Thermal mass is usually positively associated with energy efficiency and thermal comfort in buildings. However, the slow response of heavyweight constructions is not beneficial at all times, as these dynamic effects may actually also increase heating and cooling energy demand during intermittent operation or can cause unwanted discomfort. This study investigates the potential of energy simulations to support the exploration-driven development of two innovative responsive building elements: “Spong3D” and “Convective Concrete”. Both use fluid flow (Spong3D: water, Convective Concrete: air) inside the construction to reduce building energy demand by exploiting the use of natural energy sinks and sources in the ambient environment, aiming to make more intelligent use of thermal mass. During the development of these concepts, different simulation tools were used alongside experiments for e.g. materials selection, climate analysis, comfort prediction and risk assessment. By presenting the results from a series of simulation studies and by reflecting on their application, this paper shows how computational building performance analyses can play a useful role in ill-defined R&D processes.@en