Importance of ESP, Gas
Pressure, and Voltage for
Gas-Fired Units
Presented by
Bruce Standerwick
1
Importance of ESP, Gas
Pressure, and Voltage for
Gas-Fired Units
Part 1:
The Importance of ESP
on Gas-Fired Units
2
Two Cases When Actual ESP not
Equal to Design ESP
Case A: Actual ESP > Design ESP
 Case B: Actual ESP < Design ESP

3
Design Point
TSP – “W.C.
2.1”
CFM in 1000’s
4,100 cfm
4
Actual Operation: Case A
2.6”
TSP – “W.C.
2.1”
CFM in 1000’s
3,780 cfm 4,100 cfm
5
Case A: Actual ESP > Design
ESP

Solutions:
1. Adjust sheave if possible
2. Change sheave and possibly belts
6
Actual Operation: Case A
3.0 BHP
2.1”
2.6 BHP
TSP – “W.C.
2.6”
CFM in 1000’s
3,780 cfm 4,100 cfm
7
Case A: Actual ESP >Design
ESP

Solutions:
1. Adjust sheave if possible
2. Change sheave and possibly belts
3. Need (1), (2) and possibly larger motor
size with new motor controls -- Will
motor fit?
8
Motor Compartment of DFC
9
Case A: Actual ESP > Design
ESP

Solutions:
1. Adjust sheave if possible
2. Change sheave and possibly belts
3. Need (1), (2) and possibly larger motor
size with new motor controls -- Will
motor fit?
4. Shaft deflection may require larger shaft
and bearings
10
Fan Assembly Under
Construction
11
Motor Compartment of DFC
12
Operating Point
New
Operating
Point
TSP – “W.C.
Design
Point
CFM in 1000’s
3,900 cfm
13
Fan Assembly Under
Construction
This dimension is
smaller on a fan with
a narrow housing
14
Case A: Actual ESP > Design
ESP

Solutions:
1. Need sheave change
2. Need (1) and larger motor and controls
3. Need (1), (2) and possibly larger motor
size with new motor controls -- Will
motor fit?
4. Shaft deflection may require larger shaft
and bearings
5. Different fan because new cfm/TSP point
is not in operating range of fan in unit 15
Actual Operation: Case B
2.1”
TSP – “W.C.
1.6”
CFM in 1000’s
4,550 cfm
4,100 cfm
16
Case B: Actual ESP < Design
ESP

Solutions:
1. Adjust sheave if possible
2. Change sheave and possibly belts
17
When Actual ESP is Different
From Design ESP

Conclusions:
● It’s easier to slow a fan down
than to speed it up
● It’s safer to overestimate the ESP
than to underestimate it!
18
Importance of ESP, Gas
Pressure, and Voltage for
Gas-Fired Units
Part 2:
The Importance of Gas
Pressure for Gas-Fired Units
19
Typical Gas-Fired Pipe Train
in Piping Compartment
20
Typical Direct Gas-Fired
Pipe Train
Gas manifold;
start of factory
furnished and
piped
components
Main Gas
Pressure
Regulator
Main
Gas
Valve
Auxiliary Maxitrol
Gas
Modulating
Valve
Gas Valve
Test
Port
Test
Port
Main
Test Gas
Port Shutoff
Valve
Pilot
Pilot Gas Pilot Gas Pilot Orificed
Shutoff Pressure Gas Needle
Valve
Regulator Valve Valve
21
Direct Gas-Fired Burner in
Burner Compartment
22
Direct Gas-Fired Burner at
Full Fire
23
Max. Gas Inlet Pressure
Min. Gas Inlet Pressure
Typical Direct
Gas-Fired
Heater Rating
Plate
24
Two Cases Where Actual Gas
Pressure not Equal to Design Gas
Pressure
Case A: Actual Gas Pressure >
Design Gas pressure
 Case B: Actual Gas Pressure <
Design Gas pressure

25
Case A: Actual Gas Pressure >
Design Gas Pressure
¾” I.P.S. gas
manifold; 5
psig actual
gas pressure
instead of
10-14” w.c.
per design
Main Gas
Pressure
Regulator
Main
Gas
Valve
Auxiliary Maxitrol
Gas
Modulating
Valve
Gas Valve
Test
Port
Test
Port
Main
Test Gas
Port Shutoff
Valve
Pilot
Pilot Gas Pilot Gas Pilot Orificed
Shutoff Pressure Gas Needle
Valve
Regulator Valve Valve
26
Solution for Case A:Actual Gas
Pressure > Design Gas Pressure

Install a
High Gas
Pressure
Regulator
27
Case B: Actual Gas Pressure <
Design Gas Pressure
2” I.P.S.
manifold;
10” w.c. gas
pressure
instead of 12 psig per
design
Main Gas
Pressure
Regulator
Main
Gas
Valve
Auxiliary Maxitrol
Gas
Modulating
Valve
Gas Valve
Test
Port
Test
Port
Main
Test Gas
Port Shutoff
Valve
Pilot
Pilot Gas Pilot Gas Pilot Orificed
Shutoff Pressure Gas Needle
Valve
Regulator Valve Valve
28
Case B: Actual Gas Pressure <
Design Gas Pressure

Solutions:
1. Add section to burner
2. Modify sheet metal in burner
section
29
When Actual Gas Pressure is
Different From Design Gas Pressure

Conclusions:
● It’s much easier in the field to add
a high gas pressure regulator than
to rebuild a gas train/burner
● It’s safer to underestimate the gas
pressure than to overestimate it!
30
Importance of ESP, Gas
Pressure, and Voltage for
Gas-Fired Units
Part 3:
The Importance of Voltage
on Gas-Fired Units
31
Motor Compartment of DFC
32
Components That Could be
Affected by a Voltage Change








Disconnect Switch and/or Distribution Block
Fuses and Fuse Blocks
Circuit Breaker
Transformers
Starter and Overload Contactors
Motor(s)
Wiring and conduit to motor(s)
Wiring diagram
33
Relationship Between Volts
and Amps
HP is proportional to volts times amps
 If : HP1 = HP2 then:
(volts x amps)1 = (volts x amps)2 or
(volts1/volts2) = (amps2/amps1)
 Amps are inversely proportional to
volts at constant horsepower.

34
Two Cases Where Actual Voltage
not Equal to Design Voltage
Case A: Actual Voltage > Design
Voltage
 Case B: Actual Voltage < Design
Voltage

35
Case A: Actual Voltage >
Design Voltage
Disconnect Switch and/or
Distribution Blocks
No change
Fuses and Fuse Blocks
Fuses probably change; fuse blocks also if
different fuse type required
Circuit Breaker
Probably need to change so it will trip when
necessary.
Transformers
Must change unless original transformer is
tri-voltage (208/230/460).
Starters
No change
Overload Contactors
Probably need to change so it will trip when
necessary.
Motor(s)
Must change unless original motor is trivoltage (208/230/460).
Wiring and Conduit
No change
36
Case B: Actual Voltage <
Design Voltage
Disconnect Switch and/or
Distribution Blocks
Non-fused disconnect may change; fused
disconnect will change
Fuses and Fuse Blocks
Fuses probably change; fuse blocks also if
different fuse type required
Circuit Breaker
Doesn’t change because it’s downstream of
transformer
Transformers
Must change unless original transformer is
tri-voltage (208/230/460)
Starters
Must change
Overload Contactors
Must change
Motor(s)
Must change unless original transformer is
tri-voltage (208/230/460).
Wiring and Conduit
May change depending on original amp
rating
37
When Actual Voltage is Different
From Design Voltage


Conclusions:
● Fewer components are likely to need
changing if the voltage goes up
(amps go down) rather than if the
voltage going down (amps go up)
● It’s safer to underestimate the
voltage than to overestimate it!
Wiring diagram, specification sheet
and rating plate must be replaced if
the voltage changes
38
Importance of ESP, Gas
Pressure, and Voltage for
Gas-Fired Units
The End
Thank You!
39