The HPT heat pump test bench is a closed-loop test bench for functional testing of air-to-water heat pumps according to DIN EN 14511. The advantageous closed-loop design uses an insulated chamber with conditioning units for temperature and humidity outside the chamber. The conditioned air runs in a closed circuit (closed-loop). This design provides excellent, uniform temperature and humidity conditions throughout the chamber. The temperature and humidity control of the different climate points according to DIN EN 14511 is accurate and dynamic. An optimized safety concept enables safe tests with refrigerants with low GWP.