Bill Chalmers- Gulf Coast Green 2010

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Enthalpy Wheel Fundamentals

Author: Bill Chalmers, Page Southerland Page

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Bill Chalmers- Gulf Coast Green 2010

  1. 1. Gulf Coast Green Enthalpy Wheel Fundamentals Renovating the Future April 16, 2010
  2. 2. Energy Recovery Wheel Application Fundamentals <ul><li>Bill Chalmers P.E., LEED® AP, CEM, GBP, CDT </li></ul><ul><li>Agenda </li></ul><ul><li>How energy recovery wheels work </li></ul><ul><li>Why energy recovery wheels should be used </li></ul><ul><li>Rules to follow to avoid commonly made mistakes </li></ul><ul><li>Follow the rules to make jobs work well avoid giving energy recovery a bad reputation </li></ul>
  3. 3. Energy Recovery Wheel Application Fundamentals <ul><li>Ventilation is required for occupant health and comfort </li></ul><ul><li>Exhaust air required for toilets, odorous areas and general exhaust </li></ul><ul><li>Energy recovery uses the exhaust air to heat and cool outdoor air </li></ul>
  4. 4. Energy Recovery Wheel Application Fundamentals <ul><li>How it Works – Sensible Heat Recovery </li></ul><ul><li>Wheel slowly rotates from one airstream to another </li></ul><ul><li>Wheel substrate (typically aluminum) transfers the heat </li></ul><ul><li>Transfer heat from hot outdoor air to relatively cool exhaust air in summer </li></ul><ul><li>Transfer heat from relatively warm exhaust air to cold outdoor air </li></ul>Handout Page 7
  5. 5. Energy Recovery Wheel Application Fundamentals <ul><li>How it Works – Latent Heat Recovery </li></ul><ul><li>Wheel slowly rotates from one airstream to another </li></ul><ul><li>Desiccant coating the wheel transfers moisture (latent energy) </li></ul><ul><li>Transfer moisture from humid outdoor air to dry exhaust air in summer </li></ul><ul><li>Transfer moisture from exhaust air to dry outdoor air </li></ul><ul><li>Vapor pressure differential is the driving force transferring water vapor. </li></ul>Handout Page 6
  6. 6. Energy Recovery Wheel Application Fundamentals Molecular sieve is a man made material with controlled pore openings to adsorb only certain type of vapors and gases. Pore opening Supply Air Outdoor Air Return Air Latent heat (moisture) transfer Handout Page 6 Water vapor in supply air stream is adsorbed on the desiccant Because the vapor pressure in the colder exhaust air stream is lower the water vapor pressure on the desiccant surface, the water is desorbed and exhausted back to the outside
  7. 7. Energy Recovery Wheel Application Fundamentals Outdoor Air 97°F, 64 gr/lb (69.1°Fwb) Supply Air 80°F, 63.2 gr/lb Return Air 75°F, 64 gr/lb (50% R.H.) Exhaust Air 92°F, 63.8 gr/lb Effectiveness = (97-80)/(97-75) = 77.3% Cooling Mode (Peak Design Day) Lubbock, TX Handout Page 9
  8. 8. Energy Recovery Wheel Application Fundamentals Outdoor Air 11°F, 5.4 gr/lb Supply Air 60.4°F, 49.9 gr/lb Return Air 75°F, 64 gr/lb (50% R.H.) Exhaust Air 25.6°F, 18.5 gr/lb Effectiveness = (75-11)/(60.4-11) = 77.2% Heating Mode (Peak Design Day) Lubbock, TX Handout Page 9
  9. 9. Energy Recovery Wheel Application Fundamentals <ul><li>1100 Peachtree, Atlanta GA </li></ul><ul><li>Operates 5 days/week, 12 hours/day </li></ul>Conventional ERU Outdoor air 52,000 cfm Exhaust air 31,200 cfm Capital cost – AHU $56,000 $110,000 Capital cost – Chiller $91,000 (260 tons) $43,000 (123 tons) Capital cost – Electric preheat $7,000 (600 kW) $0 Total Capital Cost $182,000 $176,000 Annual Savings $51,100
  10. 10. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #1 – Energy Recovery is worthwhile even if exhaust air is 50% of outdoor air and occupied hours are limited </li></ul><ul><li>Take capital cost credit for chillers, heating, humidifiers and electrical service. </li></ul><ul><li>Typically, energy recovery is free. </li></ul>Conventional ERU Outdoor air 52,000 cfm Exhaust air 31,200 cfm Capital cost – AHU $56,000 $110,000 Capital cost – Chiller $91,000 (260 tons) $43,000 (123 tons) Capital cost – Electric preheat $7,000 (600 kW) $0 Total Capital Cost $182,000 $176,000 Annual Savings $51,100
  11. 11. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #2 – Do not size chillers, boilers, heating coils and electrical service for cooling and heating loads if the wheel fails. </li></ul><ul><li>If wheel fails, fix it. </li></ul><ul><li>Use whatever cooling and heating is available and decrease the outdoor air quantity during failure. </li></ul><ul><li>If building has multiple units and operation is critical, allow extra capacity for one wheel failure. </li></ul>Conventional ERU Outdoor air 52,000 cfm Exhaust air 31,200 cfm Capital cost – AHU $56,000 $110,000 Capital cost – Chiller $91,000 (260 tons) $43,000 (123 tons) Capital cost – Electric preheat $7,000 (600 kW) $0 Total Capital Cost $182,000 $176,000 Annual Savings $51,100
  12. 12. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #3 Collect all available exhaust air </li></ul><ul><li>restrooms </li></ul><ul><li>janitors closets </li></ul><ul><li>general lab exhaust </li></ul><ul><li>general exhaust </li></ul><ul><li>locker rooms </li></ul><ul><li>copy rooms </li></ul><ul><li>Do not include kitchen, laundry or fume hoods. </li></ul><ul><li>The greater the amount of exhaust air, the higher the wheel efficiency. </li></ul>
  13. 13. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #4 Decide the acceptable type of wheel </li></ul><ul><li>8” deep aluminum substrate </li></ul><ul><li>2” deep mylar substrate </li></ul><ul><li>If mylar is acceptable, then specify it because it is almost certainly less expensive than aluminum. </li></ul>
  14. 14. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #5 Select the allowable wheel velocity </li></ul><ul><li>I recommend 700 to 800 fpm and maximum 1” w.g. APD. </li></ul><ul><li>Manufacturers recommend 500 fpm. Manufacturers also like selling bigger wheels. </li></ul>Handout Page 8 Size 43 Size 28 Velocity (fpm) 500 750 APD (in. w.g.) .45 .72 Efficiency .87 .83
  15. 15. Energy Recovery Wheel Application Fundamentals <ul><li>Preface to Rules #6, 7,8 and 9 </li></ul><ul><li>Cross contamination must be minimized by: </li></ul><ul><ul><li>fan configuration </li></ul></ul><ul><ul><li>seals </li></ul></ul><ul><ul><li>purge </li></ul></ul><ul><ul><li>desiccant type </li></ul></ul>
  16. 16. Energy Recovery Wheel Application Fundamentals <ul><li>Rule # 6 Select Fan Configuration </li></ul><ul><li>Exhaust air must be negative relative to outdoor air to prevent cross contamination </li></ul><ul><li>I recommend configuration 1 because return air is usually slightly negative relative to outdoor air path. </li></ul><ul><li>Blow through supply fan is usually very positive relative to return air causing high purge volumes and noise. I recommend avoiding this configuration. </li></ul>Handout Page 16
  17. 17. Energy Recovery Wheel Application Fundamentals <ul><li>Rule # 7 </li></ul><ul><li>Allow for purge volume in fan selections </li></ul>Handout Page 15
  18. 18. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #8 Choose between labyrinth seals and brush seals </li></ul>Handout Page 5
  19. 19. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #9 </li></ul><ul><li>Choose desiccant type </li></ul><ul><li>3 Angstrom cross contaminates the least. Use for critical applications such as general lab exhaust and hospitals </li></ul><ul><li>4 Angstrom recommended for most applications. </li></ul><ul><li>I recommend against other desiccants, particularly if odorous exhaust like from restrooms and janitor’s closet is being exhausted </li></ul>
  20. 20. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #10 </li></ul><ul><li>ALWAYS put minimum MERV 6 filters upstream of wheel on supply AND exhaust </li></ul><ul><li>Wheels can be cleaned, but large items (bugs, trash) can clog and damage the wheel. </li></ul>
  21. 21. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #11 </li></ul><ul><li>In cold climates, put the preheat coil upstream of the wheel on the supply air to avoid frosting and freeze stat tripping. </li></ul>Handout Page 20
  22. 22. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #12 </li></ul><ul><li>Control sequence: </li></ul><ul><li>If outdoor air enthalpy is above the exhaust enthalpy, run the wheel at 100% </li></ul><ul><li>If outdoor air enthalpy is below the exhaust enthalpy, but outdoor air temperature is above supply air temperature, wheel is off </li></ul><ul><li>If outdoor air temperature is below supply air temperature, modulate the wheel to achieve the supply air temperature. </li></ul>Handout Page 19 to 21
  23. 23. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #13 </li></ul><ul><li>Install air pressure measurement across supply and exhaust to measure airflows. </li></ul>Return Air Supply Air Exhaust Air Outside Air ® Outside Air Damper Exhaust Air Damper
  24. 24. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #14 </li></ul><ul><li>Use two control valves sized for 1/3 and 2/3 flow respectively to allow for low flow conditions. </li></ul><ul><li>This is particularly important if the coil is selected for wheel failure. </li></ul>
  25. 25. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #15 </li></ul><ul><li>Never say energy recovery does not fit! </li></ul><ul><li>Select the wheel at 700 fpm and use high velocity in the outdoor air and exhaust section. </li></ul>Plan View Section View
  26. 26. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #16 </li></ul><ul><li>wheel manufacturers are good at making wheels </li></ul><ul><li>air handling manufacturers are good at making air handlers </li></ul><ul><li>controls companies are good at doing controls </li></ul><ul><li>Specify an air handler complete with wheel installation and include a control sequence for the controls vendor. </li></ul>Plan View
  27. 27. Energy Recovery Wheel Application Fundamentals <ul><li>Rule #17 – Obey Rules #1 to #16 </li></ul><ul><li>When energy recovery goes bad, it gives the technology a bad reputation and all the benefits are lost </li></ul>Torn plenum wall Fan fell off its base
  28. 28. Energy Recovery Wheel Application Fundamentals <ul><li>Thanks for your interest! </li></ul><ul><li>I am available until 2 pm if more information is needed. </li></ul>
  29. 29. Energy Recovery Wheel Application Fundamentals

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