Control development and sizing analysis for a 5th generation district heating and cooling network using Modelica

Abstract

5th generation district heating and cooling networks (5GDHC) are a relatively new concept. They are based on the idea that a single district loop at a ambient temperature range can be used for heating and cooling simultaneously. This paper improves on a 5GDHC called the reservoir network. The study updates the sewage heat exchanger plant model to more realistically represent seasonal changes, uses the novel pump models with variable efficiency, introduces a ground coupled district pipe model to consider the inertia of the district network and a new control strategy for storage and sewage heat exchanger was implemented. the new approach reduced operating costs, mainly due to pumping cost for storage, sewage heat exchanger plant and distribution pump, while increasing the overall robustness of the approach in different sizing conditions. Thanks to the new controller, the pumping consumption was reduced by 21% with respect to the baseline, while showing that the approach is robust against design changes such as reduction in borehole field size and increasing the sewage heat exchanger size, since the pumping energy savings become 29%. Lastly borehole field temperature stability was analyzed through a 40Y simulation.