Variable Speed Pumping in Condensing Boiler Systems

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  • Slide #27: Using outdoor reset could result in a higher return water temperature. With two-way valves and no bypass then with given coil load the higher the entering water temperature the colder the leaving water temperature. Verify with a coil program or using the log mean square difference.
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  • 1. Variable Speed Pumpingin Condensing BoilerSystemsGet the Savings you paid for!October 9, 2012
  • 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 EnvironmentPage 2
  • 3. Overview  Life Cycle Cost of Hot Water Systems  Demand Side System Opportunities  Transmission System Opportunities  Supply Side System Opportunities  Next StepsPage 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 pumpPage 4
  • 5. Traditional Boiler LCC ExamplePage 5
  • 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 examplePage 6
  • 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  ControlsPage 7
  • 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 seasonPage 8
  • 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.Page 9
  • 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.Page 10
  • 11. Transmission Opportunity  Reducing Pumping Costs  Reduced System Flow BenefitsPage 11
  • 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 functionPage 12
  • 13. Reduced System Flow Benefits  Reduced transmission (pump) energy  Improved efficiency of condensing boiler  Reduced maintenance costPage 13
  • 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 evaluatedPage 14
  • 15. Efficiency Levels of Gas-Fired Hot Water BoilersPage 15
  • 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 dropsPage 16
  • 17. Getting The “Rated” Efficiency Boost Out of Condensing Boilers (>90% Efficiency)Page 17
  • 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 AirPage 18
  • 19. Applying Condensing Boilers vs Furnaces 100% 95% Efficiency 90% 85% 80% 75% 60°F 80°F 100°F 120°F 140°F 160°F 180°F 200°FPage 19 Entering Water/Air Temperature
  • 20. Applying Condensing Boilers vs Furnaces 100% 95% Efficiency 90% 85% 80% 75% 60°F 110°F 160°FPage 20 Entering Water/Air Temperature
  • 21. Applying Condensing Boilers vs Furnaces 100% 95% Efficiency 90% 85% 80% 75% 60°F 80°F 100°F 120°F 140°F 160°F 180°F 200°FPage 21 Entering Water/Air Temperature
  • 22. Three Rules for “Energy Value” of Condensing Boiler System 1) Return Water Temperature! 2) Return Water Temperature! 3) Return Water Temperature!Page 22
  • 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 F180°F160°F Air Handler/VAV Radiators140°F120°F100°F Mix 80°F 60°F 40°F Mixed or Cooled Air 20°F 0°F-20°FPage 23Page 23
  • 24. Central System Designed for Condensing Boiler Gas at 3,500 F Boiler180°F Boiler Water 160 F Average +160°F Air Handler/VAV Radiant140°F Radiators Floor120°F Heated Air100°F Mix 80°F 60°F 40°F Mixed or Cooled Air 20°F 0°F-20°FPage 24
  • 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 ratePage 25
  • 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% iciencyPage 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 systemPage 27
  • 28. Outdoor Reset Lowers Water Temperature As the heating load goes down, less temperature difference is needed to drive the heat flow.180°F160°F Boiler Water 150 F Average140°F120°F100°F 80°FSpace 75 F 60°F 40°F 20°F 0°F-20°FPage 28
  • 29. Combined Outdoor Reset & VSDPage 29
  • 30. Getting The “Rated” Efficiency Boost Out of Condensing Boilers (>90% Efficiency)Page 30
  • 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 BoilerPage 31
  • 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 valvesPage 32
  • 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-RisePage 33
  • 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 TemperaturePage 34
  • 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.pdfPage 35
  • 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.Page 36
  • 37. Questions?Page 37
  • 38. Bonus Slides  The following slides are bonus material that was cut from the final, live presentation due to time constraints.Page 38
  • 39. Condensing Boiler Sensitivity to Excess Air  Controlling Excess Air Even More Important  Excess air reduces concentration of water vapor  Dewpoint decreasesPage 39
  • 40. Traditional Factor of Burner “Excess Air” Is Even More CriticalPage 40
  • 41. Condensing Boiler Comparison to Direct- Fired Heater Direct-Fired HeaterPage 41
  • 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 HeaterPage 42