A simulation model for the design and analysis of district systems with simultaneous heating and cooling demands

Latest generations of district heating and cooling systems are characterised by low network temperature with uninsulated pipes, decentralised heat pumps and chillers to modulate the network temperature, and shared energy flows between interconnected buildings. This paper presents a simulation model for the design and analysis of these systems. The model was developed using the Modelica language and it consists of component models from thermal, fluid, and control domains. The model was employed to simulate and analyse the first existing Swedish district system with simultaneous heating and cooling demands and bidirectional energy flows. The system currently connects nine buildings with total respective annual heating and cooling demands of 4.2 and 1.2 GWh. Simulation results revealed several benefits for integrating district and heat pump technologies, including (1) sharing energy flows between interconnected buildings to cover 40 % of the total carried heat in the network, (2) reducing the total purchased energy by 69 % compared to a traditional four-pipe district system, and (3) reducing distribution losses by 28 % compared to traditional networks with insulated pipes. The model can be utilised to support future research and development of new advanced district heating and cooling systems.