Integrated evaluation of energy and water use in air-cooled and adiabatic condensers – a case study in an office building

• Adiabatic condensers are compared to conventional air-cooled condensers in chillers. • Adiabatic condensers yield energy savings in all climate regions studied. • Energy savings economically counterweight the additional on-site water consumption. • Global water consumption is favorable where water use at power generation is high. The energy efficiency and water consumption of an air-conditioning system are critical considerations, especially in locations where water scarcity is a real threat. Compared with conventional air-cooled chillers, evaporative pre-cooling in adiabatic condensers improves energy efficiency but comes with the drawback of a high-water consumption. However, the source water consumed off-site at power plants during electricity generation remains largely overlooked. This study provides one of the first integrated assessments of both on-site and off-site water use in evaporative cooling for air-cooled condensers. Herein, the effects of replacing conventional air-cooled condensers in the chiller of a small office building with adiabatic condensers were analysed in terms of energy efficiency and both the off-site and on-site water consumption. Fourteen locations representing eight climate types and different electricity mixes were considered. In all cases, the energy efficiency was improved by at least 13% and reached 39% under the harshest summer conditions. The adiabatic condensers were also favourable in terms of global water consumption when the electricity mix implied high off-site water consumption. In locations where hydropower accounts for a large share of the country’s electricity mix, global water consumption using the adiabatic condensers was up to 20% lower than that using air-cooled condensers. In contrast, the adiabatic condensers had higher global water consumption in locations with low off-site water consumption. For water-to-electricity tariff ratios below 26.87, the improvement in energy efficiency is an effective counterweight against any increase in global water consumption from an economic perspective. However, under future energy mixes with larger contributions from solar PV and wind, the overall water footprint of adiabatic cooling is expected to rise due to the low water intensity of these renewable sources. Moreover, the water scarcity of a given location must be considered when determining the most suitable type of heat rejection for the chiller condenser.