Many rural communities in South Africa do not have running water or electricity. The fetching and heating of water is therefore a time consuming and expensive daily ritual. The use of energy sources such as wood or coal are not readily available and cause environmental pollution. Although solar water heaters are commonly available in South Africa, they are very seldom used in rural areas. Whilst this can mostly be attributed to a high system cost, current designs also do not cater for specific rural problems such as the transporting or purification of water. A prototype model, designed with such an approach in mind, has already been constructed by TEMM International (Pty.) Ltd. The Solar Heat Barrow (SHB) was developed in the 1992 to 2003 period with the intention of combining a number of functions at low cost. Specific requirements were: low cost, a suitable design and materials for manufacture in large volume, sufficiently durable taking into account the harsh conditions of use. suitability for cases where no in-house piped water supply was available, the use of appropriate technology and the improvement of quality of life. The unit combines the absorption of solar radiation, the heating of a relatively small volume of water, the transport of the water from the point of supply and the storage of the hot water until it is used. Untreated water sources such as surface waters (streams, rivers, lakes, etc.) or unprotected open wells are the vehicles for waterborne bacterial diseases such as cholera and typhoid fevers. In the case where water is collected from these sources, the SHB has a build-in Purification Dispenser that purifies the water in the collector against waterborne bacterial diseases. Certain research questions need to be answered. They will be answered by demonstrating the SHB in two communities where no in-house piped water supply is available and by establishing the socio-economic response of the users. The research questions are as follow: What are the responses of the users concerning the SHB, in comparison to those of a control group, regarding its operation, durability, utility and satisfaction of needs? What is the daily use of hot water and the reduction in energy use and cost? To what extent will the target community purchase the SHB at the full or subsidised commercial price? Is there a business case that can be developed for the large scale production, marketing. financing and Small, Medium and Micro Enterprises (SMME) development of the SHB? It was decided to choose a community in the Valley of Thousand Hills in KwaZulu Natal as the demonstration site. The name of the community is Mabedlane. It is a remote rural area 20 km's north of Botha's Hill and is situated along the Umgeni River. The community is dependent on the river for domestic water. Most families are headed by women. The area has low levels of infrastructure, poor roads, a high unemployment rate and poor health facilities. The first survey, which was conducted before the test period started, showed a very positive response from potential users. From 112 questionnaires that were given to the people of Mabedlane, all indicated that they were interested in a product that can transport and heat water for domestic use. The socio-economic study has shown that the price per unit needs to be adapted as 85% of the people who participated in the survey indicated that they would only pay less than R100 for the product. 15% indicated that they would pay between RlOO and R200. From the second and third questionnaires it was clear that the users were satisfied with the heating performances of the SHB. The community was very interested in purchasing a SHB. They have realised that a SHB will improve their standard of living and regard it as a necessity in their day to day activities. It is apparent that people, who will benefit from a SHB most, are those who will not be able to pay the full retail price. Therefore, new business strategies have to be researched when implementing the SHB to the target market in South Africa. The idea of considering ways to sponsorlfund the SHB must also be investigated. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.

Many rural communities in South Africa do not have running water or electricity. The fetching and heating of water is therefore a time consuming and expensive daily ritual. The use of energy sources such as wood or coal are not readily available and cause environmental pollution. Although solar water heaters are commonly available in South Africa, they are very seldom used in rural areas. Whilst this can mostly be attributed to a high system cost, current designs also do not cater for specific rural problems such as the transporting or purification of water. A prototype model, designed with such an approach in mind, has already been constructed by TEMM International (Pty.) Ltd. The Solar Heat Barrow (SHB) was developed in the 1992 to 2003 period with the intention of combining a number of functions at low cost. Specific requirements were: low cost, a suitable design and materials for manufacture in large volume, sufficiently durable taking into account the harsh conditions of use. suitability for cases where no in-house piped water supply was available, the use of appropriate technology and the improvement of quality of life. The unit combines the absorption of solar radiation, the heating of a relatively small volume of water, the transport of the water from the point of supply and the storage of the hot water until it is used. Untreated water sources such as surface waters (streams, rivers, lakes, etc.) or unprotected open wells are the vehicles for waterborne bacterial diseases such as cholera and typhoid fevers. In the case where water is collected from these sources, the SHB has a build-in Purification Dispenser that purifies the water in the collector against waterborne bacterial diseases. Certain research questions need to be answered. They will be answered by demonstrating the SHB in two communities where no in-house piped water supply is available and by establishing the socio-economic response of the users. The research questions are as follow: What are the responses of the users concerning the SHB, in comparison to those of a control group, regarding its operation, durability, utility and satisfaction of needs? What is the daily use of hot water and the reduction in energy use and cost? To what extent will the target community purchase the SHB at the full or subsidised commercial price? Is there a business case that can be developed for the large scale production, marketing. financing and Small, Medium and Micro Enterprises (SMME) development of the SHB? It was decided to choose a community in the Valley of Thousand Hills in KwaZulu Natal as the demonstration site. The name of the community is Mabedlane. It is a remote rural area 20 km's north of Botha's Hill and is situated along the Umgeni River. The community is dependent on the river for domestic water. Most families are headed by women. The area has low levels of infrastructure, poor roads, a high unemployment rate and poor health facilities. The first survey, which was conducted before the test period started, showed a very positive response from potential users. From 112 questionnaires that were given to the people of Mabedlane, all indicated that they were interested in a product that can transport and heat water for domestic use. The socio-economic study has shown that the price per unit needs to be adapted as 85% of the people who participated in the survey indicated that they would only pay less than R100 for the product. 15% indicated that they would pay between RlOO and R200. From the second and third questionnaires it was clear that the users were satisfied with the heating performances of the SHB. The community was very interested in purchasing a SHB. They have realised that a SHB will improve their standard of living and regard it as a necessity in their day to day activities. It is apparent that people, who will benefit from a SHB most, are those who will not be able to pay the full retail price. Therefore, new business strategies have to be researched when implementing the SHB to the target market in South Africa. The idea of considering ways to sponsorlfund the SHB must also be investigated. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.

Purpose: This degree project aims to study how different choices regarding the size, location and type of windows affect daylight entry in an apartment building in Västerås. We have chosen to calculate the energy requirement when changing the window type, size and shielding factor. The purpose is also to come up with solution proposals that balance daylight input and energy for a smaller energy need in the apartment building. Method: The research method is based on a literature study that will lay the foundation for the work and a case study where a visit to the concerned building has been carried out. Interviews have also been conducted with experts in daylight and energy issues. Energy calculations and daylight- related calculations have also been made using the computer program Daylight Visualizer. The goal of the program is to find out the value of the daylight factor in two different apartments on two different floors. In each apartment, three different rooms in three different latitudes (north, west, and south) have been studied. Results: The results present several factors that affect daylight intake. These are screening angles, orientation, room height, room depth, building structure and placement of balconies. The properties of the windows in terms of daylight transmittance (LT value) and solar heat gain (g value) are very important to get a good result regarding both daylight and heat in the building. The balance between daylight and solar heat gain to reducing the energy needs for heating during the winter and cooling during the summer. The result based on the computer program for the first window alternative show that that the value of the daylight factor in all three rooms on the 12th floor (third floor) was between 0.59–0.31% and on the 19th floor (tenth floor) 1.01– 0.91%. The calculations of the energy balance show as monthly results, and the calculated annual need for active heating is about 27 MWh / year. The corresponding result according to calculations by the consulting company Kadesjös is approximately 59 MWh / year, but the difference between its calculations has not been studied further in this degree project. Conclusions: The calculation results indicate that the building has a very limited energy requirement for active heating in relation to its size and this is logical given that the heat losses are relatively small in terms of transmission, Exhaust and supply air ventilation with heat recovery (FTX system), and air leakage. The heat losses through window glazing in this case constitute to only about 12% of the building's total heat losses.

The industrial sector not only has a big contribution to global emissions but also a low share of renewable energy for heat demand. Knowing that most of the energy consumption in industry is heat and that half of it is at medium-low temperature (below 400 ºC), it is a great market for the integration of solar thermal technologies. Following the criteria of high heat demand and low-temperature requirements, five promising industrial sectors and their processes have been analysed: food and beverage, paper and pulp, chemical, textile and mining. Steam generation at supply level has been considered one of the most promising systems considering its integration advantages and the potential of direct steam generation plants. The market potential study has been geographically determined performing an MCA; countries all over the world have been assessed considering their heat consumption in the promising sectors and other conditions that enhance the SHIP feasibility such as solar radiation levels, favourable energy policies, previous experience in SHIP plants, ease of doing business, etc. The price of natural gas has been also considered after selecting Europe as a suitable market. The potential heat demand that this technology could cover has been estimated considering limitations as the competitiveness with other renewable heat sources, the expected heat recovery potential for some sectors, the solar fraction of the region and roof space of the factories. The results show that the five countries with bigger potential are Germany, France, Netherlands, Italy, and Spain, while the sectors with the most suitable market are food and beverage, and chemical. A case study has been selected based on the previous conclusions: a Fresnel direct steam generation plant in Sevilla (Spain) characterized thanks to the data provided by the company Solatom. The plant has been modelled using the software TRNSYS, taking special consideration in the Fresnel performance, the dynamic steam drum behaviour and its influence on the start-up time of the plant. The results achieved through the techno-economic analysis show that parameters such as solar radiation, conventional fuel prices and EU ETS prices have a major impact on the economic indicators. A sensitivity analysis shows that locations with radiation levels above 1750 kWh/m2 have positive values for NPV, and above 2250 kWh/m2 the cost of generating solar heating (LCOH) is under European natural gas prices. In addition to this, fuel prices above 50 €/MWh, which are common for SMEs, results in payback periods under 10 years. Future trends depict favourable scenarios as current European policies are causing a rapid growth of the ETS. Therefore, solar heat in industrial processes can be a feasible alternative, or work as a complement, to conventional systems. Its deployment is driven by supportive policies, high radiation levels, costly fuels prices (such as the ones for SMEs) and the necessity of reducing GHG emissions and decrease the independence on fossil energies. / Industrisektorn har inte bara ett stort bidrag till globala utsläpp utan också en låg andel förnybar energi för värmebehov. Att veta att det mesta av energiförbrukningen i industrin är värme och att hälften av den är vid medelhög låg temperatur (under 400ºC), är det en fantastisk marknad för integration av solvärmeteknik. Enligt kriterierna för högt värmebehov och lågtemperaturkrav har fem lovande industrisektorer och deras processer analyserats: mat och dryck, papper och massa, kemikalier, textil och gruvdrift. Ånggenerering på leveransnivå har ansetts vara ett av de mest lovande systemen med tanke på dess integrationsfördelar och potentialen hos direkta ånggenereringsanläggningar. Marknadspotentialstudien har fastställts geografiskt med en MCA; länder över hela världen har bedömts med tanke på deras värmeförbrukning i de lovande sektorerna och andra förhållanden som förbättrar SHIP-genomförbarheten, såsom solstrålningsnivåer, gynnsam energipolitik, tidigare erfarenhet av SHIP-anläggningar, lätt att göra affärer etc. Priset på naturgas har också övervägs efter valet av Europa som en lämplig marknad. Det potentiella värmebehovet som denna teknik kan täcka har uppskattats med tanke på begränsningar som konkurrenskraft med andra förnybara värmekällor, den förväntade värmeåtervinningspotentialen för vissa sektorer, solfraktionen i regionen och fabrikernas takutrymme. Resultaten visar att de fem länderna med större potential är Tyskland, Frankrike, Nederländerna, Italien och Spanien, medan de sektorer som har den mest lämpliga marknaden är mat och dryck samt kemikalier. En fallstudie har valts utifrån de tidigare slutsatserna: en Fresnel-ångproduktionsanläggning i Sevilla (Spanien) som kännetecknas av uppgifterna från företaget. Anläggningen har modellerats med hjälp av programvaran TRNSYS, med särskild hänsyn till Fresnel-prestanda, det dynamiska ångtrummans beteende och dess inflytande på anläggningens starttid. De resultat som uppnåtts genom den tekno-ekonomiska analysen visar att parametrar som solstrålning, konventionella bränslepriser och EU: s ETS-priser har stor inverkan på de ekonomiska indikatorerna. En känslighetsanalys visar att platser med strålningsvärden över 1750 kWh/m2 har positiva värden för NPV och över 2250 kWh/m2 är kostnaden för att generera solvärme (LCOH) under europeiska naturgaspriser. Utöver detta leder bränslepriser över 50 €/MWh, som är vanliga för små och medelstora företag, till återbetalningsperioder under tio år. Framtida trender visar gynnsamma scenarier eftersom europeisk politik orsakar en snabb tillväxt på ETS. Därför kan solvärme i industriella processer vara ett genomförbart alternativ eller fungera som ett komplement till konventionella system. Dess utplacering drivs av stödjande politik, höga strålningsnivåer, dyra bränslepriser (som de för små och medelstora företag) och behovet av att minska växthusgasutsläppen och minska självständigheten för fossila energier.

Low-emissivity (low-E) window films are designed to improve the energy performance of windows and prevent indoor overheating by solar radiation. These films can be applied to different types of glazing units without the need for changing the whole window. This characteristic offers the possibility to improve the energy performance of the window of old and historic buildings for which preservation regulations say windows should remain more or less unchanged. This research aims to figure out to what extent a low-E window film can improve thermal comfort and energy performance of an old three-storey historic stone building in the cold climate of Mid-Sweden. In this research, first, with help of the simulation software “IDA ICE”, the entire building was modelled without window films in a one-year simulation. Second step was to add the low-E window films (3M Thinsulate Climate Control 75 (CC75)) to all the windows and repeat the simulation. Comparison between the results of the two cases revealed an improvement in energy use reduction as well as the thermal comfort when applying the films. For the application of the window films, a cost analysis using payback method was carried out which showed a long- time payback period. Although an investment with a long-time payback period is considered as a disadvantage, for historic buildings with very strict retrofit regulations specially when it comes to the building’s facades, application of the low-emissivity window films for better energy performance and thermal comfort is among the recommendable measures, but not necessarily the best.

<p>This project deals with the potential of membrane stratified solar ponds which consist of two water layers, where one is a salt solution here, and a separating translucent membrane. An experimental pond was set up to study the thermal behaviour of such collector systems. The input is mainly solar radiation, sometimes when the ambient temperatures are higher than the pond temperatures also heat from the environment is transferred into the pond.</p><p>The measured temperatures of the pond, the ambient temperature, the global radiation and wind speed were the basis data for thermal calculations which showed that the pond was working well as a solar collector and thermal storage system all in one. Heat was not extracted from the pond however, only the losses to the environment were studied.</p><p>It was found out that the pond temperatures were higher than the ambient temperature over the whole measurement period of 12 days, and insulation and pollution problems as well as future prospects and suggestions for further studies are discussed at the end of this paper.</p>

This project deals with the potential of membrane stratified solar ponds which consist of two water layers, where one is a salt solution here, and a separating translucent membrane. An experimental pond was set up to study the thermal behaviour of such collector systems. The input is mainly solar radiation, sometimes when the ambient temperatures are higher than the pond temperatures also heat from the environment is transferred into the pond. The measured temperatures of the pond, the ambient temperature, the global radiation and wind speed were the basis data for thermal calculations which showed that the pond was working well as a solar collector and thermal storage system all in one. Heat was not extracted from the pond however, only the losses to the environment were studied. It was found out that the pond temperatures were higher than the ambient temperature over the whole measurement period of 12 days, and insulation and pollution problems as well as future prospects and suggestions for further studies are discussed at the end of this paper.

The food industry is a large consumer of industrial energy. A very large portion of this energy is needed in the form of thermal energy at medium to low temperatures. Fossil fuels remain the dominant sources of this energy. This combination provides various possibilities to reduce energy consumption and CO2 emissions with heat recovery, but also with the integration of solar process heat. Energy efficiency must provide the context, or background, of such considerations, and is therefore a very important aspect of them. It is a complex task to design an efficient heat supply with a variety of energy sources. An analysis of standards for energy audits, guides for energy efficiency and guides for solar process heat integration confirms that complexity. However, no available methodology considers all the necessary steps. These must range from analysis of the existing heat supply to the redesign of an efficient heat supply system. The focus must be on heat sources with waste heat and on solar process heat that might be used to complement the conventional sources. The design of a process heat system is mainly the task of design engineers in engineering offices. Specific tools and measures are needed to support these experts. However, the companies of the food industry sector employ their own energy engineers for energy issues. These people are actually the decision makers responsible for the configuration of the company energy supply systems, who also possess knowledge of the processes in their industry subsector. The expertise of the energy engineers varies within a broad range and is also connected to their area of responsibility. Therefore, it is important to consider these energy engineers when developing a methodology. The development of the methodology proposed herein consists first of the configuration of the tools and measures, which were assigned to four elements and functions. Second, the methodology so developed was applied at two companies in cooperation with their energy engineers, in detailed case studies. The feedback from the energy engineers is therefore a main objective and provides a background for evaluation of the usability of the methodology. It demonstrates the expertise required of the energy engineers, for the application of the tools and measures provided. Moreover, the development and application of the methodology involving real companies demonstrates the necessity of getting feedback from energy engineers. That finding is very important, and has been insufficiently considered in previous guides or methodologies. It is proposed that further work be aimed at providing additional case studies to extend the use of this methodology to other parts of the food industry.

Un nouveau procédé de trigénération thermo-hydraulique fonctionnant à partir d'énergie thermique basse température (80 à 110 °C) a été étudié pour assurer les différents besoins du secteur résidentiel. Le terme "thermo-hydraulique" se réfère à l'utilisation d'un liquide incompressible qui permet de transférer le travail hydrauliquement entre différents composants ou sous-systèmes, permettant d'améliorer l'efficacité de la chaine de conversion énergétique. Un modèle quasi-statique a été développé pour évaluer les performances énergétiques des différentes variantes du procédé. Ces calculs ont permis de définir parmi un large choix, quels fluides de travail étaient les plus appropriés. Ces calculs ont été complétés par une étude quasi-dynamique et dynamique permettant un meilleur dimensionnement du procédé. Enfin, une étude de fonctionnement annuel a été réalisée à partir du modèle quasi-statique pour évaluer l'évolution des performances ainsi que sa production d'énergie sur une année complète de fonctionnement. Ces études montrent que le couple fluide R1234yf/R1233zd semble le plus approprié à un fonctionnement en climat méditerranéen. L'étude annuelle montre qu'en considérant les données climatiques de la ville de Perpignan, le procédé permet d'amplifier l'énergie solaire collectée d'un facteur de 1,32 en moyenne et permet d'atteindre un COP solaire de 0,24 en mode rafraichissement. Quand les besoins thermiques sont satisfaits, l'intégralité de l'énergie solaire captée est valorisée pour produire de l'électricité avec un rendement moyen annuel de 4,2%. / A new process based on thermal-hydraulic conversion actuated by low-grade thermal energy (80–110 °C) is investigated and aims at providing trigeneration energy features for the residential sector. "Thermo-hydraulic" term refers to a process involving an incompressible fluid used as an intermediate medium to transfer work hydraulically between different thermal operated components or sub-systems allowing to improve the efficiency of the energy conversion chain. A model, assuming steady-state operations, is developed to assess the energy performances of different variants of this thermo-hydraulic process as well as various pairs of working fluids. These calculations were completed by a quasi-dynamic and dynamic models allowing a better sizing of the process. Finally, an annual study was realized from the quasi-static model in order to estimate the evolution of the performances as well as its power production over a complete year of functioning. For instance, in the frame of a single-family home, located in the Mediterranean region, the working fluid pair (R1234yf/R1233zd) is investigated in detail in order to estimate the annual performances. For domestic houses, the process aims at amplifying the solar energy collected by a factor of 1.32 for heating purpose, provides a cold production with a solar COP of 0.24 and generates electricity from the remaining solar energy with an efficiency of 4.2%.

Transitioning the industrial sector’s energy system to renewable sources is crucial to reduce climate change. There is no exception for China, currently having the highest absolute levels of greenhouse gas (GHG) emissions in the world. The industrial sector accounts for about two thirds of the national energy consumption and coal is the country’s most important energy source. The integration of alternative energy sources such as solar can help transitioning the country’s energy system. By presenting a techno-economic analysis, this thesis gives an indication for profitability and in what extent there is a potential to cover the steam demand with a decentralized solar heat technology for two industries, fish and textile, in the Zhejiang province in eastern China. The used solar technology is a system with parabolic trough collectors (PTCs) with an integrated gas fired boiler. The PTC-system is compared with a coal-fired centralized supplier. The analyzed factors were roof area, solar irradiation, solar fraction, cost for steam from the centralized suppliers and cost of coal and natural gas. The maximum CO2 reduction is found to be dependent on the potential installation area. The greater area installed, the larger is the capacity and thus also the CO2 savings. The share of total steam demand covered by solar is directly proportional to the demand in relation to the installed solar capacity. The fish industry, having the lowest steam demand in relation to the roof area, is found to be able to save the largest relative proportion of CO2 emissions. Different scenarios are presented, modifying the fuel cost and fuel type for the PTC-system’s boiler, adjusting the steam cost from the centralized suppliers and using two different solar fractions of 35% and 50%. The CO2 savings depends on what fuel is being used and the solar fraction. Larger CO2 reductions are possible with a gas fired boiler compared to a coal fired one. But using a coal fired boiler makes it more economically profitable, matching the low coal price used for the centralized supplier. The scenario with most CO2 reductions is attained when using a high solar fraction of 50% and a natural gas fired boiler. The annual CO2 savings is then ranging from 15 tons per year for the company having the lowest steam capacity, up to 2090 tons/year for the company with one of the highest. Another significant factor is the companies’ seasonal activity. For the company having the least amount of active days per year (84 out of 365 days), the PTC-system is unprofitable whichever scenario. However, fuel costs for the boiler is found to be one of the most significant factors for the outcome determining if the investigated PTC-system is profitable or not. For all of the companies, there was only one that could provide all its steam demand with the PTC-system. This indicates that other energy sources need to be integrated to provide the steam demand of the enterprises with a renewable energy system. / Att omvandla industrins energisystem med förnyelsebara energikällor är väsentligt för att bromsa klimatförändringarna. Det är inget undantag för Kina, som nuvarande har de största absoluta nivåerna av utsläpp av växthusgaser i världen. Industrin står för ca två tredjedelar av den nationella energiförbrukningen och kol är landets största energikälla. Integrerandet av andra alternativ såsom solenergi kan dock hjälpa till i landets energiomvandling. Denna rapport syftar till att presentera en tekno-ekonomisk analys av en decentraliserad solfångare och ge indikation på lönsamhet samt i vilken grad tekniken kan förse behovet av ånga för två industrier, textil och fiske, i Zhejiang provinsen i östra Kina. Den solfångarteknik som används är ett system med Parabolic trough collectors (PTCs) med integrerad gaseldad ångpanna. Systemet jämförs med kraftvärmeverk som drivs med kol. De analyserade faktorerna är takytan, solar fraction, solinstrålning, kostnad för ånga samt ångpannans bränslekostnader. Besparingarna för CO2-utsläpp beror på den potentiella installationsytan. Ju större installationsyta, desto högre kapacitet och därmed högre CO2-besparingar. Andelen av behovet ånga som kan förses med solfångare är i direkt proportion till takytan och det totala behovet. Fiskeindustrin, som har lägre ångbehov i relation till takyta, visar sig kunna spara den största relativa mängden CO2-utsläpp. Olika scenarier presenteras, där bränslekostnaden och typ av bränsle för PTC-systemets ångpanna modifieras, kostnaden för ånga från de centraliserade leverantörerna justeras och solar fraction ändras mellan 35% och 50%. Besparingarna i CO2-utsläpp beror på vilket bränsle som används samt solar fraction. Större CO2-reduktion är möjlig med en gaseldad panna jämfört med en koleldad. Dock är en koleldad panna lönsammare när den matchar det låga priset på kol som används för de centraliserade leverantörerna. Scenariot med de största CO2-besparingarna uppnås med en hög solar fraction på 50% och en naturgaseldad panna. De årliga CO2-besparingarna varierar från 15 ton per år för det företag som har den lägsta ångkapacitet, upp till 2090 ton per år för ett företag med en av den högsta kapaciteten ånga. En annan viktig faktor är företagens aktivitet per år. Företaget som har minst aktiva dagar per år (84 av 365 dagar), är ej lönsamt i något av de testade scenarierna. Bränslekostnaderna för pannan har emellertid visat sig vara en av de viktigaste faktorerna för resultatet som avgör om det undersökta PTC-systemet är lönsamt eller inte. Bland alla företagen fanns det bara ett som kunde förse hela sitt ångbehov, med PTC-systemet. Detta indikerar att andra energikällor måste införas för att förse företagens ångbehov med ett förnybart energisystem.