Earth-air-tunnel heat exchanger (EATHE) systems are insufficient to meet the thermal comfort requirements in summer conditions. Therefore, evaporating cooling has been integrated with EATHE to enhance the thermal comfort hours. Economics of integrated EATHE-evaporative cooling system to reduce/avoid the use of air-conditioner and electric heater is analyzed by evaluating simple Internal Rate of Return (IRR) on investment. For this analysis a transient and implicit model based on computational fluid dynamics has been used for evaluating the energy saving obtained by the use of EATHE system integrated with evaporative cooling. Four base cases of existing systems, i.e. air-conditioner and electric heater have been considered for carrying out the economic analysis. Moreover, three different types of blower (i.e. energy efficient blower, standard blower and inefficient blower) have been considered for evaluating the energy saving and financial viability of the proposed system. These results of IRR calculation shows that wherever, the existing air conditioner and heaters are efficient, their replacement with proposed EATHE system is not a technically and economically viable option. It is observed that the IRR value is greatly dependent on the electric tariff and the energy efficiency of the blower used in the proposed EATHE system. (C) 2012 Elsevier B.V. All rights reserved.