Improvement of both indoor climate and energy savings

The City of Aarhus decided to renovate the school as an Aa + Energy Renovation project, thus requiring improvement of the indoor climate and savings on energy bills.

Built in 1976, Tranbjerg School Department Grønløkke was in need of general renovation, including upgrading of the classrooms and improvement of the indoor climate.

Aa+ energy renovation project

The City of Aarhus decided to renovate the school as an Aa + Energy Renovation project, thus requiring improvement of the indoor climate and savings on energy bills.

With this holistic approach, engineering consultancy Ekolab set about finding the best solutions for the overall renovation, including ventilation, which represented the largest part of the renovation.

The choice

With top marks in the various categories and the best overall score, the choice fell on Airmaster decentralised ventilation units, integrated in a ventilation ceiling from Troldtekt®.

The analyses carried out by EKOLAB included economy, operation and indoor climate. Energy savings as a result of the renovation were included in the overall economic consideration. The six solution scenarios considered feasible and included in the analysis were four scenarios with centralised ventilation and two scenarios with decentralised ventilation.

Developer: The city of Aarhus, Aa+ Energy Renovation Project

Consultant: Ekolab

Ventilation ceilings have been installed in 32 classrooms as well as in corridors and communal areas. ​
The different room types and sizes have different ventilation requirements​, so four different sizes of ventilation units have been used.

Ventilation unit:

22 x AM 1000
8 x AM 800
3 x AM 500
2 x AM 300
Ventilation ceiling: Troldtekt® acoustic, white
The recommended solution using Airmaster decentralised ventilation units had the best overall economy over a 15-year period.
Mike Vinge, Engineer and Project Manager, Ekolab.

Top marks on indoor climate

Improving the indoor climate was an important part of the renovation and therefore weighted highly in the choice of solution. The recommended solution scored top marks on all indoor climate parameters. The parameters were studied for an indoor climate with 28+2 people and that the solution could, among other things, maintain a CO2 level below 900 PPM.

Best overall economy over a 15-year period

The recommended solution had the best overall economy over a 15-year period. The investment itself was not the lowest, but it was the best solution in terms of the overall economy by virtue of its lowest energy consumption.

Lowest energy consumption

Both the quality of the indoor climate and the energy bill will be improved greatly by effective demand management. The ventilation units are controlled by the CO2 level, so they switch on when the room is in use and switch off again when the room is vacated. This means that no unnecessary energy is wasted in rooms that do not require ventilation.

Day-to-day operation

Day-to-day operation is controlled by Airmaster’s built-in automation, which has been integrated in the school’s BMS system via BAC-Net IP. Service personnel are notified when it is time for a service and filter change.

With decentralised units, there are more filters to change than with centralised units, but no valves to be checked on the duct system. There is less impact in the event of stoppages with decentralised units, and there is greater flexibility, as well as far lower energy consumption. This was also included in the analysis.

The construction process

The renovation project started in the summer of 2016, when the building itself was dismantled and renovated during the summer holidays. Work on the heating, ventilation, new ceilings and lighting took place after the holiday while the school was in use.

Four temporary classrooms were established at the school, ensuring that there were four “makeshift classes” to make use of at all times. This way, four classrooms could be renovated at a time, without having to rehouse pupils.


Other topics included in the analysis were "Buildability and durability". This included analyses of cable racks and fire and smoke protection.

  • Supply air: No ducts; the Airmaster units sit on exterior walls with direct access to fresh air, so there are zero costs for cleaning ducts.
  • Exhaust: Used air from the rooms is led to the ventilation units via the ducted exhaust fixture.
  • Fire and smoke protection: There are no costs for fire and smoke protection because the units are mounted in the fire cells they operate and do not pass through other areas.


Aarhus city council decided, as part of its budgeting for 2013, to initiate investment in systematic energy renovation of the municipality’s building stock. The City of Aarhus aims to realise a fundamental reduction of CO2 emissions through economically viable energy savings. At the same time, the aim was to gain significant side benefits in the form of a better indoor climate, for example. The renovation projects go under the heading of “Aa+ Energirenovering” (Aa+ Energy Renovation) and are one of the City of Aarhus’ own contributions towards achieving the CO2030 objectives.

Ready for a breath of fresh air

At Airmaster, we are “decentral” through and through. We are unrivalled when it comes to creating the best indoor climate and optimal well-being because we take each room and its occupants into account – and because we constantly strive to improve on what we do.

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