Different energy balances for the redesign of nearly net zero energy buildings: An Italian case study

The currently developing concept of a Net Zero Energy Building introduces new challenges and research problems. The calculation of a net zero energy balance is heavily influenced by the energy carrier weighting factors that are chosen, which can deeply influence the future energy market towards adopting specific energy technologies. The following paper proposes an analysis of different definitions and conventions for Net Zero Energy Buildings that employ different calculation methodologies and apply different weighting factors to an Italian case study. The case study, which is called “the Leaf House”, is one of the first examples of a nearly net zero energy building in Italy. A building simulation and model calibration were performed using monitored data. Energy balances were calculated for the case study. Scenarios for a building redesign were then proposed, with the aim of reaching an electricity target of net zero energy. Reaching a primary energy building balance of net zero is easier when using symmetric weighting because it allows renewable energy to account for avoided national mix energy generation. The results show that symmetrical balances are nearly fulfilled for the existing building and asymmetrical ones are below zero. In the redesign scenarios, the symmetrical weighting scenarios exceed the zero target by 34.10 and 20.83MWh/year. The asymmetrically weighted balances show a variable trend in that auto-consumption and high load-matching are highly favourable because the theoretical ‘zero auto-consumption’ scenario would yield the worst result and would be the only one below the Net Zero threshold. Although symmetric weighting approaches could be viewed as robust physical approaches for renewables (e.g., the primary energy conversion factors for PV are usually close to 1), they can become a heavy burden during the market development of renewable energy technologies, highly favouring auto-consumption and energy storage to minimise energy import from the grid.