What is design concentration of 60 fahrenheit?
First need to know design concentration (% per volume), normally 7 for class C fires.
Second need to know design temp of your room (that maybe is the 60F??).
Third go to NFPA 2001 (2015 edition) Table A.5.5.1(i) HFC-227ea Total Flooding Quantity (U.S. Units)
From there determine weight requirement (lb/ft3)
Then multiply that to your room volume (ft3), that is now your clean agent capacity (lb)
Go to your manufacturer (fike, tyco, etc.) catalog and select a tank that would fit your clean agent capacity.