Several studies show that from about 20% to 50% more solar energy can be recovered by using photovoltaic systems that track the sun rather than systems set at a fixed angle. For overcast or cloudy days, recent studies propose the use of a set position in which each photovoltaic panel faces toward the zenith (horizontal position). Compared to a panel that follows the sun’s path, this approach claims that a horizontal panel increases the amount of solar radiation captured and subsequently the quantity of electricity produced. The present work assesses a solar tracking photovoltaic panel hourly and seasonally in high latitudes. A theoretical method based on an isotropic sky model was formulated, implemented, and used in a case study analysis of a grid-connected photovoltaic system in Montreal, Canada. The results obtained, based on the definition of a critical hourly global solar radiation, were validated numerically and experimentally. The study confirmed that a zenith-set sun tracking strategy for overcast or mostly cloudy days in summer is not advantageous.
Modeling phase change materials behavior in building applications: Comments on material characterization and model valid...Published: 01 January 2014 by Elsevier BV in Renewable Energy
In a recent meeting of IEA's Annex 23, several members presented their conclusions on the modeling of phase change materials behavior in the context of building applications. These conclusions were in agreement with those of a vast review, involving the survey of more than 250 journal papers, undertaken earlier by the group of École de technologie supérieure. In brief, it can be stated that, at this point, the confidence in reviewed models is too low to use them to predict the future behavior of a building with confidence. Moreover, it was found that overall thermal behaviors of phase change material are poorly known, which by itself creates an intrinsic unknown in any model. Models themselves are most of time suspicious as they are often not tested in a very stringent or exhaustive way. In addition, it also appears that modeling parameters are somewhat too simplified to realistically describe the complete physics needed to predict the real life performance of PCMs added to a building. As a result, steps are now taken to create standard model benchmarks that will improve the confidence of the users. Hopefully, following these efforts, confidence will increase and usage of PCM in buildings should be eased.
What cultural traits could we possibly share with any extraterrestrial civilization? It could be argued that every civilization has to face the same challenge: How to distribute resources between different tasks and/or individuals. Limitations of resources and conflicting interests are likely to be universal problems. In many cases, no perfect solution exists and cultural tradition plays a role in the choice of the allocation procedure. Being simultaneously universal and culturally oriented, the allocation problem is especially suitable as a topic of discussion between civilizations. Two theories attempt to solve the problem of fair resource distribution: equity theory and social choice theory. Both theories are described within a mathematical framework, which eases their translation into interstellar messages. Equitable sharing procedures and electoral procedures are intellectual tools developed to deal with conflicting individual interests for the best outcome for the group at large. Therefore, both equity and social choice theories are products of civilizations seeking to better manage interactions between individuals with selfish tendencies. In such circumstances, altruism should emerge as a prized quality that would be encouraged by extraterrestrial societies, but that is difficult to achieve at the level of individuals due to natural tendencies for selfishness. Therefore, social choice and equity theories are topics of discussion that should provide common ground for communication with any civilization that is struggling, like we are, to build a fairer society.
It is often claimed that the cheapest energy is the one you do not need to produce. Nevertheless, this claim could somehow be unsubstantiated. In this article, the authors try to shed some light on this issue by using the concept of energy return on investment (EROI) as a yardstick. This choice brings semantic issues because in this paper the EROI is used in a different context than that of energy production. Indeed, while watts and negawatts share the same physical unit, they are not the same object, which brings some ambiguities in the interpretation of EROI. These are cleared by a refined definition of EROI and an adapted nomenclature. This review studies the research in the energy efficiency of building operation, which is one of the most investigated topics in energy efficiency. This study focuses on the impact of insulation and high efficiency windows as means to exemplify the concepts that are introduced. These results were normalized for climate, life time of the building, and construction material. In many cases, energy efficiency measures imply a very high EROI. Nevertheless, in some circumstances, this is not the case and it might be more profitable to produce the required energy than to try to save it.
Study of the influence of roof insulation involving local materials on cooling loads of houses built of clay and strawPublished: 01 July 2012 by Elsevier BV in Energy and Buildings
In this paper, the thermal efficiency of a solar air collector called unglazed transpired collector (UTC) has been investigated both experimentally and numerically (CFD). Experimental measurements included the following variables: the temperatures of the air entering and leaving the UTC for three air mass fluxes, three distinct irradiations and two plenums thicknesses. A commercial finite volume software (Fluent) was used to model the heat transfer through the UTC. Turbulent effects were modelled by the RNG k–ɛ turbulence model. It was found that a weak heat exchange process mainly took place at the plenum; the maximum efficiency differences expected between the two plenums widths (5 and 15 cm) was 2.85%.
Numerical Simulation of Thermal Storage by Latent and Sensible Heat in a Porous Vertical Channel: Performance Analysis a...Published: 01 January 2012 by Informa UK Limited in Numerical Heat Transfer, Part A: Applications
This work proposes a two-dimensional numerical analysis of storage material properties—thermal mass and energy density—in a vertical channel filled with porous media for two storage modes: sensible and latent. The porous channel, into which air flows at low speed, is limited by two walls: one is heated with a constant uniform heat flux, while the other is assumed to be adiabatic. The conservation equations, using a model with two temperatures and involving the Darcy-Brinkman law, describe the behavior of the simplified system. The mathematical model, thus formed, is solved using COMSOL. Glass beads (sensible) and especially encapsulated PCMs (latent) where investigated. Numerical simulations showed that latent heat provides the advantage of improving the thermal inertia and the energy density of the system while controlling the temperature of the porous domain.
Magnetic control of natural convection in the horizontal Bridgman configuration: symmetric and non-symmetric cross secti...Published: 01 March 2011 by Informa UK Limited in International Journal of Computational Fluid Dynamics
This study deals with the electromagnetic damping of free-convective flows in cavities such as those used in the crystal growth horizontal Bridgman configuration. The cavities are filled with a dilute electrically conducting alloy and are subjected to a horizontal temperature gradient. The flow is steady and laminar under an external, vertical, transversal and uniform magnetic field. Several cross sections of the cavities were investigated and can either be centro-symmetric or not. The governing equations for such problems are two coupled partial differential equations, for the velocity and the induced magnetic fields, coupled with a third integral equation for mass conservation. A finite element method has been developed, and the numerical results for the variation of the velocity and the induced magnetic field in terms of the Hartmann number show a considerable decrease in convection intensity as the Hartmann number increases. Results also reveal the presence of the well-known Hartmann and parallel layers. For non-centro-symmetric sections, results show the way the flow reorganises into two cells as the Hartmann number increases.
Environmental considerations have called for new developments in building technologies to bridge the gap between this need for lower impacts on the environment and ever increasing comfort. These developments were generally directed at the reduction of the energy consumption during operations. While this was indeed a mandatory first step, complete environmental life cycle analysis raises new questions. For instance, for a typical low thermal energy consumption building, the embodied energy of construction materials now becomes an important component of the environmental footprint. In addition, the usual practice in life cycle analysis now appears to call for some adaptation—due to variable parameters in time—to be implemented successfully in building analysis. These issues bring new challenges to reach the goal of integrated design, construction, commissioning, operation, maintenance, and decommissioning of sustainable buildings.
Energy storage components improve the energy efficiency of systems by reducing the mismatch between supply and demand. For this purpose, phase-change materials are particularly attractive since they provide a high-energy storage density at a constant temperature which corresponds to the phase transition temperature of the material. Nevertheless, the incorporation of phase-change materials (PCMs) in a particular application calls for an analysis that will enable the researcher to optimize performances of systems. Due to the non-linear nature of the problem, numerical analysis is generally required to obtain appropriate solutions for the thermal behavior of systems. Therefore, a large amount of research has been carried out on PCMs behavior predictions. The review will present models based on the first law and on the second law of thermodynamics. It shows selected results for several configurations, from numerous authors so as to enable one to start his/her research with an exhaustive overview of the subject. This overview stresses the need to match experimental investigations with recent numerical analyses since in recent years, models mostly rely on other models in their validation stages.
The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency for its new science satellite, SCISAT-1. Dr. Peter Bernath of the University of Waterloo is the ACE Mission Scientist, and ABB is the industrial contractor for the development of the ACE primary instrument. The ACE primary instrument is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible and near infrared imager. The FTS, operating from 2.4 to 13.3 microns, will measure at an unapodised resolution of 0.02 cm-1 the infrared absorption signals that contain information on different atmospheric layers to provide vertical profiles of atmospheric constituents. Its highly folded design results in a very high performance instrument with a compact size. The imager will monitor aerosols based on the extinction of solar radiation using two filtered detectors at 1.02 and 0.525 microns. The instrument also includes a suntracker, which provides the sun radiance to both the FTS and the imager during solar occultation of the earth’s atmosphere. In order to meet all science objectives, the instrument line width of the ACE-FTS has to be smaller than 0.028 cm-1. There are however different instrument function contributors affecting the width and the symmetry of spectral lines. These contributors are related to effects inherent to the instrument. This paper will describe these different effects and their impacts on the instrument line shape (ILS). Results obtained during the ILS characterisation of the flight model will be presented. A short description of a correction algorithm is also discussed.
The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency for its next science satellite, SCISAT-1. ACE consists of a suite of instruments in which the primary element is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible (525 nm) and near infrared imager (1020 nm). A secondary instrument, MAESTRO, provides spectrographic data from the near ultra-violet to the near infra-red, including the visible spectral range. In combination the instrument payload covers the spectral range from 0.25 to 13.3 micron. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature will be made by solar occultation from a satellite in low earth orbit. The ACE mission will measure and analyze the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A high inclination (740), low earth orbit (650 km) allows coverage of tropical, mid-latitude and polar regions. This paper will describe the metrology scheme, based on an IR laser diode, as well as algorithms that are needed to fully calibrate, along the wavenumber axis, the spectra measured by the ACE instrument.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
The Cross-track Infrared Sounder (CrIS) is part of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) series of polar-orbiting spacecrafts. The CrIS sensor forms a key component of the larger Cross-track Infrared/Microwave Sounding Suite (CrIMSS) and is intended to operate within the context of the CrIMSS architecture. The CrIS instrument is a Michelson interferometer infrared sounder covering the spectral range of approximately 3.9 to 15.4 microns. CrIS provides cross-track measurements of scene radiance to allow the calculation of temperature and moisture vertical distributions in the Earth's atmosphere. We present sensor data record (SDR) level 1B algorithms that are needed on ground in order to produce meaningful data meeting all requirements of the NPOESS CrIS instrument. Level 1B data are made of geolocated, radiometrically and spectrally (spatial frequency) calibrated spectra with annotated quality indicators. CrIS SDR algorithms include, among others, radiometric calibration with phase error correction, interferometer fringe count error handling and correction of the instrument line shape (ILS) distortion.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency for its next science satellite, SCISAT-1. ACE consists of a suite of instruments in which the primary element is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible (525 nm) and near infrared imager (1020 nm). A secondary instrument, MAESTRO, provides spectrographic data from the near ultraviolet to the near infrared, including the visible spectral range. In combination, the instrument payload covers the spectral range from 0.25 to 13.3 micron. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature will be made by solar occultation from a satellite in low earth orbit. The ACE mission will measure and analyze the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A high inclination (74°), low earth orbit (650 km) allows coverage of tropical, mid-latitude and polar regions. This paper will describe level 1 algorithms that are needed on ground in order to produce meaningful data meeting all requirements of the ACE FTS instrument. Level 0 data are as downlinked from the spacecraft. Level 1A data are decoded (CCSDS, bit trim) interferograms from individual acquisition channels. Level 1B data are made of spectrally (spatial frequency) calibrated transmittances with annotated quality indicators. Some key ACE FTS L1B algorithms include, non-linearity characterization/correction, robust interferometer fringe count error handling, spectral calibration from Solar reference lines, transmittance computation with phase error correction, and correction of the instrument line shape (ILS) distortion.
A detailed analysis of the oxygen abundance profile has been carried out on a sample of spiral galaxies from which very good data was available. The early-type galaxies of our sample display gradients that are flatter, and overall levels of O/H abundances that are higher, than those of normal late-type galaxies. Early-type galaxies show an identical trend in the behavior of extrapolated central abundance versus morphological type to that shown by late-type galaxies with strong bars, even in the absence of a bar. On a diagram showing extrapolated central abundances versus morphological types, two clearly separated sequences appear: late-type barred galaxies and early-type (barred or unbarred) galaxies clearly fall on a sequence 0.5 dex in abundance below that of normal late-type galaxies. This behavior is consistent with theoretical models of morphological evolution of disk galaxies by the formation and dissolution of a bar over a period of a few 109 yr, where later type galaxies (Sd, Sc, SBc) evolve into earlier-type disk galaxies (Sb, Sa) through transitory SBc and SBb phases.
I have compiled the very best data published on abundance gradients. From this sample of 29 galaxies, some information can be gained on the mecanism of morphological evolution in disk galaxies. From this sample, I find that early-type galaxies show an identical trend in the behavior of extrapolated central abundance versus morphological type to that shown by late-type galaxies with strong bars, even in the absence of bar! On a a diagram showing extrapolated central abundance versus morphological type, two sequences appear: late-type barred galaxies and early-type galaxies (barred or not barred) fall on sequence 0.5 dex below that of normal late-type galaxies. This behavior is consistent with a scenario of morphological evolution of disk galaxies by formation and dissolution of a bar over a period of a few 109 yr, where later type galaxies (Sd,Sc,Sbc, evolve into earlier-type disk galaxies trough transitory SBc and SBb phases.