The EU is committed to achieve climate-neutrality by 2050. Despite the achieved goals, further improvements are still required to reduce the primary energy demand. In particular, the building sector still shows great potential for energy efficiency improvements especially for cooling. While conventional air cooling systems are widely used, their primary energy demand is quite high and their thermal comfort quite low. Thermally activated building systems (TABS) can generally improve the cooling performance due to their large surfaces and thermal masses for heat transfer and storage, but still show potential for improvements in energy efficiency. Therefore, this study investigates further improvements in energy efficiency and user comfort with a novel TABS design in concrete ceilings by e.g. using a higher coolant temperature and manipulating the heat transfer across surfaces. Condensation is avoided by enhancing temperature uniformity at the surfaces. Thus, a lower minimal coolant supply temperature can be used to increase the maximum cooling capacity during challenging weather. The novel TABS is tested for two different heat sink configurations, a heat pump driven by electricity of PV panels and nocturnal sky radiators. Both systems show a good performance. The cooling capacity of the nocturnal sky radiators ensures thermal comfort for up to two storeys, while the heat pump with PV modules ensures it up to 13 storeys for a fixed roof area. However, the cooling capacity of the novel TABS with both heat sink systems strongly depends on the individual site and weather conditions.