Analysis of a wastewater based low temperature district heating system with booster heat pumps for new and existing residential buildings

District heating networks play a key role in the transition towards sustainable cities, due to their ability to efficiently provide space heating and domestic hot water to buildings located in urban areas. Although an increasing number of buildings is being refurbished, a significant portion of the building stock during next decades will still be made by old buildings with low thermal insulation. The potential of recovering energy from a low temperature heat source and to efficiently supply it to both new and existing residential buildings through a heat pump based district heating system (HPDH) is here investigated on the case study of Abano Terme (Italy), where a large volume of wastewater is discharged to the environment at the temperature range 35-55°C. In particular, an analysis is carried out to compare a district heating system with distributed heat pumps (d-HPDH) to a more conventional one with central heat pump and auxiliary gas boiler (c-HPDH). Simulation of neighborhood heat demand and district heating operation are based on internally developed models in MATLAB/Simulink. A brief description of the models is given here. A real neighborhood consisting of 98 buildings of different age classes has been simulated. Both HPDH systems bring a sharp drop in primary energy consumption with regard to the current situation made of individual gas boilers. The efficiency improvement of the d-HPDH over the c-HPDH is expected to increase with growing number of new and recently constructed buildings. When the latter consume 21% of heat demand, the seasonal coefficient of performance of d- HPDH is 4% higher than c-HPDH.