Simple payback is a number, typically in years, for the time it takes to pay for an initial investment. It does not account for the time value of money. Equation: (Initial Investment Cost)/(Cost savings per year)
Example:
The installed cost of the High Efficiency system was $10,000. It saves $2500/year. The Simple payback is equal to $10,000/($2,500/year) = 4 years