Heat pumps in combined heat and power systems

Heat pumps have previously been proposed as a way to integrate higher amounts of renewable energy in DH (district heating) networks by integrating, e.g., wind power. The paper identifies and compares five generic configurations of heat pumps in DH systems. The operational performance of the configurations is investigated at both local and system level considering different DH network temperatures, different fuels and different production technologies in the DH network. The results show that in terms of system performance and cost of fuel one or two configurations are superior for all of the considered cases. When considering a case where the heat pump is located at a CHP (combined heat and power) plant, a configuration that increases the DH return temperature proposes the lowest operation cost, as low as 12 EUR MWh−1 for a 90 °C - 40 °C DH network. Considering the volumetric heating capacity, a third configuration is superior in all cases. Finally, the three most promising heat pump configurations are integrated in a modified PQ-diagram of the CHP plant. Each show individual advantages, and for two, also disadvantages in order to achieve flexible operation.