The Scientific Journal of Riga Technical University
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Exploring the Control of the Position of the Isotherms of the Heat Pump Cycle in an Air Handling Unit: An Experimental study
Full text linkThe use of heat pumps in the building heating and cooling supply chain is increasing, and air-to-air heat pumps are increasingly being installed in modern air handling units. The energy conversion modes of such devices are constantly changing due to the constant change in the state of the outdoor air (temperature, humidity). Flexibility, the ability to efficiently and rationally respond to ambient air parameters, is an important feature of choosing the operating mode of energy transformers and their control. The overall seasonal efficiency of the air handling unit depends on it. Modern commercial heat pumps have two control degrees of freedom. They have a variable-speed compressor and an electronic expansion valve. This combination of control components once made it possible to increase the seasonal efficiency of heat pumps. For a long time, the possibility of controlling the cycle in this way prevailed, and only electronic control tools were improved. Little attention is paid to how the changes in the thermodynamic cycle are combined with the energy demands of air preparation corresponding to the outdoor temperature. It would be relevant to look for additional components of the heat pump circuit that could control its operating cycle, which could increase the efficiency indicators of the air preparation process. The article’s authors seek to introduce an additional component into traditional measures of heat pump control, providing the third degree of freedom of the control cycle. For this purpose, studies are being conducted to experimentally assess the impact of the volume of the heat pump system on the shifts of the isotherms of its thermodynamic operating cycle. The results show that the system volume parameter has the potential for regulation capabilities in controlling the operation of a heat pump, so it is worthwhile to further develop and study such a technological solution in more detail
Bibliometric Review of Electrification of Enterprise and Last-Mile Delivery Fleet
Full text linkThe impact of transport on carbon emissions accounts for 16.2 % of total global emissions, of which road transport accounts for 11.9 %. Road freight accounts for 40 % of road transport emissions and 4.76 % of global CO2 emissions. This study analyses the existing scientific literature in the field of transport electrification for transport companies in general and for ‘last mile delivery’ logistics companies specializing in urban delivery within parcel collection networks. The purpose of this study is to determine the state of the art for electric vehicles in fleets and how this topic can be assessed for sustainability. Bibliographic validation is primarily quantitative and is the most efficient method for dealing with the large volumes of information from the Web of Science (WoS) and Scopus databases. VOSviewer software was used to map the relationships between the most frequently used keywords in academic articles. The results show a small number of research papers addressing the electrification of fleet transportation. Only 1 of 523 WoS publications and 1 of 656 fleet transport publications in Scopus covered last-mile delivery for the selected period (1985–2022). It should also be noted that only 39 publications in 1987 in WoS database and 29 papers in 1891 in Scopus on transport electrification have sustainability rating links. The study reveals a lack of research in the subfield of transport electrification. The authors conclude that more research on sustainability criteria for fleet electrification is needed to support a smooth transition to EVs within this specific subfield of transport and to contribute to emission decrease in transport sector
Unlocking the Impact of Climate Change Mitigation Policies: A Comprehensive Study of Clean and Dirty Innovation Dynamics
Full text linkAchieving the Paris Climate Agreement’s goal of limiting global warming to 1.5 °C to 2 °C by the end of the century will require massive investments in environmental technologies and a drastic shift away from high-carbon technologies. This paper investigates the impact of climate change mitigation policies on clean energy innovation. A statistical evaluation of the impact of public policies on the rate and direction of innovation for a lowcarbon future is complicated by the nature of the data and the absence of benchmarks. In addition, the statistical analysis is further complicated by the spillover effects between clean and dirty innovation and by the lag effects. In this paper, the authors assess the effects of both public policies, such as carbon taxes and green subsidies, and economic and environmental conditions, such as oil prices, large recessions, climate-related disasters, etc., on clean innovation using a nonparametric method based on the copula distribution of clean innovation. The authors collect data from the European Patent Office (EPO) Worldwide Patent Statistical (PATSTAT) Database, both on clean and dirty patents. This database is managed by the EPO and compiles data from patent offices around the world. The emphasis is put on inventions for which a patent application has been submitted to the United States Patent and Trademark Office (USPTO). The inventions are dated based on the date of their first patent application. Clean innovation refers to patents in areas such as renewable energy generation and electric vehicles, while dirty innovation refers to fossil-based energy generation and internal combustion engines. The authors employ a novel nonparametric test against pairwise differences, especially in tail dependence structures, which we measure with tail copulas, thereby avoiding the possibility of parametric misspecification. This method also permits to examine the effects of various interventions and economic conditions on different portions of the distribution, with a particular emphasis on tail dependence. The authors identify nonlinear dependence structures between clean innovation, public policies, and economic determinants like the oil price and recession. By comparing the effects of clean and dirty innovation, we can determine whether the effect on clean innovation is distinct. The findings indicate that the tightening of environmental policies since the early 1990s has statistically and economically contributed to the increase in clean innovation. The findings can bolster public support for green R&D. In addition, they suggest that green policies may be able to increase the knowledge diffusion of clean innovation
Exploring the Differential Effects of Urban Heat Islands on Energy Use and Carbon Emissions in Warm and Cold Climates: a Case Study of North Africa and North Europe
Full text linkThe urban heat island (UHI) phenomenon has differential impacts on energy use and carbon emissions in buildings depending on the climate of the region and the urban planning strategies in place. This study explores the differential effects of UHI on energy use and carbon emissions in warm and cold climates, using North Africa and North Europe as case studies. We address the following research questions: 1) How does the UHI phenomenon impact energy use and carbon emissions in buildings in these regions? 2) What urban planning strategies are currently in place to mitigate the negative impacts of UHI on energy demand and emissions in these regions? 3) How effective are these strategies in mitigating the negative impacts of UHI on energy demand and emissions in both warm and cold climates? 4) What additional urban planning strategies could be implemented to reduce further the negative impacts of UHI on energy demand and emissions in both warm and cold climates? The UHI increases energy bills and emissions due to the higher demand for cooling energy in warm climates, while in cold climates, UHI reduces energy demand and emissions by decreasing the need for heating energy. Urban planning strategies, such as incorporating green space, using reflective materials, choice of colors, and designing for natural ventilation, can effectively mitigate the negative impacts of UHI on energy demand and emissions in both warm and cold climates. However, the effectiveness of these strategies varies depending on the climate of the region and the specific urban context. In this study, we will provide a recommendation for urban planning strategies that can be implemented to further reduce the negative impacts of UHI on energy demand and emissions in both warm and cold climates. Our study contributes to the understanding of the UHI phenomenon. It provides insights for urban planners and policymakers in developing effective strategies to reduce energy use and carbon emissions in buildings and cities
Off-shore and On-shore Macroalgae Cultivation and Wild Harvesting: an LCA-based Evaluation from Baltic Case Studies
Full text linkSeaweeds are organisms with unique characteristics. They contain a broad spectrum of micro and macro elements (i.e., minerals, carbohydrates, proteins, lipids, pigments, and vitamins). Furthermore, they have a very high growth rate and are present in large quantities and species in nature. Therefore, they represent an ideal feedstock for a biorefinery concept. Historically, macroalgae used in biorefineries have been harvested directly from the sea or the shores (off-shore technique). However, recent studies are analysing the possibility of creating on-shore cultivation facilities. This research aims to perform a Life Cycle Assessment (LCA) study that analyses and compares the environmental impact of two seaweed cultivation and wild harvesting techniques in the Baltic conditions based on existing pre-commercial and commercial projects. Inventory data are collected directly from two macroalgae producers in the Baltic Sea region (one wild harvester and one on-shore), integrated with literature, and then normalized to the selected functional unit, i.e., 1 ton of harvested fresh macroalgae. The results, implemented with SimaPro 9.4 software, determine which of the two techniques has the highest environmental impact and which are the most sensitive environmental indicators. Furthermore, the results underline the critical parameters for the two cultivations (i.e., fuel consumption and electricity), contributing to identifying environmental benchmarks for further optimization strategies. The alternative scenarios analysis included in the study aims to explore and highlight the effect of the variation of selected input parameters or assumptions to provide a consistent assessment of the uncertainty of the model outputs and the main findings in terms of environmental impacts
Dynamic U Value Measurement for Indoor Temperature Prediction with NN
Full text linkNowadays, monitoring and automated control are key for the power-efficient and comfortable use of buildings. As the demand for the indoor climate grows, the complexity of building control increases due to the increased number of controlled systems within the building. Therefore, control methods capable of assessing the dynamics of a task and controlling a building independently, are gaining popularity. One of these methods is a model-based predictive control, the energy efficiency of which is directly dependent on the accuracy of predictions of the state of the building. To analyse changes in the dynamics of the internal climate of a building caused by temperature changes, a relatively short history of measurements is needed. However, the analysis of changes in structural properties caused by moisture transfer requires much longer-term historical data. It is known that even neural network architectures with large core memories such as Long Short-Term memory could lose information on large time-series data. In addition, from mathematical point of view, moisture transfer is more complex than heat transfer. As a result, the approximating function for a neural network becomes more complicated, which leads to a decrease in energy performance. To solve this problem, a pre-processing technique to obtain the U value in real time is introduced. The results of a numerical simulation in WUFI6, verified by measurements, showed that the U value of an experimental construction could change by ~10 % due to moisture transfer. The experiments with 3-year monitoring data showed that usage of the proposed method in some cases reduces the average mean squared error of neural network in indoor climate forecast by ~8 %
Optimizing Biobutanol Production: Analysis of Feedstock Selection, Pre-treatment Methods, and Microorganism Strains for Biobutanol Production from Agricultural and Industrial By-products
Full text linkThis study presents an analysis of key elements of biobutanol production, including feedstock selection, pre-treatment methods, and microorganism strains. Using laboratory experiments, we evaluated the ability of different microorganisms to convert various agricultural and industrial by-products into biobutanol. We tested three microorganism strains: C. acetobutylicum DSM 792, C. beijerinckii DSM 6423, and C. saccharoperbutylacetonicum DSM 14923. The results showed that biodiesel production residues, various agricultural hydrolysates, yeast residues, and milk processing residues were the most suitable feedstocks for biobutanol production. In addition, the authors explored different pre-treatment methods, such as microbial and chemical hydrolysis, to enhance the efficiency of biobutanol production. Our findings provide valuable insights for optimizing biobutanol production processes in line with sustainable and cost-effective production principles
Extraction of Apple Pomace from Juice Production Using Supercritical CO2 Extraction
Full text linkApple pomace, a by-product of apple juice and cider production, is a sustainable raw material from which valuable products such as nutritional supplements and pectin can be obtained. It contains significant amounts of antioxidant compounds that have been linked to several health benefits. Both traditional and new technologies can be used to extract valuable components from apple pomace, with an emphasis on new and environmentally friendly methods. One such technique is the use of supercritical CO2 extraction. This method is considered environmentally friendly, and it can be used to extract valuable compounds such as antioxidants and pectin from apple pomace. This article examines the extraction parameters of apple pomace and analyses the valuable substances in the extract samples. Apple pomace is a promising source of carbohydrates, proteins, amino acids, fatty acids, phenolic compounds, vitamins, and other compounds with a vast range of food applications
Mobile Thermal Energy Storages as Complementary Technology to District Heating Networks
Full text linkDistrict heating networks (DHN) are an important backbone of today´s heat supply with high potential to contribute to a reduction of greenhouse gas emissions, if their heat sources are increasingly transformed into renewable ones. However, an economically viable application of such networks requires adequate occupancy rates and power density along the lines, because the infrastructure causes significant effort in terms of investment, operation and maintenance. This is one of the reasons, why DHN are mostly implemented in urban regions. On the other hand, industrial plants are not always located within the meaningful range of DHN, although they require huge amounts of heat as well as release significant amounts of waste heat, depending on the specific industrial sector. The utilisation of mobile thermal energy storages (M-TES) can be a possibility to close the gap of energy transfer between a DHN and the industry or even directly between two or more industrial plants. The intention of this approach is to transfer heat by charging a mobile heat storage at the producer and transfer it to the consumer by means of common transport and available infrastructure, e.g. by a truck on the road. In this way, the M-TES concept could serve as a complementary heat supply technology for regions without DHN or it could even be a competitor to DHN for the case that it might by economically advantageous. M-TES was already investigated in the past, even by experimental implementation, but with the energy prices of 2015 is was financially not feasible [1]. As energy markets had to face unknown fluctuations in 2022, the research work presented by this paper had the aim to analyse the M-TES concept for the current situation. Therefore, a comprehensive economic evaluation was performed, based on VDI2067, for calculating the levelised costs of heat (LCOH) for M-TES. This investigation was done for the three main types of heat storing mechanisms, namely sensible, latent and thermochemical storages. In each category, several material types were considered to meet possible requirements of the specific application, e.g. in terms of temperature demand. This updated analysis of M-TES yielded positive results for thermochemical and latent heat storages, as the LCOH are significantly lower compared to the heat costs of DHN in Austria in 2022. However, the transportation distance is the most sensitive parameter in this study, which restricts the viability of M-TES to near surroundings
Municipal Solid Waste Management towards Climate Neutrality
Full text linkIn line with the European Union’s move and the Green Deal initiative, Latvia needs to reduce CO2 emissions by 2030 and reach their complete elimination by 2050. Since waste management sector is associated with high greenhouse gas emissions, the sector will experience changes in the near future, and its sustainable development is linked to overcoming technical, economic and environmental challenges. The work aims to find solutions to the development of the waste sector in an environmentally sound manner, ensuring that the sector is closer to climate neutrality in 2050. Waste management is at the forefront of major changes and challenges in achieving regulatory objectives. In view of the changes expected and taking place in the sector, it is essential to carry out studies on resource and material recovery optimization options and potential for waste streams to be recycled and the energy recovery potential for non-recyclable streams. Acquiring knowledge and raising awareness of the role of changing management practices in saving CO2 emissions – avoided emissions – will allow the sector to move towards climate neutrality. This article analyses biodegradable waste management options and proposes the optimal solution for biodegradable waste management towards climate neutrality