Tools › Building Systems › Energy › Energy Savings and Payback › Example
DOE Motor Systems Tip Sheet #1: energy saved by a NEMA Premium motor
| Tool | Energy Savings and Payback |
| Source | U.S. Department of Energy (2012). Motor Systems Tip Sheet #1: When to Purchase NEMA Premium Efficiency Motors. Advanced Manufacturing Office, Washington, DC. Example and Table 1. |
| Level | Undergraduate |
Problem
A 75 hp motor runs 8,000 hours a year at 75 % load. Estimate the annual energy and cost saved by replacing a 92.0 % efficient motor with a 95.5 % efficient NEMA Premium motor at $0.08/kWh, and check the tip sheet's table for 10 to 200 hp motors.
Inputs to Enter
- Quick calculators on (default): motor 75 hp, 75 % load, 8,000 h/yr, old efficiency 92 %, new efficiency 95.5 %, $0.08/kWh (the defaults)
- Table 1 rows: 10 hp 86.7 → 92.2 %; 25 hp 89.9 → 93.8 %; 50 hp 91.6 → 95.0 %; 100 hp 92.2 → 95.3 %; 200 hp 93.3 → 96.2 %
Answers
- Input power = hp × load × 0.746 / η: 75 × 0.75 × 0.746 / 0.92 = 45.61 kW before, 43.94 kW after, a 1.672 kW reduction
- Saving 1.672 kW × 8,000 h = 13,373 kWh/yr, $1,070/yr at $0.08/kWh
- Table 1 (8,000 h, 75 % load): 3,105, 5,160, 8,630, 15,680, 29,350 kWh/yr, reproduced within 2 % because the efficiencies are printed to 0.1 %
Notes
The motor fields hold this example by default; the result sits in the Quick Calculators section of the page.