ECOS 2020 ::Alternative solutions for the optimal integration of decentralized heat-pumps in district heating/cooling networks

The new low-grade district heating (DH) networks operate at temperature levels of around 8-12°C and use decentralized heat pump (HP) units to raise the temperature in buildings for heating and domestic hot water (DHW) production. Such advanced networks have the advantage of being able to serve both for heating (in winter) and cooling (in summer) but correspond to significant pressure losses because of the low differential temperature on the primary network. Also, the performance of the heat pumps depends strongly on the temperature of the network. A high pinch differential temperature between the DH network and the temperature level of energy supply for heating and hot water process in the building corresponds to an important consumption of electricity in the decentralized HP units. This paper presents new solutions and configurations of integrating heat-pumps in advanced district heating/cooling networks in order to minimize the pinch temperature while allowing high differential temperatures on the primary network, then minimizing both the flow rate on the networks and the total exergy losses. Thermodynamic models of heat-pumps have been developed in order to simulate different configurations of integration where the performances in term of exergy efficiency on the substation are determined in function of the temperature of the network and the differential temperature on the primary network. The models have been applied: first to simulate the performance of a reference heat-pump system based on a classical “anergic” low-temperature (8/12°C) advanced heating/cooling network and also to compare with the proposed integrated HP system. Results show that an exergy efficiency of the substations units of more than 55% can be achieved for the proposed concepts, reducing electricity consumption of about 20% compared to the “anergic” DH network decentralized heat-pumps