Preferred Utilities Mfg. Corp.31-35 South St. • Danbury • CT

www.preferred-mfg.com

Electrical Energy &

Fuel Savings Using

Advanced Boiler Controls

Preferred Utilities Manufacturing Corp

Introduction

Introduction Fuel Savings

Stack Losses Electrical Savings

Fan Basics Fan and System Curves VFD Basics

Savings Summary

Introduction

This discussion focuses on upgrading existing burners from Jackshaft Control to FD Fan Variable Frequency Drives (VFD) Speed Control with Oxygen Trim to Save Energy and Provide Rapid Payback.

VFD are currently being applied to motors through out industry.

Typical Applications

Firetube Boilers over 400 Bhp Watertube Boilers Boilers with Seasonal Load Swings:

Hospitals Universities Prisons Airports Military Bases

Fuel Savings

Combustion Efficiency

Chemistry:

Air = O2 + N2

Fuel = C + H

3O2 + N2 + 2C + 4H 2CO2 + 2H2O + N2

Time + Temperature + Turbulence

Excess Air

Combustion Theory

Excess Air Required for Burners

Excess Versus Deficient Air

Variations in Air Composition

“Standard” air has 0.0177 LB. O2 per FT3

Hot, humid air has less O2 per cubic ft 20% less at 95% RH, 120OF, and 29.9 in. Hg

Dry, cold air has more O2 per cubic ft 10% more at 0% RH, 32OF, and 30.5 in. Hg

Combustion controls must: Adapt to changing air composition or Allow at least extra excess air at “standard”

conditions

Variations in Air Composition

Burner

Temperature = 120 FRelative Humidity = 95%Pressure = 29.9 in HgLess lbs of O2 + N2 per cu ft

Fuel Flow( C + H )

H2O

H2O

Forced Draft Fan(Constant Volume)*

Combustion Air( O2 + N2 )

H2O

H2O

N2

N2N2

N2

N2

N2

N2

N2

N2N2

N2

N2

N2N2

N2

N2N2N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2N2

N2N2N2

N2

N2

N2

N2

N2O2 O2

O2

O2

O2

O2

O2

O2

O2

O2

O2O2

O2

H2O

Variations in Air Composition

Burner

Combustion Air( O2 + N2 )

Temperature = 32 FRelative Humidity = 0%Pressure = 30.5 in HgMore lbs of O2 + N2 per cu ft

N2N2

Fuel Flow( C + H )

N2

N2

N2

N2N2N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2N2

N2

N2

N2

N2

N2

N2

N2N2

N2

N2

N2

N2

N2N2

N2

N2

N2

N2

N2

N2

N2

N2

N2N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2 N2

N2

N2

N2

N2 N2N2

N2

N2

N2

N2

N2N2N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

N2

O2

O2

O2

O2

O2

O2

O2

O2

O2O2

O2

O2

O2

O2

O2O2

O2

O2O2

O2

O2

O2

O2

Forced Draft Fan(Constant Volume)*

At these ambient conditions the burner has extra O2 & N2

Control System Errors

Combustion control system can not perfectly regulate fuel and oxygen flows. Therefore, extra excess air must be supplied to the burner to account for control system errors…

Hysteresis (non-repeatability): linkage slop, valves, dampers, and fuel pressure regulator

Fuel flow for a given valve position varies with temperature and pressure

Combustion Control Objectives

Maintain proper fuel to air ratio at all times Too little air causes unburned fuel losses Too much air causes excessive stack losses Improper fuel air ratio can be DANGEROUS

Always keep fuel to air ratio SAFE Interface with burner management for:

Purge Low fire light off Modulate fuel and air when safe to do so

Jackshaft Fuel-Air Ratio Control

To / F rom L91 P ressure tro l

OIL

GAS

PT

STEAM

E xistingJackshaftA ctua tor

Existing Jackshaft Burner

Electrical Savings

Fan Basics Fan and System

Curves Motor & Electrical

Systems Basics VFD Basics

VFD System Basics

Variable Frequency Drive The Inputs are a 4-20mA FD Fan Speed Demand

and Motor AC Voltage Output is a “Variable Frequency” AC Motor speed follows the 4-20mA input Motor manufactures strongly recommend a

Motor rated for Inverter Service for long life» These motors can with stand higher surge voltages

VFD provides Electrical Energy Savings due to: Oversized Fans Oversized Motors Partially Loaded Boilers Minimizing Damper Hp Losses

VFD System Basics

Centrifugal Fan Exploded View

Reference 1

Vortex Dampers

Inlet vanes give an initial spin (or vortex) to air entering a centrifugal fan. By adjusting angle of vanes the degree of spin and volumetric output are regulated.

Reference 3

Inlet Control Vanes

Reference 2

Inlet or Outlet Dampers

Inlet or opposed blade dampers assure even distribution of air immediately downstream from the damper. By adjusting angle of blades the volumetric output are regulated.

Reference 1

Flow vs Fan Hp

Non-Vortex Dampers Vortex Damper Speed Control

Reference 1

Fan Hp Summary Dampers substantially increase Fan Hp and Fan

kW Consumption. Dampers are Evil! Inlet Vortex Dampers waste less Hp than any type

of inlet and outlet Blade Dampers. Variable Speed Fans Control air flow with

minimum fan shaft Hp. Variable Speed Fans have been field proven in

thousands of HVAC air handler applications.

Adjustable Frequency Drive (AFD) Adjustable SPEED Drives (ASD) VARIABLE Frequency Drives (VFD) VARIABLE SPEED Drives (VSD) Inverters Frequency Converters Drives

Different names for the same thing.

Variable Frequency Drives

Motor Speed Control

Pulse Width Modulation (PWM)

On or Off, voltage does NOT modulate.

PWM allows IGBT’s to run cool for long life, so all VFD’s use PWM.

However, PWM dV/dt causes spike voltages

dv/dt - Change in Voltage over Time Poor Drives - up to 3500V/us Good Drives - 900V/us on 500 feet

Lower Peak Voltages Extend Motor Insulation Life

Voltage Spikes

Do we need a VFD rated Motor ? NO

230 V Motors Strong Probability: NO

460 V motors with: < 50 ft wire run, good drives almost eliminate problems.

However, you can NOT guarantee it. Motor age and heat naturally degrade the motor wire insulation. The customer should know that there is a small risk.

If motor insulation fails, the VFD is not damaged, but the user must pay to have the motor re-wound or replaced.

YES 575 V Motors

Combustion Air Fan Hp Savings

Reference 1

Combustion Air Flow, %Full Load

Mo

tor

Po

we

r(H

P)

Inp

ut,

% F

ull

Lo

ad

Variable Speed Control

Damper Control HP Savings

Savings Summary

$0

$500

$1,000

$1,500

$2,000

$2,500

$3,000

$3,500

20% 40% 60% 80% 100%Boiler Load (%)

Op

erat

ing

Co

st S

avin

gs

Fuel Savings

Electrical Savings

Fuel Savings

Electrical Savings

+

Fuel Savings: Seasonal Air Density

and Humidity Changes Fuel Pressure and

Temperature Changes Fuel Btu and Viscosity

Variations Worn Linkage

Components (Hysteresis)

Electrical Savings: Minimizing Damper

Pressure Drop - damper is 100% open for maximum kWh savings, (Partially closed at low fire to maximize burner turndown)

Oversized Fans Oversized Motors Partially Loaded Boilers

Energy Savings

Advanced Burner Control

Energy Savings

Important Factors Boiler Size? Loading Service? Exit Gas Temperature? (Boiler Pressure

Determines) Electrical Cost? (10 cents, 4 cents?) Fuel Cost? Utility Rebate?

Unique Energy Savings Tool

Savings Estimate Based on:

Boiler size Motor HP Air Damper Type Current O2 Level Projected O2 Level Flue Gas Temperature Seasonal Loading Data Fuel Cost Electrical Cost

If You Can’t Get Field Data

% O2 Improvement = 1 - 2 % Heating Boiler Seasonal Loading =

Boiler Firing Rate 0% 20% 40% 60% 80% 100% % Per Year 25% 5% 20% 15% 30% 5%

Process Boiler Seasonal Loading = Boiler Firing Rate 0% 20% 40% 60% 80% 100% % Per Year 5% 5% 20% 20% 30% 20%

Natural Gas Cost $4.50 / 1000ft3 Fuel Oil Cost $0.90 / gal Electricity Cost $0.75 kWh Flue Gas Temperatures - 10 psi-350 F, 120 psi-475 F

Conservative Assumptions

Things You Need To Know

Utility Energy Rebates North East Utilities, CL&P - offers a 50 % rebate

of the VFD price and cost of installation. They use standard numbers. They require paper work to be submitted Local VFD rep will be able to give the local

rebate offer.

Large Firetube Scenario Steam Boiler: 600 bhp capacity @ 10 psi (193 F), 350 F flue gas temp.

20 ppm, 60 hp fan motor, parallel blade outlet damper controls air flow Utilities Cost: Fuel Gas: $4.5 / 1000 ft3) / Electricity: 5 cents / kwh

Operation: Process boiler, 50 weeks a year service, » Shutdown - 10 % of year / 20 % Load - 20 % of year» 40 % Load - 20 % of year / 60 % Load - 20 % of year» 80 % Load - 20 % of year / 100 % Load - 10 % of year

Oxygen Trim Improvement: Field service engineer has determined that the burner excess air performance can be improved as follows:» 20 % Load - 6% to 4.5 % O2 / 40 % Load - 6% to 4.5 % O2 Wet» 60 % Load - 5% to 3.5 % O2 / 80 % Load - 4% to 2.5 % O2 Wet » 100 % Load - 4% to 2.5 % O2 Wet

Utility Rebate: 50% of VFD Cost and installation » (use VFD list price as an estimate)» Existing Jackshaft Actuator: 150in-lbs

Large Firetube Scenario

Large Firetube Scenario

Installed System PaybackOxygen Trim / VFD Payback Comparison

(with 0% VFD & VFD Installation Rebate, 1% O2 Wet Improvement)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

20% 40% 60% 80% 100%

Boiler Load (%)

Pay

bac

k (Y

ears

)

300 bhp 500 bhp 600 bhp 900 bhp 1200 bhp

300 Bhp Payback vs.O2 Decrease

300 BHP Oxygen Trim / VFD Payback Comparison(with 50% VFD & VFD Installation Rebate)

3.97

3.283.40 3.46

4.83

3.47

2.692.59

2.43

2.772.84

2.051.82

1.59 1.58

2.47

1.701.46

1.23 1.16

0

1

2

3

4

5

6

20% 40% 60% 80% 100%

Boiler Load (%)

Pay

bac

k (

Yea

rs)

0.5% O2 Decrease 1% O2 Decrease 2% O2 Decrease 3% O2 Decrease

Preferred Utilities Manufacturing Corp

For further information, contact...

Preferred Utilities Manufacturing Corporation31-35 South Street. • Danbury • CT

T: (203) 743-6741 • F: (203) 798-7313www.preferred-mfg.com