Currently, evaluating the performance of internally cooled/heated liquid desiccant dehumidification system (ICHLD) is complicated, requiring a large number of iterative calculations. This study developed a simplified numerical model, for obtaining the outlet parameters of all fluids (air, solution and heating/cooling fluid) and system performance of dehumidifiers and regenerators in ICHLD accurately and directly. The model was built by defining three kinds of effectiveness, i.e. enthalpy effectiveness, moisture effectiveness and temperature effectiveness. Based on the parameter study under different design and operation conditions, the correlations of effectiveness were obtained by multiple linear regressions, using heat and mass transfer gradients and other related parameters as variables. Comparisons between our results and those by existing mathematical models show that the composite errors are acceptable, with an average difference of 14.5% for dehumidifiers and 6.83% for regenerators. Similar trends were also observed in comparisons with previous experimental data, with average errors about 20%. The inlet solution temperature has a greatest impact on the enthalpy effectiveness and moisture effectiveness. The temperature effectiveness is mainly determined by the temperature difference between cooling/heating fluid and solution. This simplified model is very useful for researchers and engineers, especially those interested in the dynamic performance of ICHLD systems. (C) 2012 Elsevier B.V. All rights reserved.