Application of the Water-Energy Nexus approach to assess the sustainability of air conditioning systems

In the context of global warming and the increasing demand for air conditioning, understanding the sustainability of energy and water systems is crucial. This paper applies the Water-Energy Nexus approach to air conditioning (HVAC) equipment, comparing traditional systems (TS) based on Vapour Compression Refrigeration with Indirect Evaporative Cooling-based systems (IES), in terms of electricity use and total water consumption. The analysis considers 19 cities across different regions, incorporating national energy mixes, climate data, building types, various HVAC configurations and water stress indicators. The results show that IES can offer significant energy savings – up to 43 % - particularly in dry climates and in buildings with high sensible thermal loads. Although IES generally consumes more water than TS, the Water-Energy Nexus framework reveals that the water evaporated during IES operations must be offset by the water saved through reduced electricity generation. A net total water saving is achieved when the Water Consumption Factor (WCF) of the electricity grid reaches values in the range of tens of m3/MWh. This study, by adopting a life cycle-informed perspective, provides a significant contribution to understanding the overall sustainability of air conditioning systems: it offers a deeper insight into the complex trade-offs between energy efficiency and water use within the HVAC sector and the built environment.