What is a cascade heat pump?

The cascade heat pump consists of 4 systems: the chilled water system, the low-temperature refrigeration cycle using R22, the high-temperature heat pump cycle using R134a and the hot water system. The cascade heat pump produces both chilled water for cooling application and hot water for heating application.

A cascade heat pump hot water system for high-temperature inactivation of the new coronavirus in medical sewage includes a cascade heat pump hot water subsystem and a high-temperature sterilization sewage treatment subsystem. The cascade heat pump hot water subsystem includes a first compression heating cycle and a The second compression and heating cycle, the first compression and heating cycle includes a first compressor, a condensing evaporator, a regenerator, a first throttle valve, and a compound evaporator that are connected in sequence; the second compression and heating cycle includes sequentially connected The second compressor, the air cooler, the second throttle valve and the condensing evaporator; the high temperature sterilization sewage treatment subsystem includes the sewage secondary treatment cycle and the heat storage standing pool. The system can not only perform high-temperature sterilization and sterilization treatment on sewage containing a large number of pathogenic microorganisms, chemical pollutants and radioactive pollutants, but also recover the waste heat of medical sewage to be discharged to preheat the sewage that has not been subjected to high-temperature sterilization. The energy saving advantage of the system is improved.

A method and device for controlling start-stop of a cascade heat pump defrosting compressor; the method comprises: detecting whether the first system satisfies the defrosting condition; if the first system satisfies the defrosting condition, according to a preset start-stop control The rules control the first primary compressor to be turned on for defrosting; control the second system to enter the heating mode; the embodiment of the present application coordinates the defrosting action of the compressor according to the start-stop control rules to avoid the cascade heat pump During defrosting, the primary side high pressure protection or the secondary side low pressure protection is triggered to improve the defrosting efficiency. At the same time, the second system is heated to avoid a sudden drop in water temperature and ensure the stability of the defrosting process.