Increasing awareness of energy efficiency and climate change has led to new developments in the building sector, including the concept of passive house, low carbon buildings, and even zero emission buildings. Low carbon houses and zero emission buildings achieve their common objectives by applying all available green design techniques, strategies and technologies. Due to this broad definition, a building can be considered as low carbon or zero emission by installing onsite renewable energy technologies, or simply by tapping into off-site zero emission energy sources, such as hydro, wind farms, etc. (Torcellini, 2006). On the other hand, the concept of passive house focuses on the energy efficiency aspect of the building. Passive house takes the conventional passive solar building design principles as a starting point and combines them with an air-tight and well insulated building envelope to derive very low energy buildings. The heating requirement for passive house buildings is targeted to be as low as 15kWh/m2/year in Germany, compared to 250kWh/m2/year to heat an average apartment there. The Passive House Institute defines a passive house as “a building in which a comfortable interior climate can be maintained without active heating and cooling systems” (Passive House Institute, 2010).
A typical passive house is a well-insulated and highly air-tight building, with stringent design and construction standards. It is primarily heated by passive solar and other internal heat gains, and equipped with an energy recovery ventilator for a constant and balanced fresh air supply.
As a starting point, passive house design addresses and exploits elements from the building’s surrounding context (e.g., land form, sun, wind, rain, vegetation, etc.) and organises the interior of the building to maximise energy savings and indoor environment quality. In addition, passive house design and technologies have to address the following:
- Excellent insulation: the insulation standards are very stringent in order to limit thermal loss through conductivity and radiation.
- Air-tight construction: in order to complement and not deplete the insulation performance, air-tight construction is required to limit thermal losses through direct air flow between indoors and outdoors.
- Ventilation with heat recovery: with air-tight construction, operable windows are not favoured as they have great potential for thermal loss. Fresh air intake for ventilation is instead taken from energy-and-heat recovery ventilators, which transfer the thermal energy from discharged air to incoming fresh air to make the temperature of incoming air close to that of the indoor air temperature. An additional opportunity exists to channel incoming air through ducts buried underground. The constant earth temperature, which is often warmer in the winter and cooler in the summer, helps pre-heat/pre-cool the incoming air. The process is also known as subsoilheat exchange. Afterward, the pre-heat/pre-cool air will go through the above mentioned heatrecovery process (Feist, 2005).
Passive house design and technologies are most appropriate for temperate climate conditions, such as Europe and North America. Although the concept of passive house has been expanded to other climatic regions, the principles of air-tight construction and super-insulation are still being debated, especially their application in warmer climatic conditions. The following application requirements are discussed within the proven application parameter in temperate climatic context, which is where passive house design technologies were originally developed.
In order to achieve its objectives, a passive house has to first deploy all design strategies to meet climate responsive design principles. The key principles are:
- Good orientation: to respond positively to land form, sun path and seasonal prevailing wind directions.
- Self shading design: where windows or glazing areas are exposed to hot afternoon sun, they should be shaded by other components of the buildings, such as balconies above, planter boxes, roof overhang, or sun-shading devices.
- Compact form: to reduce building envelope area and thus heat loss.
- Spatial organisation: to locate less habitable areas, e.g., storeroom and bathroom, on the western side of the building to act as additional thermal buffer; and to expose living room with glazing/window toward the south for sunlight accessibility.
In addition to the above, some application requirements to achieve the key passive house standards are:
- Insulation: besides providing sufficient insulation in the building envelope, it is important to pay attention to prevent thermal bridges through weak areas by using a triple glazing system for windows, careful construction details at joints between floor slab and walls, walls and window frame, the window frame itself, wall to ceiling, and roof construction.
- Air-tight construction: operable windows and doors should be detailed with air-tight construction, especially along the edges of door and window panels. As a guide, these unsealed joints should have air leakage of less than 0.6 times the house volume per hour.
- Air quality control measures: with air-tight construction, indoor air quality becomes more important to occupants’ health. Therefore, air quality control measures should be undertaken during design and construction stages. These include, but not are not limited to: selecting building materials and adhesives with low/no volatile organic compounds, and carrying out a proper flush-out procedure, in which the newly completed buildings are fully opened for air circulation for a required continuous period before occupancy.
- Ventilation system: heat recovery from exhaust air using air-to-air heat exchanger is applied to achieve a recommended 80% efficiency. It is also important to locate the warm air ducts inside the heat envelope and cold air ducts outside (Passive House Institute, 2010). However, in warm climatic regions, the opposite is recommended.
To achieve the above key stringent standards, many building science research projects related to passive houses have been carried out, leading to the development of software called Passive House Planning Package (PHPP). PHPP is an energy modelling programme that projects energy usage in the building design by taking into account almost every aspect related to energy consumption, including the site’s weather data, orientation, type of construction, materials used, window designs and locations, ventilation system, appliances, lighting and other electrical equipment used in the building. As more post-occupancy data has become available and the concept of passive houses has been expanded to other regions of the world, PHPP has been continuously upgraded and refined, including the addition of simulations for other climates around the world.
Feasibility for implementation
Different regions have different: climatic conditions, availability of construction materials and conventional practices. Even within the temperate regions, the difference in extreme temperature, humidity, opportunity for geothermal, etc., can still be identified. Therefore, while the principles of passive houses and related technologies can be applied in various temperate regions, the actual quantitative standards and construction detailing can vary. It is useful for a local area to have an overall feasibility study and to undertake research on the most suitable practices and standards for passive houses. The findings can then be used to form design guidelines and standards, which serve as a reliable springboard for largescale adoption.
Although passive house principles and technologies can be taken up by individual building owners and potential building owners through a bottom-up approach, good support from institutional settings, such as local building codes based on passive house principles and supporting demonstrations in public building projects, can facilitate stronger uptake and implementation.
Passive house technologies require highly skilled technicians to implement good and precise construction details i.e., air-tightness, no thermal bridges, etc. Therefore, capacity building and local workforce training are key requirements.
It is also noted that many developing countries do not have the manufacturing capacity to locally produce passive house components and materials, e.g., insulation, triple glazed windows, etc. Importing these components and materials are too expensive and increase the embodied carbon of the products. Therefore, it is important to extend capacity building and institutional settings to support and nurture local manufacture’s uptake and upgrade for the production of passive house components and materials.
The main market of passive houses is in Europe, with Germany and Austria taking the lead, with a smaller market in North America. As of May 2009, it is estimated that there are about 19,100 passive house projects in Europe (Lang, 2009). Passive house projects are anticipated to be widely adopted in the construction and property market in Europe. It is projected that by 2015, there will be about 260,000 passive house projects in Europe with a total floor area of about 85.2 million square metres of new buildings and 6.2 million square metres of retrofitted buildings (Lang, 2009). Among developing country regions, Eastern Europe has the highest market penetration prospects for passive house design and technologies, thanks to the similar climate and the geographical proximity to other European regions, where the passive house concept has been taken up and implemented.
Passive house design and technologies are not limited to residential buildings. In recent years, other building types, such as schools and offices have also applied passive house design and technologies, which deliver good energy efficiency results.
Passive house design and technologies bring benefits to environmental development, including energy saving for artificial lighting, heating, ventilation and air conditioning. Due to design optimisation for daylight and thermal comfort, passive house design and technologies offer building occupants better thermal comfort, indoor environment, indoor air quality and visual connection to outdoors. These benefits lead to a healthier and higher quality of life.
Due to the fact that passive house design and technologies do not rely on active systems and high-tech equipment to deliver environmental benefits, passive house design and techniques can also be considered one of the cost effective mitigation options. The resulting lower energy demand from passive houses helps reduce electricity peak load, and create further savings by avoiding additional investment to increase the capacity of the local power infrastructure and power plants.
The promotion of passive house implementation also helps upgrade the skills of local construction work forces and improve building and living standards for the local residents. This results in better job prospects, healthier communities and greener economies.
The implementation of passive house principles and technologies incurs some additional investment cost to provide high-performance envelope insulation, triple glazing windows, air-tight construction, heatrecovery ventilators, stringent construction details and so on. However, it is argued that an incremental investment cost can be balanced by avoiding costs of investing in sophisticated heating, ventilation and air conditioning (HVAC) systems and their high operating costs. Instead of investing in HVAC systems, passive houses invest in better building envelopes, which also improves the building’s durability and its life span. As a rule of thumb, a passive house is considered to be cost effective when “the combined capitalised costs (construction, including design and installed equipment, plus operating costs for 30 years) do not exceed those of an average new home” (Passive House Institute, 2010).
Feist W. (2005). First Steps: What Can be a Passive House in Your Region with Your Climate? Darmstadt: Passive House Institute.
Lang G. W. (2009). International Passivhaus Database 1. Period of Documentation 2007 – 2009: 20,000 Passivhaus Projects in Europe. Intelligent Energy Europe & PASS-NET. [Online]: www.pass-net.net/downloads/pdf/report_international_ph-database.pdf
Passive House Institute (accessed on 20 Nov. 2010). Passive house Construction Check List. [Online]: www.passiv.de/07_eng/index_e.html
Torcellini P, Pless S., Deru M. & Crawley D. (2006). Zero Energy Buildings: A Critical Look at the Definition. USA: National Renewable Energy Laboratory.