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Getting airtightness and ventilation right;
‘Build tight ventilate right’ - why are we still debating this??
Nick Grant; E...
Why Airtightness?
• Comfort
• Health
• Avoiding fabric damage
• (Also energy saving)
Comfort
Air velocity >0.15 m/s needs 1 - 2 K
higher air temperature
AECB Carbonlite Course
Building protection
Control Layer Priorities:
1. a rain control layer
2. an air control layer
3. a vapor control layer
4. ...
Airtightness metrics
• Permeability (m/h) or air changes at 50
Pa test pressure. For average house
we can assume they are ...
Energy kWh/(m2.a)
10m/h permeability, MEV 0.4 ach Part L range U values.
55kWh/(m2.a) vent
and infiltration loss
Heating
M...
Add 90% efficient MVHR.
Energy kWh/(m2.a)
Saves 7kWh/(m2.a)
48kWh/(m2.a) vent
and infiltration loss
Improve airtightness to 0.6 ach.
Energy kWh/(m2.a)
Saves 42 kWh/(m2.a)
6kWh/(m2.a) vent
and infiltration loss
Add Passivhaus windows and insulation to 0.6 ach.
Energy kWh/(m2.a)
Saves another
28kWh/(m2.a)
Heating
Additional energy loss due to this is ignored in the previous calculations
Thermal bypass
Imagine standing on a windy moun...
Mind the gap
How airtight to go? - Energy
WRT Energy efficiency, AECB
Silver Standard Suggests:
n50 < 3 MEV*
n50 < 1.5 MVHR
MEV = Mecha...
Does MEV need good airtightness?
With leaky fabric or trickle vents,
bedrooms can become the exhaust route
for moist air.
...
MEV & tight fabric
•For MEV to ventilate well you need
excellent airtightness.
For MVHR to ventilate well
you don’t!
(For ...
Airtightness ROI?
Effort/cost Airtightness
step change in approach
• Design to be 100% airtight
• Can’t design to a leakag...
How to design in airtightness
warm blooded animal has
structure on inside
cold blooded animal has
structure on outside
if ...
As in nature:
structure
air barrier
insulation
wind barrier
external structure
Rain screen, maybe
walls as well
Timber, st...
Not like these
These are all good
Straw!
Or thisStandard 2”x4” platform
frame timber building.
Wrapped with airtight
membrane then externally
insulated, e.g. with ...
Factory version in Maine
Rarely practical to leave
access to air barrier up to
blower door test. Do it right
once.
Cars an...
Wind-tightness; same idea
Very fiddly, lots of tape Wind tight & cheaper to build
Some combine airtightness
& wind tightne...
Ventilation
• Controls relative humidity
• beware over ventilation in winter, particularly non domestic
• Removes pollutan...
Natural is best?
• Natural Ventilation is a misnomer - random leaks or manual
• Good control requires some motive force gr...
Basic ventilation options
Option Comfort Health Energy Cost Airtightness
Leaky fabric Poor Poor Poor Free N/a*
Manual
vent...
QA of ventilation system
• MEV probably easiest to get right.
• Needs excellent airtightness to ensure good air quality an...
Learning from Passivhaus
MVHR
No need to reinvent the wheel
Beds Living Circ' Bath/kitchen
e.g. cascade approach to avoid ...
Conclusions
• Leaky building leads to poor air quality, poor comfort and waste of energy
• We need controlled ventilation ...
Learn More
www.passivhaustrust.org.uk
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Getting Airtightness and Ventilation Right

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Getting airtightness and ventilation in buildings right. Presented at EcoBuild London in 2015. Ventilation and airtightness is commonly misunderstood. How to design for airtight, draft free construction. Airtightness is key to building comfort and energy efficiency.

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Getting Airtightness and Ventilation Right

  1. 1. Getting airtightness and ventilation right; ‘Build tight ventilate right’ - why are we still debating this?? Nick Grant; Elemental Solutions ecobuild 2015 @ecominimalnick
  2. 2. Why Airtightness? • Comfort • Health • Avoiding fabric damage • (Also energy saving)
  3. 3. Comfort Air velocity >0.15 m/s needs 1 - 2 K higher air temperature AECB Carbonlite Course
  4. 4. Building protection Control Layer Priorities: 1. a rain control layer 2. an air control layer 3. a vapor control layer 4. a thermal control layer Building Science Corporation USA Still common to hear misconceptions about letting the building ‘breathe’ or ‘good to have some air movement’ about 100x more significant than vapour diffusion
  5. 5. Airtightness metrics • Permeability (m/h) or air changes at 50 Pa test pressure. For average house we can assume they are about the same number. • Average infiltration 5-10% of this so 10 ach @ 50Pa is about 0.5-1 air change on average but varies considerably with wind and temperature. Blower door test
  6. 6. Energy kWh/(m2.a) 10m/h permeability, MEV 0.4 ach Part L range U values. 55kWh/(m2.a) vent and infiltration loss Heating MEV assumed rather than manual vents because we can calculate the energy.
  7. 7. Add 90% efficient MVHR. Energy kWh/(m2.a) Saves 7kWh/(m2.a) 48kWh/(m2.a) vent and infiltration loss
  8. 8. Improve airtightness to 0.6 ach. Energy kWh/(m2.a) Saves 42 kWh/(m2.a) 6kWh/(m2.a) vent and infiltration loss
  9. 9. Add Passivhaus windows and insulation to 0.6 ach. Energy kWh/(m2.a) Saves another 28kWh/(m2.a) Heating
  10. 10. Additional energy loss due to this is ignored in the previous calculations Thermal bypass Imagine standing on a windy mountain top wearing all your woolies but no coat
  11. 11. Mind the gap
  12. 12. How airtight to go? - Energy WRT Energy efficiency, AECB Silver Standard Suggests: n50 < 3 MEV* n50 < 1.5 MVHR MEV = Mechanical Extract Ventilation MVHR = Mech’ Vent with Heat Recovery AKA Comfort Ventilation *NB. For good air quality MEV requires better airtightness — 0.6 Elemental Solutions
  13. 13. Does MEV need good airtightness? With leaky fabric or trickle vents, bedrooms can become the exhaust route for moist air. As bedroom temperatures are typically lower this results in high RH and risk of mould and dust mites. High RH High RH Elemental Solutions
  14. 14. MEV & tight fabric •For MEV to ventilate well you need excellent airtightness. For MVHR to ventilate well you don’t! (For supply air ventilation - might need vents in wet areas) Elemental Solutions
  15. 15. Airtightness ROI? Effort/cost Airtightness step change in approach • Design to be 100% airtight • Can’t design to a leakage target TightLeaky
  16. 16. How to design in airtightness warm blooded animal has structure on inside cold blooded animal has structure on outside if you want to build an insulated building, where does the structure go?
  17. 17. As in nature: structure air barrier insulation wind barrier external structure Rain screen, maybe walls as well Timber, steel, concrete, brick . . . .
  18. 18. Not like these
  19. 19. These are all good Straw!
  20. 20. Or thisStandard 2”x4” platform frame timber building. Wrapped with airtight membrane then externally insulated, e.g. with Larsen Trusses. GreenBuilding Advisor n50 = 0.36 ach at first attempt
  21. 21. Factory version in Maine Rarely practical to leave access to air barrier up to blower door test. Do it right once. Cars and aeroplanes aren't oozing squirty foam and mastic. insulation air barrier structure plus services plus some insulation allowed Chris Corson EcoCor Maine. Photo Nick Grant “Quality means doing right when no one is looking” Henry Ford
  22. 22. Wind-tightness; same idea Very fiddly, lots of tape Wind tight & cheaper to build Some combine airtightness & wind tightness on outside. IMHO jury out on whether this is OK in our climate because of interstitial condensation risk.
  23. 23. Ventilation • Controls relative humidity • beware over ventilation in winter, particularly non domestic • Removes pollutants • will always be present whatever the building is made of • Removes excess heat • reports of stuffiness are usually due to high temperature not poor air quality • ventilation is not a good solution to excessive IHGs and solar gain
  24. 24. Natural is best? • Natural Ventilation is a misnomer - random leaks or manual • Good control requires some motive force greater than varying wind and stack effect, i.e. a fan (3-10W per person for a house) • We previously assumed natural in summer and mechanical in winter is good but find windows left shut in summer, noise, rain, insects, fear of intruders, drafts etc. Result - worse indoor air quality in summer than winter. • Humans are not good at sensing air quality and RH. Free download: katedeselincourt.co.uk
  25. 25. Basic ventilation options Option Comfort Health Energy Cost Airtightness Leaky fabric Poor Poor Poor Free N/a* Manual vents Poor Poor Poor Cheap N/a MEV OK OK Medium Inexpensive Tight MVHR Excellent Excellent Good ‘Expensive’ Tight * airtight fabric still required to protect building
  26. 26. QA of ventilation system • MEV probably easiest to get right. • Needs excellent airtightness to ensure good air quality and comfort • Sound - fans often turned off because of noise but getting better • MVHR most challenging • Sizing, important not to over ventilate • Duct design • Cold duct insulation • Balancing • Sound - fans often turned off because of noise - not a problem with quality kit Passivhaus Standard includes best practice MVHR design and commissioning
  27. 27. Learning from Passivhaus MVHR No need to reinvent the wheel Beds Living Circ' Bath/kitchen e.g. cascade approach to avoid over ventilation
  28. 28. Conclusions • Leaky building leads to poor air quality, poor comfort and waste of energy • We need controlled ventilation for health of building and occupants - even if the building is not airtight • This needs to be designed and installed correctly, no easy answers • ‘Natural ventilation’ = more nature, mould dust mites etc © Nick Grant; Elemental Solutions @ecominimalnick
  29. 29. Learn More www.passivhaustrust.org.uk

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