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HIGH EFFICIENCY COMMERCIAL WATER HEATERS OBTAINING ALL OF THEIR BENEFITS

HIGH EFFICIENCY COMMERCIAL WATER HEATERS OBTAINING ALL OF THEIR BENEFITS. St. Louis Chapter ASPE March 6, 2012 Don Behrmann, P.E. I. INTRODUCTION. A PROPHET IN HIS OWN VILLAGE DISTANCE FROM HOME NECESSARY TO BE AN EXPERT WHY KNOW MORE ABOUT HIGH EFFICIENCY COMMERCIAL WATER HEATERS?.

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HIGH EFFICIENCY COMMERCIAL WATER HEATERS OBTAINING ALL OF THEIR BENEFITS

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  1. HIGH EFFICIENCY COMMERCIAL WATER HEATERSOBTAINING ALL OF THEIR BENEFITS St. Louis Chapter ASPE March 6, 2012 Don Behrmann, P.E.

  2. I. INTRODUCTION • A PROPHET IN HIS OWN VILLAGE • DISTANCE FROM HOME NECESSARY TO BE AN EXPERT • WHY KNOW MORE ABOUT HIGH EFFICIENCY COMMERCIAL WATER HEATERS?

  3. II. EXPLANATION OF TERMS • STEADY-STATE EFFICIENCY • STANDBY LOSS • OVERALL EFFICIENCY • HIGH EFFICIENCY

  4. II. EXPLANATION OF TERMS • LOW MASS WATER HEATER • FLUEWAY • DEWPOINT OF WATER VAPOR IN PRODUCTS OF COMBUSTION FROM NATURAL GAS • NON-CONDENSING MODE OPERATION

  5. II. EXPLANATION OF TERMS • CONDENSING MODE OPERATION • PARALLEL FLOW HEAT EXCHANGER • COUNTERFLOW HEAT EXCHANGER • EXCESS AIR IN COMBUSTION PROCESS

  6. II. EXPLANATION OF TERMS • RADIANT HEAT TRANSFER • NATURAL CONVECTION HEAT TRANSFER • FORCED CONVECTION HEAT TRANSFER

  7. II. EXPLANATION OF TERMS•PRECIPITATION OF SOLIDS

  8. II. EXPLANATION OF TERMS•EFFICIENCY LOSS DUE TO SCALE

  9. III. OPPORTUNITIES TO INCREASEWATER HEATER EFFICIENCY • INCREASE STEADY-STATE EFFICIENCY BY IMPROVING COMBUSION PROCESS • CHEMICAL REACTION FORMULA FOR COMBUSTION OF NATURAL GAS, WHICH IS PRIMARILY METHANE GAS CH4 + O2 CO2 + H20 BALANCE FORMULA (1) CH4 + (2) O2 (1) CO2 + (2) H2O

  10. III. OPPORTUNITIES TO INCREASEWATER HEATER EFFICIENCY • SUBSTITUTE AIR IN FORMULA, WHICH IS 20% O2 AND 80% NITROGEN (1) CH4 + (2) 02 + (8) N2 (1) CO2 + (8) N2 + (2) H20 • CONVERT TO VOLUME (1) cf CH4 + (2) cf 02 + (8) cf N2 (1) cf CO2 + (8) cf N2 + (0) cf H20

  11. III. OPPORTUNITIES TO INCREASEWATER HEATER EFFICIENCY • 10 cf OF AIR REQUIRED FOR EACH cf OF NATURAL GAS TO ACHIEVE PERFECT COMBUSTION • ADDITIONAL COMBUSTION AIR ABOVE 10 cf PER cf OF GAS IS EXCESS AIR • INCREASE EFFICIENCY BY REDUCING EXCESS AIR VIA BETTER AIR/FUEL MIXING

  12. III. OPPORTUNITIES TO INCREASEWATER HEATER EFFICIENCY • INCREASE STEADY-STATE EFFICIENCY BY IMPROVING HEAT EXCHANGER DESIGN • TURBULENT FLUE GAS FLOW POSSIBLE DUE TO FAN ASSISTED BURNER

  13. III. OPPORTUNITIES TO IMPROVEWATER HEATER EFFICIENCY• COUNTERFLOW HEAT EXCHANGER DESIGN

  14. III. OPPORTUNITIES TO INCREASEWATER HEATER EFFICIENCY • OPERATE IN CONDENSING MODE WHEN POSSIBLE • REDUCE STANDBY LOSS FROM HEATER FLUEWAYS • REDUCE STANDBY LOSS FROM HOT WATER STORAGE TANK

  15. III. OPPORTUNITIES TO INCREASEWATER HEATER EFFICIENCY • REDUCE STANDBY LOSS BY MINIMIZING BURNER CYCLING RATE • REDUCE STORED HOT WATER TEMPERATURE WHILE STILL COMPLYING WITH CODE REQUIREMENTS TO AVOID LEGIONELLA BACTERIA

  16. III. OPPORTUNITIES TO INCREASEWATER HEATER EFFICIENCY • MINIMIZE PRECIPITATION OF SOLIDS AND THEIR ADHERENCE TO HEAT TRANSFER SURFACES

  17. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSA. STORAGE TANK WITH ATMOSPHERIC BURNER BENEATH AND ONE FLUEWAY WAS INITIAL DESIGN • COST EFFECTIVE • LOW STEADY-STATE EFFICIENCY (75% APPROX) • HIGH EXCESS AIR (65%) • HIGH STANDBY LOSS (66%) • HIGH PRECIPITATION OF SOLIDS AND ADHERENCE • TO HOTTEST SURFACES—BOTTOM TANK HEAD • AND FLUE TUBE—DUE TO GRAVITY WATER • CIRCULATION

  18. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSB. DESIGN IMPROVEMENT #1—STORAGE TANK WITH MULTIPLE FLUE TUBES, REFRACTORY LINED COMBUSTION CHAMBER, AND FORCED DRAFT BURNER BENEATH • Higher steady-state efficiency (81% approx) due to lower excess air volume (30%) and lower leaving flue gas temp, but parallel flow heat exchanger • Lower standby loss, but burner comb air damper didn’t close fully • Higher overall efficiency • Higher cost • High precipitation of solids and adherence to hottest surfaces—bottom tank head and all flue tubes

  19. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSC. DESIGN IMPROVEMENT #2—VENT DAMPER ADDED TO ATMOSPHERIC TANK-TYPE HEATER TO REDUCE STANDBY LOSS • No steady-state efficiency improvement over initial design (75%) • High excess air (65%) • Lower standby loss • Lower overall efficiency than forced draft • Lower cost than units with forced draft burner

  20. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSD. DESIGN IMPROVEMENT #3—LOW MASS WATER HEATER WITH ATMOSPHERIC BURNER, CIRCULATING PUMP, AND REMOTE STORAGE TANK • No steady-state efficiency improvement (75%) • High excess air (65%) • Reduced standby loss from storage tank since no flueways in tank if pump not continuous • Similar overall efficiency to improve-ment #2, forced draft burner design • Slower or no calcium buildup in heat exchanger due to high water velocity • Higher cost due to piping

  21. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSE. DESIGN IMPROVEMENT #4—SIMILAR TO #3 EXCEPT WITH FAN ASSISTED ATMOSPHERIC BURNER • Steady-state efficiency improvement (81% vs 75%) due to lower excess air (45% vs 65%) • Water heater cost higher due to fan assisted atmospheric burner, but overall system cost not significantly higher

  22. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSF. DESIGN IMPROVEMENT #5—SIMILAR TO #3 EXCEPT WITH MEDIUM EFFICIENCY WATER HEATER WITH PREMIX FAN ASSISTED SEALED COMBUSTION MODULATING BURNER, HEAT EXCHANGER WITH MORE SURFACE AREA, AND WATER SURROUNDED COMBUSTION CHAMBER

  23. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSF. Design Improvement #5 • Steady-state efficiency improvement (84-87%) due to water surrounded combustion chamber, lower excess air (24%) and lower flue gas exit temp • Lower flueway standby loss due to resistance to natural convection air flow through heat exchanger when off • Lower standby loss due to reduced burner cycling resulting from full modulation firing 4:1 turndown

  24. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSF. Design Improvement #5 • Increased application flexibility due to sealed combustion and sidewall venting • Medium efficiency water heater much more expensive • System cost significantly higher, but payback reasonable

  25. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSG. Design improvement #6, where we are today—similar to #3 except with condensing mode operation, counterflow stainless steel corrosion resistant heat exchanger, premix variable speed combustion air fan, biased gas valve, low excess air, full modulation firing control, fiber mesh burner suitable for high turndown ratio, sealed combustion

  26. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSG. Design Improvement #6 • Steady-state efficiency improvement (95%) due to lower flue gas exiting temperature and operation in condensing mode • Counterflow heat exchanger with large surface area and water surrounded combustion chamber allows high radiant heat transfer rate and close approach of leaving flue gas temperature to entering water temperature

  27. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSG. Design Improvement #6 • High efficiency can be maintained throughout life of heater due to high water velocity heat exchanger that reduces or eliminates calcium buildup on heat transfer surfaces • Lower flueway standby loss due to resistance to air flow through heater during off cycle • Low standby loss due to reduced burner cycling resulting from full modulation firing with 20:1 turndown ratio • PVC vent pipe suitable due to low flue gas exiting temperature greatly reduces vent system cost • Application flexibility due to sealed combustion and sidewall venting

  28. IV. EVOLUTION OF HIGH EFFICIENCY WATER HEATERSG. Design Improvement #6 • High efficiency water heater more expensive than medium • System cost higher than medium efficiency, but payback reasonable.

  29. V. HIGH EFFICIENCY WATER HEATER FEATURES • Valuable to owners if domestic hot water systems are designed and installed to deliver all of the benefits

  30. VI. STANDARD & MEDIUM EFFICIENCY LOW MASS HEATER APPLICATION • Chimney required with sufficient draft to overcome vent system losses • Minimum inlet gas pressure of 7” w.c. • On/off temperature controls • Water piping designed to prevent non-condensing heater from operating in condensing mode

  31. VI. STANDARD & MEDIUM EFFICIENCY LOW MASS HEATER APPLICATION

  32. VII. HIGH EFFICIENCY LOW MASS WATER HEATER APPLICATION • Corrosion resistant chimney constructed of PVC pipe required, but vent system doesn’t have to provide draft • Sealed combustion allows drawing outside air for combustion eliminating the need for introducing combustion air into the mechanical equipment room and eliminating freeze potential in cold weather. Allows greater flexibility in locating and installing systems. • Resistance temperature detector (RTD) required in storage tank and another is factory installed in heater discharge for proper control of modulating burner • Water piping designed to introduce lower temperature water possible into condensing mode heater to maximize condensing rate

  33. VII. HIGH EFFICIENCY LOW MASS WATER HEATER APPLICATION

  34. VIII. WATER HEATER DESIGN ADVANCES ARE BENEFICIAL TO OWNERS & THE USA • Designs have improved greatly • Proper specification, system design and installation is crucial to realize all benefits • Proper application will result in lower maintenance, lower energy cost and lower energy consumption for owner and our country • Potential savings are great due to the large number of systems in operation—almost all commercial and industrial buildings have a domestic hot water system • Consider a high efficiency water heater on future projects

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