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Modeling and Experiments for a CO2 Ground-Source Heat Pump with Subcritical and Transcritical Operation
Wei Wu1, Harrison M Skye2, John J Dyreby3
1School of Energy and Environment, City University of Hong Kong, Hong Kong, China.
Energy Conversion and Management
|February 3, 2023
Summary
This study developed a CO2 ground-source heat pump (GSHP) model and prototype, showing promising performance, especially at lower temperatures. Further optimization could enhance its environmental benefits and efficiency compared to traditional systems.
Area of Science:
- Thermodynamics
- Heat Transfer
- Refrigeration Systems
Background:
- Ground-source heat pumps (GSHPs) offer high energy efficiency.
- Carbon dioxide (CO2) is an environmentally friendly refrigerant with zero ozone depletion potential (ODP) and low global warming potential (GWP).
- Residential heat pump technology requires continuous innovation for improved environmental performance.
Purpose of the Study:
- To develop and validate a detailed model for a CO2 liquid-to-air GSHP system.
- To investigate the performance of a prototype CO2 GSHP in residential cooling and heating applications.
- To compare the performance of the CO2 GSHP with a conventional R410A GSHP.
Main Methods:
- Development of a comprehensive thermodynamic and transport process model for the CO2 GSHP, simulating both subcritical and transcritical operations.
- Experimental cooling tests of a prototype CO2 GSHP, including ISO 13256-1 standard conditions and extended tests at various entering liquid temperatures (ELTs).
- Comparative analysis of experimental data against the developed model predictions and published data for a commercial R410A GSHP.
Main Results:
- The model accurately predicted prototype CO2 GSHP performance, with errors within 6.7% for COP and 4.9% for sensible capacity.
- The CO2 GSHP demonstrated higher cooling COP and total capacity than the R410A GSHP at ELTs below 20 °C.
- At standard cooling conditions (ELT 25 °C), the CO2 GSHP achieved a COP of 4.14, compared to 4.43 for R410A; at part-load (ELT 20 °C), CO2 achieved 4.92 versus 4.99 for R410A.
Conclusions:
- The developed CO2 GSHP model provides a reliable tool for performance simulation and optimization.
- CO2 GSHPs show competitive and superior performance in certain conditions, highlighting their potential as a sustainable alternative.
- Future research should focus on system optimization, such as ejector integration and heat exchanger design, to enhance CO2 GSHP performance across a wider range of operating conditions.
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