This document provides details from an energy audit lecture on fans. It discusses terms used in fan performance such as CFM, static pressure, sone, BHP, RPM, and TSS. It also outlines the steps of an energy audit including collecting fan data, measuring parameters like power consumption, air flow rates and pressures. The document analyzes fan performance based on laws relating flow, pressure and power to fan speed. It explores energy conservation opportunities like variable speed drives and improving duct insulation. An example problem calculates the air-fuel ratio for a coal with given composition burned at 30% excess air.

1. LECTURE – 10.09.2014
By
P. Kanthasamy
Principal Technical Officer
Environmental Technology Division
CSIR- Central Leather Research Institute
Adyar, Chennai- 600 020
Email:samyji@gmail.com Mobile:9445587722

2. ENERGY AUDIT OF FANS

3. TERMS USED IN FAN
TERMS
Cfm-Cubic Feet Per Minute. A measure of airflow.
cf
m
Ps- Static Pressure. Resistance to airflow measured in inches of water gauge.
Ps
s
one
Sone-A measure of loudness. One sone can be approximated as the loudness of a quiet
refrigerator at a distance of 5 feet. Sones follow a linear scale, that is, 10 sones are twice as
loud as 5 sones.
BHP-Brake Horsepower. A measure of power consumption. Used to determine the proper
motor horsepower and wiring.
Bhp
Horsepower. Used to indicate a fan’s motor size.
hp
RPM- Revolutions Per Minute. Measure of fan speed.
r
p
m
T
STS- Tip Speed. The speed of the tip of a fan wheel or prop measured in feet per minute.
AMCA- Air Movement & Control Association. A nationally recognized association which
establishes standards for fan testing and performance ratings. AMCA also license air volume
and sound certified ratings.
A
MCA

4. BACKGROUND
Thermal power plant has several fans such as Induced draft
(ID) fans, Forced draft (FD) Fans, Primary air fans (PA
fans). These fans contribute to significant auxiliary power
consumption. ID fans alone contribute to about 12% of total
auxiliary power consumption
ID Fan System
Steps Involved
Data collection
Observations and
Analysis
Exploration for energy
conservation measures
Report preparation

5. DATA COLLECTION
Collect detailed design specification & operating parameters
Fans Parameters ( FD, ID and PA Fan )

6. DATA COLLECTION
Collect detailed design specification & operating parameters
Fans Parameters ( FD, ID and PA Fan )- contd…

7. DATA COLLECTION
Details of the fans and ducting system:
 Collect the schematic diagram / network of the
ducting system
 Collect Performance characteristics of all fans
 Compile design, Performance Guarantee Test,
previous best and last energy audit values with
respect to fans and draft system which include
excess air
 If the fans are operated in parallel then it is
advised to collect the performance curve for the
parallel operation
 Air quality and pressure equipments at the users
as per the design requirements

8. INSTRUMENTS REQUIRED
Power Analyzer: Used for measuring electrical parameters such
as kW, kVA, pf, V, A and Hz
Temperature Indicator & Probe
Stroboscope: To measure the speed of the driven equipment and
motor
Sling hygrometer or digital hygrometer
Anemometer
On line instruments – (calibrated)
Digital Manometer of suitable range and appropriate probes for
measurement of pressure head and velocity head.
Pitot tubes
Additional pressure gauges with appropriate range of
measurement and calibrated before audit.

9. MEASUREMENTS & OBSERVATIONS TO BE MADE
Energy consumption pattern of fans
Motor electrical parameters (kW, kVA, Pf, A, V, Hz, Total
Harmonic Distortion(THD) of fans
Fan operating parameters to be measured/monitored for
each Fans are:
1. Discharge / flow rates
2. Pressure (suction & discharge)
-Static pressure
-Dynamic pressure
-Total pressure

10. MEASUREMENTS & OBSERVATIONS TO BE MADE
3. Damper position / guide vane position/ VSD Setting
4. Temperature of fluid handled
5. Load variation
6. Power parameters of fans
7. Fan operating hours and operating schedule
8. Pressure drop in the system (between discharge
and user point)
9. Pressure drop and temperatures drop across the
equipment
10. Fan /Motor speed

11. MEASUREMENTS & OBSERVATIONS TO BE MADE
 Oxygen content, flow, temperature and pressure
measurement across in exhaust gas path
- Before and after air pre heater
- Before and after economizer
-Before and after ID fan
- Before and after ESP
- In case where flow measurement (for air pre heater
and ESP) is not possible, it can be estimated based on mass
balance principles, stoichiometric analysis,

12. ENERGY CONSUMPTION PATTERN
 If the plant is monitoring the energy consumption, it is suggested
to record the data and monitor the daily and monthly consumption
pattern. (Collect data for 12 months)
 Work out the total consumption of fans to arrive at percentage to
the total consumption of the auxiliary consumption
 If the energy meters are not installed to fans, instantaneous
measurements can be carried out, based on the loading pattern the
daily consumption can be worked out as per following table-
Energy consumption pattern

13. FAN OPERATING EFFICIENCY
EVALUATION
The parameters to be studied in detailed are:
 Air /gas rates of fans / main ducts
 Static pressure and dynamic pressure and total
pressure
 Power consumption of fan (for estimating the
operating efficiency of the fans)
 Monitor present flow control system and
frequency of control valve operation if any (for
application of variable speed drives)
 Fill up the following data sheet for every fan

14. FAN OPERATING EFFICIENCY
EVALUATION
Performance parameters for fans

15. FAN OPERATING EFFICIENCY
EVALUATION

16. FAN LAWS
Flow ? Speed Pressure ? (Speed)2 Power ? (Speed)3
x x x
Q N
Q N
1 =
1
2 2
2
SP N
SP N
= æ ö çè ÷ø
1 1
2 2
3
kW N
kW N
= æ ö çè ÷ø
1 1
2 2
Varying the RPM by 10%
decreases or increases air
delivery by 10%.
Varying the RPM by 10%
decreases or increases the
static pressure by 19%.
Varying the RPM by 10%
decreases or increases the
power requirement by
27%.
Where Q – flow, SP – Static Pressure, kW – Power and N – speed (RPM)

17. FANS PERFORMANCE ASSESSMENT
Static pressure
• Potential energy put into the system by the fan
Velocity pressure
• Pressure arising from air flowing through the duct. This is
used to calculate velocity
Total pressure
• Static pressure + velocity pressure
• Total pressure remains constant unlike static and velocity
pressure

20. TRAVERSE POINTS FOR VELOCITY
MEASUREMENT

21. FAN OPERATING EFFICIENCY
EVALUATION
Fan static kW = Q in m3/ s x static pr. developed by fan in mmwc
102
Fan static efficiency % Fan static kW x 100
Input kW to motor x hm
Fan total kW = Q in m3/ s x total pr. developed by fan in mmwc
102
=
Fan mechanical Efficiency = Fan total kW x 100
Input kW to motor x hm
Parameter Details Unit
Q Air flow rate m3/ s
Static pressure Difference between discharge & suction pressure mmwc
Fan static/ total kW Static / total power consumption of the fan kW
Input kW to motor Measured power consumption of the motor kW
hm Efficiency of the motor at operating load
Total pressure Difference between discharge & suction pressure mmwc

22. FAN OPERATING EFFICIENCY
EVALUATION
Corrected air density, g =
273 X 1.293
273 + Air temperature in 0 C
Velocity in m / s =
Cp x Ö2 x 9.81 x Diff. velocity pr. in mmwc x g
g
Parameter Details Unit
Cp Pitot tube constant 0.85 or as given
by manufacturer
g Density of air or gas at test condition Kg / m3
Volumetric flow (Q), m3/s = Velocity, m/s x Area, m2

23. FAN OPERATING EFFICIENCY
EVALUATION
In case of gas flow measurement of ID fans, where it is not
possible to measure the gas flow, then the mass flow method
can be adopted, provided the oxygen content and actual coal
flow measurements are available. For flow estimation through
this method, the following are required:
 Stoichiometric air requirement (work out based on the coal
composition)
 Oxygen content at ID fan inlet (measured)
 Excess air (estimate)
% Excess air = (%O2 in flue gas x 100) / (21 – O2 in flue gas)
 Coal flow (based on actual measurement or on average
basis)
 Fly ash content (assumed based on past data)

24. FAN PERFORMANCE ANALYSIS
While in case air flow measurement for FD and PA fans the
following instruments (which ever are suitable) can be used
 Thermal anemometer
 Vane type anemometer
 Pitot tube along with micro manometer can be used
 Online measuring instrument
If the fans are operating in parallel, it is advised to measure
all above parameter for every fan separately to evaluate the
individual performance. However combined parameters of
flow and head need to be verified with Performance curve for
parallel operation

25. FAN PERFORMANCE ANALYSIS
Compare the actual values with the design / performance test
values if any deviation is found, list the factors with the details
and suggestions to over come.
 The investigations for abnormality are to be carried out for
problems.
 Enlist scope of improvement with extensive physical checks /
observations.
 Based on the actual operating parameters, enlist
recommendations for action to be taken for improvement, if
applicable such as- Replacement of fans, Impeller replacement,
VFD application.
Cost analysis with savings potential for taking improvement
measures.

26. Recirculation
Damper
IGV
VFD
Ideal
FAN PERFORMANCE ANALYSIS
Power
25 50 75 100
Flow
100
75
50
25
FFllooww ccoonnttrrooll

27. FAN PERFORMANCE
ANALYSIS
System characteristics and Fan curves
Impact of speed reduction

28. FAN PERFORMANCE ANALYSIS
Visual survey of insulation & the ducting system:
 Insulation status (measure the surface temperature with the
aid of surface thermocouple / infrared pyrometer or by using
thermal imaging cameras)
 Bends and ducting status
 Physical condition of insulation
 Identification of locations where action is required to improve
the insulation (provide with detailed techno-economics)
 Improvement options for ducting systems if any
 Sources of air ingress

29. FAN PERFORMANCE ANALYSIS
Study of air ingress in to the system:
 Before and after air preheater
 Before and after ESP
 Before and after ID fan
The difference in the oxygen gives the extent of air ingress in to the
system. Measurements of oxygen content across all units in flue gas
path, indicates the locations where ingress is occurring

30. EXPLORATION OF ENERGY
CONSERVATION POSSIBILITIES
Improvement of systems and drives:
 Use of energy efficient fans
 Change of impeller with energy efficient impeller
 Correcting inaccuracies of the fan sizing
 Use of high efficiency motors
 Fan speed reduction by pulley diameter modifications for optimisation
 Option of two speed motors or variable speed drives for variable duty
conditions
 High Performance Lubricants: The low temperature fluidity and high
temperature stability of high performance lubricants can increase energy
efficiency by reducing frictional losses
 Use of energy efficient transmission systems (Use of latest energy
efficient transmission belts)

31. EXPLORATION OF ENERGY
CONSERVATION POSSIBILITIES
Improvement in operations:
 Minimising excess air level in combustion systems to reduce FD fan
and ID fan load.
 Minimising air in-leaks in hot flue gas path to reduce ID fan load and
cold air in-leaks
 Minimising system resistance and pressure drops by
 improvements in duct system / Insulation aspects
Deviations in air flow rates
Measures to up keep the performance
After the identification of energy conservation measures,
detailed techno-economic evaluation has to be carried out

33. PROBLEM
• A particular coal has the following ultimate analysis on a dry
basis percent by mass:
Component Percent by Mass
• Sulfur 0.6
• Hydrogen 5.7
• Carbon 79.2
• Oxygen 10.0
• Nitrogen 1.5
• Ash 3.0
This coal is to be burned with 30% Excess Air. Calculate the Air-fuel
ratio on a mass basis.

34. SOLUTION
• One approach to this problem is to write the combustion equations
for each of the combustible elements per 100 kg of fuel. The molar
compostion per 100 kg of fuel is found first
• Kmol S/ 100kg fuel = 0.6/32 = 0.02
• Kmol H2/ 100kg fuel = 5.7/2 = 2.85
• Kmol C/ 100kg fuel = 79.2/12 = 6.60
• Kmol O2/ 100kg fuel = 10.0/32 = 0.3
• Kmol N2/ 100kg fuel = 1.5/28 = 0.05
The combustion equations for the combustible elements are now
written which enables us to find the theoretical oxygen required.
S+ O2 SO2
0.02S + 0.02 O2 0.02 SO2
H2 + 1/2O2 H2O
2.85H+2.85/2 O2 2.85 H2O
C+O2 CO2
6.60C+ 6.60O2 6.60CO2
Total Oxygen required For S = 0.02
H2 = 1.42
Total Oxygen Required
=0.02+1.42+6.60=8.04
8.04 kmol O2 required /100kg of fuel
0.31 kmol O2 is available in fuel /100
kg
8.04-.31= 7.73 kmol

35. SOLUTION
• Air-Fuel Theo = [7.73 +7.73 (3.76)] x 28.97/100
= [36.7948x 28.97]/ 100
= 10.659 kg air/kg fuel
For 30% excess air the air fuel ratio is
AF = 1.3 x 10.659= 13.856 kg air/kg of fuel