Sustainable heating alternatives for 1960's and 1970's renovated apartment buildings

The Finnish Government target of carbon neutrality by 2035 is challenging for the district heat (DH) systems of Finnish cities, as nearly 50% of the DH fuels are still fossil or peat. The DH price in Finnish cities is rising intensively. To avoid energy poverty, it is imperative to develop low-carbon DH solutions affordable for all customers. The feasibility of various low-carbon scenarios supplying a DH network is investigated with three different energy renovation levels. Biomass combustion technologies (combined heat and power (CHP) and heat only boiler (HOB)) and waste heat recovery technologies (Heat Pump and Electric Boiler) are analyzed. The economic and sensitivity analyses of the DH network are carried out from utility and end-user viewpoints. The operation cost and break-even price of heat are calculated in different renovation levels. Biomass HOB has the lowest operation cost at all renovation levels followed by waste heat-heat pump. Waste heat-heat pump + electric boiler has the lowest total cost, 53–58 €/MWh, at all renovation levels. Waste heat recovery scenarios were found sensitive to changes in electricity price. Waste heat-heat pump has the lowest overall emissions, whereas biomass combustion causes high emissions of biogenic CO₂, NO_x and particulate matter.