Research On Optimization Of Earth To Air Heat Exchanger System Based On Genetic Algorithm

As nearly 33%of the world’s energy is consumed in heating and cooling buildings,in order to save energy and protect the environment,scholars have carried out many studies in the hope of reducing the consumption of traditional energy sources through the use of renewable energy sources.Among the various renewable energy sources,geothermal energy is very effective in thermal applications such as heating or cooling of spaces.The Earth to air heat exchanger system(EAHE)is a shallow geothermal energy utilisation technology that uses the ground’s storage of cold and heat from nature to cool or heat the outdoor air flowing through the ducts,which is then transported to the building above ground for the purpose of cooling or warming the room,thereby reducing the building’s energy consumption.The purpose of this paper is to find the optimum EAHE design parameters for the Qingdao area.To this end,a simulation model proposed using parametric design methods is used to evaluate the performance of the EAHE in Qingdao,China.The model predicts the performance and feasibility of the EAHE and generates a variety of desired results with a single click.The accuracy of the model’s predictions was also verified by actual field tests.Firstly,the parameters affecting the heat transfer performance of the EAHE are analysed to identify the specific effects of changes in each parameter on the heat transfer effectiveness of the system.At the same time,calculations were carried out on the EAHE,including heat transfer efficiency(η),thermal capacity,economic payback period and its impact on the indoor thermal environment of the building.It was found that the lower the air velocity inside the duct,the deeper the burial depth,the longer the pipe length and the smaller the pipe diameter,the better the overall EAHE heat transfer effect.At the same time,it was found that when the building is connected to an EAHE,the indoor thermal load is effectively reduced during the winter and summer seasons.Subsequently,in order to streamline the number of influencing parameters in the subsequent optimisation process,a sensitivity analysis was carried out with the aid of a2~k factorial test to identify the parameters that have a significant impact on the heat transfer effect of the EAHE.The results show that the four parameters that have a significant influence on the heat transfer effect of the system are:duct radius,duct internal air velocity and duct burial depth,while the other influencing parameters are negligible.The heating energy efficiency ratio(COP)and the cost of energy recovery(CER)are then used as the two objectives for this optimised design,due to the contradictory relationship between COP and CER,i.e.one objective is worsened by the improvement of the other.For this reason,a genetic algorithm needs to be introduced for multi-objective optimisation to determine the corresponding Pareto front.Finally,a set of solutions is taken from the Pareto front with the help of a multi-objective decision making method as the optimal solution for this optimal design.The results show that the system performs best in Qingdao when the internal wind speed,pipe radius,pipe length and pipe burial depth are 1.2m/s,0.1m,48m and 3.7m respectively.The corresponding COP and CER values are 14.68 and 0.11 Yuan/k Wh respectively.