Abstract: The high return water temperature of CO₂ unit in this paper means that the water temperature at the inlet of the unit is higher than 35℃. If the heat generated by CO₂ unit can not be used in time, the return water temperature will rise and the energy efficiency of the unit will be decreased. Aiming at the problem of high return water temperature, puts forward an optimized frequency conversion control strategy for high return water temperature, improves the adaptability of the unit to high return water temperature, experiments are carried out to verify the control strategy. The experimental results are consistent with the control strategy, which can improve the performance and guide the application of CO₂ heat pump under high temperature return water condition.

Key words: CO₂ heat pump, Return water temperature, Frequency conversion control, Experimental research