Drive Efficiency

Fan Efficiency System Effects & 

System Leakage

Fan Selection System Design

Potential for Air System Savings
Fan Efficiency Ratio(FER) =

Fan Efficiency

Baseline Efficiency

• Varies along the fan curve

• Independent of fan type or category

• Two test configurations: ducted and non-ducted

• Think of the Baseline Efficiency as a minimum 

allowable fan efficiency (FER ≥ 1.0 is compliant)

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Fan Efficiency Ratio
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Airflow

Pressure

Fan Input Power

Power

Pressure

Fan Efficiency Ratio (FER) 

Efficiency

FER varies along the fan curve
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Airflow

Pressure

Fan Efficiency Ratio - FER

0

1.0

2.0

FER

Pressure

Fan Efficiency Ratio (FER) 

FER varies along the fan curve
Static vs. Total Efficiency

• Ducted fans can use both static and velocity 

pressure to overcome system pressure losses. 

Ducted fans should be selected using total 

pressure and total efficiency is the correct 

measure of fan efficiency.

• With non-ducted fans, any velocity pressure at 

the fan discharge is immediately dissipated, 

making it unusable for any further work. Nonducted fans must be selected and compared using 

static pressure, so static efficiency is the 

appropriate measure.

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Baseline Efficiency

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Increasing Fan Size

6

Increasing System Pressure

and Fan Complexity
Baseline Efficiency

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Efficiency above the surface exceeds the baseline (FER>1)

7
In terms of efficiency:

Fan Efficiency Ratio =

Fan Efficiency

Baseline Efficiency

In terms of power:

Fan Efficiency Ratio =

Baseline Power

Fan Input Power

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Fan Efficiency Ratio
Baseline Efficiency Equations

For fans tested with a ducted outlet:

ηt,baseline = ηt,target × Q

Q+Q0

×

Pt

Pt+P0

For fans tested with a non-ducted outlet:

ηs,baseline = ηs,target × Q

Q+Q0

×

Ps

Ps+P0

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Baseline Power Equations

For fans tested with a ducted outlet:

Hbaseline =

Q + Q0 × Pt + P0

6343 × ηt,target

For fans tested with a non-ducted outlet:

Hbaseline =

Q + Q0 × Ps + P0

6343 × ηs,target

parameters in blue are constants, 6343 is for I-P only

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Baseline Power Equations

For fans tested with a ducted outlet:

Hbaseline =

Q + 250 × Pt + 0.4

6343 × ηt,target

For fans tested with a non-ducted outlet:

Hbaseline =

Q + 250 × Ps + 0.4

6343 × ηs,target

parameters in blue are constants, 6343 is for I-P only

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FER Baseline Constants

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P0 impacts this 

curvature. P0 was 

established at 0.40” 

(100 Pa) to match 

range of products 

available. 

Q0 impacts this 

curvature. Q0 was 

established at 250 

cfm (0.12 m3/s) to 

match diameter 

effect of FEG curves. 

Target efficiencies,

ηs,target and ηt,target

determine the overall 

level of the entire surface.
6/9/2015 13

Airflow

Pressure

Fan Efficiency Ratio - FER

0

1.0

2.0

FER

Pressure

If this is what the metric looks like,

 what will the regulation look like?
FAN EFFICIENCY RATIO

FER = 1.10 means 10% energy savings over baseline

Body FER Requirement

Federal

Regulation FER ≥ 1.0 at Peak & Design Point 

ASHRAE 90.1 FER ≥ 1.0 at Design Point

ASHRAE 189.1 FER ≥ 1.1 at Design Point

Rebates FER = Savings over Baseline

How could FER be used?

14
What does this mean to Fan Selections?

 

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1 in. wg 2 in. wg 3 in. wg 4 in. wg 5 in. wg 6 in. wg

CFM RPM BHP FER RPM BHP FER RPM BHP FER RPM BHP FER RPM BHP FER RPM BHP FER

6000 830 1.39 1.47 1051 2.79 1.33

7000 900 1.72 1.38 1092 3.18 1.35 1267 4.83 1.28

8000 979 2.14 1.26 1142 3.64 1.34 1306 5.41 1.30 1458 7.34 1.25

9000 1064 2.66 1.14 1209 4.28 1.28 1358 6.13 1.29 1499 8.15 1.27 1633 10.3 1.23

10000 1152 3.28 1.03 1280 4.95 1.22 1411 6.86 1.28 1550 9.11 1.26 1674 11.3 1.25 1798 13.8 1.22

11000 1242 3.98 0.93 1359 5.79 1.15 1479 7.84 1.22 1597 10.0 1.26 1722 12.5 1.24 1835 14.9 1.24

12000 1336 4.82 0.84 1441 6.73 1.08 1549 8.82 1.19 1660 11.1 1.23 1770 13.6 1.25 1883 16.3 1.23

13000 1431 5.80 0.75 1528 7.86 1.00 1627 10.1 1.13 1728 12.4 1.19 1828 14.9 1.23 1932 17.6 1.23

14000 1527 6.94 0.67 1617 9.09 0.93 1707 11.3 1.07 1799 13.8 1.15 1897 16.6 1.18 1987 19.1 1.22

15000 1625 8.23 0.61 1706 10.4 0.86 1791 12.8 1.01 1878 15.5 1.10 1964 18.1 1.16 2054 21.1 1.19

16000 1724 9.68 0.55 1798 12.0 0.80 1879 14.6 0.95 1957 17.2 1.06 2038 20.0 1.12

17000 1823 11.3 0.50 1892 13.7 0.75 1967 16.4 0.90 2041 19.1 1.01

18000 1923 13.1 0.46 1986 15.6 0.69 2056 18.4 0.85

 

 
What does this mean to Fan Selections?

6/9/2015

Fan

Size

(in.)

Fan

Speed

(rpm)

Fan

Power

(bhp)

Actual

Total

Efficiency

Baseline

Power

(bhp)

Baseline 

Total 

Efficiency FERH

18 3238 11.8 40.1% 7.96 59.4% 0.67

20 2561 9.56 49.5% 7.96 59.4% 0.83

22 1983 8.02 59.0% 7.96 59.4% 0.99

24 1579 6.84 69.1% 7.96 59.4% 1.16

27 1289 6.24 75.8% 7.96 59.4% 1.28

30 1033 5.73 82.5% 7.96 59.4% 1.39

33 887 5.67 83.4% 7.96 59.4% 1.40

36 778 6.01 78.7% 7.96 59.4% 1.32

Electronic Fan Selection Software based on Total Pressure

Design Point 10,000 CFM at 3.0” Pt

16
What does this mean to Fan Selections?

6/9/2015

Airflow

Static Pressure

FER 1.1

FER 1.2 FER 1.0

Multiple Speed Fan Performance Curves 

“Relatively High Efficiency Fan” – Large selection area

FER 0.9

Peak Efficiency

17
What does this mean to Fan Selections?

6/9/2015

Airflow

Static Pressure

Multiple Speed Fan Performance Curves

“Relatively Low Efficiency Fan” – Small selection area

FER 0.9

FER 0.8 FER 1.0

FER 0.7

Peak Efficiency

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What does this mean to Fan Selections?

6/9/2015

Airflow

Static Pressure

Multiple Speed Fan Performance Curves

“Relatively Low Efficiency Fan” – Small selection area

FER 0.9

FER 0.8 FER 1.0

FER 0.7

Peak Efficiency

Maximum speed

in which FER ≥ 1.0 at 

Best Efficiency Point

Regulation

...FER must be 

1.0 or greater at the

Best Efficiency Point at 

the Maximum RPM.

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Case Study: Square Inline Fan

• Ducted inlet, ducted outlet

• Inexpensive

• Easy to install

• Easy to maintain

• Low efficiency

Fan shown without side for 

viewing internal components

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Square Inline Fan – Size 30 (30” wheel)

Entire Selection Range

Min RPM

Max RPM

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Square Inline Fan – Size 30

Best Efficiency Point

Min RPM

Max RPM

Best Efficiency Point (BEP)

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Square Inline Fan – Size 30

Range of Fan Total Efficiency

Min RPM

Max RPM

Best Efficiency Point 

(BEP)

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Square Inline Fan – Size 30

Actual Fan Selections from 2012

295 Fans with Motors ≥ 1 hp

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Square Inline Fan – Size 30

Proposed Regulation: FER ≥ 1

Approximately 40% of fan selections met the requirement

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Square Inline Fan – Size 30

Selections covered by size 36

Approximately 70% of fan selections met by size 30 and 36

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Square Inline Fan – Size 30

Selections covered by size 42

Approximately 90% of fan selections met by sizes 30, 36, and 42

15,000 CFM 

at 0.5” Pt

6/9/2015 27
Fan Model

Design

BHP

FER Oper Cost

($/year)

Weight

(lbs)

Housing

Width

Budget

Cost

Payback

(years)

Sq Inline 30” 5.33 0.62 $1363 571 46” $3300 -

Sq Inline 42” 2.92 1.12 $758 735 58” $4050 1.22

Mixed Flow 27” 2.77 1.18 $719 611 41” $6700 5.28

Product Substitution

Design Point: 15,000 CFM at 0.5” Pt

30” Sq Inline 42” Sq Inline 27” Mixed Flow

New

Square Inline 

Fan with 

Improved 

Efficiency!!!

New

Lower Cost 

Mixed Flow 

Fan!!!
Allowable Selection Range: 

FER ≥ 1 at the Design Point of Operation

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Allowable Speed Range: 

FER ≥ 1 at the BEP at the Max RPM

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Square Inline Fan – Size 30

Actual Fan Selections from 2012

Reduced max RPM eliminates

8% of fan selections and

15% of connected load

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Extended Products (wire-to-air)

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Shaft Power (BHP)

Electrical Power (kW)

AMCA 207