The Study Of Heat And Moisture Transfer Characteristics Of Earth-to-Air Heat Exchanger

With the increasingly serious energy crisis and environmental issues world,exploiting green energy have been received worldwide attention.Obviously,solar energy is exactly the ideal type which is inexhaustible and pollution-free.A large amount of solar radiation is stored at superficial layers of the ground and soil temperature decreases rapidly with the increasing depth of the soil.As a result,the soil temperature under 4 m is nearly constant.Earth-to-air heat exchanger(EAHE)is a new energy efficient technology of renewable energy.Utilizing the geothermal as heat source and sink,the earth-to-air heat exchanger can heat and cool the ambient air for reducing the energy consumption of buildings,which realizes the concept of cross-quarter usage of resources.Accordingly,the investigation of earth-to-air heat exchanger is carried out in this paper.In the whole earth-to-air heat exchanger system,the heat transfer between buried pipe and soil and heat and moisture transfer in soil relates directly to the ground source heat pump operation efficiency.In this paper,through the method of combining numerical simulation and experiment,on the coupled heat and moisture transfer rule in unsaturated soil around the earth-to-air heat exchanger under dynamic thermal-moisture environment in the sunlight greenhouse made a preliminary study.Based on fluid dynamics in porous medium,heat and mass transfer theory and so on,a transient bi-dimensional mathematical model of coupled heat and moisture transfer in unsaturated soil around the earth-to-air heat exchanger in the cylindrical coordinate is established.Furthermore,a bi-dimensional elliptical heat and mass transfer calculation program is developed for this mathematical model by using FORTRAN language,Fortran PowerStation 4.0 is selected for debugging platform.The accuracy and feasibility of self-complied calculation program is verified through experimental data.Through numerical simulation and experimental study,some main conclusions are summarized as follow:the distribution of soil temperature and moisture concentration field interrelate.The migration of soil moisture concentration is directional.The distribution of soil moisture concentration field in the radial and axial direction is distinctly different.There is a moisture concentration peak in the radial direction under the action of soil gradient and moisture concentration gradient.The moisture movement,which occurs both in the liquid and in the vapor phases,gives rise to a transport of sensible and latent heat,which again influences the temperature distribution.Moreover,the change rate of soil temperature field is faster than that of moisture field.The distribution of soil moisture field is spatially delayed.