Strategies to raise the off-design efficiency of chiller machines

Most HVAC systems in large buildings are equipped with centrifugal chillers which are typically designed for maximum efficiency at 70% at 80% of their full-load. But, below about 30% full-load, their part-load efficiency starts to deteriorate rapidly (increasing kilowatts per ton). For older centrifugal chillers, this rapid drop may start at even higher part-load, rendering their operation at low part-load undesirable. In many cases chillers are over-sized, forcing operation below 50% of the full-load most of the time. Furthermore, the field performance of most chiller machines is genearlly not documented, and there is no tradition of recording chiller performance history. There is growing incentive-driven interest in chiller monitoring. But, field visits, discussions with HVAC engineers and opinions from manufacturers have proven that virtually no chiller systems are currently monitored for kilowatts per ton. Only recently has field data gathering been initiated, and part-load performance of chillers in the field started drawing serious attention. The problem, however, still remains poorly disclosed to the end-user. As a result, chiller machines actually operate at much lower efficiency than the design values. There are opportunities for profoundly improving their field performance. Part-load operation is particularly poor for sites with single centrifugal chillers. This research is an appraisal of strategies for improving the part-load performance of chiller systems. A review of simulation results and field data indicate that chiller machines operate at higher kilowatts per ton than allowed for by current technology. Energy consumption of various chiller types and configurations for a generic building indicate that there are possibilities for lowering chiller energy consumption, and these opportunities can be harvested with simple measures.     

Design, modeling, and hardware correlation of a 3.2Gb/s/pair memory channel

With the rapid advance of silicon process technology, it is now possible to design input/output (I/O) circuits that operate at multigigabit data rates. As a result, accurate modeling and analysis of high-speed interconnect systems is essential to optimize the performance of the overall system. This paper describes the interconnect design, modeling, simulation, and characterization methodologies that are essential to achieve multigigabit data rates. It focuses on the physical layer verification and hardware correlation of functional systems and silicon to ensure robust system operation over 3.2Gb/s data rate using conventional low-cost packaging and printed circuit board (PCB) technologies. In order to capture conductor and dielectric losses, as well as other high-frequency effects of three-dimensional structures, accurate measurement-based simulation techniques that directly incorporate frequency-domain parameters from measurement or electromagnetic solver parameters into circuit simulation tools using fast Fourier transform (FFT) and bandlimiting windowing techniques are developed. Finally, simulation waveforms are correlated with prototypes at both component and system levels in both time and frequency domains.     

Heat recovery from automotive engine

Heat recovery from automotive engines has been predominantly for turbo-charging or for cabin heating. Studies relative to application of the recovered heat to run absorption chillers is scarce. In this project, a 10.55 kW (three ton) absorption chiller was modified for hot gas intake and matched to a 2.8 L V6 internal combustion engine. Mathematical model and experimental test results suggest that the concept is thermodynamically feasible and could significantly enhance system performance depending on part-load of the engine. However, possible challenges during transient operations as well as issues related to scalability and reliability require further investigation.     

Low‐grade heat‐driven Rankine cycle,a feasibility study

Conversion of low‐grade heat to high‐quality energy such as electricity using the Rankine cycle poses serious challenges. When such conversion is possible, it is invariably expensive or unacceptable due to environmental concerns associated with the working medium. The low‐grade heat can either be from exhaust systems or from solar radiation. Thus, the topic addresses a very useful subject, combining energy efficiency and renewable energy. Although high‐grade heat recovery and energy conversion is a mature technology widely covered by the literature, low‐grade energy conversion, especially using thermodynamic cycles, has not been sufficiently addressed to date. This paper addresses the feasibility of a low‐grade heat‐driven Rankine cycle to produce power using a scroll expander, a low toxicity, low flammability, and ozone‐neutral working fluid. A cost benefit analysis of the recommended system shows that it is a viable option for solar power generation, at about one‐third the cost of a comparable photovoltaic system. Copyright © 2008 John Wiley & Sons, Ltd.     

Aero-elastic behavior of a flexible blade for wind turbine application: A 2D computational study

This paper presents a computational study into the static aeroelastic response of a 2D wind turbine airfoil under varying wind conditions. An efficient and accurate code that couples the X-Foil software for computation of airfoil aerodynamics and the MATLAB PDE toolbox for computation of the airfoil deformation is developed for the aero-elastic computations. The code is validated qualitatively against computational results in literature. The impact of a flexibility of the airfoil is studied for a range of design parameters including the free stream velocity, pitch angle, airfoil thickness, and airfoil camber. Static aero-elastic effects have the potential to improve lift and the lift over drag ratio at off-design wind speed conditions. Flexibility delays stall to a large pitch angle, increasing the operating range of a flexible blade airfoil. With increased thickness the airfoil deformation decrease only linearly.     

Parametric dependence of a morphing wind turbine blade on material elasticity

A few recent works have suggested a morphing blade for wind turbine energy conversion. The concept is derived from fin and wing motions that better adapt to varying load conditions. Previous research has provided the fluid mechanic justification of this new concept. This paper establishes a parametric relationship between an asymmetric wind turbine blade and constituent material modulus to predict the geometric response of the morphing blade for a given material characteristic. The airfoil’s trailing edge deflection is associated to a prescribed fluid exit angle via the Moment Area (MA) method. Subsequently, a mathematical model is derived to predict material deformation with respect to imparted aerodynamic forces. Results show that an airfoil, much like a tapered beam, can be modeled as a non-prismatic cantilevered beam using this well established method.     

Chemical composition of naturally fermented buttermilk

Naturally fermented buttermilk, prepared from soured cream or milk, was collected during two seasons from sixteen farms in northern Ethiopia, to study chemical composition and flavour compounds. Protein, fat, organic acids, carbohydrates and volatile compounds were quantified using Kjeldahl, Gerber, high‐pressure liquid chromatography (HPLC) and headspace GC methods, respectively. Widely differing concentrations of organic acids and volatile compounds among samples indicated variable fermentation in the products. This indicates the need for the introduction of the standardisation of the process to supply the market with homogenous buttermilk products.     

Identification and characterization of human B-cell epitopes in recombinant antigens of Leishmania aethiopica

Recombinant DNA fragments from Leishmania aethiopica that code for epitopes which react with human antibodies have been characterized by cross-hybridization studies and DNA sequence analysis. Twenty clones could be grouped into seven different groups (I-VII), probably representing seven different L. aethiopica antigens. The DNA sequences of representative clones from the seven groups have been obtained and the amino acid sequence of the respective recombinant antigens established. The recombinant antigens have been analysed by epitope scanning with patient sera, and octapeptides that contain potential B-cell epitopes have been identified in all seven recombinant antigens. These octapeptides have further been tested with additional patient sera and control sera, and three octapeptides (HAFCHEEG, YHSSVVHD and SYAPCSLK) were found to contain major epitopes recognizing specific antibodies in nine, seven and four, respectively, of the twenty sera tested. Fifteen of the twenty sera reacted with one or more of these three octapeptides.     

Process oriented industrial classification based on energy intensity

The Standard Industrial Classification (SIC) code has been used in the United States to categorize manufactured products. This classification is useful for many commercial and business related applications. However, when checked against energy use data collected through the Industrial Assessment Center (IAC) of San Diego State University (SDSU), the energy use profile of the SIC groups showed objectionable deviations within each group, rendering the code less than useful for overall energy based grouping and analyses. In this paper, a Process Oriented Energy Intensity Classification (POEIC) is introduced. When examined with data from about 270 plants of the IAC, this new classification offered more coherent and consistent energy use profile with smaller standard deviation for the selected energy intensity parameters than that of the SIC code.     

Dilemma of roof rainwater quality: applications of physical and organic treatment methods in a water scarce region of Mekelle,Ethiopia

The public health field has built a body of literature showing health benefits from improvements in water quality. However, the connection between roof harvested rainwater and health is not well documented especially in developing countries. Understanding the application of locally available treatment methods provides insight into this problem. This paper reports on experimental investigations where rainwater collected from a typical domestic roof in Mekelle, Ethiopia was treated using Moringa stenopetala seed, sand filter and boiling. The quality of the raw and treated roof harvested rainwater were compared against the Ethiopian and World Health Organization drinking water standards to investigate its suitability as a supplement for potable water supply. The pollutants analysed were total coliforms and turbidity. A significant improvement of turbidity and total coliforms was observed. This implies that application of plant coagulant followed by filtration can sufficiently treat rainwater and can be used as a low-cost treatment option in water scarce areas.