In-Field Performance of Condensing Boilers
Transcript of In-Field Performance of Condensing Boilers
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IN‐FIELD PERFORMANCE OF CONDENSING BOILERS
Lois B. ArenaSteven Winter Associates, Inc.March 2012
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Why Research Hydronic Heating?
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© 2012 Steven Winter Associates, Inc. All rights reserved
Reasons to Research Boilers
Approx. 14 million homes (11%) in the US are heated with a steam or hot water system
Almost 70 percent of existing homes were built prior to 1980 Boilers built prior to 1980 generally have AFUE’s of 0.65 or
lower Energy savings of 20+% are possible by simply replacing older
boilers with standard boilers & up to 30% with condensing boilers.
Optimizing condensing boilers in new and existing homes could mean the difference of 8‐10% savings with little to no additional investment.
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Overview of Systems Evaluated
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Overview of Previous Research
Previous Research – 3 Phases:Monitoring and Evaluation of 6 Existing Homes Bench Top Research from Thomas Butcher at BNL Design, Monitoring & Evaluation of 3 New Homes
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Basic System Configuration
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Outdoor Reset Curve
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Gaps Identified
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Technology & Industry Gaps
Installed efficiency lower than rated efficiency Most software tools can’t properly model hydronic heating
Lack of guidance for contractors w/ respect to design, controls and commissioning
Safety features protecting boilers decrease efficiency
Response time is extremely slow
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Critical Parameters Affecting Efficiency
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Factors Affecting Efficiency of Installed Systems
Con ‐Primary/secondary loop ‐ contributes to higher than optimal return water temperatures to the boiler
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Factors Affecting Efficiency of Installed Systems
Con ‐ Flow rates are higher than anticipated, contributing to higher than optimal return water temperatures.
Table 1. Summary of Space Heating Operating Conditions from Existing Home Monitoring
Boiler Curve Settings [°F]
House Baseboard Length
Boiler Capacity
# of Zones
Flow Rate1
Frequency of
Condensing Outdoor Reset Ts,max Tout,min Tout,max Ts,min
ft kBtuh # gpm
#1 52 unknown 1 3.1 69% Y 180 0 72 95#2 38.5 50 2 5.3 59% Y 185 5 68 95#3 61 80 3 4.8 60% Y 180 5 68 95#4 32 80 1 3.3 20% N2 200 5 68 95#5 41 50 2 5.2 14% Y3 185 5 68 145#6 54 80 2 4.3 16% N 201 5 68 95
1Flow rate recorded through primary loop. 2The outdoor reset, although installed, is not registering in the controller. 3The minimum boiler supply temperature was set to 145 °F because the toe kick heater in the kitchen would not activate below that.
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Boiler Efficiency vs. Return Water Temp
84
86
88
90
92
94
96
80 100 120 140 160
Return Water Temperature (F)
Effic
ienc
y (%
) 165 F Supply
145 F Supply
125 F Supply
165 F, reduced flow
Reproduced with permission from Thomas Butcher, BNL
Steady state efficiency vs. return water temperature
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Factors Affecting Efficiency of Installed Systems
Con ‐Maximum boiler output temperature is typically set to 180°F or higher for both space and domestic hot water heating.
Frequency of Condensing at Different Ts,max(1, 2 & 3 gpm)
Ts,min 150 160 170 180 95 99% 91% 87% 90% 80% 77% 79% 68% 64% 66% 57% 53%105 99% 87% 83% 86% 72% 67% 71% 58% 54% 56% 47% 44%110 99% 84% 79% 82% 66% 60% 62% 50% 45% 48% 41% 39%115 98% 80% 73% 72% 56% 50% 48% 42% 35% 40% 34% 32%120 97% 70% 60% 66% 45% 40% 43% 34% 24% 32% 25% 23%
Results for bin temperature profile in Ithaca, NY
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Factors Affecting Efficiency of Installed Systems
Any control technique which reduces the return water temperature, including lowering the boiler set
point and/or reducing the loop flow rate will significantly improve the achieved efficiency.
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Factors Affecting Efficiency of Installed Systems
Flow Rates were higher than specified: Contractors don’t have standard, simple methods for measuring and/or setting flow rates.
Until recently, low flow residential pumps for which the flow can be set, have been difficult to find.
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Factors Affecting Response Time
Recovery from setback Extremely slow in all homes monitored – more than 2 hours for a 5 degree setback.
Location of outdoor reset sensor is important to system performance
Appears to get worse with increasing outdoor temperatures
Differential setting can affect recovery time
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Factors Affecting Response Time
01002003004005006007008009001000
020406080
100120140160180
12:00 AM 2:24 AM 4:48 AM 7:12 AM 9:36 AM 12:00 PM 2:24 PM 4:48 PM 7:12 PM 9:36 PM 12:00 AM
Natural Gas Use (Btu/m
in)
Tempe
rature (°F)
House #2 ‐ February 20, 2010
Return Temp Outdoor Temp Supply Temp Natural Gas Use
0.00.51.01.52.02.53.03.54.04.55.0
5557596163656769717375
12:00 AM 2:24 AM 4:48 AM 7:12 AM 9:36 AM 12:00 PM 2:24 PM 4:48 PM 7:12 PM 9:36 PM 12:00 AM
Flow Rate (gpm
)Tempe
rature (°F)
House #2 ‐ February 20, 2010
1st Floor 2nd Floor 1st Floor Pump 2nd Floor Pump DHW Pump
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Factors Affecting Response Time
0
200
400
600
800
1000
1200
020406080100120140160180
12:00 AM 2:24 AM 4:48 AM 7:12 AM 9:36 AM 12:00 PM 2:24 PM 4:48 PM 7:12 PM 9:36 PM 12:00 AM
Natural Gas Use (Btu/m
in)
Tempe
rature (°F)
House #1 ‐ April 24, 2010
Return Temp Outdoor Temp Supply Temp Natural Gas Use
0.00.51.01.52.02.53.03.54.04.55.0
5557596163656769717375
12:00 AM 2:24 AM 4:48 AM 7:12 AM 9:36 AM 12:00 PM 2:24 PM 4:48 PM 7:12 PM 9:36 PM 12:00 AM
Flow Rate (gpm
)Tempe
rature (°F)
House #1 ‐ April 24, 2010
1st Floor 2nd Floor 1st Floor Pump 2nd Floor Pump DHW Pump
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Improving Efficiency & Response Time
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Changes Made in Last Round of Testing
Proper sizing of boiler mandatory Outdoor reset control a must. Lower Ts,max on reset curve Reduce flows to achieve 20° ΔT at design – 30% savings in pump energy going from high to low speed.
Size baseboard for low‐flow & Ts,max from above –oversizing is OK.
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Results of Changes Made in Last Round of Testing Performance Results:
Phase III – all condensed over 96% of year in space heating mode
Phase I – 60‐69% in space heating mode
Estimated Savings (remember: small house) Translates to approximately 3% improvement in efficiency for a Phase III house ≈ $20/yr
30% savings in pump power ≈ $10‐$15/yr Extra 20’ of baseboard ≈ $160, payback is ≈ 5 years
NOTE: w/out outdoor reset, 15‐20% condensing.
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Continuing Research
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Upcoming Research
2 New Homes Similar construction to first round of research Same climate Applicability to retrofit applications Industry Sanctioned Designs Looking at line losses, baseboard piping, boost vs. setback
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Upcoming Research – System A
High mass boiler, zone valves, variable speed pump
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Upcoming Research – System B
Low mass, indirect tank, adjustable speed pumps on zones –compare performance of primary loop vs. a buffer tank
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Recommendations for Improving Response Time & Comfort
Proper sizing of boiler mandatory Raise Tout,min on boiler curve slightly Proper placement of outdoor reset sensor Recommend boost controls or eliminate setback If setback is desired, increase length of baseboard to improve response time (will increase efficiency as well)
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Questions?
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Thank You.
Lois B. Arenawww.swinter.com