Ground Source Heat Pump Sub-Slab Heat Exchange Loop Performance in a Cold Climate Nick Mittereder and Andrew Poerschke IBACOS, Inc. November 2013 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, subcontractors, or affiliated partners makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:[email protected] Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: [email protected] online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste Ground Source Heat Pump Sub-Slab Heat Exchange Loop Performance in a Cold Climate Prepared for: The National Renewable Energy Laboratory On behalf of the U.S. Department of Energy’s Building America Program Office of Energy Efficiency and Renewable Energy 15013 Denver West Parkway Golden, CO 80401 NREL Contract No. DE-AC36-08GO28308 Prepared by: Nick Mittereder and Andrew Poerschke IBACOS, Inc. 2214 Liberty Avenue Pittsburgh, PA 15222 NREL Technical Monitor: Michael Gestwick Prepared under Subcontract No. KNDJ-0-40341-03 November 2013 iii [This page left blank] iv Contents List of Figures ............................................................................................................................................ vi List of Tables .............................................................................................................................................. vi Definitions .................................................................................................................................................. vii Acknowledgments ................................................................................................................................... viii Executive Summary ................................................................................................................................... ix 1 Introduction and Background ............................................................................................................. 1 1.1 Problem Statement ...............................................................................................................1 1.2 Project Objective ..................................................................................................................2 1.3 Ground Loop Description ....................................................................................................2 2 Experimental Approach ....................................................................................................................... 4 2.1 System Operation .................................................................................................................4 2.2 Measured Parameters ...........................................................................................................5 3 Measured Results ............................................................................................................................... 10 3.1 Basement Floor Temperatures ...........................................................................................10 3.2 Soil Temperatures ..............................................................................................................10 3.3 Soil Moisture Content ........................................................................................................13 3.4 Soil Thermal Conductivity .................................................................................................13 3.5 Basement Floor Heat Flux .................................................................................................14 3.6 Ground Loop Working Fluid Temperatures ......................................................................16 4 Economic Analysis ............................................................................................................................. 20 5 Discussion and Conclusions ............................................................................................................ 21 5.1 Heat Exchanger Parameters ...............................................................................................21 5.2 Design Considerations .......................................................................................................22 5.3 Future Research .................................................................................................................23 References ................................................................................................................................................. 24 Appendix A: Excerpt from “Cooperative Agreement DE-FC26-08NT02231. Building America Final Technical Report” (Oberg 2010)—Pittsburgh Lab Home Heating, Ventilation, and Air Conditioning.................................................................................................................................. 25 Appendix B: Updated TRNSYS Simulation and Model Validation ....................................................... 33 Appendix C: Excerpt from “Cooperative Agreement DE-FC26-08NT02231. Building America Final Technical Report” (Oberg and Bolibruck 2009)—Pittsburgh Lab Home Sub-Slab TRNSYS Results ................................................................................................................................. 46 v List of Figures Figure 1. The cold-climate Pittsburgh Lab Home .................................................................................... 1 Figure 2. Building America climate map, showing the location of the Pittsburgh Lab Home ............ 2 Figure 3. GSHP sub-slab ground heat exchange loop composed of ¾-in. high density polyethylene piping .............................................................................................................................. 3 Figure 4. Plan view showing the type, location, and name of sub-slab loop instrumentation devices ................................................................................................................................................... 6 Figure 5. Section view showing the type and location of sub-slab loop instrumentation devices ................................................................................................................................................... 7 Figure 6. Typical soil TC installation ......................................................................................................... 7 Figure 7. Typical soil moisture sensor installation ................................................................................. 8 Figure 8. Typical TC installation for measuring soil temperature directly below the slab insulation ............................................................................................................................................... 8 Figure 9. Typical installation of basement floor TC and heat flux sensor ............................................ 9 Figure 10. Basement floor temperatures ................................................................................................ 10 Figure 11. Soil temperatures measured directly below the slab insulation ........................................ 11 Figure 12. Soil temperatures measured at the ground loop depth ...................................................... 11 Figure 13. Soil temperatures measured 24 in. below the ground loop depth ..................................... 12 Figure 14. Soil moisture content ............................................................................................................. 13 Figure 15. Measured basement floor heat flux....................................................................................... 15 Figure 16. Measured results for basement slab temperatures............................................................. 16 Figure 17. Daily average outdoor ambient, ground loop fluid, and soil temperatures ...................... 17 Figure 18. TRNSYS results for ground loop temperatures ................................................................... 18 Figure 19. Heat pump COP versus EWT ................................................................................................. 18 Figure 20. Estimated relationship between soil thermal conductivity and specific peak load ........