Abstract Optimizing energy consumption in the cities might present a significant impact on decarbonization strategies approaching carbon neutral future in 2050. Positive Energy Block initiative is targeted particularly to densely build environments promoting shared on-site renewable energy production and storage, using smart grids, internet and communication technologies, Internet of Things and other highly advanced energy efficiency technologies within the neighborhoods. Research presented focuses on transition from traditional urban block to Positive Energy Block in valuable environment of historic city center exploring possibilities of waste heat regeneration and on-site renewable energy technologies. Energy consumption data is analyzed and the conception for possibilities of on – site renewable energy generation and waste heat recovery from data centers and cooling units in selected urban block is drawn. The results indicate that very ambitious targets for energy efficiency improvement are needed to achieve positive energy block – 65% and 60% for electricity and heating consumption, respectively. Possible savings of CO2 emissions are 45–50 kg/m2 per year.