is passivhaus a step too far? south pacific passive house conference auckland 2015
TRANSCRIPT
Passivhaus, a step too far?Isn’t pretty good, good enough?
Inaugural South Pacific Passive House Conference
Auckland 2015
Nick Grant
Elemental Solutions
UK Passivhaus Trust
@ecominimalnick
2 common criticisms
• It’s not economic in our mild UK/ Californian/New Zealand/Australian climate.
• It’s not economic in our cold Swedish/ Maine/Russian climate.
Our Self BuildBest Practice Assumptions 1995 (Year 12BP -
UK)• Straw cheap and excellent U value.
• If maxing U values no point in modelling energy
• Wood is a cheap zero carbon fuel (just don’t want to spend every weekend cutting it).
• Use natural vent, crazy using electricity to save firewood with HRV.
• Double glazing had similar U value to Triple.
• Install windows in plane of rain screen for robust water tightness, must open out.
• Need a porch and sun space as buffer zones.
1.3 ach without tapes or membranes
100mm EPS considered extreme!
Thermal bridge free foundation slab
DIY roof trusses
Built by a Sheila
Images Nick Grant
Image Nick Grant
Image Nick Grant
Drawn; Jon BroomeThe Green Self Build Book
Basic construction proved sound and has formed the basis for many projects since:
Almost a Passivhaus?A pretty good house?
Retrospective PHPPMissed Passivhaus by a factor of 6!
• 91kWh/(m2.a) v 15 PH target!
• Form factor about 5
• Bump-outs shade the windows in winter.
• No HRV
• High spec’ double glazing in plane of rain screen
EnerPHit with PH components?• Same energy use as now but better comfort.
• EnerPHit refurb £50k? House cost us £40k to build
• Crippled by poor form factor (about 5)
before After EnerPHit?
Why Passivhaus?
• Is the 10 W/m2 or 15 kWh/(m2.a) arbitrary?
Physics definition
“A Passive House is a building, for which thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air, which is required to achieve sufficient indoor air quality – without the need for additional recirculation of air.”
Are we tunnelling through the cost-benefit barrier?
Passive House Design, Gonzalo & Vallentin
?
Supply air heating?
• In the UK it costs more– Special fan coil– Buffer to stop tank-less heater cycling– Doesn’t work with simpler cascade vent approach– Ducts need insulating - cost & space– Still need towel rail circuit unless electric
• Not good for large houses and non domestic• Complicated to make some rooms warmer or cooler• Extra heat tends to go upstairs• Weather data & design critical . . . . etc.
So Why 10W/m2 –15kWh/(m2.a)
• Inspired by a brilliant thought experiment that changed the industry
• It works and seems about right!
• If you don’t aim for something, you’ll fall for anything – a slippery slope
• We don’t have to decide the optimum standard for every component on every job
• It is easier to hit a target that isn’t moving
• It forces us to do sensible things:
16Via Graham Irwin, Inhabit
The real savings of going far enough• Forces us to radically simplify
– We can’t just add some insulation & better windows
• Forces us to sort the form factor
• Forces us to consider fenestration carefully
• Forces us to design for airtightness- We can’t just spend more time chasing leaks
• Forces us to prioritise what we spend the budget on
• Simplifies controls
• Simplifies heat distribution
• Guarantees comfort and air quality
• Avoids the ‘comfort take’ rebound effect
It can stop us making expensive mistakes over and over!
Image Nick Grant
Non-Standard Buildings
“A Passive House is a building, for which thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air, which is required to achieve sufficient indoor air quality – without the need for additional recirculation of air.”
Once again:
Non-Standard Buildings
• Archive - insufficient ventilation to deliver the required heat or cooling
• Schools & offices - much more ventilation/m2 but vent & heat out of sync’
• Care homes etc much higher gains
• Tiny buildings, poor form factor, high gains
Hereford Archive & Records CentreA very Eco-Minimal passive approach
Image Nick Grant
Key design strategy:Office isolated from cooler
repository
22°C this side all year
14°C this side is ideal
Image Nick Grant
Energy balance using PHPP
• Simplest form• Low IHGs 0.6W/m2
• c.a. 1 air change/day• No HRV• RH 40-60%• RH buffering by contents• Temp 14°C-20°C• No cooling• Supply air dehumidification• Inspired by Tim Padfield
www.conservationphysics.org
Image Juraj Mikurcik Architype
Usual construction but masonry load bearing inner
Initial blower door test:3,532m3 over 3 floors.C ring too big (85cfm min).
<0.04 ach @ 100PaFinal test with duct blaster!
Great airtightness details developed with contractor – their first Passivhaus
Image Nick Grant
Image Nick Grant
27Image Nick Grant
Simplicity; a hard disciplineArchive repository fresh air supply, what we planned:
DX cooling for summer
dehumidification
small fanfilter
Simplicity; a hard disciplineArchive repository fresh air supply, what we got:
Self build ‘Passivhaus’ guitar making workshop
for retired ArchitectImage Nick Grant
Quick check in PHPP, just incase!• 7.7m2
• 107kWh/m2.a??
• Form factor 8.8 (Heat loss area/TFA, <3 is good)
Gains/m2 highIt works!
Image Nick Grant
34Paper and article available on www.elementalsoutions.co.uk
Why Not Passivhaus?
Crossover climates/lifestyles
But what if we need to keep out the dust?
Laurie Baker, Kerala
Passivhaus Claims
Free download:
www.passivhaustrust.org.uk
Clear & easily verifiable• blower door
• thermography
• PHPP
• components & materials
Trades description• fake goods
• consumer law
• annoys those doing it properly
Conclusions
• The Passivhaus Standard makes us go far enough to get genuine benefits
• Still room for improvement– simplification & improved robustness not more
complication
• Sometimes Passivhaus doesn’t fit and that’s OK– It is not the only option and you don’t have to do it