787 ECS
I was surprised to hear (although my source might be wrong) that the 'No bleed' 787 ECS system still uses an air cycle pack. Instead of R-134a or other phase change refrigerants. Once you have dedicated pressurization turbines (electrically driven) and an electrically driven pack compressor, why not go to a refrigerant requiring lower mass flow (smaller, lighter plumbing and heat exchangers)?
Anyone have a link to a 787 ECS system description and/or trade study between the two system types?