Thermal performance of earth air tunnel heat exchanger has been investigated under transient conditions for three different soil conditions considering three operating modes. In first operating mode EATHE works continuously for 12 h, in second mode it works for 60 min and then it is off for 20 min and in the last mode EATHE runs for 60 min and remains off for 40 min. In second and third mode EATHE is operated for 12 h intermittently. CFD model was developed in GAMBIT (version 2.2.3), simulated in FLUENT (version 6.3) and then validated with experimental data. CFD analysis has been carried out using a three-dimensional transient numerical model. Air temperature drop and heat transfer between air and soil is calculated considering different thermal properties of soils. Higher thermal conductivity (1.28 Wm(-1) K-1) soil should be used in first mode of 12 h continuous operation as it improves the performance by 5.04% as compared to least thermal conductivity soil and soil with poor thermal conductivity (0.52 Wm(-1) K-1) shows performance improvement of 1.81% when operated in intermittent operation as compared to continuous running. (C) 2014 Elsevier B.V.All rights reserved.