Operation Control And Energy Management Of A Variable Capacity Direct Expansion Solar Assisted Heat Pump Water Heater

Solar energy is a kind of clean energy which can reduce the dependence on traditional energy sources.The technology of solar heat pump integrates effectively solar energy heat utilization and heat pump technology,which is used for heating and supplying domestic hot water.It is one of the effective technologies to achieve building energy conservation,renewable energy utilization and pollutant emission reduction.The operation control and energy management of a direct-expansion solar-assisted heat pump(DX-SAHP)water heater is studied in this paper.The main contents are as follows:The working principle of the DX-SAHP water heater was analyzed.A DX-SAHP water heater prototype,using R134a as refrigerant,was designed and built.It mainly consists of a bare flat-plate solar collector/evaporator,a variable-frequency rotary-type hermetic compressor,a micro-channel condenser,a hot water tank,and an electronic expansion valve(EEV).A data acquisition and control system was set up,and a software program based on Kingview data acquisition and monitoring was developed to ensure the acquisition,display,and storage of the real-time data.In addition,the system could control the opening of electronic expansion valve and compressor speed automatically.The operation control and energy management strategy of DX-SAHP water heater is proposed,after analyzing a large number of experimental data.The strategy mainly includes:the initial opening algorithm of EEV and initial compressor speed algorithm during the start-up phase;the compressor speed adjustment method and degree of superheat control algorithm based on the EEV opening during the normal operation phase,and a reasonable running time of the system.The proposed control strategy is conducive to the stable and efficient operation of the system and the more reasonable utilization of energy.The micro-controller based on the DX-SAHP water heater was completed,including the selection of various components on the micro-controller,the control circuit design,the PCB design,the programming software,and debugging.The control system mainly includes microcomputer minimum system,electronic expansion valve drive module,RS485 communication module,display module,temperature acquisition module,key scanning module,clock module,etcA large number of experiments are conducted on the proposed operation control and energy management strategy.The results show that the initial rotation speed of the compressor and the initial opening of the EEV can be calculated accurately during the start-up stage of the system.The degree of superheat approaches the target range of 5-10? within shorter time after system start-up.In the normal operation of the system,the degree of superheat is stably controlled within the target range,compressor speed control effect is good,and the heating time error is within 5%.The system COP can reach 6 basically,and the average power consumption is 1.1 kW·h every day on the summer conditions.The system COP can reach 4,and the average power consumption is 2.356 kW·h every day on the winter conditions.Thus,the proposed operational control and energy management strategy is effective to enable the system operate safely,efficiently and stably.