Challenges in reaching positive energy building level in apartment buildings in the Nordic climate: A techno-economic analysis

Abstract

Buildings consume significant amount of final energy and they emit large amount of CO2 emissions. To address this issue, nearly zero energy buildings is becoming a common in many countries, while research is advancing towards the positive energy building (PEB) target by utilizing renewable energy that can support reducing the emissions from the building stock. The aim of this study, is to design and model a renewable-based energy system for a real demo apartment building in Nordics (Finland) in order to be a PEB, by exceeding the building’s heating, cooling and plug load demands. The novelty of this study is to assesses the fulfillment of the PEB level in cold climate, by simulating various technologies (such as photovoltaic-thermal (PVT) system, heat pump (HP), wind turbines, seasonal thermal energy storage etc.) their integration with the building, its controls strategies, types of load included in the energy balance and definition of building boundaries across which the balance is calculated. TRNSYS simulation software is mainly used for dynamic simulation of the energy system. The electricity import and export, the life cycle cost (LCC), and the onsite energy matching factors are calculated to estimate the performance of the proposed system. In addition, the challenges related to the building’s limited physical boundary are discussed. The results of this study shows that, if all the demands are included, i.e. heating, cooling and plug loads, then it is difficult to reach the PEB level. In this case, the investment cost in the energy system is around 47–62% of the LCC and the rest is the operational cost. On the other hand, the PEB level is relatively easier to achieve if the plug loads are excluded, then the investment cost is around 88–100% of the LCC and there can be positive cash flow due to larger energy export than import. The PEB level is possible to be achieved when all the demands are included if the building boundary is extended to a virtual boundary outside its physical boundary that allows the addition of more renewable generations or by changing the building’s shape that allows the more installations of renewables on the roof. In this scenario, the investment cost on the energy system is around 62–91% of the LCC. Compared to the building cost, the energy system cost is generally low, i.e. around 1.2–4.3% of the building cost.. It can be concluded that in the Nordic conditions, it is difficult to reach the PEB level for the buildings in urban areas if the all the building’s energy demands are included. Renewable energy generations, such as additional PVT and wind turbines, are needed to be installed in an extended (virtual) boundary of the building if the PEB criterion has to be met when considering all the energy demands. Investment cost of the renewable energy system is low compared to the building’s cost, therefore, such renewable-based solutions can be provided with small additional cost, along with the new building’s cost, so that PEB and carbon neutrality targets can be achieved.