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Underfloor Air Distribution

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Daniel H. Nall, PE, FAIA, FASHRAE, LEED Fellow, BEMP, HPDP
Syska Hennessy Group
May 2017

Published in: Engineering

Underfloor Air Distribution

  1. 1. UNDERFLOOR AIR DISTRIBUTION DANIEL H. NALL, PE, FAIA, FASHRAE, LEED FELLOW, BEMP, HPDP SYSKA HENNESSY GROUP MAY 2017
  2. 2. This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited. Syska Hennessy Group © Syska Hennessy Group 2015 Copyright Materials
  3. 3. • Temperature, Humidity, Ventilation all controlled by a single Sensor • Much Energy Expended in Moving Air Around • Energy Expended for Conditioning Areas where People Aren’t • Poor Comfort Maintenance due to Space Temperature Variation DISADVANTAGES OF COMMON HVAC SYSTEMS
  4. 4. WHAT IS UNDERFLOOR AIR DISTRIBUTION? • Use of an Access Floor Plenum as Supply Air Path • Use of Floor Diffusers to Supply Air to Space • Exploitation of Space Temperature Stratification • High Return
  5. 5. • Plenum Facilitates IT and Power Cabling • Air Distribution Simplified by Floor Plenum • Economical Accommodation of Space Reconfiguration (Churn) • Economical Provision of Personal HVAC Control • Improved Indoor Air Quality because of Stratification of Contaminants WHY UNDERFLOOR AIR DISTRIBUTION?
  6. 6. COMPONENT TRADITIONAL UNDERFLOOR HVAC SYSTEM Amounts $/SF $ $/SF $ 3. Floors and Roof Beam Penetrations 100,000 SF 0.25 $25,000 0 EA 0.00 $0 Premium for Structural details - SF 0.00 $0 100,000 SF 0.50 $50,000 Raised Floor - SF 0.00 $0 100,000 SF 8.50 $850,000 0.25 $25,000 9.00 $900,000 4. Interior Partitions Electrified furn/partitions premlum 400 STN 1000.00 $400,000 $0 Drywall 4,000 LF 65.00 $260,000 4,000 LF 70.00 $280,000 Cores, conference, etc. 6.60 $660,000 2.80 $280,000 7. Finishes Paint Ceiling & services 100,000 SF 1.00 $100,000 100,000 SF 1.00 $100,000 Carpet 11,112 SY 30.00 $333,360 11,112 SY 30.00 $333,360 4.33 $433,360 4.33 $433,360 11. HVAC Main Loop 66,000 LB 3.50 $231,000 20000 LB 3.50 $70,000 Branch ducts 50,000 LB 3.50 $175,000 8,000 LB 4.00 $32,000 Plenum Divers - FT 0.00 $0 20,000 FT 8.00 $160,000 Diffusers/registers 500 EA 68.00 $34,000 40 EA 68.00 $2,720 Insulation 60,000 SF 1.50 $90,000 0 SF 0.00 $0 Hot water reheat 5,000 LF 22.00 $110,000 5,000 LF 18.00 $90,000 Terminals 80 EA 1600.00 $128,000 280 EA 500.00 $140,000 7.68 $768,000 4.95 $494,720 12. Electrical Power Distribution 100,000 SF 2.00 $200,000 100,000 SF 1.50 $150,000 Receptacles 926 EA 76.00 $70,376 300 EA 70.00 $21,000 Duct (in floor) outlets & raceway 626 EA 50.00 $31,300 0 EA 0.00 $0 Cable management 4,000 LF 26.00 $104,000 2,000 LF 3.00 $6,000 Light fixtures 2,000 EA 220.00 $440,000 2,000 EA 220.00 $440,000 Low voltage signal and alarm systems 100,000 SF 1.50 $150,000 100,000 SF 1.50 $150,000 9.96 $995,676 7.67 $767,000 Subtotal 28.82 $2,882,036 28.75 $2,875,080 Design Contingency 10% 2.88 $288,204 2.88 $287,508 Total 31.70$ 3,170,240$ 31.63$ 3,162,588$ % Savings Net 1st Cost Savings 0.2% 7,652$ FIRSTCOSTCOMPARISONS: UNDERFLOORVS.CONVENTIONAL
  7. 7. DESIGN PROCESS • Rethink design issues and typical solutions • Consider expanded opportunities • Integrated design - trade-offs between systems • Address code issues & local approvals
  8. 8. TECHNICAL ISSUES • Avoiding Cold Feet • Exploiting Stratification • Uniform Supply Temperatures • Controlling Humidity • Modulating Heating and Cooling Capacity • Leakage • Construction Sequence/ Housekeeping
  9. 9. ACCESS FLOOR AND WIRING
  10. 10. FLOOR DISPLACEMENT DIFFUSER
  11. 11. FLOOR VARIABLE VOLUME TERMINAL AND DIFFUSER
  12. 12. SUPPLY AIR JET PERSISTENCE
  13. 13. STRATIFICATION • Artifact of Buoyancy and Non-Mixing Air Delivery • Potentially Increases Comfort • Improves Occupant Air Quality • Reduces total Air Delivery Volume • Maximize temperature rise between chest level and ceiling • Minimize temperature rise from foot to chest
  14. 14. STRATIFICATION FACTORS • Supply Air Jet Persistence • Ratio of Air Volume to Cooling Load • Concentration of Heat Gains
  15. 15. RATIO OF SUPPLY AIR FLOW TO LOAD
  16. 16. SUPPLY TEMPERATURE BEHAVIOR - TEMPERATURE • Heat Gain from Structural Slab and Access Floor Tile • Flow Distance from Plenum Injection to Diffuser - Vortices
  17. 17. Supply Plenum Ceiling-floor radiation Floor-room convection Return Plenum Return Plenum Slab Slab Treturn Treturn Treturn Tceiling Tcarpet Tplenum Troom, near floor = 72°F Slab-supply plenum conduction/convection Slab-supply plenum conduction/convection Floor-supply plenum conduction/convection Return-ceiling convection Return-slab convection Room Raised Floor Panels Ceiling-slab radiation 0.6 cfm/ft2, 65°F 78°F PLENUM HEAT BALANCE
  18. 18. PREDICTED DISTRIBUTION OF ROOM COOLING LOAD Heat gain into space 100% Extraction 57% Through floor 14% Through slab 29% Total into plenum 43% Baseline results – hung ceiling
  19. 19. CORPORATE HEADQUARTERS BUILDING: SUPPLY PLENUM TEMPERATURE VARIATION
  20. 20. PLENUM DESIGN – NY TIMES HQ
  21. 21. Typical Tower Floor Plan Third Floor Plan Ground Floor Plan Typical Floor Plan
  22. 22. CFD MODEL
  23. 23. NY TIMES – INITIAL PLENUM DESIGN
  24. 24. NY TIMES – NO STUB DUCTS – FULL FLOW
  25. 25. NY TIMES – NO STUB DUCTS – FULL FLOW
  26. 26. PLENUM DESIGN - VERIFICATION Images Provided by the Center for the Built Environment, University of California Berkeley
  27. 27. PRIMARY AIR SYSTEMS – ISSUES • Required Supply Air Dry Bulb Temperature • Required Supply Air Dew Point Temperature • Required Plenum Pressure • Adequate Supply Air Distribution
  28. 28. PRIMARY AIR SYSTEMS – TECHNOLOGIES • Bypass Central Station Units Underfloor Air Highways Pressure Control Dampers • Air Towers (Column Fans) Direct Pressure Fan VFD Control Distributed Fan Locations
  29. 29. CENTRAL STATION BYPASS AIR HANDLING UNITS
  30. 30. NY TIMES PLAN WITH UNDERFLOOR AIR HIGHWAYS
  31. 31. AIR TOWERS
  32. 32. AIR TOWERS
  33. 33. PERIMETER SYSTEMS - ISSUES • Cooling Thermostatic Control for Envelope Load Variations Maintenance of Stratification • Heating Thermostatic Control of Heat/Cool Changeover Control of Window Wall Downdrafts Energy Efficiency
  34. 34. PERIMETER SYSTEMS - TECHNOLOGY • Underfloor Fan Coils Updraft Flow Enhances Stratification Maintenance/Furniture Conflict Continuous Updraft vs. Incremental • Overhead Fan Coils Downdraft Flow Conflicts with Interior Zone Flow Overhead Maintenance May not Require Furniture Disassembly
  35. 35. NEW YORK TIMES HEADQUARTERS UNDERFLOOR FAN COILS WITH CONTINUOUS DIFFUSERS
  36. 36. UNDERFLOOR FAN COILS
  37. 37. PERIMETER FAN COILS WITH INCREMENTAL DIFFUSERS Images and Equipment by York International
  38. 38. UPFLOW PERIMETER SYSTEM STRATIFICATION NY Times – Transverse Section
  39. 39. UNDERFLOOR HEATING AND COOLING FAN COILS
  40. 40. CHEUNG KONG CENTER
  41. 41. OVERHEAD FAN COILS • Accessibility Advantages • Heating Issues • Cooling Issues
  42. 42. OVERHEAD FAN COILS – COOLING AT DIFFUSER
  43. 43. OVERHEAD FAN COILS – HEATING
  44. 44. OVERHEAD FAN COILS: STRATIFICATION Return Grills Lights Supply Plenum Return Plenum Curtain Wall Linear Ceiling Diffusers People Sun Spot
  45. 45. Discovery Communications Headquarters Silver Spring, Maryland CASE STUDY – SAP US HEADQUARTERS
  46. 46. East/West  Thermostatic Underfloor VAV Fan Terminals  Two pipe changeover coils for heating/peak cooling 46 North Perimeter  Perimeter Upflow Slot Diffusers, non-fan forced  Thermostatic Dampers for Diffusers  Overhead Electric Radiant Panels interlocked with cooling dampers SAP HEADQUARTERS: PERIMETER STRATEGIES
  47. 47. SAP HQ INTERIOR HVAC STRATEGY  Manually Adjustable Swirl Diffuser for Open- Office  Thermostatic Diffusers for Private Offices  Fan Coils with Electric Reheat and CO2 Sensors for Large Conference Rooms 47
  48. 48. SAP: UNDER FLOOR AIR SYSTEM 48
  49. 49. CASE STUDY – BASF US HEADQUARTERS
  50. 50. UFAD SYSTEM FLOOR LAYOUT 50
  51. 51. 51 CFD STUDY OF FLOOR SUPPLY PLENUM
  52. 52. BASF EVAPORATIVE CONDENSER DX CUSTOM PENTHOUSE  Refrigerant Temperature Range Comparable to Water Cooled Water Chiller  Condenser Recirculation Pump Much Smaller than Condenser Water Pump  No Chilled Water Pump  Reduced Fouling of Refrigerant Heat Transfer Surfaces  Small Centrifugal Compressors Slightly Higher EIR Compared with Large Centrifugal Water Chillers  Variable Speed Drive Improves part Load Performance  Overall Energy Savings Compared with Water Cooled Chiller Plant 52
  53. 53. 53 CUSTOM PENTHOUSE LAYOUT
  54. 54. 54 HUDSON YARDS, NYC FINANCIAL HQ
  55. 55. 55 HUDSON YARDS, NYC FINANCIAL HQ
  56. 56. HUDSON YARDS, NYC FINANCIAL HQ  Over 28% energy savings for chilled water service with dual temperature plant o 38% reduction in IPLV for 55°F (12.8°C) chiller compared with standard o Waterside economizer full cooling almost 50% of hours compared with 34% of hours for standard system  Significantly reduced interior zone overcooling due to high temperature SAT (66°F, 18.9°C)  Significantly reduced thermal degradation due to high temperature of supply air in plenum.  Reduced airflow due to low temperature (60°F, 15.6°FC) recooled air at perimeter.  ASHRAE Journal “Engineers Notebook”, June, 2017 56
  57. 57. • Overwhelming Cause of Project Failure • Mutli-Disciplinary, Multi-Trade Issue • Leakage Rates of 40% have Been Identified • Three Types of Leakage: –Into the Occupied Space –Into the Return Path, Bypassing Occupied Space –Into the Exterior Envelope LEAKAGE
  58. 58. • Allowable up to 0.25 cfm per square foot • Gasketed Floor Boxes • Leakage Rated Access Tiles • Offset Grid of Access Floor Tile and Carpet Tile • Trim Detail for Access Floor at Walls and Columns LEAKAGE INTO OCCUPIED SPACE
  59. 59. • Completely Undesirable • Tape and Seal all Walls at Floor Slab • Firestopping Detail at Slab/Exterior Wall Join • Firestop all Piping, Cabling Floor Penetrations • Isolate and Seal All Core Wall Penetrations for Cabling • Make Underfloor Supply Plenum a Bathtub LEAKAGE INTO RETURN PLENUM
  60. 60. • Can Cause Water Damage to Exterior Wall • Provide Solid Interior Finish Surface to Spandrel Panel in Plenum • Firestopping Details • Curtain Wall Details • Make Underfloor Supply Plenum a Bathtub LEAKAGE INTO EXTERIOR WALL
  61. 61. PLENUM LEAKAGE CONTROL
  62. 62. • Supply Plenum Must be Completely Clean for Operation • Concrete Floor Slab is Sealed • Sequence of Cleaning and Installation –Slab Sealing –Drywall Installation and Finishing –Pedestal Installation –Final Floor Installation • Designer/Contractor/Owner Summit to Create Installation Sequence CONSTRUCTION SEQUENCE/HOUSEKEEPING
  63. 63. Acknowledgements: Alcoa Corporate Headquarters Architect – The Design Alliance, Pittsburgh, PA Building Services Engineers – Roger Preston +Partners Atlanta, GA, Dodson Engineering, Pittsburgh PA New York Times Headquarters Architect – FX Fowle, New York, NY Renzo Piano Building Workshop Building Services Engineers – Flack + Kurtz, NYC
  64. 64. Questions THANK YOU Underfloor Air Distribution Systems Daniel H. Nall, FAIA, PE, FASHRAE, LEED, Fellow, BEMP HBDP dnall@Syska.com

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