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Assumptions about Indoor Environments

Learn about assumptions, issues, and impacts of wall construction on indoor environments. Understand the importance of ventilation, humidity control, and the impact of vapor resistance. Conclusions on maintaining comfort and safety.

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Assumptions about Indoor Environments

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  1. Assumptions about Indoor Environments Mark Lawton P.Eng Patrick Roppel M.A.Sc.

  2. Wall Section • Latex paint • R-8 batt • DensGlass • SA Membrane • R-8 Semi-Rigid FG • Air Space • Stucco

  3. Ventilation • Operable windows • Range hood • Bathroom fans on timer (principal exhaust) Corridor pressurization system serving most suites

  4. Issues • Very High indoor RH • Winter moisture collection in DensGlass • Mold growth on interior surfaces • Condensation damage on window sills

  5. Impact of Wall Construction • There must be sufficient insulation outboard of an impermeable layer to control the time that the temperature of the sheathing is below the dewpoint of the interior air. • VBBL allows the ratio of insulation outboard/insulation inboard of impermeable surface to be 0.2 • Lstiburek suggests ratio for Marine climate without VB is 0.3 • Ratio 0.7 for R8 is 0.5 for R12 and

  6. Obvious Questions • Why is humidity so high? • Extraordinary sources? • Inadequate use of ventilation systems? • Insufficient capacity of ventilation systems? • Is control by ventilation practical? • Capacity • Operating time • Supply air source • How would a vapour barrier affect performance

  7. Monitored Interior Conditions

  8. Comparison of Outdoor and Indoor Vapour Pressure Little difference in summer Larger difference in coldest months

  9. Capacity of principal exhausts

  10. Corridor Supply Air • Measure flow to corridors generally matched the VBBL required capacity of suites on the corridor • Some suites not served by indoor corridor • Most doors weather-stripped

  11. Indoor Vapour Pressure Depends on: • Moisture sources • Typically in range of 2 kg/day per person • Rate of air change • In tight building can average as low as 0.15 to 0.25 ACH • For a given set of indoor and outdoor vapour pressures conditions, there can be a range of solutions

  12. Indoor Humidity ASHRAE Design Comfort Limit

  13. Indoor Humidity • Winter 2004 – Suite 611 • 7 kg/day moisture generation • Limited use of bathroom fan (noisy) • Undercut blocked • Room heat turned down & door closed • Top floor

  14. CO2 Measurements • Suite 205 • Fan with window open at 480 PPM • Peak with fan at 1200 PPM • Range of 680 to 1800 PPM without fan • Operating temperature routine constant

  15. Impact of Ventilation • Suite 205 • Range of 36 to 47% RH with fan • Range of 42 to 56% RH without fan • Fan flow measured at 37 cfm

  16. Impact of Ventilation • Suite 205 • 4 kg/day moisture generation • Overall trend is consistent • Difference by peak ventilation • Difference by peak moisture

  17. Impact of Ventilation • Suite 311 • Data limited • Peak at 4000 without fan • Peak at 2500 with fan • Fan flow measure at 44 cfm

  18. Impact of Ventilation • 1-D Hygrothermal Model (WUFI) • RH at exterior sheathing (inside) • 0.3 ACH improvement results in RH maintained below 90% • 0.6 ACH improvement results in RH maintained below 85%

  19. Impact of Vapour Resistance • 1-D Hygrothermal Model (WUFI) • Retarding paint (35 ng/m2 Pa s) • Decreases wetting potential from interior • Allows drying to interior

  20. Impact of Winter Indoor Operating Temperature Number of Hours that Exterior Sheathing is below Interior Air Dewpoint

  21. Conclusions • Inadequate ventilation leads to unsatisfactory conditions for both humidity and other contaminants. • Ventilation that meets the requirements of a principal exhaust fan in the code for noise, capacity, and duration is likely sufficient for most units if it is on, and exhausted air is replaced with fresh air. • Must keep the occupant’s comfort in mind or risk them overriding controls. • For high humidity indoor environments, vapour resistance at the interior surface is recommended to control the wetting potential from the interior air.

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