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WIND ENERGY FOR THE BUILT ENVIRONMENT(Project WEB)

Assessment of Wind Energy Utilisation Potentialin Moderately Windy Built-up Areas

N. S. Campbell, S. Stankovic

BDSP PartnershipSummit House,27 Sale Place,

London W2 1YR,UK

Contract JOR3-CT98-0270

PUBLISHABLE FINAL REPORT

1st September 1998 to 31st August 1999

Research funded in part byTHE EUROPEAN COMMISSION

in the framework of theNon Nuclear Energy Programme

JOULE III

WEB – JOR3-CT98-0270 Publishable Final Report (Update)

BDSP Partnership October 2000

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Table of Contents

1 ABSTRACT..........................................................................................................................................................2

2 CONSORTIUM PARTNERS ............................................................................................................................4

3 OBJECTIVES......................................................................................................................................................5

4 TECHNICAL DESCRIPTION..........................................................................................................................6

5 RESULTS..............................................................................................................................................................8

5.1 REVIEW OF EXISTING PROJECTS ..........................................................................................................................85.2 GENERAL GUIDELINES FOR INTEGRATION OF WIND TURBINES .............................................................................85.3 GENERIC TECHNIQUES AND OPTIONS FOR THE INTEGRATION OF WIND TURBINES ................................................95.4 PERFORMANCE OF GENERIC OPTIONS FOR INTEGRATION OF WIND TURBINES................................................... 115.5 OPTIMISED INTEGRATION OF WIND TURBINES.................................................................................................. 12

5.5.1 Aerodynamic / Energy Optimisation............................................................................................... 135.5.2 Architectural, Structural and Environmental Optimisation........................................................ 14

5.6 DESIGN, CONSTRUCTION AND FIELD-TESTING OF PROTOTYPE BUILDING/WIND CONCENTRATOR .................... 195.6.1 Objectives............................................................................................................................................ 195.6.2 Design and Construction.................................................................................................................. 205.6.3 Overall Results from Field-Testing................................................................................................. 225.6.4 Utilisation of Results......................................................................................................................... 25

6 CONCLUSIONS............................................................................................................................................... 27

7 EXPLOITATION PLANS AND ANTICIPATED BENEFITS................................................................... 28

8 PHOTOGRAPHS TO ILLUSTRATE POTENTIAL APPLICATIONS OF THE PROJECT.............. 31

9 APPENDIX A.................................................................................................................................................... 32



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1 Abstract

Wind Power is now a mature technology for electricity generation, boasting aninstalled world-wide capacity in excess of 10,000 MW. Continuing planning problemswith the siting of wind farms are driving development of huge offshore turbines.Instances of integration in the urban environment, however, remain scarce.

Successful urban integration will require that proposed developments fully address theconcerns of planners, pressure groups and the general public with regard to theirenvironmental impacts. The turbines must also be capable of producing a significantproportion of the annual electricity demand of the building in which they are housed orof neighbouring buildings – say 20% as a minimum. These buildings must be inherentlyenergy efficient, otherwise the turbine(s) risk being seen as a gimmick.

The focus of the current project has been on the development of wind enhancementand integration techniques which improve the annual energy yield per installation byconcentrating the low to moderate wind speeds typical of most urban areas in Europe.This involved balancing and reconciling aesthetic, aerodynamic, architectural,environmental and structural concerns. Specific achievements include :

• development of methods for predicting and assessing energy and environmentalimpacts of integrating wind turbines into the urban environment;

• classification of optimal building forms. ‘Kidney’ or ‘boomerang’ profiles were foundto be the best footprint shapes for twin tower structures. The addition ofaerodynamic cross-pieces (infills) linking the building towers and closely fittingaround the turbine(s) was found to further enhance performance;

• development of prototype structural systems - for supporting turbines and isolatingvibrations from buildings - and safety devices.

Field-testing of small wind turbines (both VAWT and HAWT) integrated into aprototype aerodynamic building employing these principles was successfullycompleted. In comparison to an equivalent stand-alone machine, the turbine(s)integrated into the building produced :

• power at lower cut-in wind speeds;• substantial power enhancement for effective angles of wind incidence up to 60º;• satisfactory power output (i.e. > 50%) when the wind is effectively coming at right

angles to the building/turbine.

The key results from the field-testing – the enhanced performance of wind turbine(s)integrated into an optimised aerodynamic structure - could also be exploited in otherareas of the wind energy industry, e.g. offshore technology. This would also requiredetailed design and testing at intermediate to large scales.



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Suggested acronyms for the technology are ‘Urban Wind Energy Conversion Systems’(UWECS) and ‘Building Augmented Wind Turbines’ (BAWTS).

The true potential for integration of wind energy into urban environments can only beassessed if and when real schemes enter the planning process in different countries.The current project has sought to provide design guidance to inform this process.



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2 Consortium Partners

Organisation & Role Address Contact Name Contact Details

BDSP Partnership Ltd.(BDSP)

Co-ordinatorsEnvironmental Engineers

Summit House,27 Sale Place,London,W2 1YR,UK.

Mr. Sinisa Stankovic

(Director)

Tel : +44 (0)20 7298 8383Fax: +44 (0)20 7298 8393

E-mail: [email protected]: www.bdsp.com

Imperial College of Science,Technology & Medicine.(IC)

Aerodynamicists

Department of AeronauticsPrince Consort Road,London,SW7 2BY,UK.

Prof. Mike Graham

(Head of Dept.)

Tel: +44 (0)20 7594 5074Fax: +44 (0)20 7584 8120

E-mail: [email protected]: www.ic.ac.uk

Mecal Applied Mechanics BV.(MECAL)

Mechanical/Structural Engineers(Wind Energy)

Steenriet 16a,Postbus 286,NL-7500 AG,Enschede,Nederlande.

Ir. Frans Brughuis

(Manager Product GroupWind Turbines)

Tel: +31 (0)53 433 4300Fax: +31 (0)53 433 8080

E-mail: [email protected]: www.mecal.nl

University of Stuttgart.(UST)

Architects and Planners

Institut für Baukonstruktion undEntwerfen L2,Geschister-Scholl-Straße24B (7. OG),D-70174 Stuttgart,Deutschland.

Prof. Stefan Behling

(Head of Dept.)

Tel: +49 (0)711 121 39 87Fax: +49 (0)711 121 32 52

E-mail: [email protected]: www.uni-stuttgart.de



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3 Objectives

The key objectives for the project were :

• the development of techniques for both integrating and enhancing powerproduction from wind turbines sited in urban locations (characterised as low tomoderate wind speed areas, having mean annual wind speeds in the range 2 to5.1 m/s), and for assessing their performance and environmental impacts.

• the utilisation of a holistic approach addressing all relevant issues :aerodynamics, aesthetics, architectural space optimisation, energy production,environmental impacts on people and surroundings (e.g. noise, safety),structural design and integration, urban planning etc. To include the use ofspecialist research methods including wind tunnel testing on scale models andcomputational fluid dynamics (CFD) simulations.

• proving/demonstrating the utility of these techniques by constructing andmeasuring the performance of a small scale prototype building or windconcentrator with an integrated wind turbine – both a Horizontal-Axis WindTurbine (HAWT) and Vertical-Axis Wind Turbine (VAWT) to be tested.

VAWTs are not currently being manufactured on a commercial scale foreconomic and reliability reasons, however, their aesthetics are often found tobe more appealing to the architectural community than the propeller-likeHAWTs. Hence, it was considered important to test both generic turbine types1

(Figure 1).

HAWT VAWT

Figure 1: The small scale HAWT and VAWT tested during project WEB

1 HAWTs can, in contrast, essentially be thought of as mass-produced devices, and economics aredriving the development of ever larger machines (with blade diameters greater than 70m)



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4 Technical description

The work programme was divided into seven well-defined and (mainly sequential)tasks. These are summarised overleaf in Table 1.

Please note that in the results section that follows, the specific results from individualtasks have been integrated into the text, in order to aid understanding of the keyresults of the project as a whole



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Task Title / Description / Associated Deliverable(s)

1Project Definition

To define the scope and key parameters under which the project will run through a series of initial team meetings to which international experts willbe invited. Deliverable : Internal Report.

2Typical Wind Regimes and Case Studies

To identify and categorise typical wind regimes prevailing in urban locations using historical statistical wind data, and to classify specific Europeantowns/cities accordingly. Deliverable : Internal Report.

3Wind Enhancement and Integration techniques

To define, develop and evaluate techniques for integration and power enhancement from wind turbines placed in urban locations, usingsophisticated engineering software tools as necessary. To optimise the most promising of these techniques holistically, paying regard to : energyperformance; aesthetics; architectural integration; environmental and structural design impacts. Deliverables: 2 Internal Reports.

4Small-Scale Model Design and Testing

To optimise the aerodynamics / energy performance of the most favoured solutions produced during Task 3 (e.g. shape, orientation to prevailingwind etc.), by empirical wind tunnel testing of scale models. Deliverables : Internal Report; Prototype Models; Specification for Task 5.

5Design, Construction and Field-Testing Of Two Wind Turbine Types

To translate the findings of Tasks 3 & 4 into the design, construction and field-testing of 2 prototype wind concentrators for a small-scale HAWT andVAWT respectively. Deliverables: 2 Prototypes; Internal Report on performance of Prototypes.

6Environmental Implications

To assess the environmental impacts of the techniques developed in Task 3 and tested in Tasks 4 and 5. These will be key in determining the likelyuptake of the technology. Issues to be addressed to include : public safety; noise; vibration and resonance; broadcasting interference; planningimplications. Deliverable : Internal Report.

7Design Guidelines, Performance Specification and Economic Assessment

Utilising the results of the preceding tasks, to define design guidelines for the integration of wind energy in the urban environment, performancespecifications for prototype buildings/wind concentrators, and to assess the economics of integration. Deliverables: 3 Internal Reports.

Table 1: Description of the specific tasks set out in the project work programme



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5 Results

5.1 Review of Existing ProjectsAn initial review found the expected small number of existing projects where windturbines have even been used in the built environment. Two examples are illustrated inFigure 2:

Shenley Lodge Turbine,Milton Keynes, UK

'Green Building' ,Temple Bar, Dublin, Ireland

Figure 2: Existing examples of stand-alone wind turbines located in urban areas

More imaginative attempts at integration of wind power can be found, for instance, insome innovative housing schemes in the Netherlands, and in the ironical use of windturbines on the roof of the Dutch Pavilion at EXPO-2000 in Hanover. In all cases,however, either the power generated by the turbine, and / or the level of integration islow. Some larger scale schemes using turbines placed on harbour walls or offshorecan be found near Copenhagen and in several other European locations.

5.2 General Guidelines for Integration of Wind TurbinesHighly engineered integration of one or more wind turbines into a building or structuremust overcome some formidable problems, if it is to be successful, e.g.:

• a stand-alone turbine is free to yaw (turn) into the direction of the prevailingwind in order to optimise power extraction, whereas most buildings are by theirvery nature static structures (unable to turn to face the wind);

• turbines used in wind farms are normally located a substantial distance(>500m) away from surrounding properties to ameliorate their noise and safety(if not visual) impacts;

• the mean wind speeds in urban areas are lower than in rural locations due tothe resistance caused by the presence of buildings and infrastructure (thepower extracted by a wind turbine depends on the cube of the wind speed).



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Following discussions at the initial meetings, the team agreed on several rules ofthumb that should be satisfied if substantial benefit is to be derived from theintegration of wind energy into the built environment:

• the building(s) - whose electricity demands the wind turbines(s) will partially meet -must be inherently energy efficient for any integrated wind turbine(s) to have asignificant impact on the nett energy balance of the building(s).

• wind turbine(s) integrated into the built environment should be capable of producinga significant proportion (i.e. at least 20%) of the annual electricity demand of thesurrounding building(s). Otherwise, the turbine(s) would become a primarilyaesthetic feature – which would be unsatisfactory from both an environmentalviewpoint and that of clients, planners, designers and occupants.

• a given development should not benefit the global environment to the detriment ofthe local environment (e.g. visual impact, noise, broadcasting interference).

5.3 Generic Techniques and Options for the Integration of Wind TurbinesThere are essentially 3 generic techniques available for integrating wind turbines intothe urban environment:

• Fully integrating one or more turbines into a (new) building so that they drive thearchitectural form;

• Retro-fitting turbines onto existing buildings;• Landscaping stand-alone wind turbines into urban environments, which can supply

surrounding buildings.

A matrix of generic options for integrating wind turbines into the rectangular block orsquare-edged shapes commonly found in the built environment was developed duringthe initial phase of the project, as pictured in Figure 3:

Figure 3: Generic Options for integrating a wind Turbine into a Building

Retro-fitting turbines into buildings, using one of the generic options shown in Figure 3,will generally be very difficult unless very small turbines (generally contributing aninsubstantial fraction of the building’s electricity demand) with small impacts on thebuilding and surroundings are considered.



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Flat roofs, for example, are typically littered with plant, which would disturb the flowover the top of the building and reduce yields, as well as creating turbulence, whichmay accelerate blade fatigue. The perception of the risks of shedding of a turbineblade and adverse acoustic impacts makes retrofits less attractive. Systems forisolating the vibration of the turbines from the building and the need for acousticenclosures will also incur cost penalties. Mounting and maintenance of retrofittedturbines also presents a considerable challenge.

Figure 4: Possible categories of urban location where the integration or placement ofstand-alone wind turbines could be considered

Examples of typical classes of urban locations where stand-alone turbines could beconsidered are shown in Figure 4. They are characterised by high levels of existingnoise and industrial uses. Obviously, a thorough investigation of the risks to peopleand property would be required for each unique site, including evaluating the riskscaused by a possible scenario, e.g. the shedding of a turbine rotor blade.



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Noise and visual impact studies would also be a vital component of the planningprocess. The cumulative potential energy contribution from introducing sensitively sitedstand-alone turbines would probably be the greatest of the three generic options, butcould only be assessed once test cases had entered the planning systems of severalmember states.

With these factors in mind, the focus of the project moved towards integration in newbuildings.

5.4 Performance of Generic Options for Integration of Wind TurbinesThe relative performances of the generic options (Figure 3) were evaluated using amatrix of weighted qualitative and quantitative criteria by the partners.

Wind tunnel testing on small-scale models (IC) was used in parallel with computationalfluid dynamics simulations (BDSP) to assess the impact on energy extraction from the‘integrated’ turbines, and to visualise and study flow patterns.

Calibrated GauzeMesh ‘Turbine’

Motorised Model Turbine Visualisation of Streamlinesin Flow using Dye

Figure 5: Techniques used in wind tunnel testing

Figure 5 illustrates the methods used in the wind tunnel modelling for representing and(indirectly) assessing the power extracted from a wind turbine2. An analogous methodto the use of the gauze mesh can be used in computational simulations, where digital3-D models of the building and turbine are placed in a virtual wind tunnel. Comparisonof the computational and experimental methods revealed good agreement in mostcases. A range of velocity profiles corresponding to real atmospheric boundary layersfound in urban and city-centre locations, and a range of wind directions could besimulated both experimentally and computationally.

2 Note that the model turbines are in fixed position (i.e. not free to yaw).



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The base case for comparison purposes was taken to be of a free yawing stand-alone wind turbine with identical diameter blades mounted on a mast at normalheight above the ground (e.g. as it would be in a wind farm).

Figure 6: Predicted Performances for Generic Options (Square-Edged Buildings)

Figure 6 shows the results of the energy assessment. Key points to note are that :

• when averaged over all angles of incidence3, the power output from all the genericoptions will be less than from a stand-alone machine. Effectively, it is detrimental inenergy terms to integrate wind turbines into square-edged buildings4

• the power outputs for zero yaw (i.e. when the prevailing wind is normal to theplane of the turbine) for the twin tower option, did, however, indicate that somesort of power enhancement effect is possible – when separation of flow isprevented, suggesting that more aerodynamic building forms could provepromising.

5.5 Optimised Integration of Wind TurbinesThe partners decided to proceed with a more detailed evaluation and development ofthe two most promising generic options for integration of a wind turbine:

• Suspension between twin towers• Suspension in a ducted hole within a building

3 classification of towns and cities (Task 2) revealed that few possessed a strongly uni- or bi-directionalwind regime, and most could broadly be classed as omni-directional.4 a stand-alone machine mounted at roof level on top of an aerodynamic enclosure could work.



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5.5.1 Aerodynamic / Energy Optimisation

The first stage of this process was to evaluate the aerodynamic potential of differenttwin tower shapes. The team agreed to look at a whole gamut of shapes, fromconventional square-edged block shapes (Figure 6) – which “don’t work”aerodynamically - through circles onto optimised aerofoil shapes.‘Kidney’ or ‘boomerang’ profiles, like those displayed in Figure 7, were found to be thebest footprint shapes for twin tower structures, and could also work if swept into 3dimensions to form a ducted hole.

Figure 7: Sample CFD results showing typical 'boomerang' and 'kidney' profiles

Sketches based on the theme of aerodynamic twin tower structures were translatedinto a series of foam architectural models by UST, e.g. Figure 8 (overleaf). Theseexplored single and multiple turbine designs, and different designs for the linksbetween the towers (which effectively form ducted holes).

Wind tunnel testing on these models and CFD studies using equivalent digital modelsrevealed a number of interesting findings:

• fully 3-dimensional designs (Figure 8) produce a superior performance to thoseconsisting of 2 independent symmetrical towers (Figure 5);

• the use of horizontal wings (of any reasonable aerodynamic sectional profile) willalways enhance output from the turbine(s) – particularly where they form acomplete close fitting 3-dimensional aerodynamic duct shape (hole) in which aturbine can sit;

• optimum performance is obtained for smooth, rounded shapes;• when averaged over all angles of incidence, the power extracted from an

integrated turbine could be up to one and a half times that available from thereference case of a stand-alone machine mounted at the same height;

• In the case of a multi-turbine building, the structure acts to average out the velocityprofile, lessening the expected difference in performance between the lowermostand uppermost turbines5.

5 wind speeds increase with height above ground according to a ‘log law’ profile



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Figure 8: Prototype Twin Tower Building with spaces for 3 wind turbines

These results tend to corroborate existing (ongoing) experimental research in the windenergy industry, where attempts have been made to augment or enhance the poweroutput of a turbine by surrounding it within a thin aerodynamic shell – forming a similarshape to the inner surface of a ducted hole that would be provided by a building.

This research suggests that:

• the maximum power enhancement that can be attained by employing a windconcentrator or diffuser is ~2;

• the level of power enhancement is proportional to the increase in mass flow ratethrough the swept area of the turbine (rather than the cube of mean wind speed).

- results that will also hold for integration of wind turbines into buildings6.

5.5.2 Architectural, Structural and Environmental Optimisation

While a large part of the project is based on the reasonable premise that integration ofwind turbines into buildings must be beneficial in energy terms to be a realisticpossibility, careful attention has been taken to ensure that a wide range of factors areevaluated in the development of wind enhancement and integration techniques.

6 note that a diifuser augmented wind turbine (DAWT) will yaw to face into the direction of the prevailingwind, while the orientation of a turbine in a building will be fixed.



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While general points can be made, many will have to be evaluated on a project-by-project basis, probably as part of an environmental impact assessment, and enforcedvia the application of specific conditions attached to planning permissions. Forexample, the turbines could be visible from many different vantagepoints over severalkilometres. Similarly, CFD and or wind tunnel analysis would undoubtedly be requiredto study flow patterns and the impact of surrounding structures, to ensure that boththe expected energy performance from the integrated turbines and pedestrian comfortcriteria are achievable.An important factor will also be the extent to which a psychological acceptance (of thenecessity) for wind power (renewable energy) exists in the minds of the participants,particularly the public and planners.

This section touches on some of the larger impacts of integration of wind turbines intostructures, but is by no means exhaustive.

Architectural and Aesthetic Impacts

A wide range of architectural designs has been explored during the project, includingdesigns incorporating multiple turbines (Figure 8). Of course, the structure could bepurely used to harvest the wind and be unoccupied, however, integration into largecommercial buildings is an interesting possibility (particularly as the turbines would behigher off the ground, avoiding disturbances to wind flow from surrounding buildings).

Aerodynamically optimal shapes (Figure 7) tend to be sub-optimal in terms ofeconomic organisation of floor space and building services. Neither will theynecessarily produce energy efficient buildings, particularly if they contain deepsections where natural daylighting and ventilation are precluded.Office space adjacent to the turbines will inevitably be less attractive and thereforevaluable due to concerns over noise transmission, flickering of the rotating blades,possibility of electromagnetic interference with computers and telecoms etc. etc.

A sensible means of spatial organisation would therefore be to place service areas(i.e. technical, lifts, stairs, cores) bordering onto the turbine (Figure 9, overleaf), asthey have less onerous requirements than normal office space and can provide abuffering role for the rest of the floor.



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Figure 9: Preliminary floor layout for a twin tower building with integrated turbine(s)

The infills, linking the twin towers structures for aerodynamic purposes, which havequite uniquely curved shapes could also be potentially turned into ‘sky lobbies’ –containing walkways, plants, restaurants etc. However, acoustic studies (see below)have suggested that the surfaces of these infills facing the turbine would need to usematerials which are very efficient acoustic absorbers, probably conflicting with adesire for lightness of structure and transparency.

Structural Impact

A sophisticated means of suspending a wind turbine from a building will be essential tothe overall uptake of overall technology. Unfortunately, it is difficult to improve/optimiseexisting technology, as this has never been attempted before. Moreover, the windenergy and construction industries have few links, but many different (industry)standards.

Starting from the premise of the generic options (Figure 3), it has been possible toassess the loads that would be experienced by the turbine(s) and building in eachcase (by using an existing simplified standardised methodology).

These generic design concepts have been evaluated according to a number ofweighted quantitative and qualitative criteria, e.g. aesthetics, impact on aerodynamics,maintenance, manufacture, strength-to-weight ratios etc. Finite Element Method(FEM) analysis has been used to achieve efficient use of materials and, hence, moreoptimal prototype designs.



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A detailed design study on one promising configuration, i.e. suspending a turbinebetween twin towers (Figure 9), has shown this to be feasible mechanically. Severaloptions can meet the necessary strength requirements in all instances with reasonablematerial use, small deformations and allowable stresses.There will also obviously be significant associated impacts on the structural systemsused within the building, which will require stiffening and (passive or active) vibrationcontrol measures, to cope with both the static and dynamic loadings induced by theweight and rotation of the turbine(s).

Safety Design

Safety will clearly be a major issue for the public, planners, developers and insurers,particularly as turbines may be mounted high up on buildings, increasing the radius ofproximity. Failure of a UWECS could occur in several ways, e.g.:

• shedding of (parts of) a blade during operation;• ice forming and being thrown off the blades during winter;• a failure of the turbine suspension system;

- and all possible scenarios leading from these failures would have to be identified andevaluated in quantifying the individual and group risk posed by the development.

Statistical data on HAWTs is readily available, although not for the less widelymanufactured and used VAWT designs. However, the effects on the turbine of placingin within a ducted hole cannot be predicted with complete certainty based on currentknowledge.

Measures, which require major re-design of the turbines themselves, will inevitablylead to increased costs and unfavourable economics. Secondly, while ‘invisible’ safetyimprovements are undoubtedly important; there is a need to provide visible safetydevices, which crucially enhance both safety (of people and property) and the publicperception of safety. In it’s most basic form, this might entail a safety cage placedaround the wind turbine(s).

Prototype designs for a safety device, which could be fitted to a real building whereturbine(s) are suspended within ducted holes within a building, have been developedand assessed (Figure 10, overleaf).



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Safety Device in situ Honeycomb Mesh Design Radial Mesh Design

Figure 10: Illustration of the Design and Deployment of a Prototype Safety Device

Performance requirements for external safety devices have been identified and amatrix of design options set out on macro, mesa and micro levels (e.g. position,design, materials, automation etc.). In performance terms, they must ideally:

• enhance safety and the perception of safety• be environmentally friendly (i.e. avoid bird kills etc.)• be capable of withstanding exposure to climatic elements over life span;• be structurally sound and capable of absorbing impact energies;• reduce average wind speeds through the ducted hole as little as possible• reduce turbulence in the wind to reduce fatigue loads on the turbine• be aesthetically attractive;• reduce shadow and light flickering from the blades;• be acoustic absorbers rather than propagators• be easily transportable and maintainable• reduce electromagnetic interference;• be cost effective.

The structural functionality of a large number of comparable designs for safety deviceshave been compared quantitatively, together with qualitative judgements on otherimportant factors, e.g. aesthetics/visual impact, aerodynamics.

A radial mesh safety device – having a visual appearance akin to a spider’s web(Figure 10) - positioned both in front of and behind a wind turbine and attached to thebuilding, is suggested as the best option – pending future detailed design studies.

Noise Emissions

The predominant mechanism of noise generation from wind turbines is aerodynamicnoise radiated from the blades, although mechanical sources also exist in themachines.



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Despite a considerable amount of legislation relating to noise in most member states,the lack of precedents means that planning conditions will probably have to be set ona case-by-case basis. One of the potential attractions of placing wind turbines inurban areas is the high level of existing background noise, which can reach up to70dBA.

Prediction of noise emission and propagation for building integrated turbines willobviously be much more complex than the simple point source models (scaled usingmanufacturers’ data on the specific turbine(s)) generally adopted when predictingsound pressure levels perceived by receivers on the ground in the vicinity of isolatedwind farms. For example, common materials such as tarmac and concrete havestrong reflection effects on sound. There may also be very complex aeroacousticphenomena induced by the form of the building itself, the flow over it and vibrations ofthe building itself, which will be difficult to predict.A series of computational studies were carried out using an acoustics softwarepackage. Noise emission from a notional 30m diameter HAWT suspended betweentwin towers (Figure 10) was modelled using a disk of point sources in an attempt toaccount more precisely for the interaction between the tips of the turbine blades andthe surrounding structure. Although no experimental data exists to validate the findings,a number of broad conclusions can be drawn :

• It is preferable to place the wind turbine inside infills rather than between twoindependent towers, as the infills act to reflect sound waves away from the towersand also shield pedestrians at ground level. However, the sound pressure levelsinside the infills themselves will be an important design issue.

• Acoustic treatment of the envelope of the infills (using material such as acousticplaster, expanded polyurethane foam, fibreboard etc.) will certainly be required,and the acoustic properties of any safety device (Figure 10) will be important. Thisis also likely to assist in ensuring that sound pressure levels on facades ofneighbouring buildings (not otherwise shielded) fall within acceptable limits – anaspect also studies during the project.

5.6 Design, Construction and Field-Testing of Prototype Building/WindConcentrator

5.6.1 Objectives

The most important part of the project has been to seek to demonstrate that the windintegration and enhancement techniques developed would actually work in practice,albeit on a scaled prototype.



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The partners agreed that three configurations for both a small-scale HAWT and VAWTwould be field-tested :

• stand-alone wind turbine – to benchmark the machine performance• mounted between twin towers – semi-concentrated• mounted between twin towers with infills – fully concentrated

5.6.2 Design and Construction

The small scale HAWT and VAWT7 (with rotor diameters of around 2.0m) wereidentified fairly quickly, purchased and transported to the Rutherford AppletonLaboratory (RAL) site in Southern England for performance testing (Figure 1).

The design for the prototype building or Full-Scale Model (FSM) evolved during thecourse of the project, through a series of aerodynamic, structural and architecturaldesign studies.

Figure 11: Photographs of the Prototype Aerodynamic Building (FSM) without infills

during testing with the HAWT at the RAL Site

7 both are 3 bladed machines. The VAWT uses a combination of Darrieus and Savonius blades.



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The (structural) design of the FSM was executed by MECAL on behalf of the partners,and can be seen in Figure 11. It has a number of innovative features :

• an economic structural design using standardized components;• the FSM is mounted on a base frame which can turn manually on a circular rail,

enabling the orientation of the prototype to be easily varied;• the gap between the two FSM towers can be varied to allow concentration and

vibration issues to be explored;• thin riveted aluminium cladding on top of the internal wooden tower skeletons,

allows reasonably smooth aerodynamic surfaces to be obtained;• provision of a safety mesh to protect the turbine in extreme conditions.

The FSM was eventually pre-fabricated in the Netherlands by a Dutch Contractor (X2),who were attracted by the challenge, and shipped to the UK for assembly at the RALsite in March 2000. The quotes obtained from UK contractors during the tenderingprocess were, on the whole, extremely high.

A set of ‘infills’ or aerodynamic cross-pieces linking the towers and closely fitting roundthe turbine(s) were subsequently added in July 2000. These were designed to bothenhance the performance and aesthetics of the prototype.

Figure 12: Close-up of the Infills fitted to the Prototype Building (FSM)

Automated monitoring procedures were set-up and developed by RAL to log the dataproduced during the testing, and some independent measurements of noise andvibration data were taken by IC.

Contractual changes during the course of the project led to delays, which significantlyreduced the time available for field-testing of the prototype building or Full-ScaleModel (FSM) from 1 year to 6 months.



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5.6.3 Overall Results from Field-Testing

The performances of the two stand-alone machines were obtained with only minorexperimental problems. The machines are small and generate comparatively smallamounts of power (in comparison to the huge MW HAWT turbines now being built),Testing showed that both had fairly poor coefficients of performance, with the HAWTbeing the more efficient of the two.

A recently introduced methodology for testing of small wind turbines was used in theset-up of the field-testing, and in the analysis and presentation of performance data.This was adapted and extended for the prototype building to cope with the expecteddependency of performance on the effective angle of incidence of the wind onto theprototype. This problem is demonstrated in Figure 14 – the effective angle ofincidence (CYAW – Concentrator Yaw) must be determined from the orientation of theprototype (concentrator)8 and the prevailing (mean) wind direction.

Figure 13: Determining the effective angle of wind incidence onto the prototype

Sample results plots are shown in Figure 14 (overleaf) for the HAWT in the prototypebuilding without infills – the configuration for which the largest data set was collected.

In this example, the data has been sorted into 30º sectors prior to averaging, in similarfashion to the way historical statistical wind data is presented in the European WindAtlas. The label ‘Sector 0’ refers to a 30º sector about CYAW = 0º (encompassingresults for -15º <= CYAW <= +15º) and so on. More details on the content andlabelling of Figure 14 can be found in Appendix A.

8 It is assume that the turbine is aligned with the main axis of the prototype (fixed during testing).



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Figure 14: Sample results plots from field-testing of prototype building (FSM)



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The key findings are as follows:

• an integrated wind turbine will (as expected) produce more power than a freely-yawing stand-alone machine mounted at the same height :

• power generation generally starts in wind speeds at least 1 m/s below the cut-inwind speed of the stand-alone turbine. This will considerably enhance energycollection in low wind speed sites (typical of urban areas).

• Optimum power enhancement does not occur when the wind is normal to theswept area of the turbine, but when the effective angle of incidence is in around30° (Figure 14). This phenomenon is also suggested by the wind tunnel and CFDtests.

• the HAWT and the VAWT turbines both show enhanced performance within theprototype building for an incident wind angle (CYAW) range of ±60° (Figure 14).

• substantial power (i.e. > 50% of that produced by a stand-alone machine) is stillgenerated even at very acute wind angles, when the wind is effectively incident atright angles onto the prototype and the turbine may be effectively operatingdownwind (with a corresponding reduction in performance).This is obviously due to complex flow phenomenon, e.g. flow remaining attachedbetween the towers even while the wind direction is rapidly fluctuating. This can beobserved visually at the RAL site by looking at the ‘tufts’ or ‘tell-tails’ attached tothe towers (Figure 12). These factors are also suggested in the CFD results,shown in Figure 15 overleaf.

• power enhancement (accounting for conversion losses) for both turbines isimproved by a large ratio at low wind speeds (where the stand-alone turbine wouldbe producing minimal power) and appears to reach a lower ratio at high windspeeds. The performance the performance of the HAWT in the prototype withoutinfills is improved by a factor of between 1.2 and 1.3 (depending on incident windangle) at 8 m/s, and the VAWT by a larger factor (probably due to its particularcharacteristics).

• the infills further enhance the performance of the HAWT in the concentrator whenoperating in low wind speeds, but insufficient data on their angular performancewas collected to draw firm conclusions on this aspect. Testing with the VAWT wasnot possible due to time constraints.The design of the infills is not completely optimised due to the surface roughnesscaused by fabricating the complex curvature from sheets of aluminium (Figure 12),and a conservative gap (100mm+) has been left between the edges of the (HAWT)blades and the inner surface of the infills to prevent the likelihood of collisionscaused by excessive vibration (lead to a dissipation of their concentrating effect).



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• Sources of asymmetry are also present in the results scatter, e.g. theidiosyncrasies of the test site and the fact that the turbines rotate in a particulardirection (tending to favour winds from particular sectors – a factor also suggestedby wind tunnel tests using a motorised model turbine (Figure 5)).

Figure 15: Results from CFD Simulations confirming the variation in wind enhancementwith angle of wind incidence onto the prototype building9

5.6.4 Utilisation of Results

Attempts to extrapolate findings from the noise and vibration measurements have metwith limited success, due, respectively to the problems with measuring acomparatively small noise source against background levels, and inconsistencies insome measurement parameters.

Publication of the full results from the field-testing is intended as a key component ofthe dissemination plans for the project (Section 7), so that they can be subjected torigorous scientific scrutiny. Further field-testing may follow, as, for instance, it was notpossible to subject the prototype to higher wind speeds, due to testing taking placethrough the spring and summer.

9 red areas indicate high velocities and good wind enhancement, blue areas the opposite.



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This will also be useful in properly assessing the problems with scaling-up thetechnology, and the validity of the field-testing results in predicting the performance ofmuch larger turbines (probably of no more than ∅10-35m rotor diameter due toenvironmental impacts on surroundings) integrated into real buildings/structures.

Using a spreadsheet methodology developed during the project, which allows thefollowing data to be combined:

• Angular power enhancement factors from the field-testing of the prototype• Statistical wind data for a particular town/city from the European Wind Atlas• Manufacturers’ performance data on particular (full-scale) wind turbines• Maintenance and outage factors for the turbines

- it was possible to (conservatively) estimate the potential increase in annual powerproduction from a 250kW, ∅30m diameter turbine integrated into a scaled-up versionof the FSM, compared to the equivalent freely yawing stand-alone machine.

Several town/cities were selected (based on the classification of wind regimes carriedout during the early stages of the project) as shown in Table 2:

Annual Power Production (MWh)(Capacity Factor)

Town/City Wind RegimePredominant Wind Direction

Mean Wind Speed at 30 | 60m Stand-Alone@30m height

UWECS@60m height

Increase inEnergy Yield

(%)

Dublin

Weakly Uni-directional

WSW

5.84 m/s | 6.44 m/s

549.8

(0.24)

730.4 – 816.8

(0.33–0.37)

32.8 – 48.6

Munich

Strongly Uni-directional

WSW

3.73 m/s | 4.11 m/s

199.3

(0.09)

335.0 – 341.2

(0.15-0.16)

68.0 – 71.2

Lyon

Bi-directional

N-S

3.51 m/s | 3.87 m/s

205.7

(0.09)

354.7 – 357.2

(0.16)

72.4 – 73.7

London

Omni-directional

SSW

4.66 m/s | 5.13 m/s

303.8

(0.14)

485.1 – 524.6

(0.22–0.24)

59.7 – 72.7

Table 2: Assessing performance enhancement by wind turbine integration

Testing on a much larger prototype building incorporating a larger scale machine (of atleast ∅12m rotor diameter) would be required to add weight to the findings of thefield-testing from project WEB in terms of extrapolating performance data. However,even if the concentration effect at very acute angles were not to be replicated, it isclear that a combination of a higher suspension height and a well-designedaerodynamic building form could produce acceptable energy yields. This might alsomake the results of interest within the wind energy industry, where the building couldbe thought of as an unoccupied structure design to enhance power output from theintegrated wind turbines.



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6 Conclusions

Project WEB has achieved all the key objectives mentioned above in Section 2.

Wind enhancement and integration techniques have been developed (in conjunctionwith methods for assessing their performance and environmental impacts) to improvethe annual energy yield for wind turbines located in built-up areas. They act byconcentrating the low to moderate wind speeds typical of most urban Europeanlocations. Specifically this has involved :

• identifying and assessing types of urban locations where wind turbines could beplaced (either as stand-alone machines or integrated into buildings)

• studying the performance of a complete range of building forms – including bothaerodynamic and non-aerodynamic shapes

• assessment of energy potential by use of wind-tunnel testing on small-scalemodels and computational fluid dynamics simulations

• development of methods for analysing the wind regimes in specific urban locationsusing statistical wind data, and, for assessing the potential annual energycontribution of one or more turbines integrated into a building.

• exploration of building aesthetics with reference to visual impacts of such schemes

• optimisation of architectural space for favoured building shapes

• development of prototype structural systems for supporting turbines and isolatingvibrations from buildings

• development of prototype safety devices to address public safety concerns

• study of impact of noise emissions from integrated turbines on building andimmediate surroundings

• development of servicing strategy for buildings to ensure energy efficientoperation.

Field-testing of small wind turbines (both VAWT and HAWT) integrated into aprototype aerodynamic building embodying these principles has successfullydemonstrated that integration can work in aesthetic and energy terms.

The key result from the field-testing of the prototype building – the demonstration ofthe enhanced performance of wind turbines integrated into an optimised aerodynamic



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structure - could also be exploited in other areas of the wind energy industry, e.g.offshore technology. This would similarly require detailed design and testing atintermediate to large scales to enable proper assessment of cost, benefits and risks.

Suggested acronyms for describing the technology developed during the currentproject are ‘Urban Wind Energy Conversion Systems’ (UWECS) and ‘BuildingAugmented Wind Turbines’ (BAWTS).

7 Exploitation plans and anticipated benefits

A detailed exploitation plan formed part of the original proposal for project WEB.These activities are classed as outside the scope of R&D project proposals, so thisaspect of the original proposal was not included in the scope of the actual project.

The assessments made in the original exploitation plan remain largely valid, i.e. thedevelopment of the UWECS prototype is not at a sufficiently advanced commercialand industrial level to warrant patent rights. The partners in the project have alreadysubmitted a detailed proposal for an action under the EC ALTENER II programme(“Wind Energy in the Build Environment”, November 1999) based on disseminating thefindings of project WEB. Although this proposal was unsuccessful, the partners willconsider refining and re-submitting the proposal for a future call once the currentproject is officially finished.

The partners agreed at the final team meeting in August 2000 on an initial combineddissemination effort following completion, as shown in Table 3 overleaf.It is likely that the commercial partners, MECAL and BDSP, will (jointly orindependently) explore further opportunities for collaboration and commercialexploitation of the results of the project.

WEB – JOR3-CT98-0270 Publishable Final Report


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Activity Details Timescale(months)

Open Day(s)

At least one ‘Open Day’ will be held in conjunction with the Rutherford Appleton Laboratory in the UK. All partners will be involved. Invitations will be sent to selected guests (e.g. architects, engineers, planners, wind energy professionals, policy formers), mediaorganisations (TV, radio) and other interested parties (environmental organisations) throughout Europe. The key results of the project willbe explained using a variety of presentation techniques, and visitors will be able to see the prototype building with integrated wind turbine inoperation. Further events (including in different member states and ideally open to the general public) may subsequently be planned depending onthe level of interest.

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Publication of amain resultsposter

All partners will be involved in producing a poster summarising the key results from WEB, together with a selection of images generatedduring the project. The poster will be completed by December 2000. It will be displayed in partners’ offices, on exhibition stands and at wind and constructionindustry gatherings. It may also be sent to selected parties with the consent of all partners. The aim is to raise awareness, interest and discussion among major potential investors in this technology.

6

Publication ofmain results onthe internet

The publishable final report will be placed on the internet sites of the partners, and will contain more in-depth information than the posterabove. Publication via other important internet sites, such as that maintained by the European and American Wind Energy Associations (EWEA& AWEA respectively) will be encouraged. Additional non-confidential material may be published in this way, by agreement between the partners. The aim is to reach the maximum number of interested parties (including, for example, students) in the most economical way. It will alsoensure that the results of the research remain accessible far beyond a timescale of 3 years following the end of the project.

6

Publication ofconference andjournal papers

All partners will be involved in producing a general paper summarising the results of the current project to be presented at the EuropeanWind Energy Association (EWEA) Conference in the Summer of 2001. One or more partners will publish specialist papers focussing on specific results (e.g. performance of the prototype building). Non-participating partners will be kept informed of such developments.

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ResearchOpportunities

All Partners will put forward and discuss further proposals for joint research and dissemination of existing results under the EC ALTENER,EC ENERGIE and other international or national programmes. For example, this might include scaling up the prototype building to morerealistic dimensions and then monitoring its performance. Over the longer term this may well involve collaboration with different partners, and detailed development of specific technologies.

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Table 3: Planned Dissemination Activities



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The project has sought to directly address the problem of providing reliable, non-polluting renewable sources of electricity at acceptable cost which will be essential inachieving the goal of sustainable development and in reducing the threat posed byglobal phenomena such as climate change. It does so by exploring the new use of anexisting renewable energy source (wind).The size of the market for wind energy in the built environment is difficult to gauge, particularly as (in Western Europe) the vast majority of buildings are alreadyconnected to highly reliable supply grids through which electricity from largecentralised power stations is already distributed. There will be a number or risks involved in the necessary next step of scaling UWECStechnology up to a realistic scale, since although existing wind turbine and constructiontechnology can be harnessed, several technological innovations will be required. Afurther demonstration project is likely to be required. Estimating the initial and long-term unit prices for electricity generated by buildingintegrated wind turbines is therefore difficult. However, given the likely electricity tariffstructures in place in individual member states, the fastest economic payback will beobtained by using the electricity generated directly in the building (i.e. displacing gridsupplies) and only exporting electricity to the grid when an excess is available. The potential cumulative contribution (in terms of the percentage of the annual EC ornational electricity demand that could be produced) will remain difficult to assess, untilreal developments enter the planning process in multiple member states. It will dependon the attitudes and/or policies of many different actors – national and regionalgovernments, investors, developers, planners, architects, engineers, utility providers,insurers, general public, environmental organisations - which will also certainly varyfrom country to country across the EC.

Although wind turbines can be retrofitted to existing buildings, the greatest potentiallies in new build where design and planning for the presence of wind turbines can beincorporated from the offset. Exploitation of UWECS technology in other areas of thewind energy industry, e.g. development of offshore technology, is, however, apossibility that should be explored.

Over the medium term, say, 10-15 years, it is likely that integration of wind turbines inthe built environment could provide a (small, but important) fraction of the overallcontribution from renewable energy sources.An estimation of the potential cumulative contribution of integration of wind energy inthe environment based on a number of criteria is made in the final confidential reportto the EC.



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8 Photographs to illustrate potential applications of the project

Figure 16: A Montage of Images showing the Prototype Aerodynamic Building withIntegrated Wind Turbine (HAWT) built and tested during Project WEB



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9 Appendix A

Key points to note about the data and graphs displayed in Figure 14 are as follows :

The raw experimental data (recorded at 2-second intervals) was processed andanalysed to give sets of 1minute and 10 minute averages.

The data has been sorted into 30º sectors prior to averaging, in similar fashion to theway historical statistical wind data is presented in the European Wind Atlas.

Trendlines (polynomial curve fits) through these averaged data sets are displayed inFigure 14, although there will obviously be a degree of scatter in the data.

The black lines indicate the measured performance of the HAWT in stand-alone mode(the reference case).

The term ‘Power Enhancement Ratio’ displayed on the y-axis of the lower graphdenotes the ratio of the power generated by the HAWT in the prototype building tothat generated by the stand-alone machine (mounted at the same height on the sametower) for a given wind speed.

The exact meaning of the labels shown on the graphs is given in Table 4.

Label Meaning Angles of IncidenceSector 0 30º sector centred on CYAW of 0º. -15º <= CYAW <= +15ºSector 30 Averaged results for 2 30º sectors

centred on CYAW ± 30º.-45º <= CYAW < -15º+45º <= CYAW < +15º

Sector 60 Averaged results for 2 30º sectorscentred on CYAW of ± 60º.

-75º <= CYAW < -45º+75º <= CYAW < +45º

Sector 90 Averaged results for 2 30º sectorscentred on CYAW of ± 90º.

-105º <= CYAW < -75º+105º <= CYAW < +75º

Table 4: Explanation of legend labels shown on Figure 14 (overleaf)

Note that for Sectors 30, 60 and 90 are actually averages of average results. This hasbeen used to simplify the presentation and interpretation of data in Figure 14.

The actual results for, say, -45º <= CYAW < -15º and +45º <= CYAW < +15º will notbe identical, as their a number of sources of asymmetry present, e.g. :

• different surface roughness/obstacles upstream of the prototype buildingdepending on wind direction due to the idiosyncrasies of the RAL site;

• the HAWT rotates in a specific direction (clockwise in this instance), which maytend to enhance or diminish the effect of wind coming from particular sectors;

• sources of experimental error (i.e. shading of anemometers).

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