Use the Planning & Engineering NTP
Go to Power Engineering.
Go to Chapter on Component power consumption.
There are charts for individual cards, but there is a chart for module power comsumption assuming all slots are filled to capacity.
NT5D21 Core/Network Module 260 watts x2 = 520
NT8D37 IPE Module 460 watts x6 = 2760
Pedestal 50 watts x2 = 100
Add them up and use the formula on the next page.
BTU (thermal load) = total power dissipation x 3.41
This will get you in the ball park.
There is a typo in my NTP.
For air conditioning purposes, 1 ton = 1200 BTU.
This should say, 1 ton = 12000 BTU.
Keep reading the Power Calculation Guidelines.