Turbulent flow at 190 m height above London during 2006-2008: A climatology and the applicability of similarity theory

Flow and turbulence above urban terrain is more complex than above rural terrain, due to the different momentum and heat transfer characteristics that are affected by the presence of buildings (e.g. pressure variations around buildings). The applicability of similarity theory (as developed over rural terrain) is tested using observations of flow from a sonic anemometer located at 190.3 m height in London, U.K. using about 6500 h of data. Turbulence statistics—dimensionless wind speed and temperature, standard deviations and correlation coefficients for momentum and heat transfer—were analysed in three ways. First, turbulence statistics were plotted as a function only of a local stability parameter z/Λ (where Λ is the local Obukhov length and z is the height above ground); the σ_i/u_* values (i = u, v, w) for neutral conditions are 2.3, 1.85 and 1.35 respectively, similar to canonical values. Second, analysis of urban mixed-layer formulations during daytime convective conditions over London was undertaken, showing that atmospheric turbulence at high altitude over large cities might not behave dissimilarly from that over rural terrain. Third, correlation coefficients for heat and momentum were analyzed with respect to local stability. The results give confidence in using the framework of local similarity for turbulence measured over London, and perhaps other cities. However, the following caveats for our data are worth noting: (i) the terrain is reasonably flat, (ii) building heights vary little over a large area, and (iii) the sensor height is above the mean roughness sublayer depth

Improving a pavement-watering method on the basis of pavement surface temperature measurements

Pavement-watering has been studied since the 1990's and is currently considered a promising tool for urban heat island reduction and climate change adaptation. However, possible future water resource availability problems require that water consumption be optimized. Although pavement heat flux can be studied to improve pavement-watering methods (frequency and water consumption), these measurements are costly and require invasive construction work to install appropriate sensors in a dense urban environment. Therefore, we analyzed infrared camera measurements of pavement surface temperatures in search of alternative information relevant to this goal. Firstly, surface temperature reductions of up to 4{\textdegree}C during shading and 13{\textdegree}C during insolation were found. Secondly, the infrared camera successfully detected temperature spikes indicative of surface drying and can therefore be used to optimize the watering frequency. Measurements made every 5 min or less are recommended to minimize relevant data loss. Finally, if the water retaining capacity of the studied pavement is known, optimization of total water consumption is possible on the sole basis of surface temperature measurements.Comment: Published in Urban Climat

Simulation of a model-based optimal controller for heating systems under realistic hypothesis

An optimal controller for auxiliary heating of passive solar buildings and commercial buildings with high internal gains is tested in simulation. Some of the most restrictive simplifications that were used in previous studies of that controller (Kummert et al., 2001) are lifted: the controller is applied to a multizone building, and a detailed model is used for the HVAC system. The model-based control algorithm is not modified. It is based on a simplified internal model

Final Causality in the Thought of Thomas Aquinas

Throughout his corpus, Thomas Aquinas develops an account of final causality that is both philosophically nuanced and interesting. The aim of my dissertation is to provide a systematic reconstruction of this account of final causality, one that clarifies its motivation and appeal. The body of my dissertation consists of four chapters. In Chapter 1, I examine the metaphysical underpinnings of Aquinas’s account of final causality by focusing on how Aquinas understands the causality of the final cause. I argue that Aquinas holds that an end is a cause because it is the determinate effect toward which an agent’s action is directed. I proceed by first presenting the general framework of causality within which Aquinas understands final causality. I then consider how Aquinas justifies the reality of each of the four kinds of cause, placing special emphasis on the final cause. In Chapter 2, I consider final causality from the perspective of goodness and explore the reasons why Aquinas thinks that the end of an action is always good. For even if one was convinced that the end of an action is indeed a cause, one might still resist attributing any normative or evaluative properties to the end, much less a positively-valenced normative property like goodness. In this chapter, I show how, given Aquinas’s metaphysics of powers and his characterization of goodness as that which all desire, it follows that every action is for the sake of some good. In Chapter 3, I consider Aquinas’s account of the relation between final causality and cognition. In many passages throughout his corpus—most famously in the fifth of his Five Ways—Aquinas advances the claim that cognition plays an essential role in final causality. In this chapter, I explore Aquinas’s account of the relation between final causality and cognition by reconstructing his Fifth Way and investigating the metaphysical foundations on which it rests. While the first three chapters of my dissertation focus on Aquinas’s account of final causality from the perspective of the ends of individual agents, in Chapter 4 I broaden my focus to consider the way in which the account of final causality developed in these earlier chapters shapes Aquinas’s philosophical cosmology. I argue that, on Aquinas’s view, when an individual agent acts for an end, it is plays a role in a larger system, e.g. a polis, an ecosystem, or the universe itself

Control of micro-CHP and thermal energy storage for minimising electrical grid utilisation

The efficient use of combined heat and power (CHP) systems in buildings presents a control challenge due to their simultaneous production of thermal and electrical energy. The use of thermal energy storage coupled with a CHP engine provides an interesting solution to the problem—the electrical demands of the building can be matched by the CHP engine, while the resulting thermal energy can be regulated by the thermal energy store. Based on the thermal energy demands of the building the thermal store can provide extra thermal energy or absorb surplus thermal energy production. This paper presents a multi-input multi-output inverse-dynamics-based control strategy that will minimise the electrical grid utilisation of a building, while simultaneously maintaining a defined operative temperature. Electrical demands from lighting and appliances within the building are considered. In order to assess the performance of the control strategy, a European Standard validated simplified dynamic building physics model is presented that provides verified heating demands. Internal heat gains from solar radiation and internal loads are included within the model. Results indicate the control strategy is effective in minimising the electrical grid use and maximising the utilisation of the available energy when compared with conventional heating systems

PREDICTIVE CONTROL OF POWER GRID-CONNECTED ENERGY SYSTEMS BASED ON ENERGY AND EXERGY METRICS

Building and transportation sectors account for 41% and 27% of total energy consumption in the US, respectively. Designing smart controllers for Heating, Ventilation and Air-Conditioning (HVAC) systems and Internal Combustion Engines (ICEs) can play a key role in reducing energy consumption. Exergy or availability is based on the First and Second Laws of Thermodynamics and is a more precise metric to evaluate energy systems including HVAC and ICE systems. This dissertation centers on development of exergy models and design of model-based controllers based on exergy and energy metrics for grid-connected energy systems including HVAC and ICEs. In this PhD dissertation, effectiveness of smart controllers such as Model Predictive Controller (MPC) for HVAC system in reducing energy consumption in buildings has been shown. Given the unknown and varying behavior of buildings parameters, this dissertation proposes a modeling framework for online estimation of states and unknown parameters. This method leads to a Parameter Adaptive Building (PAB) model which is used for MPC. Exergy destruction/loss in a system or process indicates the loss of work potential. In this dissertation, exergy destruction is formulated as the cost function for MPC problem. Compared to RBC, exergy-based MPC achieve 22% reduction in exergy destruction and 36% reduction in electrical energy consumption by HVAC system. In addition, the results show that exergy-based MPC outperforms energy-based MPC by 12% less energy consumption. Furthermore, the similar exergy-based approach for building is developed to control ICE operation. A detailed ICE exergy model is developed for a single cylinder engine. Then, an optimal control method based on the exergy model of the ICE is introduced for transient and steady state operations of the ICE. The proposed exergy-based controller can be applied for two applications including (i) automotive (ii) Combined Heat and Power (CHP) systems to produce electric power and thermal energy for heating purposes in buildings. The results show that using the exergy-based optimal control strategy leads to an average of 6.7% fuel saving and 8.3% exergy saving compared to commonly used FLT based combustion control. After developing thermal and exergy models for building and ICE testbeds, a framework is proposed for bilevel optimization in a system of commercial buildings integrated to smart distribution grid. The proposed framework optimizes the operation of both entities involved in the building-to-grid (B2G) integration. The framework achieves two objectives: (i) increases load penetration by maximizing the distribution system load factor and (ii) reduces energy cost for the buildings. The results show that this framework reduces commercial buildings electricity cost by 25% compared to the unoptimized case, while improving the system load factor up to 17%

Influence of the three-dimensional effects on the simulation of landscapes in thermal infrared

International audienceThe paper deals with the modelling of landscapes for the simulation of very high spatial resolution images in the thermal infrared range, from 3 to 14 μm. It focuses on the influence of the 3-D effects on the simulation. The major relevant physical processes are described. Examples are made, comparing simulations obtained with 2-D and 3-D representation of the landscape. They help in classifying the relative influence of each process. The necessity to take into account a 3-D landscape representation for the simulation of very high spatial resolution images in the infrared range is also demonstrated

Influence of geology and hydrogeology on heat rejection from residential basements in urban areas

Urbanization and limited land availability have resulted in the increased utilization of underground structures including residential basements in largely populated cities such as London, with an average addition of 200 basements per year in some boroughs. Residential basements kept at a comfortable temperature level throughout the year significantly contribute to heat fluxes in the subsurface as well as an increase in ground temperature. Understanding the ground thermal status is crucial in managing the significant geothermal energy potential in urban areas as well as the sustainable development of the urban underground, and in maintaining the energy efficiency of underground structures. In this proof-of-concept study, a 3D finite element approach accounting for coupled heat transfer and groundwater flow in the ground was used to investigate the influence of ground conditions on the heat rejection rate from basements. A detailed analysis was made of ground, above ground and underground built environment characteristics. This study demonstrates that the amount of heat from basements rejected to the ground constitutes a significant percentage of the total heat loss from buildings, particularly in the presence of groundwater flow. The extent of thermal disturbance in the ground varies depending on the ground characteristics. The volume of thermally disturbance ground inversely correlates with the groundwater flow rate in ground mainly consisting of highly permeable material. However, a direct correlation exists when the thickness of permeable soil layer decreases. A larger horizontal to vertical ratio of ground thermal disturbance is observed when the thickness of permeable soil layer increases