Urban Microclimate Analysis for High Performance Office Buildings

<p>This research explored whether urban microclimate analysis has significant impacts on high-performance office buildings. It studied the effects of detailed three-dimensional urban microclimate modelling on building performance simulation. The feasibility and necessity of developing an urban microclimate simulation system were explored. Currently, individual parameters of urban microclimate are modelled by individual programs. However, there was no individual software that could model airflow, Urban Heat Island (UHI) effects and building energy performance at the same time. A simulation system made it possible to model these features of urban microclimate together. Apart from the reliability of programs, accessibility and compatibility were also important for building a simulation system. The goal of this research was to determine the relative scale of the likely microclimate impacts on energy performance, not to present a system that made a precise estimate of these effects in combination. The scale of the variations of results due to changes of urban microclimate parameters were more significant than the values of the results themselves. This is because the focus of the research was on determining to what degree each parameter made a difference in the building performance. The goal was to determine whether it is necessary to model every urban microclimate parameter when their individual effects are combined. The parameters of urban microclimates included horizontal parameters like urban wind and UHI, and vertical parameters like lapse rate, urban boundary layer. In this research, the urban microclimate was modelled in three dimensions, but the process of urban microclimate modelling was time-consuming. This leaded to one of the central questions of the thesis: is there value in the time spent? How big is the scale of the influence of urban microclimate detailed modelling on the prediction of building performance? Is it worthwhile to model three-dimensional urban microclimates? When there is not enough time to calibrate all parameters, what are the parameters’ priorities? A prototypical high-rise office building was modelled based on the data about high-rise office buildings in London. Firstly, the effects of the horizontal parameters were explored. The UHI has larger effects than urban wind. Secondly, the significance of vertical parameters was also explored. At a lower floor, the influence of the wind speed exponent and the boundary layer thickness on building performance simulation is bigger than that of the air temperature gradient coefficient. However, at a higher floor, the influence of the air temperature gradient coefficient is bigger. Finally, a multilayer modelling method was developed to explore the inconsistent vertical variations. The multilayer model consists of the portion in the Urban Canopy Layer (UCL) and the portion in the Urban Boundary Layer (UBL). The effects of vertical variations increase with the distance between the studied height and the UCL height. The feasibility and necessity of developing the simulation system of urban microclimate detailed modelling were demonstrated in the climate of London. In different climates, is it still necessary? The effects of urban microclimate detailed modelling on windy, continental, and tropical climates were also studied. The necessity of urban microclimate detailed modelling has been demonstrated because the combined effects produced around -25% change in London’s climate and Wellington’ climate at most. In Beijing’s climate the change was around -6% and in Singapore’s climate was 2.2% at most. The UHI has a big impact in moderate and continental climates. In a continental climate, there is a big difference in the monthly thermal load prediction. It helps engineers optimize the design of heating in winter and cooling in summer. The effects of urban wind in a windy climate are bigger than those in other cities. The precision of vertical variations has very limited influence, especially in the tropical climate. The air temperature gradient in a tropical climate changed thermal load prediction a lot. The parameters’ priorities in different climates are different. There is no consistent pattern of one factor being less important than the others across all these climates. Therefore, to model the thermal performance of tall buildings in dense urban environments it is necessary to develop a simulation system that can model the Urban Heat Island, and the differences in 3D of variations of temperature, sun and wind within and above the Urban Canopy Layer. Finally, from the one case study examined, modelling urban microclimate in detail is more important for natural ventilation systems than for HVAC systems. Overall, the simulation system of urban microclimate modelling was developed gradually. It is necessary to develop the simulation system to approach a real urban circumstance. The accuracy of the detailed urban microclimate model depends on the engineers’ requirements. The priority of urban microclimate parameters depends on climatic features.</p>

Urban Microclimate Analysis for High Performance Office Buildings

<p>This research explored whether urban microclimate analysis has significant impacts on high-performance office buildings. It studied the effects of detailed three-dimensional urban microclimate modelling on building performance simulation. The feasibility and necessity of developing an urban microclimate simulation system were explored. Currently, individual parameters of urban microclimate are modelled by individual programs. However, there was no individual software that could model airflow, Urban Heat Island (UHI) effects and building energy performance at the same time. A simulation system made it possible to model these features of urban microclimate together. Apart from the reliability of programs, accessibility and compatibility were also important for building a simulation system. The goal of this research was to determine the relative scale of the likely microclimate impacts on energy performance, not to present a system that made a precise estimate of these effects in combination. The scale of the variations of results due to changes of urban microclimate parameters were more significant than the values of the results themselves. This is because the focus of the research was on determining to what degree each parameter made a difference in the building performance. The goal was to determine whether it is necessary to model every urban microclimate parameter when their individual effects are combined. The parameters of urban microclimates included horizontal parameters like urban wind and UHI, and vertical parameters like lapse rate, urban boundary layer. In this research, the urban microclimate was modelled in three dimensions, but the process of urban microclimate modelling was time-consuming. This leaded to one of the central questions of the thesis: is there value in the time spent? How big is the scale of the influence of urban microclimate detailed modelling on the prediction of building performance? Is it worthwhile to model three-dimensional urban microclimates? When there is not enough time to calibrate all parameters, what are the parameters’ priorities? A prototypical high-rise office building was modelled based on the data about high-rise office buildings in London. Firstly, the effects of the horizontal parameters were explored. The UHI has larger effects than urban wind. Secondly, the significance of vertical parameters was also explored. At a lower floor, the influence of the wind speed exponent and the boundary layer thickness on building performance simulation is bigger than that of the air temperature gradient coefficient. However, at a higher floor, the influence of the air temperature gradient coefficient is bigger. Finally, a multilayer modelling method was developed to explore the inconsistent vertical variations. The multilayer model consists of the portion in the Urban Canopy Layer (UCL) and the portion in the Urban Boundary Layer (UBL). The effects of vertical variations increase with the distance between the studied height and the UCL height. The feasibility and necessity of developing the simulation system of urban microclimate detailed modelling were demonstrated in the climate of London. In different climates, is it still necessary? The effects of urban microclimate detailed modelling on windy, continental, and tropical climates were also studied. The necessity of urban microclimate detailed modelling has been demonstrated because the combined effects produced around -25% change in London’s climate and Wellington’ climate at most. In Beijing’s climate the change was around -6% and in Singapore’s climate was 2.2% at most. The UHI has a big impact in moderate and continental climates. In a continental climate, there is a big difference in the monthly thermal load prediction. It helps engineers optimize the design of heating in winter and cooling in summer. The effects of urban wind in a windy climate are bigger than those in other cities. The precision of vertical variations has very limited influence, especially in the tropical climate. The air temperature gradient in a tropical climate changed thermal load prediction a lot. The parameters’ priorities in different climates are different. There is no consistent pattern of one factor being less important than the others across all these climates. Therefore, to model the thermal performance of tall buildings in dense urban environments it is necessary to develop a simulation system that can model the Urban Heat Island, and the differences in 3D of variations of temperature, sun and wind within and above the Urban Canopy Layer. Finally, from the one case study examined, modelling urban microclimate in detail is more important for natural ventilation systems than for HVAC systems. Overall, the simulation system of urban microclimate modelling was developed gradually. It is necessary to develop the simulation system to approach a real urban circumstance. The accuracy of the detailed urban microclimate model depends on the engineers’ requirements. The priority of urban microclimate parameters depends on climatic features.</p>

Modelling of parallel dynamics of a pellet-produced plasmoid

The parallel expansion of a dense, pellet-produced plasmoid is modelled with parameters relevant to pellet fuelling experiments in the Wendelstein7-X stellarator. Good agreement is found between the analytical theory and more detailed modelling. In particular, much of the energy deposited in the pellet by the ambient plasma is transferred to the pellet ions by the ambipolar electric field during the expansion. The validity of the hydrodynamic treatment of the plasmoid and the ambient plasma is discussed.

North Atlantic Oscillation response in GeoMIP experiments G6solar and G6sulfur: why detailed modelling is needed for understanding regional implications of solar radiation management

The realization of the difficulty of limiting global-mean temperatures to within 1.5 or 2.0 ∘C above pre-industrial levels stipulated by the 21st Conference of Parties in Paris has led to increased interest in solar radiation management (SRM) techniques. Proposed SRM schemes aim to increase planetary albedo to reflect more sunlight back to space and induce a cooling that acts to partially offset global warming. Under the auspices of the Geoengineering Model Intercomparison Project, we have performed model experiments whereby global temperature under the high-forcing SSP5-8.5 scenario is reduced to follow that of the medium-forcing SSP2-4.5 scenario. Two different mechanisms to achieve this are employed: the first via a reduction in the solar constant (experiment G6solar) and the second via modelling injections of sulfur dioxide (experiment G6sulfur) which forms sulfate aerosol in the stratosphere. Results from two state-of-the-art coupled Earth system models (UKESM1 and CESM2-WACCM6) both show an impact on the North Atlantic Oscillation (NAO) in G6sulfur but not in G6solar. Both models show a persistent positive anomaly in the NAO during the Northern Hemisphere winter season in G6sulfur, suggesting an increase in zonal flow and an increase in North Atlantic storm track activity impacting the Eurasian continent and leading to high-latitude warming over Europe and Asia. These results are broadly consistent with previous findings which show similar impacts from stratospheric volcanic aerosol on the NAO and emphasize that detailed modelling of geoengineering processes is required if accurate impacts of SRM effects are to be simulated. Differences remain between the two models in predicting regional changes over the continental USA and Africa, suggesting that more models need to perform such simulations before attempting to draw any conclusions regarding potential continental-scale climate change under SRM.

Low frequency operation and micro-controller implementation for multilevel quasi Z source inverter in photovoltaic application

A microcontroller based pulse width modulation implementation for multilevel quasi Z source inverter is proposed in this paper. The component design of quasi z source inverter (qZSI) is first considered with continuous and discontinuous mode of operations. The low switching frequency operation of multilevel quasi Z source inverter is proposed in this paper. The detailed modelling for qZSI is then established for effective implementation of PIC microcontroller (PIC 16F877A) for generating the switching signals. A prototype of five level quasi z-source inverter have been developed and the control signal to the gate drivers have been applied by properly adjusting the shoot through and non shoot through switching states. The hardware result shows the effective implementation of the proposed scheme.

REDUCED COMPLEXITY MODELING OF SHORELINE RESPONSE BEHIND OFFSHORE BREAKWATERS

Prediction of the shoreline response behind offshore breakwaters is essential for coastal protection projects. Due to the complexity of the processes behind the breakwaters (e.g., wave diffraction, currents, longshore transport), detailed modelling needs high computational efforts. Therefore, simplifying the process effect in a simpler coastline model could be efficient. In this study, the coastline evolution model ShorelineS is used. A new routine was implemented in the model to adjust the wave heights and angles behind the offshore breakwaters. Two approaches from the literature and a newly introduced one were tested in this study. The model free grid system was used to simply track the breaker line; such an advantage also helped to form tombolo, which is not common for these types of models. The tests showed promising results for single and multi breakwaters systems; however, the newly introduced approach still needs further testing and refinement for better performance and less computational cost.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/mdCpmSQFO1Y