Anthropogenic heat flux from air-conditioning: direct measurements and meteorological controls

Anthropogenic heat is a central component of the urban energy balance. Until now it is primarily estimated by inventory methods or modelling approaches. In this study, we directly measured the anthropogenically emitted sensible heat from an air-conditioning system. Measurements of exhaust air temperature and volumetric flow rate were taken from 01 June 2025 to 31 August 2025 at a university building of Technische Universität Braunschweig, Germany. The anthropogenic sensible heat flux (Q H ) was calculated with these measurements and evaluated by descriptive statistics. Correlation and regression methods were used to investigate the relationship between Q H and meteorological variables. The sensible heat flux of air-conditioning ranged from 0 to 269 W m −2 building floor area (mean: 27 W m −2 ). Ambient air temperature and vapour pressure were found to be the strongest predictors. The regression slopes indicate that Q H from AC increased by approximately 3.6–4.5 W m −2 per 1 K increase in air temperature, and by 4.3–4.4 W m −2 per 1 hPa increase in vapour pressure. The observed co-dominance of air temperature and vapour pressure questions commonly used parameterisations of Q H based on air temperature alone, particularly for combined AC-ventilation systems. However, the moderate model performances of R 2 between 0.55 and 0.75 indicate additional influencing factors. This study provides the first direct measurements of anthropogenic heat from an air-conditioning system and offers reference values for inventory or modelling approaches.