Modeling of turbine mass flow rate performances using the Taylor expansion

The turbine is a key component of many equipment and systems, such as air cycle refrigeration and gas-turbine engines. Existing turbine mass flow rate models need to be improved to increase the prediction accuracy and extrapolation performance for control and diagnosis-oriented simulation. This work proposes a novel methodology for building a regression model, which makes use of the Taylor series to expand functions to deal with variables with small variation and develops a single partly empirical model to present a component performance map. With the methodology, a general regression model of mass flow rates of inward radial turbines is built. Measured data of a turbocharger turbine and a simple air cycle machine turbine are used for the regression analysis to validate the methodology and model. Model predictions agree with measured data very well, proving that the proposed methodology and the model are highly reliable. Comparison of the proposed model with the best existing model searched shows that the present model reduces the mean absolute percentage error by more than 50%, and has much better extrapolation performance as well.     

Using a shading matrix to estimate the shading factor and the irradiation in a three-dimensional model of a receiving surface in an urban environment

In an urban environment, grid-connected building integrated photovoltaic (PV) systems can be subject to complex shading patterns. The study of the shadows projected by nearby buildings and other elements around a PV surface permits cutting down energy losses due to the module’s partial shading and improving the system’s performance ratio, so that the energy production costs can be lower. This paper presents a methodology that estimates the shading factor and irradiation on a three-dimensional model of a receiving surface in an urban environment. The main innovations introduced by this methodology are the building of a shading matrix composed by direct shading factor values around the whole sky dome and the analysis of the shading impacts on direct beam, isotropic diffuse, circumsolar diffuse and horizon brightening diffuse solar radiation components. The shading matrix improves the time spent on long simulation periods and permits an easy numerical integration over the sky to obtain the diffuse shading factors. Using this feature, a plug-in to the Google SketchUp three-dimensional modeling software was built to test this methodology. A series of similar results were obtained between actual measurements and estimates conducted by the plug-in.     

A numerical simulation tool for predicting the impact of outdoor thermal environment on building energy performance

A building affects its surrounding environment, and conversely its indoor environment is influenced by its surroundings. In order to obtain a more accurate prediction of the indoor thermal environment, it is necessary to consider the interactions between the indoor and outdoor thermal environments. However, there is still a lack of numerical simulation tools available for predicting the interactions between indoor and outdoor microclimate that take into account the influences of outdoor spatial conditions (such as building forms and tree shapes) and various urban surface materials. This present paper presents a simulation tool for predicting the effect of outdoor thermal environment on building thermal performance (heating/cooling loads, indoor temperature) in an urban block consisting of several buildings, trees, and other structures. The simulation tool is a 3D CAD-based design tool, which makes it possible to reproduce the spatial forms of buildings and constructed surface materials in detail. The outdoor thermal environment is evaluated in terms of external surface temperature and mean radiant temperature (MRT). Simulated results of these temperatures can be visualized on a color 3D display. Building heating/cooling loads and indoor air temperature (internal surface temperature) can also be simulated. In this study, a simulation methodology is described, and a sensitivity analysis is conducted for a wooden detached house under different outdoor conditions (building coverage, adjacent building height, surrounding with trees or no-trees). Simulation results show that the simulation tool developed in this study is capable of quantifying the influences of outdoor configurations and surface materials on both indoor and outdoor environments.     

A conceptual framework to model interfacial contamination in multiproduct petroleum pipelines

Interfacial contamination of batches of refined petroleum products transported through multiproduct pipelines is a long standing problem in the petroleum industry. Determination of the extent of mixing depends on various factors including fluid properties, operating conditions and flow regimes. The convective-diffusion model along with a fictional parameter, known as the axial dispersion coefficient introduced by Sir G. I. Taylor, is the commonly employed methodology to evaluate longitudinal mixing. However, the model was formulated with a uniform turbulent or laminar flow across the entire flow field. It is argued that the assumption of a uniform flow regime leads to inaccuracies in predicting the extent of contamination at the interface. This study incorporates both the turbulent and the viscous effects in predicting the interfacial contamination volume. Taylor’s analysis of dispersion coefficients has been reviewed, and an improved model combining the weighted effects of the viscous boundary layer contributions and the turbulent core contributions to axial dispersion is proposed. The proposed model provides a possible explanation for the underlying physics of interfacial contamination in flow through straight pipes without pipe fittings and other devices. A comparison of the model predictions with literature data demonstrates the importance of considering both turbulent and viscous effects to achieve better overall prediction accuracy.     

Artificial neural networks applications in building energy predictions and a case study for tropical climates

This study presents artificial neural network (ANN) methods in building energy use predictions. Applications of the ANN methods in energy audits and energy savings predictions due to building retrofits are emphasized. A generalized ANN model that can be applied to any building type with minor modifications would be a very useful tool for building engineers. ANN methods offer faster learning time, simplicity in analysis and adaptability to seasonal climate variations and changes in the building's energy use when compared to other statistical and simulation models. The model herein is presented for predicting chiller plant energy use in tropical climates with small seasonal and daily variations. It was successfully created based on both climatic and chiller data. The average absolute training error for the model was 9.7% while the testing error was 10.0%. This indicates that the model can successfully predict the particular chiller energy consumption in a tropical climate. Copyright © 2005 John Wiley & Sons, Ltd.     

Simple tool to evaluate the impact of daylight on building energy consumption

This paper presents a simple building simulation tool for integrated daylight and thermal analysis. The tool is capable of importing the thermal and visual properties for different glazings and shading positions from the Window Information System (WIS) program. A coupled ray-tracing and radiosity methodology is used to derive the daylight levels for different sky conditions. Both detailed daylight distribution for a particular day and time and hourly discrete values on a yearly basis may be obtained. For an integrated simulation the hourly daylight levels are fed into an existing simple thermal simulation program capable of calculating energy demand and the indoor environment. Straightforward control systems for general and task lighting systems have been implemented together with a shading control strategy that adjusts the shading according to the indoor operative temperature, the risk of glare and the profile angle of the sun. The implemented daylight calculation method allows for shades from the window recess and overhang, and for distant shades blocking the sky vault. Comparisons with the ray-tracing program Radiance show that the accuracy of this approach is adequate for predicting the energy implications of photoresponsive lighting control. The amount of input is small, which makes the tool useful for integrated daylight optimisation in the early design process.     

Evaluation of the thermal performance indices of a ventilated double window through experimental and analytical procedures: Uw-values

Simulations to evaluate energy demand for heating and cooling and thermal comfort are becoming more and more common place in the building design process, at least in the most complex cases. In all detailed or simplified calculations, to analyse heat transfer to and from a building, several input parameters are needed. The inputs for the simulation of a whole building are at least the building geometry, the building envelope thermal indices (like thermal transmittance or the solar heat gain coefficient) and typical local climatic data. In a ventilated double window, the air flow through the channel between the two windows makes its thermal performance highly dynamic and dependent on the air flow characteristics. For a whole building simulation, single coefficients or easily calculated coefficients are needed for each facade system, including ventilated systems. In this paper, equivalent thermal transmittance coefficients for a ventilated double window are assessed and presented. For that, experimental measurements in the absence of solar radiation (night period) were used to identify tendencies and validate calculations. Furthermore, simulations were done in order to estimate the U_w-values of the ventilated double window under different windows configuration and different air flow rates. These values can then be used in whole building simulation programmes.     

Analytic model for passively-heated solar houses—II. Users guide

The results of a recently-developed analytic theory for predicting the long-term thermal performance of passively-heated solar houses are cast in a form that is amenable to immediate use by designers. Specific detailed calculations are carried out for direct gain and water wall houses. The simple manner in which the effects of assorted building modifications (glazing area, thermal mass, storage absorbance and night insulation) can be included is illustrated. These calculations require no degree of mathematical sophistication beyond the use of a hand calculator. The methodology illustrated offers the user a flexibility beyond that of the parameterizations of existing computer simulation results in that the user is not limited to a “reference” building, and the method applies equally well to all types of passively-heated solar buildings.     

Analysis methodology, experimental investigation, and computer optimization of a passive solar commercial building in the Belgian climate

The Fondation Universitaire Luxembourgeoise (FUL) building (completed in 1986) has been selected as a Belgian candidate for participation in the IEA (International Energy Agency) Task XI project devoted to passive solar commercial buildings. Therefore, an evaluation methodology has been set up and a monitoring plan has been defined and performed. Together with this experimental investigation, intensive computer simulation work has defined an optimized design of the building. The main results show that the recorded performance can be improved to an extent of 15% energy savings, which yields a correct performance for a passive solar building in the temperate maritime Belgian climate.     

An evaluation of the appropriateness of using overall thermal transfer value (OTTV) to regulate envelope energy performance of air-conditioned buildings

This paper inquires into whether overall thermal transfer value (OTTV) is an appropriate building envelope energy performance index for use in regulatory control. First, a historical review of the use of OTTV in American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) Standard 90 is presented, followed by a review of more recent work on its further development and application. The major deficiencies of OTTV are then discussed, and simulation study results meant to highlight the impacts of such deficiencies are presented. The study embraced air-conditioned office buildings and air-conditioned high-rise residential buildings in Hong Kong. Results of this study clearly show that the OTTV calculated with the use of pre-calculated coefficients may not truly reflect the thermal performance of a building envelope. Therefore, a second thought should be given to the use of OTTV in building energy codes.     

Solutions of Falkner–Skan equation with heat transfer by Fourier series

In this paper, we solve the Falkner–Skan equation with heat transfer through an expansion in Fourier series, results are improved by incorporating an asymptotic analysis for the Fourier series coefficients. The results show that the classical expansion in Fourier series together with the incorporation of an asymptotic analysis for coefficients of the series delivers a solution with very good accuracy and rapid convergence when it is compared with other methods of solution found in the literature as finite difference and shooting method.     

预制舱类工业建筑能耗模拟软件PCES的设计与开发

  [目的]  建筑能耗模拟软件是建筑节能设计与建筑能耗评估重要的支持工具,而现行的建筑能耗模拟软件难以满足预制舱类工业建筑能耗分析及机柜级微环境控制设计的需求。  [方法]  提出了预制舱类建筑热平衡模型,基于该物理模型开发出预制舱类建筑能耗计算软件PCES,通过工程案例证明了PCES能客观地反映建筑物的能耗分布规律。  [结果]  计算表明:PCES可以实现对预制舱建筑围护结构、舱内热状况以及机柜级热环境状况进行求解,适用于工程节能设计与能耗分析。  [结论]  研究成果可实现建筑参数设定、能耗模拟与建筑热过程及能耗分析。     

Performances of multi-vane expanders

Multi-vane expanders possess many advantages as prime movers for organic Rankine-cycle power systems utilising low grade energy as the heat inputs, particularly for low power outputs (i.e. <10kW). The performances of these devices can be improved considerably by optimising their design parameters and by controlling their operating conditions. To achieve this, mathematical models were developed and computer codes composed for predicting the performance characteristics of multi-vane expanders, as functions of their design and operating variables. The constructed computer programs were applied to two existing designs. Also, a series of tests was carried out on the two considered expanders, using the low grade energy organic Rankine-cycle test rig at Cranfield Institute of Technology. The testing of the expanders was conducted in parallel with the theoretical analysis in order to determine the operational constraints and practical coefficients required for the computer simulation and to verify the validity of the models developed. The analytical predictions of the performance characteristics of the expanders have been compared with experimentally obtained observations. Due to the nature of the simplifying assumptions, a power correction factor was needed to match the analytical predictions with the experimental results to within a ±22 per cent relative deviation zone, over the investigated range of operating conditions.     

A study on the reliability assessment methodology for pipelines with active corrosion defects

A study on the probabilistic methodology for the estimation of the remaining life of pressurized pipelines containing active corrosion defects is presented. This reliability assessment is carried out using several already published failure pressure models. A steady state corrosion rate is assumed to estimate the growth in the dimensions of corrosion defects. The first-order second-moment iterative reliability method, the Monte Carlo integration technique and the first order Taylor series expansion of the limit state function (LSF) are used in order to estimate the probability of failure associated with each corrosion defect over time. The uncertainty of the statistical variables on which the LSF depends are modeled using normal and lognormal distributions and the sensitivity of pipeline reliability to these variables is evaluated. This extended probabilistic analysis framework is applied to a sample operating pipeline which was inspected using a high resolution magnetic flux leakage inspection tool.     

A hierarchical methodology for the mesoscale assessment of building integrated roof solar energy systems

Buildings and other engineered structures that form cities are responsible for a significant portion of the global and local impacts of climate change. Consequently, the installation of building integrated renewable energy sources such as photovoltaic or solar thermal systems on building rooftops is being widely investigated. Although the advantages for individual buildings have been studied, as yet there is little understanding of the potential benefits of urban scale implementation of such systems. Here we report the development of a new methodology for assessing the potential capacity and benefits of installing rooftop photovoltaic systems in an urbanized area. Object oriented image analysis and geographical information systems are combined with remote sensing image data to quantify the rooftop area available for solar energy applications and a renewable energy computer simulation is included to predict the potential benefits of urban scale photovoltaic system implementation. The new methodology predicts energy generation potential that can be utilized to meet Arizona’s Renewable Portfolio Standard 2025 renewable energy generation requirements.     

Analytical approach of thermosyphon solar domestic hot water system performance

An efficient and simple simulation approach for thermosyphon solar water heaters has been developed and compared with experimental data. This approach, valid for solar-only systems, gives the ability to link the system main design and constructional parameters with the expected energy output through an analytical determination of the coefficients of the characteristic input–output equation of the system. The proposed methodology can be used not only for energy optimization of the system in the design phase but also for evaluation of test results of an existing system in order to improve it further.     

Applicability of calculation methods for conduction transfer function of building constructions

Conduction transfer function (CTF) is widely used to calculate conduction heat transfer in building cooling/heating loads and energy calculations. It can conveniently fit into any load and energy calculation techniques to perform conduction heat transfer calculations. There are three popular methods, direct root-finding (DRF) method, state-space (SS) method and frequency-domain regression (FDR) method to calculate CTF coefficients. The limitation of a methodology possibly results in imprecise or false CTF coefficients. This paper investigates the applicability of three methods as Fourier number and thermal structure factor are varied and in detail explains the sources that introduce error in the CTF solutions. The results show that the calculation error of SS and DRF methods becomes increasing as the reciprocal of the product of Fourier number and thermal structure factor becomes increasing. The maximal error even reaches almost 100%. However, the calculation error of FDR method always remains within 1% no matter how Fourier number and thermal structure factor are varied. Thus, FDR method is more robust and reliable than SS and DRF methods. And it is more practical to calculate CTF coefficients and may be a better choice to calculate the cooling/heating loads for building structures for the architect/designer.     

A numerical method to estimate temperature intervals for transient convection–diffusion heat transfer problems

This paper presents a numerical method to estimate intervals of temperature for transient convection–diffusion heat transfer problems when uncertainty of thermal parameters is characterized by the interval. A deterministic relationship of interval variables between temperature and thermal parameters is setup by Taylor series expansion and the interval analysis, and the lower and upper bounds of temperature can be estimated by a temporally piecewise adaptive algorithm and FEM. A prescribed computing accuracy at each discretized time interval can be achieved via an adaptive process for different size of time step, thus the computing accuracy over the whole time domain can be maintained. A 2D numerical example is provided to verify the proposed approach, and a good accordance can be observed in the comparison of results given by the combinatorial, probability and proposed approaches. The impact of the order of Taylor expansion and the size of time step on the result is discussed.     

Research and application of a power-flow-calculation method in multiterminal VSC-HVDC power grid

For demonstrating a multiterminal voltage-source converter (VSC)-based high-voltage DC (HVDC) (VSC- HVDC) project, this study puts forward a technical route for calculating the power flow in a 500-kV VSC-HVDC power grid in comparison with that of an AC power grid. The Jacobian matrix used in the power-flow calculation was deduced through methods such as Newton-Laphson iteration and Taylor series expansion. Further, the operation effect of power- flow calculation on a true bipolar VSC-HVDC power grid was analyzed briefly. The elements of the Jacobian matrix corresponding to VSC were studied under the mode of droop control and the control strategy of VSC-HVDC power grid was analyzed in detail. The power-flow calculation model for VSC-HVDC power grid of the master-slave control mode was simplified using the PQ decomposition method of the power-flow calculation of an AC power grid. Moreover, a four-terminal model of the Zhangbei VSC-HVDC demonstration project was established and tested on MATLAB. The simulation results under two kinds of operating conditions were analyzed and compared to the results of BPA; the deviation between the power-flow results was studied. The results show that the proposed calculation method can provide a feasible support for calculating the power flow in VSC-HVDC grids.     

A multi-operational ventilated photovoltaic and solar air collector: application, simulation and initial monitoring feedback

This paper concerns the application of the first European example of a roof mounted, multi-operational ventilated photovoltaic and solar air collector, development of a detailed simulation methodology for such a system, and gives a brief outline of monitored findings after six months of operation. The aim for this simulation development was to provide a method that can aid future system design and optimize performance in line with energy requirements for specific buildings. This work is discussed in relation to two key investigations into the simulation of building integrated hybrid PV thermal collectors.