Up to 8 percent less heating energy: Recent study by the Passive House Institute

WHAT WAS RESEARCHED?

  • The study compares aluminium, stainless steel and plastic spacer bars:
  • • in two modern, conventional low-energy houses with triple and/or double glazing and one passive house – each with a living space of 156 m²
  • • in different climate zones
  • • in relation to opportunities for saving heating energy and reducing CO2
  • The key results at a glance

    For the first time, the independent Passive House Institute in Darmstadt calculated the influence of the spacer bar in the insulating glass in windows on the overall energy requirements of buildings in different climate zones. Compared with aluminium spacer bars, highly efficient plastic spacer bars result in significantly lower energy consumption, CO2 emissions and heating costs in buildings both in the cool/moderate climate and cold climate.

    The sample locations chosen were Frankfurt (Germany) for the cool/moderate climate and Helsinki (Finland) for the cold climate. They therefore represent the climate zones in the following countries: UK, Ireland, Scandinavia, Poland, Czech Republic, Slovakia, Benelux, Northern Italy, the Baltic states, Austria, Switzerland.

    Here are the key results:

  • A study by the Passive House Institute: Information for architects and building owners

    According to the study, building owners and tenants save 8.6 percent of total heating energy in a cool/moderate climate and 7.1 percent in the cold climate zone if, instead of spacer bars made of aluminium, highly efficient plastic spacer bars are used in the windows of a conventional low-energy building. This shows that the spacer bar is a small component with a big impact. The "warm edge” increases the energy efficiency of buildings.

    The spacer bar: 
    A key component in energy-saving windows

    The spacer bar sits at the edge of the insulating glass and keeps the panes at a distance. It creates a cavity between the panes, which is normally filled with the noble gas argon for a better insulating effect. There are spacer bars made from aluminium, stainless steel and plastic on the market. The highly efficient plastic spacer bar is known as a “warm edge”. The spacer bar is now really the centre of attention. As the study clearly shows: after the glass and the frame, the spacer bar is the third most important component for the energy performance in modern heat insulating windows.  

    Lower heating costs with a warm edge    

    According to the study, compared with aluminium spacers, plastic spacer bars ensure that building owners and tenants have to pay less energy costs – and do so throughout the entire period of use. For example: in the low-energy building with triple glazing studied, over a period of use of 40 years, that represents a saving of between 2260 and 2463 Euro, depending on the climate zone. Heat insulating windows with highly efficient composite spacer bars are slightly more expensive to buy. However, the bottom line shows that building owners and tenants save money.

    Greater living comfort and less risk of mould

    Plastic spacer bars in windows offer more comfort: the temperatures on the inside of the windows remain pleasant even in the winter. In addition, the warm edge prevents the build-up of condensation at the edge of the glass, reducing the risk of mould there. High-quality plastic spacer bars increase quality of life and the value of the building.

    Less CO2 emissions

    If a building needs less energy, it reduces CO2 emissions. The results of the study clearly show that anyone can make a surprisingly large contribution to the energy transition by making the right choice when it comes to a small, efficient component.

    It makes the difference: the heat transmission coefficient

    If the spacer bar has a poor – i.e. high – heat transmission coefficient, a lot of heat is lost to the outside – even with an excellent frame and high-tech glass. However, there are big differences in performance when using plastic spacer bars. A highly efficient warm edge, as used in the study, has a linear thermal conductivity of 0.14 W/(mK). The value for stainless steel is 0.6 and for the aluminium spacer bar – the clear back marker – it is a massive 160 W/(mK).

    Greater design freedom for windows 

    As less energy is lost when using windows with efficient plastic spacer bars, larger window surfaces can be achieved on the east-facing and west-facing sides of buildings. According to the study, on the south-facing side, they enable “heating energy requirements falling even to the level of full glazing”. 

    Download the study

    The study, including a summary table with all the results, can be found here.

  • A study by the Passive House Institute: information for window manufacturers

    In a modern, conventional, triple-glazed low-energy house, depending on the climate zone, heating costs of between 23 and 25 Euro per linear metre at the edge of the glass can be saved over the period of use if highly efficient plastic spacer bars are used in insulating glass windows instead of aluminium spacers.

    Lower heating costs for customers – market opportunity for the windows industry 

    According to the study, end customers can save so much on heating costs that a window with a warm edge is worthwhile for them despite the slightly higher purchase price. For example: in the low-energy building with triple glazing looked at in the study, over a period of use of 40 years, that represents a saving of between 2463 Euro in heating costs in a cool/moderate climate, and 2260 Euro in the cold climate zone. In the low-energy building with triple glazing, the savings are 1864 and 1690 Euro respectively. For window manufacturers and insulating glass manufacturers, this offers a concrete economic opportunity, as high-quality plastic spacer bars are only slightly more expensive per linear metre to purchase than spacer bars made of aluminium.

    Less building heating energy thanks to the warm edge

    In comparison with aluminium spacer bars, the energy savings when using efficient plastic spacer bars were as follows:

    in a cool/moderate climate
    • in the low-energy building with triple glazing studied: 8.6 percent
    • in the low-energy building with double glazing studied: 5.6 percent
    • in the Passive House building studied: 22 percent

    in a cold climate
    • in the low-energy building with triple glazing studied: 7.1 percent
    • in the low-energy building with double glazing studied: 4.8 percent
    • in the Passive House building studied: 28 percent

    These numbers confirm that the "warm edge” increases the energy efficiency of windows and thus of buildings.


    It makes the difference: the heat transmission coefficient

    After the glass and the frame, the spacer bar is the third most important component for the energy performance in modern heat insulating windows. If the spacer bar has a poor – i.e. high – heat transmission coefficient, a lot of heat is lost to the outside here – even with an excellent frame and high-tech glass. However, there are big differences in performance when using plastic spacer bars. A highly efficient warm edge, as used in the study, has a linear thermal conductivity of 0.14 W/(mK). The value for stainless steel is 0.6 and for the aluminium spacer bar – the clear back marker – it is a massive 160 W/(mK).


    The study can assist you when providing advice and when making sales

    For the first time, the study by the Passive House Institute has produced figures that demonstrate the benefits of warm edge spacer bars in comparison to other spacer bars in black and white. Window manufacturers can use these figures when advising customers and making sales. 


    Download the study

    The study, including a summary table with all the results, can be found here.

  • Small component, big impact

    Be it as a result of the demographic shift, urbanisation or increasing industrialisation: global energy demand is rising constantly – however, the heating and cooling of indoor areas makes up an enormous part of total energy consumption around the world. In order to make an active contribution to the energy transition in future, it is important to find out what simple measures can be taken to effectively intervene.

    A simple principle holds true here: less energy consumption = less CO2 emissions. Depending on the climate zone, the three building types analysed in the study saved up to 340 kg CO2 per year over their living space of 156m² each when high-quality plastic spacer bars were used instead of aluminium spacer bars in the windows. Depending on the location, the building’s heat energy savings were up to 8.6 percent for the low-energy house with triple glazing, up to 5.6 percent for the low-energy house with double glazing and up to 28 percent for the Passive House. 

    The study by the Passive House Institute examined the savings for each building: we can now actually calculate the specific contribution the warm edge can make to the energy transition. Come back and have another look!

  • Download the PHI study