本研究以電腦套裝軟體TRNSYS來模擬計算自然循環面蓋式太陽能熱水系統在國內之運作，以經典氣象年來作為氣象資料，將台灣與離島共30個氣象站進行模擬並計算輔助電熱棒所需電量，藉此估算具參考價值的太陽分率估算結果，期望對於國內使用太陽熱水器之節電量有更多了解。
本研究先模擬在臺南歸仁校區的太陽能熱水系統，對TRNSYS內參數設定進行驗證，據此將系統效率斜率固定在5.953 W/m2.K，並設定儲水桶夜間熱損失，日累積輻射量之大小分布在本研究中區分為低(日射量≦ 13 MJ/m2) 、中( 13 MJ/m2 < 日射量≦ 20 MJ/m2)、高(日射量 > 20 MJ/m2)，三個全日空輻射量情況來討論。歸納出全日空輻射量越多，效率截距則需要設定越大，而效率截距由全日空輻射量多寡來決定，低全日空輻射量效率截距為0.71，中全日空輻射量效率截距為0.79，高全日空輻射量效率截距為0.83，做此設定值所得運算結果與實際儲水桶溫度變化最為相近。
本研究使用條件為夏季(4月至9月)洗澡水溫40度，冬季(10月至3月)洗澡水溫45度，洗澡前儲水桶若未達到設定溫度55度的話，則會開啟輔助加熱棒。TRNSYS模擬全國30個氣象站的年耗電量(含電熱損失5%)，北部都會區(臺北、板橋與新竹)平均年耗電量為1251度電，受到東北季風影響最明顯的地區為基隆，年耗電量為1494度電。中部地區(臺中、梧棲與嘉義)平均年耗電量為735度電。南部都會區(臺南與高雄)因緯度較北中部低，日輻射量較高且環境平均溫度也高，平均年耗電量為509度電。東部地區(宜蘭、蘇澳、花蓮、成功、台東與大武)平均年耗電量為1021度電，宜蘭、蘇澳與花蓮則是也會受到東北季風的影響，年耗電量平均為1277度電。離島部分，平均年耗電量為1198度電。高山地區(玉山、阿里山與日月潭)平均年耗電量為2233度電。整體來看臺灣，本島的東北部年耗電量高於中南部。
台北與板橋的年度太陽分率落在69%，竹子湖與鞍部則是在58%左右，原因為氣象站位於山區易形成雲霧導致日射量低，環境溫度也低。中部地區來看，台中與嘉義的年度太陽分率落在84%，梧棲因靠海線，太陽分率為78%。高雄、恆春與恆春的年太陽分率落在87%。東部地區年度太陽分率最小的為宜蘭與蘇澳，宜蘭為69%、蘇澳為68%，其餘落在72 ~ 82%。馬祖的年度太陽分率為66%，為離島地區最小的，其餘離島大多落在70 ~ 80%。玉山與阿里山的年度太陽分率落在58% 到59%間，為全台最小。整體年度太陽分率來看，呈現本島中南部高於本島東北部。

In this study, TRNSYS software was used to simulate and calculate the performance of a natural circulation flat-plate solar water heating system in Taiwan. The meteorological data followed that for a typical meteorological year. Thirty weather stations located in Taiwan and in the outlying islands were simulated in order to calculate the electricity use for the auxiliary heating rods. This estimate was used as the solar fraction estimation result in the form of a reference value in an attempt to clarify the degree to which domestic solar water heaters save electricity.
Performance of a solar hot water system was simulated at Kuei-Ren campus of National Cheng Kung University in order to verify the parameter settings in TRNSYS. The system efficiency slope was fixed at 5.953 W/m2.K, and it was necessary to set the night heat loss for the water storage tank and confirm the daily cumulative global radiation. In this study, the daily cumulative global radiation was divided into low (radiation ≦ 13 MJ/m2-day), medium (13 MJ/m2-day < radiation ≦ 20 MJ/m2-day), and high (radiation > 20 MJ/m2-day). After simulating the daily cumulative global radiation at the three levels under consideration, we concluded that the efficiency intercept can be determined based on the amount of global radiation. The low global radiation efficiency intercept was 0.71; the medium global radiation efficiency intercept was 0.79, and the high global radiation efficiency intercept was 0.83. The calculated results obtained at these setting values were the closest to the actual temperature changes in the water storage tank.
In this study, the bathwater temperature was set to be 40°C in summer (April to September), and 45°C in winter (October to March). If the water storage bucket did not reach the set temperature of 55°C at the appropriate time, this turned on the auxiliary heating rods. The overall annual solar fraction performance showed a trend indicating that the central and southern parts of Taiwan have higher solar fractions than the northeastern parts. The results of a linear regression conducted on the twenty-eight weather stations indicated the values comparing the annual power consumption with the annual solar fraction, excluding Yushan and Alishan. The linear regression was performed using an equation in the form y = - 5078 x + 4902, and the R-squared value was 0.9758. It was observed that a larger solar fraction results in lower annual power consumption.

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