Graduate Thesis Or Dissertation
 

Analysis and simulation of dual-source heat pumps with three-fluid evaporators

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/s1784p85t

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  • When the ambient temperature drops, air-source heat pumps deliver less heating per unit of power input and usually cannot provide for the heating load. Therefore, dual-source heat pumps can offer an attractive alternative. In the context of this work, a dual-source heat pump operates as an air-source unit under normal conditions but as a water-source unit when ambient air conditions are unfavorable. The main objective of this thesis is the analysis and computer simulation of a dual-source heat pump with a three-fluid evaporator. This includes the mathematical analysis and the development of the performance model for the three-fluid evaporator. For the two-phase state in the evaporator, the mixed model based on the Baroczy correlation was used to calculate the pressure drop and Shah's chart method was used to calculate the heat transfer coefficient. Using the three-fluid evaporator model, a dual-source heat pump model was developed based on the Oak Ridge National Laboratory (ORNL) model for air-source units. An optimization method, using the Modular In-Core Non-Linear Optimization System (MINOS) package, was applied to determine the optimal design variables for the evaporator. Finally, using weather data and load conditions, the annual performance factor (APF) simulation program for this heat pump was developed to obtain the optimal capacity, optimal switching temperature, minimum water temperature and so on. The results from the three-fluid evaporator model show that the developed model predicts pressure drops and overall heat transfer coefficients within 3 to 21 percent error range in comparison to experimental data. The coefficient of performance (COP) of the water-source operation of the dual-source heat pump was 20 percent greater than when the unit was operated as an air-source heat pump at 8.3 °C (47 F). Under the same conditions, the dual-source APF also reflected a 45 percent increase when compared to purely air-source operations. The nominal size of the dual-source heat pump (compressor, condenser and evaporator) can be reduced to a value three-fifths that of the air-source heat pump that would normally be specified under identical conditions.
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