1 INTRODUCTION New challenges were opened with the recast of the Energy Performance of Buildings Directive, (EPBD-Recast, 2010), requiring by 2020 that new buildings be “nearly Zero-Energy Buildings” (nearly ZEB). But, for some of European Member States, nearly ZEB are not defined in detail. Therefore, a more consistent definition is the Net ZEB (Sartori et al., 2011), intended as on-grid ZEB’s, meaning ‘buildings connected to the grid’ delivering as much energy to the supply grids as they use from the grids (Laudsten, 2008). Net ZEB’s are energy producer buildings besides consumers and, therefore, they use as much renewable energy sources (RES) as possible to compensate the energy requirements of the building. Sustainable cities require energy-efficient buildings, i.e. buildings where the use of energy is minimized without compromising the occupants comfort standards, namely for heating, cooling, lighting and indoor air quality. In order to increase the overall energy efficiency in cities and fa- cilitate the integration of RES into urban energy networks, building-to-grid interaction should be reinforced, requiring, from the buildings’ perspective, energy-efficient ‘interactive’ buildings (EeIB). Henceforth, EeIBs actively interact with multiple-carrier energy networks (e.g. electric grid, thermal network, gas pipelines) by providing up-to-date information, valuable for the en- ergy networks management. Therefore, not only energy flows, from or to an EeIB, are im- portant, but also the information flows, based on accessing and predicting time-dependent ener- gy flows. This is the context that frames the work here developed, following the objectives of EERA Joint Programme on Smart Cities (2011). The energy networks modeling of Niemi et al. (2012) is an example of simulating multi- carrier energy networks including renewable energy generation, where buildings are simplified to nodes in the grid. In the load-generation approach (Sartori et al., 2011), buildings are evaluat- ed by their energy demand (consumption or load) and energy supply (production or generation). Energy Performance Certificate: a valuable tool for building-to- grid interaction? Marta Oliveira Panão Laboratório Nacional de Energia e Geologia, Unidade de Eficiência Energética, Lisboa, Portugal marta.oliveira@lneg.pt Helder Gonçalves Laboratório Nacional de Energia e Geologia, Unidade de Eficiência Energética, Lisboa, Portugal helder.goncalves@lneg.pt ABSTRACT: New challenges were opened with the recast of Energy Performance of Buildings Directive, requiring by 2020 that new buildings be “nearly Zero-Energy Buildings” (nearly ZEB). In addition to consumer buildings, Net ZEBs are also producers’ by using as much re- newable energy sources as possible to compensate the building energy load. Sustainable cities require energy-efficient buildings, i.e. buildings where the use of energy is minimized without compromising the occupants comfort, namely for heating, cooling, lighting and indoor air quali- ty. But smart cities require energy-efficient ‘interactive’ buildings, which integrate multiple- carrier energy networks and provide up-to-date valuable information for their management, where buildings are simplified to single nodes characterized by their energy load, generation, storage and conversion, applying the load-generation approach. The information currently avail- able in the Energy Performance Certificate is not relevant for estimating the time dependent building energy load, but it can be easily improved by including a few descriptive parameters.