Analysis of Secondary-Loop Refrigeration Systems Using Carbon Dioxide as a Volatile Secondary Refrigerant

Thermodynamic analysis of a novel energy-efficient refrigeration system subcooled by liquid desiccant dehumidification and evaporation

The environmental degradation becomes a great matter of concern due to use and disposal of Chloro-Fluoro-Carbons (CFCs) and Hydro Chloro-Fluoro-Carbons (HCFCs) as refrigerants in conventional refrigeration and air conditioning systems. This leads to extensive research into development of alternate refrigeration systems. Solar energy which is renewable source of energy is available abundantly in the environment. This study deals with the design and development of eco-friendly solar powered thermoelectric refrigeration system. In rural areas where people have to deal with electricity problems, this thermoelectric module will be very helpful to them as it runs on solar energy. Vegetables, Food items and other different required things can be preserved in it. In thermoelectric refrigeration system, the mechanical parts and coolants which are used in conventional refrigeration systems get eliminated and a thermoelectric module is used instead which is cost effective and vibration free. The objective of this study is to develop a working thermoelectric refrigeration system to cool a volume of 5 lit capacity cabinet that utilizes the Peltier effect to cool and maintain a selected temperature range of 8<sup>0</sup>C to 15 <sup>0</sup>C. Solar panel is used to provide the required energy to run this system.

With increased concern about the impact of refrigerant leakage on global warming, a number of new supermarket refrigeration system configurations requiring significantly less refrigerant charge are being considered. In order to help promote the development of advanced systems and expand the knowledge base for energy-efficient supermarket technology, the International Energy Agency (IEA) established IEA Annex 26 (Advanced Supermarket Refrigeration/Heat Recovery Systems) under the ''IEA Implementing Agreement on Heat Pumping Technologies''. Annex 26 focuses on demonstrating and documenting the energy saving and environmental benefits of advanced systems design for food refrigeration and space heating and cooling for supermarkets. Advanced in this context means systems that use less energy, require less refrigerant and produce lower refrigerant emissions. Stated another way, the goal is to identify supermarket refrigeration and HVAC technology options that reduce the total equivalent warming impact (TEWI) of supermarkets by reducing both system energy use (increasing efficiency) and reducing total refrigerant charge. The Annex has five participating countries: Canada, Denmark, Sweden, the United Kingdom, and the United States. The working program of the Annex has involved analytical and experimental investigation of several candidate system design approaches to determine their potential to reduce refrigerant usage and energy consumption. Advanced refrigeration system types investigated include the following: distributed compressor systems--small parallel compressor racks are located in close proximity to the food display cases they serve thus significantly shortening the connecting refrigerant line lengths; secondary loop systems--one or more central chillers are used to refrigerate a secondary coolant (e.g. brine, ice slurry, or CO2) that is pumped to the food display cases on the sales floor; self-contained display cases--each food display case has its own refrigeration unit; low-charge direct expansion--similar to conventional multiplex refrigeration systems but with improved controls to limit charge. Means to integrate store HVAC systems for space heating/cooling with the refrigeration system have been investigated as well. One approach is to use heat pumps to recover refrigeration waste heat and raise it to a sufficient level to provide for store heating needs. Another involves use of combined heating and power (CHP) or combined cooling, heating, and power (CCHP) systems to integrate the refrigeration, HVAC, and power services in stores. Other methods including direct recovery of refrigeration reject heat for space and water heating have also been examined.

Ice rinks have a high coinciding cooling and heating demand which turns them into ideal heat recovery applications. By using carbon dioxide (CO2) as a refrigerant in a transcritical operation, required high temperatures (e.g. for dehumidification, space heating and hot water) can be supplied which in combination with a suitable heating system design can result in very high heat recovery performance. This study compares the measured energy performance and life-cycle cost of five ice rinks in Sweden recently retrofitted from conventional refrigeration systems (HFC and ammonia) to transcritical carbon dioxide refrigeration systems with heat recovery. The field measurements show that the operational energy use can be cut down by as much as 55% which makes the investment profitable in comparison with the previous conventional systems. Furthermore, in some cases the ice rink also became self-sufficient on its own recovered heat, eliminating the need for an external heating system.

Assessment of a novel defrost method for PV/T system assisted sustainable refrigeration system

Performance comparative study of a solar-powered adsorption refrigerator with a CPC collector/adsorbent bed

Simulation and optimization of a R744 two- temperature supermarket refrigeration system with an ejector

Refrigeration systems are crucial in retail food stores to ensure appropriate merchandising of food products. This paper compares four different CO2 refrigeration system configurations in terms of cooling performance, environmental impact, power consumption and annual running costs. The systems studied were the conventional booster refrigeration system with gas bypass (reference system), the all CO2 cascade system with gas bypass, a booster system with a gas bypass compressor, and integrated cascade all CO2 system with gas bypass compressor. The weather conditions of London, UK, and Athens, Greece, were used for the modelling of energy consumption and environmental impacts to represent moderate and warm climatic conditions respectively. The control strategies for the refrigeration systems were derived from experimental tests in the laboratory on a conventional booster refrigeration system. The results from the analysis showed that the CO2 booster system with gas bypass compressor can provide best performance with 5.0% energy savings for the warm climate and 3.65% for the moderate climate, followed by the integrated cascade all CO2 system with gas bypass compressor, with 3.6% and 2.1% savings over the reference system for the warm and moderate climates respectively.

<div class="section abstract"><div class="htmlview paragraph">Recent attempts to find energy-efficient thermal management systems for electric and plug-in hybrid electric vehicles have led to secondary loop systems as an alternative approach to meet dynamic heating and cooling demands and to reduce refrigerant charge. The choice of refrigerant for the primary refrigeration cycle is an important issue regarding the overall system performance. In this work, an HFC refrigerant (R-134a) and a natural refrigerant (R-744) are evaluated regarding a potential use in secondary loop systems. To meet the demands of R-744 cycles such as higher system pressure, most components have to be redeveloped. Nonetheless the use of the environmentally friendly refrigerant has advantages such as better applicability and performance in heat pump systems under cold ambient conditions. This work presents Modelica-based design and simulations of secondary loop automotive refrigeration systems with the HFC refrigerant in a subcritical and R-744 in a transcritical primary cycle. Under defined use cases and environmental conditions, both primary cycles are compared resulting in a better performance for HFC in a summer scenario and for R-744 under winter conditions.</div></div>

Thermodynamic performance enhancement of booster assisted ejector expansion refrigeration systems with R1270/CuO nano-refrigerant

The conventional refrigeration systems make the refrigerating effect using vapour compression or vapour absorption cycle. The main component of this conventional system is compressor which has the moving parts and so that suffers from the mechanical losses and leads to the lower coefficient of performance. The refrigerant, commonly used in the conventional system, is Hydro-Fluro-Carbon or HFC causes vulnerability effect in the environment. Thermoelectric refrigeration system could be an alternative of the conventional refrigeration system so that the environmental hazards and the loss of mechanical power could be avoided. The present work in this paper deals with the refrigeration system with water cooling using thermoelectric Peltier Effect. The contribution of this proposed work is to make a low cost thermoelectric refrigeration system where a steep fall in temperature can be achieved.

Thermodynamic analysis and economic assessment of a carbon dioxide hydrate-based vapor compression refrigeration system using load shifting controls in summer

In conventional bus refrigeration systems, R134a is used extensively as working fluid. According to the international agreements and European parliament directive, studies of mobile refrigeration systems have focused on the alternative refrigerants which have lower global warming potential (GWP). Natural refrigerant R744 (CO2) is one of the best alternative refrigerants with low GWP value, but R744 transcritical refrigeration systems have very low coefficient of performance (COP) value with respect to artificial refrigerant systems. In this study, a two-phase ejector was added as an expansion valve in the transcritical refrigeration system in order to overcome low COP. Transcritical ejector refrigeration system is compared with a standard transcritical refrigeration system for different parameters based on energy and exergy analysis. Results show that COP improvement can be achieved by about 26% and exergy destruction decreased by about 22% for proper design in a Mediterranean climate zone.

Absorption cooling systems – Review of various techniques for energy performance enhancement

Proposal and parametric study of solar absorption/dual compression hybrid refrigeration system for temperature and humidity independent control application