Optimal retrofit of district heating network to lower temperature levels

The transition of existing second-generation district heating networks (DHN) towards lower temperature levels for operation can lead to energy savings and to fewer constraints for the pipes and substations. However, retrofitting measures on the distribution network are often inevitable in order to still guarantee heat demand satisfaction.This paper presents a methodology to efficiently identify and alleviate existing limitations for temperature lowering in the design of a DHN distribution network. After having identified the most restrictive assets through existing methods, we apply a multi-objective optimization on a dynamical thermal hydraulic simulator for selecting the most efficient modifications on the DHN to attain our target.We apply the developed methodology on a test case representing real DHN operation, and featuring 60 consumers and 260 pipes. The maximum operating temperature is decreased significantly and various modifications for retrofitting are proposed as a set of optimal solutions, forming a Pareto front approximation. This work, through the combined use of a non-linear, dynamic simulator, and a multi-objective optimization framework, allows also to consider a variety of assets (exchangers, pumps, pipes ...) as retrofitting targets and, thus, potentially identifies interesting solutions beyond common practices.