Thesis (M.S.) University of Alaska Fairbanks, 2019Ground source heat pumps (GSHPs) can be an efficient heating and cooling system in much of the world. However, their ability to work in extreme cold climates is not well studied. In a heating-dominated cold climate, the heat extracted from the soil is not actively replaced in the summer because there is very little space cooling. A ground source heat pump was installed at the Cold Climate Housing Research Center (CCHRC) in Fairbanks, Alaska with the intent to collect data on its performance and effects on the soil for at least ten years. Analysis shows GSHPs are viable in the Fairbanks climate; however, their performance may degrade over time. According to two previous finite element models, the CCHRC heat pump seems to reach equilibrium in the soil at a COP of about 2.5 in five to seven years. Data from the first four heating seasons of the ground source heat pump at CCHRC is evaluated. The efficiency of the heat pump degraded from an average coefficient of performance (COP) of 3.7 to a mediocre 2.8 over the first four heating seasons. Nanofluids are potential heat transfer fluids that could be used to enhance the heat transfer in the ground heat exchanger. Improved heat transfer could lower installation costs by making the ground heat exchanger smaller. A theoretical analysis of adding nanoparticles to the fluid in the ground heat exchanger is conducted. Two nanofluids are evaluated to verify improved heat transfer and potential performance of the heat pump system. Data from the CCHRC heat pump system has also been used to analyze a 2-dimensional finite element model of the system's interaction with the soil. A model based on the first four years of data is developed using Temp/W software evaluates the ground heat exchanger for a thirty-year period. This model finds that the ground heat exchanger does not lower the ground temperature in the long term.Alaska Energy Authority and the Denali Commission Emerging Energy Technology Fund grant, Alaska Housing Finance CorporationChapter 1: Thesis introduction -- 1.1 Introduction -- 1.2 Cold climate ground source heat pumps - Literature review -- 1.3 Nanofluids - Literature review -- 1.4 Objectives of this thesis and summary of chapters -- 1.5 Nomenclature -- 1.6 Greek symbols -- 1.7 Subscripts -- 1.8 References. Chapter 2: The CCHRC heat pump demonstration project -- 2.1 Introduction -- 2.2 Background -- 2.2.1 Design and installation -- 2.2.2 The heat pump unit -- 2.2.3 Maintenance and history -- 2.3 Data collection -- 2.3 Data collection -- 2.3.2 Mechanical system -- 2.4 Installation costs -- 2.4.1 Operating cost -- 2.5 Savings of the heat pump over using oil -- 2.6 CCHRC GSHP results -- 2.6.1 Observed GHE temperatures -- 2.6.2 Permafrost -- 2.6.3 Surface treatments -- 2.6.4 Heat delivered -- 2.6.5 COP -- 2.7 Discussion -- 2.8 Conclusions and recommendations -- 2.9 Nomenclature -- 2.10 References. Chapter 3: Analytical study of a cold climate ground source heat pump with Al₂O₃ nanofluid in the ground heat exchanger -- 3.1 Introduction -- 3.2 GSHP fluid properties -- 3.3 Nanofluid properties -- 3.5 Heat transfer and pumping power calculations -- 3.6 Analytical results -- 3.7 Discussion -- 3.8 Conclusions -- 3.9 Nomenclature -- 3.10 Greek symbols -- 3.11 Subscripts -- 3.12 References. Chapter 4: GSHP soil model -- 4.1 Introduction -- 4.1.1 Past soil models for this heat pump -- 4.2 Software package -- 4.2.1 Governing equations -- 4.3 Domain and grid layout -- 4.4 Material properties -- 4.5 Boundary conditions -- 4.6 Model correlation -- 4.7 Results -- 4.9 Conclusion -- 4.10 Nomenclature -- 4.11 Greek symbols -- 4.12 Subscripts -- 4.13 References. Chapter 5: Thesis conclusions and recommendations -- 5.1 Conclusions -- 5.2 Recommendations for future research -- 5.2.1 Cold climate heat pump -- 5.2.2 Nanofluids in the heat pump -- 5.2.3 Finite element model of the ground heat exchanger -- 5.3 Nomenclature -- 5.4 References
