Página 1 dos resultados de 397 itens digitais encontrados em 0.008 segundos

Análise exergética e termoeconômica de um sistema solar termodinâmico de aquecimento de água; Exergetic and thermoeconomic analysis of a solar heat-pump system for water heating

Silva, Yuri Cambrussi da
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
POR
Relevância na Pesquisa
66.34%
Este trabalho avalia e propõe melhorias a um sistema solar termodinâmico de aquecimento de água, que consiste em uma bomba de calor na qual o evaporador é um painel solar e o condensador é um trocador de calor utilizado para aquecer água. Para otimizar o sistema, são realizadas análises teóricas de exergia e termoeconomia de um aquecedor fabricado no Brasil pela Solary – Aquecedores Termodinâmicos. Na resolução das equações decorrentes dessas análises e obtenção das propriedades termodinâmicas do refrigerante R134a utiliza-se do programa Interactive Thermodynamics. Os resultados indicam uma eficiência exergética de 12% e custo total (incluindo aquisição do equipamento) de R$ 0,7170 por hora de funcionamento. Duas propostas de melhoria são analisadas: aumento do rendimento isentrópico do compressor e aumento da temperatura do evaporador. Esta última apresenta os melhores resultados, atingindo um rendimento de 17% e custo total de R$ 0,6383 por hora.; This study evaluates and proposes improvements to a thermodynamic solar water heater, that consists of a heat-pump in which the evaporator is a solar panel and the condenser is a heat exchanger used to heat water. To optimize the system, theoretical analysis of exergy and thermoeconomics of a heater produced in Brazil by Solary – Thermodynamic Heaters are performed. In the solution of the equations resulting from these analyses and obtain the thermodynamic properties of the R134a refrigerant...

Drying kinetics of tomato by using electric resistance and heat pump dryers

Queiroz, R.; Gabas, A. L.; Telis, VRN
Fonte: Marcel Dekker Inc Publicador: Marcel Dekker Inc
Tipo: Artigo de Revista Científica Formato: 1603-1620
ENG
Relevância na Pesquisa
66.36%
Drying kinetics of tomato was studied by using heat pump dryer (HPD) and electric resistance dryers with parallel and crossed airflow. The performance of both systems was evaluated and compared and the influence of temperature, air velocity, and tomato type on the drying kinetics was analyzed. The use of HPD showed to be adequate in the drying process of tomatoes, mainly in relation to the conversion rate of electric energy into thermal energy. The heat pump effective coefficient of performance (COPHT,EF) was between 2.56 and 2.68, with an energy economy of about 40% when compared to the drying system with electric resistance. The Page model could be used to predict drying time of tomato and statistical analysis showed that the model parameters were mainly affected by drying temperature.

Desenvolvimento de um sistema de purificação de água com bomba de calor; Development of a water purification system with heat pump

Lorena Aires Lombardi Queiroz
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 06/05/2011 PT
Relevância na Pesquisa
66.43%
O processo mais simples para que a água alcance pureza adequada é a destilação convencional, porém este método tem como inconvenientes seu alto gasto com energia elétrica e seu elevado consumo de água. Buscando alternativas para produzir água purificada com economia de energia elétrica e água de resfriamento, mas com produção quanto à pureza equivalente ao convencional, surge a possibilidade da elaboração de um sistema de purificação de água pela desumidificação do ar com o auxílio de uma bomba de calor. O equipamento projetado para a purificação de água opera segundo um ciclo termodinâmico de refrigeração e é composto por duas partes: uma bomba de calor por compressão de vapor, do tipo ar-ar acoplada em um duto de ar, e uma câmara, onde ocorre a umidificação do ar, com ar recirculado. Foram testados, ainda, dois tipos de umidificadores, com recheio de vidro e um nebulizador A água produzida pode ser considerada purificada já que apresentou valores de condutividade elétrica entre 4 e 5 µS/cm. A bomba de calor apresentou um melhor desempenho quando foi utilizado o nebulizador, já que os COP obtidos foram maiores do que os obtidos nos ensaios com recheio de vidro, referente à umidificação adiabática; The simplest process for water to reach adequate purity is the conventional distillation...

Otimização térmica e econômica de bomba de calor para aquecimento de água, utilizando programação quadrática sequencial e simulação através do método de substituição Newton Raphson; Thermal and economic optimization of heat pump for heating water, using sequential quadratic programming and simulation by substitution Newton Raphson method

Obed Alexander Córdova Lobatón
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/12/2011 PT
Relevância na Pesquisa
66.44%
O trabalho apresenta metodologias computacionais de otimização e simulação para o desenvolvimento do projeto de um sistema de bomba de calor para aquecimento de água em prédios residenciais, especialmente para uso em banho na região de Campinas. O sistema bomba de calor foi simulado focando o estudo nos trocadores de calor (evaporador e condensador). Cada componente foi otimizado mediante uma análise térmica e econômica que permitiu reduzir custos de investimento e de operação através do desenho e dimensionamento de cada trocador; todo foi feito através de um algoritmo de otimização usando o método de SQP (Programação Quadrática Sequencial) e auxiliado pela função fmincon do ambiente MatLab® Uma vez selecionado o melhor conjunto de elementos de cada trocador de calor, o projeto ótimo foi simulado a diferentes condições de operação através do Método de Substituição-Newton- Raphson. Os resultados obtidos reafirmam que as bombas de calor permitem uma grande economia de energia quando comparados com outros tipos de aquecimento de água, especialmente, o chuveiro elétrico.; This work presents computational methodologies, of optimization and simulation for design of a heat pump system, for heating water in residential buildings...

Comparação das eficiências energéticas entre sistemas de bombas de calor para atendimento às demandas de ar condicionado e aquecimento de água em edifício; Comparison of energy efficiencies among heat pump systems to meet the demands of air conditioning and water heating in a building

Max Mauro Lozer dos Reis
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/07/2014 PT
Relevância na Pesquisa
66.57%
Neste trabalho foi realizado um conjunto de simulações numéricas de diferentes sistemas de bombas de calor em diferentes condições de funcionamento, para atender simultaneamente às demandas do ar condicionado e do consumo de água quente em edifício. Foram consideradas na proposta deste trabalho duas máquinas independentes, uma bomba de calor responsável pelo aquecimento e um ciclo de refrigeração para resfriamento da água. Além disso, foi investigado a possibilidade de empregar os efeitos de aquecimento e resfriamento de uma única bomba de calor padrão, duas bombas de calor em cascata e um sistema com dois estágios de compressão com separador de gás flash. Para estas alternativas fez-se necessária a complementação da energia térmica através de uma bomba de calor auxiliar para atender a demanda total de água quente e fria e os desempenhos dos sistemas de bombas de calor foram comparados através de uma análise energética. Um programa em ambiente MATLAB® foi desenvolvido e envolveu relações termodinâmicas e de transferência de calor para os sistemas de bombas de calor e sistema de distribuição de água quente e fria para o edifício, a fim de aproximar o funcionamento dos sistemas reais. Utilizaram-se ferramentas como o método de Substituição-Newton-Raphson...

Performance analysis of an endoreversible heat pump system for optimal air–ground or water environmental exergy potential utilization

Canhoto, Paulo; Reis, A. Heitor; Miguel, António F.
Fonte: John Wiley and Sons, Ltd Publicador: John Wiley and Sons, Ltd
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.27%
This paper reports the optimization of a ground or water source heat pump system for housing applications with respect to the best exergy performance and maximum environmental exergy potential use. The analysis presented also offers the opportunity of exploring a new objective for the optimization of the use of exergy sources: ‘In any system powered by an external exergy source optimization is achieved when the exergy flux to the environment is minimum under the existing constraints’. This corresponds to utilizing the supplied exergy to overcome the total irreversibilities of such a system only. The environmental exergy utilization and the exergy output to the environment are analyzed in connection with this objective.

Exergy and optimisation of a ground or water source heat pump system for maximum environmental exergy potential utilization

Canhoto, P.; Reis, A.H.; Miguel, A.F.
Fonte: CGE-UEvora Publicador: CGE-UEvora
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.27%
This paper presents the exergy analysis and optimisation of a ground or water source heat pump system for housing applications with the purpose of best performance and maximum environmental exergy potential use.

Experimental Analysis of an Indirect Solar Assisted Heat Pump for Domestic Water Heating

BRIDGEMAN, Andrew George
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
66.58%
Due to rising energy costs and increasing environmental awareness, various methods of energy conservation are being investigated. In the residential sector, both solar and heat pump systems have been extensively tested. Recently, combinations of solar and heat pump systems have been developed for both space heating and water heating. These systems have the capability to provide better performances than either of the systems operating on their own. The solar collector benefits from a lower fluid (glycol) inlet temperature which increases efficiencies, and the heat pump benefits from higher evaporator temperatures due to the additional solar energy collected. For this study, a prototype of an Indirect-Solar Assisted Heat Pump for use in the Canadian environment was constructed, instrumented and tested. Controlled, constant temperature tests, as well as solar profile tests were conducted and the heat transfer rates, natural convection flow rate, and heat pump coefficient of performance (COP) were calculated. These values were then compared to simulation results based on a model developed in a previous feasibility study. The experimental COPs calculated ranged from 2.3 to 3.3 throughout the full range of tests which were conducted with supply temperatures ranging from 0°C – 40°C. The simulated results consistently overestimated the experimental results by between 12% - 15%. New empirical heat exchanger relationships were developed for the model bringing the simulated results within 5% of the experimental results for tests run at glycol flow rates of 77 and 154 kg/hr. These relationships were used to refine the model...

Performance Analysis of a Transcritical CO2 Heat Pump Water Heater Incorporating a Brazed-Plate Gas-cooler

Murray, PORTIA
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
66.36%
This study focuses on the experimental testing and numerical modeling of a 4.5 kW transcritical CO2 heat pump water heater at Queen’s University in the Solar Calorimetry Laboratory. Due to the predicted high heat rejection temperatures in a transcritical vapour-compression cycle, buoyancy driven thermosyphon flow through a brazed-plate gas-cooler was proposed to promote tank stratification and to improve system performance. The performance was evaluated through a series of experimental sensitivity and static tank charge tests. A TRNSYS model was also created and verified to simulate the performance of the system under a detailed user demand schedule for a week of operation. The TRNSYS model used a parametric table created with a steady-state model of the vapour-compression system in EES that was validated against experimental data to a standard error of the Y-estimate of ±0.073 kW for heating capacity, ±1.01°C for gas-cooler exit temperature, and ±0.086 for COP. A series of tank charge tests were conducted under thermosyphon flow and forced flow rates at 1 L/min, 2 L/min, and 4 L/min. The thermosyphon charge test produced the highest level of stratification and a total COP of 3 at an average flow rate of 0.73 L/min. All of the forced convection cases operated with a higher degree of mixing. TRNSYS model simulations with hot water draws found that the thermosyphon flow configuration performed with a higher degree of stratification under regular user demand while simulations with high flow rates resulted in a mixed tank at a high temperature. Results predicted an 11% reduction in required heat energy input to the storage...

Evaluation of an Indirect Solar Assisted Heat Pump Water Heater in the Canadian Environment

ELLIOTT, BRYN DAVIS
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
66.6%
Solar Domestic Hot Water systems and air-source heat pumps offer the potential for energy savings in residential hot water production, however their performance is limited in cold climates, where the low ambient temperature reduces the collector efficiency or the heat pump coefficient of performance. Combining these systems into a Solar-Assisted Heat Pump can alleviate these limitations by reducing the required collector temperature and by providing an increased heat pump evaporator temperature. This study is a continuation of the development of an Indirect Solar-Assisted Heat Pump undertaken at the Queen’s University Solar Calorimetry Laboratory. Previously, a numerical study compared its performance to existing technology, and based upon this feasibility analysis, a prototype was constructed for controlled laboratory tests using simulated solar input. In the current study, the prototype was modified to include a novel hybrid collector such that its performance under actual weather conditions throughout the year could be assessed. On sunny days, the system experienced daily averaged collector efficiencies between 0.47 and 0.88, depending on the flow rate and season. Averaged heat pump coefficients of performance of 2.54 to 3.13 were observed. Overcast days experienced reduced coefficients of performance...

Solar Hot Water Heater Augmented with PV-TEM Heat Pump

PRESTON, NATHANIEL
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
66.61%
Solar assisted heat pumps (SAHPs) can provide higher collector efficiencies and solar fractions when compared against standard solar hot water heaters. Vapour compression (VC) heat pumps require environmentally hazardous refrigerants and moving parts which increase maintenance costs and place limits on operating conditions. Thermoelectric modules (TEMs) use solid state electronics to pump heat without moving parts or refrigerants. This study investigated the performance of a SAHP system utilizing an array of thermoelectric modules as the heat pump. A component model was developed to simulate the TEM heat pump performance using TRNSYS software and results were compared against those determined experimentally. A simplified model was unable to accurately predict TEM performance. The model was therefore refined to incorporate empirically determined parameters. An apparatus was constructed to measure the performance of a small photovoltaic array driven TEM heat pump and simulation results using the component model were found to be in agreement. Several SAHP configurations were simulated using TRNSYS and compared with vapour compression SAHPs previously studied at the QSCL. The TEM ISAHP provided a Free Energy Ratio (FER) of 46% and a collector efficiency of 36% whereas the VC ISAHP provided 54% and 76% respectively. The photovoltaic (PV) driven ISAHP system was able to achieve a higher FER of 50% with the use of a 2 module PV array and a reduced thermal collector area. Further optimization is required to improve TEM heat pump performance in this configuration and reduce the photovoltaic array size. The use of a maximum power point tracker into the PV/TEM system should be investigated as panel efficiency losses reached up to 30% in the configuration studied. The possibility of incorporating combined PV/T modules could decrease costs and also warrants further study. Critical factors in the success of a TEM driven solar assisted heat pump will include the improvement of thermoelectric materials performance...

Otimização econômica de um sistema bomba de calor e reservatório térmico para aquecimento de água para fins domésticos em edifício; Economic optimization of a system heat pump and thermal storage tank for heating water for domestic purposes in building

Bruno Gimenez Fernandes
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/10/2012 PT
Relevância na Pesquisa
66.61%
O objetivo do presente trabalho está na otimização econômica de um sistema com bomba de calor utilizado no aquecimento de água para banho em um edifício com reservatório térmico, para armazenamento de água quente. A otimização da bomba de calor envolve relações termodinâmicas, econômicas, de transferência de calor e mecânica dos fluidos, com o objetivo de obter o menor custo de aquecimento equivalente (CEA) da bomba de calor e do sistema. Dando continuidade a outros trabalhos já realizados na Unicamp, destacam-se neste trabalho a inclusão de perdas de carga na bomba de calor, maiores limites das variáveis não lineares a serem otimizadas, relações de transferência de calor mais realistas e a simulação do reservatório térmico de água, obtendo um volume compatível com a demanda do edifício e a eficiência da bomba de calor, durante sua utilização. No projeto preliminar, é utilizado o método de Substituição - Newton Raphson, obtendo as áreas iniciais de transferência de calor dos trocadores de calor (evaporador e condensador), o coeficiente de desempenho (COP), vazão do fluido refrigerante R- 134a (utilizado na bomba de calor), a potência do compressor, entre outros. No projeto otimizado, os valores obtidos na simulação anterior são considerados como estimativas iniciais no processo de otimização. Nesse processo o algoritmo de otimização escolhido é a Programação Quadrática Sequencial (SQP)...

Exergy Analysis and Optimisation of a Ground or Water Source Heat Pump System for Maximum Environmental Exergy Potential Utilisation

Canhoto, Paulo; Reis, A. Heitor; Miguel, António F.
Fonte: CGE-Geophysics Centre of Evora Publicador: CGE-Geophysics Centre of Evora
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.27%
This paper presents the exergy analysis and optimisation of a ground or water source heat pump system for housing applications with the purpose of best performance and maximum environmental exergy potential use. The present analysis also offers the opportunity of defining a new objective function for the optimisation of the use of exergy sources: 'In any system powered by an external exergy source optimisation is achieved when the exergy flux to the environment is minimum under the existing constraints”. This corresponds to utilizing the available exergy to overcome the total irreversibilities of such a system only. The environmental exergy utilisation and the exergy output to the environment are analysed in relation with this objective.

Thermodynamic analysis of the reverse Joule?Brayton cycle heat pump for domestic heating

White, Alexander
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
66.31%
The paper presents an analysis of the effects of irreversibility on the performance of a reverse Joule?Brayton cycle heat pump for domestic heating applications. Both the simple and recuperated (regenerative) cycle are considered at a variety of operating conditions corresponding to traditional (radiator) heating systems and low-temperature underfloor heating. For conditions representative of typical central heating in the UK, the simple cycle has a low work ratio and so very high compression and expansion efficiencies and low pressure losses are required to obtain a worthwhile COP. An approximate analysis suggests that these low loss levels would not necessarily be impossible to achieve, but further investigation is required, particularly regarding irreversible heat transfer to and from cylinder walls. In principle, recuperation improves the cycle work ratio, thereby making it less susceptible to losses, but in practice this advantage is compromised when realistic values of recuperator effectiveness are considered.

Effect of heat transfer on the performance of a thermoelectric heat pump driven by a thermoelectric generator

Chen,Lingen; Meng,Fankai; Sun,Fengrui
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2009 EN
Relevância na Pesquisa
66.55%
A model of a thermoelectric heat pump driven by a thermoelectric generator with external heat transfer irreversibility is proposed. The performance of the combined thermoelectric heat pump device obeying Newton's heat transfer law is analyzed using the combination of finite time thermodynamics and non-equilibrium thermodynamics. Two analytical formulae for heating load versus working electrical current, and the coefficient of performance (COP) versus working electrical current, are derived. For a fixed total heat transfer surface area of four heat exchangers, the allocations of the heat transfer surface area among the four heat exchangers are optimized for maximizing the heating load and the COP of the combined thermoelectric heat pump device. For a fixed total number of thermoelectric elements, the ratio of the number of thermoelectric elements of the generator to the total number of thermoelectric elements is also optimized for maximizing both the heating load and the COP of the combined thermoelectric heat pump device. The influences of thermoelectric element allocation and heat transfer area allocation are analyzed by detailed numerical examples. The optimum working electrical currents for maximum heating load and maximum COP at different total numbers of thermoelectric elements and different total heat transfer areas are provided...

Heating load, COP, exergy loss rate, exergy output rate and ecological optimizations for a class of generalized irreversible universal heat pump cycles

Chen,Lingen; Feng,Huijun; Sun,Fengrui
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2010 EN
Relevância na Pesquisa
66.54%
The optimal performance of a class of generalized irreversible universal steady flow heat pump cycle model, which consists of two heat-absorbing branches, two heat-releasing branches and two irreversible adiabatic branches with the losses of heat-resistance, heat leakage and internal irreversibility is analyzed by using finite time thermodynamics. The analytical formulae about heating load, coefficient of performance (COP), exergy loss rate, exergy output rate and ecological function of the universal heat pump cycle are derived. Moreover, performance comparisons among maximum COP condition, a given exergy output rate condition and maximum ecological function condition are carried out by using numerical examples. It is shown that the ecological function objective is an excellent candidate objective with the ideal of an ecological and long-term goal. The effects of heat leakage and internal irreversibility on the cycle performance are discussed. The universal cycle model gives a unified description of seven heat pump cycles, and the results obtained include the performance characteristics of Brayton, Otto, Diesel, Atkinson, Dual, Miller and Carnot heat pump cycles with the losses of heat-resistance, heat leakage and internal irreversibility.

Exergy-based ecological optimization for an endoreversible variable-temperature heat reservoir air heat pump cycle

Bi,Yuehong; Chen,Lingen; Sun,Fengrui
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2009 EN
Relevância na Pesquisa
66.53%
An ecological performance analysis and optimization based on the exergetic analysis is carried out in this paper for an endoreversible air heat pump cycle with variable-temperature heat reservoirs. An exergy-based ecological optimization criterion, which consists of maximizing a function representing the best compromise between the exergy output rate and exergy loss rate (entropy generation rate and environment temperature product) of the heat pump cycle, is taken as the objective function. The analytical relation of the exergy-based ecological function is derived. The effects of pressure ratio, the effectiveness of the heat exchangers, the inlet temperature ratio of the heat reservoirs and the ratio of hot-side heat reservoir inlet temperature to ambiént temperature on ecological function are analyzed. The cycle performance optimizations are performed by searching the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for fixed total heat exchanger inventory and the optimum heat capacity rate matching between the working fluid and the heat reservoirs, respectively. The influences of some design parameters, including heat exchanger inventory and heat capacity rate of the working fluid on the optimal performance of the endoreversible air heat pump are provided by numerical examples. The results show that the exergy-based ecological optimization is an important and effective criterion for the evaluation of air heat pumps.

Performance optimization of an air source heat pump water heater using mathematical modelling

Tangwe,Stephen; Simon,Michael; Meyer,Edson L; Mwampheli,Sampson; Makaka,Golden
Fonte: Journal of Energy in Southern Africa Publicador: Journal of Energy in Southern Africa
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2015 EN
Relevância na Pesquisa
66.43%
In South Africa, there is an ongoing constraint on the electricity supply at the national grid to meet the demand. Eskom is implementing various measures such as the Integrated Demand Management and the promotion and encouragement of the use of energy efficient devices like an Air Source Heat pump (ASHP) water heater to replace the high electrical energy consuming conventional geysers for sanitary hot water production. The ASHP water heater market is fast gaining maturity. A critical mathematical model can lead to performance optimization of the systems that will further result in the conservation of energy and significant reduction in global warming potential. The ASHP water heater comprises of an ASHP unit and a hot water storage tank. In this study, a data acquisition system (DAS) was designed and built which monitored the energy used by the geyser and the whole building, the temperature at the evaporator, condenser, tank outlet hot water, tank inlet cold water, the ambient temperature and relative humidity in the vicinity of the ASHP evaporator. It is also worthy to mention that the DAS also included to a flow meter and two additional temperature sensors that measured the volume of water heated and inlet and outlet water temperature of the ASHP. This work focused on using the mathematical equation for the Coefficient of Performance (COP) of an ideal Carnot's heat pump (CHP) water heater to develop basic computation in M-file of MATLAB software in order to model the system based on two reservoir temperatures: evaporator temperatures (Tevp) of 0°C to 40°C (approximated to ambient temperature...

Thermodynamic analysis of a direct expansion solar assisted heat pump water heater

Yousefi,Masoud; Moradali,Misagh
Fonte: Journal of Energy in Southern Africa Publicador: Journal of Energy in Southern Africa
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2015 EN
Relevância na Pesquisa
66.39%
In this paper, the thermodynamic performance of a direct expansion solar assisted heat pump (DX-SAHP), which is used to heat domestic water from 20°C to 45°C, is theoretically investigated. The system includes a 3m² single-cover flat plate solar collector, 0.150m³ water tank and 70m tube immersed in the water tank as a condenser. The effect of various parameters such as radiation on the collector surface, compressor speed and the ambient temperature on the coefficient of performance (COP) are calculated. Results show that obtained COP is considerably more than that of a conventional heat pump water heater when radiation on the collector is high. Also, increasing collector area and reducing compressor speed enhance COP. The same occurs when the ambient temperature increases. For instance, at an ambient temperature of 15°C and 450 w/m² irradiation on collector surface, the calculated COP was 6.37.

A review on opportunities for the development of heat pump drying systems in South Africa

Kivevele,Thomas; Huan,Zhongjie
Fonte: South African Journal of Science Publicador: South African Journal of Science
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2014 EN
Relevância na Pesquisa
66.57%
Recently, it has been discovered that heat pump drying is an efficient method of drying for drying industries. Heat pumps deliver more heat during the drying process than the work input to the compressor. Heat pump drying is a more advanced method than the traditional South African industrial and agricultural drying methods, such as direct/indirect sunlight, wood burning, fossil fuel burning, electrical heating and diesel engine heating. Heat pump dryers provide high energy efficiency with controllable temperature, air flow and air humidity and have significant energy-saving potential. In the last decade the market for heat pump systems for water heating and space cooling/heating has grown in South Africa, but the development of heat pumps for industrial and agricultural drying is very slow. As a result of high increases in fossil fuel prices and electricity in South Africa, as well as the problem of CO2 emissions, green energy, energy saving and energy efficiency are imperative. The development of heat pump drying systems in South Africa is an efficient way to solve energy problems in drying applications as this technology is still in its infancy. We review studies on heat pump drying and compare the methods therein with the most common methods of drying in South Africa