This paper presents a comparative study of a counter-cross flow plate heat recovery exchanger, which operates as an indirect evaporative air cooler in cooling conditions. In the study, thermal performance of this exchanger with different placement modes (vertical and horizontal) was investigated by numerical simulation based on original mathematical model. To validate the numerical model, vertically and horizontally positioned prototypes with the same exchangers were made and tested on the test rig. According to the test results, the numerical model has a satisfactory accuracy. For these two types of prototypes, influence of supply and exhaust air inlet parameters (temperature and relative humidity) on the thermal performance of the two prototypes in both constant inlet airflow rate and variable inlet air flow rate was researched. The results show that, under conditions of constant airflow rate with variable supply air parameters, the outlet supply air temperature of the exchanger set vertically is 1.41-2.40 degrees C lower than that of exchanger set horizontally, meanwhile, 24-44% more cooling capacity is obtained by the vertical exchanger. It indicates that placement mode has important effects on thermal performance of the exchangers and the exchanger set vertically always shows a better performance. The main reason is considered to be the existence of larger dry areas in exhaust air channels of the horizontal exchanger that reduce the heat transfer between supply air and exhaust air. Therefore, characteristics of the heat transfer in horizontal exchangers was especially studied in this paper. (C) 2018 Elsevier Ltd. All rights reserved.