Dissertations and Theses
Date of Award
2026
Document Type
Dissertation
Department
Mechanical Engineering
First Advisor
Prathap Ramamurthy
Keywords
Heat Pump, Natural Refrigerant, Transcritical System, Exergy Analysis, Heat Transfer
Abstract
Fossil-fuel based heating systems used in the residential buildings in northeastern U.S region are not only inefficient but also largely responsible for the greenhouse gas emissions in U.S. Electrification of the buildings has been proved to be the most efficient way to reduce the greenhouse gas emissions where Heat Pumps can be the best alternative to replace the natural gas based heating system to accelerate the electrification process. Among different types of heat pumps, the Air Source Heat Pump (ASHP) system is widely used due to the easy installation and energy efficiency. Conventional heat pump technologies use various types of hydrofluorocarbons (HFC) refrigerants which are also responsible for greenhouse gas emissions. Therefore, natural refrigerant such as which is naturally available, eco-friendly, non-toxic, non-flammable, and non-corrosive can be a good alternative to the HFC refrigerants. R744 has zero ozone depletion potential (ODP) and a global warming potential (GWP) of 1 which is almost thousand times lower than the HFC refrigerants.
In this study, air source heat pump systems with natural refrigerant and conventional refrigerant R410A have been tested and analyzed comparatively to determine the feasibility of air source heat pump systems for space heating applications in northeastern U.S winter climates by replacing the natural gas based heating system as part of the global & local efforts for decarbonizing the buildings. A dedicated testing facility was built inside the laboratory which could produce outdoor winter conditions to test the air source heat pumps inside a climate-controlled chamber. All the necessary sensors and hardware were used to complete the instrumentation, and NI LabVIEW was used to build the data logging and monitoring interface.
Blackbox models were developed for both R410A and R744 systems and validated against experimental data analysis. The 1st and 2nd law analysis were performed along with comprehensive exergy analysis of the systems. Comparative performances of the R410A and R744 systems were investigated in terms of coefficient of performance (COP), 2nd law efficiency and exergy loss with the variation of outdoor temperatures from 32°F to 50°F. The R410A system showed better performance compared to R744 system at different outdoor temperatures. For both R744 and R410A system, the major exergy loss happened in compressor while the gas cooler in R744 system showed higher exergy loss than the condenser in R410A system. Based on overall exergy destruction, R744 performed better in higher outdoor temperatures while R410A performed better in lower outdoor temperatures. This study revealed that the natural refrigerant R744 () based ASHP systems can be a potential alternative to replace the natural gas-based heating systems and phase out the existing high ODP & GWP refrigerants for residential space heating applications in cold regions.
Recommended Citation
Rob, S M Abdur, "Design, Testing And Controls For Air Source Heat Pump System In Cold Climates Using Natural & Conventional Refrigerants" (2026). CUNY Academic Works.
https://academicworks.cuny.edu/cc_etds_theses/1243
