A school district of that size can save that much in a single year on their electric bill with an intelligent HVAC system.
I don't sell HVAC systems but I've seen this happen firsthand in a school district. Proper energy management programs are critical.
85% or so of a school district budget goes directly to personnel. That piece of the budget is considering operating expense. Other operating expenses? Transportation, energy, internet, phone, etc. The other piece of the budget is capital--used for buildings, equipment over a certain threshold or life expectancy. In most states there are very strict rules and amounts of money provided for both operating budgets and capital budgets. You can't co-mingle money between the two buckets--you can't pay teachers out of capital funds for instance.
So a $2M capital purchase that saves $2M in operating expenses directly impacts a district's ability to put teachers in the classroom. Then the HVAC system is a fixed asset, depreciated over the life expectancy of the building or buildings it serves and the financial impact on the budget is lessened.
As a taxpayer you may not care about this mundane detail and only want to scream about the expense. A more proper response is to scream to your state legislature about this arcane set of rules that forces school districts to make decisions like this.