The Fan Energy Index (FEI) Calculator measures how efficiently a fan performs compared to a baseline standard. FEI is a unitless ratio that compares a fan’s actual input power to the power of a reference fan operating under the same conditions.
This metric helps users select energy-efficient fans that meet building codes or green certification criteria. It also promotes better fan design and energy savings in HVAC systems.
This tool belongs to the HVAC Energy Rating and Compliance Calculators category.
formula of Fan Energy Index Calculator
Primary FEI Formula:
Fan Energy Index (FEI) = Baseline Power / Actual Fan Power
Where:
- Baseline Power is the power a standard-efficient fan would use at the same flow and pressure
- Actual Fan Power is the power used by the fan being evaluated
Expanded Baseline Power Formula:
P_baseline = (Q × ΔP_total) / (η_ref × η_motor × η_drive)
Where:
- Q = airflow rate (in m³/s or CFM)
- ΔP_total = total pressure rise (Pa or inH₂O)
- η_ref = reference fan efficiency (standard-defined)
- η_motor = motor efficiency (assumed or standard, e.g., 0.9)
- η_drive = drive efficiency (belt/direct, e.g., 0.95)
FEI is a performance-based metric; higher values indicate more efficient fans. An FEI ≥ 1.00 means the fan performs as well or better than the reference.
Reference Table: Sample Fan Energy Index Values
| Airflow (CFM) | Pressure Rise (inH₂O) | Actual Power (hp) | Baseline Power (hp) | FEI |
|---|---|---|---|---|
| 5000 | 2.0 | 4.0 | 5.0 | 1.25 |
| 7500 | 1.8 | 6.0 | 6.5 | 1.08 |
| 10000 | 2.5 | 8.5 | 10.0 | 1.18 |
| 6000 | 1.2 | 2.2 | 3.0 | 1.36 |
| 8500 | 3.0 | 9.0 | 12.0 | 1.33 |
This table helps engineers and specifiers quickly identify high-performing fan setups.
Example of Fan Energy Index Calculator
Suppose a fan operates at 6000 CFM with a total pressure rise of 2.0 inH₂O. It consumes 5 horsepower of actual input power. Standard values: η_ref = 0.65, η_motor = 0.9, η_drive = 0.95.
First, convert airflow and pressure to consistent units or apply directly:
P_baseline = (6000 × 2.0) / (0.65 × 0.9 × 0.95 × 6356) ≈ 6.3 hp
Then compute the Fan Energy Index:
FEI = 6.3 / 5.0 = 1.26
This means the fan is 26% more energy efficient than the standard reference, making it a good choice for energy-conscious applications.
Most Common FAQs
A higher FEI shows that the fan consumes less energy than a baseline model at the same flow and pressure. This leads to lower operating costs and better energy performance.
FEI provides a performance metric that designers can use to choose the most efficient fan for a given application, ensuring compliance with standards like ASHRAE 90.1 or DOE regulations.
No, FEI is a system-level metric that factors in airflow, pressure, and reference conditions. Fan efficiency simply shows how much input energy becomes air movement, without comparing it to a standard.