Constant-temperature water supply system employing carbon dioxide heat pump, and control method therefor

A control method for a constant-temperature water supply system employing a carbon dioxide heat pump, it adopting a constant-temperature water supply system employing a carbon dioxide heat pump, the constant-temperature water supply system comprises:

• a primary side loop;
• a secondary side water supply pipeline having a water inlet and a water outlet;
• a heat pump water heater provided in the primary side loop;
• and
• a heat exchanger provided between the primary side loop and the secondary side water supply pipeline,
• wherein the heat exchanger comprises a first heat exchange tube and a second heat exchange tube arranged to exchange heat with each other, the first heat exchange tube is arranged in the primary side loop, the second heat exchange tube is arranged in the secondary side water supply pipeline, and the primary side loop and the secondary side water supply pipeline are connected to each other in a heat exchange manner through the heat exchanger,
• wherein the primary side loop further comprises at least one vertically arranged return water tank, a bottom of the return water tank is provided with a return water outlet that communicates with the heat pump water heater, a side portion of the return water tank is provided with a plurality of return water inlets connected to the heat exchanger in a vertical direction in sequence, each of the return water inlets is provided with a return water valve, the return water tank is provided with a plurality of return water tank temperature sensors for detecting water temperature in the return water tank corresponding to a height of each of the return water inlets, and an outlet of the first heat exchange tube is provided with a return water temperature sensor for detecting temperature of the water at the outlet of the first heat exchange tube, and
• wherein the control method comprises:
• detecting a first water temperature at the outlet of the first heat exchange tube by the return water temperature sensor;
• detecting second water temperatures at different heights of the return water tank by the plurality of return water tank temperature sensors;
• comparing differences between the first water temperature and each of the second water temperatures;
• and
• opening a return water valve corresponding to a return water tank temperature sensor of the plurality of return water tank temperature sensors associated with a smallest difference of the differences to return water.