Investigation of indoor thermal comfort in warm-humid conditions at a German climate test facility

As a result of climate change outdoor temperature and humidity are predicted to increase within the next decades in Germany, especially in the Upper Rhine area. As indoor summer conditions will be affected by this change, responses of 136 subjects to warm-humid conditions have been investigated in a test-facility at the Karlsruhe Institute of Technology (KIT). Nine experimental conditions with high operative temperature (to) and different relative humidity (RH) levels (26 °C, 28 °C or 30 °C combined with 50%, 65% or 80%) were scheduled, with each participant experiencing two of the possible combinations. In contradiction to the German addendum of the European standard EN 15251, where a single upper limit for humidity ratio (HR) of 11.5 g/kg is recommended in summer, results indicate that human responses are additionally dependent on current temperature and other factors like thermal history. A linear regression model using operative temperature and humidity ratio is shown to describe the percentage of acceptability and is used to derive an extended comfort zone for seated activity in summer conditions (met = 1.1 and clo = 0.5). Thermal acceptance is compared to other studies (using effective temperature) and proves to be significantly lower with the German subjects than with participants who are adapted to a hot-humid climate. PMV shows underestimation of thermal sensation at elevated air humidity, up to 0.5 scale points under certain conditions.