Energy saving potential of climate adaptive building shells - Inverse modelling of optimal thermal and visual behaviour

In common building design practice energy performance calculation programs or, in the best case, dynamic building simulation programs are used to optimize the properties of a building shell. However, even with use of dynamic building simulation programs adaptive behaviour, in terms of changing building shell properties, is not easy to simulate since many inputs - like insulation values, window ratio, etc. are ‘fixed’ values. The result of these optimization calculations is therefore rather an optimization in fixed design values then a set of ideal optimal adaptive behaviour building shell parameters. In the Dutch FACET project (Dutch acronym: ‘Adaptive façade technology for increased comfort and lower energy use in the future’) a quest for the ideal building shell with adaptive, variable properties is performed. Since the standard way of simulating does not allow fully adaptive building shell behaviour, a completely new, inverse modelling approach is set up. The key question here is: "What would be the ideal, dynamic properties of a building shell to get the desired indoor climate at variable outdoor climate conditions?" By reversing the design approach, and using inverse modelling, a set of ideal, hypothetical building shell parameters is computed for different climate conditions at various time steps (seasons, daynight, instantaneous), for different building categories like offices, schools and dwellings. This ‘ideal’ adaptive behaviour will make it possible to maximize indoor comfort and to minimize energy use for heating, cooling, ventilation and lighting. It does not start with having existing concepts in mind, but instead focuses on clarifying the theoretical potential of adaptive architecture. In the TRNSYS and Radiance simulations the building shell input is given as a black box, with a wide range of possible (combinations of) thermal and visual properties. Technologies and materials to meet the requirements can be more futuristic but also very ‘down to earth’. Partial solutions are already available, in low or high tech solutions, such as smart glazing, variable vacuum insulation, insulating window covering, etc. Further technology development is expected to be desired to fully meet the ideally adaptive behaviour requirements. Based on state of the art ‘adaptive temperature’ criteria optimal thermal behaviour was simulated in a first step. This gives the energy saving potential for an optimal thermal adaptive building shell. In a second step the computed optimal daylight characteristics of the building shell is given by optimizing visual comfort in Radiance. In a next step, both visual and thermal behaviour is optimized in an integral way, using a multi objective criteria approach. This paper describes the thermal and visual simulation optimization results of the FACET project. Preliminary results show that optimal adaptive building shell properties can reduce the total heating and cooling demand by a factor 10 compared to state of the art new built offices. For the Netherlands this means a factor 3 compared to the very efficient passive house technology. In the case of offices the heat demand is practically eliminated and the cooling demand can be reduced significantly by a factor two. The resulting extremely low energy demand means that less effort is needed to enable zero energy, or energy producing buildings in the future