冷樑送風系統氣流分佈模擬與氣流率(DR%)之分析研究

A Study on Air Distribution Simulation and Draught Rate (DR%) Analysis for Chilled Beam Air Supply Systems

莊士平(Shih-Ping Chuang)

指導教授 ： 蔡尤溪

國立臺北科技大學/機電學院/能源與冷凍空調工程系碩士班/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00290

摘要

本研究針對冷樑送風系統之氣流分佈模擬，分析其溫度、速度場以及DR%(氣流率)。此外冷樑(chilled beam)常見的問題，例如盤管結露問題，在地處高溫高濕的台灣言，冷樑送風系統在設計時需透過適當的外氣量控制與濕度控制來防止室內盤管結露。本文以實際案例透過eQuest軟體的熱負荷估算可準確評估送水溫度與送水流量，且使用上班前預冷運轉策略來置換室內高溫高濕的空氣，可避免上班後的冰水送水入冷卻盤管時所造成結露。
透過CFD軟體依不同誘導風比(IR5、4、3)、冷樑設置間距不同(3.6m、3.8m、4.0m、4.2m)，共設計出7種case來分析其不同參數配置對於氣流分佈的影響，本研究可看出在不同誘導風比(IR)下的溫度場差異不明顯，可能是侷限在假設條件之送風量差異不大所產生的結果。而每個case的共通點，水平面高0.1m相較1.1m風速較快且溫度較低，且平均速度方面水平面高0.1m相較1.1m高出約30~60%。另外在冷樑不同安裝間距，可發現在大於4.0m以上間距的氣流、溫度分佈較均勻；溫度分佈均勻相對的舒適度也會提升。
並且以ISO7730熱舒適之DR%(氣流率)指標來評估分析因風吹造成對人體之不舒適百分比，可作為設計者與施工人員參考的依據。冷樑出風口方向採對吹方式相較平行擺放有較低的DR%，而風速越高對DR%影響是成正比的，另外7種case在水平面高0.1m的DR％相較1.1m高出約47~93%，而且可以看出溫度場與速度場的分佈是受發熱源所影響的。綜述以上論點在平均風速以及DR%幾乎都大於ISO7730所建議的數值，可能是因為室內熱負荷約為80m2/W大於建議值的70m2/W。

關鍵字

冷樑 ； 冷卻樑板 ； 氣流率 ； 氣流分佈模擬 ； 誘導風比

並列摘要

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.

並列關鍵字

chilled beam ； chilled ceiling ； Draught Rate ； air distribution simulation ； Induction Ratio

參考文獻

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