An interesting tool for testing and check phases of HVAC systems was developed, in order to evaluate thermal comfort parameters only measuring temperature and relative humidity in moderate environments, for a wide range of clothing thermal insulation. A simplified approach to thermal comfort was developed in the seventies by Rohles, who found a correlation between PMV, air temperature and relative humidity, for sedentary activity and clothing thermal insulation equal to 0.6 do. An improvement of Rohles model is proposed, aiming to extend results in a wider range of clothing thermal insulation (0.25-1.65 do). Data from experimental campaigns in moderate environments were used to implement a function PMV = PMV(T, RH) and diagrams PMV vs. temperature, for different values of relative humidity, were traced (nine equations and diagrams for male, female, and both sexes, and for three ranges of I-cl). Standard deviation between measured and calculated data was evaluated and a mean error on PMV of +/- 0.22 was found; a T-Student test was also performed and results were significant. Mean Radiant Temperature data were used to calculate Operative Temperature and to correlate to PMV and to Neutral Temperature, corresponding to thermal comfort, by means of linear regression method. (C) 2012 Elsevier Ltd. All rights reserved.