Over the past decade we have seen a development which aims to transfer buildings from energy consumers to net-energy providers. There are two complementing approaches to achieve the above goal (1) to reduce the overall energy consumption of buildings – primarily of the building services systems and (2) to integrate go-generators into building systems to enable buildings to harvest different forms of renewable energy. A well-known development is the integration of PV-panels into the buildings’ fabric to generate electrical energy which can be sold to the grid.