Urban Wind Generation: Comparing Horizontal and Vertical Axis Wind Turbines at Clark University in Worcester, Massachusetts

Electricity production must shift towards carbon neutral sources such as wind power to mitigate the impacts of climate change. The wind resource in urban environments is challenging to predict but technologies, including computational fluid dynamics software, are making it possible. This software pinpoints suitable placement for wind turbines through models that show wind acceleration patterns over a building. Horizontal axis wind turbines (HAWTs) have dominated the wind industry but vertical axis wind turbines (VAWTs) offer potential to outperform HAWTs in urban environments. VAWTs can handle turbulent and unconventional wind and generate energy at slower speeds, which is beneficial for these areas. A case study at Clark University in Worcester, Massachusetts analyzes the functionality of a HAWT and a VAWT. The machines are compared by their efficiencies due to an imbalance of rated power outputs. The machines’ average maximum power coefficients are similar. However, when the R2 values of the turbine’s power curves are compared the VAWT demonstrates greater capacity to track changes in the wind. This research is the first step in redefining the power systems employed at Clark University and the data will be utilized to find better locations for the wind turbines

Integration of aero-elastic belt into the built environment for low-energy wind harnessing: current status and a case study

Low-powered devices are ubiquitous in this modern age especially their application in the urban and built environment. The myriad of low-energy applications extend from wireless sensors, data loggers, transmitters and other small-scale electronics. These devices which operate in the microWatt to milliWatt power range and will play a significant role in the future of smart cities providing power for extended operation with little or no battery dependence. Low energy harvesters such as the aero-elastic belt are suitable for integration with wireless sensors and other small-scale electronic devices and therefore there is a need for studying its optimal installation conditions. In this work, a case study presenting the Computational Fluid Dynamics modelling of a building integrated with aero-elastic belts (electromagnetic transduction type) was presented. The simulation used a gable-roof type building model with a 27° pitch obtained from the literature. The atmospheric boundary layer flow was employed for the simulation of the incident wind. The work investigates the effect of various wind speeds and aero-elastic belt locations on the performance of the device giving insight on the potential for integration of the harvester into the built environment. The apex of the roof of the building yielded the highest power output for the aero-elastic belt due to flow speed-up maximisation in this region. This location produced the largest power output under the 45° angle of approach, generating an estimated 62.4 mW of power under accelerated wind in belt position of up to 6.2 m/s. For wind velocity of 10 m/s, wind in this position accelerated up to approximately 14.4 m/s which is a 37.5% speed-up at the particular height. This occurred for an oncoming wind 30° relative to the building facade. For velocity equal to 4.7 m/s under 0° wind direction, airflows in facade edges were the fastest at 5.4 m/s indicating a 15% speed-up along the edges of the building

On the Flow over High-rise Building for Wind Energy Harvesting: An Experimental Investigation of Wind Speed and Surface Pressure

The human migration from rural to urban areas has triggered a chain reaction causing the spiking energy demand of cities worldwide. High-rise buildings filling the urban skyline could potentially provide a means to improve the penetration of renewable wind energy by installing wind turbines at their rooftop. However, the above roof flow region has not received much attention and most results deal with low-rise buildings. This study investigates the flow pattern above the roof of a high-rise building by analysing velocity and pressure measurements performed in an atmospheric boundary layer wind tunnel, including four wind directions and two different roof shapes. Comparison of the surface pressure patterns on the flat roof with available low-rise building studies shows that the surface pressure contours are consistent for a given wind direction. At 0◦ wind direction, a separation bubble is detected, while cone vortices dominate at 30◦ and 45◦. The determining factor for the installation of small wind turbines is the vicinity to the roof. Thus, 45◦ wind direction shows to be the most desirable angle by bringing the substantial amplification of wind and keeping the turbulence intensity low. Decking the roof creates favourable characteristics by overcoming the sensitivity to the wind direction while preserving the speed-up effect

On roof geometry for urban wind energy exploitation in high-rise buildings

The European program HORIZON2020 aims to have 20% of electricity produced by renewable sources. The building sector represents 40% of the European Union energy consumption. Reducing energy consumption in buildings is therefore a priority for energy efficiency. The present investigation explores the most adequate roof shapes compatible with the placement of different types of small wind energy generators on high-rise buildings for urban wind energy exploitation. The wind flow around traditional state-of-the-art roof shapes is considered. In addition, the influence of the roof edge on the wind flow on high-rise buildings is analyzed. These geometries are investigated, both qualitatively and quantitatively, and the turbulence intensity threshold for horizontal axis wind turbines is considered. The most adequate shapes for wind energy exploitation are identified, studying vertical profiles of velocity, turbulent kinetic energy and turbulence intensity. Curved shapes are the most interesting building roof shapes from the wind energy exploitation point of view, leading to the highest speed-up and the lowest turbulence intensity

높이에서 체적까지

학위논문(박사) -- 서울대학교대학원 : 환경대학원 환경계획학과, 2023. 2. 김태형.Urban form is a major factor in explaining the interaction between human activities and the environment. Historically, research on urban form principally focused on horizontal forms, and its primary goal was the improvement of urban spaces efficiency and functionality. However, the two-dimensional properties of urban form, such as land-use change, are not sufficient to explain changes in urban climate. In recent years, there has been growing interest in the geometrical structure created by vertical urban form and its impact on urban climate, particularly urban temperature. While some indicators of vertical urban form have been shown to impact temperature, there remain gaps in our understanding, including a lack of consistent measurement standards and an incomplete understanding of the complex interactions within space. This study aimed to systematically analyze the impact of vertical urban form on air temperature. First, this study proposed vertical urban form indices to investigate the effect on air temperature. Despite recognition of the impact of vertical urban form on air temperature, previous studies have not systematically analyzed the measurement criteria of vertical urban form and its impact on air temperature. To address these deficits, four measurable indices were proposed: Vertical, Variance, Volume, and Vacant. These indices have been identified as key factors that regulate the effect of urban form on air temperature, including factors based on previous research including shade, heat capacity, and ventilation performance. The proposed indices, including 1-dimensional (height), 2-dimensional (planar), and 3-dimensional (volumetric) indices, were analyzed to examine the effects of individual and interacting indices on air temperature. The indices are interdependent, and therefore, deep learning models were used to account for the interaction between them. A prediction model was constructed using a 2-layer artificial neural network, and the impacts of the individual and interactive indices were derived using the Shapley additive explanation (SHAP) method, which is an analytical method that explains the output of machine- and deep-learning models. The influence of individual and interactive vertical urban forms on a local scale varies based on the specific characteristics of these forms. The complicated airflow caused by the conflicting effects of shadows and ventilation performance and the interrelationships between urban forms can make it difficult to make generalizations. This study aimed to analyze the differences in the impact of urban form characteristics on a local scale. It is important to consider that temperature mitigation strategies should be tailored to specific urban form characteristics, as different critical indices were identified in areas with dense low-rise or high-rise buildings. The results of the study showed that four indices of vertical urban form have a significant impact on urban air temperature. During the summer, the degree of openness (Vacant) and the average spatial height (Vertical) are critical factors in regulating air temperature. The shading effect of high-rise buildings and the ventilation performance provided by the openness improve thermal comfort. A significant finding was the interaction between spatial vacancy and height, as shown by the SHAP dependence plot. Sensitivity levels varied depending on whether the openness was above or below average. In areas with low openness, spatial height was more sensitive, and the temperature rapidly increased with low building height. In densely packed, low-height areas, cooling effects from shading or ventilation cannot be expected. This study revealed that maintaining low spatial density beneath the urban canopy layer is a practical way to decrease the urban temperature on a local level. The spatial density was composed of spatial vacancy and height. Previous studies substituted building volume (Volume) with spatial density, emphasizing the negative impact of building volume on urban temperature. The results of this study showed that better ventilation from high spatial vacancy and improved shading from height could effectively mitigate the urban temperature by offsetting the impact of building volume on temperature rise. For instance, although the total building volume is high, a dense area of high-rise buildings has better thermal comfort than a dense area of low-rise buildings. This is because high-rise buildings create shading and have larger spatial vacancies, which enhance ventilation and reduce temperature. It is essential to understand spatial density in terms of the interplay between spatial vacancy and height. New insights were added by the relationship between spatial vacancy and building volume and the relationship between spatial height and height variation (Variation). When a spatial vacancy is low and building volume is high, the air temperature becomes more sensitive to the volume, causing rapid temperature increases in certain areas. Additionally, areas with low and constant heights experience a rapid rise in temperature. In addition, this study confirmed that the impact of urban form on temperature varies depending on urban characteristics on a local scale. Using the gaussian mixture model, urban form characteristics were classified into five clusters, which can be summarized as follows. Cluster 1 is a dense low-rise building area with constant height. Cluster 2 is a dense low- and mid-rise building area next to a stream. Cluster 3 is an area with a concentration of mid- and high-rise buildings of varying heights. Cluster 4 is an area with mid- and high-rise buildings with ample spatial vacancy. Cluster 5 is an area close to green spaces and rivers. The significant indices of the vertical urban form varied based on the cluster type. This result implies that the strategy for reducing regional temperature should be tailored to the specific urban form characteristics. The contribution of this dissertation research can be divided into both theoretical and practical aspects. Theoretically, this research comprehensively explains the relationship between vertical urban form and urban temperature. The complex interactions between urban forms have resulted in difficulties when generalizing the results of previous studies; however, this study offers insight into the significance of vertical urban form indices and the impact of their interactions. Practically, this research suggests pragmatic policy interventions for urban planners and designers aiming to mitigate urban temperatures. Because the physical environment of cities cannot be easily altered from the top down, a careful approach is necessary. Furthermore, resources are limited, making it crucial to prioritize the methods used. In sum, the results of this study can help improve cities' thermal environments.도시형태는 인간 활동과 환경의 상호작용을 설명하는 주요한 요인이다. 전통적으로 도시형태에 관한 탐구는 대부분 수평적인 형태에 관심을 두었다. 도시 공간의 효율과 기능의 향상은 수평적 형태를 결정하는 주요한 요소였다. 그러나 토지이용변화와 같은 도시형태의 평면적 속성은 열섬 효과와 같은 기후의 변화를 설명하기에 부족하다. 최근 들어 도시의 수직형태가 만드는 기하학적 구조가 도시 기후에 미치는 영향에 대한 관심이 증가하였다. 특히, 도시 온도와 관련하여 일부 수직 도시형태 지표가 온도에 미치는 영향이 보고되지만 여전히 수직 도시형태에 관한 수용가능한 측정 기준이 불일치하고, 공간에서 일어나는 복잡한 상호작용을 설명하지 못하는 실정이다. 이에 이 연구는 수직 도시형태가 대기 온도에 미치는 영향을 체계적으로 분석하였다. 수직 도시형태가 대기 온도에 미치는 영향을 살펴보기 위해 먼저 수용가능한 지표를 제안하였다. 도시의 수직형태가 도시 온도에 미치는 영향에도 불구하고 수직 도시형태 측정 지표와 온도에 미치는 영향에 관한 체계적인 분석은 부족하다. 이에 선행연구를 검토하여 도시 온도를 조절하는 측정 가능한 수직 도시형태를 네 가지 지표로 제안하였다. 네 가지 지표는 알파벳 V로 시작하는 네 단어로 높이(Vertical), 높이 변위(Variance), 체적(Volume), 개방성(Vacant)이다. 제안된 지표는 기존 연구에서 도시형태가 도시 온도에 미치는 효과인 그늘, 열 용량, 환기 성능을 조절하는 주요한 요인으로 지목되었다. 제안된 지표는 개별 및 상호관계 영향을 중심으로 분석되었다. 연구에 사용된 도시형태 지표는 도시형태가 온도에 미치는 다양한 효과를 살펴보기 위해 1차원(높이), 2차원(평면)과 3차원(체적) 지표를 모두 포함한다. 공간의 연속성을 고려하면 도시형태 지표 간에 상호관계가 필연적으로 발생할 수밖에 없다. 이에 지표 간의 상호관계를 고려하기 위해 딥러닝 모형을 분석에 사용하였다. 분석은 2-레이어 인공신경망으로 예측 모형을 구축하고, 이를 설명하는 분석 방법인 SHAP를 통해 지표의 개별 및 상호관계에 대한 영향력을 도출하였다. 도시형태가 만드는 그늘 및 환기성능의 모순적인 효과와 도시형태 간의 상호관계는 도시 공간의 기류를 다양하고 복잡하게 만들어 일반화하기 어렵게 한다. 이에 수직 도시형태의 개별 및 상호작용 효과는 로컬규모의 도시형태 특성에 따라 다르게 나타날 가능성이 높다. 이를 식별하기 위해 이 연구는 로컬규모에서 도시형태 유형에 따른 도시형태 영향력의 차이를 살펴보았다. 예컨대, 저층건물 밀집지역과 고층건물 밀집지역에서 중요하게 나타나는 지표가 다르다면 온도를 완화하기 위한 접근이 달라야 한다. 분석 결과 네 가지 수직 도시형태 지표는 도시의 대기온도에 유의미한 영향을 미치고 있었다. 여름철에는 공간의 개방성(Vacant)과 공간높이(Vertical)가 온도를 낮추는 중요한 지표였다. 고층 건물이 만드는 그늘효과와 도시의 개방성에 의한 환기성능이 열 쾌적성을 개선하는 데 도움을 주었다. 중요한 점은 개방성과 공간높이의 상호관계에서 발견된다. SHAP의 의존성 플랏을 통해 개방성과 공간높이의 관계를 살펴본 결과 개방성이 평균 이하인 지역과 평균 이상이 지역에서 공간높이에 대한 민감도가 다르게 나타났다. 전자가 후자에 비해 높이에 더 민감하게 반응하였는데, 개방성이 낮은 지역에서 건물높이가 낮을수록 온도의 급격한 상승이 목격된다. 공간높이가 낮고 건물이 밀집된 공간은 그늘효과나 환기성능과 같이 온도 저감 효과를 기대할 수 없어 온도가 급격히 상승하는 현상이 나타날 수 있다. 이 연구의 결과는 UCL 이하에서 공간 밀도를 낮게 유지하는 것이 로컬 규모에서 도시의 온도를 낮추는 좋은 대안이라는 것을 보여주었다. 공간 밀도는 개방성과 높이를 통해 조절할 수 있는 것으로 드러났다. 도시화와 온도의 관계를 살펴본 일부 연구는 공간밀도를 건물 체적과 동일시하여 온도에 양의 영향을 미치는 도시화의 부정적인 효과를 강조한다. 하지만 이 연구는 체적이 온도 증가에 미치는 영향에 비해 적절한 개방성에 의한 환기성능과 고층건물에 의한 그늘 효과를 향상시켜 도시의 온도를 저감할 수 있음을 밝혔다. 예컨대, 고층건물 밀집지역은 저층건물 밀집지역에 비해 총 건물 체적은 높지만 높은 건물이 만드는 그늘효과와 건물 사이의 충분한 간격이 환기성능을 향상시켜 온도를 저감할 수 있다. 이 결과는 공간밀도가 체적이 아닌 개방성과 공간높이의 상호 관계에 의해 이해되어야 함을 보여준다. 개방성과 건물 체적, 공간높이와 높이 변위의 상호관계에서도 새로운 통찰이 발견되었다. 개방성과 건물 체적의 경우 개방성이 낮으면 대기 온도는 체적에 더 민감하게 반응하여 급증하는 지역이 나타났다. 공간높이와 높이 변위의 관계에서는 높이가 일정하고 낮은 지역에서 온도가 급격히 상승하는 현상이 발견되었다. 연구에서 설정한 수직 도시형태 지표는 체적과 높이 변위가 온도에 양의 영향을 미쳤지만 개방성과 공간높이를 조절하여 온도가 급증하지 않거나 낮추는 접근 방법이 있음을 시사한다. 또한, 이 연구는 로컬규모에서 도시형태 유형에 따라 도시형태가 온도에 미치는 영향이 다르게 나타나고 있음을 확인하였다. 도시형태 유형은 가우시안 혼합 모형을 통해 다섯 가지 군집으로 구분되었으며, 각 군집의 특성은 다음과 같이 정리 가능하다: 군집 1은 높이가 일정한 저층건물 밀집지역, 군집 2는 작은 하천에 인접한 저층 및 중층 건물 밀집지역, 군집 3은 다양한 높이의 중층 및 고층 건물 밀집 지역, 군집 4는 개방감이 뛰어난 중층 및 고층 건물 조성지역, 군집 5는 녹지와 하천 인접지역. 각 군집의 도시형태 유형에 따라 수직 도시형태 지표의 중요도가 다르게 나타났다. 이는 도시형태 유형에 따라 지역의 온도 저감을 위한 실행 전략이 달라져야 함을 시사한다. 도시형태가 만드는 복잡한 상호관계는 기존 연구에서 제시된 연구의 결과를 일반화하여 도시공간에 적용하기 어렵게 만든다. 이 연구는 수직 도시형태 지표의 중요도와 지표 간의 상호관계에 대한 통찰을 제공하였다. 이를 통해 학술적 측면에서 수직 도시형태와 도시 온도의 관계에 대한 이해의 깊이를 더하였고, 실천적 측면에서 도시계획가와 설계자들에게 도시 온도 완화를 위한 바람직한 정책적 수단을 제시하였다. 도시의 물리적인 환경에 대한 변화는 손쉽게 하향식으로 적용할 수 없으므로 신중한 접근이 필요하다. 또한, 자원의 한계가 있으므로 방법의 우선순위를 통해 적용할 필요가 있다. 이 연구의 결과는 도시가 보다 나은 열 환경을 조성할 수 있도록 도울 것이다.제 1 장 서론 1 제 1 절 연구의 배경 1 제 2 절 연구의 내용 4 제 2 장 이론적 배경 및 선행연구 고찰 7 제 1 절 도시형태 7 제 2 절 도시 기후 15 제 3 절 에너지 이동 및 균형 21 제 4 절 도시형태의 온도 조절 25 제 5 절 연구의 차별성 34 제 3 장 연구 가설 37 제 1 절 논거 37 제 2 절 가설 46 제 4 장 연구 방법 49 제 1 절 연구 대상지역 49 제 2 절 분석 단위 57 제 3 절 Data 60 제 4 절 분석 방법 70 제 5 절 연구 변수 82 제 5 장 연구 결과 93 제 1 절 기초 통계 93 제 2 절 수직 도시형태의 효과 분석 100 제 3 절 도시형태 유형 군집 114 제 4 절 도시형태 유형에 따른 온도 변화 129 제 6 장 토의 139 제 1 절 수직 도시형태 지표의 영향 139 제 2 절 도시형태 지표의 상호작용 144 제 3 절 도시형태 유형 148 제 7 장 결론 156 제 1 절 이론적 기여 156 제 2 절 정책적 함의 160 제 3 절 연구의 한계 163 부록 I. 군집 성능 검증 164 부록 II. 도시형태 변수의 군집별 분포도 176 참고 문헌 178 Abstract 206박

Urban Wind Turbines: A Feasibility Study

There is an existing body of research into noise, vibration and wind regime concerns associated with urban wind turbines demonstrating the detrimental effects of these topics on the energy yield potential and therefore financial worth of an installation. Much of the research has focused on wind regime assessment and optimum roof top placement via CFD modeling offering generalised guidelines showing a potential for wind power to contribute towards lowering London's CO2 emissions. Unfortunately, without benefiting from appropriate planning assessment, a number of early urban turbines failed and have risked irreversibly tarnishing the concept. Hitherto no studies have been specifically conducted on the urban potential of building integrated wind turbines. As integration is bespoke, typically determined by the architecture, it is unknown whether existing guidelines for roof mounted wind turbines could be directly applied. It is probable that each installation would merit its own assessment and analysis procedure. This study aims to investigate the differences between roof mounted and building integrated turbines in terms of assessment, operation and urban potential. In response to these differences it is intended to demonstrate how a successful installation can be achieved. Comparisons between two urban sites, one smaller, roof mounted HAWT and one larger, building integrated HAWT have been made via noise, vibration, CFD and atmospheric data recorded and analysed over two years to build a comprehensive understanding of the inherent urban issues. The prospect of successfully situating an urban turbine is complex in nature and considering the high installation costs and high level of design and engineering required to do so it is imperative that their energy yield provide a satisfactory return on investment and efficient supply of power without adversely impacting upon the surrounding environment or themselves. This study concludes that a multifaceted approach is necessary to achieve an efficient building integrated turbine, comprised of: (i) accurate local noise surveys to establish the local acoustic environment to inform acceptable turbine operating ranges, (ii) specific noise modeling of manufacturer provided data or, where none is available, acoustic testing of the proposed turbine across all applicable wind speed ranges, (iii) comprehensive vibration assessment, not only of the turbine tower/system but also of the turbine housing and any lower residential floors to ensure no natural frequencies will be excited and to prevent any vibration transmission via appropriate mounting, isolation or damping where necessary, (iv) the acquirement of site specific wind data to inform architectural design, turbine selection and placement. If monitoring at hub height is not possible it has been found that it may be acceptable to monitor in close proximity and then extrapolate the results using CFD analysis and wind profile methods, (v) CFD modeling of the surrounding topography, the turbine mount and/or enclosure. These areas are discussed with potential areas of noise and vibration control and turbine optimisation, specific to the case studies, investigated. Further to the aforementioned study an investigation into a new method of assessing noise and vibration levels associated with average anemometry recorded wind speeds has been presented so as to attain average levels per wind speed bin without being skewed by impulsive gusts

The effect of turbulence in the built environment on wind turbine aerodynamics

Urban Wind Energy is a niche of Wind Energy showing an unstoppable trend of growth in its share in the tumultuous DIY energy market. Urban Wind Energy consists of positioning wind turbines within the built environment. The idea is to match energy production and consumption site so to increase the efficiency of the system as energy losses and costs due to the transportation, conversion and delivery of energy are virtually zeroed. Many aficionados advocate the advantage of such a technology for the environment and argue that a greater diffusion might overcome its flaws as a newborn technology. However, no urban wind application to date is known to have been successful in providing but a derisory amount of ‘clean’ energy. The reason for this fiasco lies in the way research in urban wind energy is conducted, i.e. mostly concerned either in improving the efficiency of wind energy converters, or the assessment of the available wind resource. Very few works have considered the technical implications of placing a wind energy converter, one of the most complex aerodynamic devices, in a complex inflow such as that found in built environments, of which very little is known in terms of its turbulence environment. In fact, it has long been acknowledged that the power output, the fatigue limit state or the total service-life downtime of a wind turbine is well correlated with turbulence at the inflow