POLYVEST® HT

Sara: I recently read an article in a technical journal that really impressed me. It claimed that up to 50 percent of heat from houses is lost through doors and windows that are not properly sealed. That’s a lot, and we need to minimize it for the good of the planet. Conversely, high-quality windows are an effective way to reduce the heat lost through windows. What energy cost savings can be achieved by fitting state-of-the-art windows in our apartments and houses?

Alexandra: The potential savings vary depending on the house. For example, they are influenced by the local climate, the structure of the building, and the building materials. The size of the house and the quality of the insulating glass and the entire window have to be considered. If we take an average detached house, at current gas prices¹, savings of up to €1,000 a year are possible if you compare the cost of heating a building with old single-glazing and one with modern, high-quality double-glazing with a permanent seal. Assuming that high-quality modern insulating glass has a lifetime of 30 years, that’s an enormous saving.

Sara: Are there any legislative changes to building regulations that have to be considered when choosing windows for public or private buildings?

Alexandra: Yes, quite a bit is happening. The EU Commission and the EU Council recently agreed on key points for a revision of the buildings directive. In broad terms, the main aims of the revised directive are for all new buildings to be zero-emission by 2030 at the latest and for the building stock to be zero-emission by 2050.

New public buildings have to meet these standards by 2028. Based on the new definition, zero-emission buildings are buildings with a very high energy performance that require very little or no energy, do not generate CO₂ emissions from fossil fuels, and have very low or no operational greenhouse gas emissions. Minimum energy performance standards are to be introduced for the renovation of existing buildings.

That should encourage the renovation of houses and apartments. Priority should be given to buildings with a very poor energy profile in order to continuously improve the energy performance of existing buildings. As well as energy-related targets, the new legislation will consider the health and wellbeing of people using the buildings.

Sara: Installing windows with thermal insulation reduces energy consumption. It also reduces CO₂ emissions. The potential to reduce the carbon footprint is enormous.

One study shows that up to 100 million tons of CO₂ a year could be avoided in European countries by installing energy-efficient windows with multiple glazing. So, your solutions could make a massive contribution, couldn’t they?

¹ As of November 2022

Alexandra: Correct. One of the best ways of making a house more energy-efficient is optimal insulation. Today’s windows are designed to do exactly that. Double- or triple-glazing with a durable gas seal can avoid several metric tons of CO₂ a year because energy losses are far lower than with older single-glazing or a drafty window.

Sara: Insulating glass windows are made from two or more panes of glass with special coatings and an inert gas filler. The durability and reliability of insulating glass depend to a large extent on the quality of the sealants that are used. At H.B. Fuller | Kömmerling you make high-quality sealants for energy-efficient window systems. How does the sealant system work?

Alexandra: The sealant holds the insulating glass unit together through an edge seal, which is also a reliable barrier that retains the gas and prevents moisture penetration. If the quality of the sealant is not good, the insulating inert gas can seep out of the space between the panes of glass or water vapor can penetrate it. That greatly reduces both the thermal insulating properties of the windows and their sound insulation.

Sara: A modern insulating glass window really is more high-tech than I thought. I find it interesting that the quality of the sealant guarantees that windows with multiple glazing retain their heat and sound insulating properties. What about the edge seal? How is it structured?

Alexandra: From the outside, the edge seal on the insulating glass unit is rather unspectacular. All you can see is a black compound that runs right around the inside of the unit. But there is much more to it.

The edge seal is a dual seal comprising a primary and a secondary sealant. The main purpose of the primary sealant is to retain the gas in the insulating chamber and prevent penetration by moisture. The secondary sealant bonds the panes of insulating glass to one another. It forms a structural bond. At the same time, it enhances the sealing properties and protects the primary sealant from exposure to weather.

Sara: The demands made on the two sealants are very different. Is that reflected in the choice of polymers?

Alexandra: The primary sealant is normally made of polyisobutylene with thermoplastic properties. Secondary sealants can be made from various chemical substances and polymers, including polyurethanes, polysulfides, and silicones. They have to be “designed” so that they can reliably compensate for the pressure on the primary sealant in order to protect it most effectively.

Sara: What criteria are used to select the secondary sealant?

Alexandra: Various aspects have to be considered. Silicones have high UV resistance. They are often used in frameless glazing, which is exposed to direct sunlight for a long time. By contrast, polyurethane and polysulfide sealants have very good resistance, low water vapor diffusion, and low gas permeation. High-quality polyurethane sealants have the lowest water vapor diffusion. They are also flexible and bond with many types of surfaces such as glass, metal, and plastics.

Sara: Polyurethane sealants are available as one- or multi-component systems. Depending on their formulation, they may be either rigid or flexible. For window glass, two-component systems are preferred because of their elastic properties in order to prevent warping as a result of changing thermal loads. And that is where Evonik plays an important role. We market POLYVEST® HT, a high-quality binder for polyurethane sealants, which are needed to manufacture modern, energy-efficient insulating glass windows that minimize energy losses from buildings and effectively reduce CO₂ emissions.