Dissertation

Selection of the Most Efficient Technology for Refrigeration Systems Without Negative Temperatures for Capacities Lower than 250 KW Using Natural or Low-GWP Gases

de Castro César Machado, Francisco Guedes

2022

Overview

Since the last decades of the 20th century, efforts have been made to counter the environmental threat of using refrigerant gases with high ozone depletion and global warming potential in the refrigeration sector, leading to a proliferation in solutions that employ natural gases, such as carbon dioxide. Since the revival of this fluid as a refrigerant gas, efforts to increase the performance of carbon dioxide refrigeration systems to further affirm the potential of this refrigerant in the industry lead to the design and manufacturing of new components, such as ejectors, which can recover part of the lost expansion work.Systems employing two types of ejectors – high-pressure and liquid ejectors – were studied theoretically with the support of a refrigeration software and compared with a typical parallel compression system for three European locations with different climates – Hannover, Porto, and Seville. Hourly ambient temperature measurements were downloaded and organized in temperature bins to enable the simulation of the systems’ behaviour for each city. The addition of the high-pressure multi-ejector revealed an increase in average annual COP of 2% for Hannover and 5% for Porto and Seville while the incorporation of a liquid ejector in the parallel compression system showed an increase of 8%, 20% and 14% in annual average COP for cities of Hannover, Porto, and Seville respectively, assuming that the flooded evaporators in these systems can maintain a temperature 4˚C greater than the evaporators in a traditional parallel compression system, by increasing the global heat transfer coefficient in the heat rejection to the evaporator.Regarding the energy consumption of the compressors, the use of high-pressure multiejectors enabled electricity savings of 5%, 6%, and 7% for the cities of Hannover, Porto, and Seville respectively. The addition of liquid ejectors leads to electricity savings of 12% for Hannover, 16% for Porto, and 11% for Seville. Taking the electricity cost for each country into account and calculating the acquisition costs by dimensioning the components to be added to the parallel compression system, the electricity costs savings was compared with the operating costs to financially evaluate the investment for these refrigeration solutions. Considering the concept of time value of money, it was estimated that the payback period for the high-pressure ejector additional components is 6 years for Hannover and Porto and 4 years for Seville, while the payback period for the liquid ejector ones is 1 year for Hannover and Porto and 2 years for Seville.

• Publisher: ProQuest Dissertations & Theses
• Subject: Chlorofluorocarbons / Energy consumption / Finance / Financial analysis
• ISBN: 9798265421739