19th January, 2016 | Clare Parry

A hot topic in Passivhaus circles for nearly as long as the standard has been around, the net effect of building ultra-low energy buildings is again under the spotlight following commentary and presentation of a paper at the Architectural Science Association Conference in Melbourne in December 2015. Attracting more expansive media reporting, this paper (Crawford, et al., 2015) follows, and refers to, a previous study on the embodied energy of a Passivhaus home (Crawford & Stephan, 2013), making sweeping conclusions regarding the pursuit of low-energy construction.

It is widely accepted and communicated by those involved in Passivhaus, as well as the policy makers of the EU, that the target of net zero energy buildings (NZEB) is neither useful for reducing energy use (net or peak) nor an accessible target for most buildings. As a result, the directive for all buildings in the EU is to be nearly zero energy (nZEB), and this is a critical differentiation. “Nearly zero” refers to the inherent performance of the building itself: it requires a well-designed building that in itself demands very little energy input to utilise (i.e. keep cool and/or warm and otherwise operate). Nearly zero is about simplification of design, not throwing technological fixes at a bad idea. Net zero, on the other hand, is a simple exercise for accountants. Regardless of the inherent attributes of the building, it could use all the energy in the world and simply offset this with energy inputs on site. While some might argue the net effect could be the same, it can be a very inefficient use of materials, technology and with no real benefits to infrastructure.

Passivhaus is placed exactly where it is on the cost-energy curve precisely because this is the point at which major heating systems (i.e. a boiler or furnace) are deemed unnecessary, because of the thermal comfort and energy efficiency gained through the approach. Where cost can be attributed to additional materials and effort, so, too, this chart might also indicate the sweet-spot or a similar idealised point in the embodied energy investment for a building, being the point at which operational efficiencies and embodied energy meet a compromise.

Figure 1: Cost-Energy curve for Passivhaus (this version borrowed from ingenius.com 

Key facets of the Passivhaus standard include the provision of a highly insulated and airtight building envelope as well as a significant reduction in overall building energy use, including plug loads. Many other aspects of the standard are misunderstood or mythologised to the point of Chinese whispers. Although airtight, additional efficiencies are gained when natural ventilation is utilised during favourable ambient conditions. The building is constructed to be airtight so that when conditions require it, it can be utilised as such. Would you open the windows for ventilation during a heat wave, or a blizzard? Your Passivhaus is designed to remain efficient during the extremes. With over 50,000 Passivhaus projects in climates ranging from Antarctica to Jakarta, the breadth of solutions has surely been examined.

A continued criticism of the standard is the focus on cutting energy use of a building. A criticism – sounds bizarre? But this originates from detractors who claim it’s too stringent and not relevant for all climate zones.

Designed around the requirements of the international comfort standard ISO 7730 Ergonomics of the Thermal Environment, the standard is, by definition, adaptable, and is also based entirely around local climatic conditions. While it’s true that this standard denotes parameters for which most people are comfortable (using PPD and PMV), as in any building there is scope for accommodating individual comfort levels, within reason. Bedrooms are typically designed to be cooler zones, as most people sleep better in slightly cooler temperatures. Good-practice mechanical services design principles are required, and humidity is removed at the source in kitchens, bathrooms and utilities. The comfort parameters (e.g. temperature, humidity, air volumes) for a classroom in Darwin are not the same as for an office building in Hobart in winter. Adaptability is key to the standard’s success.

The target for the standard originated when one of the founders, Wolfgang Feist, noted that, although building performance requirements were being increased through regulation and ‘better’ design, the actual energy use of buildings was not decreasing.  As a physicist, Feist was ‘offended’ by this contravention of the simple laws of physics. So he made it a mission to find out what the construction industry was getting so wrong. And so was born the Passivhaus standard.

One of the key methods to achieving the standard and improving building performance involves the addition of materials, notably insulation, higher spec windows and airtightness measures (often tapes and membranes). Thus, a key concern becomes one of compromise: for any added embodied energy, is there a quantifiable benefit in the long term?

The Crawford & Stephan study (2013) takes aim fairly and squarely at the Passivhaus standard. As the study notes, embodied energy is not taken into account in the Passivhaus certification, but also that, while the embodied energy of insulation in a Passivhaus is significant, “the insulation material should therefore be carefully chosen”. Any proponent of holistic sustainable design would agree that it should always be this way. Although, there are many, many ‘eco’ design standards that focus on different key areas, and do not take embodied energy into account; even one of the greenest – the Living Building Challenge – requires a project to offset any embodied energy but does not make any specific call to minimise it (but awareness is a key initial step!).

Figure 2: Seattle’s Bulitt Centre. The expansive canopy of solar panels, along with careful design, makes this building net zero energy (NZEB). Studies suggest that the canopy could have been 35% smaller had the project targeted Passivhaus, a nZEB strategy, as a starting point (although the building makes significant energy contributions to the grid). (image: (c) Nic Lehoux, via Living Futures Institute

It’s clear, though, that a truly ‘sustainable’ Passivhaus building must consider not just the operational energy outcomes, but also the type of construction and the required specification improvements. Highly variable by sector and location, there isn’t a single answer here, and common myths prevail. If you end up with 300mm of insulation or triple glazing in a temperate climate then you have likely over-specified, received poor advice or need to revisit your design. In Victoria, with a swinging climate that sees relatively cool winters of sub-zero mornings and summers with scorching heights of up to 45°C, RT4 walls and carefully selected double glazing is likely sufficient. But, as any building designer will understand, it’s all about clever use of your palette. If you must make a glass box, then it’s likely you’ll find you will struggle with Building Code compliance let alone Passivhaus, and triple glazing could be your burden. You’ll also most likely need extensive shading and/or other complex solar control measures. It’s not uncommon for newly designed commercial buildings to utilise glass with effective SHGC down to 0.2, potentially including treatments such as a frit, because they simply must be fully glazed. [At a guess there is some miscommunication between client, architect and/or developer as to what a premium client requires these days, but the message is sold as one of luxury and sophistication. Never mind the post-occupancy complaints regarding glare and discomfort, the exorbitant energy bills and/or the maintenance on technical control systems. But I digress.]

Mention Passivhaus to almost anyone, and they will immediately assume that triple glazing is compulsory. While it’s true that this is a common theme in European projects, it’s rare for them to be required in Australian projects. The Crawford study utilising triple glazed, argon filled windows (U-value 0.6 W/m2K) to contribute to the thermal performance of the home, which might have been necessary for this particular design in the Belgian climate. On local projects, a Passivhaus Designer would assist the architect to either rationalise the window placement or size, to reduce the need for such expensive and difficult to source products. Certainly in Australia, these windows would have been prohibitively expensive for most projects, and most would ultimately have been imported from European manufacturers.

A further key point is the technology selected to provide that residual heating or cooling load. The Crawford study replaces a gas boiler with an electric in-line duct heater. With the ‘standard’ house already quite energy efficient, as per local requirements in Belgium, the replaced heater was already perhaps quite small. Further, by its very nature, the electric heater’s greenhouse gas emissions, per kWh, are much larger just because of the selected fuel. It’s also unclear as to whether the study includes fugitive emissions of gas fuel (those lost in transit to site), said to be up to 10%. Heat pumps can provide low intensity heating and also provide hot water, and can also be coupled with solar thermal or photovoltaic to further reduce electricity use

The study also directly compared two versions of a single home design, making modifications to achieve both what was considered ‘typical’ for the considered region (Belgium) and to achieve the Passivhaus standard. While it is possible to adapt almost any design to the standard, more compact designs achieve better results, and, at 330m2 floor area for a four person home (2 adults, 2 children), the home cannot be considered ‘compact’. Sadly, though, it’s probably quite typical of many Australian homes.  

A further reduction in life-cycle embodied energy is the maintenance and durability impacts of designing to the Passivhaus standard. There is limited real-world data around this, save for the original Passivhaus in Darmstadt, Germany. These buildings are designed for longevity, carefully considered to eliminate condensation and mould, usurping issues like rot and degradation of the materials hidden within the construction. By extension, the homes are more durable and less likely to require replacement of materials and, perhaps ultimately, demolition and replacement. If we consider current building practices, it is likely that many buildings being constructed today and including those in the recent past (20 years) would not survive the requisite 80 years as noted in most LCA studies; horror stories from volume builders include those regarding homes that require rebuild in under 10 years. By contrast, a Passivhaus building should survive many decades without the routine degradation or damage, save for extremes. The main items requiring replacement or maintenance are active systems including the ventilation unit, as well as typical considerations such as kitchens, bathrooms, air conditioners (where used) and domestic hot water heaters.

But – let’s be blunt – what are the shortcomings of the Passivhaus standard? Usually they are project specific. For example, projects including commercial kitchens can be complex, and historic or otherwise sensitive retrofits often just cannot accommodate the requirements, even using the EnerPHit standard. And both examples would often do not survive the “value management” process. Additional costs for Passivhaus buildings can spiral out of control, particularly where not utilising the expertise of an experienced designer or builder. And speaking to suppliers, even Australian arms of experienced European suppliers, can feel like hitting a brick wall.

Passivhaus allows a large degree of flexibility in how the standard is delivered. Just three criteria – heating/cooling demand or load, airtightness and total primary energy demand – are stipulated. How you get there is up to you. Perhaps this is where a great number of arguments might start – including the one about embodied energy! – but this is perhaps one of the standards strengths.

One of the biggest headaches for most local projects is the design team. One weak link – an unwilling builder, a reluctant engineer, a short-sighted investor or an ill-informed client – can make the whole process painful or impossible. It’s typically easier not to engage in such a process, with the best ways to drive change being to engage with an enthusiastic team (led by a willing architect), and the best way to answer any critics is to deliver successful projects.

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