台北能源筏式基礎熱交換之行為與分析

Abstract

台灣夏季炎熱，造成冷氣用電增加，供電量吃緊。此外，冷氣所產生的廢熱，也會導致周圍環境溫度增加，在台北造成熱島效應。能源基礎為新興的綠能源技術，為解決上述問題的其中一種解方。該技術是在地工基礎構造物內埋設地熱交換管，將冷氣製造的廢熱透過水傳輸，並使用地源熱泵驅動管內水持續循環。廢熱透過地熱交換管和基礎附近溫度較低的土壤進行熱交換，以有效降低冷氣使用時的能耗。本研究以COMSOL Multiphysics數值模擬進行熱交換分析，探討台北一處實際能源基礎案例。該案例選用能源筏式基礎，將地熱交換管埋設於筏基板中，地熱交換管總長達6720 公尺，共40迴圈。本研究旨在探討能源基礎對周圍土壤溫度分布的影響，並進一步評估地熱交換管形式及間距對熱能交換效率的影響。研究結果期望建議熱能交換效率最佳化的地熱交換管形式，以供工程實務設計參考。 本研究透過三維數值模型分析能源筏式基礎的熱交換行為，模擬結果顯示土壤溫度及管道出口流體的溫度在3週後達到穩定狀態，每日地源熱泵系統運作10小時，出口流體溫度隨著每日運行的週期變化，在地源熱泵系統開始與結束運作時，其出入口流體溫度的最大和最小溫差分別為7°C和4°C。地熱交換管對土壤溫度的水平影響距離約為地熱交換管寬度的1.6倍，表示地熱交換管對周圍土壤的影響距離很小，對鄰近建築物基礎與土壤溫度影響不大。參數研究結果顯示管道間距和排列樣式明顯影響熱交換效率，當管道間距0.1 m時，Meander和Loop管道樣式前後半部管道互相交錯排列過小的管道間距使出口流體溫度受入口流體加熱，由於鄰近管道的溫度影響，在管道間距0.1 m時的管道出口流體溫度高於管道間距1 m的結果；Snake和Swirl管道樣式則是前後半部管道分開，管道間距小不會使出口流體溫度受入口流體加熱，因此地熱交換管的管道長度越長，管道出口流體溫度最低。地源熱泵系統較傳統氣冷式空調系統每年節省約34 %的耗電量，相當於每年可節省約20176元的電費。

This study focuses on the investigation of the behavior of an energy raft foundation study in Taipei. The energy raft foundation was installed to provide heating and cooling to a 13-story and 3-basement residential building in Xindian district and it consisted of 40 loops having a total heat exchanger length of 6720 m. A 3D numerical model was established and validated against field measurements. The thermal response of the energy raft foundation, including soil and geothermal pipe temperature distributions, was investigated. A series of parametric studies were conducted to evaluate the effects of geothermal pipe spacing and patterns on heat exchange efficiency. The results from numerical simulations indicate the pipe outlet fluid temperature increased and decreased during the daily operation cycle. The maximum and minimum temperature differences between the inlet and outlet fluid temperatures were 7 and 4 °C at the beginning and the end of the operation, respectively. The horizontal influence distance of the soil temperature caused by the geothermal pipe was relatively short, approximately 1.6 times the width of the pipe loop, suggesting the geothermal pipe had little influence on the soil temperature of the adjacent building's foundation. The parametric study results indicate the combination of pipe spacing and pattern significantly influenced heat exchange efficiency. For the snake and swirl patterns (where the first and second halves of the pipe are separated), the pipe outlet fluid temperature was lowest at a pipe spacing of S = 0.1 m. For the meander and loop patterns (where the first and second halves of the pipe are alternately arranged one after the other), the pipe outlet fluid temperature at S = 0.1 m was higher than that at S = 1.0 m due to the temperature influence from adjacent pipes. Based on the findings in this study, an optimal design of the pipe configuration is discussed.