The Value of Air Leakage Testing in Large Commercial Buildings

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The energy required to heat and cool outdoor air and infiltration air is a significant fraction of thermal loads. This project has developed diagnostic procedures to identify air leaks and methods to calculate the savings from air sealing large commercial and institutional buildings. Envelope air sealing could significantly reduce large building energy consumption, but no systematic research has identified the most cost-effective strategies for Minnesota buildings.

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The Value of Air Leakage Testing in Large Commercial Buildings

  1. 1. s The Value of Air Leakage Testing in Large Commercial Buildings An Overview of Study Findings November 7, 2013 Technical Difficulties: Anna Jursik at ajursik@mncee.org Dave Bohac P.E. | Director of Research
  2. 2. Counting the Capacity that Didn't Hatch: The Rate Mitigation Effect of DSM Programs This webinar will provide an analysis overview, highlighting how the effects on revenue differ from the levelized cost calculations currently used, and how historical and ongoing benefits from DSM program activity might be framed in the future. Jenny Edwards Innovation Exchange Program Manager Target Audience • Utility DSM managers • Energy policy experts • Policy-makers Thursday, Dec. 12th 11:00 – 12:00 CST Register at www.cee.org/Innovation-Exchange
  3. 3. s The Value of Air Leakage Testing in Large Commercial Buildings An Overview of Study Findings Dave Bohac P.E. | Director of Research
  4. 4. Acknowledgements This project was supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources through a Conservation Applied Research and Development (CARD) program
  5. 5. Large Building Tightness Specification • Measure the air flow rate needed to pressurize & depressurize the building by 75Pa (0.3 in. wc.) • Divide by the building envelope area – typically the exterior walls + roof + floor (6 sides) • Results from 387 US C&I buildings o Average = 0.72 cfm/ft2 o Range 0.03 – 4.3 cfm/ft2
  6. 6. Code Requirements • US Army Corp Engineers = 0.25 cfm/ft2 o Tested over 300 buildings o Average = 0.16 cfm/ft2 • IECC 2012 (7 states) whole building compliance path = 0.40 cfm/ft2 • Washington State: Buildings over five stories require a whole building test, but do not have to pass a prescribed value. • City of Seattle : All buildings require a whole building test, but do not have to pass a prescribed value.
  7. 7. Why do we care about building air leakage? • HVAC systems pressurize buildings to eliminate infiltration – don’t they? • When HVAC is off => air infiltration • Pressurization not always effective or implemented correctly • NIST/Persily tracer gas results – infiltration can be significant
  8. 8. Air Handler Pressurization =10,500 – 2,075cfm 10,500 cfm 2,075 cfm 4 Story 60,000sf Office Building: leakage = 27,000 cfm@75Pa, 0.5 cfm@75/ft2
  9. 9. Roof Top Unit Operation 2,075 cfm 10,500 cfm
  10. 10. Single-zone Constant Volume AHU • Supply and Return Fans turn on/off by schedule • Outside Air Damper has a minimum position setpoint for ventilation • Relief Damper controls air exhausted from the building Relief Air 2,075 cfm – Exhaust Fans Relief Air Damper 25% open Mixed Air Damper 75% open Outside Air 10,500 cfm From Space Return Fan MAT Sensor DAT Sensor Outside Air Damper 25% open To Space Supply Fan Heating Coil Cooling Coil
  11. 11. Air Handler Pressurization 10,500 cfm 2,075 cfm 4 Story 60,000sf Office Building: leakage = 27,000 cfm@75Pa, 0.5 cfm@75/ft2
  12. 12. Air Handler Pressurization 10,500 cfm 2,075 cfm 4 Story 60,000sf Office Building: leakage = 27,000 cfm@75Pa, 0.5 cfm@75/ft2
  13. 13. Air Handler Pressurization 10,500 cfm 2,075 cfm Infiltration >> 4 Story 60,000sf Office Building: leakage = 27,000 cfm@75Pa, 0.5 cfm@75/ft2
  14. 14. Single-zone Constant Volume AHU • Economizer operation o Mild weather when building needs cooling o Open outdoor air dampers, exhaust dampers follow; OA – EA stays the same? Relief Air 16,175 cfm – Exhaust Fans Relief Air Damper 60% open Mixed Air Damper 40% open Outside Air 24,600 cfm From Space Return Fan MAT Sensor DAT Sensor Outside Air Damper 60% open To Space Supply Fan
  15. 15. Variable Volume AHU with VAV Boxes • Supply and Return Fans o Supply fan VFD modulates to meet Duct Static Pressure (DSP) Setpoint o Return fan lags supply fan to maintain positive pressure V F D Return Fan 77% speed V F D DSP Sensor (typically 2/3 down supply duct) Supply Fan 87% speed
  16. 16. Model Infiltration: Range of Flow Imbalance Minimum outside air = 20,300cfm 1 Story 60,560ft2 Elementary School: leakage = 44,670 cfm@75Pa (0.75cfm@75/ft2)
  17. 17. Model Infiltration: Range of Flow Imbalance Minimum outside air = 20,300cfm 1 Story 60,560ft2 Elementary School: leakage = 14,890 cfm@75Pa (0.25cfm@75/ft2)
  18. 18. Model Infiltration: Range of Flow Imbalance Envelope Leakage= 0.75 cfm@75Pa/ft2 Avg Infil. (cfm) Avg Infil. (ach) Heat Load (therms/yr) % Space Heating Cost ($) -3,450 2,986 0.25 7,264 19% $4,213 HVAC Flow Imbalance, OA - EA (cfm) 0 3,450 6,900 2,444 2,077 1,849 0.20 0.17 0.15 6,114 5,260 4,732 16% 14% 12% $3,546 $3,051 $2,745 17,250 1,652 0.14 4,308 11% $2,499
  19. 19. Model Infiltration: Range of Flow Imbalance Envelope Leakage= 0.75 cfm@75Pa/ft2 Avg Infil. (cfm) Avg Infil. (ach) Heat Load (therms/yr) % Space Heating Cost ($) -3,450 2,986 0.25 7,264 19% $4,213 HVAC Flow Imbalance, OA - EA (cfm) 0 3,450 6,900 2,444 2,077 1,849 0.20 0.17 0.15 6,114 5,260 4,732 16% 14% 12% $3,546 $3,051 $2,745 17,250 1,652 0.14 4,308 11% $2,499 Envelope Leakage= 0.25 cfm@75Pa/ft2 Avg Infil. (cfm) Avg Infil. (ach) Heat Load (therms/yr) % Space Heating Cost ($) -3,450 1,725 0.14 4,004 10% $2,322 HVAC Flow Imbalance, OA - EA (cfm) 0 3,450 6,900 951 708 678 0.08 0.06 0.06 2,439 1,875 1,813 6% 5% 5% $1,414 $1,087 $1,052 17,250 676 0.06 1,809 5% $1,049
  20. 20. Air Leakage Test Video
  21. 21. How leaky or tight are US buildings? • Test results compiled by the National Institute of Standards and Technology (NIST) – Emmerich and Persily – over the past 15 years • 387 commercial and institutional buildings • NOT RANDOM: researchers, low-energy programs, private testing firms • Used to model air infiltration energy loads and help establish leakage standards
  22. 22. NIST Results from US whole building tests 6-sided at 75Pa (cfm/ft2) Mean Std Dev Min 0.35 0.38 0.03 0.29 0.20 0.06 0.40 0.15 0.11 0.54 0.40 0.05 0.30 0.23 0.09 0.36 0.30 0.03 Dataset Efficiency Vermont ASHRAE RP 1478 Washington Other VT/NH Other All new data Qty 36 16 18 79 10 159 All previous data 228 0.92 0.70 0.09 4.28 All Buildings 387 0.72 0.63 0.03 4.28 USACE & Navy 300 0.16 Emmerich and Persily 2013 USACE Std = 0.25 Max 1.78 0.75 0.64 1.73 0.75 1.78
  23. 23. NIST Results: Frequency Histogram USACE Std = 4.5 20-25% meet Std Multiply by 0.055 >> cfm/ft2 Emmerich and Persily 2013
  24. 24. NIST Results: Weak Trends • Tighter – office, education, public assembly & long-term health care • Leakier – retail, restaurants, industrial • Leakier exterior walls – frame, masonry/metal, & frame/masonry
  25. 25. NIST Results: Effect of Building Size Buildings > 54,000ft2 twice as tight 0.55 cfm/ft2 Emmerich and Persily 2013
  26. 26. NIST Results: Effect of Climate Heating degree days > 3,600 one third tighter 0.55 cfm/ft2 Emmerich and Persily 2013
  27. 27. NIST Results: Effect of Age 138 buildings with no air barriers built since 1950 – no strong trend Colder climate 0.55 cfm/ft2 Emmerich and Persily 2013
  28. 28. NIST Results: LEED Buildings • 23 LEED buildings; average = 0.29 cfm/ft2 • Significantly tighter than average of other 364 buildings • Slightly (5%) leakier than other 56 buildings with an air barrier
  29. 29. NIST Results: Effect of Air Barrier Buildings with air barrier are 70% tighter Page 30 USACE Std = 4.5, 0.25cfm/ft2 Emmerich and Persily 2013
  30. 30. NIST Results: Effect of Air Barrier Compare no air barrier to tight construction 0.1 cfm/ft2 Page 31 1.0 cfm/ft2 USACE Std = 4.5, 0.25cfm/ft2 Emmerich and Persily 2013
  31. 31. NIST Building Infiltration & Energy Models • Multizone infiltration and energy model • Compared air infiltration and energy use for: o “typical” - no air barrier reported leakage (4x USACE) o “target” – good practice (40% below USACE) • Five cities in different climate zones
  32. 32. NIST Building Infiltration & Energy Models Two-Story, 24,000ft2 Office Building One-Story, 12,000ft2 Retail Building Emmerich and Persily 2013 Page 33
  33. 33. Model Infiltration: Range of Envelope Leakage Minimum outside air = 20,300cfm 1 Story 60,560ft2 Elementary School: HVAC Imbalance = 3,450 cfm
  34. 34. Model Infiltration: Range of Envelope Leakage 1 Story 60,560ft2 Elementary School: HVAC Imbalance = 3,450 cfm Avg Infil. (cfm) Avg Infil. (ach) Heat Load (therms/yr) % Space Heating Cost ($) 0.05 305 0.03 855 2% $496 NIST office building model: 1.0 cfm/ft2 = 0.23 ach 0.1cfm/ft2 = 0.05 ach 0.1 417 0.03 1,139 3% $661 Building Envelope Leakage (cfm@75/ft2) 0.15 0.25 0.4 0.75 481 708 1,094 2,077 0.04 0.06 0.09 0.17 1,305 1,875 2,832 5,260 3% 5% 7% 14% $757 $1,087 $1,643 $3,051 1.25 3,539 0.29 8,867 23% $5,143 2 5,751 0.47 14,322 37% $8,306
  35. 35. Minnesota Leakage Study: work scope • Conduct investigations on 25 buildings: floor area of 25,000 to 500,000 ft2 • Air seal and pre/post leakage tests on X 7 buildings 6 • Continuous building pressure and HVAC operation data for 50 to 200 days • CONTAM pre/post air flow models that include mechanical system leakage and pressure effects • Compute infiltration/energy reductions
  36. 36. Building Characteristics Floor # Constr Building ID Area (sf) Stories Elem School TF 59,558 1 Middle School 138,887 3 Small Office 26,927 1 Univ Library 246,365 3 Elem School PS 60,968 1 Library/Office 55,407 1 Year 1951 1936 1998 1967 1965 2007 Wall Type Masonry & corrugated metal panel Cast concrete w/CMU infill EFIS tip up (3 walls) and CMU block Cast concrete w/CMU infill & brick ext CMU w/brick exterior Steel studs & brick or stone cladding 3 elementary & middle schools: 1936 to 1965 with additions 60,000 – 139,000sf University Library 246,000sf Small Office 27,000sf Library/Office 55,000sf
  37. 37. Minnesota Leakage Study: leakage results All 7 buildings at least 25% tighter than the US Army Corp standard of 0.25 cfm/ft2 Envelope Floor Area (ft2) Air Leakage at 75Pa 6 Sides Building ID Area (ft2) 6 Sides2 (cfm) (cfm/ft2) Elem School TF 59,558 146,977 27,425 0.19 Comm. College 95,000 164,844 28,881 0.18 Middle School 138,887 208,733 32,818 0.16 Small Office 26,927 65,267 9,177 0.14 Univ Library 246,365 171,712 23,356 0.14 Elem School PS 60,968 145,766 17,602 0.12 Library/Office 55,407 139,965 12,321 0.09 Minimum 26,927 65,267 9,177 0.09 Mean 97,587 149,038 21,654 0.14 Median 60,968 146,977 23,356 0.14 Maximum 246,365 208,733 32,818 0.19 EqLA # Constr (ft2) 15.2 17.2 16.6 4.6 13.1 9.6 6.9 4.6 11.9 13.1 17.2 Stories 1 2 3 1 3 1 1 Year 1951 1996 1936 1998 1967 1965 2007
  38. 38. Comparison to US Buildings 7 building average is 85% less than the US average, slightly less than US Army Corp average 6 buildings
  39. 39. Tighter Buildings in Colder Climates? 7 building average is 85% less than the US average 6 buildings
  40. 40. Air sealing focused on roof/wall Canopy leakage at exterior wall
  41. 41. Air Sealing Reduction “Tight” buildings tightened by 9% Air Leakage at 75Pa (cfm) Building ID Elem School TF Comm. College Middle School Small Office Univ Library Elem School PS Library/Office Minimum Mean Median Maximum Pre 27,425 28,881 32,818 9,177 23,356 17,602 12,321 9,177 21,654 23,356 32,818 Reduction Post 22,699 28,133 28,872 8,470 21,963 15,837 11,369 8,470 19,620 21,963 28,872 (cfm) 4,726 748 3,947 708 1,392 1,765 953 708 2,034 1,392 4,726 (%) 17% 3% 12% 8% 6% 10% 8% 3% 9% 8% 17% Leakier Tighter Air sealing work confirmed by visual, smoke puffer, and IR inspections
  42. 42. Air Sealing Reduction More expensive to seal tighter buildings? Air Sealing Cost Building ID Elem School TF Comm. College Middle School Small Office Univ Library Elem School PS Library/Office Minimum Mean Median Maximum Total ($/CFM75) ($/ft2) $ 18,550 $ 3.92 $ 6,822 $ 17,845 $ 23.86 $ 17,273 $ 23,700 $ 6.00 $ 8,434 $ 4,768 $ 6.73 $ 10,058 $ 15,918 $ 11.43 $ 65,159 $ 26,700 $ 15.13 $ 38,132 $ 1,152 $ 1.21 $ 1,297 $ 1,152 $ 1.21 $ 1,297 $ 15,519 $ 9.76 $ 21,025 $ 17,845 $ 6.73 $ 10,058 $ 26,700 $ 23.86 $ 65,159 Leakier Tighter
  43. 43. Air Sealing Reduction Contractor estimates better for leakier buildings? Leakage Area EqLA (ft2) Building ID Elem School TF Comm. College Middle School Small Office Univ Library Elem School PS Library/Office Pre 15.2 17.2 16.6 4.6 13.1 9.6 6.9 Post 12.5 16.2 13.8 4.1 12.8 8.9 6.0 Sealed Area (sf) Reduction (ft2) 2.7 1.0 2.8 0.5 0.2 0.7 0.9 Contractor Estimated (%) Roof/Wall 18% 8.84 6% 5.47 17% 11.73 10% 2% 7% 14.45 13% Total 11.49 5.47 14.98 Meas/Est 0.31 0.19 0.24 Leakier 16.94 0.05 Tighter Building Leakage < Estimated sealing
  44. 44. Air Sealing Energy Savings Modeled Infiltration and Energy Savings Space Heat Gas Use (Therms/yr) Building ID Elem School TF Comm. College Middle School Small Office Univ Library Elem School PS Library/Office Avg Leakage Savings Total Infiltration Infil/Total Infil (cfm) Red. (%) (Therm/yr) ($/yr) 40,224 3,468 9% 1,296 17% 811 $ 470 32,095 5,168 16% 1,730 3% 88 $ 53 44,469 14,950 34% 4,814 12% 1,397 $ 810 8% 249 6% 35 $ 18 26,563 3,530 13% 1,453 10% 325 $ 188 18,108 4,194 23% 1,503 8% 170 $ 109 Payback Cost ($) $ 18,550 $ 17,845 $ 23,700 $ 4,768 $ 15,918 $ 26,700 $ 1,152 Able to seal “tight” buildings, but work was not cost effective (years) 39 339 29 904 142 11
  45. 45. Mechanical System Leakage Part of building envelope when not operating Mean 49% 0.06 cfm/ft2 (6 sides) Range 17% to 103% 0.02 to 0.12 cfm/ft2 Two most recently built (1998 and 2007) had low leakage
  46. 46. Building Pressure Measurements Average building pressure at ground level (Pa) -20 < OAT < 0 unoccupied occupied Comm. College Elem School PS Middle School High School Elem School TF Library/Office Sports Arena Univ Class T Univ Union High Rise Office Clinic 1 Clinic 2 Clinic 3 Univ Class SH Maximum Minimum Median -10 -4 -6 6 -11 -10 -49 0 6 -49 -6 -13 11 11 -13 -10 0 < OAT < 20 unoccupied occupied -6 -4 0 -10 -4 -6 -6 -3 -11 0 0 -5 -2 1 -7 -4 0 -4 -11 -39 -9 -6 0 -39 -6 -5 -35 -11 11 11 -35 -4 20 < OAT < 45 unoccupied occupied -2 -2 -6 -7 -3 -4 -4 0 -9 -48 -10 -27 -6 -3 0 -48 -5 3 4 -3 -3 2 -4 -1 3 2 -44 -2 -23 -6 9 9 -44 -2 45 < OAT <70 unoccupied occupied 0 0 -3 -6 -1 -2 -4 12 -7 -32 -9 1 12 -32 -2 12 4 2 4 3 2 9 12 8 -21 2 -11 1 7 12 -21 4 70 < OAT <90 unoccupied occupied 1 1 5 6 0 -3 1 1 -9 27 -6 -2 1 -1 1 -6 0 27 -9 1 No buildings operating greater than 10Pa at ground level Most have higher pressure during occupied hours
  47. 47. Building Pressure Measurements 20F < outside temp <= 45F Roof level pressures are higher – few operating greater than 10Pa
  48. 48. Building Pressure Measurements 20F < outside temp <= 45F Roof level pressures are higher – few operating greater than 10Pa
  49. 49. Summary • • • • • • Tight buildings: 85% tighter than U.S. average & at least 25% below Army Corp standard – due to cold climate location? Sealing = 9% reduction, more reduction and less expensive for leakier buildings Contractor over-estimated sealing area Long paybacks for air sealing work Including mechanical systems increased leakage by 17 to 103% (0.02 to 0.12 cfm/ft2) HVAC systems tend to pressurize buildings. Not as great as typical design practice
  50. 50. Additional Slides
  51. 51. ASHRAE Research: selection criteria • Goal: 24 to 36 existing mid- and high-rise buildings (16 Completed) • Non-residential • 4 stories or higher • Sustainability certification (14 of 16) • Built after the year 2000 • Climate zones 2-7 (All 6 Zones Represented)
  52. 52. ASHRAE Research Project: leakage results • Average = 0.29 cfm/ft2 • Green building = 0.32 cfm/ft2; others = 0.22 cfm/ft2 • Air barrier specified and envelope expert = 0.13 cfm/ft2; others = 0.39 cfm/ft2 • Unsealing HVAC penetrations increased leakage by average of 27% with range of 2% to 51%
  53. 53. ASHRAE Research Project: leakage sites • Roof/wall intersection • Soffits and overhangs • Mechanical rooms, garages, basements, loading docks • Roll-up and overhead doors
  54. 54. Single-zone Constant Volume AHU • Supply and Return Fans o On/Off according to schedule o May cycle on to maintain night setback temperature Return Fan Supply Fan
  55. 55. Roof Top Unit Operation
  56. 56. What about Energy Recovery Ventilators? • Why not run the exhaust air through an ERV to recovery some of that energy instead of forcing it out through the envelope? • Need a tighter envelope to accomplish ERVs with infiltration control
  57. 57. Dave Bohac P.E. Center for Energy & Environment | Director of Research dbohac@mncee.org Megan Hoye, LEED AP Center for Energy & Environment | Engagement Coordinator mhoye@mncee.org
  58. 58. Thank you!
  59. 59. 1. Three to four take aways 2. Tell them what to look for 3. Sdf..

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