外殼晝光利用對空調及照明耗能影響之研究

Abstract

台灣身處在亞熱帶的地區，全年強烈的直達日射及熱季較長的情況下，為了解決建築室內環境的高溫，需要消耗相當大量的空調能源。因此，常見的建築外殼設計策略有增設外遮陽板、縮減開口率、改變使用的玻璃材質等，藉由阻擋或減少直射進入室內的輻射熱來降低空調耗能，但是，也因此阻絕了部分晝光進入室內，而可能需要額外的人工照明以彌補照明量，如此一來，不但造成照明耗能增加，照明所連帶的發散熱也會造成額外的空調能源消耗。 除了建築能源的考量外，室內環境中的視覺舒適度也是需要被考慮的。過去有研究指出，視覺舒適度對人員的工作效率和學習效率是有正面影響的，而良好的外殼設計除了有助於提升視覺舒適度，也可以避免過亮晝光所帶來的不舒適感，所以，本研究會同時探討外殼設計對建築能源及視覺舒適度的影響。 為了深入了解不同外殼設計所致影響，本研究探討了不同室型、遮陽板設計、玻璃材質選用等因子，透過了光環境模擬軟體DAYSIM和建築能源模擬軟體EnergyPlus，對全因子配列的1458個不同外殼設計辦公空間，分別進行光環境和建築能源的模擬，而後進行結果數據的ANOVA(變異數分析)統計分析和相關探討，以得到各外殼設計策略的影響效果和挑選最佳的外殼設計組合。由於建築能源和視覺舒適度屬不同種類指標而難以挑選出最佳方案，因此，本研究透過引用文獻的人員生產力計算公式，將室內環境品質轉換為人員工作效率，以進行經濟上的評估和比較。 研究成果顯示，視覺舒適度和建築節能大致上呈現正相關，若提升可利用晝光比率(Useful Daylight Index, UDI(300-2000))，因晝光利用而帶來的照明節能和因發散熱減少的空調節能都會相當顯著；外殼設計策略上，室型、開口率和玻璃材質都有相當大的影響效果，然而，這些因子在建築能源間或與視覺舒適度間會出現需要權衡的情況，如開口率40%時相較總平均值有1.7 kWh/m2.a的空調節能效果，但也有-1.4%的UDI(300-2000)負效果，因此必須謹慎的挑選因子的水準；三種室型之中，具有最佳視覺舒適度及建築節能的是寬長型室型，因為採光較易而容易提升晝光品質，也能因此節省下建築能源，若和全開燈和大開窗的基線建築相比，在UDI(300-2000)最多可改善33.4%，在UDI(>2000)最多可改善62.6%，在建築能源最多可改善56.9%(空調為33.8%，照明為23.0%)。

In Taiwan, which is in the subtropical area in Asia, there is much intensive beam radiation among whole year, and the hot season is longer than cold one. To resolve the problem of indoor high temperature, a large amount of HVAC energy needs to be consumed. Thus, some common strategies for building envelope design are exterior shading device, reducing the WWR (Window to Wall Ratio), or changing the glazing types. By blocking or reducing part of the radiation heat from outdoors, it helps to save more HVAC energy consumption. However, those strategies also hinders some daylight from entering into the room, therefore increasing additional artificial lighting to compensate for the lack of lights. So, lighting energy increases, and the heat gain from the lighting system also causes additional cooling energy. In addition to consideration of building energy, visual comfort in indoor environment needs to be considered as well. Previous studies have pointed out that visual comfort have positive impact on both work and learning efficiency. A well designed building envelope can both enhance visual comfort and avoid the discomfort caused by excessive daylight. So, the impact of different building envelope designs on both building energy and visual comfort are conducted in this study. In order to deeply understand influence of different building envelope design, this study investigated several factors, such as room shapes, shading device designs, glazing types, and so on. Through daylighting simulation tool (DAYSIM) and building energy simulation tool (EnergyPlus), totally 1458 office cases with different envelope designs are simulated. Then, the simulation results were analyzed through ANOVA (Analysis of variance) and discussed so as to find out influence of each factor and some optimal building envelope designs. Since building energy could not be compared with visual comfort directly, it’s hard to find the best one among all cases. Hence, according to a formula from a citation, which can convert Indoor Environment Quality (IEQ) index into human productivity, in order to evaluate and compare each case on an economic basis. The simulation results shows that visual comfort is positively correlated with energy saving benefits. If UDI (Useful Daylight Index) is enhanced, the energy-saving benefits from less lighting demand and decreased HVAC energy due to less heat gain from lighting device will be significant. Among all factors of building envelope design, room shape, WWR, and glazing types are the most influential. However, sometimes there are compromise between building energy and visual comfort in these factors. For example, WWR of 40% has a mean effect of 1.7 kwh/m2.a, which is compared to the total average of performance, but it also has negative impact of -1.4% on UDI(300-2000). As a result, it’s necessary to carefully pick proper level of the factor. Among the three room shapes, the wider one has the best visual comfort and energy-saving benefit. Because it’s easier to utilize the daylight and improves the quality of indoor daylight, more building energy could be saved. If compared to baseline, which is set as light-on during workhour and WWR of 80%, UDI(300-2000) could be improved by 33.4%, and UDI(>2000) could be reduced by 62.6%. In terms of building energy, it could be reduced by totally 56.9% (33.8% for HVAC energy, and 23.0% for lighting energy).