Modelling framework for integration of large-scale heat pumps in district heating using low-temperature heat sources: A case study of Tallinn, Estonia

The paper presents a modelling framework that may be used to plan the integration of large-scale HPs in district heating (DH) areas. By use of the methodology both optimal HP capacities to be installed and optimal choice of heat source to be used during the year are identified by minimizing total cost of ownership including investment and operational costs. The modelling framework uses mixed-integer linear programming and hourly calculations over one year. Seasonal variations of the heat source temperatures, capacity limitations and HP coefficient of performance as well as technical constraints were taken into account. The DH network of Tallinn, Estonia, was used as a case study. Six different heat source types were identified for 13 potential locations of large-scale HPs. The results showed that the integration of large-scale HPs in the DH network of Tallinn is economically feasible. It was found that 122 MW HP capacity could be installed without compromising the operation of sustainable base load units. The heat sources needed for obtaining this solution were sewage water, river water, ambient air, seawater and groundwater. It was further shown that the Lorenz efficiency depends on the variations of heat source temperatures