Design and Lab Implementation of an Air Source Transcritical CO2 Heat Pump

Author

Geoffrey Turbeville, CUNY City CollegeFollow

Date of Award

2025

Document Type

Thesis

Department

Mechanical Engineering

First Advisor

Prathap Ramamurthy

Second Advisor

Jorge E. Gonzalez-Cruz

Keywords

Transcritical CO₂ Heat Pump, Natural Refrigerants, Cold Climate HVAC, Building Decarbonization, Low-GWP Refrigerants, Air-Source Heat Pump (ASHP)

Abstract

A laboratory-scale air-source transcritical CO2 heat pump (TCHP) was developed to evaluate the performance of low-global-warming-potential (GWP) refrigerants for cold climate applications. A custom climate chamber was also constructed to simulate winter weather conditions typical of the northeastern United States. Both the TCHP and the chamber were fully instrumented to collect temperature, pressure, and mass flow data, which were used to calculate the co- efficient of performance (COP) in accordance with ASHRAE standard refrigerant enthalpy methods. Prior to testing the CO2 system, the experimental setup was benchmarked using a commercially available R410A heat pump manufactured by LG.

The climate chamber maintained steady-state outdoor conditions by combining continuous cooling from the system’s original evaporator coil with resistive heating controlled via feedback loops. Custom controllers for the TCHP were developed using ESP32 microcontrollers and open-source libraries. Controller gains were empirically tuned based on system response data, enabling precise operation of the heat pump and flexibility for future implementation of advanced control strategies.

Results demonstrate the technical feasibility of using CO2 —a natural refrigerant with a GWP of 1—in air-source heat pumps for space heating while operating in cold climates. Comparative testing showed that the CO2 system can achieve competitive performance with an R410A system, which relies on a synthetic refrigerant with a GWP of over 2000. This study highlights the potential for natural refrigerants to meet both environmental and performance goals in residential HVAC systems.

Recommended Citation

Turbeville, Geoffrey, "Design and Lab Implementation of an Air Source Transcritical CO2 Heat Pump" (2025). CUNY Academic Works.
https://academicworks.cuny.edu/cc_etds_theses/1257