The passive house window is not really a window type. The term passive house window relates to the thermal insulation characteristics of the window. A passive house standard window features a particularly high thermal insulation value. The heat transfer coefficient Uw has to comply with the European standard and be less than or equal to 0.8 W/m2K. Every window with an Uw-value less than or equal to 0.8 W/m2K is therefore a passive house window and suitable for installation in passive houses and is eligible for support through corresponding programs.
Passive house windows are not restricted to installation in passive houses only. Windows complying with the passive house standard can be used in refurbishment projects for older buildings as well as in any new building. Passive house windows enhance living comfort and help reduce heating costs substantially!
The advantages of passive house windows at a glance
- High level of coziness – no “pockets of cold air” developing in the proximity of the window.
- No temperature swings caused by different temperature layers in the proximity of the window.
- The inside surface temperature of a passive house window does not drop below 17 degrees centigrade, even in winter.
- As a result of the very good insulating properties it is no longer essential to install heating elements near the window area. This allows for additional freedom when designing and furnishing your home.
- The extra costs for a passive house are minimal nowadays and amortization is realized quickly due to the high level of energy efficiency.
Passive house windows – a technology that makes sense!
The outstanding thermal insulation properties of a passive house window are first and foremost due to its very high quality frame technology in combination with triple glazing. The U-value of the finished window is a function of the U-value of the frame, the glazing, and the spacer installed for the edge seal. You can find more detailed information on the calculation of U-values on our Info Page U-values.
Passive house windows also feature a high solar energy transmittance. This means that the natural heat from the sun’s radiation can be utilized more effectively. This enhances the energy balance of the building and reduces the annual primary energy requirement. Thus, besides all the advantages relating to living comfort, passive house windows are particularly suitable for reducing energy and heating costs. Together these advantages offer builders and homeowners a clear advantage, especially when used in new buildings and refurbishment projects.
Why Passive House
- Protection for building owners from future energy price increases
- Great return on investment
- Increased comfort due to more-uniform interior temperatures (this can be demonstrated with comparative isotherm maps)
- Reduced requirement for energy austerity
- Reduced total cost of ownership due to improved energy efficiency
- Reduced total net monthly cost of living
- Extra cost is minimized for new construction compared to a retrofit
- Higher resale value as potential owners demand more ZEBs than the available supply
- The value of a ZEB building relative to a similar conventional building should increase every time energy costs increase
- Future legislative restrictions, and carbon emission taxes/penalties may force expensive retrofits to inefficient buildings
The Passive House concept represents today’s highest energy standard with the promise of slashing the heating energy consumption of buildings by an amazing 90%. Widespread application of the Passive House design would have a dramatic impact on energy conservation. Data from the U.S. Energy Information Administration shows that buildings are responsible for 48% of greenhouse gas emissions annually and 76% of all electricity generated by U.S. power plants goes to supply the Building Sector [Architecture2030]. It has been abundantly clear for some time that the Building Sector is a primary contributor of climate-changing pollutants, and the question is asked: How do we best deal with our building energy needs and with those of our environment and of our pocketbook? In the realm of super energy efficiency, the Passive House presents an intriguing option for new and retrofit construction: in residential, commercial, and institutional projects.
A movement toward the construction of highly efficient houses originated in the late 1980’s, when a rigorous energy standard for new buildings was established in Sweden. Swedish professor Bo Adamson and German physicist Wolfgang Feist designed a building system that met and even exceeded this standard – the Passive House. The standard is based on research first started in North America in the 1970’s and 80’s. The first prototype, a four-unit row house structure, was built in 1990 in Darmstadt, Germany.
Today, many in the building sector have applied this concept to design, and build towards a carbon-neutral future. Over the past 10 years more than 15,000 buildings in Europe – from single and multifamily residences, to schools, factories and office buildings – have been designed and built or remodeled to the passive house standard. A great many of these have been extensively monitored by the PassivHausInstitut in Darmstadt, analyzing and verifying their performance. Even governmental agencies have adopted passive house standards in their policy-making (read more about the EU Commission’s intent to implement the Passive House Standard.).
The Passive House concept is a comprehensive approach to cost-effective, high quality, healthy, and sustainable construction. It seeks to achieve two goals: minimizing energy losses and maximizing passive energy gains. Simple enough, but achieving these goals has led to extraordinary results: a Passive House uses up to 90% less energy for space heating and cooling than a conventionally constructed house. The Passive House standard is the world’s most rigorous standard for energy-efficient construction.
To attain such remarkable energy savings of 90%, Passive House designers and builders work together to systematically implement the following seven principles:
- Super insulate
- Eliminate thermal bridges
- Create a building envelop that is infiltration-free through airtight construction
- Provide proper ventilation by specifying energy or heat recovery ventilation
- Specify high-performance windows and doors
- Optimize passive-solar and internal heat gains
- Model energy gains and losses using the Passive House Planning Package (PHPP)
In a Passive House, the entire envelope of the building – walls, roof, and floor or basement – is well insulated. How well insulated depends a lot on the climate zone. To achieve the Passive House standard in Berkeley, California only 6 inches of blown-in cellulose insulation is required while a home in Duluth, Minnesota, might need 16 inches – almost three times as much. Often the first feature of a Passive House that catches a visitor’s attention is the unusual thickness of the walls. Thickness is needed to accommodate the required level of insulation but the Passive House designers still have a wide range of different types of insulation to choose from, including cellulose, high-density blown-in fiberglass, polystyrene, ozone-friendly spray foam, vacuum insulated panels (VIPs), and straw bale. No matter which type of insulation is used, Passive House builders must make sure that the product is installed correctly. Technicians using thermo graphic imaging can directly measure the application and performance of insulation. These cameras can readily detect heat loss; therefore they can help identify areas where insulation is insufficient, incomplete, damaged, or settled.
Eliminate Thermal Bridges
Heat flows out of a building by the easiest available path – the path of least resistance. It will pass very quickly through an element that has a higher thermal conductivity than the surrounding material, forming what is known as a thermal bridge. Thermal bridges can significantly increase heat loss, which can create areas in or on the walls that are cooler than their surroundings. In a worst-case scenario, when warm, moist air condenses on a cooler surface; moisture and mold problems can result. In a Passive House, there are few or no thermal bridges, which mean negligible heat loss through this detail. It is critical for the Passive House designer and builder to reduce or eliminate thermal bridges by limiting penetrations and by using heat transfer-resistant materials. Analysis of thermal bridge free details occurs during the design phase through resource library and analytical tools such as THERM. Thermographic imaging can be used to determine how effective efforts to eliminate thermal bridges have been.
Create a Building Envelop that is Infiltration-free Through Airtight Construction
Airtight construction helps the performance of a building by reducing or eliminating drafts – whether hot or cold – thereby reducing the need for space conditioning. Air tightness also helps prevent warm, moist air from penetrating the structure, condensing inside the wall, and causing structural damage. Airtight construction is achieved by wrapping an intact, continuous layer of airtight materials around the entire building envelope. Insulation materials are generally not airtight; the materials used to create an intact airtight layer include various membranes, tapes, plasters, glues, shields, and gaskets. The air tightness of a house provides a measurable dimension of the quality of construction. Testing air tightness requires use of a blower door, which is essentially a large specialized fan. A technician uses the fan to assess how much air is infiltrating the building through all of its gaps and cracks. Specific leaks can be detected during the blower door test by employing tracer smoke, which allow any leaks to be readily detected and addressed. Passive Houses are extremely airtight and have been built from timber, masonry, prefabricated elements, and steel framing members. Air tightness does not mean that you can’t open the windows. Passive House has fully operable windows, and most are designed to take full advantage of natural ventilation or stack effect to help maintain comfortable temperatures in the spring, fall, and even summer, depending on the local climate. Depending on the user’s habits and behaviors, windows can be opened without dramatic loss of energy.
Provide Proper Ventilation by Specifying Energy or Heat Recovery Ventilation
Perhaps the most common misconception regarding Passive Houses concerns airflow. “A house needs to breathe”, builders might say disapprovingly, when first presented with the idea of building very tight homes. A Passive House does breath – exceptionally well. Rather than breathing unknown volumes of air through uncontrolled leaks, Passive Houses breathe controlled volumes of air by mechanical ventilation that acts as the “lung” of the building. Through the use of an energy recovery ventilator (ERV) or heat recovery ventilator (HRV) in cold, dry climates, the Passive House constantly sips fresh outside air and quietly exhausts stale inside air back outside the house. All this is done with very little energy loss and creates an exceptionally healthy indoor air quality. The ERV constantly exhausts odors and moisture from the kitchens and bathrooms at a very controlled rate, while at the same time the ERV brings in fresh outside air and delivers it in an extremely quite way to the bedrooms, living rooms and dining rooms of the Passive House. The ERV runs 24 hours a day – 7days a week, but it does so in an extremely energy efficient way by moving small volumes of air at all times and exchanging energy while allowing for air flow. It is important to note that the exhaust air from the bathrooms and kitchens is not mixed with the incoming air supplied to the bedrooms and other living areas. The two streams of air pass each other, exchange energy, but do not touch or mix, making the Passive House one of the healthiest building standards in the world.
Specify High-Performance Windows and Doors.
Windows in a Passive House are designed, oriented, and installed to take advantage of the free passive-solar energy that can be gained through them. Passive House windows and doors are extremely well built incorporating, tightness, thermal breaks, minimal air infiltration and ex filtration – all of which leads to extraordinary high R-values. The R-value is further enhanced by using low-emissivity (low-e) coatings on the window glazing. These are microscopically thin, transparent layers of metal or metallic oxide deposited on the surface of the glass. The coated side of the glass faces into the gap between the two panes of a double-glazed window. The gap is filled with low-conductivity argon or krypton gas rather than air, greatly reducing the window’s radiant heat transfer. This allows Passive House designers to select from an arsenal of incredibly energy efficient windows that allow for high, moderate, or low solar gains, providing a range of options for houses in all climates, from heating dominated to cooling dominated. The Passive House window eliminates any perceptible cold radiation or convective cold airflow, even in periods of extreme weather.
Optimizing Passive-Solar and Internal Heat Gain
Not only must designers of Passive Houses minimize energy loss, they must also carefully manage energy gains. The first step in designing a Passive House is to consider how the orientation of the building – and its various parts – will affect its energy losses and gains. There are many issues to be considered. Where the window should be positioned to allow for maximum sunlight when sunlight is wanted and minimal heat gain when heat gain is not wanted The more direct natural lighting there is, the less energy will be needed to provide light. Designers can enhance occupants’ enjoyment of available sunlight by orienting bedrooms and living rooms to the south, and putting utility rooms and closets where sunlight is not needed, to the north. However, it is not always possible to site a house in this ideal way. There may be buildings, trees, or landforms that cast shadows during short winter days, blocking out much of the low sunlight. The designer may also need to accommodate the homeowners’ demand for a certain view – a view that would not be available in an ideal orientation. Windows are designed, oriented, and installed to take advantage of the passive-solar energy that can be gained through them. But the goal is not simply to allow for as much solar gain as possible. Some early super-insulated buildings suffered from overheating because not enough consideration was given to the amount of solar gain that the house would experience. The designer of the Passive House will balance and match solar gain within the home’s overall conditioning needs – and within the window budget.
In the Northern Hemisphere, in climates dominated by heating loads, windows on the north allow for no direct solar gain, while those on the south allow for a great deal of it. In summertime, and in primarily cooling climates, it is very important to prevent solar heat gain. This can be accomplished by shading the windows. Roof eaves of the proper length can effectively shade south-facing windows when the sun is higher in the sky during summer. All while still allowing for maximum solar gain in the winter when the sun is lower in the sky and the days are colder. Deciduous trees or vines on a trellis can also block out sunlight in the summer and admit it in the winter. In climates that have significant air conditioning needs the designer will limit un-shaded east and west-facing windows, and specify only windows that have low solar gain, low e-coatings. During the morning and late afternoon, low angled sunlight can generate a great deal of heat in such windows.
Another, perhaps less obvious source of heat gain is internal. Given the exceptionally low levels of heat loss in a Passive House, heat from internal sources can make quite a difference. Household appliances, electronic equipment, artificial lighting, candles, and people – all can have a significant effect on the heat gain in a Passive House. Passive House designers play an active role in what appliances and lighting systems are selected and they must take into account the heat gain from those sources when they calculate overall internal heat gain.
Use the PHPP (Passive House Planning Package)
There are many elements of Passive House design that need to be integrated with one another. These include wall thickness, R-or U-values, thermal bridges, air tightness, ventilation sizing, windows, solar orientation, climate, and energy gains and losses. The PHPP is a powerful and accurate energy-modeling tool that helps a designer to integrate each of these elements into the design, so that the final design will meet the Passive House standard. The PHPP starts with the whole building as one zone of energy calculation. The designer inputs all of the basic characteristics of the house – orientation, size, and location of windows, insulation levels, and so on. The PHPP can even be used to model such advanced features as solar water heating for combined space and water heating, or the contributions of natural ventilation for nighttime cooling. The PHPP then computes the energy balance of the design. If needed, the designer can change one or more elements – like the size or location of a window, for example – within the PHPP and model the effect of those changes on the overall energy balance. Experienced Passive House designers often work with their drawing programs and their PHPP both operating at the same time.
The developers of the Passive House concept mastered the integration of all these developments into a functional system to create a highly energy-efficient building. This concept can reduce heating energy consumption as much as 90% or more.
The number of inhabited Passive Houses in Europe today approaches the tens of thousands. They are not limited to homes. Schools, office buildings, health facilities and large-scale housing projects have also been built to the Passive House Standard. This number, and the variety of designs, proves that the Passive Houses are not exotic research projects, but completely normal homes. Passive Homes are not full of complicated technology, but instead feature intuitive and simple devices, devices that any occupant can easily manage.
This approach to building represents a wonderful opportunity for American companies to grow and excel. While many of the products are already available in the U.S. market, advancement in building components, like windows and doors, are now limited and primarily imported from German manufacturers. American businesses, from engineers to manufactures, are poised to become the leaders in this area and part of our energy solution.
Information for this document was obtained from Homes for a Changing Climate, Passive Houses in the U.S. by KatrinKlingenberg, Mike Kernagis, and Mary James. ©2009 Aspen publishers.
This paper was compiled by David Gano and Professor Laura Briggs
Key Links and resources:
- Passive House Institute US
- Passive House Case Study (143 page PDF)
- Passive Houses Directory (German site translated to English)
- E-colab.org (US Energy Consultants that have built 3 Passive Homes in Illinois
The European Retrofit Model
Recommendations for retrofit buildings using the European model approach
Existing building retrofits in Europe can take 15 to 20 years to complete, including changing windows, retrofitting the roof, and adding external insulation. Most building refurbishment in Europe is done step by step in a phased manor. The phased approach starts with master plan that shows the finished building and how its new energy efficient components will work together to reach a high level of energy efficiency. Most of the renovations include elements such as window replacements, new roofs, new heating systems and insulation. Most property owners will prolong renovations until replacement of certain elements such as windows or HVAC system becomes a necessity. In most cases major retrofits are too expensive to complete in one step. While doing a retrofit, certain improvements could be made to improve the overall performance of the building. For example, adding a new roof to replace a roof in need of repair and then adding additional insulation will save energy and at the same time will not greatly increase the cost. It is always a good recommendation to improve the air tightness of the building while performing a retrofit. High performance retrofits are the most cost efficient when major work already needs to be done on the building. In conclusion, using a team of energy consultants and architects to properly lay out a phased plan of action to turn an energy inefficient building into a energy efficient building, has a greater chance of success if its phased in. This lets the property owner spread out the work and spread out the cost of the project. This can lead to a better performing building by enabling the owners to control their finances.
For single component renovations we are recommending to improve each element of the building that is being renovated such as: roof, walls, HVAC, passive house windows, appliances and etc.