Can ground source heat pumps perform well in Alaska?

The long heating season and cold soils of Alaska provide a harsh testing ground for ground source heat pumps (GSHPs), even those designed and marketed for colder climates. Fairbanks, Alaska has 7,509°C heating degree-days18 (13,517°F HDD65) and only 40°C cooling degree-days18 (72°F CDD65). This large and unbalanced heating load creates a questionable environment for GSHPs. In addition, soil temperatures average around freezing (0°C/32°F); the soil may be permafrost year-round, just above freezing, or in an annual freeze-thaw cycle. In 2013 the Cold Climate Housing Research Center (CCHRC) installed a GSHP at its facility in Fairbanks. The heat pump replaced an oil-fired condensing boiler heating a 464 m2 (5,000 ft2)office space. The ground heat exchanger was installed in a marginal area underlain with permafrost near 0°C (32°F). The intent of the installation was to observe and monitor the system over a 10-year period in order to develop a better understanding of the performance of GSHPs in ground with permafrost and to help inform future design. The system enjoyed one season of better-than-expected performance, averaging a COP of 3.7its first winter. By the third winter, the COP had dropped to an annual average of 3.2 and ice had started to develop in the area around the heat extraction coils. A combination of physical monitoring and numerical modeling is used to evaluate the heat pump system

MP 2009-09

As the price of traditional fossil fuels escalates, there is increasing interest in using renewable resources, such as biomass, to meet our energy needs. Biomass resources are of particular interest to communities in interior Alaska, where they are abundant (Fresco, 2006). Biomass has the potential to partially replace heating oil, in addition to being a possible source for electric power generation (Crimp and Adamian, 2000; Nicholls and Crimp, 2002; Fresco, 2006). The communities of Tanana and Dot Lake have already installed small Garn boilers to provide space heating for homes and businesses (Alaska Energy Authority, 2009). A village-sized combined heat and power (CHP) demonstration project has been proposed in North Pole. In addition, several Fairbanks area organizations are interested in using biomass as a fuel source. For example, the Fairbanks North Star Borough is interested in using biomass to supplement coal in a proposed coal-to-liquids project, the Cold Climate Housing Research Center is planning to test a small biomass fired CHP unit, and the University of Alaska is planning an upgrade to its existing coal-fired power plant that could permit co-firing with biomass fuels. The challenge for all of these projects is in ensuring that biomass can be harvested on both an economically and ecologically sustainable basis

Testing and analysis of a ground source heat pump in Interior Alaska

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

Impact of Intake and Exhaust Ducts on the Recovery Efficiency of Heat Recovery Ventilation Systems

The heat recovery efficiency of ventilation systems utilizing heat recovery ventilators (HRVs) depends not only on the heat recovery efficiency of the HRV units themselves but also on the intake and exhaust ducts that connect the HRV units to the outside environment. However, these ducts are often neglected in heat loss calculations, as their impact on the overall heat recovery efficiency of HRV systems is often not understood and, to the knowledge of the authors, a mathematical model for the overall heat recovery efficiency of HRV systems that accounts for these ducts has not been published. In this research, a mathematical model for the overall heat recovery efficiency of HRV systems that accounts for the intake and exhaust ducts was derived and validated using real-life data. The model-predicted decrease in heat recovery efficiency due to the ducts was in reasonable agreement (relative error within 20%) with the real-life measurements. The results suggest that utilizing this model allows for more correct ventilation heat loss calculations compared to using the heat recovery efficiency of the HRV unit alone, but more field studies are needed to verify the accuracy of this model in a wide range of applications

Impact of Intake and Exhaust Ducts on the Recovery Efficiency of Heat Recovery Ventilation Systems

The heat recovery efficiency of ventilation systems utilizing heat recovery ventilators (HRVs) depends not only on the heat recovery efficiency of the HRV units themselves but also on the intake and exhaust ducts that connect the HRV units to the outside environment. However, these ducts are often neglected in heat loss calculations, as their impact on the overall heat recovery efficiency of HRV systems is often not understood and, to the knowledge of the authors, a mathematical model for the overall heat recovery efficiency of HRV systems that accounts for these ducts has not been published. In this research, a mathematical model for the overall heat recovery efficiency of HRV systems that accounts for the intake and exhaust ducts was derived and validated using real-life data. The model-predicted decrease in heat recovery efficiency due to the ducts was in reasonable agreement (relative error within 20%) with the real-life measurements. The results suggest that utilizing this model allows for more correct ventilation heat loss calculations compared to using the heat recovery efficiency of the HRV unit alone, but more field studies are needed to verify the accuracy of this model in a wide range of applications

Empirical Study of the Effect of Thermal Loading on the Heating Efficiency of Variable-Speed Air Source Heat Pumps

Heating buildings with air source heat pumps (ASHPs) has the potential to save energy compared to utilizing conventional heat sources. Accurate understanding of the efficiency of ASHPs is important to maximize the energy savings. While it is well understood that, in general, ASHP efficiency decreases with decreasing outdoor temperature, it is not well understood how the ASHP efficiency changes with different levels of thermal loading, even though it is an important consideration for sizing and controlling ASHPs. The goal of this study was to create an empirical model of the ASHP efficiency as a function of two independent variables–outside temperature and level of thermal loading. Four ductless mini-split ASHPs were evaluated in a cold chamber where the temperature (representing the outdoor temperature) was varied over a wide range. For each temperature, the ASHP performance data were collected at several levels of thermal loading. The data for all four ASHPs were combined and approximated with an analytical function that can be used as a general model for the ASHP steady-state efficiency as a function of the outside temperature and level of thermal loading. To the knowledge of the authors, no such empirical model that is solely based on third-party test data has been published before. While limitations exist, the model can be used to help guide future selection and operation of ASHPs

Empirical Study of the Effect of Thermal Loading on the Heating Efficiency of Variable-Speed Air Source Heat Pumps

Heating buildings with air source heat pumps (ASHPs) has the potential to save energy compared to utilizing conventional heat sources. Accurate understanding of the efficiency of ASHPs is important to maximize the energy savings. While it is well understood that, in general, ASHP efficiency decreases with decreasing outdoor temperature, it is not well understood how the ASHP efficiency changes with different levels of thermal loading, even though it is an important consideration for sizing and controlling ASHPs. The goal of this study was to create an empirical model of the ASHP efficiency as a function of two independent variables–outside temperature and level of thermal loading. Four ductless mini-split ASHPs were evaluated in a cold chamber where the temperature (representing the outdoor temperature) was varied over a wide range. For each temperature, the ASHP performance data were collected at several levels of thermal loading. The data for all four ASHPs were combined and approximated with an analytical function that can be used as a general model for the ASHP steady-state efficiency as a function of the outside temperature and level of thermal loading. To the knowledge of the authors, no such empirical model that is solely based on third-party test data has been published before. While limitations exist, the model can be used to help guide future selection and operation of ASHPs