Numercial Simulation And Performance Analyses On The Earth-to-air Heat Exchanger

EAHE (Earth to Air Heat Exchanger) based on mix-ventilation has a considerableapplication prospect for its good technique practicability, relatively low operationexpense, and excellent energy conservation efficiency.This study firstly gave an analysis of the external disturbance factors of soiltemperature and then discussed the condensation condition and the calculating methodin the process of air handling. This research built the database of soil temperature fromthe parameters of soil thermal properties. Through analysis of the soil temperatureduring the operation of EAHE, summarizing that EAHE had a very weak influence onthe soil temperature in the condition of intermittent operation.In4-meter-depth, the soilcould maintain an annual average temperature around±1℃.A one-dimension modelwas proposed to calculate the outlet temperature and relative humidity on the basis oftheabove simplified model.Compared with the experiment data of Nebraska State University, the calculationerrors of temperature in the process of heat exchange and outlet temperature parametersduring the experiment rest within5%,which certified the accuracy of the simplifiedmodel.This study calculated the influence that EAHE parameters had on temperature andhumidity of heat transfer performance.In device parameters, pipe length, diameter hadlimited impact on theEAHA efficiency,If the pipe range is40-60cm and pipe diameter iswithin0.9cm, the heat change efficiency will keep above60%. On the contrary, theburied depth of EAHE connected to heat exchanger temperature determined the outlettemperature. For the operation parameters, inlet parameters is generally determined bythe environment and varied velocitywhich means different terminal load.Based on the analysis and calculation of the simplified model, e-NTU (efficiency-theNumber of Transfer Unit) design method was proposed for EAHE parameterscalculation. Through a typical design, the EAHE system can provide60%of thebuilding, which can support the summer ventilation need for Beijing area.