Passivhaus – Unravelling the Numbers 3

Tuesday, April 19th, 2016
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It’s not uncommon for those in the Passivhaus world to get into heated discussions around the detailed concepts covered by the standard, whether it can be applied the world over or whether it works at all.

Discussion abounds over how it delivers real comfort and real savings, alongside real benefits for health and well-being. But many discussions start on less than equal footing, with many misconceptions about the standard. Here are a few great ones:

Passivhaus is an energy standard

Right out of the box, this is one of the biggest misconceptions of the standard; that it was created purely for saving energy. Not true! The fundamental basis of Passivhaus is the international thermal comfort standard ISO 7730 Ergonomics of the Thermal Environment, or thermal comfort. What are buildings for again? Oh, that’s right – people!

Passivhaus is just another tool; throw it in the basket with the rest of them

Passivhaus isn’t a system or a tool “invented” by anyone – in fact, the Passivhaus principle was discovered. Passivhaus has evolved from the study of existing buildings and great practices used across many hundreds of years when complex systems for comfort just weren’t available. Centuries of experience – can’t beat that.

The stated 120kWh/m2 per annum is a huge amount for an energy allowance! Particularly when, on a domestic scale, you compare to NatHERS.

Yes, it is! I have two points here though:

  1. This is the total energy use for the WHOLE building, not just HVAC – computers, lights, heater, ventilation system, TV, kettle, phone charger, fridge and so on.
  2. The calculation for energy use in Passivhaus is primary energy. This means it takes into account the amount of energy back at the source (i.e. primary), which is what the 120 refers to. For Victoria, this is brown coal, for Tassie it’s hydro or diesel generators or Victoria’s brown coal (or whatever the balance is at time of writing.) Plus, it includes all the inefficiencies and losses to produce and transport that energy to the point of use. Generally, the accepted calculation is to divide by 2.6 (the primary energy factor) meaning that the energy allowance at the building is more like 46kWh/m2 per annum. This figure is tougher to achieve!

The primary energy factor used in past versions of the PHPP calculation has been directly transplanted from Europe and this generally works in our favour, particularly in areas where we burn coal as our primary source. With the release of the new PHPP version 9 and Passivhaus certifications – Plus and Premium – projects now need to get the regional primary energy factor approved before certification. In this way, the calculation is more accurate, and the Passivhaus standard is more locally relevant. Additionally, the standard seeks advancement in the decarbonisation of the local electricity grid. An aspirational objective.

15kWh/m2 per annum is a lot for heating or cooling

The standard is targeted at a ‘sweet spot’ for energy efficiency versus increased capital investment. This is the point at which you can begin to make drastic changes to the size and type of HVAC systems you put in but any further would require complex technological fixes or extreme building envelopes. The standard of 15kWh/m2 equates to roughly 8 Star NatHERS in Melbourne, and how many dwellings achieve this, in modeling or (more importantly) in practice? Passivhaus is an as-built standard which is a key selling point.

Passivhaus costs more – lots more

This one is a grey area, but suffice it to say, it shouldn’t cost considerably more. While it is anticipated that building to the standard might cost more for early adopters, it’s tricky to say how much.

Locally, leading projects have been at the bespoke or luxury end of the market, and so the figures could be skewed anyway. And you could argue that, in Australia, we are starting from a low base with which to compare. Windows are generally the biggest additional cost element, along with added “risk factor” from builders and their view that this is going to be a significant undertaking.

Long-term data from Europe shows that Passivhaus can be achieved for around three to eight per cent more than standard building practices. But as the minimum compliance standard increases and the market adjusts, it can be cost neutral and often cheaper to build Passsivhaus. That’s right – cheaper! Why? Because you can reduce the size of necessary HVAC systems (plant and ducting) and potentially also give plant space back as occupiable area. Passivhaus should appeal most to those who retain interest in a building long-term, with ongoing savings adding directly to the bottom line. And that’s not even considering the lower vacancy rates and potentially higher rents due to more desirable space.

And the local tide is turning. There are now a number of projects in Australia targeting Passivhaus at no additional cost, including those on large scale (multi-unit residential) and single dwellings.

Passivhaus hasn’t evolved with the times

Recent criticism leveled at the standard took a jab at the fact that the metrics to achieve Passivhaus haven’t moved since its inception. Far from being a static tool, the calculation tool behind Passivhaus, the PHPP, is now up to version 9, and there is now a SketchUp plugin that enables users to work from 3D models with PHPP interoperability.

The PHPP also provides peak heating and cooling loads for sizing mechanical systems and, while most modeling protocols suffer a sizeable performance gap (up to 250 per cent), the PHPP has remained one of the most accurate tools for predicting actual in-use energy consumption on the planet (within 0.5 per cent.)

The standard also evolved to better suit retrofit projects with EnerPHit, and there are now Passivhaus Plus and Premium certifications to reward on-site energy production and net positive energy buildings. The standard has now also been successfully implemented across a huge range of building typologies and construction systems. The key criteria remain largely unchanged because they are indeed simple building directives, with a large degree of flexibility in how to achieve them. This is a key strength of the standard.

It isn’t suitable for hot climates

“American molecules and atoms are different to those in the rest of the world.” A stinging barb from Bronwyn Barry, co-chair of the North American Passive House Network, when highlighting how this same argument plays out in the USA.

The Passivhaus standard is based on building physics, and there’s nothing more universal than heat transfer. The Passivhaus standard did originate in the cold climes of Germany, but its evolution was on a global scale. The founders, Bo Adamson in particular, travelled the globe and researched the effects of different building strategies and practices across the ages in many climates, including Scandinavia, the Middle East and China.

Hot climates were common themes, and the absence of cooling even in these climates was just a necessity due to available technology; thus, strategies excluding heat dominated.

There are now a number of Passivhaus dwellings in operation in Australia, including in climates where it gets quite hot, such as Castlemaine, Canberra and Adelaide. While early data is limited, anecdotal feedback from occupants is very positive.

So what’s great about Passivhaus?

It simplifies the design. Being a fabric-first approach, the standard short-circuits the usual approach of taking a poorly designed building and throwing technology at it to make it work. The systems required to keep a Passivhaus building comfortable are simpler and less energy-intensive to run, and are often cheaper due to the reduction in air-conditioning loads and associated reticulation.

What’s not to love? Feel free to feed the discussion!

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  1. Barry B.

    I have nothing against Passivhaus, but feel a proliferation of multiple standards is a confusing thing for the market – a given jurisdiction should do its best to have a single standard which encompasses all aspects of building efficiency and energy performance.

  2. Jim D

    We are designing and building a net zero energy home with passive house infiltration standards in a Michigan climate. The passive house target is difficult to meet without building a rectangular box, long axis south with most windows on the south side. Though this can be elegant it is also aesthetically limiting. The PHPP and PHIUS standards do not measure actual performance but only computer modeled performance. Actual performance is more important than modeled performance. Many passive house owners add to square footage, outbuildings, additional appliances, etc… after certification. What good is that? These certifications are expensive and have not kept up with the falling prices of on site power generation and storage (solar, wind, batteries). Don't waste your money on certification. Design your home for your needs anticipating the rapidly evolving energy generation and storage technology. Design for growing some of your own food. Design for aging in place (not typical of the vertical nature of passive homes). Design for aesthetics that make you feel good every day. These are more important Pattern Language principles. Also remember pictures always look pretty even if they may not function well. Describe and write out your behavioral sequences; they will inform your design. Some of these new standards are just in it for the money. If we are really serious about green building, we would significantly and rapidly change the international building code not create alternative certifications.

    • Jean SmilingCoyote

      What a pleasant surprise to see your mention of Pattern Language principles! A major problem I have with Passivhaus for regions which have a High Risk of Extreme Winds per FEMA 320 (in the USA), is that the requirements for the building envelope which I want to resist an EF3 tornado, are hard to reconcile with Passivhaus design. Of course, Germany doesn't have a big tornado risk. In general, we agree that there are many values that one might well want to include into the design and construction of a house. Some are functionality, extreme-wind resistance, hail protection, fire protection, handicapped-accessibility… One of my values is to minimize the use of matter and energy. Jim, I don't know exactly where you are doing this project in Michigan, but suggest you check FEMA 320 and see if Uncle Sam thinks you should include a "safe room" for extreme-wind protection.