Floor plan

What is the impact of window frames on energy consumption?

In a new paper published this week, a team of researchers studied the impact of window frames on energy consumption and city-wide replacement strategies to reduce this impact in Japan. The article appeared in the journal Energiesand scientists from Japan and Korea contributed to the research.

Study: Impact of window frames on the annual energy consumption of residential buildings and its contribution to CO2 City-wide emission reductions. Image Credit: New Africa/Shutterstock.com

Study context

The growing world population and rapid levels of urbanization have placed enormous demands on energy consumption and, consequently, an increase in carbon emissions. Power generation, transport, the construction sector and multiple heavy industries exploit large amounts of fossil fuels.

In many countries, the construction sector alone is responsible for around 40% of total energy consumption, and reducing this figure is key to achieving zero emissions goals.

Among construction elements, windows are responsible for a large part of heat loss due to the significant difference in their thermal transmittance values ​​compared to other components. Conversely, due to the transmission of solar energy through the glazing, windows can also contribute to heating.

Window frames represent a small fraction of the total building area, but nevertheless have a potentially large impact on heat loss and therefore on energy consumption due to their insulating properties and materials. Many poorly insulated window frames are still in use around the world, usually constructed from aluminum. Aluminum has a much higher thermal conductivity than PVC, which is preferred in modern buildings.

In 2020, 10.1% of all window frames were aluminum in Japan, with aluminum/PVC composite frames being used in 67.5% of all applications. PVC window frames were used in 22.5% of all applications in the same year. In Europe and America, the figure for PVC frames is 50%. Therefore, there is significant room for improvement in the Japanese market.

Cross section of (a) aluminum frame including the wall, (b) aluminum frame, (c) composite frame (aluminum and polyvinyl chloride [PVC]), and (d) PVC frame.

Cross section of (a) aluminum frame including the wall, (b) aluminum frame, (vs) composite frame (aluminum and polyvinyl chloride [PVC]), and (D) PVC frame. Image credit: Choi, Y et al., Energies

The study

The authors identified that although research has focused on improving the thermal performance of window frames by studying the relevance of heat transfer, there has been a lack of city-wide studies.

Some articles in the current literature have demonstrated heat loss and energy consumption savings due to the use of low conductivity materials for window frames. A study looked at replacing aluminum frames with fiberglass reinforced composite PVC in an office building, showing an almost 20% reduction in total energy consumption. However, many studies have focused on single buildings and overlooked the citywide impact.

This study has three main objectives. It aims to identify the impact of frame materials on energy consumption, quantify the contribution of highly insulated frames installed in new city-wide buildings to energy savings, and discuss how whose improved thermal insulation of window frames can contribute to national countermeasures to reduce greenhouse gases. emissions.

Temperature distribution for each reference frame.  PVC, polyvinyl chloride.  (a) Aluminum;  (b) Compound;  (c) PVC.

Temperature distribution for each reference frame. PVC, polyvinyl chloride. (a) Aluminum; (b) Composite; (vs) PVC. Image credit: Choi, Y et al., Energies

Study results

Of the three window frame materials (aluminum, aluminum/PVC composite, and PVC) studied in the research, the thermal transmittance value of PVC was the lowest at 1.88 W/m2. K. This value was determined using two-dimensional simulation methods.

Regional averages demonstrated an annual decrease in energy consumption of 0.75% using frames with improved thermal performance. The amount of CO2 the emissions saved per household per year is equivalent to 1-3 cedar trees using PVC window frames. Additionally, the authors found that in seven regions of Japan, this figure translates to several hundred thousand cedars. This demonstrates significant city-wide energy savings.

The city-level energy-saving effect, even in areas that commonly use PVC window frames in Japan, is proportional to the number of new houses built each year. Continuous improvement in window frame insulation is essential, even in regions where PVC is the preferred material for window frame applications.

Floor plan of a reference building.

Floor plan of a reference building. Image credit: Choi, Y et al., Energies

Impact of the study

The document provides information relevant to window frame dealumination efforts. The authors said their findings could help predict future energy saving potentials for national efforts to mitigate heat loss and energy consumption from residential and commercial buildings. The results of their study can inform both new construction and renovations to improve the energy efficiency of buildings. In addition, national policy makers could benefit from the study.

A major limitation of the study is that it only analyzed about 17.2% of new domestic buildings in Japan. Future studies will address this limitation by extending the study methodology to all new Japanese housing units.

Further reading

Choi, Y., Ozaki, A. & Lee, H (2022) Impact of window frames on the annual energy consumption of residential buildings and its contribution to CO2 City-wide emission reductions Energies 15(10) 3692 [online] mdpi.com. Available at: https://www.mdpi.com/1996-1073/15/10/3692

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