Airtightness trends in New Zealand homes and apartments, what...
Transcript of Airtightness trends in New Zealand homes and apartments, what...
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Airtightness trends in New Zealand homes and apartments, what are we achieving, and how can we balance the ventilation needsSteve McNeil
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Why worry about airtightness?
One component to providing warm, dry and healthy buildings is a reduction of energy use
By increasing insulation, and reducing air leaks, we can make significant progress from current code settings
It also allows better control of ventilation
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NZ Building Code and energy performance
30,000
20,000
-0
10,000
Un-insulated, single glazing
Towards zero heating Casual and
solar gains RoofWalls Floor
Glazing
Ventilation
Win
ter
he
at lo
ss –
kWh
@ 1
8 C
Insulated, single glazing
Insulated, double glazing
Ro
of
Walls
Floo
rG
lazing
Ve
ntilatio
n
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Airtightness trends - Residential
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Pre 1960 60-69 70-79 80-89 90-99 2000-2009 2010+
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What about apartments?
• Airtightness of apartments project aiming to find this out.
• Preliminary results for new apartments are similar to modern homes 2-3 ACH@50Pa common
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Energy is only one part of the puzzle though
Insulation, heating and ventilation all need to be considered
Good IAQ and comfort needs a balance between each of these three components
Source management particularly important for moisture
“Build tight – ventilate right”
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Impact of increasing airtightness
• Energy outcome is good
• Ventilation (G4) has not moved with the trend though
• Reliance on occupants to open windows…
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Perfluorocarbon Tracer Study
• Activated carbon samplers
• 4 Rooms
• 3-4 week exposure
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Airtightness trends - Residential
0
5
10
15
20
25
30
35
40
45
Pre 1960 60-69 70-79 80-89 90-99 2000-2009 2010+
AC
H @
50
Pa
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ACH @ 50 Pa
Survey Results, with calculated infiltration (from WAVE)
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Air ch
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Measured ventilation ratesVentilation Rate
EstimatedInfiltration from blower door
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A different metric?
• Plenty of confusion
N50 result is NOT the average infiltration for a building
/20 ‘rule of thumb’ to convert
But…
Closer to /40 for airtightness of 4ach@50Pa
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Infiltration rates with airtightness – benchmarked
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Envelope permeability instead?
• m3/hr/m2@50Pa
• Becomes a property of the surface of the building, so we can treat it like R-value, U-value
• Takes away the confusion converting n50
• Has a positive impact for larger buildings – surface area to volume ratios in these buildings makes n50 targets easier to meet
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Regardless of the metric…
• More guidance needed for ventilation
• We cant leave it to be an afterthought
• Industry practice needs to improve…
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Where to now?
• New builds, not much more effort needed, just education about continuity.. (particularly for more interesting buildings)
• “Build tight – ventilate right”
• Older building retrofit?
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Potential leaks sealed
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Model Buildings
What is the project?
• The project comprises experimental and simulation activities to support the next generation of the building code. The work packages address a number of questions in the Warmer, Drier,
Healthier Buildings and Exceeding the Minimum programmes.