The system efficiency of desiccant air dehumidification is usually evaluated by a coefficient of performance (COP) that is defined as the ratio of the cooling capacity and the sum of net electrical power input. The common efficiency evaluation method has many weaknesses especially if applied on Liquid type of desiccant, low humidity different between inlet and outlet, and also on the system that has automatic operating control. This paper offers a solution for weaknesses of common method with a proposed novel. method to evaluate the performance of liquid desiccant air dehumidification system. (C) 2011 Elsevier B.V. All rights reserved.