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. 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.

GCHE Loops

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, , , and 56.39°F (12.245, , , and °C). The specific temperatures above were used since they are the maximum and minimum temperatures for both the open and closed loops.

Computational Analysis

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.

Milestones/Deadlines DeadlineMilestone 9/30Complete Project Proposal 9/30Start COMSOL simuation 10/7Complete Open Loop – Single Pass Calculation for Air 10/9Complete Open Loop – Multiple Pass Calculation for Air 10/14Complete Closed Loop – Single Pass Calculation for Air 10/16Complete Closed Loop – Multiple Pass Calculation for Air 10/18Analyze/Compare Calculations for Air 10/20Post Process First Progress Report 10/21Complete First Progress Report 26-OctComplete Open Loop – Single Pass Calculation for Second Fluid 28-OctComplete Open Loop – Multiple Pass Calculation for Second Fluid 2-NovComplete Closed Loop – Single Pass Calculation for Second Fluid 3-NovComplete Closed Loop – Multiple Pass Calculation for Second Fluid 4-NovAnalyze/Compare Calculations for Second Fluid 11-NovComplete Second Progress Report 11/18Complete COMSOL Simulation 11/26Analyze/Compare COMSOL Simulation with Calculation Performed for the Two Other Fluids 12/2Complete Final Draft 12/16Complete Final Report