Comprehensive Analysis of Carbon Dioxide Heat Pumps

I. What is a CO₂ heat pump:
The CO₂ heat pump (R744) uses natural carbon dioxide as the circulating refrigerant. It extracts low-level thermal energy from air, water bodies, and industrial waste heat with a small amount of electricity, converting it into high-temperature usable heat energy. Unlike traditional fluorine-based refrigerants such as R410A and R134a, this machine belongs to the category of natural working fluid heat pumps.
According to IEA data, in 2024, heat pumps will account for 12% of global home heating, and the penetration rate of low-carbon heat pumps is less than 5%. CO₂ heat pumps, with their low-carbon and efficient characteristics, can replace traditional refrigerants and achieve billions of tons of carbon emission reduction, making them an important HVAC technology for carbon neutrality.

II. Operating Mechanism of Transcritical Circulation:
Critical parameters of CO₂: 31.2℃, 7.38MPa. These are the key to achieving transcritical circulation. Conventional heat pumps rely on the latent heat release during refrigerant liquefaction; CO₂ is compressed by a compressor to a supercritical high pressure (＞7.38MPa, up to 10MPa+), and the gas cooler does not undergo phase change but relies on sensible heat release, resulting in outlet water temperatures above 90℃.
The released CO₂ is cooled and pressurized by the expansion valve, then vaporizes in the evaporator and returns to the compressor to complete the entire cycle. The temperature and pressure on the high-pressure side can be independently adjusted, optimizing the overall efficiency of the system.

III. Highlights of the Eight Core Products:
1. Large volume cooling capacity, excellent heat exchange performance, compact and small structure of the unit;
2. ODP ≈ 0, low GWP, no ozone layer damage, environmentally friendly;
3. Suitable for running during off-peak electricity periods, significantly reducing operating energy costs;
4. Stable physical and chemical properties, non-toxic and non-flammable, suitable for various accessories and lubricants;
5. High latent heat of vaporization, thermodynamic conditions are compatible with heat pump systems;
6. Compression ratio is only 2.5 – 3.0, the compressor has higher efficiency;
7. The outlet water temperature can be adjusted from 55 to 90℃, and still produces hot water at -20℃ low-temperature environment. 8. CO₂ has abundant reserves and is readily available, making it the most environmentally friendly alternative refrigerant to Freon.

IV Comparison with conventional air-source heat pumps:
Refrigerant: Ordinary heat pump R32/R410A, CO₂ heat pump R744 (GWP = 1, much lower than 1300 of R134a, ODP = 0);
Circulation: Conventional subcritical phase change heat release, CO₂ cross-critical sensible heat exchange;
Water temperature: Conventional upper limit 50-60℃, CO₂ can reach 55-95℃; Heating in cold regions: Under -20℃ conditions, the heating efficiency of the CO₂ heat pump is 30% to 50% higher than that of the R134a model. The heat management advantage of new energy vehicles is particularly prominent.

V. Industry Prospects and Existing Weaknesses:
Prospects:
Many countries have incorporated heat pumps into their carbon neutrality plans. Six domestic departments have introduced policies to support heat pumps. Cross-critical CO₂ heat pumps have been included in the national energy-saving equipment directory.
The global commercial CO₂ heat pump market will exceed 12 billion US dollars in 2025. China will be the leading producer and seller domestically, with 55% of the global production capacity. The number of related patents has increased by an average of 47% in the past three years.
The application scope has expanded from building heating to industrial high-temperature heating: food drying, papermaking and chemical industries, industrial waste heat recovery, and low-temperature heating for new energy vehicles.

Weakness: The critical pressure of CO₂ is relatively high, and the pressure during the transcritical process can reach up to 10 MPa. The standards for pipe fittings, seals, and materials used in the unit are extremely strict, and the overall cost of the machine is much higher than that of ordinary air-source heat pumps.