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Maximizing Boiler Plant Efficiency
Presenter: Dan Watkins, LEED BD+C
Sales Engineer Bornquist, Inc.
Efficient Boiler Design
• Boiler Types – Efficiency Definition – Non-Condensing – Condensing
• Maximizing Efficiency – Understanding Efficiency – Outdoor Reset – Short Cycle Prevention – Hybrid Systems
Efficient Boiler Design
• Combustion Efficiency – 100 percent of efficiency minus the percentage of heat lost up the vent.
• Thermal Efficiency – The combustion efficiency minus the jacket losses of the boiler. Based on ANSI Z21.13. For boilers 300,000 to 12.5 million Btu.
• A.F.U.E. – The measure of annual efficiency of a boiler that takes into account the cyclic on\off operation and associated losses as it responds to changes in load. For boilers under 300,000 Btu
Efficient Boiler Design
• Non-Condensing – Cast Iron – Steel Tube – Copper Fin – Modulating
• 75-88% Efficiencies
Efficient Boiler Design
• Condensing – Cast Aluminum – Stainless Steel – Cast Iron – Dual Heat
Exchanger
• 85-99% Efficiencies depending on operating conditions
3/20/12 Condensing Boilers 6
98
% E
FF
ICIE
NT
….can reach efficiencies of 98% - and more…..
Thermal efficiency
MARKETING AND REALITY
3/20/12 Condensing Boilers 7
ENERGY CONTENT OF NATURAL GAS
SENSIBLE HEAT 89.8%
Heat that can be measured or felt by a change in temperature
LATENT HEAT 10.2%
Latent – Definition: Latin for “hidden”
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NON-CONDENSING BOILER HEAT FLOW
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CONDENSING BOILER HEAT FLOW
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What is a Condensing Boiler?
A condensing boiler is a boiler which has a heat exchanger that is made of materials which will withstand acidic condensate.
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Materials on the market:
Aluminum Alloy SA 240 316Ti 316L Cast Iron?
Copper Tube w/ secondary heat exchanger
MATERIAL CHOICES FOR CONDENSING BOILERS
3/20/12 Condensing Boilers 12
Oil Gas
Flue gas condensate
Typical household sewage
pH-Value Basic Acidic
0 1 2 3 4 5 6 7 8 9 10 11 12
0 1 2 3 4 5 6 7 8 9 10 11 12
Ammonia Lake water
Tap water
Distilled water
(neutral)
Clean rain water
Rain water
Vinegar
Lemon juice
Battery acid Gastric acid
CORROSIVE FLUE GAS CONDENSATE
pH Values of various fluids
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What about Efficiency?
Condensing boilers are NOT 99% efficient all of the time.
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120oF return water 100% input 87% efficiency Where is the
condensation?
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With efficiencies like this . . .
. . . our customers have reduced their fuel bills by up to 80%.
Now you can, too!
140°F EWT
120°F EWT
100°F EWT
80°F EWT
Condensing/Modulating Boiler
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LATENT HEAT RECOVERY
WATER VAPOUR LIQUID
Water vapor turns to liquid when it is reduced in temperature.
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Simplified Chemical Combustion Formula: CH4 + 2 O2 CO2 +2 H2O
HEAT RECOVERY FROM FLUE GASES
Water vapor (steam) containing latent heat
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LATENT HEAT RECOVERY 1 pound of water
144 Btus
Ice melting (Latent heat of fusion)
Water vaporizing (Latent heat of condensation)
Steam
Ice
970 Btus
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WATER VAPOUR DEW POINT
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NATURAL GAS COMBUSTION
1 part gas 10 parts air
+Excess air
More excess air = Lower CO2% Lower C02% = Lower dew point temperature Lower dew point temp. = Less condensation
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Higher CO2 =Higher Dew point =More Condensation
Dew
poi
nt w
ater
vap
or
77
86
95
104
113
122
131
140
oF oC
25
30
35
40
45
50
55
60
CO2 in Vol % 2 3 4 5 6 7 8 9 10 11 12
Natural Gas (95% CH4)
CO2% of flue gas influences dew point temperature
WATER VAPOR DEW POINT
Lower CO2 =Lower Dew point =Less Condensation
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Heat Exchanger Design:
PRIMARY HEAT EXCHANGER DESIGN
SECONDARY HEAT EXCHANGER DESIGN
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PRIMARY HEAT EXCHANGER DESIGN
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SECONDARY HEAT EXCHANGER
Efficient Boiler Design Condensing Boiler Design Guidelines
• Design system for lower water temperatures – Use larger delta T’s – Radiant floor heat / snow melt – Water Loop Heat Pumps
• Select boiler plant for small turndown capabilities
• Save initial cost by using both condensing and non-condensing boilers when possible
Efficient Boiler Design
• Outdoor Reset – Designing a Reset Curve
• Cycle Efficiency – How the cycle suffers – Adjusting the differential – Buffer Tanks
• Piping Systems
Maximizing Efficiency
Efficient Boiler Design – Outdoor Reset
Boiler Plant Cycle Efficiency
28
29
CHICAGO, IL
Cycle Efficiency Curve Analysis
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Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Energy Use Per Unit o
f Loa
d (e.g., HDDs)
Energy Use (T
herm
s, DecaThe
rms, etc.)
31
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
New
Ene
rgy Use Per Unit o
f Loa
d (e.g., HDDs)
Old Ene
rgy Use Per Unit o
f Loa
d (e.g., HDDs)
32
New
Ene
rgy Use Per Unit o
f Loa
d (e.g., HDDs)
Old Ene
rgy Use Per Unit o
f Loa
d (e.g., HDDs)
33
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
New
Ene
rgy Use Per Unit o
f Loa
d (e.g., HDDs)
Old Ene
rgy Use Per Unit o
f Loa
d (e.g., HDDs)
34
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Energy Use Per Unit o
f Loa
d (e.g., HDDs)
Energy Use (T
herm
s, DecaThe
rms, etc.)
35
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Energy Use Per Unit o
f Loa
d (e.g., HDDs)
Energy Use (T
herm
s, DecaThe
rms, etc.)
36
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Total HDD x Best Therms/HDD = What’s Possible
Total Therms – What’s Possible = What Was Wasted
37
The E/L Curve Fast Calcula@on…
Billing Period Therms HDDs Therms/HDD
December
January
February
March
etc
Total Therms Total HDD
Best ?
38
1…track small fracPonal loads at high efficiency
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To achieve HCE performance, you must…
2…make the efficiency rise as the load falls
3…size boilers so all loads fall within plant modulaPon range
4…use low mass boilers for jockey service
5…use modulaPng burners
6…opPmally match fuel input to real-‐Pme load
Piping Design Examples
40
Boiler Piping Examples
BOILER BOILER BOILER BOILER
42
Boiler Piping Examples
Boiler Piping Examples
Boiler Piping Examples
Boiler Piping Examples
Boiler Piping Examples
Boiler Piping Examples
Boiler Piping Examples
Boiler Piping Examples
Boiler Piping Examples
Hybrid Boiler System
Buffer Tank Example
Using a buffer tank to add 200 gallons will increase firing to almost 3 minutes for a 20 °F delta T. Using reset on the system loop could allow for a 50 or 60 °F delta T. Using a 60 °F delta T would mean a minimum run time of over 8 minutes!
Buffer Tank Example
180
140
180
140
Buffer Tank Example
Condensing Boiler
Non-‐condensing Boilers
Buffer Tank Example
Non-‐condensing Boilers
BufferTank
Condensing Boiler
Buffer Tank Example
Design Guidelines
• Utilize Buffer tanks and water temperature reset
• Design for long on/off cycles • Boilers do not need to be same size/style • Use small, modulating boilers as a
“jockey” boiler • Design for efficiency during light loads
Final Thoughts
• System design is typically more important than individual equipment selections.
• Energy retro-fits should be based potential savings and initial cost.
• Every building and every system is different, so there is no one-size-fits-all approach to Energy Saving Design.
Thank You!
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