| Seawater-soil dual source heat pump system can make full use of marine energy and geothermal energy to meet the cold and heat demand of buildings,which is one of the typical clean energy supply systems,which is of great significance for reducing the carbon emissions of buildings in coastal cities.At present,the heat transfer characteristics of its front-end heat exchanger under complex periodic boundary conditions have yet to be analyzed.In addition,the traditional numerical model cannot meet the real-time control requirements of the system under continuous and variable working conditions.In this study,the heat transfer characteristics of seawater-soil dual source heat pump system under complex periodic boundary conditions were studied.Firstly,the resistance and capacitance model of the unsteady heat transfer process of the heat exchanger at the front end of the capillary of the system is constructed by thermoelectric analogy.Secondly,by comparing the resistance-capacitance model with the commonly used CFD numerical simulation model,the accuracy and rapidity of the model are verified.Finally,the key factors affecting the resistance-capacitance characteristics and heat flow harmonics of the system are analyzed.Under the parameter settings of this study,the main conclusions are as follows:(1)Based on the experimental bench of a seawater-soil dual-source heat pump system in Qingdao,the star resistance capacity model of the capillary front-end heat exchanger was constructed,and the accuracy and rapidity of the model were verified by using the measured data and CFD numerical simulation model.The results show that under the premise of ensuring that the accuracy difference of the results is small,the simulation time of the CFD numerical simulation model is more than 120 times that of the resistance-capacitance model.(2)The valley value of heat transfer per unit area of capillary heat exchanger appeared on August 28 in the cooling season and February 8 in the heating season,when its heat transfer performance was the worst,82.68W/m~2 and 31.24W/m~2,respectively.Compared with the outdoor temperature,the phase lag of the seawater temperature curve in the cooling season and heating season is about 18 days and 15 days,and the heat exchange lag of the heat exchanger is about 23 days and 20 days,respectively.The area F’of the heat exchanger calculated based on the highest and lowest air temperatures is 3.16%and 1.73%less than the area F calculated based on the minimum heat exchange capacity,respectively.(3)The increase of seawater seepage velocity,heat exchanger burial depth,capillary tube length,backfill material and thermal conductivity of seabed base layer effectively improved the heat transfer performance of capillary heat exchanger.The increase of the buried depth,the specific heat capacity of the backfill material volume,and the porosity of the heat exchanger will strengthen the stability of the heat exchanger operation and prolong its thermal response time to seawater temperature.(4)Through the variance-based global sensitivity analysis(Sobol method),the sensitivity of the design parameters of the model heat exchanger to the harmonic response of the output energy flow is studied,and the results show that the thermal conductivity of the backfill material is the biggest factor affecting the heat transfer performance of the heat exchanger,and the buried depth of the heat exchanger is the most important factor affecting its operating stability and thermal response time.This study lays a theoretical foundation for the optimal design and energy-saving operation of the subsequent seawater-soil dual-source heat pump system. |
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