Numerical simulation of room airflow using different types of ventilation methods

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Numerical simulation of room airflow using different types of ventilation methods

 

Author: Leung, Chi
Title: Numerical simulation of room airflow using different types of ventilation methods
Degree: M.Eng.
Year: 2011
Subject: Ventilation.
Air flow -- Measurement.
Office buildings -- Heating and ventilation -- China -- Hong Kong.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xiii, 114 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2449804
URI: http://theses.lib.polyu.edu.hk/handle/200/6408
Abstract: The traditional mixing ventilation, displacement ventilation (TDV) and under-floor supply air-conditioning (UFAC) systems are the most common mechanical ventilation nowadays. Although TDV is widely used in European country, traditional displacement ventilation and under-floor supply air-conditioning system are not commonly used in Hong Kong due to inadequate large scale experimental data for the performance of displacement system in Hong Kong. This study provide preliminary simulation data for further on-site experiment in Hong Kong office. In this study, the computational fluid dynamic (CFD) simulation program was employed to study the air flow of different ventilation methods in a simulated typical Hong Kong office. The thermal comfort of different ventilation in high cooling load density office was investigated by using CFD program code Fluent. The model with different supply air velocity was introduced to examine the performance of different ventilation methods in Hong Kong condition. The vertical temperature difference, PPD and PMV were employed to examine the thermal comfort of different ventilation methods. The results showed that TDV and UFAC can provide generally higher thermal comfort than MV. MV showed high draft risk due to high indoor air velocity and high air velocity under the diffuser. For TDV and UFAC with proper design still can provide acceptable thermal comfort in high cooling load environment The numerical study showed that the performance of TDV and UFAC are highly affected by the supply air volume and supply velocity. The high draft risk might appear around the floor diffuser. In order to maintain the low supply airflow, the bigger diffuser units were required for these ventilation methods. However, the high supply airflow was required to maintain the vertical temperature difference. Therefore, the balance between the supply air volume and temperature is very important for UFAC. TDV offers the high flexibility on high cooling load environment. The indoor velocity and temperature are unevenly distributed in the room. However, the relatively high air velocity was shown in the floor level. The draft might appear when the supply air volume further increase. A good system design is very important for tradition displacement ventilation system. In high cooling load condition, all these ventilation method required high supply air volume to maintain the desirable indoor environment. The draft risk and vertical temperature different are the most significant reason which causes the thermal discomfort. In order to maintain the low supply air velocity, the bigger diffuser was required for tradition displacement ventilation and under-floor supply air conditioning system. Despite of system cost, both TDV and UFAC showed the high flexibility in the office with Hong Kong configuration.

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