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Project

The impact of electrically heated window panes on thermal conditions

Client

Finnglass Oy

Implementer

Sweco Rakennetekniikka Oy

Commission

Report on the impact of electrically heated window panes on thermal comfort, energy consumption and the carbon footprint, incl. CFD, energy and carbon footprint calculations and design instructions

Year of implementation

2019–2021

Affordable and clean energy
Climate Action

Finnglass windows improve thermal condition and carbon emission management

The Finnish glazing solution expert Finnglass wants to develop the responsibility of its production, which requires an assessment of its products’ impact on thermal conditions and carbon footprints of buildings. This information was gathered by using Sweco’s energy, carbon footprint and CFD calculation.

Finnglass is a Finnish expert on electrically heated glass with nearly 40 years of experience in active glazing solutions. The company’s greatest value is improving people’s well-being. “Understanding our customers is important to us, because today’s offices, for example, are about working conditions, not just square metres,” says Finnglass’s CEO Timo Saukko. Thermal conditions have a significant impact on the satisfaction of those using the premises. “According to studies, the most common complaints users have concern the space being too hot or cold.”

A responsible supplier impacts the customer´s carbon footprint

Responsibility permeates all operations at Finnglass, and all production processes related to roughing and smoothing glass are already carbon neutral. “We only use green electricity produced with renewable energy and the waste heat from our own processes,” Saukko says. Indeed, Finnglass also wanted to determine the impact of electrically heated glass on the thermal conditions and carbon footprint of buildings. “We want to present our customers with proven solutions.”

Sweco’s independent experts are investigating the energy consumption and carbon footprint of electrically heated glass in three different cases. “We combined Finnglass panes with underfloor heating, fan coil units embedded in the floor and coil units installed on floor surfaces,” says Sweco’s energy and carbon footprint calulcation expert Kari Nöjd. This was followed by a comparison of the impact of underfloor heating and electrically heated glass on the thermal distribution and thermal comfort of the space.

CFD calculations simulate indoor climate conditions reliably

The research methods included energy and condition simulations, carbon footprint calculations and demanding CFD calculations. “CFD calculation requires supercomputers and special expertise, because the reliability of the calculations is fully dependent on the expert’s skills,” Timo Saukko emphasises. “Sweco has a high level of CFD and carbon footprint calculation competence.”

According to Sweco’s Leading CFD Specialist Eero Kokkonen, ensuring thermal conditions and thermal comfort in the design of even slightly more complex spaces is extremely challenging without CFD calculations. “In addition to temperature, air flow speed and turbulence also affect thermal comfort,” he says. The feeling of draught, for example, is a sum of many factors, such as geometry, window placement and the terminals of the ventilation system and their locations.

The indoor climate is often designed based on averages. The average temperature of the entire space can, however, be a poor representation of the thermal conditions near tall windows, for example. “The design should not settle for being good on average. The conditions should be good throughout the space,” Kokkonen stresses.

According to calculations, underfloor heating alone cannot ensure the thermal comfort of spaces on cold days. The size, number and surface temperature of windows have a significant impact. “If the surface temperature of a window pane is lowered to one degree below room temperature, an unpleasant draught can be felt near the window,” Kokkonen says. Electrically heated panes improve the user experience and functionality of the space. In addition to this, there is no need to install heaters or coil units in front of glass facades, which takes away from the architecture. “It also improves the efficient use of the space.”

Opportunity to optimise the carbon footprint

Based on a report, electrically heated panes can be used to meet the E value requirements set for new construction. The panes can also be used to optimise heating costs and carbon emissions.

“The operation of electrically heated panes is easy to control, enabling them to only be heated when there are people in the hotel room or scenic restaurant, for example,” Nöjd says. “When electrically heated windows are used when needed alongside a geothermal heat system, for example, they can be used to achieve a smaller carbon footprint than district heating alone.”

Finally, Sweco experts draft planning instructions that help architects, HVAC designers and electrical engineers take the characteristics of the electrically heated panes into consideration. “Each designer wants to design buildings that meet high indoor climate and low-carbon requirements. We believe that it is important to provide them with the right information,” Saukko says.

“Our production processes are already carbon neutral, because we only use green electricity produced with renewable energy and the waste heat from our own processes.”
– Timo Saukko, Finnglass

 

“When electrically heated windows are used when needed alongside a geothermal heat system, for example, they can be used to achieve a smaller carbon footprint than district heating alone.”
– Kari Nöjd, Sweco

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