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“ It ' s a good and a bad thing ,” Woods said . “ It ' s good that more people can benefit from improved comfort , but it also means a lot more energy is used , and carbon emissions are increased .”
To calculate the emissions to manage both temperature and humidity , the researchers divided the globe into a fine grid measuring 1 degree of latitude by 1 degree of longitude . Within each grid cell , the following characteristics were considered :
• population ,
• gross domestic product ,
• estimated air conditioner ownership per capita ,
• carbon intensity of the grid , and
• hourly weather .
They ran nearly 27 000 simulations across the globe for representative commercial and residential buildings .
Climate change is affecting ambient temperatures and humidity around the globe , making it warmer and more humid . As part of the study , the researchers considered the impact of the changing climate on air conditioner energy use by 2050 . For example , the study projects air conditioner energy use to increase by 14 % in the hottest climate studied ( Chennai , India ) and by 41 % in the mildest ( Milan , Italy ) by 2050 . The increase in global humidity is projected to have a larger impact on emissions than the increase in global temperatures .
“ We ’ ve already made the existing , century-old technology nearly as efficient as possible ,” Woods said . “ To get a transformational change in efficiency , we need to look at different approaches without the limitations of the existing one .”
Existing vapor compression technology is optimised to cool our buildings using a “ vapor compression cycle .” This cycle uses harmful refrigerants to cool air down low enough to wring out its moisture , often over-cooling the air and wasting energy . Improving the vapor compression cycle is reaching practical and theoretical limits , thus pointing to a need to leap-frog to an entirely new way to cool and dehumidify buildings .
New technologies that split this cooling and humidity control problem into two processes show potential to improve efficiency by 40 % or more . One such technology space is the use of liquid desiccant-based cooling cycles such as the many liquid desiccant air conditioning technologies that NREL is currently developing with many partners , such as Emerson and Blue Frontier .
The researchers point out that the use of liquid desiccants fundamentally changes the way humidity is controlled and has a theoretical efficiency limit that is 10 times higher than the vapor compression cycle alone . A hypothetical technology — at only half this new limit — would reduce cooling-energy emissions by 42 % in 2050 , with the equivalent of avoiding 2 460 million tons of carbon dioxide annually . RACA
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RACA Journal I May 2022 www . hvacronline . co . za