Carbon dioxide overlapping type heating system, and control method therefor

A method for controlling a carbon dioxide overlapping heating system,

• wherein the carbon dioxide overlapping heating system comprises a low-temperature-stage loop and a high-temperature-stage loop and a heating loop,
• wherein the low-temperature-stage loop comprises an evaporator, a gas-liquid separator, a low-temperature-stage compressor, an intermediate heat exchanger condensing pipe, and a low-temperature-stage expansion valve which are arranged in series in the low-temperature-stage loop sequentially,
• wherein the high-temperature-stage loop comprises an intermediate heat exchanger evaporating pipe, a high-temperature-stage compressor, a condenser condensing pipe, and a high-temperature-stage expansion valve which are arranged in series in the high-temperature-stage loop sequentially,
• wherein the heating loop comprises a condenser evaporating pipe, a user-side heat exchange assembly, and a water pump which are arranged in series in the heating loop sequentially,
• wherein the user-side heat exchange assembly comprises a plurality of user-side heat exchange units arranged in parallel, and each user-side heat exchange unit comprises a flow control valve and a user-side heat exchanger arranged in series,
• wherein the intermediate heat exchanger condensing pipe and the intermediate heat exchanger evaporating pipe are arranged together to exchange heat with each other, and the condenser condensing pipe and the condenser evaporating pipe are arranged together to exchange heat with each other, and
• wherein the low-temperature-stage compressor and high-temperature-stage compressor are both variable-frequency compressors, and the water pump is a variable-frequency water pump,
• the method comprising:
• 1) calculating a target temperature Ts,i of an i-th room according to room information, obtaining an outdoor temperature Ta through an ambient temperature sensor, and obtaining a current indoor temperature Tt,i of the i-th room through an indoor temperature sensor;
• 2) calculating an outlet temperature Tout=(Tt,1, Tt,2, . . . , Tt,n, Ts,1, Ts,2, . . . , Ts,n) required for a refrigerant in an outlet of a condenser according to Ts,i, Ta and Tt,i, and calculating a heat load Qi=ϕi(Tt,i, Ts,i, Ta) required for the i-th room;
• 3) calculating an appropriate opening degree EXPi=EXPi(ΔTi, Qi) of an i-th flow control valve according to the difference ΔTi between the current indoor temperature Tt,i of the i-th room and the target temperature Ts,i of the i-th room and the heat load Qi, and adjusting the flow control valve according to the numerical value of EXPi.