Control method and control device for variable-frequency and variable-capacity heat pump hot-air drying system

A method for controlling a heat pump-type double-circulation hot-air drying system, comprising the following steps:

• i) setting a temperature control parameter as a preset temperature control curve parameter;
• ii) detecting and monitoring an outlet air temperature, and a temperature and humidity of a drying room;
• iii) dynamically adjusting a set temperature according to a preset temperature control curve;
• and
• iv) selecting, according to a current set temperature, a double-circulation dynamic operation mode of the heat pump-type double-circulation hot-air drying system;
• wherein, the heat pump-type double-circulation hot-air drying system comprises a hot-air double-circulation loop, an air supply regulation valve, an inner circulation air valve, a latent heat condenser, a sensible heat condenser, and a double-path unloading branch, wherein the hot-air double-circulation loop is composed of an air supply circulation loop and an inner circulation loop;
• the air supply regulation valve and the inner circulation air valve are used for adjusting a circulation air volume of the hot-air double-circulation loop;
• the latent heat condenser and the sensible heat condenser are connected in series to a main circulation pipeline of a refrigerant;
• the double-path unloading branch is formed by connection of an unloading electromagnetic valve, a first throttle valve and a second throttle valve;
• the double-circulation dynamic operation mode is selected from the group consisting of a single-circulation conventional heating mode, a double-circulation pressure reduction and unloading mode, a double-circulation temperature reduction and unloading mode, and a double-circulation double-path unloading mode, wherein:
• in the single-circulation conventional heating mode, the unloading electromagnetic valve is closed, and the refrigerant circulates along the main circulation pipeline;
• the inner circulation air valve is opened by 0%, the air supply regulation valve is opened by 100%, and the double-circulation hot-air drying system produces low-temperature hot air at an outlet air temperature below 45° C. by the air supply circulation loop;
• and a control device controls the outlet air temperature by changing an operation interval or operation frequency of a compressor;
• in the double-circulation pressure reduction and unloading mode, the unloading electromagnetic valve and the second throttle valve are opened, the first throttle valve is closed, and part of the refrigerant is diverted by the unloading electromagnetic valve to directly enter a vapor-liquid separator via the second throttle valve while the refrigerant circulates along the main circulation pipeline;
• the inner circulation air valve is opened by 50%-55%, and the air supply regulation valve is opened by 50%-45%;
• and the control device adjusts circulation air volumes of the air supply circulation loop and the inner circulation loop to control the outlet air temperature, so that medium-temperature hot air having an outlet air temperature of 45-65° C. is produced;
• in the double-circulation temperature reduction and unloading mode, the unloading electromagnetic valve and the first throttle valve are opened, the second throttle valve is closed, and part of the refrigerant is diverted by the unloading electromagnetic valve to enter an evaporator via the first throttle valve in parallel connection with an expansion valve while the refrigerant circulates along the main circulation pipeline;
• the inner circulation air valve is opened by 55%-65%, and the air supply regulation valve is opened by 45%-35%;
• and the control devices adjusts the circulation air volumes of the air supply circulation loop and the inner circulation loop to control the outlet air temperature, so that medium high-temperature hot air having an outlet air temperature of 65-75° C. is produced;
• in the double-circulation double-path unloading mode, the unloading electromagnetic valve, the first throttle valve and the second throttle valve are opened, and the refrigerant is diverted by the unloading electromagnetic valve while circulating along the main circulation pipeline, partial of the refrigerant enters the evaporator via the first throttle valve in parallel connection with the expansion valve, and remaining of the refrigerant directly enters the vapor-liquid separator via the second throttle valve;
• the inner circulation air valve is opened by 65%-75%, and the air supply regulation valve is opened by 35%-25%;
• and the control device adjusts the circulation air volumes of the air supply circulation loop and the inner circulation loop to control the outlet air temperature, so that high-temperature hot air having an outlet air temperature over 75° C. is produced.