From "ASPE Data Book Vol.4 service hot water systems" ,you can find hot water demand per fixtures for hospitals.Multiplying fixtures quantity by demand, find the total demand,multiply it by demand factor (0,25) then multiply by storage factor (0,60) to find storage capacity.
HOT WATER DEMAND FOR HOSPITALS LT/FIXTURE AT 60°C
FIXTURE DEMAND (lt.)
Basin (private) 7,6
Basin (public) 23
Bathtubs (cont.flow) 625
Sinks 76
Showers 284
Demand factor 0,25
Storage factor 0,60
Regards,
Ercan