Corey Eastwood, CGCS said: Unfortunately it never pencils out. The $ savings would take tens of years to break even. The savings is in a complete disaster callapse at the wrong time. That is the positive argument.
I put one together last year. 20 years minimum, and thats excluding the time value of money, and the return you could be earning on the money if you didnt do it. If you are going to spend 2 mil on a new system the alternative - invest the money - say you could get 5%. Thats 100k per year return. It's pretty hard to show that spending 2 mil on a system would save you over 100k per year - unless you are in a pretty extreme situation. And even if you can, that only covers the interest, you still have to cover the 2 mil in principal.
Corey has it right. Risk of catastrophic failure/just plain worn out need to be the primary justification.