Internal thermal management cooling strategies for high-temperature heat pump

High-temperature heat pumps (HTHPs) are crucial for achieving low-carbon industrial heating, aligning with carbon neutrality goals. However, their widespread adoption faces challenges such as electronic component and lubricant degradation at high temperatures. Effective thermal management is essential for expanding HTHP applications. External cooling demands additional space and causes energy losses for system. Internal direct-throttling (DT) cooling is limited by the heat pumps with temperature lift above 60 °C, because of the increasing vapor fraction and inadequate cooling capacity after throttling under large temperature lift. Thus, this paper first proposes an innovative large-subcooling (LS) strategy for heat pumps with large temperature lift, followed by theoretical and experimental studies in a R1233zd(E) HTHP. However, the cooling temperature is still limited by the evaporation temperature of 70 °C because of the needed pressure difference. A throttling-ejection (TE) cooling strategy is then proposed targeting as the solution for HTHP with high-temperature heat source. Three internal cooling strategies are theoretically compared in cooling and thermodynamic performances. The TE cooling shows latent heat enhancement 1–15 % higher than LS and 33–116 % higher than DT, resulting in required coolant mass flow rate decreasing around 1–14 % and 2–65 % compared with LS and DT, respectively. Since the TE cooling can achieve vapor injection, the system efficiency improves by 1.2–4.2 %, making it as the preferred option. Finally, a selection map is summarized to guide the thermal management strategy of heat pumps.