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Analysis of A Ground Coupled Heat Exchanger. Brett Walsh Master of Engineering In Mechanical Engineering Rensselaer Polytechnic Institute at Hartford. Introduction/Background. Improve the efficiency of heating, ventilation and air conditioning (HVAC) systems.
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Analysis ofA Ground Coupled Heat Exchanger Brett Walsh Master of Engineering In Mechanical Engineering Rensselaer Polytechnic Institute at Hartford
Introduction/Background • Improve the efficiency of heating, ventilation and air conditioning (HVAC) systems. • A ground coupled heat exchanger can be used in either a heating or cooling mode by taking advantage of a “near constant” ground temperature.
Problem Description • Analyze a ground coupled heat exchanger in an effort to optimize an already efficient design. • Analysis will be performed for a ground coupled heat exchanger that utilizes the following • Open and/or Closed loop • Single or multiple passes • Multiple fluids • Calculations were performed to determine the required length of underground pipe based on a specified outlet temperature with varying inlet temperatures.
Methodology/Approach • This study will use an analytical and computational approach to analyze a ground coupled heat exchanger. • Heat transfer analysis will involve the use of the following equations: • Conservation of Energy • Heat Transfer Rate Equation • As well as, an evaluation of the total thermal resistance between the two fluids (i.e., between the air and/or ethylene glycol and the ground).
Methodology/Approach • The two common methods: • Log Mean Temperature Difference (LMTD) • Effectiveness-NTU (ε-NTU) • LMTD method will be used to optimize the various ground coupled heat exchangers designs and analyze their efficiency.
Resources Required • The resources required for the complete of this project are including, but not limited to, the use of the following textbooks: • Introduction to Thermodynamic and Fluids Engineering • Convective Heat and Mass Transfer • Fundamentals of Engineering Thermodynamics • Transport Phenomena • Microsoft Office and COMSOL Multiphysics will be used for analysis, post processing, and compilation.
Analytical Analysis • The Open Loop Ground Couple Heat Exchanger draws outside air underground to be heated or cooled, depending on the temperature, to a temperature of 55°F. The length of pipe required to achieve an outlet temperature of 55°F for varying inlet temperatures.
Computational Analysis • Computational analysis was performed at 4 different temperatures for air and ethylene glycol. Analysis was performed at 4.0, 50, 90, and 95°F (-15.54, 10, 32.75, and 34.9°C) for air. Similar analysis was performed for ethylene glycol at 54.04, 54.129, 55.127, and 56.39°F (12.245, 12.294, 12.849, and 13.547°C). The specific temperatures above were used since they are the maximum and minimum temperatures for both the open and closed loops.
Results • The goal of this project was to have a complete analysis of a ground coupled heat exchanger that utilizes an open and/or closed loop, that is either a single or multiple pass heat exchanger and that uses of different fluids in the system. Analysis was performed to determine what is the optimal ground coupled heat exchanger design is. • Based on the results of the analysis, a closed loop ground couple heat exchanger with ethylene glycol and a secondary heat exchanger between the ethylene glycol and air, achieved the required outlet temperatures for both ethylene glycol and air. The temperatures were accomplished using the least amount of pipe.
