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Transcript of 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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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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Boiler Classifications
Pressure and Temperature
Fuel
Heat Exchanger Type
Materials
6
Draft Type
Burner Type
Chamber Type
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Boiler Classifications
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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Boiler Classifications
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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Boiler Classifications
Pressure and Temperature Fuel
Heat Exchanger Type• Water Tube
Straight tube
Bent tube
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• Fire Tube Single pass
Multiple pass
• Modular / Sectional Materials Draft Type
Burner Type
Chamber Type
Source: ASHRAE, used with permission
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Boiler Classifications
Pressure and Temperature Fuel
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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Boiler Classifications
Pressure and Temperature Fuel
Heat Exchanger Type
Materials
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Draft Type
• Atmospheric (natural draft)• Forced draft• Induced draft
Burner Type
Chamber Type
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Boiler Classifications
Pressure and Temperature Fuel
Heat Exchanger Type
Materials
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Draft Type
Burner Type
• One Stage• High/Low Fire• Modulating
Chamber Type
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Boiler Classifications
Pressure and Temperature Fuel
Heat Exchanger Type
Materials
Draft Type
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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
Source: ASHRAE, used with permission
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Some Typical Boilers
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Typical Commercial BoilersTypical Commercial Boilers
COPPER OR STEEL BENT TUBEBOILER
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COPPER FIN-TUBEBOILER
Source: ASHRAE, used with permission
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FireFire--Tube BoilersTube Boilers
3 pass wetback
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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
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Source: Cleaver Brooks, used with permission
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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
Source: Cleaver Brooks, used with permission
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Dryback vs Wetback Dryback vs Wetback
Dryback - turnaround area isrefractory lined• Easier maintenance
Wetback - turnaround zone is water-
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,refractory lining• Cheaper
• Higher maintenance (for steam)• Slightly more efficient• Poorer circulation – loose stay bolts?
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Industrial Water TubeIndustrial Water Tube
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D Style A StyleO Style
Source: Cleaver Brooks, used with permission
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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
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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
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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
Source: Cleaver Brooks, used with permission
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NOx Regulations and NOxControl
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Bay Area Air Quality ManagementDistrict – Boiler Regulations
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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
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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
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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
Source: Cleaver Brooks, used with permission
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Flue Gas RecirculationFlue Gas Recirculation
34
Internal FGR External FGR
Source: Cleaver Brooks, used with permission
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Efficiency Basics
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Boiler Efficiency (not well known)Boiler Efficiency (not well known)
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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
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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
41Source: Cleaver Brooks, used with permission
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Parallel PositioningParallel Positioning
42Source: Cleaver Brooks, used with permission
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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
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Previous Energy Code (Title 24)Previous Energy Code (Title 24)
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ASHRAE ASHRAE 90.190.1--20072007
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§ 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
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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…
53Source: Hewitt, BSE Magazine, June 2005, used with permission
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Forced Draft…Forced Draft…
54Source: Hewitt, BSE Magazine, June 2005, used with permission
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Condensing at 180 HWST…Condensing at 180 HWST…
55Source: Hewitt, BSE Magazine, June 2005, used with permission
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Condensing at 110 HWST…Condensing at 110 HWST…
56Source: Hewitt, BSE Magazine, June 2005, used with permission
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Effect of HWST SetpointEffect of HWST Setpoint
57Source: Hewitt, BSE Magazine, June 2005, used with permission
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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
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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
74Source: Lochinvar, used with permission
Secondary HX’s
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Secondary HX s
75Source: Lochinvar, used with permission
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
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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)
daily gas data: 95 mil Btu input
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)
daily gas data: 26 mil Btu input
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: