Northwest Solar Vacuum Tube Water Heater-Air Source Heat Pump Heating System Control Strategy Optimization

Winter heating with clean energy is very important for coal substitution in rural areas of China.In Northwestern China,winter weather is usually below zero and winter heating lasts at least 5 months,which is a big expense for rural residents.It is well known that solar energy,air source heat pump and other energy-saving technologies could effectively cut down on the expenditure.However,it is difficult to consider the economics and stability of winter heating with free solar energy alone,and the cost of winter heating with a heat pump alone is too high for locals to afford.Therefore,our team proposed the concept of air source heat pump assisted solar energy and established a solar vacuum tube collector-air source heat pump system in Lvhua Village,Lanzhou City,which experimentally proved its good performance in heating the cold areas of Northwest China.In order to further improve the heating performance of the system,a control strategy that integrates solar energy and air energy is proposed to address the problems of the existing control strategy of maximum solar energy utilization.Firstly,this paper takes the solar vacuum tube collector-air source heat pump experimental system as the research object,analyzes the heating building heat load,establishes the simulation platform of the system based on TRNSYS software and verifies it with experimental data,simulates the operation of the existing system using the maximum utilization of solar energy control strategy for the heating season,and completes the preliminary performance analysis and evaluation.Then,we proposed two control strategies for integrated utilization of solar energy and air energy using temperature control parameters alone and temperature and time control parameters,and used Genopt software to implement a multi-objective optimization algorithm that takes into account the peak and valley electricity prices for clean heating in Gansu,the energy supply characteristics of the system,and the energy demand of the building.The optimization algorithm is used to optimize the control parameters.Finally,the control strategy with the best comprehens ive evaluation index is used as an example to evaluate the operation performance,economy and environmental protection of the optimized strategy for the heating season.The main research findings are as follows:（1）The control strategy of maximizing the use of solar energy（strategy 1）,when operating,showed that the total solar radiation irradiated to the collector surface during the whole heating season was 12,130.5 k Wh,the effective solar heat collection amount was 7,114.2 k Wh,the average heat colle ction efficiency was 56.2%,and the solar energy guarantee rate was 43.4%;the COP of the air source heat pump showed seasonal changes,with the minimum value of 2.65,the maximum value of 3.41,and the average value of 2.94,The COP of the air-source heat pump showed seasonal variations,with a minimum value of 2.65,a maximum value of 3.41 and an average value of 2.94,while the COP of the solar heat pump showed no seasonal variations,with a minimum value of 3.17,a maximum value of 3.80 and an average v alue of3.48;the total power consumption of the composite system was 5428.2 k Wh,with a minimum energy efficiency ratio of 2.50,a maximum value of 13.74 and an average value of 3.02,and a rate-of-combustion efficiency of 14.8%during the heating season.The ambient temperature during the operation of the air source heat pump is relatively low,which can be adjusted by changing the control strategy.（2）The control parameters of the control strategy for the integrated use of solar and air energy are the use of temperature and time control（strategy II）and the use of temperature control alone（strategy III）in two ways,specifically the detection of tank temperature,ambient temperature,and room temperature and the detection of tank temperature,time,and room temperature,respectively.Both control methods can effectively reduce the power consumption of the system’s heating season operation,but strategy II’s control method is more suitable for this system.（3）When this system is optimized by strategy,the optimization results of the particle swarm algorithm and the Hooke-Jeeves hybrid algorithm,with optimal energy conservation and the optimal comprehensive evaluation index as the objective function,are basically the same.The values of optimal,and₂)for energy conservation are 9,19 and 46℃,respectively,and the objective function is 7.9%;the values of optimal,and₂)are 9,19,45.5℃,and the objective function is7.3%;the optimal economic,,and₂)are 9,19,and 35℃,and the objective function is 7.4%.（4）The effective heat collection of the water heater under the optimized strategy is 6811.3 k Wh lower than that of strategy I by 302.8 k Wh,the average heat collection efficiency is 56.2%lower than that of stra tegy I by 2.5%,the solar guarantee rate is41.6%lower than that of strategy I by 1.8%;the average COP of air source heat pump and water source heat pump are 3.04 and 3.54 higher than that of strategy I by0.10 and 0.06,respectively The average COP of a ir source heat pump and water source heat pump are 3.04 and 3.54,respectively,which are 0.10 and 0.06 higher than that of strategy 1,with improvements of 3.4%and 1.7%,respectively;the system energy efficiency ratio is 3.28,which is 0.26 higher than that of strategy 1,with an improvement of 8.6%.（5）The solar vacuum tube collector-air source heat pump heating season system under the optimized strategy consumes 5000.4 k Wh,saves 4272.9 kg of standard coal;the primary energy saving rate is 67.9%,and the values of strategy I are 5428.2 k Wh,4100.1 kg,and 65.2%,respectively;the annual value of cost is 6591.8 yuan,and the dynamic payback period is 5.8 years;the CO ₂ emission reduction is 10660.2 kg,the SO₂ emission reduction is 82.0 kg,and the dust emission reduction is 82.0 kg.Under the optimized strategy,the solar vacuum tube collector-air source heat pump heating system has good performance in terms of energy savings,economy,and emission reduction.The innovation of this paper is to propose a control strategy of the integrated use of air and solar energy with two control parameters for the existing solar vacuum tube collector-air source heat pump heating system that fully utilizes the heating system characteristics and reduces energy consumption.And the multi-objective optimization of control parameters by the particle swarm algorithm and the Hooke-Jeeves hybrid algorithm is realized through the Genopt software,which helps to promote this system in the rural areas of northwest China.