The limitations of PassivHaus, does less electricity actually mean green?

As it stands, residential buildings are responsible for around 10 per cent of Australia’s total energy consumption. And yet, despite a general unwillingness from the majority of the public to adopt more holistic approaches to sustainable housing, the residential sector’s fraction of the nation’s energy glut is actually decreasing.

The Australian Government’s 2015 ‘Australian Energy Update’ report suggests that this has been in response to higher electricity prices—not necessarily because consumers (and designers) are becoming more active in the sustainable building movement.

A recent research paper by PRDnationwide’s National Research Manager, Dr Diaswati Mardiasmo all but confirms this inference. Mardiasmo explains that the delivery rate of sustainable housing is below expectations due to the dearth of clear information being absorbed by the public about their many features and benefits. Basically, explains Mardiasmo, stakeholders are hesitant to add certain ‘green features’ to their houses because they either don’t know about them or don’t see the monetary benefit they bring to the home.

The major drain on residential energy consumption is space conditioning which is currently the largest energy user in the average Australian home, accounting for around 40 per cent of the sector’s energy consumption, and is only becoming more popular.

But in light of the growing price of electricity, using renewable energy sources and low-energy appliances to lower a home’s energy bill does give the designer at least one tangible way to sell ‘green building’ to the consumer. The question is though, does less electricity actually mean green?

SELLING ENERGY EFFICIENCY IS VIABLE

One type of housing design dedicated to limiting the energy consumption of residential buildings is the German-born PassivHaus Standard (Passive House) which, in short, targets both superior energy efficiency and thermal comfort for a home.

Certified Passive Houses focus on significantly reducing the space heating demand of the home to lower than 15kWh/sqm per year and also imposes that the overall primary operational energy consumption should be lower than 120 kWh/sqm per year. This is mainly achieved through a super-sealed and insulated building envelope which allows a maximum air leakage equivalent to 0.6 air changes per hour at 50 Pascals (ACH50).

The building materials and methods of construction used to achieve Passive House certification are uncommon in Australia and, reportedly, more costly, but estimates are that Passive Houses will use 75-90 per cent less energy than a typical building.

The secondary goal of Passive Houses is to ensure the building has good indoor air quality, and it might please Australians to know that if they choose Passive House they can actually keep their beloved air-conditioners, or at least a version of it. Passive Houses generally use either a sophisticated heat-recovery or energy-recovery ventilation system for air conditioning which employ a cross flow heat exchanger between the air coming into the building and the outbound air flow to keep the internal temperatures stable and fresh air circulation constant.

Other building materials such as double or triple glazed windows with thermally broken frames and high levels of insulation are also standard with Passive Houses but not necessarily the norm in Australia.  German-born Passive House builder, Bernward Buchler claims that there is a real shortage of appropriate and affordable Australian-made products suitable for Passive House construction, so much so that he also sells imported double and triple glazed windows and doors from Germany.

But Buchler’s comments came over a year ago following his completion of Australia’s first Passive House with Max Pritchard Architect. Since then more Australian Passive Houses are popping up around the country and they’re being made (predominantly) with Australian building materials.

OPERATIONAL VERSUS LIFE CYCLE ENERGY DEMAND

Creating Passive Houses from Australian materials is significant because it can help lower the embodied energy of the building, which, according to Robert H. Crawford and Andre Stephan of the University of Melbourne, is one of the shortfalls of the Passive House standard.

Their 2013 research paper, The Significance of Embodied Energy in Certified Passive Houses, actually shows that certified passive houses do not always result in net energy savings compared to less energy efficient buildings.

Their research methodology, which measured the life cycle energy demand of a building rather than the just its operational energy, showed that a standard house with the same geometry, structure, finishes, and number of occupants can actually have a lower life cycle energy demand than a Passive House building.

“The additional materials required in a passive house, combined with the choice of energy source have a significant impact on their total energy demand,” reads the paper’s conclusion.

“Current European building energy certifications and regulations, which focus mainly on space heating and operational energy aspects, do not necessarily result in a lower overall energy consumption.”

“If the aim of these regulations and schemes is to reduce energy consumption and associated greenhouse gas emissions, these instruments must adopt wider system boundaries, including the embodied energy in building materials.”

THE CHALLENGE

The operational energy performance of a Passive House could be considered a valuable commodity in the contemporary climate where electricity prices are climbing and consumers are constantly looking at new ways to cut their energy bills or to relocate to more energy efficient homes. Another bonus is that they’re also (reportedly) very comfortable to live in – also a tangible way to sell a building and one of the major factors of consideration for those renovating, building or buying a home.

On the other hand, selling a building based on its life cycle energy is more difficult as it’s less visible, measurable and understandable. Perhaps it takes a special type of client, with knowledge of its benefits to the environment, to want to buy or build these types of residences. For Dr Mardiasmo at least, the answer is educating the consumer, something building designers are in a great position to do.

[AD]

Submit a Comment

Your email address will not be published. Required fields are marked *