Hello
In the data center, heat is often removed from the equipment by increasing the airflow, this is expressed in CFM, an increase in CFM equates to an increase in heat removal. There must be enough CFM that the equipment does not overheat. so the larger fan modules you have on the chassis the better cooling you will get for the chassis and its modules.
In other hand, talking about tons, remember that air contiditoning systems are rated in tons, so this refers to your data center cooling system, this is not actually the same if we talk about a Nexus chassis, you know that the role played by a fan module in the chassis is to take the cold aisle air flow, cool the internal components, thereby releasing the hot air from the chassis.
I am not an especialist in data center design, nevertheless I think you're trying to find information that is not concerned to the Cisco equipment, but to your data center cooling system desing. So this documentation could be useful for you.
https://www.cedengineering.com/userfiles/HVAC%20Cooling%20Systems%20for%20Data%20Centers.pdf
HTH
