This document discusses variable speed pumping in condensing boiler systems. It covers the life cycle costs of hot water systems and components like boilers and pumps. It also discusses opportunities to improve efficiency on the demand side through temperature setpoints and resets, on the transmission side by reducing pumping costs, and on the supply side by applying condensing boilers. Key considerations for condensing boilers include driving down return water temperature, outdoor reset controls, and domestic hot water system design. Utilities offer rebates to help customers implement efficiency improvements.
2. Presenters
Brian Hammarsten, CEM – Trade Relations
Manager at Xcel Energy
Peter Vinck – Senior Energy Efficiency Engineer
at Xcel Energy
Russ Landry PE, LEED® AP - Senior Mechanical
Engineer at the Center for Energy and
Environment
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3. Overview
Life Cycle Cost of Hot Water Systems
Demand Side System Opportunities
Transmission System Opportunities
Supply Side System Opportunities
Next Steps
Page 3
4. Component Life Cycle Cost
Condensing Boiler
1 MMBTU boiler purchase = approx $20,000
Lifetime cost for the gas to operate boiler = $112,800
Of the total cost of ownership, only 17% goes to the
purchase price of that boiler
Circulator Pump
5 hp pump costs = approx $2,000
Lifetime cost for the energy to operate pump = $26,750
Of the total cost of ownership, only 7.5% goes to the
purchase price of the pump
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6. System LCC
System LCC* – Condensing Boiler, 2-way valve to heat
exchangers, vfd on pump
Total Equipment = $53,000
1 MMBTU condensing boiler purchase = $20,000
Valves & Piping modifications = $8,000
Pump and Drive package = $5,000
Labor and misc materials = $20,000
Total Energy Costs = $202,650
Lifetime cost for gas= $112,800
Lifetime cost for pump = $26,750
Lifetime cost for fans = $63,100
Of the total cost of ownership, only 15% to 30% goes to the
purchase price of the initial equipment purchase
* This is a theoretical example
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7. Hot Water Systems
Demand
Space heating
Domestic water
Process
Transmission (Piping, Pumps
& Valves)
Pumps
Piping
Coils
Supply Side
Condensing boiler
Combustion air fan
Feed water pump
Controls
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8. Demand Side Opportunity
Demand side opportunity investigation
Temp set points? In your process do you really need 190
degree water or will 175 work?
Outside air temperature supply water reset temperature
Domestic Hot Water heating in off season
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9. Outside air temp. vs supply water temp
Temperature resets can be a great opportunity you might be missing during the higher outside air
temperatures. Giving you lower losses due to over heating as well as lower return water helping
a condensing boiler.
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10. Demand Side (cont.) – Domestic Hot Water heating in
off season
Boilers are left in operation to support domestic hot
water heat during summer.
Consider separating the systems in order to increase
efficiency of domestic hot water year round.
This would save on equipment life, energy costs,
redundancy, etc.
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12. Reducing Pumping Costs
If you have anything in this list, you may have
some opportunity to reduce cost.
Throttle valve-control system
Bypass (recirculation) line normally open
Multiple parallel pump system with same number of
pumps always operating
Constant Pump operation in a batch environment or
frequent cycle batch operation in a continuous process
Cavitations noise (at pump or elsewhere in the system)
High system maintenance
Systems that have undergone change in function
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13. Reduced System Flow Benefits
Reduced transmission (pump) energy
Improved efficiency of condensing boiler
Reduced maintenance cost
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14. Supply Side Opportunity
Applying Condensing Boilers
Big Savings Potential
Unique ―green‖ investment opportunity when
replacing boiler or building new building
>15% ROI for some projects
But… Savings Depend Heavily on Operating
Conditions
New construction optimal design very different
from typical boiler system
Retrofit situations must be carefully evaluated
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16. How Condensing Boilers get that
Efficiency “Boost”
Water Vapor Generated by Burning Natural Gas is
Condensed
Water vapor is natural product of burning natural gas
About 12% of flue gas is water vapor, but….
Condensing Energy ≈ 2,000 F of Vapor Temperature Drop
Condensation Only Occurs at Low Water Temperatures
Flue gas dewpoint ~130 F
Efficiency keeps improving as temperature drops
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17. Getting The “Rated” Efficiency Boost Out
of Condensing Boilers (>90% Efficiency)
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18. Chart for Showing Moisture in Air Issues
Curve at Top Shows When ―Air‖
Can’t Hold Any More Moisture
(aka dewpoint or saturated)
Once at the Top,
Cooling More
Condenses Moisture
Out of Air
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22. Three Rules for “Energy Value” of
Condensing Boiler System
1) Return Water Temperature!
2) Return Water Temperature!
3) Return Water Temperature!
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23. Getting Heat Into a Space in a Building:
Gas, Coal or Oil
“Typical” Central System
3,500 – 4,000 F
Boiler ~350 to
Avg Boiler Water 170 F 400 F
180°F
160°F
Air Handler/VAV
Radiators
140°F
120°F
100°F
Mix
80°F
60°F
40°F Mixed or
Cooled Air
20°F
0°F
-20°F
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24. Central System Designed for Condensing Boiler
Gas at 3,500 F
Boiler
180°F
Boiler Water 160 F Average +
160°F
Air Handler/VAV
Radiant
140°F
Radiators
Floor
120°F
Heated Air
100°F
Mix
80°F
60°F
40°F Mixed or
Cooled Air
20°F
0°F
-20°F
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25. Carrying Heat from One Place to Another
Heat Carried by Water or Air
Depends on temperature change (TD or T)
Depends on water or air flow rate
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26. System Piping: Driving Return Water
Temperature Down
Boiler Efficiency
Typical Flow
Low Flow
100%
Avoid 3-way/4-way Valves on Main Line
Reduced Flow Brings Down Return Temperature 95%
iciency
Page 26 If Mixed Boilers – Cold Water & Max Load to Condensing
90%
27. System & Load Affects on Condensing
Boiler Efficiency “Boost”
Lower Flow (e.g. Pump VSD & 2-way Valves)
Pump Energy Savings
Low Return Water Temperature = Condensing Boiler
Efficiency Improvement
If low delta, may be good opportunity in any system
Outdoor Reset Control
Reduces Load from Overheating & Pipe Heat Loss
Lower Return Water Temperature = Condensing Boiler
Efficiency Improvement
If high temperatures in mild weather, may be good
opportunity in any system
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28. Outdoor Reset Lowers Water Temperature
As the heating load goes down, less temperature difference is needed to drive the heat flow.
180°F
160°F
Boiler Water 150 F Average
140°F
120°F
100°F
80°F
Space 75 F
60°F
40°F
20°F
0°F
-20°F
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30. Getting The “Rated” Efficiency Boost Out
of Condensing Boilers (>90% Efficiency)
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31. Service Hot Water: Driving Return Water
Temperature Down
Traditional Coil-In Tank Requires High Boiler
Temperatures
Efficiency > Traditional Water Heaters
Efficiency Sacrificed with Condensing Equipment
>130 F
130 F
Boiler
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32. Key Design & Application Considerations:
Preventing Problems
Product-Specific Issues
Small water passages in old cast iron system
Pressure drop compatibility with system
Flow rate compatibility (short-cycling)
Control coordination
Dual temperature inlets
General Load & System Issues
Ability to provide adequate heat w/low return temperatures
Ability to reduce flow rate w/out branch balance problems
2-way valves on loads to replace 3-way valves
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33. Key Design & Application Considerations:
Preventing Problems (cont.)
Venting Considerations
Design & Installation Details to Deal with Condensate
Sidewall Venting Can Cause Moisture Problems With
Large Boilers
Orphaned Water Heater
Vent Cost Key Factor @Bottom of Hi-Rise
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34. Key for Condensing Boiler Efficiency:
Driving Return Water Temperature Down
Space Heating Elements
System Piping
System Control—Pump
System Control—Temperature
Service Hot Water 100%
95%
Boiler Efficiency 90%
85%
80%
75%
80°F 100°F 120°F 140°F 160°F 180°F
Entering Water Temperature
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35. In Conclusion....
Condensing Boilers Can Be a Great, Green Investment
Success Depends on Different Approach by All
Minimize return water temperature!
Minimize return water temperature!
Minimize return water temperature!
High Efficiency Boiler Information
Air-Conditioning, Heating, and Refrigeration
Institute (www.ahrinet.org)
EnergyStar.gov
California Energy Commission web site
Consortium for Energy Efficiency
www.cee1.org/gas/gs-blrs/gs-blrs-main.php3
www.cee1.org/gas/gs-blrs/Boiler_assess.pdf
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36. Utility “Key”
Utilities offer rebates to customers to help pay for the
identification, energy savings quantification, and for the
changes once implemented.
Check with your electric and gas utility to see what rebates the offer
There are several here today
Programs to look for:
Study (investigation process) – Heating System Optimization, C/I Turn
Key, Audits
Tune ups – Boiler Tune ups, Steam Trap Leak Study, Recommissioning
Prescriptive Measures – O2, Stack Dampers, pipe insulation, new
boilers, VFDs, Motors
Custom – Insulation of valves, rebates for industrial process heating
systems, most demand side measures, piping modifications, adjust temp
set points.
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38. Bonus Slides
The following slides are bonus material that was
cut from the final, live presentation due to time
constraints.
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39. Condensing Boiler Sensitivity to Excess Air
Controlling Excess Air Even More Important
Excess air reduces concentration of water vapor
Dewpoint decreases
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42. Chart for Showing Moisture in Air Issues
Moisture is Much More Diluted
in Direct-Fired Heater
It Reaches a Lower Temperature,
but Never Condenses
(THANKFULLY!)
Direct Fired Heater
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