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Publication Date

2022-5

First Advisor

Denise McKahn

Second Advisor

Judith Cardell

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Engineering

Keywords

geothermal, dynamic, modeling, renewable energy, sustainability

Abstract

A two control-volume with 10 states model was presented in MATLAB and Simulink for studying the heat transfer process of a coaxial geothermal heat exchanger at Smith College, Northampton, Massachusetts. Mass and heat transfer governing state equations for each control volume are derived using the conservation of energy. This quasi-2D control oriented model takes the mass flow rate, the inlet temperature of the working fluid as well as the undisturbed ground temperature at different depths as inputs, and generates simulations of working fluid temperature at 200ft, 400ft, 600ft, 800ft, and 1000ft along with the depth of the heat exchanger as outputs. An experiment was conducted to record the underground thermal dynamic behaviors by first turning off the heat pump for a period of time and then turning it back on, resulting in the system flow rate change. The calibrated Distributed Temperature Sensing (DTS) readings were recorded and collected to show the static water temperature change over time as the operational data for model parameter tuning purposes. Water temperature changes over time at five different depths (200ft, 400ft, 600ft, 800ft, and 1000ft) were plotted and denoted as operational data in the model. Parameters were calibrated based on physical properties and heat transfer coefficients were then manually tuned to explore the model fidelity. Due to the lack of a quantified ground hysteresis temperature profile, the model fails to model both transient and steady-state responses at all five depths of the borehole well. Future works are recommended as integrating a new control volume to capture the undisturbed ground temperature dynamics which leverages consecutive heating and cooling operation impacts, and adding a real-time working fluid flow rate monitor to improve model fidelity.

Rights

©2022 Xinyue Zou. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

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