Integration of trigeneration and CO2 based refrigeration systems for energy conservation

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.Food retail with large supermarkets consumes significant amounts of energy. The environmental impact is also significant because of the indirect effect from CO2 emissions at the power stations and due to the direct effect arising from refrigerant leakage to the atmosphere. The application of trigeneration (local combined heat, power and refrigeration) can provide substantial improvements in the overall energy efficiency over the conventional supermarket energy approach of separate provision of electrical power and thermal energy. The use of natural refrigerants such as CO2 offers the opportunity to reduce the direct impacts of refrigeration compared to conventional systems employing HFC refrigerants that possess high global warming potential. One approach through which the overall energy efficiency can be increased and the environmental impacts reduced, is through the integration of trigeneration and CO2 refrigeration systems where the cooling generated by the trigeneration system is used to condense the CO2 refrigerant in a cascade arrangement. This research project investigates experimentally and theoretically, through mathematical modelling and simulation, such a system and its potential application to supermarkets. A small size CO2 refrigeration system for low and medium food temperature applications was designed and constructed to enable it to be integrated with an existing trigeneration system in the refrigeration laboratory at Brunel University to form an integrated trigeneration and CO2 refrigeration test facility. Prior to the construction, the design of the system was investigated using mathematical models developed for this purpose. The simulations included the CO2 refrigeration system, CO2 evaporator coils and the integration of the trigeneration and CO2 refrigeration systems. The physical size of the design and component arrangement was also optimised in a 3D AutoCAD model. A series of experimental tests were carried out and the results showed that the medium temperature system could achieve a very good COP, ranging from 32 to 60 due to the low pumping power requirement of the liquid refrigerant. The low temperature system performed with average steady state COP of 4, giving an overall refrigeration system COP in the range between 5.5 and 6. Mathematical models were also developed to investigate the application of the integrated trigeneration and CO2 refrigeration system in a case study supermarket. The models were validated against test results in the laboratory and manufacturers’ data. The fuel utilisation efficiency and environmental impacts of different trigeneration and CO2 refrigeration arrangements were also evaluated. The results indicated that a system comprising of a sub-critical CO2 refrigeration system integrated with a trigeneration system consisting of a micro-turbine based Combined Heat and Power (CHP) unit and ammonia-water absorption refrigeration system could provide energy savings of the order of 15% and CO2 emission savings of the order of 30% compared to conventional supermarket energy systems. Employing a trigeneration system with a natural gas engine based CHP and Lithium Bromide-Water sorption refrigeration system, could offer energy savings of 30% and CO2 emission savings of 43% over a conventional energy system arrangement. Economic analysis of the system has shown a promising payback period of just over 3 years compared to conventional systems.Department for Environment, Food & Rural Affairs(DEFRA)-Advanced Food Manufacturing LINK Programm

Studi Eksperimental Kinerja Temperatur Dan Energi Integrasi Bio-PCM Pada Chest Freezer

Chest freezer pada operasionalnya memerlukan beban transien yang fluktuatif dari waktu ke waktu sesuai dengan kondisi lingkungan. Untuk mampu memenuhi kebutuhan beban pendinginan maksimum, chest freezer umumnya dirancang dengan kapasitas lebih besar dari beban pendinginan yang dibutuhkan. Akibarnya sistem chest freezer kurang efisien dan kurang handal akibat sering mati-hidup selama operasi. Oleh karena itu perlu dikembangkan sistem chest freezer yang dapat mengurangi siklus mati-hidupnya kompresor dan menghemat penggunaan energi fosil. Penelitian ini mengkaji teknologi refrigerasi chest freezer dengan siklus kompresor yang kecil dan memiliki potensi untuk diintegrasikan dengan sumber energi terbarukan. Pendekatan teknologi yang diterapkan adalah teknologi chest freezer berbasis vegetable oil phase change materials (bio-PCM). Hasil investigasi menunjukkan bahwa penggunaan bio-PCM dapat menurunkan siklus kompresor dan mampu menjaga temperatur produk di bawah -15 derajat C. Konsumsi energi teknologi freezer yang diusulkan relatif sama dengan freezer tanpa bio-PCM. Tetapi bio-PCM dapat membuat chest freezer sangat potensial diintegrasikan dengan sumber energi surya

Compras Públicas : estudo de caso da Universidade de Brasília

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Economia, Administração e Contabilidade, Departamento de Economia, Mestrado Profissional em Gestão Econômica de Finanças Públicas, 2014.É crescente a preocupação da administração pública com suas atividades que envolvem as licitações, com o anseio de adquirir produtos e serviços de qualidade com menos dispêndio possível. Este trabalhou analisou a gestão do processo de compras em uma Instituição Federal de Ensino Superior na sua fase externa das compras; ou seja: desde o recebimento das propostas até a homologação da compra. O referencial teórico abordou definições vinculadas ao assunto e voltadas, principalmente, para modalidade de compras: pregão eletrônico – PE. A metodologia utilizada, de abordagem qualitativa, permitiu, a partir da análise documental no portal comprasnet do governo federal, realizar um diagnóstico da situação atual e elaborar sugestões de melhorias no processo de compras da Universidade de Brasília. Na análise dos dados pode-se verificar que a implantação de sistemas de gestão da qualidade pode propiciar melhoria no processo de compras, principalmente em sua fase interna e contribuir para sua economicidade e eficiência, permitindo uma melhor relação entre a área jurídica e desta com a área de compra. Foi, também, verificada a necessidade de mais autonomia da Diretoria de Compras. Tais medidas terão impacto direto no desempenho dos processos, maior economicidade e eficiência, consequentemente. _________________________________________________________________________ ABSTRACTThere is a growing concern of public administration about their activities involving bids, looking forward to acquire products and quality services with the less expenditure possible. This work analyzed the purchase process management in a Federal Institution of Higher Education on its external phase of purchasing, that is: from the reception of tenders to the approval of the purchase. The theoretical reference covered definitions related to the subject and related, mainly, to the purchasing mode known as electronic trading. The methodology, of qualitative approach, allowed to make a diagnosis of the current situation and to prepare suggestions for improvements in the purchasing process at UnB from the full documental analysis on the Comprasnet portal of federal government. By analyzing the data it can be seen that the implementation of quality management systems can provide improvements in the purchasing process, especially in its internal phase and contribute to its economy and efficiency, allowing a better relationship between the legal department and the purchasing area. It was also verified the need for more autonomy to the Purchasing Directory. Such measures will have a direct impact on the procedures performance as well as greater economy and efficiency consequently

Integration of CO2 refrigeration and tri-generation systems for supermarket Applications

The environmental impact of supermarkets is significant not only because of the indirect effect from CO2 emissions at the power stations but also due to the direct effect arising from refrigerant leakage to the atmosphere. One approach through which the overall energy efficiency can be increased and the environmental impacts reduced, is through the integration of CO2 refrigeration and trigeneration systems where the refrigeration generated by the trigeneration system is used to condense the CO2 refrigerant in a cascade arrangement. Such a system is being investigated by Brunel University and a number of commercial organisations in the UK. This paper presents results of simulation studies that investigate the seasonal energy and environmental performance of such a system in a medium size supermarket

Performance optimization of a secondary refrigerant display cabinet using tests and CFD modelling

In this paper a computational investigation to address some of the design parameters that have significant effects on the performance of a secondary refrigerant refrigerated display cabinet is presented. The investigated design parameters include air curtain velocity, width, discharge angle and positioning of the air curtain outlet from the front edge of the display cabinet’s top shelf. In addition the effect of using honeycomb on the flow path at the air curtain outlet was also investigated. A 3D CFD model was constructed to assess the effect of the side flow on the performance of the vertical display cabinet. The suitability of using 2D CFD to carry out the display cabinet design optimization was investigated and it was concluded that for the length of the cabinet considered, the flow could be assumed to be two-dimensional for most of the cabinet length. The results also indicated that the optimum air curtain mass flow rate constituted approximately a third of the total air mass flow rate. For the geometry considered with respect to air curtain discharge and top shelf outer edge position it was found that shaping the honeycomb to produce more uniform flow and reduce recirculation at the inner edge of the air curtain outlet improved the air curtain performance and led to a 4% reduction in the cabinet load

Investigation of the performance characteristics of an ammonia-water absorption chiller in a tri-generation system arrangement

Trigeneration systems have been used in a number of applications including commercial buildings and industrial facilities. Most of these have been for space cooling applications with a smaller number for refrigeration applications in the food processing industry which requires temperatures below 0oC. This paper is concerned with the investigation and development of modular trigeneration systems for food industry applications based on the integration of microturbines and ammonia water absorption refrigeration systems. Specifically, the paper presents results of experimental investigations on the performance of a 12 kW capacity ammonia-water absorption refrigeration system driven by thermal energy recovered from the exhaust gases of a microturbine in a trigeneration arrangement. The heat transfer between the microturbine exhaust heat exchanger and the generator of the absorption refrigeration system is performed by a heat transfer fluid in a closed heat transfer loop. Tests were performed at different brine temperatures and heat transfer fluid temperatures. The performance of the unit was evaluated and found to compare favourably with the performance of a directly gas fired absorption chiller. In addition, the overall efficiency of the trigeneration system was also evaluated

Investigation of the performance characteristics of an ammonia-water absorption chiller in a tri-generation system arrangement

Trigeneration systems have been used in a number of applications including commercial buildings and industrial facilities. Most of these have been for space cooling applications with a smaller number for refrigeration applications in the food processing industry which requires temperatures below 0oC. This paper is concerned with the investigation and development of modular trigeneration systems for food industry applications based on the integration of microturbines and ammonia water absorption refrigeration systems. Specifically, the paper presents results of experimental investigations on the performance of a 12 kW capacity ammonia-water absorption refrigeration system driven by thermal energy recovered from the exhaust gases of a microturbine in a trigeneration arrangement. The heat transfer between the microturbine exhaust heat exchanger and the generator of the absorption refrigeration system is performed by a heat transfer fluid in a closed heat transfer loop. Tests were performed at different brine temperatures and heat transfer fluid temperatures. The performance of the unit was evaluated and found to compare favourably with the performance of a directly gas fired absorption chiller. In addition, the overall efficiency of the trigeneration system was also evaluated

The Strength of Authenticity in Developing Rural Tourism (A Case Study of Tri Eka Buana Village)

Purpose: This study aims to determine the strategies used in the authenticity of Tri Eka Buana Village, Bali, Indonesia, as a tourist attraction. Research methods: This research is a research mixed method with analytical techniques using the Internal Factor Analysis (IFAS), External Factor Analysis (EFAS), Internal-External Matrix (IE), SWOT, and Quantitative Strategic Planning Matrix (QSPM) Analysis. Findings: Based on the results of the IFAS matrix analysis, the main strength is that it has beautiful natural and artificial potential such as Bukit Abah, Danu Seliwah Temple, Dukuh Sakti Waterfall, Umananing Malini dance and Balinese Arak that can attract tourists, while the main weakness is that access to tourist objects is inadequate, such as a narrow and irregular parking area. Based on the results of the EFAS matrix analysis, it is known that the main opportunity is the development of Tri Eka Buana Village by involving local communities so as to minimize unemployment, preserve cultural and natural traditions while the main threat faced is competition between other tourism objects that have developed. The results of the IE Matrix research place the village in theposition Growth (Cell I). Implication: SWOT analysis resulted in 8 alternative strategies of authenticity from the 8 strategies, 3 priority strategies were obtained and have been calculated through the QSPM Matrix with a total TAS of 194.13, 193.57, and 186.46, namely optimizing the potential promotion of Tri Eka Buana Village Karangasem Bali through the media. social media such as Instagram, Facebook, and websites

Commercial refrigeration - An overview of current status

[EN] Commercial Refrigeration comprises food freezing and conservation in retail stores and supermarkets, so, it is one of the most relevant energy consumption sectors, and its relevance is increasing. This paper reviews the most recent developments in commercial refrigeration available in literature and presents a good amount of results provided these systems, covering some advantages and disadvantages in systems and working fluids. Latest researches are focused on energy savings to reduce CO2 indirect emissions due to the burning of fossil fuels. They are focused on system modifications (as dedicated subcooling or the implementation of ejectors), trigeneration technologies (electrical, heating and cooling demand) and better evaporation conditions control. Motivated by latest GWP regulations that are intended to reduce high GWP HFC emissions; R404A and R507 are going to phase out. Besides hydrocarbons and HFO, CO2 appears as one of the most promising HFC replacements because its low contribution to global warming and high efficiencies when used in transcritical and low-stage of cascade systems.The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte" for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012".Mota Babiloni, A.; Navarro Esbri, J.; Barragán Cervera, Á.; Moles, F.; Peris, B.; Verdú Martín, GJ. (2015). Commercial refrigeration - An overview of current status. International Journal of Refrigeration. 57:186-196. doi:10.1016/j.ijrefrig.2015.04.013S1861965