Cost optimal and net zero energy office buildings solutions using small scale biomass-based cogeneration technologies

In this study, four different small scale biomass-based cogeneration heat and power (CHP) technologies along with three conventional energy generation systems serving an office building in Helsinki, Finland are investigated to find the local cost-optimal solutions for minimum energy performance for each as well as the global cost optimal solution. The Energy Performance of Building Directive (EPBD) comparative framework methodology is followed. All building combinations are simulated by IDA-ICE 4.5 software including building energy efficiency measures/packages; external wall insulation, window type, and envelope air-tightness, and building service system packages including ventilation system, and daylight control. The reference case is defined consisting of reference building built in accordance with the current building code served by district heating and vapor compression cycle cooling system (DH-VCR). The results show that the pellet boiler with vapor compression refrigeration system (PB-VCR) has global cost-optimal solution. When the CHP capacities are sized to cover the peak thermal demands, the low power-to-heat (P/H) ratio CHP technologies have life cycle cost (LCC) less than the reference case, while the CHP technologies with high P/H have higher LCC. The reason of that is the high investment cost relating to higher associated electrical capacities as well as high operational energy costs due to lower thermal efficiency. However, optimizing the CHP capacity and installing auxiliary pellet boiler makes that all investigatedCHP technologies have LCC less than the reference case. Furthermore, the net zero energy building (NZEB) solutions extended - by implementing photovoltaic system (PV) - for the cost-optimal solutions have lower LCC than those extended based minimum energy performance solutions.