Exergy analysis is a technique for systems and processes that can be used to evaluate the distribution of availability losses in a system, so that measures and priorities with improvement potential can be developed. This article investigates the difference between the amount of exergy consumption and exergy loss (irreversibility) in the two methods of humidification, namely Constant Enthalpy Humidification (CEH) and Constant Temperature Humidification (CTH) in a Heating Ventilation and Air Conditioning (HVAC) system. In this work a 15 x 9 x 3 m room with a 10000 cfm Air Handling Unit (AHU), and a 30 and 25 m of supply-and-return duct (30-25, respectively) are considered to investigate the exergy consumptions and irreversibilities of the components in the two humidification methods. The results show that the summation of irreversibilities in CEH is less than the CTH. In addition the power input of CEH in design condition is 12% less than the CTH, mostly due to large exergy consumption of the steam preparation in the humidification process. It can be concluded that CEH has superiority over the CTH due to less exergy consumption in the HVAC systems. (C) 2016 Elsevier B.V. All rights reserved.