Cold Climatic Conditions Research Articles

Field study on the effect of vegetation on the performance of soil methanotrophy-based engineered systems – Column experiments

Current literature provides conflicting information on the role vegetation plays when considering methane (CH4) oxidation potential of engineered Biosystems, such as landfill biocovers (LBCs), bio-windows and methane biofilters. The primary objective of this study was to determine whether the impact of vegetation on biological CH4 oxidation was positive or negative and to explain the reasons for the observations using a variety of experiments. A total of eight flow-through columns (two alfalfa, two native grass, two canola and two bare-soil replicates) were set up outdoors to simulate field operation in cold climatic conditions. Each column was layered with 18 cm of topsoil and 32 cm of compost mixture (compost 30%: topsoil 70% v/v) as packing material and treated with CH4 fluxes ranging from 180 to 815 g CH4 m−2 d−1. The bare-soil columns exhibited the highest CH4 oxidation rate of 455 g CH4 m−2 d−1, while the maximum CH4 oxidation rates for the vegetated columns ranged between 147 and 171 g CH4 m−2 d−1 with the alfalfa column showing the lowest. Gas profiles of vegetated columns showed high concentrations of nitrogen (N2) and oxygen (O2) at all depths, possibly due to increased permeability created by the plant root systems. Quantitative Polymerase Chain Reaction (q-PCR) assessment showed that pmoA gene copy numbers, indicative of methanotrophic population levels, were higher in bare-soil columns than in vegetated columns. The Illumina based sequencing of 16S rRNA gene showed that Type I methanotrophs dominated both vegetated and bare-soil columns. Soil incubation experiments conducted to determine oxidation kinetic parameters also indicated greater methanotrophic activity in the bare-soil columns than in vegetated columns. The plant data collected at the end of the column experiments provided clear evidence of CH4 escape due to preferential pathways created by plant roots (reaching 38 cm, 31.5 cm and 26.5 cm by alfalfa, canola and native grass, respectively) that resulted in decreased CH4 oxidation in vegetated columns. The study results clearly demonstrate that vegetation decreases CH4 oxidation at high loading rates, notwithstanding the type of vegetation.

Isotopic tracing and quantitative assessment of rainwater in a separate sewer system in Tiszavasvári, Hungary

The hydrological processes that commonly occur within the sewer system i.e., rainwater percolation or groundwater infiltration, can be easily described applying water isotopes. This study investigates the potential of tritium and stable isotope composition (δ2H and δ18O) of water for tracing rainwater entering urban sewer and estimating the amount. The work consists of collecting and analyzing wastewater and rainwater samples over a six-day-long period including a 30-min-long rainfall event, and then applying the isotopic results to determine the mixing ratios in the sewer pipes and the sensitivity of the applied tracing methods. Results reveal that the isotopic composition of wastewater reacts to inflowing rainwater sensitively: detectable flow rate increase resulting from rainfall is 0.62 m3h-1 for tritium, 2.49 m3h-1 for δ18O and 1.25 m3h-1 for δ2H. While applying variation of discharge, these values are 12.15 m3h-1 and 18.91 m3h-1 in daytime and nighttime, respectively. Due to the more positive stable isotope values of precipitation in the summer half-year, isotopic difference of rainwater and groundwater (being less enriched) is more notable, subsequently, traceable amount of parasitic rainwater in case of the examined area is lower than in the winter half-year. In case of groundwater recharged under cold climate conditions sampling should be carried out in summer in the night hours, after an at least three-day-long dry period. Though, all three isotopic tracers applied in this study proved to be suitable to detect small amount of parasitic precipitation, tritium came out as the most sensitive one.

Prospection of Psychrotrophic Filamentous Fungi Isolated from the High Andean Paramo Region of Northern Ecuador: Enzymatic Activity and Molecular Identification.

The isolation of filamentous fungal strains from remote habitats with extreme climatic conditions has led to the discovery of a series of enzymes with attractive properties that can be useful in various industrial applications. Among these, cold-adapted enzymes from fungi with psychrotrophic lifestyles are valuable agents in industrial processes aiming towards energy reduction. Out of eight strains isolated from soil of the paramo highlands of Ecuador, three were selected for further experimentation and identified as Cladosporium michoacanense, Cladosporium sp. (cladosporioides complex), and Didymella sp., this last being reported for the first time in this area. The secretion of seven enzymes, namely, endoglucanase, exoglucanase, β-D-glucosidase, endo-1,4-β-xylanase, β-D-xylosidase, acid, and alkaline phosphatases, were analyzed under agitation and static conditions optimized for the growth period and incubation temperature. Cladosporium strains under agitation as well as incubation for 72 h mostly showed the substantial activation for endoglucanase reaching up to 4563 mU/mL and xylanase up to 3036 mU/mL. Meanwhile, other enzymatic levels varied enormously depending on growth and temperature. Didymella sp. showed the most robust activation at 8 °C for endoglucanase, β-D-glucosidase, and xylanase, indicating an interesting profile for applications such as bioremediation and wastewater treatment processes under cold climatic conditions.

Investigation of Biofouling and Its Effect on the Properties of Basalt Fiber Reinforced Plastic Rebars Exposed to Extremely Cold Climate Conditions.

For the first time, the possibility of penetration of mold fungi mycelium and spore-forming bacteria into the structure of basalt fiber reinforced plastic rebars has been shown in laboratory and field experiments. Biological contamination at the “fiber-binding” border reveals areas of swelling and penetration of mold fungi mycelium and bacterial spore cells into the binder component. After the exposure of samples at extremely low temperatures, strains of mold fungi of the genus Aspergillus were also isolated from the surface of the rebars. Additionally, spore-forming bacteria of the genus Bacillus immobilized for samples from two years ago. This indicates the high viability of immobilized strains in cold climates. Aboriginal microflora isolated by the enrichment culture technique from the samples was represented by: actinobacteria of the genera Nocardia and Streptomyces; yeast of the genus Rhodotorula; and mold fungi of the genus Penicillium. It was shown that the enrichment culture technique is a highly informative method of diagnosing the bio-infection of polymer composite materials during their operation in extremely low temperatures. The metabolic activity of the cells of cryophilic microorganisms isolated from experimental samples of basalt fiber reinforced plastic rebars was associated with the features of the enzymes and fatty acid composition of the lipid bilayer of cell membranes. In the case of temperature conditions when conventional (mesophilic) microorganisms stop developing vegetative cells, the process of transition of the lipid bilayer of cell membranes into a gel-like state was activated. This transition of the lipid bilayer to a gel-like state allowed the prevention of crystallization and death of the microbial cell when the ambient temperature dropped to negative values and as a result, after thawing, growth resumed and the metabolic activity of the microorganisms was restored. Studies have been carried out on the effect of biodepletion on the elastic strength characteristics, porosity and monolithicity of these materials, while at the same time, after a two year exposure, the strength preservation coefficient was k = 0.82 and the porosity increased by more than two times. The results show that the selected strains affect the properties of polymeric materials in cold climates in relation to the organic components in the structure of polymer composites.

Design of Metal–Dielectric Multilayer Coatings for Energy‐Efficient Building Glazing

A systematic approach to the design of metal–dielectric multilayer coatings is proposed for energy‐efficient building glazing application. Thirty‐six coatings were modeled with alternating metal (Ag, Au, Cu) and dielectric (TiO2, Ta2O5, ITO, ZrO2, SiO2, Al2O3) thin films in three‐layer (3L) and five‐layer (5L) configurations. It is found that the optical performance is less affected by the bottom dielectric layer compared with the metal and middle/top dielectric layers. The 5L coatings offer a competitive modulation of optical properties, ensuring an optimal balance between luminous transmittance and infrared reflectance. 5L configuration ensures a higher visible transmittance in the whole visible region with peak values close to those of unfunctionalized glass (≈85%), i.e., 3–4% higher compared with the 3L configuration. The optical properties of the optimized multilayers are then used as inputs to building energy models of typical office buildings located in extreme cold and hot weather conditions. The 5L–Ag configurations achieve significant reductions in cooling loads under hot climate conditions (around 15%) without compromising access to daylight (important driver of occupants’ comfort and wellbeing). However, under cold climate conditions, cooling energy savings are outweighed by unintended increases in heating loads, confirming the need for more climate‐driven glazing research efforts.

Including snowmelt in influent generation for cold climate WRRFs: comparison of data-driven and phenomenological approaches

A data-driven model was proposed for generating the influent flow and water temperature dynamics including the impact of snowmelt under cold climate conditions. The performance was compared with a phenomenological model.

Characteristics and quality of leaves of different clones of mulberry in the Mu Us Desert

Mulberry is an important economic tree species. Both leaves and fruits have important economic value, Due to the dry and cold climate conditions in the Mu Us desert, the varieties suitable for cultivation in the Mu Us desert are unique. There are a large area of wild mulberry trees naturally distributed in the Mu Us Desert in Northwest China, through the investigation and selection of mulberry trees in this area, the three excellent clones collected, MWS-1, MWS-2 and MWS-3, were compared with the mulberry variety SX-1 bred in Shaanxi Province for growth, quality and drought resistance etc research. The most suitable mulberry varieties for growing in the Mu Us desert area were screened out. A comparative analysis of the leaves of four mulberry clones was made using the membership function. The leaf quality of the four mulberry clones, according to the average membership function, it can be sorted as MWS-1>SX-1>MWS-2>MWS-3. Through a deeper and more systematic understanding of the biological characteristics of the four clones of mulberry, it provides a strong theoretical support for the production, popularization and application of mulberry in the Mu Us Desert in the future.

A long-term study on the effect of a hydrophobic treatment on the moisture balance and durability of a reinforced concrete structure in a road tunnel

Concrete structures in the vicinity of seawater or deicing salts on roads in regions with cold climatic conditions, are exposed to chlorides. Transport of chlorides in concrete due to capillary suction during drying and wetting cycles as well as diffusion in combination with carbonation tends to result in corrosion of the rebar and loss of structural integrity. This damage mechanism mainly applies to directly weathered components. After a longer service life, however, components that are not directly exposed, such as concrete surfaces outside the spraying water area of a tunnel, are also affected. A long-term study over 12 years was performed to investigate the effect of hydrophobic treatment on the moisture balance and durability of a suspended tunnel ceiling compared to an untreated surface with the same exposure. Embedded sensors installed in the concrete structure and an online monitoring system were used to measure the electrical resistivity of the concrete and the corrosion rate of the steel reinforcement over time. Furthermore, the data obtained were combined with climate measurements in the tunnel to gain new insights on the effect of tunnel climate on the damage mechanism. The measurements allowed to prove the long-term effect and correct application of hydrophobic treatment. With these results it is possible to make a more precise estimation of the condition and the deterioration process of the tunnel ceiling and to optimize the rehabilitation schedule.

Comprehensive Energy Consumption Analysis of an Electric Vehicle Advanced Thermal Management System with Waste Heat Recovery in Cold Climate Conditions

Comprehensive Energy Consumption Analysis of an Electric Vehicle Advanced Thermal Management System with Waste Heat Recovery in Cold Climate Conditions

Postdiapause reproduction of spotted-wing drosophila (Diptera: Drosophilidae) in realistically simulated cold climatic springtime conditions of Québec, Canada

Abstract Knowing the biology and ecology of Drosophila suzukii (Diptera: Drosophilidae) is important to predict its potential for permanent establishment in cold climatic regions. We studied the reproductive potential of postdiapause male and female flies collected in lowbush blueberry fields in late season over two years. After being submitted to a six-month cold-winter regime, survivors were exposed to a simulated springtime warming regime to monitor reproductive potential and expected population growth. Overwintered fly survivors of both sexes that were aged up to nine months after field capture reproduced successfully in spring and early summer when mated to nondiapause flies experimentally made available for mating as potential migrant colonisers from lower latitudes. Relative to control nondiapause flies, the lifetime fertility of postdiapause flies was reduced by 84% in females and 70% in males, revealing large fitness costs of reproductive diapause under cold stress. Modelling potential reproduction of overwintered flies in warming conditions using models parametrised for age-dependent fertility rate and diapause status showed that nondiapause migrant flies would be strongly advantaged over locally overwintered postdiapause flies due to precocious reproductive maturity, broader pattern of age-specific fertility, and higher lifetime fertility.

Monitoring and detection of new endemic foci of canine leishmaniosis in northern continental Italy: An update from a study involving five regions (2018-2019).

Canine leishmaniosis (CanL) is an emerging zoonosis caused by Leishmania infantum and transmitted in southern Europe by phlebotomine sand flies of the subgenus Phlebotomus (Larroussius). Endemic foci of CanL have been recorded in northern continental Italy since early 1990s and attributed to the northward expansion of vector populations due to climatic changes in association with travelling/relocated infected dogs from the southern Mediterranean littoral. In this study, further spread of endemic Leishmania foci was monitored during 2018-2019 in five regions (Aosta Valley, Piedmont, Lombardy, Veneto and Friuli-Venezia Giulia), with focus to territories where investigations were not performed, or they have been inconclusive. Clinical cases of CanL identified by local veterinary practitioners and confirmed by reference diagnosis centers were regarded as autochthonous if their origin from, or travel to, areas endemic for CanL were excluded in the previous ≥2years. Around these index cases, i) serosurveys for L infantum were carried out where indicated, ii) sampling from potential autochthonous cases in healthy or clinically-suspected resident dogs was intensified by collaborating veterinary practitioners, and iii) suitable sites were investigated for the presence of competent phlebotomine vectors. Fifty-seven municipalities whose enzootic status of CanL was unreported before 2018, were identified as endemic. The stability of 27 foci recorded over the past decade, was also confirmed. Competent phlebotomine vectors, mainly Phlebotomus perniciosus, were collected for the first time in 23 municipalities. The newly recorded endemic municipalities appear to be distributed over a west-to-east decreasing gradient: 30 in Piedmont, 21 in Lombardy, 4 in Veneto and 2 in Friuli-Venezia Giulia. As regards Veneto, it should be noted that a relatively restricted territory was investigated as several municipalities of the region had already been surveyed and detected as endemic for CanL in the past. Cold climate conditions of the easternmost region of Friuli-Venezia Giulia bordering non-endemic territories of Slovenia, are probably less favorable to L infantum transmission.

The connections between river terraces and slope deposits as paleoclimate proxies: The Guadalaviar - Turia sequence (Eastern, Iberia Chain, Spain)

This study, focused on the well-exposed terrace deposits of the Guadalaviar and Turia rivers and associated slopes, provides a better understanding of the genetic connection between river-terrace sediments and slope accumulations in a setting influenced by temperate to cold (extraglacial) climates: the Sierra de Albarracín and Alfambra–Teruel depression (Iberian Chain, eastern Spain). The terrace system comprises seven levels, Qt1 to Qt7. In the two older levels (Qt2 and Qt3) lateral connections with thick stratified slope screes were observed. The lower terraces (Qt4 to Qt7) have less expressive slope deposits. New Optically Stimulated Luminescence (OSL) ages, using quartz-OSL and pIRIR290, were obtained from these Quaternary deposits. Qt2 is dated ~310 to 270 ky (Marine Isotope Stage (MIS) 9–8); Qt3 dates from ~175 to 150 ky (MIS 6), Qt4 from ~136 to 80 ky (MIS 5e–a) and Qt5 from ~23 ky (MIS 2); Qt6 has a tufa dated to 10–4.6 ky (early–middle Holocene), while Qt7 probably records the last 4 ky (late Holocene). The thick slope deposits connected with the upper parts of the Qt2 and Qt3 terraces were generated under the cold-climate conditions of MIS 8 and MIS 6, respectively. These are the oldest dated slope deposits connected with fluvial terraces documented in the Mediterranean region, their preservation and recognition thus being of considerable significance. Chronological correlation of the glacial–interglacial cycles of the Pyrenees with the marine isotope stages conforms to the interpretation of paleo-environmental data and sedimentary controls of terrace genesis in extraglacial fluvial basins under temperate- to cold-climatic conditions.

Feasibility and performance analysis of a hybrid GAX-based absorption-compression heat pump system for space heating in extremely cold climate conditions

Absorption heat pumps (AHPs) can be thermally activated by low-grade heat sources for space heating. The efficiency can be greatly improved by adopting GAX-based internal heat recovery, which lifts the heat source temperature demand and deteriorates the cold climate condition adaptability, and thus immensely limits the widespread application. In this paper, a hybrid GAX-based absorption-compression heat pump (ACHP) system is proposed to expand the geographical scope of application in extremely cold climate conditions, to lift the heat supply temperature, and more importantly to utilize heat sources of lower temperatures. A mathematical model was developed and validated in comparison with experimental and theoretical results from the literature. Feasible generation-evaporation temperature (Tg-Te) conditions to enable GAX were presented in detail. Coefficient of performance (COP), primary energy ratio (PER), heat supply temperature, heating capacity, and heat duty of main components were investigated concerning different working conditions. The possible sensible and latent heat recovery ratio of the GAX was explored. The results show that when Pr increases, the feasible Tg-Te area moves towards the lower Tg and Te sides. The system can be utilized for building floor heating with PER above 1.116, COP higher than 1.614, temperature lift (ΔTlift) up to 81.85 °C even when ambient air temperature (Tamb) is down to −40.6 °C, and for fan coil heating when Tamb is above −40.0 °C with PER above 1.074, COP over 1.615 and ΔTlift up to 85.92 °C. The system can utilize heat sources down to 80 °C by adjusting the working pressure ratio (Pr), highlighting the possibility of integration with solar collectors for heating purposes.

Influence of water cut and rates of cooling on oil flow

Oils with anomalous properties are characterized by large values of density, viscosity, high content of paraffinic hydrocarbons and asphaltene-resinous substances (up to 30%), high pour point (3538C), which increases the likelihood of complications in the processes of production, field gathering and oil treatment. Therefore, for many countries with cold climatic conditions, the problem of improving the low-temperature properties of oils is one of the most pressing problems in the production and transportation of hard-to-recover oils. Recent studies show that the rates of heating / cooling processes have a great influence on the rheological properties of natural oil mixtures during heat treatment. The experience of operating oil fields shows that in oil gathering and transportation systems, due to the water cut of oils and the aggressiveness of formation waters, persistent oil emulsions are often formed, which complicate the commercial preparation of oils.
 The article presents the results of studies of the influence of the water cut factor on the transportation of well products, as well as the effect of the cooling rate on the pour point of oil emulsions. Laboratory studies have shown that an increase in the water content in emulsions of more than 40% leads to a significant increase in viscosity over the entire temperature range. It is also shown that an increase in water cut increases the pour point of oil by 7-14С.

Optimization of Window Design for Daylight and Thermal Comfort in Cold Climate Conditions

Window design affects the overall performance of a building. It is important to include window design during the initial stages of a project since it influences the performance of daylight and thermal comfort as well as the energy demand for heating and cooling. The Norwegian building code facilitates two alternative methods for achieving a sufficient daylight, and only guidelines for adequate indoor thermal comfort. In this study, a typical Norwegian residential building was modeled to investigate whether the criteria and methods facilitate consistent and good performance through different scenario changes and furthermore, how the national regulations compare to European standards. A better insulated and more air-tight building has usually a lower annual heating demand, with only a marginal decrease in the daylight performance when the window design is unchanged. A more air-tight construction increases the risk of overheating, even in cold climates. This study confirms that a revision of the window design improves the overall performance of a building, which highlights the importance of proper window design. The pursuit of lower energy demand should not be at the expense of indoor thermal comfort considering the anticipated future weather conditions. This study indicates that criteria for thermal comfort and daylight, if clearly defined, can affect the energy demand for heating and cooling, as well as the indoor climate positively, and should be taken into account at the national level. A comparison between the national regulations and the European standards was made, and this study found that the results are not consistent.

Multifamily building energy retrofit comparison between the United States and Finland

Due to the high heating demand, energy savings in residential buildings in cold climates has played an important role in reducing carbon emissions. This study aims to investigate differences between the United States and Finland regarding characteristics and energy retrofit practices of current multifamily buildings (MFBs). The study focuses on net zero energy or nearly zero energy performance in cold and very cold climatic conditions. First an overview is presented of the status of multifamily housing stocks in the two countries, followed by an explanation of energy use patterns of residential buildings in both countries. Then, building codes related to energy efficiency in Finland and the United States are examined as well as major differences between the codes. Lastly, to further understand the different strategies and techniques used in energy retrofit projects, a dataset of 57 MFBs from both countries, both net zero energy buildings (ZEB) and nearly zero energy buildings (nZEB), were collected and analyzed. The preliminary results indicate three differences: (1) For the existing national MFB stock, the United States has a higher average energy use (EUI), at 266 kWh/m2 per year (cold and very cold regions), compared to that of Finland, at 235 kWh/m2 per year, (2) Finland has more stringent energy code requirements that contribute to lower energy use in studied case projects with a mean EUI of 80 kWh/m2 per year compared to 148 kWh/m2 per year in the U.S. sample,(3) In the Finnish studied cases, the heating and ventilation systems play a more critical role in explaining the building energy use differences in the sample, while in the U.S. cases, building envelope thermal properties explained the energy use intensity variations in the sample. Overall, the comparison of the Finnish and American cases showed that good technical practices from Finland can be learned to reduce the heating demand in cold and very cold climate regions of the United States.

Stable water isotopes as a tool for assessing groundwater infiltration in sewage networks in cold climate conditions

Effective identification and quantification of groundwater (GW) infiltration into sewage collection networks represents an important step towards sustainable urban water management. In many countries, including northern regions, sewage networks are aging to the point where renovation is needed. This study focused on the utilization of stable water isotopes as tracer substances for GW infiltration detection. The main objectives were to investigate the validity of the method for quantifying GW infiltration in cold climate conditions and to test the robustness of this method under assumed low GW infiltration rates. In general, the stable water isotopes (δ18O) produced reliable results regarding origin identification and quantification of GW infiltration rates in winter conditions (continuous below zero temperatures and snow accumulation during preceding months). The 1.6‰ distinction between the δ18O isotope composition signals of the two water sources (drinking water from river and groundwater) in the studied network was sufficient to allow source separation. However, a larger distinction would reduce the uncertainties connected to GW-fraction identification in situations where low GW infiltration rates (<8%) are expected. Due to the climate conditions (no surface water inflow), GW infiltration to the network branch monitored represented the totality of I/I (infiltration/surface inflow) flows and was estimated to reach a maximum daily rate of 6.5%. This being substantially lower than the 29% yearly average I/I rate of ca 29% reported for the city's network. Overall, our study tested the stable water isotope method for GW infiltration detection in sewage networks successfully and proved the suitability of this method for network assessment in cold climate conditions. Isotope sampling could be part of frequent monitoring campaigns revealing potential infiltration and, consequently, the need for renovation.

Electrical Resistivity of Conductive Leather and Influence of Air Temperature and Humidity

Leather is a material that has been used in different applications for centuries. Today, living in the era of high-tech­nology, we are surrounded by smart products. For this reason, traditional products must be changed or im­proved in order to support and make us more comfortable while using them. For instance, the touch screen display in electronics products is a smart phone’s or a tablet computer’s primary input device. Still, traditional leather will not function properly in a cold climate or other specific conditions. To make it conductive in such conditions, the double in-situ polymerization of the pyrrole coating method was used. The aim of this study was to observe the electrical properties of conductive leather. At the same time, it stands up to a wide range of different air temperatures, and relative and absolute humidity. These properties are essential because de­signers and textile engineers should be familiar with them when they decide to use materials in different smart products. Electricity conductivity tests were carried out in year-round temperatures from 7.5 °C to 28.1 °C, with a relative humidity from 18% to 77% and a vapor air concentration from 2.77 g/kg to 12.46 g/kg. The so-called “multiple-step method” was used to test leather’s electrical resistivity for the first time. The method considers a material’s compressional properties and provides an indicator inherent for a material’s electrical properties, regardless of the mass and shape of samples. The results showed a strong dependence between water vapor air concentration and electrical resistivity, described using the formula ρ = 1.3103 H−1.04 Ωm, with a correlation coefficient of 0.87. There was no relation between relative humidity and electrical resistivity, and resistivity and air temperature. Also, the results confirmed again that changes in the shape of the sample used during tests did not influence the measurement’s results, but supported the appropriateness of the measuring method.

Towards standards in the analysis of wind turbines operating in cold climate – Part A: Power curve modeling and rotor icing detection

Analyzing the performance of wind turbines operating in cold climate conditions is a complex matter. The lack of any widely used standards adds to the challenge of comparing turbine performance between and within a wind farm. It proves to be an even bigger issue when alternative operational strategies, including ice protection systems (IPS) are implemented and their performance has to be assessed. Before making any comparison between turbines, it is important to build robust power curve models that are not influenced by secondary factors (e.g. temperature and wind orientation). An accurate power curve model allows to detect more precisely any ice formed on the rotor. This paper details a process that allows to build a simple power curve model while minimizing the influence of temperature and wind direction. The piecewise function used to represent the power curve yields a precise parametric representation while being more robust to outliers. Different tools being used to evaluate the performance of the model are presented. With these tools it was possible to observe that standard air density corrections were not able to completely compensate the effect of temperature on the power output. The analysis also provides comprehensive definitions of the different periods composing an icing event. A simple and efficient ice detection threshold using only the power curve is proposed and validated. Using this threshold, algorithms defining significant production loss periods and icing events are presented. The different tools introduced in this paper can decrease significantly the uncertainty in the available power estimation, which proves to be crucial when comparing the performance of multiple turbines.

Thermal analysis of 8.5 MVA disk-type power transformer cooled by biodegradable ester oil working in ONAN mode by using advanced EMAG–CFD–CFD coupling

Power transformers are the first devices used to transfer the electrical energy produced in power plants to the grid to supply the industrial and individual receivers with electricity. The heat generation in windings and core, being an effect of the power losses, is usually dissipated in large units by using mineral oils, which are harmful to the environment. Nowadays, the industry and global society seek environmentally-friendly alternatives. One of the most promising substitute for their high biodegradability, safety in operation, and favourable thermo-physical properties are natural ester oils. For this reason, a numerical study of 8.5 MVA disk-type power transformer cooled using conventional mineral oil and a commercially used rapeseed ester oil is presented in this paper. Moreover, due to different thermal behaviour of the considered oils, the comparison was made for the unit working in different seasons of hot and moderate climate zones (Argentina and Poland). In the numerical approach, electromagnetic (EMAG) and computational fluid dynamics (CFD) models were used for a detailed study of the selected device. In particular, a novel and very efficient EMAG–CFD–CFD coupling procedure was developed to assess the cooling of the large power transformer. Such a coupled computational procedure allowed for the detailed investigation of the power loss, oil flow characteristics, and temperatures with a satisfying computational effort. The results showed that the average windings temperatures are higher by 2–9 K when the ester oil is used, dependent on the ambient conditions. The hotspot temperature in the low voltage windings increased by up to 9 K and up to 18 K in the high voltage windings using ester oil. According to the results, the oil duct construction requires modification in the high voltage region for transformers cooled using mineral oil in cold climate conditions.