“Earth, Wind & Fire – Natural Air Conditioning”

Dr. Ben Bronsema received his doctorate from the Technical University of Delft in 2013 aged 78 after eight years of research into “Earth, Wind & Fire – Natural Air Conditioning”.

Sustainability pioneers Amstelius and Dutch Green Company, together with Dr. Bronsema, were awarded an RVO innovation subsidy in 2014 in order to further develop and realise the world’s first specific nearly zero-energy building in accordance with the innovative ‘Earth, Wind & Fire’ (EWF) concept. As overall coordinator, Dutch Green Company – together with various TKI EnerGO (RVO) research partners – granted a subsidy to the value of €500,000.


In the EWF concept, a Ventec roof (also known as Power Roof 1.0) was developed with the natural extraction of ventilation air as its most important function. Wind energy was generated with the help of wind turbines in the overpressure area. The return on investment proved insufficient due to low revenues and high costs. Not exactly a cost-effective solution.

Inspired by Power Roof 1.0, an idea was born. Bert Blocken of the Technical University of Eindhoven and Ben Bronsema of Delft Technical University discussed the option of adapting the Power Roof 1.0 by making use of vertical axis wind turbines as well as the enhanced wind speeds in the Venturi Roof. This was to become known as the Power Roof 2.0.


The reasoning behind additional fundamental research was the need to optimise the power coefficient of the turbines in order to arrive at a level of wind energy generation in the built-up area that delivered a positive return on investment. The wind turbines in the wind park in the Venturi Roof needed to comply with specific aerodynamic and electromechanical requirements, including:

  • The morphology of the roof;
  • The blade-shape of the turbines; and
  • The anticipated energy production.

The standard turbines on the market at the time were unable to perform at the required level, whereby a seamless solution was required for the BREEZE project. A supplementary subsidy application for the development of a prototype of the wind turbine by the Technical University of Eindhoven was unfortunately rejected. Based on provisional simulations with 40 turbines in the Power Roof 2.0, the theoretical models generated a significant amount of energy: 200,000 kilowatt hours. Regrettably, however, the production of wind energy by the envisaged turbines amounted to an annual average of only 62,000 kilowatt hours. Neither did this suggest a doable business case.


It was then decided to develop a Power Roof 3.0 in which the vertical axis turbines would be located on the roof in a multiple curved surface, whereby use would be made of the acceleration impact of the wind, as was the case in Power Roof 2.0. The morphology of the roof shape was optimised with the help of simulation. Together with Luc Heijnen of Troades, a vertical axis turbine was procured from Windspire in the United States for further research in a wind turbine belonging to the Von Karman Institute for Fluid Dynamics (VKI) in Leuven. On the basis of these practical tests, the effectiveness of the blade profile and the blade angle was investigated with the help of the simulation model developed by the Technical University of Eindhoven. A rough calculation with the manufacturer’s data indicated that this could well develop into a positive business case. The test of the vertical axis turbine in the VKI wind tunnel, however, was disappointing in terms of results. A number of alternatives were then tried out – 28 vertical axis turbines, and then 20 – at approximately three-metre height, but the estimated annual amount of power generated was no more than 100,000 kilowatt hours. This was still insufficient for the realisation of the Power Roof 3.0 required to build an energy-neutral building such as the BREEZE project.



The alternative then proposed was the generation of solar energy with the help of customised building-integrated PV panels on the facade, in the solar chimneys, on the awning and on the roof. Total energy proceeds amounted to 200,000 kilowatt hours per year.

During the fundamental research in the 2014-2015 period, Ben Bronsema spearheaded the further development of the EWF concept for Hotel Breeze. We worked together with the world’s most sophisticated companies and the technical universities of both Delft and Eindhoven and the renowned Von Karman Institute for Fluid Dynamics to develop the technical components for this research project.