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Is Passivhaus a step too far? South Pacific Passive House Conference Auckland 2015

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Is the Passivhaus standard too extreme for a mild climate such as New Zealand? Do we really need to do all the modelling and calculations if we max out the insulation and air tightness? Nick Grant's first presentation at the first South Pacific Passive House Conference in Auckland aims to explore these questions.

Published in: Design

Is Passivhaus a step too far? South Pacific Passive House Conference Auckland 2015

  1. 1. 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. 2. 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.
  3. 3. Our Self Build Best 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.
  4. 4. 1.3 ach without tapes or membranes 100mm EPS considered extreme! Thermal bridge free foundation slab DIY roof trusses
  5. 5. Built by a Sheila Images Nick Grant
  6. 6. Image Nick Grant
  7. 7. Image Nick Grant
  8. 8. Drawn; Jon Broome The Green Self Build Book Basic construction proved sound and has formed the basis for many projects since: Almost a Passivhaus? A pretty good house?
  9. 9. Retrospective PHPP Missed 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 
  10. 10. 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?
  11. 11. Why Passivhaus? • Is the 10 W/m2 or 15 kWh/(m2.a) arbitrary?
  12. 12. 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.”
  13. 13. Are we tunnelling through the cost-benefit barrier? Passive House Design, Gonzalo & Vallentin ?
  14. 14. 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.
  15. 15. 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:
  16. 16. 16 Via Graham Irwin, Inhabit
  17. 17. 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
  18. 18. It can stop us making expensive mistakes over and over! Image Nick Grant
  19. 19. 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:
  20. 20. 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
  21. 21. Hereford Archive & Records Centre A very Eco-Minimal passive approach Image Nick Grant
  22. 22. Key design strategy: Office isolated from cooler repository 22°C this side all year 14°C this side is ideal Image Nick Grant
  23. 23. 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
  24. 24. Image Juraj Mikurcik Architype Usual construction but masonry load bearing inner
  25. 25. Initial blower door test: 3,532m3 over 3 floors. C ring too big (85cfm min). <0.04 ach @ 100Pa Final test with duct blaster! Great airtightness details developed with contractor – their first Passivhaus Image Nick Grant
  26. 26. Image Nick Grant
  27. 27. 27Image Nick Grant
  28. 28. Simplicity; a hard discipline Archive repository fresh air supply, what we planned: DX cooling for summer dehumidification small fan filter
  29. 29. Simplicity; a hard discipline Archive repository fresh air supply, what we got:
  30. 30. Self build ‘Passivhaus’ guitar making workshop for retired Architect Image Nick Grant
  31. 31. Quick check in PHPP, just incase! • 7.7m2 • 107kWh/m2.a?? • Form factor 8.8 (Heat loss area/TFA, <3 is good)
  32. 32. Gains/m2 high It works! Image Nick Grant
  33. 33. 34 Paper and article available on www.elementalsoutions.co.uk
  34. 34. Why Not Passivhaus? Crossover climates/lifestyles But what if we need to keep out the dust? Laurie Baker, Kerala
  35. 35. 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
  36. 36. 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

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