Discrepancies inherent in the application of optimal operative temperatures, estimated on the basis of PMV, and the need to arrive atusable values for the new Czech Government Directive No. 361/2007 Code and the new European Standard prEN 4666:2009 Aerospace Series, aircraft integrated air quality and pressure standards, criteria and determination methods led to a series of experiments based on the physiological human body response to be commissioned. Experiments on 32 subjects (university students) enabled the following to be estimated: (1) the total balance of hygrothermal flows between the human body and the environment and (2) the optimal operative temperature as a function of the subject's activity and clothing. This, in turn, enables the optimal operative temperatures both for air-conditioned and naturally ventilated buildings to be established in a novel and simple way without the discrepancies inherent in the PMVbased method.