冷樑送風系統氣流分佈模擬與氣流率(DR%)之分析研究

Abstract

This study is about the air distribution simulation of chilled beam systems. The temperature and velocity field were analyzed so to determine the draught rate (DR%) for the application of chilled beam air-conditioning. The common problems of the chilled beam system such as coil condensation were addressed as Taiwan is located in high temperature and humidity region. Therefore the chilled beam design requires appropriate consideration of outdoor air volume and humidity control so to prevent coil condensation. Pre-cooling before work hours is can be solution for the above problems. An actual case was analyzed with eQuest for cooling, then an accurate assessment of supply water temperature and flow rate can be calculated so to avoid the condensation. Different induction ratio (5, 4 and 3) and chilled beam spacing (3.6m, 3.8m, 4.0m and 4.2m) were investigated for the impact on the air distribution. The results show that different induction ratio has no obvious influence on the temperature distribution, and could be due to small difference in total air volume. The common point for all the cases is that the air velocity is higher and the temperature is lower at 0.1m height level than at 1.1m height level. The mean air velocity is at 0.1m is higher than 1.1m for about 30 ~ 60%. In addition for chilled beam spacing above 4.0m the airflow and temperature distribution is more even. Then higher comfort would be achieved. In ISO 7730 standard a thermal comfort indicator DR% is the discomfort level expressed as the percentage of people predicted to be unsatisfied. This value can be used in the design and construction of air-conditioning systems. For the air supply of chilled beam counter direction is better than parallel flow as it would result in lower DR%. The DR% is proportional to the mean air velocity that affects persons in a room. For the seven cases studied DR% at 0.1m level is higher than 1.1m level for about 47 ~ 93%. It can also be seen that the temperature and velocity fields are affected by the heat source. In summary for the cases studied the mean air velocity and DR% are mostly higher than the recommended value of the ISO7730 standard. The probable cause could be the cooling load is about 80m2 /W, greater than the nominal value of 70m2 /W.