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