Boiler Seminar

8/20/2019 Boiler Seminar

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Designing Efficient BoilerDesigning Efficient BoilerSystems for CommercialSystems for Commercial

BuildingsBuildings

Jeff Stein, PE

Taylor Engineering

Alameda, CA

PG&E Energy

Center May 2010


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Handouts

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When prompted enter the following (case sensitive)•

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Double click on a file to download it or highlight the

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AGENDA

Boiler Classifications Some Typical Boilers NOx Regulations and NOx Control Efficiency Basics

Energy Codes

3

Boiler Efficiency Standards Efficiency Part II Choosing a Condensing Boiler HW System Design eQUEST Simulation Case Study


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Disclaimer

Manufacturer’s literature and data isused in this presentation forillustration purposes only.

We do not endorse the data or

4

recommend any particular products.


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Boiler Classifications


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Pressure and Temperature

Fuel

Heat Exchanger Type

Materials

6

Draft Type

Burner Type

Chamber Type


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Pressure and Temperature• Steam Low pressure ( 160 psig)

• Hot Water Low temperature (350F)

Fuel Heat Exchanger Type Materials

Draft Type Burner Type Chamber Type


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Pressure and Temperature Fuel

• Fuel oil• Natural gas/propane

• Electric

8

• Other (coal, wood)

Heat Exchanger Type

Materials

Draft Type

Burner Type

Chamber Type


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Heat Exchanger Type• Water Tube

Straight tube

Bent tube

9

• Fire Tube Single pass

Multiple pass

• Modular / Sectional Materials Draft Type

Burner Type

Chamber Type

Source: ASHRAE, used with permission


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Heat Exchanger Type

Materials

• Non-Condensing Carbon Steel

10

Copper

Cast Iron

• Condensing Stainless Steel

Aluminum

Cast Iron

Draft Type

Burner Type

Chamber Type


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Heat Exchanger Type

Materials

11

Draft Type

• Atmospheric (natural draft)• Forced draft• Induced draft

Burner Type

Chamber Type


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Heat Exchanger Type

Materials

12

Draft Type

Burner Type

• One Stage• High/Low Fire• Modulating

Chamber Type


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Heat Exchanger Type

Materials

Draft Type

13

urner ype

Chamber Type• Dry base – combustion chamber below water chamber • Wet base – combustion chamber surrounded by water

chamber

• Wet leg (mud leg)• Dry back• Wet back



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Some Typical Boilers


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Typical Commercial BoilersTypical Commercial Boilers

COPPER OR STEEL BENT TUBEBOILER

15

COPPER FIN-TUBEBOILER



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FireFire--Tube BoilersTube Boilers

3 pass wetback

16

4 pass wetbackHW Only

Source: Cleaver Brooks, used with permission


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Firetube BoilersFiretube Boilers

Four flue gas passes• Wetback - Water cooled rear

tube sheets

On some boilers a door can be

opened to gain access to second

17



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Scotch Marine Firetube BoilersScotch Marine Firetube Boilers

Scotch marine is mostcommon type of fire tube. Large water volume Can handle load changes

(i.e. less thermal shock) Slow responding Good for steam since

volume enables them to

18

with relatively little changein pressure. However, sincethe boiler typically holds alarge water mass, it requiresmore time to initiate

steaming and more time toaccommodate changes insteam pressure.

This happens to be a 4 passdryback



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Dryback vs Wetback Dryback vs Wetback

Dryback - turnaround area isrefractory lined• Easier maintenance

Wetback - turnaround zone is water-

19

,refractory lining• Cheaper

• Higher maintenance (for steam)• Slightly more efficient• Poorer circulation – loose stay bolts?


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Industrial Water TubeIndustrial Water Tube

20

D Style A StyleO Style



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Commercial Water TubeCommercial Water Tube

21Source: Cleaver Brooks, used with permission


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Modular / Copper Fin TubeModular / Copper Fin Tube

22

Pros• Small foot print• Lower 1st cost• Responsive• Efficient• Light weight• Quiet

Cons

• Gas / LP only• Life span• Maintenance• Venting issues• Pumping critical

• Short cycling• Hot water only Source: Raypack, Lochinvar, used with permission


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Cast Iron Sectional BoilerCast Iron Sectional Boiler

23Source: Crown Boilers, used with permission


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Thermal Shock Thermal Shock

Rapid changes in temperature (up ordown) cause thermal stresses.

• e.g. staging on a cold lag boiler

The frequency and degree contribute

24

to failure

Mini bypasses?


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Thermal Shock Thermal Shock

Tube Attachment

25

Beaded Tube

Tube End

Cooling

Tube End

Cooling

o e an

Flared Tube

Tube End

Cooling

Rolled and

Welded Tube



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NOx Regulations and NOxControl


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Bay Area Air Quality ManagementDistrict – Boiler Regulations

27


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Regulation 9, Rule 6 – Natural Gas WaterHeaters & Boilers

New boilers up to 2 MMBTU/hr

Device nanogram NOx / joule

output

28

75K to 400K BTU/hr

(storage and instantaneous)

Current: 40 (60 ppm)

1/1/2013: 14 (20 ppm)

400K to 2 MM BTU/hr

(storage and instantaneous)

Current: 20 (30 ppm)

1/1/2013: 14 (20 ppm)


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Regulation 9, Rule 7 – Boilers, SteamGenerators, Process Heaters

New and existing boilers• Some exceptions

Input (MM BTU/hr) Old NOx

Limit

New NOx

Limit

Effective Date

Non-natural gas, 40 ppmv

40 ppmv

1/1/2011

29

non-LPG heaters (10 MM

BTU/hr &

up)

(1 to 5 to


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Units

1 MBH = 1KBtuh = 1,000 Btu/hr 1 MMBtuh = 1,000,000 Btu/hr

1 Boiler HP = 33,475 Btu/hr

• E. . 100 HP = 3 million Btuh

30

Nominal capacity

• Some manufacturers use input capacity

• Others use output capacity


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NONO x x FormationFormation

The majority of NOx produced duringcombustion is NO (95%). Onceemitted into the atmosphere, NOreacts to form NO2. It is NO2 that

reacts with other ollutants to form

31

ozone.

NOx production affected by:

• flame temperature• amount of nitrogen in the fuel• excess air level• combustion air temperature.


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NONO x x ControlControl

Post Combustion Control Methods• Selective Non-Catalytic Reduction• Selective Catalytic Reduction

Combustion Control Techniques

32

• Low Excess Air Firing• Low Nitrogen Fuel Oil

• Burner Modifications – to spread out flame• Water/Steam Injection – reduces efficiency• Flue Gas Recirculation – most effective


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Flue Gas RecirculationFlue Gas Recirculation

A portion of the O2 depleted exhaustgases are recirculated back into thecombustion zone in order to lower theflame temperature (from 3,500oF to

2 900oF and reduce NOx formation.

33



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Flue Gas RecirculationFlue Gas Recirculation

34

Internal FGR External FGR



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Efficiency Basics


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Boiler Efficiency (not well known)Boiler Efficiency (not well known)

36


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Efficiency TermsEfficiency Terms

Combustion Efficiency• Includes only stack losses• Does the burner completely burn the fuel?

Thermal/Overall Efficiency

37

• how effectively is heat transferred to thewater?

Combustion Analyzer Gross/Net• Gross efficiency assumes no condensation• Net assumes 100% condensation


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Combustion EfficiencyCombustion Efficiency

Not enough air results in sooting, CO formation,back-fire, and damage to equipment - maybe evenexplosion

Too much air means fuel is being used to heat theair and results in more energy out the stack.

ROT: 20% excess air 4% O in stack

38

Air/fuel ratio control• Maintains proper air/fuel ratio over entire boiler turndown

range

• Excess air trim enhances boiler efficiency• Wide range of control strategies

Single point positioning w/jackshaft

Parallel positioning

Metered cross-limited


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Air-Fuel Ratio

CO2

CO HighestEfficiencyoperating

region

Quantity in flue gas 13.6

7.4

39

Excess Air Excess Fuel

OxygenHydrocarbons

0 11 2 Flue Gas Oxygen %

CO202

3


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Air to Fuel Ratio Affected by Air to Fuel Ratio Affected by

Ambient temp Barometric pressure

Other boilers on common exhaust

Hi/Lo or Modulatin controls

40


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Single Point PositioningSingle Point Positioning



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Parallel PositioningParallel Positioning



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Energy Codes


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Energy Code – CA Title 20

For commercial

boilers:• only full load

combustion

efficiency

• No part load or

44


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Previous Energy Code (Title 24)Previous Energy Code (Title 24)

45


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ASHRAE ASHRAE 90.190.1--20072007

46

§ 431.86 Uniform test method for themeasurement of energy efficiency of commercial

packaged boilers.• (a) Scope. This section provides test procedures that must befollowed for measuring, pursuant to EPCA, the steady statecombustion efficiency of a gas-fired or oil-fired commercialpackaged boiler.

• Refers to methods in HI BTS-2000


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Boiler EfficiencyStandards


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Boiler Rating Standard

48Source: AHRI, used with permission


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BTS-2000

Full Load Efficiency Only• No Part Load Ratings!

Inlet Water Temperature

• Non-condensing boilers: 35ºF to 80ºF!

49

Outlet water temperature: 180ºF

No limits on or corrections for room

or inlet air temperature! BTS-2000 will over-estimate real

efficiency and capacity


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Help is on the way: ASHRAE 155P

METHOD OF TESTING FOR RATINGCOMMERCIAL SPACE HEATING BOILERSYSTEMS

PURPOSE: This standard provides proceduresfor determining the steady state thermalefficiency, part load efficiency and idling energyin ut rate of individual boilers, and a lication

50

seasonal efficiency of commercial space heatingboiler systems

Committee formed in 1994 Coming soon?: public review of steady state test

methods Future version: equations and software for

calculating application seasonal efficiency –including load profile, control sequences, etc.


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ASHRAE 155P Required (R) and Optional (O) Tests

Single-

stage burner

Two-

stage burner

Automatic

step-

modulating

burner

High Return

Water

Temperature

High fire R R R

Int fire O

Low fire R R

Intermediate High fire O O O

180 / 140

180 / 140-170

51

tea y tate

Tests

Return Water

Temperature

Int fire O

Low fire O O

Low Return

Water

Temperature

High fire R* R* R*

Int fire O

Low fire R* R*

Idling TestsHigh temp R R R

Low temp O O O

Throughflow Loss TestsHigh temp O O O

Low temp O O O

*required for low return water temperature and condensing boilers only.

120 / 80

120 / 80-110

180 LWT

140 EWT


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Research for 155PResearch for 155P

Cast-iron, single stage, atmospheric burner, 180

HWST, constant flow

52Source: Hewitt, BSE Magazine, June 2005, used with permission


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Same data…Same data…



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Forced Draft…Forced Draft…



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Condensing at 180 HWST…Condensing at 180 HWST…



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Condensing at 110 HWST…Condensing at 110 HWST…



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Effect of HWST SetpointEffect of HWST Setpoint



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Input-Output Relationship at Different Leaving Water Temperatures

Expanded View of High Fire Area

0.920

0.940

0.960

0.980

1.000

220

210

200

58

0.800

0.820

0.840

0.860

0.880

0.900

0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1

Output

I n p u t 180

170

160

150

140

130

110

d l id l i


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Modulating BurnerModulating Burner

"In the modulating regime, therelationship of input (y) to output (x)is often slightly concave up, due in

part to the tendency of many burners

59

fire.“

S CO C S


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ASHRAE 155P - CONCERNS

No cycling tests at part load Allowed to retune boiler for each test

Allows 100ºF room temperature

Does not recognize temperature

60

compensa on r m con ro

Uses electricity site/source multiplierof 1

WISH LIST:• No retuning• Test at 100%, 40%, 10%, 0% (idling)


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Efficiency Part II

Wh t Aff t B il Effi i


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What Affects Boiler Efficiency

Air/fuel ratio (combustion efficiency)• Turn-down controls• Temperature compensation

HX design Inlet water temperature

Minimum flow / maximum ∆T

62

yc ng ra con ro s• Pre-purge, post-purge, stack dampers

Vessel losses – radiation and convection• room temperature, wind speed

• Boiler mass, insulation• Cool down / heat up Parasitics

• Draft fan – electric heat?• Other

All B il C d i B il b tAll B il C d i B il b t


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All Boiler are Condensing Boilers, but… All Boiler are Condensing Boilers, but…

63Source: 2008 ASHRAE Handbook, used with permission

…only Some Boilers are Designed to…only Some Boilers are Designed to


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…only Some Boilers are Designed to…only Some Boilers are Designed toCondenseCondense

Corrosion

resistantmaterials Condensate

drain

64Source: Lochinvar, used with permission

S i f C d i B il


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Science of Condensing Boilers

Natural gas combustion:

• 90% sensible heat (theoretical maximumcombustion efficiency without condensing)• 10% latent heat in water vapor

For condensation to start the HXsurface temperature must be below

the dew point (boiling point) of the

65

wa er vapor - , w cdepends on the pressure of thesteam

As the steam is condensed out, the

volume of steam is reduce, itspartial pressure is reduced, and thedew point drops

The colder the entering water themore condensing possible


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Choosing a CondensingBoiler

Ch i C d i B il


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Choosing a Condensing Boiler

Minimum flow Secondary HX Turndown Air shut-off HX material

Flue material

67

Temperature compensation Water pressure drop Max water pressure

NOx Controls – setpoint reset, adjustable deadband Water volume – more is better? Warranty

Some Condensing Boilers (this list is


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g (incomplete and data may not be correct!)

Make Model HX matFlue mateInput

(kBtuh)Turndown recirc pu min flow max ∆T

Aerco BMK SS AL29-4C 1500, 20:1 no 0 GPM 137.6 ºF

Ajax Atlas Series A Cu AL29-4C 500 to 3.5:1 optional. 30 GPM 32ºF

Bryan Triple-Flex

Buderus GB cast alu AL29-4C, 328, 441, 3:1 Comes Dependen

40 ºF

Burnham Alpine SS CVC, PVC, 80,105, 5:1 Recomme

4.2 GPM 54ºF (adjus

Cleaver Brooks Clearfire CFC SS AL29-4C 500 to 5:1 not require none 120 ºF

De Dietrich C230 ECO-A cast aluCat. II or 360 to 860 5:1 no none 81 ºF

68

Fulton Pulse PHW 2000 sch 40, AL29 4C, 300 - 5:1 No None None

Gas Master GMI SS SS 200 - 8000 "virtually 26 GPM at >150°F

Hamilton EVO SS AL29-4C, 80 to 8000 5:1 Recomme

2.2 GPM 60 ºF

Heat Transfer ModCon SS SS, PVC, 300, 500, 5:1 Requires 14 GPM 45 ºF

Hydrotherm KN cast iro Cat. IV AL 600, 1000, 5:1 Recomme

2 GPM 100 ºF

Laars Rheos Cu SS 1200, 4:1 Yes. 15.4 GPM 140 ºF

Lochinvar Intelli-fin Cu finn AL29-4C 1500, 4:1 Yes. Provi 90 GPM 80-90 ºF

Patterson Kelly PK Mach cast aluCat. IV AL 300, 450, 5:1 Recomme

15 (model 40 ºF

Raypak Xtherm Cu finn SS Cat. IV 1000, 4:1 yes 47 GPM 40 ºF

RBI Futera Fusion Cu finn Cat IV, non500 to 4:1 Yes. Provi It has it's 35 ºF

Triangle Tube Prestige Solo SS 60 to 399

ViessmannVitocrossal 300 SS Al29-4C, 3 638, 846, 3:1? (to b No. None 80°F

Weil McLain Ultra Series 3 (U cast aluPVC, CPV 80, 105, 5:1 Yes. The 3.5 GPM 50 ºF

Some Condensing Boilers


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Some Condensing Boilers

Up-fire water-tube Down-fire fire-tube

69Source: Aerco, used with permission Source: Cleaver Brooks, used with permission

Bryan Triple Flex™


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Bryan Triple-Flex™

Preheats combustion air with fluegases

70Source: Bryan Boiler, used with permission, patent pending

Buderus SB


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Buderus SB

Two return water connections

71Source: Buderus, used with permission

Minimum Flow


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Minimum Flow

Very low flow may go from turbulent to laminarat HX wall• Reduced thermal efficiency and higher stack temperature• Flashing to steam can damage heat exchanger

If the total coil flow is below the boiler min flow

then supply water is bypassed to the return,

72

w c ra ses e re urn empera ure an re ucesefficiency – this is more pronounced at low(condensing) water temperatures

Min flow may be:

• Recommendation – e.g. to limit cycling• Required primary/secondary – e.g. built-in recirculation pump• flow switch• ∆T lockout - e.g. soft lockout at 46ºF, hard lockout at 72ºF

Condensing boiler manufacturers data


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Condensing boiler manufacturers data

Thermal Efficiency of BMK1.5LN

99.3

97.5

95.1

97.5

95.896

98

100

5% Input 50% Input 100% Input ANSI Z21.13 BTS2000

73

90.9

88.388

92.8

89.1

87.2

86.6

93.9

91.4

86.6

92

93.2

88.5

8686

88

90

92

94

50 70 90 110 130 150 170

Return Water Temperature, 20ºF Rise

E f f i c i e n c y ,

%

Source: Aerco, used with permission

Secondary HX


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Secondary HX

Primary HX is non-condensing

Bypass valve maintains primary HX EWT > 130ºFSecondary loop


Secondary HX’s


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Secondary HX s


Source: Laars, used with permission

Secondary HX– When Does in Condense?


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Secondary HX– When Does in Condense?

HWRT Setpt Load Actual HWRT Result

low

no condensing since sec HX is seeing

mostly HWSThigh no condensing

biglow

condensing but bypass opens, limited

flow to sec loop, starves the load

small high no condensing

low

condensing but bypass opens, limited

flow to sec loop, starves the load

high no condensing

lowsmall

highbig

76

Could end up fixing thesetpoint above condensing andrunning 24/7 to avoid starving

the load

Turndown – The Real Story?


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Turndown – The Real Story?

A boiler can still cycle at high load if the

controller overshoots• Stabilizing the firing rate is harder when the

turndown is greater

Combustion efficiency may be worse at low

77

• Not necessarily reflected in manufacturers data

The greater the turndown the greater the risk

of flame failure with cold inlet air • Flame detector will not make if too rich or too lean• Boiler technicians often limit the turndown to 3:1

Air-Fuel Ratio


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Air-Fuel Ratio

CO2

CO HighestEfficiency

operatingregion

Quantity in flue gas13.6

7.4

78

Excess Air Excess Fuel

OxygenHydrocarbons

0 11 2 Flue Gas Oxygen %

CO202

3

Air-Fuel Field Calibration


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Air-Fuel Field Calibration

Recalibration as part of initial start-up is necessary due to

changes in the local altitude, gas BTU content, gas supplypiping and supply regulators, shipping damage, etc.

79Source: Aerco, used with permission

Air-Fuel Calibration


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Air-Fuel Calibration

Controllable minimum• ∆P across air or fuel damper/fan varies

with the square of the flow

∆P ~ flow2

80

change in flow

100 % = 4” WC

75 % = 2.2” WC

50 % = 1” WC

25 % = .2” WC

5% = 0.01” WC

Water volume


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Water volume

Boilers are getting smaller(less water)

• Reduces cool down losses• makes firing controls more

difficult and increases risk of

flashing to steam

Fire tube boilers claim more

81

better low flow performance

Source: Triangle Tube, used with permission


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Heating Hot WaterSystem Design

HW System Design


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HW System Design

Zone design• Temperatures – supply, ∆T• Coils - rows• Valves - 2-way, zone pumps

Boiler(s) – Number, equal/uneven sizing Piping design – primary-only,

83

Headered vs Dedicated Pumps Minimum Flow

• Constant flow• 3-way valves• Controlled bypass

Sequences• Boiler staging• HWST reset

Boiler System Efficiency


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Boiler System Efficiency

Boiler sizing Boiler staging

Throughflow

Design HWST and ∆T

84

• HWST reset• HW flow controls (2-way control valves)• Minimum flow controls

Piping losses – some beneficial

Leaks

Pumping energy – electric heat!

Primary Only – Dedicated Pumps


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Primary Only Dedicated Pumps

Works fine for boilers that can handle condensing on morning warmup, like atmospheric boilers. Not so good for sealed combustion (e.g.forced draft copper fin-tube)

85

Primary Only – Headered Pumps


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Primary Only Headered Pumps

More expensive and complicated than dedicated pumps for little benefit

86

Primary Only – Mixing Valve for LoopR t


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Reset Does not allow much reset without condensing Likely to short cycle

87

Primary Only – Mixing Valve in the rightl !


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place! Could result in low boiler flow if loop setpoint is high and load is low

88

Primary/Secondary


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Primary/Secondary

Maintains constant flow through boiler but does not prevent condensing onwarm up

Lower throughflow losses if primary pumps cycle with boiler at low load

89

Primary/Secondary with thermostaticl


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valves Could require boilers to run 24/7 if they are not oversized Mixing valve is open when boiler is off and may not be able to open fast

enough when boiler starts to prevent short-cycling

90

Primary Only – controlled bypass


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Primary Only controlled bypass

Maintains minimum flow but may not prevent short cycling

91

Short Cycling


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Short Cycling

Efficiency – pre-purge/post-purge Excessive wear on boiler

components (e.g. heating and

cooling)

92

Nuisance shutdowns andunexplained flame failures with flameprogrammer fault codes that have noeasily identifiable cause

Options to Address Cycling at Low Load


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p y g

Oversized pipes Some 3-way coil valves Controlled bypass Buffer tank

• Primary/sec. with tank in common leg• Primary only with tank in bypass

High turndown

93

o u ar pony o ers Boiler lockout at low loads Bigger deadband Fuzzy Logic?

• “.. the controller fires the boiler stages to provide the “targettemperature” at secondary loop sensor. It continuously samples theinlet, outlet and target temperatures. Over time, it will learn the systemcurve and adjust the firing of the stages to meet the demand in the mostefficient way”

Primary/Secondary With tank in commonleg


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leg Does not allow boiler to see cold return water at low load How to prevent overfiring with all that mass?

94

Primary Only with tank in bypass


95/140

y y yp

Boiler more likely to see cold return water (e.g. morning warmup)

95

Recommendations


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Non-condensing• Low mass, forced draft, modulating• Primary/secondary with mixing valves• Some mass in primary circuit and bypass circuit

Condensing

96

• Primary-Only with 3-way valves far away orbypass with buffer tank

Both

• Multiple or pony boilers• Large deadband on boiler cycling• Commission firing controls to insure turndown

and prevent overshoot

Firing Rate Controls


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g

How is the firing rate adjusted tomaintain setpoint?

• Internal ControlPID

97

-

Adjustable parameters

• External control

Internal Control - PID


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98

Internal Control – Mystery?


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y y

99

Internal Control – P-Only


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y

100Source: Laars, used with permission

Firing Rate – External Control


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g

4-20mA signal = 0 to 100% fire More risk of tripping over-

temperature safety?

101

Boiler Staging


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g g

Enable lead boiler if OAT


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Not required by Title 24 Pump energy goes into the water

(VFD losses do not)

Reducing pump energy increases

103

Not cost effective (VFD, ∆P sensor,controls, etc.)

• payback ~25 years VFDs can solve problems with over-

pressurized valves


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eQUEST Simulation

Simulation – eQUEST (www.doe2.com)


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105

RATED-HWR-TFor the HW-CONDENSING boiler, specifies the return water

temperature at which both the CAPACITY and HEAT-INPUT-RATIO

are defined. The default is 80°F

Source: eQUEST, used with permission

eQUEST


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106Source: eQUEST, used with permission

eQUEST


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107

HIR-FT = a curve that modifies the fuel consumption as a function of

the supply temperature and the environmental temperature. There isno defaultFor the HW-CONDENSING boiler, this curve is not

used. Instead, the HIR-FPLR curve is used, and uses both the part-

load ratio and the return water temperature.

Source: eQUEST, used with permission

eQUEST HIR=f(PLR) Curves


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eQUEST Boiler Thermal Efficiency as a function of Load Ratio

(with default full load efficiencies)

70%

80%

90%

100%

n c

y

Unstable!

108

0%

10%

20%

30%

40%

50%

60%

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100

%

Load

T h e r m a l E f f i c i e Condensing High Eff @140EWT

Condensing @140 EWT

Forced Draft

Atmospheric

eQUEST HIR=f(PLR) Curves at Low EWT


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eQUEST Boiler Thermal Efficiency as a function of Load Ratio

(with default full load efficiencies)

70%

80%

90%

100%

c y

Unstable!

109

0%

10%

20%

30%

40%

50%

60%

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100

%

Load

T h e r m a l E f f i c i e Condensing High Eff @80 EWT

Condensing @ 80 EWT

Forced Draft

Atmospheric

eQUEST Condensing Boiler Curves vs EWT


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EQUEST Standard Efficiency Condensing Boiler Thermal Efficiency vs.

Hot Water Temperature

70%

80%

90%

100%

n c y

~5% Load

110

0%

10%

20%

30%

40%

50%

50 70 90 110 130 150 170

Entering Hot Water Temperature (°F)

T h e r m a l E f f i c i

~20%Load

~60% Load

100% Load

Hi Eff. Condensing Boiler Curves vs EWT


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EQUEST High Efficiency Condensing Boiler Thermal Efficiency vs. Hot

Water Temperature

70%

80%

90%

100%

y

111

0%

10%

20%

30%

40%

50%

60%

50 70 90 110 130 150 170

Entering Hot Water Tem perature (°F)

T h e r m a l E f f i c i e n

~20% Load

~50%Load

~75% Load

100% Load

eQUEST – HW Load Sensitivity


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With SAT Reset:

112

Without SAT Reset:

Calibrating Existing Building Models


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Zones: sizing, sequences, min flow, internal loads

Systems: sizing, SAT reset

Plant: sizing, HIR, curves, staging, HWST reset

Monthly data does not tell if you match hourly load profile

113


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Case Study

Sonoma State UniversitySonoma State University


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115

Sonoma State IssuesSonoma State Issues


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Oversized/Inefficient Thermal Shock Distribution Losses Manned Operation

• Boiler does not cycle at low fire

116

reven overpressur za on ma n a n m n mumflow

• Required by code so boiler shut off at night 250F HW setpoint – based on old HX

design and fear of condensation Existing local boilers – use campus HW? Campus Expansion – new local boilers?

Taylor ScopeTaylor Scope


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Evaluate:• Energy efficiency• Ability to adequately serve the loads• Current condition and remaining useful life of existing

hot water system equipment

• Operation and Maintenance issues

117

performance and extending plant useful life.• E.g. pony boiler LCC analysis• Consider expected future capacity based on planned

campus new construction and retrofits.

Master Plan• implementation schedule for recommended retrofit

measures.

OptionsOptions


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Abandon plant? Pony boilers Improve Controls

• HWST Reset Range? OA reset? Feedback?

• Stack damper?

118

• Pumps in series with check valve• Bldg pumps could run alone at night

Fix cycling? Unmanned operation? Don’t shut off at night?

• Simulate both ways Better to use satellite boilers?

HW Plant HistoryHW Plant History


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Originally designed for 325o

F LWT,160 psi

New boilers installed in 1997

• 250 LWT / 170 EWT

119

• 360 GPM• 10:1 turndown (boiler rep says it is more

like 4:1)

Campus HW SystemCampus HW System


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120

Current Operating PracticeCurrent Operating Practice


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They run one boiler and its pump as the lead for a month then the

other, never both. Boiler Isolation valves never closed

• (Trends do not show throughflow?), operator says: only few GPM in lag Fixed HWST setpoint of 250oF The boiler is shut off every night at 10pm and restarted at 5am. Off

in summer.• (When the boilers/pumps are off at night the HWST and HWRT falls to

about 150-180 by the next morning.)

121

Manual cycling at low load

• Turn off at 220 HWRT / Turn on at 190 HWRT• Apparently the boilers will modulate down to low fire and then stay at low

fire and overheat the water until the safeties trip.

Manual Bypass Control – Maintain 80-95 psi on secondary supplyside

• Auto bypass on dP – failed. Consider using flow meter?• Operators say min flow = 350 GPM (this is also the design flow)• Operators say pipes/valves out in the loop cannot handle more than 95 psi.

HW LoadsHW Loads


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Mostly heating, some DHW Several buildings served by plant

have abandoned campus HW forDHW and added local boilers.

122

Some new and existing buildings areabandoning campus HW

Annual Burner Tuning Annual Burner Tuning


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123

Oversizing Penalty Depends on Idle LossOversizing Penalty Depends on Idle Loss


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124Source: T. Butcher, Brookhaven

Idle loss depends on HWST, pre-purge, etc.

HWST Reset and HX SelectionsHWST Reset and HX Selections


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Ives Hall 1965

Person Theater 1986

125

Art Building Renovation 1996


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126

Allen Bradley Trend Data Allen Bradley Trend Data


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Weds 1-5-05

400

500

600

230

250

270

BOILER\2\FLOW_WATER

BOILER\2\TEMP_STACK

BOILER\TEMP_RETURN

BOILER\TEMP_SUPPLY

127

0

100

200

300

12:0

0

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

6:00

AM

7:00

AM

8:00

AM

9:00

AM

10:0

0

AM

11:0

0

AM

12:0

0

PM

1:00

PM

2:00

PM

3:00

PM

4:00

PM

5:00

PM

6:00

PM

7:00

PM

8:00

PM

9:00

PM

10:0

0

PM

11:0

0

PM

12:0

0

AM

G P M

150

170

190

210

450 GPM, 50 dT, for 17 hrs = 191 mil Btu

output

avg output: 11,000,000 Btuh (44% loaded)

daily gas data: 197 mil Btu input

97% thermal efficiency! (not system effic)

Medium Load DayMedium Load Day


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Thurs 4-21-05

400

500

600

230

250

270

BOILER\1\FLOW_WATER

BOILER\TEMP_RETURN

BOILER\TEMP_SUPPLY

400 GPM, 45 dT, for 9 hrs = 80 mil Btu output

(36% loaded)


84% thermal efficiency

128

0

100

200

300

12:0

0

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

6:00

AM

7:00

AM

8:00

AM

9:00

AM

10:0

0

AM

11:0

0

AM

12:0

0

PM

1:00

PM

2:00

PM

3:00

PM

4:00

PM

5:00

PM

6:00

PM

7:00

PM

8:00

PM

9:00

PM

10:0

0

PM

11:0

0

PM

12:0

0

AM

G P M

150

170

190

210

Low Load DayLow Load Day


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Sun 5-29-05

300

400

500

230.00

250.00

270.00

BOILER\1\FLOW_WATER

BOILER\1\TEMP_STACK

BOILER\TEMP_RETURN

BOILER\TEMP_SUPPLY

400 GPM, 20 dT, for 3.2 hrs = 13 mil Btu

output

avg output: -- Btuh (--% loaded)


50% efficiency

129-100

0

100

200

12:0

0

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

6:00

AM

7:00

AM

8:00

AM

9:00

AM

10:0

0

AM

11:0

0

AM

12:0

0

PM

1:00

PM

2:00

PM

3:00

PM

4:00

PM

5:00

PM

6:00

PM

7:00

PM

8:00

PM

9:00

PM

10:0

0

PM

11:0

0

PM

12:0

0

AM

G P M

150.00

170.00

190.00

210.00

Boiler Load Profile


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Boiler Annual Load Profile (extrapolated from 2/1/08 to 4/8/08)

(negative output means boiler losses exceed boiler output)

550

600

650

700

750

800

130

-

50

100

150

200

250

300

350

400

450

-25% -20% -15% -10% -5% 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60%

Percent Output (note: 25% means hours between 20% and 25%)

H o u r s / y e a r

50% is half the

output of 1

boiler or about

12 million Btuh

Typical DayBoiler overfires


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Boiler overfires

then cycles

131

When boiler is disabled

HWST


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Obvious errors imply actualefficiency is even lower

interval output (kbtu) input (kbtu) efficiency

avg output

(kbtuh) pct load

all of feb 828,325 1,280,968 65%

132

a o marc , , ,

april 1-8 296,179 498,164 59%

march 4, 5am-12pm 34,201 45,447 75% 4717 19%

march 4, 6pm-10pm 22,540 15,387 146% 5303 21%

march 4, 7pm-9pm 9,866 7,620 129% 4933 20%

march 4, all day 50,756 71,254 71%

Efficiency vs. Load


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Boiler-1 Hourly Average Efficiency vs Load

(negative load means boiler losses exceed boiler output)

100%

150%

200%

p

u t )

133

-200%

-150%

-100%

-50%

0%

50%

-30% -20% -10% 0% 10% 20% 30% 40% 50% 60%

Load Ratio (output/capacity)

E f

f i c i e n c y ( o u t p u t / i n

Efficiency vs. HWRT


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Boiler-1 Hourly Average Efficiency vs HWRT

100%

150%

200%

n

p u t )

134

-200%

-150%

-100%

-50%

0%

150 170 190 210 230 250

Hot Water Return Temperature

E

f f i c i e n c y ( o u t p u t / i

Some Findings


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50MMBH capacity, 12MMBH peakload

$500,000/yr boiler fuel cost

Average thermal effic: 55%

135

umps are un ers ze samebut half the original ∆T)

Per Title 8, Section 778, manned

operation is not required for Low-pressure boilers, High-temperaturewater boilers, Miniature boilers, etc.

Piping Losses CalculationPiping Losses Calculation


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50,000 therm/yr Assumptions:

• 24,000 gallons• 20 degree temp drop from 10pm-5am

•

136

• All buildings have flow – no dead legs• No useful heat extraction when main HW pumps

off – could bldg pumps be extracting heat from

HX?

Deleting the HXs and reducing the HWSTwill reduce piping losses

RecommendationsRecommendations


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Add Pony Boilers Reset HWST based on building valve

feedback

Remove building heat exchangers

137

x ow re-cyc ng

Run 24/7 and serve all buildings

Run Two Pumps with One Existing

Boiler at High Load Control bypass with flow meter, if no

pony boilers

Recommendations


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138

Check valve:

-Prevent plant from pushing water the wrong way through bypass

-Prevents building pump from stealing water from other buildings

Gas Meter DataGas Meter Data


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Btu based on STANDARD Cubic Foot of Gas

• 60F / 14.73 PSIA / 1000 BTU

139

Gas meter reads in ACTUAL cubic feet Standard = Actual x Press. Factor x Temp. Factor x SuperX Factor

• Pressure Factor = (Line Pressure + Atmos Pres.) / Base pres. E.g. At 10 PSIG your factor would be (10 + 14.48)/14.73 = 1.66

• Temp Factor = (460 + Base)/(460+Line Temp)

• SuperX is really not applicable below 60 PSIG so assume 1 A “Corrector” measures line temp and pressure and corrects

meter output ($1500)

PG&E put a corrector on gas line to SSU campus (not perboiler)

Improving Existing Boiler SystemsImproving Existing Boiler Systems


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• O2 Trim accounts for boiler room

temperature• Parallel Positioning

separate actuators for gasand air valves

• Flue gas recirculation• Draft control

• Economizer • New burner – higher

turndown

• HWST reset

• Maintenance Brush out soot Chemically remove scale

PG&E Rebates:

Documents

Boiler Seminar