下氣窗對小學普通教室熱舒適性之改善策略模擬研究

A Study on the Thermo-comfortability of School Classroom Influenced by the Lower ventilative window

陳玟秀(WEN- HSIU CHEN)

指導教授 ： 胥直強

國立臺北科技大學/設計學院/建築與都市設計研究所/碩士(2008年)

https://doi.org/10.6841/NTUT.2008.00119

摘要

台灣中小學的普通教室平面單元為日治時期發展而來，早期日人為因應台灣熱帶氣候環境，所建造之學校校舍在採光窗下普遍設有下氣窗，部分光復初期建造之校舍也有此設置，但其後所建之普通教室卻不復見此種開口部設計。學生一天有三分之ㄧ以上的時間在學校，而在校的絕大部分時間都在教室內，故舒適健康的教室環境是非常重要的。部分學校採用的「分離式冷氣」並無考量到換氣問題，反而造成室內空氣品質差惡化的健康問題。所以如何使教室利用自然通風達到良好的舒適性就成為重要課題。
本研究以小學普通教室為研究對象，選定的「龍安國小」案例教室位於1樓邊間，空間面寬940㎝、淨深798㎝。該教室兩側採光窗戶為橫拉窗（高230㎝×寬95㎝），單邊走廊、前門為單開門（250㎝×90㎝），後門為雙拉門：（250㎝×165㎝），教室內有黑板、課桌椅、書櫃、講桌、老師辦公桌椅、掃地用具櫃等家具。
國內目前對於自然通風換氣之研究，多採用「現場實測」、「實驗室足尺實驗」、「風洞實驗」與「CFD模擬技術」等方法探討。本研究因案例教室開窗現場狀況與研究時間的限制，故利用「現場實測」掌握實態，並採用「CFD模擬」了解下氣窗開口因子對室內氣流之影響。本研究操作方法與步驟如下:
一、藉由「現場實測」掌握外氣環境、走廊環境、室內環境等三者之間關係，進而建置代表性之教室CFD實態模型。
二、以現場實況與CFD數值模擬結果比對，確定該工具的準確性與信賴度。
三、利用該模型作為自然通風改善室內舒適性策略之預測平台，進行「下氣窗」1.進、出風口大小2.開窗方式3.開窗位置4.開窗型式等之變化模擬，並提出最適的改善策略。
四、以案例教室「原始開窗方式」的熱舒適狀況為基準，依照改善策略模擬調整前後之通風狀況，以檢驗其改善效果。
研究結果:
ㄧ、下氣窗開口部因子之發現（外氣風速設定0.5m/s）
（一）開啟下氣窗：有助於室內氣流均佈，但呼吸帶氣流減弱。下氣窗在開啟後與教室「原始開窗方式－無下氣窗」比較，其0.4m高程風速明顯提升72％，但呼吸帶高程降低5.8％；2.1m高程降低5.5％。
（二）進、出風開口大小：進風口「大」比「小」在室內0.4m高程處之風速高出0.16m/s；而在呼吸帶以上高程處：進風口大小幾無影響，彼此間最大相差不超過0.08m/s。
（三）開窗方式：窗戶「全開」的方式其室內氣流較為均佈，且能維持氣流強度到達出風口，並有助於減少室內熱量累積。在「不開採光窗」的狀態下，開啟「上、下氣窗」之開窗方式，也能有效減少燈具與人體熱量累積。
（四）開窗位置：
1.「分段式」開口有助於提升室內風速，其風速比未採用分段式開口最大可高出0.23m/s。且與「原始開窗-無下氣窗」情況做模擬比較，其0.4m高程風速明顯提升61.2％；呼吸帶高程提升5.1％，但2.1m高程降低0.4％(此高程改善並不明顯)。
2.「靠牆外側」之「下氣窗」入風口風速達到0.4~0.49m/s；「靠牆內側」者為0.15~0.47 m/s；「靠牆中心」者為0.3~0.42 m/s，顯示開窗位置明顯影響室內氣流。且與案例教室之「原始開窗-無下氣窗」情況做模擬比較，其0.4m高程風速明顯提升72％；呼吸帶高程提升7.5％；2.1m高程提升0.6％(此高程改善並不明顯)。
（五）開窗型式：採用「橫拉」的下氣窗，室內氣流均佈狀況較其他方式佳。
二、下氣窗之通風效能策略
外氣風速隨著不同的氣候隨時改變，故本研究提出：（1）當外氣風速低、提升室內風速之策略及（2）當外氣風速高、改善風擊之策略。以案例教室「原始開窗方式－採光窗、上氣窗均開啟」的熱舒適狀況為基準，模擬結果發現：
（一） 下氣窗採取「開窗方式－全開」、「開窗位置－分段式、靠牆外側」、「開窗型式－橫拉窗」可有效提升室內舒適性。當外氣風速為0.5m/s，其室內風速比「原始開窗」情況最高提升到0.4m/s。0.4m高程風速明顯提升71.6％，呼吸帶高程提升7.5％；2.1m高程提升0.78％(此高程改善並不明顯)。當外氣風速為1m/s，其室內風速比「原始開窗」情況最高提升到0.79m/s。且人體活動範圍風速均能達到0.2m/s以上。
（二） 「開窗方式為全開」、「開窗位置-分段式、靠牆中心」、「開窗型式-橫拉窗或中央橫軸旋轉窗」之模擬結果顯示，當外氣風速過大時，採取下氣窗可有效降低呼吸帶風速，減少人體及工作面之風擊、提升舒適性。當外氣風速為2m/s時，室內靠入風口處之各高程測點風速均高於室內風速上限值1m/s，但呼吸帶風速僅高於上限值0.045 m/s（橫拉窗）與0.037m/s（中央橫軸旋轉窗），此數值對於人體感覺並不明顯。
唯當外氣風速為4m/s時，無論何種開窗方式均無法有效降低室內風速，且會在呼吸帶產生明顯高於1m/s之風速。

關鍵字

下氣窗 ； CFD數值模擬 ； 熱舒適性 ； 教室通風

並列摘要

The plan of classroom of junior high and elementary schools in Taiwan were developed from Japanese colonial period. In the early times, the classroom built by the Japanese regularly had Lower ventilative window under Daylighting window due to the tropical weather in Taiwan. Some of the dormitories built during early Taiwan’s retrocession also followed this design. However, most of the classrooms were not built in this way afterwards. Students spend one third of their days in school, and most of time are in classrooms. Therefore the comfortability of classrooms is significant. Regardless of the air circulation issue, some schools use split type air conditioners, causing poor air quality that leads to health problem. So, how to use natural air circulations to reach better comfortability in classrooms becomes an important issue.
This study fucuses on the classrooms of elementary schools, taking Lon-An Elementary School as a case. The classrooms in that school are located in first floor with wideth of 940 cm and length of 798cm. The classroms are with sliding windows (230(H) x 95 (W) cm), one hallway, front door is a conventional door(250㎝×90㎝), back door is a sliding door （250㎝×165㎝）. There are blackboards, chairs, desks, sleves, lecterns and cleaning tools.
The studies on ventilation of a building in Taiwan mostly adopt ” field study,” 「full-scale experiment」、「wind tunnel test」and “CFD simulation technique” as methodologies. Due to the limited time and the open-window classrooms in this case, this analysis applies “field study” to precisely monitor the condition in classrooms and use “CFD simulation” to understand the influence of Lower ventilative window openings on the air circulation in classrooms. The procedures are stated below:
A. Through field study, to monitor the connections between the outdoors environment, hallways and indoors surroundings to furtherly establish the CFD simulation of represented classrooms.
B. Based on the situations of the classrooms and comparisons of CFD statistics to ensure the credibility and reliability of the findings in the case.
C. By using the mould as standards to see the improvement of natural air circulations on the indoors comfortability and to simulate the 「Lower ventilative window」a. the sizes of inlet and outlet opening, b. ways of opening windows, c. the locations of windows, d. types of windows and thus to propose the best suggestions to better the environment in classrooms.
D. Taking the comfortability of the studied classroom as standard, to adjust the air circulation according to the improvement strategies.

Study Results:
I. The findings of Lower ventilative window openings （wind speed is set at 0.5m/s）
A. Opened Lower ventilative window: this helps the air circulation in classrooms but air velocity of human breathing zone decreases. Comparing the classroom with opened Lower ventilative window and that without Lower ventilative window, the air velocity at 0.4m height increases at 72% whereas breathing zone gets lower at 5.8％ and 2.1m height reduces at 5.5%.
B. The sizes of inlet and outlet opening: under 0.4m height wind speed, in the rooms with windows of large inlet opening , the wind speed is 0.16m/s higher than those with small inlet opening. When the height is above breathing zone, the sizes of inlet opening do not case any differences. The biggest difference between these two sizes is no more than 0.08m/s.
C. The way of opening windows: Wide-open windows lead to better air circulations in classrooms and it helps maintain the flow of air getting to outlet opening, which decreases heat accumulation in classrooms. Under the condition of without Daylighting window, opening high-low ventilative windows can also effectively reduce the heat accumulation from lights and human bodies.
D. The location of Windows:
a. 「separate opening mode」 helps to increase indoors wind speed and its wind speed is 0.23m/s higher than the rooms without「separate opening mode」. Besides, comparing with rooms without Lower ventilative window, the air velocity at 0.4m height raises at 61.2%, breathing zone at 5.1% but 2.1m height reduces at0.4% which is not an obvious change.
b. In the inlet opening of Lower ventilative window next to the outer side of walls, the wind speed reaches 0.4~0.49m/s, the speed is 0.15~0.47 m/s in the inner side of walls and it is 0.3~0.42 m/s in the center of walls. This shows the locations of windows greatly influence the indoors air circulation. Comparing with the studied classrooms without Lower ventilative window, the air velocity at 0.4m height obviously raises at 72%, breathing zone at7.5% and 2.1m height increases at 0.6% (this is not an obvious change).
E. Window Style: In the room with Lower ventilative window of sliding window, the air circulations are better.
II. The efficiency Strategies in air circulation of Lower ventilative window
Outdoors wind speed always changes with climate. Therefore, this study proposes: a. when outdoors wind speed is low, the indoors wind speed needs to be raised up. b. when outdoors wind speed is high, air draft needs to be prevented. Taking the studied classroom with opened Daylighting window、higher ventilative window as a standard, the results of simulations are stated below:
The indoors comfortability can be effectively upgraded when the Lower ventilative window is wide open, located inner side of walls and designed as sliding windows. When outdoors wind speed is 0.5m/s, the indoors wind speed raises to 0.4/ms, compared with the original opened windows. The air velocity at 0.4m height increases at 71.6% and breathing zone gets up at 7.5％；2.1m height raises at 0.78％(this change is not obvious.).
Under the condition of wide opened windows located in the center of walls and designed as sliding window or pivoting window, the result of simulation shows when outdoors wind speed is high, Lower ventilative window can effectively slows down the air velocity at breathing zone, decreasing its direct impact on people and increasing comfortability. When the outdoors wind speed is 2m/s, air velocity at 0.4m、1.05m、2.1m height at the inlet opening is higher than the max. of indoors wind speed, 1m/s, but the velocity at breathing zone is only higher than 0.045 m/s（sliding window） and 0.037m/s（pivoting windows）. These statistics are not obvious changes to human bodies.
When the outdoors wind speed is 4m/s, no matter which kinds of windows cannot effectively lower down the indoors wind speed and it leads to high wind speed in breathing zone.

並列關鍵字

Lower ventilative window ； CFD simulation ； Thermo-comfortability ； classroom ventilation

參考文獻

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