水平式螺旋型地埋熱交換器之間歇運行-雙效模式性能分析

Investigations on the Thermal Performance of Horizontal Spiral-coil Ground Heat Exchanger under Intermittent Operations: Alternative Operation Mode

王榮德(Rong-De Wang)

指導教授 ： 陳希立

國立臺灣大學/工學院/機械工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102297

摘要

如何有效利用能源已經是全人類需要共同努力之目標，而淺層溫能即為近年受關注之再生能源之一，利用土壤的恆溫特性，能夠依需求作為加熱或冷卻之能量來源。為了有效利用淺層溫能，必須有高熱傳效率之地埋熱交換器作為媒介，本研究將針對水平式螺旋形地埋熱交換器，探討在間歇操作模式下對於此地埋熱交換器熱傳效率之影響。
本研究所埋設之水平式螺旋型地埋熱交換器為管徑20mm、厚度2mm、圓周直徑800mm、間距150mm、長度9m。實際進行60小時TRT實驗與8小時短期間歇實驗，以實驗結果與數值模擬軟體FLUENT之模擬模型進行驗證，再利用此模擬模型進行間歇式操作之分析。間歇式操作包含冷卻模式與雙效模式，冷卻模式將一日操作時間分為冷卻期與恢復期，雙效模式則分為冷卻期與加熱期。研究結果顯示，間歇操作相對於連續不間斷操作能夠大幅提升地埋熱交換器之效能，而不同冷卻期與加熱期(或恢復期)之時間比例(稱作間歇比)所提升的效益不同，其中間歇比2雙效模式、間歇比1雙效模式、間歇比2冷卻模式、間歇比0.5雙效模式於第七天時，相對於連續運行分別提升了159%、107%、91%、65%之效能。
根據本研究之結果，適當給予土壤恢復期或著適當比例之雙效運行，能夠有效提升水平式螺旋型地埋熱交換器之效能與持久性，未來實際應用於工程時，應當視不同使用需求將間歇效能作為設計之重要參數。

關鍵字

淺層溫能 ； 地埋熱交換器 ； 水平螺旋管 ； 間歇式操作

並列摘要

Seeking solutions to utilize the energy efficiently has been a main target that all human beings need to work on, and geothermal energy has also been a popular kind of regeneration energy which can be used as the energy source of heating or cooling depending on the requirements by the constant-temperature characteristics of soil. In order to utilize the geothermal energy efficiently, it is necessary to have a ground heat exchanger with high heat transfer rate as the media. This study focuses on the horizontal spiral-coil ground heat exchanger, investigating the impact of intermittent operation on the thermal performance of this ground heat exchanger.
In this study a horizontal spiral-coil ground heat exchanger is set up with 20mm tube diameter, 2mm tube thickness, 800mm spiral diameter, 150mm pitch, 9m length. A 60 hours TRT experiment and an 8 hour sort-term intermittent operation experiment is performed to collaborate the CFD model of FLUENT software by the experiment result. The thermal performance of the ground heat exchanger under different kinds of intermittent operation is investigated by the simulation of collaborated CFD model. The intermittent operation includes cooling mode (with cooling period and recovering period) and alternative operation mode (with cooling period and heating period). The results show that the intermittent operation significantly improves the performance of the ground heat exchanger comparing to the continuous operation, and different time ratio between colling period and heating period (or recovering period) which is called intermittent ratio, improve the performance differently. Alternative operation mode of 2 intermittent ratio, of 1 intermittent ratio, and cooling mode of 2 intermittent ratio, alternative operation mode of 0.5 intermittent ratio improves the performance at the 7th day comparing to continuous operation 159%、107%、91%、65% respectively.
According to the results of this study, by proper recovering period for soil or proper ratio of alternative operation mode can improve the performance and consistency of the horizontal spiral-coil ground heat exchanger effectively. It is recommended to consider the effect of intermittent operation as an important factor under different requirements when actual application on the engineering cases.

並列關鍵字

geothermal energy ； ground heat exchanger ； horizontal spiral-coil ； intermittent operation

參考文獻

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