How schools can achieve a better indoor climate without extensive renovations
Aalborg University has spearheaded the I-DIFFER project, which has demonstrated a generally improved indoor climate at Ellehøjskolen in Aarhus, where the principles were tested. Troldtekt has been part of the project group, and one of the noticeable improvements at the school is the installation of a Troldtekt ventilation ceiling.
Having a poor indoor climate is a well-known problem, especially in Denmark’s older primary and lower secondary schools. However, renovating entire schools can be disruptive to both everyday life and finances.
Aalborg University has therefore spearheaded a project to develop a new and less invasive renovation solution, called I-DIFFER, to improve the indoor climate in buildings. The solution focuses particularly on air quality, acoustics and thermal comfort.
The I-DIFFER concept was tested at Ellehøjskolen in Aarhus, where a classroom was renovated according to the principles and a design guide was subsequently created. The project team conducted studies of the indoor climate and the students’ experience of the indoor climate and compared them with similar studies in an ordinary classroom at Ellehøjskolen.
The project was completed in the first part of 2024. In addition to Aalborg University, the project group included the City of Aarhus, EKOLAB, Windowmaster and Troldtekt.
The results from the I-DIFFER project have been documented and published in international journals. To help architects and engineers bring the concept to fruition, the team has created a design guide for future projects.
I-DIFFER at a glance
The I-DIFFER project combines several technologies: a double façade, where an extra layer has been built on top of the exterior of the existing school building, and the Troldtekt ventilation system solution with a diffuse ceiling, controlled by a newly developed solution from Windowmaster.
Together, these technologies serve a number of purposes:
- Fresh air flows through the facade over the diffuse Troldtekt acoustic ceiling and into the classroom. Ventilation is controlled by a fan.
- The façade reduces heat loss through the building envelope and allows flexible control and the use of nocturnal cooling.
- The façade minimises the amount of outside noise entering the classroom. The extra façade also protects any solar shading.
- Troldtekt ventilation panels reduce the risk of draughts at lower temperatures and improve room acoustics.
Image of the previous façade at Ellehøjskolen
Image of the new façade with an additional layer on top of the existing exterior
Report shows positive results
The results and the impact on the indoor climate have been published in a scientific report from Aalborg University.
- Indoors, CO2 concentrations were measured to examine the air quality before and after the new measures. CO2 levels above 1,000 ppm drop from 54 per cent to 22 per cent during the hours the room is in use, and the maximum values for CO2 concentrations are significantly reduced – from 3,500 ppm to 1,250 ppm.
- Previously, the temperature stood between 20-26°C for most of the time that the students used the room. After implementation, the temperature was colder 16 per cent of the time. This is also due to the fact that the measurements after implementation took place in winter with a low outside temperature and that the heat source was radiators with thermostats. We are awaiting the results of summer measurements to demonstrate the effect of nocturnal cooling in the classroom.
- The ventilation system used in the concept is adapted to the Troldtekt ventilation panels. Studies show that the reverberation time – that is, the time it takes for a sound to fade out in the room – has almost halved after the installation of the new ceiling. This has resulted in a clear difference in sound levels and the acoustic indoor climate.
- SBi’s limit value for classrooms is 0.6 seconds of reverberation time, but sound measurements showed that the actual sound level was 0.8 to 1.0 seconds before I-DIFFER. Subsequently, the values have halved and are now within the legal requirement.
More exciting results from I-DIFFER
Olena Kalyanova Larsen is an associate professor at the Department of the Built Environment at Aalborg University and participated in the I-DIFFER working group. She points to several factors that helped the project succeed:
" First, the solution is architecturally well integrated into Ellehøjskolen. Of course, there's no guarantee that this will also be the case for all other future projects, but a large part of the I-DIFFER concept has been focused specifically on architecture."
The second point she highlights is the contrast the team experienced in terms of air quality and acoustics when they visited the renovated classroom and then a regular classroom:
" Several students said that they sometimes chose to take breaks in the new classroom because it was a better space to be in. Obviously, most people prefer new spaces to old ones, but it was still remarkable to enter a classroom without the smell of packed lunches, which stood in sharp contrast to the indoor climate of the other classroom."
In addition, Olena Kalyanova Larsen emphasises that the I-DIFFER project has so far demonstrated good energy and indoor climate performance as well as a significant environmental perspective:
" The concept is easy to build and does not require major disruptions to users’ everyday lives. It can be integrated with renewable energy sources, while limiting construction waste by preserving the building's existing façade. This is particularly relevant in relation to the environmental impact of construction, which is a top priority throughout the industry. I-DIFFER doesn't solve every challenge, but it does allow us to try something different than what 'we usually do'."
Other construction projects can benefit from I-DIFFER
Lars Thomsen Nielsen is an engineer and project manager for the City of Aarhus, where Ellehøjskolen is located, and he participated in the project group for I-DIFFER:
" We thought the project sounded exciting to be a part of, and it has yielded good results at Ellehøjskolen, where the students have also been extremely satisfied."
Although no final decisions have been made on how and whether I-DIFFER will be used in the City of Aarhus, Lars Thomsen Nielsen sees several options:
" In the City of Aarhus, we have a strong focus on the indoor climate, and we are considering using renovation solutions from the project in other types of buildings, such as institutions and community centres, where sometimes there are also challenges with the indoor climate," he says, adding:
" However, this requires the ability to build a double façade on the existing building. I could see us continuing to work with the principles of I-DIFFER, but on different scales that are less intrusive – depending on what makes sense for the individual building."
Troldtekt has gained exciting insights from I-DIFFER
"Participating in a project like I-DIFFER has been exciting for Troldtekt," explains Niels Kappel, who works with product development at Troldtekt and was part of the project group.
" The results from Ellehøjskolen were positive, including shorter reverberation times and a clearly audible difference that greatly benefited the acoustic indoor climate in the classroom. In addition, the solution with outside air seeping down through the acoustic ceiling has, as expected, significantly improved the air quality in the room."
Throughout 2024, several measurements are being taken on an ongoing basis at Ellehøjskolen to see how they change with the seasons.
The researcher’s own experience kick-started the project
The idea for I-DIFFER came from Olena Kalyanova Larsen’s own experiences at the school that her children attend:
" I vividly remember how every morning, when the children were being dropped off, I would enter an east-facing classroom that was often already quite warm at eight in the morning. Then the blinds were rolled down and the windows opened.
This scenario is especially challenging in places where breaks occur at different times, as noise comes in from outside. In addition, the blinds break or are not used in a timely manner against the heat in many school rooms, she explains:
" The worst thing is if the blinds are rolled down for most of the day in spring, summer and autumn, because the choice is between keeping it warm and bright or dark and cool. Perhaps nocturnal cooling could take the edge off excessive room temperatures? This was one of many elements we wanted to address with I-DIFFER."
Facts about the I-DIFFER project
- Aalborg University has spearheaded the I-DIFFER project, which focuses on developing a concept that can improve the indoor climate in Danish primary and lower secondary schools while minimising energy consumption.
- The project group included the City of Aarhus, EKOLAB, Windowmaster and Troldtekt.
- A classroom at Ellehøjskolen in Aarhus tested the I-DIFFER concept and in 2023, measurements were taken before and after implementation, which showed improvements with lower temperatures, lower CO2 levels and shorter reverberation times.
- The project was finalised in 2024 and a report and a design guide have been published for professionals who want to continue working with the I-DIFFER principles.
