Sustainable enhancement of district heating and cooling configurations by combining thermal energy storage and life cycle assessment

District heating and cooling systems are designed and optimized to respond to the latest challenges of reducing energy demands while fulfilling comfort standards. Thermal energy storage (TES) with phase change materials can be employed to reduce the energy demands of buildings. This study considers a residential district located in Spain, where a general framework has been established to identify optimal combinations of energy conversion, delivery technologies, and operating rules. The Life Cycle Assessment (LCA) methodology was implemented within a mathematical model, and the objective function considered the minimization of environmental loads. Two environmental impact assessment methods were applied within the LCA methodology: IPCC 2013 GWP 100y and ReCiPe. Four optimal configurations were considered: a reference system (gas boiler and split-type air conditioners) and then three TES-based systems: one sensible (STES, water) and two latent (LTES1-paraffin emulsion and LTES2-sodium acetate trihydrate). Hourly environmental loads associated with electricity imports from the national grid were available. The conventional energy system always presented the worst performance from an environmental viewpoint, being penalized by the high consumption of natural gas. Regarding carbon emissions, LTES1 showed the lowest emissions, followed by STES and LTES2. Reductions in energy demands compensated the impact of paraffin, and results of STES are strongly dependent on tank design. However, considering the ReCiPe method, STES presented the lowest loads, followed by LTES1 and LTES2. Overall impacts of LTES1 with paraffin are higher than STES with water, mainly due to the paraffin and the high volume required.

Automated summary

District heating and cooling systems in Spain are analyzed using Life Cycle Assessment (LCA) methodology to identify optimal energy combinations with minimal environmental impact. Thermal energy storage (TES) with phase change materials is found to have lower environmental loads, especially systems utilizing paraffin.