Life cycle cost analysis of a multi-storey residential Net Zero Energy Building in Denmark

It is well recognized that in the long run, the implementation of energy efficiency measures is a more cost-optimal solution in contrast to taking no action. However, the Net ZEB concept raises a new issue: how far should we go with energy efficiency measures and when should we start to apply renewable energy technologies? This analysis adopts the LCC methodology and uses a multi-family Net ZEB to find the answer to this question. Moreover, it looks at the issue from the building owner's perspective, hence it should be seen as a private economy analysis. The study includes three levels of energy demand and three alternatives of energy supply systems: (1) photovoltaic installation with photovoltaic/solar thermal collectors and an ambient air/solar source heat pump; (2) photovoltaic installation with a ground-source heat pump; (3) photovoltaic installation with district heating grid. The results indicate that in order to build a cost-effective Net ZEB, the energy use should be reduced to a minimum leaving just a small amount of left energy use to be covered by renewable energy generation. Moreover, from the user perspective in the Danish context, the district heating grid is a more expensive source of heat than a heat pump for the Net ZEB. -- Highlights: → Combined heat and power systems can improve urban energy-efficiency but are often subject to planning restrictions. → An MILP optimization model is used to design integrated urban energy systems for various city sizes and technology types. → Restricting urban CHP use has little effect on overall system cost, but cost structure is different. → Restricting urban CHP use can reduce overall urban energy-efficiency by up to 24% versus a reference case.