​ Controlling humidity has a big impact on greenhouse gas emissions

 

The increasing need to cool the air in our built environment is both a cause and an effect of climate change. Air conditioning accounts for a large portion of global greenhouse gas emissions today, which is estimated at 3.9%; however, the role that humidity plays in these emissions is often overlooked. The emissions associated with reducing air humidity (i.e., removing water vapour from air) are larger than emissions associated with reducing air temperature (i.e., cooling air). The research team have shown how dramatically humidity-related emissions will increase with rising cooling demand around the world. They have calculated the minimum separation energy for removing water vapour from air and find that this is at least an order of magnitude less than the processes used today. New technologies that split this cooling and humidity control problem into two processes show potential to improve efficiency by 40% or more. One way to do this is the use of liquid desiccant-based cooling. The researchers point out that the use of liquid desiccants fundamentally changes the way humidity is controlled and has 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.



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