling techniques are presented. The CFD code used in the current study is validated by comparing its results with experimental results found in the literature. Three validation cases are conducted to assess the accuracy of the CFD model and to evaluate several turbulence models when used for indoor simulations.
The flow of cold air was studied in a 2D room at different supply temperatures and velocities and at different sensible heat loads. The velocity field and the temperature distribution were analyzed and used to calculate the effective draft temperature. And hence, the comfort level was assessed using the air diffusion performance index, ADPI. The effect of each factor was studied independently and it was found that the supply temperature and velocity have minimum effect on the room conditions. The room thermal environment was uniform and satisfactory even at low supply temperature due to the good mixing of air inside the room. Reduction in supply temperature and reduction in supply velocity each causes limited enhancement on the ADPI. The main source of drafts inside the room was the heat flux from the floor. The velocities induced by the floor heat flux were much higher than those caused by the air jet. At lower thermal loads, the induced air velocity was weaker, and hence the ADPI values increased.
It was observed that air circulates in the room under the effect of natural convection with no air supplied to the room. As the rate of heat transferred by air increased, the air circulation and velocity increased as well. Air circulation and velocity were also enhanced when the percent of the thermal load concentrated in the floor was increased in the air conditioned room. Also, it was found that separating the air jet from the ceiling does not affect the jet attachment to the ceiling. Air jet when supplied far from the ceiling was still pushed upwards by the air circulating in the room causing it to attach to the ceiling.
A brief introduction is presented explaining theory, advantages, and disadvantages of cold air systems. Also, different factors and design considerations affecting human comfort are explained. A brief literature review of previous work in the field of cold air distribution systems and indoor flow simulations is presented as well.
The basic theory and governing equations of CFD are explained, and different turbulence modeling techniques are presented. The CFD code used in the current study is validated by comparing its results with experimental results found in the literature. Three validation cases are conducted to assess the accuracy of the CFD model and to evaluate several turbulence models when used for indoor simulations.
The flow of cold air was studied in a 2D room at different supply temperatures and velocities and at different sensible heat loads. The velocity field and the temperature distribution were analyzed and used to calculate the effective draft temperature. And hence, the comfort level was assessed using the air diffusion performance index, ADPI. The effect of each factor was studied independently and it was found that the supply temperature and velocity have minimum effect on the room conditions. The room thermal environment was uniform and satisfactory even at low supply temperature due to the good mixing of air inside the room. Reduction in supply temperature and reduction in supply velocity each causes limited enhancement on the ADPI. The main source of drafts inside the room was the heat flux from the floor. The velocities induced by the floor heat flux were much higher than those caused by the air jet. At lower thermal loads, the induced air velocity was weaker, and hence the ADPI values increased.
It was observed that air circulates in the room under the effect of natural convection with no air supplied to the room. As the rate of heat transferred by air increased, the air circulation and velocity increased as well. Air circulation and velocity were also enhanced when the percent of the thermal load concentrated in the floor was increased in the air conditioned room. Also, it was found that separating the air jet from the ceiling does not affect the jet attachment to the ceiling. Air jet when supplied far from the ceiling was still pushed upwards by the air circulating in the room causing it to attach to the ceiling.
Other data
| Title | CFD SIMULATION OF COLD AIR SYSTEM IN ENCLOSED SPACES | Other Titles | إستخدام ديناميكا الموائع الحسابية لمحاكاة أنظمة توزيع الهواء البارد في الأماكن المغلقة | Authors | Ahmed Ali Youssef Abo Ashour | Issue Date | 2014 |
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