Based around the principles of the International Thermal Comfort Standard ISO 7730, Passive House aims to provide year-round optimal thermal comfort and minimum energy consumption. Compared to buildings of “standard” construction, a Passive House building will consume up to 90% less energy in operation for heating, cooling and ventilation needs.

The history of the Passive House concept goes back to 1992, when Dr Wolfgang Feist and his team opened the first Passive House in the German city of Darmstadt Kranichstein. This initial project was specifically focused on maximising the full potential for passive design initiatives, resolving the fundamental building physics of dwelling design to achieve high levels of thermal comfort and minimal energy consumption. This included optimal orientation, high levels of insulation, high performance glazing and shading, a fully airtight construction and mechanical ventilation with heat recovery. The Darmstadt Passive House and Dr Feist’s seminal work was a response to identified weaknesses in the approach to design and construction at the time.

Since this pioneering research project, the Passive House design principles have been further refined and developed into the current Passive House standard (Version 9, 2015), administered by the Passive House Institute, Germany.

Passive House is both a quantitative and qualitative design standard. Fundamentally, to be deemed to have met the Passive House requirements, a building must:

  • Demonstrate significantly minimised demands for heating and cooling (annual energy consumption or overall peak load), through design modelling (theoretical, not physical);
  • Achieve very high levels of airtightness, demonstrated through physical testing of the envelop; and
  • Demonstrate significantly reduced “Primary Energy” consumption associated with whole-of-building energy use inclusive of heating and cooling and all other energy consuming demands (e.g. lighting, domestic hot water, equipment, etc.). Primary energy is the recoverable energy contained within a fuel source (e.g. the convertible chemical energy contained in coal or natural gas).

Heating and cooling energy demands (and peak loads) are reduced through the accurate balancing of energy gains and losses; fabric heat flows, glazing and solar gains, and some building services aspects. This balancing is in context of the location and climate of the site, accounting for solar irradiation and ambient temperatures, and their changes throughout a year. In most climates the reduction of energy demands and peak loads is achieved through high levels of insulation within the thermal envelope and very high performance glazing systems, typically necessitating high-performance double glazing and potentially triple glazing systems.

Airtightness performance is achieved through meticulous planning of the envelope, inclusion of technically advanced membrane products, strict attention to sealing provisions and verification of performance through physical “blower door” testing. The exceptionally low infiltration rates exhibited by Passive House buildings necessitate the use of mechanical ventilation systems to maintain adequate indoor air quality. Consequently, the need to balance energy gains and losses is such that air-to-air heat recovery is required within the mechanical ventilation system to recover energy expended for either heating or cooling (pending season and climate).

Whole building energy consumption and primary energy demand are reduced through the production of the above envelope attributes, the selection of efficient heating and cooling systems and stringent energy efficiency performance requirements for all other energy consuming systems and appliances. The metric of primary energy is used to accurately distinguish the net impact of dwelling across different regions and countries; higher energy efficiency is required of those dwellings which are reliant on energy sources with inefficient use of primary energy (e.g. electricity generated from brown coal vs. natural gas vs. nuclear). This is generally calculated using conversion factors predetermined by the Passive House Institute for specific countries or regions.

The calculations required for understanding the heat balance and whole building energy consumption are completed using the Passive House Planning Package (PHPP). The PHPP is a simple yet comprehensive Microsoft Excel-based spreadsheet which provides for entry of all parameters of the thermal envelope design, proposed building services and associated equipment and appliances. Its origins in Central Europe often see it regarded as a standard applicable only to cold climates, however the Passive House standard has been proven as a reliable design standard for all climate zones, including very hot and humid climates.

The results calculated using the PHPP are absolute (e.g. kWh/m2, W/m2), not relative (e.g. percentage reductions from reference baselines). Minimum criteria to meet the Passive House standard can be modified (with permission of the Passive House Institute) based on the climate in which the standard is being applied. Modification of the core Passive House criteria are generally only reserved for the most severe cooling climates with significant latent dehumidification demands.

In comparison, severe heating climates (e.g. high-altitude or arctic locations) where solar, occupant, and equipment gains are complementary to maintaining thermal comfort, are not afforded flexibility in core Passive House criteria pertaining to annual energy demands and peak loads. Airtightness targets are also not adjusted on account of the climate; the same airtightness targets are applied regardless of the global location.

Passive House is a design standard with a predominant focus on the building thermal envelope and is an energy efficiency standard in its purest form.

Compensation of less than ideal thermal envelope performance through renewable energy production to achieve energy targets, for example, is not permitted for certification; a Passive House must achieve the core objectives of optimisation of energy efficient thermal comfort without offset through on-site renewable energy production.

Being predominantly focused on the building thermal envelope, aspects of the implementation and adoption of the Passive House standard are inextricably linked to climate. In regions with deep and prolonged periods of heating or cooling, where heating/cooling energy demands make up a significant portion of total annual energy, the Passive House standard is readily adopted for its defined benefits of energy savings and thermal comfort. In many regions of Central and Northern Europe, Ireland, the UK, Scandinavia and cold North American regions (Canada, Northern US states and Alaska) local building regulations reflect elements (to differing degrees) common with the Passive House standard.

In benign and temperate climates, although easier to achieve the absolute Passive House targets, the key benefits of thermal comfort or energy savings, are less pronounced, although nonetheless important. Within these regions, local building regulations are unlikely to reflect aspects of the Passive House standard, with the implications of the standard representing a significant departure from generally accepted and familiar practices.

Umow Lai was one of the first commercial consultancies in the Australian market to promote the Passive House Design Standard and our staff were deeply involved in the establishment of the Australian Passive House Association.

Our defining advantage is our integrated approach to projects with our Certified Passive House Consultants working closely with our Building Services Engineers to realise the full potential of Passive House and the energy, thermal comfort and indoor air quality benefits. Our willingness to challenge conventional practice is also highly valuable, with the Passive House concept challenging traditional building and services design.

We have successfully applied our Passive House expertise on a number of local and international projects including small modular housing, luxury residential projects with uncompromised contemporary Australian architecture, and large commercial/institutional/education projects.