R744 in heat pumps vs residential A/C

[Sabloe]

I am journalist on R744.com and was recently approached by one of our readers who is doing research on "low global warming potential refrigerants for residential air conditioning systems".

She wants to know why R744 can achieve a good COP when used for heat pump water heating but does not work so well for residential air conditioning application?

Can you help?

Thanks,

Sabloe