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Mould in Air Conditioned Buildings in Asia

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mould in air-conditioned buildings

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Mould in Air Conditioned Buildings in Asia

  1. 1. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Mould in Air Conditioned Buildings by John Herbert
  2. 2. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion
  3. 3. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion Across Asia the hot & humid climate means the outside air has higher vapour pressure (VP) than the air inside air conditioned buildings having a lower vapour pressure (VP). This difference creates a pressure gradient (P) across the building envelope, causing moisture to be transported through the building envelope in a process known as Diffusion.
  4. 4. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion Higher Vapour Pressure (VP) Lower Vapour Pressure (VP) Air Conditioned Buildings building envelope diffusion
  5. 5. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion Moisture passing through the building envelope would normally transported by air circulating in the room. Moisture, transported by the air, when it reaches the air conditioning cooling coil, the moisture is condensed to water, and drained away. So moisture does not accumulate in the building envelope.
  6. 6. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion building envelope section - NTS room air circulation transfers moisture high VP 33 degC 80% rh 3,680 pa VP low VP 24 degC 60% rh 1,752 pa VP moisture OUTSIDEINSIDE
  7. 7. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion However, if a vapour retarder such as vinyl wallpaper is lining the inside face of an external wall of an air conditioned room moisture becomes trapped behind the vapour retarder, effectively isolated from the room air circulation. Moisture accumulates beneath the vapour retarder creating damp and leading to growth of mould.
  8. 8. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion Where damp and mould occurs in a space without any air movement that rules out moisture transport by air, for example behind vinyl wallpaper or other materials impervious to air. Therefore, moisture transportation by Diffusion is the likely culprit.
  9. 9. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion building envelope section - NTS room air circulation cannot transfer moisture high VPlow VP moisture OUTSIDEINSIDE moisture trapped behind vapour retarder moisture and mould vinyl wallpaper
  10. 10. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion The challenge is not just limited to vinyl wallpaper, any vapour retarder, for example • Material with aluminium foil facing layer • Millwork, furniture with plastic laminate • Vinyl's and plastics e.g. whiteboard • Polymer based paints and coatings • Glass, including mirrors
  11. 11. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion mould vapour retarder building envelope section - NTS room air circulation cannot transfer moisture high VPlow VP moisture OUTSIDEINSIDE moisture trapped behind area of vapour retarder
  12. 12. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion Decoration of air-conditioned rooms often means the walls are finished internally with plasterboard, and windows are often trimmed with decorative millwork. Often finishes inadvertently include a vapour retarder for example foil faced thermal insulation, the vapour retarder traps moisture, and being isolated from the circulation of room air moisture accumulates causing mould.
  13. 13. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Diffusion unventilatedcavity plasterboard insulation building envelope section - NTS room air circulation cannot transfer moisture high VPlow VP moisture OUTSIDEINSIDE moisture trapped in cavity by vapour retarder
  14. 14. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Mechanical Ventilation
  15. 15. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Negative Pressurisation Mechanical Ventilation with exhaust fans drawing air from washroom, bathrooms, and kitchens create a (-ve) negative pressurisation in the building. Replacement air is drawn through any open or undercut doors, and open windows. And through any defects including leakage caused gaps around doors, windows, eaves, etc.
  16. 16. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Negative Pressurisation Air Conditioned Building negative pressure (-ve) infiltration Exhaust air fan(s) create (-ve) pressure building envelope EAF
  17. 17. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Negative Pressurisation Where the outdoor air condition is, lets say, 33 degC & 80% rh, the dewpoint temperature of the air is approx. 28.5 degC. That means if the outdoor air impinges upon a surface with a temperature below the dewpoint temperature moisture in the air will condense, causing damp and potentially mould growth.
  18. 18. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Negative Pressurisation typical room air 24 deg C 60% rh outdoor air 33 deg C 80% rh dewpoint temp 28.5 deg C condensationzone
  19. 19. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Negative Pressurisation Its understood that water ingress whether through diffusion or infiltration creates damp inside buildings, causing damage to building fabric and finishes, and then growth of mould impacting the health of its occupants. Therefore strategies are needed to account for moisture and mitigate the risk.
  20. 20. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Positive Pressurisation To manage the uncontrolled ingress of outdoor air, a PAU filters and dehumidifies the outdoor air delivering conditioned air into the building. If the quantity of conditioned air is greater than the exhaust air, this creates Exfiltration characterised by the intention leakage of conditioned air and preventing ingress of hot & humid outdoor air.
  21. 21. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Positive Pressurisation This leakage of conditioned air is intention, to minimise the risk of hot and humid outdoor air causing condensation. Often witnessed as conditioned air (cool air) spilling through the entrance door out to the street.
  22. 22. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Positive Pressurisation Air Conditioned Building positive pressure (+ve) exfiltration Exhaust air fan(s) create (-ve) pressure building envelope EAF PAU(s) create (+ve) pressurePAU
  23. 23. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Conclusions Air movement inside buildings can be complex, particularly in high rise buildings, therefore its important that every space in the building is analysed room by room, and floor by floor. Lift shafts and operation of lift cars pushing air through the shaft particularly in high rise buildings causes air movement that may impact the design strategy.
  24. 24. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Air Conditioned Building positive pressure (+ve) exfiltration Exhaust air fan(s) create (-ve) pressure building envelope EAF PAU(s) create (+ve) pressurePAU infiltration diffusion
  25. 25. © Copyright All Rights Reserved 2019www.kelcroft.com.hk Conclusions In addition external airflow (wind) creates a varying pressure on the building depending on its direction and strength which should also be considered when formulating the model to mitigate the risk of damp and mould in buildings.
  26. 26. © Copyright All Rights Reserved 2019www.kelcroft.com.hk John Herbert @johnherbert +(852) 2335 9830

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