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Compression Systems (compression + system)
Selected AbstractsA review on energy, economical, and environmental benefits of the use of CHP systems for small commercial buildings for the North American climateINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2009P. J. Mago Abstract The use of combined heating and power (CHP) systems to produce both electricity and heat is increasing rapidly due to their high potential of reducing primary energy consumption (PEC), cost, and emissions in domestic, commercial, and industrial applications. In addition to producing both electricity and heat, CHP systems can be coupled with vapor compression systems to provide cooling. This paper analyzes a natural gas engine CHP system together with a vapor compression system for different American climate zones. Performance is measured in terms of operational costs, PEC, and carbon dioxide emissions as a percent of a reference building. The objective of this paper is to compare the performance of a CHP system operating 24,h a day with a system that only operates during typical office hours. Furthermore, the system is optimized based on reducing PEC, minimizing costs, and reducing emissions. In addition, the benefits of CHP systems based on the Energy Star program and the Leadership in Energy and Environmental Design (LEED) program are presented. Results show that, in general, it is more beneficial to operate the CHP system during typical office hours than to operate the system 24,h a day. Also, the CHP system performance strongly depends on the location where it is installed. In addition to reductions in cost, primary energy, and emissions, CHP systems can help achieve the Energy Star label for commercial office buildings and help obtain LEED points that go toward achieving LEED certification status. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance improvement of the vapour compression refrigeration cycle by a two-phase constant area ejectorINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2009Nagihan Bilir Abstract The performance of a vapour compression system that uses an ejector as an expansion device was investigated. In the analysis, a two-phase constant area ejector flow model was used. R134a was selected as the refrigerant. According to the obtained results, for any operating temperature there are different optimum values of pressure drop in the suction chamber, ejector area ratio, ejector outlet pressure and cooling coefficient of performance (COP). As the difference between condenser and evaporator temperatures increases, the improvement ratio in COP rises whereas ejector area ratio drops. The minimum COP improvement ratio in the investigated field was 10.1%, while its maximum was 22.34%. Even in the case of an off-design operation, the performance of a system with ejector is higher than that of the basic system. Copyright © 2008 John Wiley & Sons, Ltd. [source] An analytical and experimental analysis of a very fast thermal transientINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2001C. Aprea Abstract According to some international standards, some products, developed for use under heavy thermal conditions, have to be tested by subjecting them for a short time to a particular heating and cooling thermal stress to allow them an acceptable future operative life. It is possible to obtain these fast thermal gradients in confined environments, called climatic chambers where the air is heated by an electrical resistance and is cooled with a finned evaporator which is linked to a vapour compression system subjected to a particular control system of the refrigerating power. In particular, in this paper the air and object tested thermal transients are studied from an analytical and experimental point of view. The study of the mathematical model is realized assuming simplified hypotheses about the air, the object and the air cooled evaporator temperature. The most complex circumstances are related to a very fast temperature decrease because under this working condition the mathematical model is characterized by a nonlinear differential system. The nonlinear term is represented by the refrigerating power that varies in a definite range with the evaporator temperature according to a sinusoid trend. For this power a suitable analytical expression, derived by the control system performance and by the compressor characteristic, has been found. The analytical,experimental comparison during a cooling thermal stress of typical products subjected to international standard tests as the electronic boards, has been carried out showing acceptable results. The model presented is useful to foresee the climatic chamber performances in the presence of a specific refrigerating power trend; this is the start-point for the design of the vapour compression plant and its control system. Copyright © 2001 John Wiley & Sons, Ltd. [source] A review on energy, economical, and environmental benefits of the use of CHP systems for small commercial buildings for the North American climateINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2009P. J. Mago Abstract The use of combined heating and power (CHP) systems to produce both electricity and heat is increasing rapidly due to their high potential of reducing primary energy consumption (PEC), cost, and emissions in domestic, commercial, and industrial applications. In addition to producing both electricity and heat, CHP systems can be coupled with vapor compression systems to provide cooling. This paper analyzes a natural gas engine CHP system together with a vapor compression system for different American climate zones. Performance is measured in terms of operational costs, PEC, and carbon dioxide emissions as a percent of a reference building. The objective of this paper is to compare the performance of a CHP system operating 24,h a day with a system that only operates during typical office hours. Furthermore, the system is optimized based on reducing PEC, minimizing costs, and reducing emissions. In addition, the benefits of CHP systems based on the Energy Star program and the Leadership in Energy and Environmental Design (LEED) program are presented. Results show that, in general, it is more beneficial to operate the CHP system during typical office hours than to operate the system 24,h a day. Also, the CHP system performance strongly depends on the location where it is installed. In addition to reductions in cost, primary energy, and emissions, CHP systems can help achieve the Energy Star label for commercial office buildings and help obtain LEED points that go toward achieving LEED certification status. Copyright © 2009 John Wiley & Sons, Ltd. [source] Operational results of an intermittent absorption cooling unitINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2002Ali R. El-GhalbanArticle first published online: 15 JUL 200 Abstract The concept of solar cooling is appealing because the cooling load is in phase with the intensity of solar energy. Many system arrangements or cycles are employed to achieve solar cooling, such as Absorption, desiccant or Rankine-vapour compression systems. The technical feasibility of driving an absorption-cooling unit by a low-temperature heat source (such as solar energy using a simple flat-plate collector) for air-conditioning applications is investigated in this work. This study aims to design and construct a prototype for an intermittent absorption refrigeration system and to examine its implementation. The operating characteristics of the considered unit are extensively investigated. In order to accomplish this strategy, the prototype was integrated in a test rig designed for this purpose and equipped with the necessary measuring instruments to determine the required operating criteria of the unit. The energy added or extracted to or from the different unit components is calculated and the system performance is analysed. The C.O.P of the unit is found to be 19% which is 2% lower than the designed value, which could be regarded as an encouraging result for more studies in this field. Copyright © 2002 John Wiley & Sons, Ltd. [source] Feedback stabilization of bifurcations in multivariable nonlinear systems,Part II: Hopf bifurcationsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 4 2007Yong Wang Abstract In this paper we derive necessary and sufficient conditions of stabilizability for multi-input nonlinear systems possessing a Hopf bifurcation with the critical mode being linearly uncontrollable, under the non-degeneracy assumption that stability can be determined by the third order term in the normal form of the dynamics on the centre manifold. Stabilizability is defined as the existence of a sufficiently smooth state feedback such that the Hopf bifurcation of the closed-loop system is supercritical, which is equivalent to local asymptotic stability of the system at the bifurcation point. We prove that under the non-degeneracy conditions, stabilizability is equivalent to the existence of solutions to a third order algebraic inequality of the feedback gains. Explicit conditions for the existence of solutions to the algebraic inequality are derived, and the stabilizing feedback laws are constructed. Part of the sufficient conditions are equivalent to the rank conditions of an augmented matrix which is a generalization of the Popov,Belevitch,Hautus (PBH) rank test of controllability for linear time invariant (LTI) systems. We also apply our theory to feedback control of rotating stall in axial compression systems using bleed valve as actuators. Copyright © 2006 John Wiley & Sons, Ltd. [source] Block merging for off-line compressionJOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 1 2007Raymond Wan To bound memory consumption, most compression systems provide a facility that controls the amount of data that may be processed at once,usually as a block size, but sometimes as a direct megabyte limit. In this work we consider the Re-Pair mechanism of Larsson and Moffat (2000), which processes large messages as disjoint blocks to limit memory consumption. We show that the blocks emitted by Re-Pair can be postprocessed to yield further savings, and describe techniques that allow files of 500 MB or more to be compressed in a holistic manner using less than that much main memory. The block merging process we describe has the additional advantage of allowing new text to be appended to the end of the compressed file. [source] Economic analysis of VenUS I, a randomized trial of two bandages for treating venous leg ulcersBRITISH JOURNAL OF SURGERY (NOW INCLUDES EUROPEAN JOURNAL OF SURGERY), Issue 10 2004C. P. Iglesias Background: The study investigated the cost-effectiveness of four-layer and short-stretch compression bandages for treating venous leg ulcers. Methods: Cost-effectiveness and cost-utility analyses were performed using patient-level data collected alongside the VenUS I leg ulcer study. The perspective for the economic analysis was that of the UK National Health Service (NHS) and Personal Social Service. The time horizon for the analysis was 1 year after recruitment. Health benefit was measured as differences in ulcer-free days and quality-adjusted life years (QALYs). Results: The mean healing time for ulcers treated with four-layer bandages was 10·9 (95 per cent confidence interval (c.i.) ,6·8 to 29·1) days less than that for ulcers treated with short-stretch bandages. Mean average difference in QALYs between compression systems was ,0·02 (95 per cent c.i. ,0·08 to 0·04). The four-layer bandage cost a mean of £227·32 (95 per cent c.i. £16·53 to £448 ·30) less per patient per year than the short-stretch bandage. Conclusion: On average, four-layer bandaging was associated with greater health benefits and lower costs than short-stretch bandaging. Copyright © 2004 British Journal of Surgery Society Ltd. Published by John Wiley & Sons, Ltd. [source] Dressing-related pain in patients with chronic wounds: an international patient perspectiveINTERNATIONAL WOUND JOURNAL, Issue 2 2008Patricia E Price Abstract This cross-sectional international survey assessed patients' perceptions of their wound pain. A total of 2018 patients (57% female) from 15 different countries with a mean age of 68·6 years (SD = 15·4) participated. The wounds were categorised into ten different types with a mean wound duration of 19·6 months (SD = 51·8). For 2018 patients, 3361 dressings/compression systems were being used, with antimicrobials being reported most frequently (n= 605). Frequency of wound-related pain was reported as 32·2%, ,never' or ,rarely', 31·1%, ,quite often' and 36·6%, ,most' or ,all of the time', with venous and arterial ulcers associated with more frequent pain (P= 0·002). All patients reported that ,the wound itself' was the most painful location (n= 1840). When asked if they experienced dressing-related pain, 286 (14·7%) replied ,most of the time' and 334 (17·2%) reported pain ,all of the time'; venous, mixed and arterial ulcers were associated with more frequent pain at dressing change (P < 0·001). Eight hundred and twelve (40·2%) patients reported that it took <1 hour for the pain to subside after a dressing change, for 449 (22·2%) it took 1,2 hours, for 192 (9·5%) it took 3,5 hours and for 154 (7·6%) patients it took more than 5 hours. Pain intensity was measured using a visual analogue scale (VAS) (0,100) giving a mean score of 44·5 (SD = 30·5, n= 1981). Of the 1141 who reported that they generally took pain relief, 21% indicated that they did not feel it was effective. Patients were asked to rate six symptoms associated with living with a chronic wound; ,pain' was given the highest mean score of 3·1 (n= 1898). In terms of different types of daily activities, ,overdoing things' was associated with the highest mean score (mean = 2·6, n= 1916). During the stages of the dressing change procedure; ,touching/handling the wound' was given the highest mean score of 2·9, followed by cleansing and dressing removal (n= 1944). One thousand four hundred and eighty-five (80·15%) patients responded that they liked to be actively involved in their dressing changes, 1141 (58·15%) responded that they were concerned about the long-term side-effects of medication, 790 (40·3%) of patient indicated that the pain at dressing change was the worst part of living with a wound. This study adds substantially to our knowledge of how patients experience wound pain and gives us the opportunity to explore cultural differences in more detail. [source] | |||||||||||||