寶特瓶中空式綠屋頂隔熱降溫實驗分析

Abstract

由於傳統綠屋頂有高載重、不易更新或維護等缺點，本研究群因而之前開發了成本效益及維護彈性較高的水盆中空式綠屋頂(BHGR)。此研究進一步分析新開發的寶特瓶中空式綠屋頂(PHGR)的隔熱與散熱降溫效益。該綠屋頂建置於校內建築屋頂上，且以相等面積同時建置本研究群之前設計的水盆中空式綠屋頂及傳統薄層綠屋頂(GR)，連同一區裸平屋頂(CR)進行隔熱效益實驗，以比較空氣層對綠屋頂隔熱效益之影響。監測項目與前一研究類似，主要監測日照、氣象、土壤含水率、水位及溫度等，以記錄器儲存資料傳至遠端電腦。依據所收集資料，比較四個屋頂表面溫度、室內溫度與熱通量等之差異。亦推估此新型綠屋頂的U-value，並以一維熱傳公式估算與比較各綠屋頂節能效益。且延續並修改之前研究的水盆中空式綠屋頂能量平衡模式，使其適用於寶特瓶中空式綠屋頂、傳統薄層綠屋頂，並與水盆中空式綠屋頂、裸平屋頂進行比較分析。 經本研究實測，分析BHGR、PHGR、GR與CR，各綠屋頂皆具有隔熱散熱降溫效果，而BHGR與PHGR s在表面溫度與度時分析皆優於GR之表現依材料估算BHGR與PHGR的熱傳係數，假設較不通風(C)與較通風(V)情況下之U-values，BHGR-C、BHGR-V 、PHGR-C與PHGR-V分別為0.93、0.84、0.96以及0.86W/m2K。本研究所建置之GR在實驗屋頂之U-values為1.26 W/m2K。利用一維熱傳公式，BHGR、PHGR及GR在實驗屋頂的節能效益分別為5.1 ~ 5.4、4.7 ~ 5.0及3.8 kWh/m2/year，在一般屋頂則因隔熱效果較好，分別為2.4 ~ 2.6、2.2 ~ 2.4及1.6 kWh/m2/year。透過能量平衡模式分析，BHGR、PHGR、GR與CR可感熱比為10.3、13.8、22.3及21.6%，藉由比GR更多的蒸發作用，降低部份屋頂表面可感熱通量，亦轉換部份儲熱成為潛熱釋放，故可感熱比較CR及GR低。由於兩HGRs能藉吸水作用維持土壤含水率，而有較高潛熱比。兩HGRs與GR之差異在於蓄水容器的存在而出現的水蒸發熱通量、因綿條毛細吸水而維持在30%以上的土壤含水率及中空層的通風條件，增加了綠屋頂的散熱途徑及散熱量，但同時也增加了水的蒸發損耗量。

For several critical problems associated with the conventional green roof, green roof is currently not widely promoted in this country. Therefore, this research group had developed the Bucket hollow green roof (BHGR), a new green roof that is expected to be more cost-effective with great flexibility in maintenance. This study was initiated for evaluating the capability and effectiveness in reducing heat transfer and energy savings for the PET-bottle based hollow green roof (PHGR), a new green roof developed in this group. To carry out this study, a PHGR was installed on the roof of a campus building, and a conventional green roof (GR) and a BHGR were also installed. And a bare roof (CR) in a similar size was simultaneously monitored for comparing their thermal reduction efficiencies, including the effectiveness of the air layers created by both PHGR and BHGR. Similar to the previous study, data such as solar radiation, weather, soil volumetric water content, water level, heat flux, and temperature were monitored and the data were transferred via Internet to a remote computer in our research laboratory. Based on the data collected, the differences of four roofs for temperatures and heat fluxes in different levels were compared and analyzed. Also, the U-values of the roofs and the energy saving of applying the green roofs were estimated by the one-dimensional heat flux equation method. Energy balance models for PHGR and GR were developed by modifying the models previously developed for the BHGR and the CR. Comparative analyses were implemented based on the results obtained from the models. According to the experimental results for BHGR, PHGR, GR and CR, All green roofs can effectively reduce heat transfer. The performance of the BHGR and PHGR is superior to that of the GR in surface temperature and degree hour analyses. The U-values of the BHGR and the PHGR were estimated to be 0.93 and 0.96 W/m2K under ventilation assumption and 0.84 and 0.86 W/m2K under poor ventilation assumption. The U-value of the GR was estimated to be 1.26 W/m2K. The annual energy savings, as estimated by the one-dimensional heat flux equation, for the BHGR, PHGR and GR are 5.1 ~ 5.4, 4.7 ~ 5.0, and 3.8 kWh/m2, respectively. For the conventional roof with a better insulated layer, the annual energy savings are approximately 2.4 ~ 2.6, 2.2 ~ 2.4 and 1.6 kWh/m2. From the energy balance analyses for roofs, the sensible heats of the BHGR, PHGR, GR and CR are about 10.3, 13.8, 22.3 and 21.6% of the net radiation.