This study is the first investigation to apply the horizontal earth tube system (HETS) for cooling in an agricultural greenhouse in the tropical climate of Thailand. The cooling performance and condensation phenomenon of HETS was monitored on the typical days of the winter, summer and monsoon seasons in Chiang Mai (northern Thailand). The experiments were undertaken in 30 m(2) of greenhouse volume with the HETS (about 38.5 m of length) buried to a depth of 1 m. The results justified that used soil as a heat basin was possible in a tropical climate and the cooling performance of HETS was moderate. As a result of the variation of solar radiation, the temperature difference of inlet and outlet air flow fluctuated less than other hot weather climates such as subtropical and Mediterranean. Therefore, the obtained cooling performances from the observation in various seasons were distinct. The maximum coefficient of performance (COP) of the typical summer day was higher than the winter and monsoon days in which the values of COP were 3.56, 2.04 and 0.77, respectively. By comparing, the COP of the experimental results and one ton of refrigeration of air conditioning, the best results demonstrate that the HETS was capable of cooling up to 74.84% in the summer. For the condensation inside HTES, the operation of the blower was an additional advantage to eliminate the negligible water condensation after cooling finished. (C) 2013 Elsevier B.V. All rights reserved.