District heating systems are gaining prominence as cities pursue decarbonization, but elevated return temperatures from building connections remain a persistent technical challenge. When customers return cooled water to the network at higher temperatures than necessary, the entire system suffers: transmission losses increase, pumps consume more electricity, and the network's capacity to serve additional buildings diminishes.
A recent simulation study examined practical solutions for multi-residential buildings, focusing on two intervention strategies: optimized pump control with minor hydraulic modifications, and a more substantial redesign using a cascade configuration.
The cascade system represents a departure from conventional practice. Rather than supplying space heating and domestic hot water in parallel—a standard approach that allows each circuit to operate independently—the cascade method prioritizes domestic hot water preparation first. Once this circuit extracts its thermal requirement, the already-warmed return water feeds the space heating loop. This sequential arrangement ensures that cooler water is progressively used, minimizing the overall return temperature to the district network.
Using measured consumption data from actual buildings, researchers calibrated their simulation model and tested various optimization scenarios. The results were compelling: modest hydraulic adjustments combined with intelligent pump control achieved a 6.6 K reduction in weighted mean return temperature, dropping from 53.5°C to 46.9°C. The cascade variant nearly doubled this improvement, reaching 41.3°C—a 12.2 K reduction.
Beyond thermal performance, the study verified that these measures maintain reliable heat supply throughout the building, addressing a critical concern for building operators. The proposed solutions are compatible with other return temperature reduction strategies documented in literature, require no changes to occupant behavior, and demand relatively low capital investment. For developers planning new district heating connections or buildings undergoing major renovations, these hydraulic optimizations offer a straightforward pathway to reducing system losses while supporting wider district heating adoption across decarbonizing energy systems.
