Intramural generation of wind energy in the Ventec Roof, hereafter denoted as Power Roof, is only theoretically investigated in this study. Further evaluation of the potential of this concept requires further scientific and empirical research.
The Earth, Wind & Fire concept allows exploitation of environmental energy from wind and sun in two ways:
• Passive: for the creation of the air flows for a natural air conditioning. The Earth, Wind & Fire research has delivered validated calculation models of this technique which can be directly utilized for use in practice. During a demonstration project, experience will be gained and it will be demonstrated that the innovative concept is sufficiently advanced for employment in construction practices – see below.
• Active: for the generation of electrical energy in the Ventec Roof. Production yields for solar energy can be relatively reliably calculated on the basis of the efficiency of the applied PV foil. For wind energy, theoretical calculations are made which could not be validated empirically due to lack of financial resources. For the further development of this “intramural” wind energy, additional research is, therefore, required.
The current trend in the development of wind energy is the construction of large-scale wind farms in windy environments, e.g. at sea or on the coast. This central power production with large to very large wind turbines is much more expensive than traditional gray power, the cost difference being compensated by subsidies. Due to the significant distance to the built environment, transport and conversion losses of the generated energy are unavoidable.
There is growing public resistance to wind turbines which originates in the danger they pose to birds, the noise nuisance, the cast shadow for residents, and the experienced “visual pollution”. These problems occur less in small-scale generation of wind energy in the built environment which, therefore, is considered a promising technology. Small wind turbines such as the Turby, a vertical axis wind turbine with a rated power of 2.5 kW (http://www.turby.nl), is specifically designed for this purpose and can be directly connected to the smart grid of the building so that generated power can be directly employed “behind the meter”. The yield of any self-utilized kWh is, therefore, equal to the “avoided cost of purchase”, which is significantly higher than the current fee for return delivery, at least in the Netherlands.
A disadvantage of small-scale generation of wind power in the built environment is that wind speeds are lower than in an open field. This can be compensated, for example, by situating the turbine on a high building. Locally high wind pressures or a local increase of wind speed resulting from the architectural design can also be exploited. This is the case with the Ventec Roof and the Power Roof described below.
Wind turbines in the Ventec Roof
The Ventec Roof is designed primarily for generation of positive and negative pressure differentials for natural air conditioning. The research indicated, however, that the Cascade Climate yields, in many cases, sufficient positive pressure for air distribution in a building. Wind turbines can be installed which are more beneficial than bypass dampers in avoiding overly high pressures in the Ventec Roof.
There are two essential differences between wind turbines in the Ventec Roof and conventional wind turbines:
• A free-standing wind turbine exploits dynamic wind pressure while the turbine in the Ventec Roof is driven by static pressure differences.
• In the case of a detached wind turbine, the air flows partially around the rotor, which is not possible with the turbine in the Ventec Roof. This signifies that the so-called Lancester-Betz limit, the maximum power coefficient, is not applicable in this case.
• Pressure differences in the Ventec Roof are much greater than pressure differences in the open air. Therefore, with turbines in the Ventec Roof, significantly higher power coefficients can be achieved than with detached wind turbines.
In addition to increased power coefficient, wind turbines in the Ventec Roof have further advantages in comparison to conventional wind turbines:
• With the positioning inside the building, any possible noise problems are easier to solve.
• No environmental permit (Wabo) is required.
• Wind turbines are part of technical building systems, allowing easy coordination of power production and power use.
• Maintenance can be accomplished in the easily accessible and protected technical room.
Wind turbines in the Power Roof
The Power Roof is a further development of the Ventec Roof which not only exploits pressure in the overpressure chamber but also increased wind speeds in the pseudo-venturi. By installing a number of vertical-axis wind turbines therein, considerable power production can be expected.
The required research is outlined as:
1. Determining the optimum dimensions and geometry of the roof overhangs for the realization of maximum pressures in the overpressure chamber.
2. Mapping on macro-level of pressures surrounding the Power Roof, windward, leeward, parallel sides and upper side.
3. Determining optimal geometric proportions and curvature of the upper- and lower roof in order to maximize power production in the pseudo-venturi.
4. Validation of CFD simulations on the basis of measurements in the wind tunnel ad 5 and 6.
Points 1- 4 are to be conducted by the Unit Building Physics and Systems at TU Eindhoven employing a CFD numerical flow simulation.
5. Producing a model of the Power Roof on a scale of 1:100 and provided with measuring points based on CFD simulations of optimized roof overhangs and roof curvatures.
6. Measuring and recording pressures ad 2 in the closed boundary layer wind tunnel at Peutz.
7. Consultation with TU Eindhoven regarding simulations and measurements.
Points 5-7 are to be performed by Peutz Molenhoek in the wind laboratory.
8. Producing a model of the optimized Power Roof on a scale of 1:20 with the required measuring points in the overpressure chamber, provided with meshes, for the simulation of the turbines.
9. Measuring and recording velocities and pressure differences across measuring points at different wind speeds and mesh densities in the open jet wind tunnel (Open Jet Facility OJF) of the Faculty of Aerospace Engineering of TU Delft.
10. Determining pressure coefficients Cp in the pressure chamber, the leeward side, and the upper side.
11. Determining maximum aerodynamic performance, theoretical turbine power, and pressure coefficients in different configurations.
Points 8-11 are to be conducted by the Faculty of Aerospace Engineering at TU Delft.
12. Calculation of noise production of wind turbines and determining possible measures to reduce noise levels inside the building and to the environment.
Point 12 is to be conducted by Peutz.
Energy with Sun and Wind
The upper roof and the illuminated section of the lower roof is provided with a thin-film PV foil consisting of a thin film photovoltaic material applied to a flexible bottom layer. In the year 2012, an efficiency of 10% was attainable with this technology, and it is expected that an efficiency of 15% is within reach. On the basis of the reference year NEN 5060:2008, a yearly yield of 100 kWh.m-2 can be calculated.
Combining wind power and sun power is an interesting option for two reasons:
• The profiles of available wind power and solar power are fairly complementary over the seasons. During summer, there is significant sunshine and little wind. During winter, there is significant wind and minimal sun.
• The share of solar energy, calculated per m2 floor area, decreases with an increase in the number of stories and, thereby, increasing building height. The share of wind power increases at increasing building height due to increased wind velocities.
Combined use of solar and wind power in Ventec Roof and Power Roof is, therefore, an interesting option. The characteristics of this combination should be further explored for different building heights and geometries.
For a detailed description of the research proposal, see hyperlink
For the year 2013, no possibilities for subsidizing wind power are available within the Dutch subsidy policy TKI EnerGO. To finance the follow-up study, “Power production in the Ventec Roof > Power Roof”, whether or not combined with subsidies from the demonstration project ad (4), potential interested parties will be sought.