| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 8.3 MB | Adobe PDF |
Authors
Advisor(s)
Abstract(s)
Devido às restrições impostas pelas políticas ambientais, é necessário substituir os HFC por fluidos que tenham um impacto ambiental reduzido, promovendo a descarbonização. O dióxido de carbono (CO2), é uma opção sustentável, dado que é armazenado nos ciclos térmicos dos sistemas e equipamentos de refrigeração e é um fluido frigorigéneo natural, “low cost”, com um PAG baixo e boas propriedades termofísicas. No entanto, os sistemas de refrigeração de CO2 operam com pressões elevadas para poderem dissipar o calor na fonte quente, geralmente o ambiente exterior, sendo necessário operar em regime transcrítico, especialmente quando as temperaturas ambientes são elevadas. Em contrapartida, os ciclos frigoríficos transcríticos de CO2 apresentam um COP inferior relativamente aos ciclos frigoríficos de outros fluidos frigorigéneos, e por isso é importante otimizar a eficiência energética nos ciclos térmicos de CO2.
Para o desenvolvimento deste documento foi efetuada uma análise de dados experimentais, obtidos através de um programa de cálculo do COP desenvolvido pela empresa, retirados a cada minuto de funcionamento da central. Foram analisados os dados de três centrais de refrigeração diferentes, central frigorífica 1, 2 e 3, cujos dados de funcionamento se referem aos meses de março, maio e julho, respetivamente.
Através da análise de dados das centrais frigoríficas reais, foi possível observar que o aumento de 1°C da temperatura ambiente faz diminuir, em média, o COP em cerca de 3,5%. Também foi possível observar que o COP diminuiu, em média, cerca de 6% com o aumento de 1 bar da pressão no depósito de líquido quando as centrais frigoríficas funcionavam sem compressão paralela. Quando as centrais funcionavam com compressão paralela verificou-se um incremento médio de 5,6% do COP com o aumento da pressão no depósito de líquido até atingir a pressão ótima, diminuindo cerca de 5% após essa mesma pressão. Observou-se que o aumento de 1°C da temperatura de evaporação MT faz aumentar em média o COP em cerca de 3,3%. Já o aumento da temperatura de evaporação LT tem muito pouco impacto no valor do COP das centrais de refrigeração. Para as mesmas condições de pressão e temperatura, o uso da compressão paralela aumenta, em média, o COP entre 8,5 e 10%. Na central de refrigeração 3, observou-se que existiu um desperdício de 7% de energia elétrica consumida pelos ventiladores do gas cooler e uma redução do COP em 10%, quando estes ventiladores operam à velocidade máxima comparando com sua a operação a 85% da velocidade máxima
Due to the restrictions imposed by environmental policies, it is necessary to replace HFC for refrigerants with low environmental impact, promoting decarbonization. Carbon dioxide (CO2) is a sustainable option, since it is stored in refrigeration systems and equipment’s thermal cycles and it is a natural refrigerant, low cost, with a low GWP and good thermophysical properties. However, CO2 refrigeration systems function with high pressures to be able to reject heat to the hot source, typically the external environment, being necessary to function in transcritical conditions, specially at high ambient temperatures. On the other hand, CO2 has a lower COP when compared with other refrigerants, being important to optimize CO2 thermal cycle’s energy efficiency. For the development of this document, it was done an experimental data analysis, with the data being provided every minute when the refrigeration plants were functioning, by a COP calculation software developed by the company. The data analysis was performed for three different refrigeration plants, plants 1, 2 and 3, analyzing data of the months of March, May and July, respectively. Through the data analysis of the real refrigeration plants, it was possible to note that the increase of ambient temperature of 1°C decreases COP by 3,5%, on average. It was also possible to note that COP decreases on average, by 6% with the increase of 1 unit bar pressure of the liquid reservoir when the refrigeration plants worked without parallel compression. When the refrigeration plants worked with parallel compression, there was an average increase of 5,6% with the increase of 1 unit bar pressure of liquid reservoir until it reached optimal pressure, decreasing approximately 5% on average, after this optimal value. It was also noted, that with the increase of 1°C of MT evaporation temperature, the refrigeration plant’s COP increased on average by 3,3%. However, LT evaporation temperature had little to none impact on the COP of the refrigeration plants. For the same pressure and temperature conditions, the parallel compression increases the COP between 8,5 to 10%, on average. It was also possible to find a waste of electricity on the refrigeration plant 3, caused by the gas cooler electricity consumption when it works at the maximum fan speed. This waste of electricity was of 7%, when compared with the refrigeration plant working with gas cooler working at 85% of maximum fan speed. The refrigeration plant’s COP was 10% higher when the gas cooler worked at 85% of maximum fan speed
Due to the restrictions imposed by environmental policies, it is necessary to replace HFC for refrigerants with low environmental impact, promoting decarbonization. Carbon dioxide (CO2) is a sustainable option, since it is stored in refrigeration systems and equipment’s thermal cycles and it is a natural refrigerant, low cost, with a low GWP and good thermophysical properties. However, CO2 refrigeration systems function with high pressures to be able to reject heat to the hot source, typically the external environment, being necessary to function in transcritical conditions, specially at high ambient temperatures. On the other hand, CO2 has a lower COP when compared with other refrigerants, being important to optimize CO2 thermal cycle’s energy efficiency. For the development of this document, it was done an experimental data analysis, with the data being provided every minute when the refrigeration plants were functioning, by a COP calculation software developed by the company. The data analysis was performed for three different refrigeration plants, plants 1, 2 and 3, analyzing data of the months of March, May and July, respectively. Through the data analysis of the real refrigeration plants, it was possible to note that the increase of ambient temperature of 1°C decreases COP by 3,5%, on average. It was also possible to note that COP decreases on average, by 6% with the increase of 1 unit bar pressure of the liquid reservoir when the refrigeration plants worked without parallel compression. When the refrigeration plants worked with parallel compression, there was an average increase of 5,6% with the increase of 1 unit bar pressure of liquid reservoir until it reached optimal pressure, decreasing approximately 5% on average, after this optimal value. It was also noted, that with the increase of 1°C of MT evaporation temperature, the refrigeration plant’s COP increased on average by 3,3%. However, LT evaporation temperature had little to none impact on the COP of the refrigeration plants. For the same pressure and temperature conditions, the parallel compression increases the COP between 8,5 to 10%, on average. It was also possible to find a waste of electricity on the refrigeration plant 3, caused by the gas cooler electricity consumption when it works at the maximum fan speed. This waste of electricity was of 7%, when compared with the refrigeration plant working with gas cooler working at 85% of maximum fan speed. The refrigeration plant’s COP was 10% higher when the gas cooler worked at 85% of maximum fan speed
Description
Keywords
Refrigeração Dióxido de Carbono Transcrítico Otimização COP Refrigeration Carbon Dioxide Transcritical Optimization COP