1. 1. Geothermal Heat Exchanger Group 7 Justin Brewer Thermal Model (Matlab) Ben Toline Fans and Contractors Kaitlyn Keen Pressure Drop (Flow Model) Ethan Smelcer Materials and Drafting Alexander Henry Cost Model Ali Alshamrani Materials and Research
2. 2. Design Earth Air Heat Exchanger Cool air by passing it through pipe(s) underground Air properties: 80F @ [1atm(14.7psia), 70% humidity] Earth composition: sand and soil mixture, 50/50 by volume Volumetric flow of 10,000 cfm Goals Lowest First Cost / Exchanger Capacity Shortest Simple Payback Period
3. 3. Design Variables Design Variable Min Increment Max Material PVC and HDPE Pipe Diameter 6 in 2 in 14 in System Length 10ft 10 ft 40 ft Columns 2 2 (25ft)/(pipe diameter) Rows 2 2 (Max Manifold Height)/(Pipe Diameter) X - Spacing (Pipe Diameter)/4 (X - Spacing)/2 (25 ft - Pipe Diameter x Collumns)/(Collumns-1) Y - Spacing (Pipe Diameter)/4 (Y - Spacing)/2 (Max Array Height - Pipe Diameter*Rows)/(Rows-1) Manifold Width changes with the array size Manifold Height changes with the array size Number of Blowers 1 1 5 Blowers in Parallel 1 evenly divided 5 Blowers in Series 1 evenly divided 5
4. 4. Pressure Drop Model Assumptions: Incompressible flow Constant volumetric flow rate Even flow through each pipe Method: Losses found at each section Total loss over system System curve generated Blower curve solutions (Newton Raphson Method)
5. 5. System Losses Minor Losses: Due to sudden expansion Due to sudden compression Due to reducers Major Losses: Due to friction losses along pipes and ductwork
6. 6. System Curve vs. Fan Curves System Curve: Defines Total Head Loss of the System over a range of flow rates
7. 7. System Curve vs. Fan Curves System Curve: Defines Total Head Loss of the System over a range of flow rates Blower Curves: Performance
8. 8. System Curve vs. Fan Curves System Curve: Defines Total Head Loss of the System over a range of flow rates Blower Curves: Performance Newton Raphson Used to solve for blower performance across system curve
9. 9. Heat Transfer Model Considerations: 3 Dimensional Transient Heat Transfer of Internal Flow Neglect pipe wall thickness? Effect of pipes on each other (i.e. spacing) Assumptions: Soil has negligible heat transfer in the lengthwise direction of the system Pipes modeled as square in Cartesian grid Equivalent resistance used to account for pipe conductivity
10. 10. Heat Transfer Model Finite Difference Method (Implicit): Nodal mesh set up Pipes within clustered grid Equivalent conductivity
11. 11. Heat Transfer Model Solution: Implicit method solves heat equations simultaneously Large time step is allowed Little heat penetration into the soil Conduction boundary 6 ft from pipe array
12. 12. Heat Transfer Model Solution: Oscillatory heat gain Steady state approached
13. 13. Heat Transfer Model Solution: Oscillatory heat gain Steady state approached Oscillatory heat transfer
14. 14. Matlab Simulation Shot Gun Approach All design combinations analyzed (Total of 68,000+ combinations) Workable Solutions fell between 8000 to 12000 cfm (Total of 6,000+ workable solutions) Thermal Model analyzed for only workable solutions Over 20 hours of computational time between 3 computers
15. 15. Cost Model Method: Found various prices for different materials (piping, sheet metal, duct, etc.) and compiled them Found labor prices and compiled them Used various combinations to evaluate first cost ratio and payback period
16. 16. Cost Model (Cont.) First Cost to Total Heat Transfer Ratio: $ = The Cost Ratio takes into account the total material cost and labor cost for given solutions The first cost is then divided by the heat transfer, E, of that system
17. 17. Cost Model (Cont.) Simple Payback Period: = $ $ $ The payback period is defined as the total first cost divided by the annual operating value minus the annual operating cost This needs to be as small as possible This is achieved by increasing the operating value while decreasing the first cost and the operating cost
18. 18. Optimization Cost model takes place in Excel Data from the Matlab program is exported to Excel Data is then processed, filtered and sorted
19. 19. Optimization Optimization Curve (mesh) in 3D space First Cost / Exchanger Capacity
20. 20. Optimization Optimization Curve (scatter) in 3D space Simple Payback Period
21. 21. Final Design First Cost / Exchanger Capacity 3 Blowers, 10 columns with 4 rows of pipes. Blower Model Industrial Fans Direct LFI-BTA12T30033M Pipe Material 6 PVC Manifold Material 20 Gauge Hot Roll Galvanized Sheet A653
22. 22. Final Design Simple Payback 3 Blowers, 10 columns with 4 rows of pipes. Blower Model McMaster-Carr 1953K35 Pipe Material 6 PVC Manifold Material 20 Gauge Hot Roll Galvanized Sheet A653
23. 23. Summary Heat Exchanger Design Approach Thousands of combinations analyzed using computer simulations Data then used to optimize results based on criteria for success
24. 24. Follow-Up Increase and/or focus design variables Focus more on cost efficiency (i.e. materials, performance, etc.) More Efficient Simulation Process
25. 25. References (1) "Air Properties." Air Properties. N.p., n.d. Web. 9 Nov. 2014. (2) Bansal, Vikas, Transient effect of soil thermal conductivity and duration of operation on performance of earth air tunnel heat exchanger, Applied energy, Volume 103, 2013, pp. 1-11. (3) R. Shankar Subramanian, Heat transfer to or from a fluid flowing through a tube. PP.1- 72- M. De Paepe, A. Janssens, Thermo-hydaulic design of earth-air heat exchangers, Energy and Buildings, Volume 35, 2003, PP. 389-397. (4) Roht Misra, Vikas Bansal, Ghanshyam Das Agrawal, Jyotirmay Mathur, Tarun Aseri, Transient analysis based determination of derating factor for earth air tunnel heat exchanger in summer, Energy and Buildings, Volume 58, 2013, pp.103-110. (5) Summary. (n.d.). Retrieved November 19, 2014, from https://neutrium.net/fluid_flow/pressure-loss-from-fittings-expansion-and- reduction-in-pipe-size/
26. 26. Questions?