Passport renewal with current Z visa

Hello, I am currently living in China. My passport will expire in Jan 2016. Yes, I have plenty of time. However, when I return to the States this summer holiday I want to renew my passport only because it is more convenient to do so. I will have a current Z (a new one issued in June of this year). If I renew my passport what becomes of the current Z? Is it cancelled along with the old passport? Will the passport office transfer it to the new passport?

Please clarify and thank you in advance!

Dave