Considering the excellent environmental properties and heating capability under wide running conditions of the natural fluid CO₂, the transcritical CO₂ heat pump system has widely been used in the application of water heaters, commercial heating and cooling, electric vehicle thermal management, etc. Since the performance was highly affected by the discharge pressure and heat recovery rate in a transcritical CO₂ system, the collaborative optimization of these two parameters was analyzed in detail in this study. The results showed that the optimal value of the system heating COP, which was the ration of heating capacity to power consumption, was better under a higher heat recovery rate and relatively lower discharge pressure, which is why these kinds of operating conditions are highly recommended from the perspective of collaborative optimization. Additionally, the heat recovery rate had a positive effect on the system performance when the discharge pressure was lower than its optimal value, while the heat recovery rate would present a passive effect on the system performance when the discharge pressure was higher than its optimal value. The relevant conclusions of this study provide a good theoretical basis for the efficient and stable operation of the transcritical CO₂ heat pump technology under the conditions of a wide ambient temperature range.

Recovering the low-temperature heat released during compressed air energy storage (CAES) charging for industrial steam generation requires a heat pump that can provide both the required steam temperature and sufficient heating capacity. This study applies a previously reported recuperated transcritical CO₂ configuration to the 11.64 MW cooling-water circuit of a 100 MW CAES plant, with water entering the evaporator at 50 °C and returning at 25 °C. The steam-generation circuit recycles saturated liquid from the flash separator and mixes it with pressurized make-up water, after which the mixture is heated at high pressure, throttled to generate steam and separated before steam superheating. At a compressor suction temperature of 97.5 °C and discharge pressure of 26.0 MPa, the system supplies 31.96 MW of heat and produces 10.79 kg s⁻¹ of steam at 0.40 MPa and 303.33 °C, with a cycle COP of 1.533, excluding pumping. Increasing the suction temperature from 94.5 to 100.5 °C raises the discharge temperature by 7.81 K but reduces COP from 1.550 to 1.520, because the compressor power increases while the expander power decreases. Although more steam is produced, its delivery temperature decreases because the fixed superheater duty supplies less heat per kilogram. Furthermore, the baseline temperature profiles identify an internal minimum temperature difference of approximately 12 K in gas cooler B, which is smaller than either terminal difference. These findings indicate that CAES cooling water can be used for 300 °C steam generation through staged CO₂ heat release, while the effects of recuperation on power consumption and heat distribution must be considered together when selecting the cycle operating conditions.

To mitigate compression heat loss during the operation of compressed air energy storage(CAES) power stations, this study proposed a design that coupled a CAES system with a heat pump system for high-temperature steam production. Focusing on waste heat utilization in a 100 MW CAES system, a tiered compression heat utilization strategy was adopted: part of the compression heat serves as a reheating source for the energy storage system’s expansion stage, while the remainder acts as a low-grade heat source for the heat pump steam generation system. This approach effectively enhances the comprehensive energy utilization efficiency of the system. Research findings demonstrated that the novel waste heat utilization system integrating a modified CAES system with a heat pump can convert 11.64 MW of secondary low-grade compressed heat into high-temperature steam. Under specific feedwater parameters(eg.,flow rate, pressure, and temperature), the system generated steam with matched operating conditions, while the heat pump subsystem achieves a Coefficient of Performance(COP) of 1.55. Analysis of variable operating conditions revealed that when the heat load of the flash-high/low-temperature regenerators remained constant, both the steam flow rate and flash rate increased with rising feedwater temperature and decreased with increasing feedwater flow rate. Furthermore, higher the feedwater flow rates combined with the lower feedwater temperature yield higher the steam temperature, peaking at 314.02 °C under optimal operating parameters; Environmental analysis indicated that the system produced substantial high-temperature steam during annual operation, achieving significant reductions in multiple pollutants emissions compared to coal-fired industrial boilers and thus providing a valuable technical reference for relevant fields.