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Evaluation of Space Humidity Control and System Energy Usage for Conventional and Advanced Unitary Equipment

Evaluation of Space Humidity Control and System Energy Usage for Conventional and Advanced Unitary Equipment. Michael J. Witte and Robert H. Henninger GARD Analytics, Inc. ASHRAE Winter Meeting, Seminar 39 “Designing for Dehumidification and Mold Avoidance”

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Evaluation of Space Humidity Control and System Energy Usage for Conventional and Advanced Unitary Equipment

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  1. Evaluation of Space Humidity Control and System Energy Usage for Conventional and Advanced Unitary Equipment Michael J. Witte and Robert H. Henninger GARD Analytics, Inc. ASHRAE Winter Meeting, Seminar 39 “Designing for Dehumidification and Mold Avoidance” January 24, 2006, Chicago, IL (Rev. May 31, 2006)Revisions on slides 12, 15-18, 20, 27-30, 32-36

  2. Acknowledgements • Preview of ASHRAE Research Project 1254RP • Evaluating the Ability of Unitary Equipment to Maintain Adequate Space Humidity Levels, Phase II • Co-funded by U.S. DOE through ARTI • Based on ASHRAE 1121-RP, Phase I Evaluation Plan, Brandemuehl and Katejanekarn, Univ. of Colorado at Boulder,June 2001 ASHRAE Seminar, M.J. Witte

  3. Objectives • Compare various unitary air conditioning system humidity control configurations for application to commercial buildings in terms of humidity control performance, operating costs, and lifecycle costs to each other as well as to conventional unitary equipment • Develop guidelines to help HVAC engineers and practitioners identify the important application characteristics and climate factors that determine which option is most appropriate ASHRAE Seminar, M.J. Witte

  4. Project Overview • EnergyPlus hourly whole-building simulations • 7 Building types • 10 Locations • 18 System types • 2 Ventilation standards • Humidity control and energy use • Economic analysis • Guidelines and recommendations ASHRAE Seminar, M.J. Witte

  5. Building Types • Small Office • Restaurant Dining Area • Large Retail • Theater • Classroom (South exposure) • Classroom-12 Month (South exposure) • Motel Guest Room (South exp.) ASHRAE Seminar, M.J. Witte

  6. Atlanta, GA Chicago, IL Dallas/Fort Worth, TX Miami, FL New York, NY Portland, OR St. Louis, MO Washington, DC Houston, TX Shreveport, LA Locations ASHRAE Seminar, M.J. Witte

  7. System Types: Case 0-2 • Case 0 – Conventional DX System • 400 CFM/ton • All CFM/ton values are nominal • “Typical” HVAC design practice • 2-stage coil • Case 1 – Base DX System • 350 CFM/ton (different equipment than Case 0) • Better dehumidification design practice • Case 2 – DX with Improved Dehumidification • 300 CFM/ton • Modified coil, compressor, etc. ASHRAE Seminar, M.J. Witte

  8. System Types: Case 3-4 • Case 3 – Base DX with Lower Airflow • 300 CFM/ton • Same coil and compressor as Case 1 • Case 4 – Air-to-Air Heat Exchanger (AAHX) • 350 CFM/ton (Case 1 equipment) • Wrap-around HX • Sensible effectiveness 0.4 • No latent transfer • Single-stage coil in all apps ASHRAE Seminar, M.J. Witte

  9. System Types: Case 5 • Case 5 – Subcool Reheat Coil • 350 CFM/ton • Normal mode same as Case 1 • Enhanced dehumidification mode • Standard mfr. option • Switch modes if 50%RHsetpoint not met ASHRAE Seminar, M.J. Witte

  10. System Types: Case 6 • Case 6 – Fan Control to Drain Coil • 350 CFM/ton • Normal mode same as Case 1 • Fan off for short time when compressor cycles off • No moisture re-evaporation • Modeled by turning off latent degradation in DX coil model – no change in fan power consumption • Ideal case – not achievable in real equipment • Can also be thought of as variable capacity control ASHRAE Seminar, M.J. Witte

  11. System Types: Case 7 • Case 7 – Bypass Damper • 350 CFM/ton • Normal mode same as Case 1 • 300 CFM/ton in bypass mode • 50 CFM/ton bypassed • Switch modes if 50%RHsetpoint not met ASHRAE Seminar, M.J. Witte

  12. Outdoor Exhaust Outdoor Return Supply System Types: Case 8 • Case 8 – Hybrid DX with Desiccant • 400 CFM/ton (Case 0) • Desiccant condition outside air stream • Mixed air to cooling coil • Control to meet 50%RH setpoint • Heat recovery to exhaust air ASHRAE Seminar, M.J. Witte

  13. System Types: Case 9 • Case 9 – Enthalpy Recovery Wheel • 350 CFM/ton (Case 1) • Enthalpy heat recovery OA and exhaust • Bypassed when not beneficial • 0.91 sensible eff. (constant) • 0.85 latent eff. (constant) ASHRAE Seminar, M.J. Witte

  14. System Types: Case 10 • Case 10 – DX Outdoor Air Preconditioning • DX Preconditioner • Evaporator in OA stream • Condenser in relief air stream • 580 CFM/ton • Standard mfr. option • Run 1st • Main DX System • 350 CFM/ton (Case 1) • Run as needed ASHRAE Seminar, M.J. Witte

  15. System Types: Case 11 • Case 11 – Base Dual Path • Outdoor air system • 2 DX coils in series • 300 CFM/ton (Case 3) • 150 CFM/ton overall • 2 stages each • 7.22C (45F) min supply • Return air system • 1 DX coil • 400 CFM/ton (Case 0) • 1 stage (last stage on) ASHRAE Seminar, M.J. Witte

  16. Supply Air Return Air System Types: Case 12 • Case 12 – Dual Path + Enthalpy Recovery • Outdoor air system • 1 DX coil • 350 CFM/ton (Case 1) • 2 stages • 7.22C (45F) min supply • Return air system • 1 DX coil • 400 CFM/ton (Case 0) • 1 stage (last stage on) ASHRAE Seminar, M.J. Witte

  17. System Types: Case 13 • Case 13 – Dual Path + AAHX • Outdoor air system • 2 DX coils in series • AAHX, 0.4 sensible, no latent • 300 CFM/ton (Case 3) • 150 CFM/ton overall • 1 stage each • 7.22C (45F) min supply • Return air system • 1 DX coil • 400 CFM/ton (Case 0) • 1 stage (last stage on) ASHRAE Seminar, M.J. Witte

  18. Outdoor Air Exhaust Air System Types: Case 14 • Case 14 – Dual Path + Desiccant • Outdoor air system • 1 DX coil • 350 CFM/ton (Case 1) • 2 stages • 7.22C (45F) min supply • Return air system • 1 DX coil • 400 CFM/ton (Case 0) • 1 stage (last stage on) ASHRAE Seminar, M.J. Witte

  19. System Types: Case 15-16 • Case 15 – Demand Controlled Ventilation • 350 CFM/ton (Case 1 equipment) • Pseudo DCV • Minimum OA based on cfm/sf spec from Std. 62 • Plus cfm/person OA tracks Occupancy Schedule • Case 16 – Dual Path + DCV • Case 11 equipment • Pseudo DCV – same as above ASHRAE Seminar, M.J. Witte

  20. System Types: Case 17 • Case 17 – Base DX with Free Reheat • Case 1 equipment • Overcool to meet 50%RH setpoint • Case 1 sizing – no oversizing for latent • “Free” hot gas reheat from DX condenser • Reheat capacity 100% of condenser heat rejection • No fan penalty for extra reheat coil • Dehumidify only when sensible load • No operation for latent-only load ASHRAE Seminar, M.J. Witte

  21. 2 Ventilation Standards • Standard 62-2001 • Referenced by many building codes • Standard 62.1-2004 • Current standard • Ventilation rates • cfm/sf, • cfm/person • Design occupant density (some change) ASHRAE Seminar, M.J. Witte

  22. 2004 vs 2001 Ventilation *Combined cfm/sf plus cfm/person vent rate **for Atlanta ASHRAE Seminar, M.J. Witte

  23. System Sizing • Sizing simulations using ideal system • ASHRAE 0.4% dry-bulb day (2001 HOF) • Design ventilation rate • “Purchased Air” • Peak sensible coil load • Net (after fan heat) • Plus 10% for oversizing • All systems sized to this net sensible capacity • Except enthalpy wheel sensible capacity credit at design dry-bulb – smaller DX capacity ASHRAE Seminar, M.J. Witte

  24. Key Modeling Assumptions • Existing simulation tool features • DX coil moisture re-evaporation (continuous fan) • Moisture capacitance (EMPD model) • New simulation tool features developed in this project • 2-Stage DX coil • Multi-mode DX coil • switchable enhanced dehumidification mode • e.g. subcool reheat • Performance curves based on published manufacturer’s data ASHRAE Seminar, M.J. Witte

  25. Life Cycle Cost • Equipment installed costs • Popular cost estimating guide for base cost • Technical literature for option costs • One option is actual mfr quote • Approximate! • Costs are highly variable, especially for non-standard options • State average commercial energy costs • 15-yr energy cost projections from EIA ASHRAE Seminar, M.J. Witte

  26. Selected Results ASHRAE Seminar, M.J. Witte

  27. ASHRAE Seminar, M.J. Witte Rev. May 2006 27

  28. ASHRAE Seminar, M.J. Witte Rev. May 2006 28

  29. ASHRAE Seminar, M.J. Witte Rev. May 2006 29

  30. ASHRAE Seminar, M.J. Witte Rev. May 2006 30

  31. ASHRAE Seminar, M.J. Witte Rev. May 2006 31

  32. Retail 2004Humidity Control ASHRAE Seminar, M.J. Witte

  33. Retail 2004Energy Cost ASHRAE Seminar, M.J. Witte

  34. Retail 2004Life Cycle Cost • Adequate humidity control and LOWER LCC • Case 12 - Dual Path w/Enthalpy Wheel • Case 9 - Base DX w/Enthalpy Wheel ASHRAE Seminar, M.J. Witte

  35. Restaurant 2004 Humidity Control ASHRAE Seminar, M.J. Witte

  36. Restaurant 2004Life Cycle Cost • Adequate humidity control but HIGHER LCC • Case 17 - Base DX w/Free Reheat • Case 14 - Dual Path w/Desiccant • Less-adequate humidity control but LOWER LCC • Case 12 - Dual Path w/Enthalpy Wheel ASHRAE Seminar, M.J. Witte

  37. Trends • Relative humidity control across system types • Fairly constant from location to location for a given combination of building type and ventilation standard • Overall number of high humidity hours changes across the board when changing locations, but the relative pattern of humidity control remains very similar ASHRAE Seminar, M.J. Witte

  38. Challenging Applications • Restaurant, Theater, Motel in humid climate • Large number of hours with moisture load but little or no sensible load – morning, evening, night • Active humidity control required • Desiccant • Reheat ASHRAE Seminar, M.J. Witte

  39. Less Challenging Applications • Retail, Office, School in humid climate • Restaurant, Theater, Motel in moderate climate • Load reduction for cost savings and less humidity • Enthalpy Wheel • DCV ASHRAE Seminar, M.J. Witte

  40. Conclusions • Generalizations based on one set of assumptions • Results tables allow some extrapolation to other cases • New simulation tool features provide designers tool to evaluate specific applications • Questions . . . ASHRAE Seminar, M.J. Witte

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