Air/Water Heat Pumps in Existing Heating and Hot Water Systems for Better Urban Air Quality and Primary Energy Savings: Scenarios of Two Italian Cities

In a previous work, a significant contribution to urban air pollution, related to fuel-fired heating systems, was recorded. Thus, the replacement of existing boilers for space heating and domestic hot water (DHW) production systems with high-temperature air/water heat pumps (which can operate with radiators, the most common terminals in the existing building stock), is proposed for the improvement of the urban air quality. Scenarios of substitution within the entire residential building stock of two Italian cities, Milan and Salerno, belonging to different climate zones and with their own thermophysical characteristics, were analyzed. For each of them, the consequences of the replacement intervention on emission reduction, primary energy savings and lower CO2 production were evaluated. The results show that reduction of primary energy consumption, evaluated at design outdoor temperature and for the present generation mix, varied between 34% and 54% in Milan and between 43% and 60% in Salerno, for two values of renewable fraction in electricity generation. The reduction of CO2 production was in the range 30–52% in Milan and 39–58% in Salerno, respectively. The only unfavorable case occurred for Milan for a completely non-renewable electricity generation scenario. The replacement intervention, which implies a significant decrease of emissions of pollutants in urban areas, is unobtrusive to citizens, since the heat pumps (HPs) are coupled with current radiators, without the internal distribution system being modified.