Energetic evaluation of a CO2 refrigeration plant working in supercritical and subcritical conditions

Sánchez, Daniel; Patiño, J.; Sanz-Kock, Carlos; Llopis, Rodrigo; Torrella, E.

doi:10.1016/j.applthermaleng.2014.02.005

Cited by 24 publications

(17 citation statements)

References 13 publications

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“…The evaporation level has been maintained artificially using an external secondary fluid system. It has not been tested using external loads, as done by Sánchez et al (2014b), because there are large increments of the cooling capacity that will difficult to interpret the results.…”

Section: Experimental Procedures and Data Validationmentioning

confidence: 99%

Experimental evaluation of a CO2 transcritical refrigeration plant with dedicated mechanical subcooling

Llopis

Nebot‐Andrés

Sánchez

et al. 2016

International Journal of Refrigeration

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125

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CO2 transcritical refrigeration cycles require optimization to reach the performance of conventional solutions at high ambient temperatures. Theoretical studies demonstrated that the combination of a transcritical cycle with a mechanical subcooling cycle improves its performance; however, any experimentation with CO2 has been found. This work presents the energy improvements of the use of a mechanical subcooling cycle in combination with a CO2 transcritical refrigeration plant, experimentally. It is tested the combination of a R1234yf single-stage refrigeration cycle with a semihermetic compressor for the mechanical subcooling cycle, with a single-stage CO2 transcritical refrigeration plant with a semihermetic compressor. The combination is evaluated at two evaporating levels of the CO2 cycle (0 and -10 ºC) and three heat rejection temperatures (24, 30 and 40 ºC). The optimum operating conditions and capacity and COP improvements are analysed with maximum increments on capacity of 55.7 % and 30.3 % on COP. KEYWORDS

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Section: Experimental Procedures and Data Validationmentioning

confidence: 99%

Experimental evaluation of a CO2 transcritical refrigeration plant with dedicated mechanical subcooling

Llopis

Nebot‐Andrés

Sánchez

et al. 2016

International Journal of Refrigeration

Self Cite

125

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“…Relation ( 8 ) shows that the optimum high-pressure values only depend on the conditions of the refrigerant at compressor suction, the characteristics of the compressor and the temperature at the outlet of the gas-cooler, and not on the compressor speed, as Liao et al [4] and Sarkar et al [5] showed, and as Cabello et al [3] verified experimentally.…”

Section: Optimization Analysismentioning

confidence: 66%

“…The accumulation tank appears commonly between those regulation devices. Also, this cycle can incorporate internal heat exchangers [7] and operate in transcritical and subcritical conditions [8].…”

Section: Introductionmentioning

confidence: 99%

A new approach to optimize the energy efficiency of CO2 transcritical refrigeration plants

Peñarrocha

Llopis

Tárrega

et al. 2014

Applied Thermal Engineering

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This paper proposes a model-free real-time optimization and control strategy for CO2 transcritical refrigeration plants that assures covering the cooling demand and continuous tracking of conditions for maximum efficiency. Our approach obtains the feedback with only three measurements, and controls the opening degree of a back-pressure valve and the speed of the compressor. The strategy minimizes the power consumption of the compressor instead of maximizing the coefficient of performance, which avoids several sensors, and we demonstrate mathematically that both approaches are equivalent. We implemented the strategy with an algorithm that includes two independent auto tuned controllers, one devoted to regulate the high-pressure and another to regulate the outlet temperature of the secondary fluid of the evaporator. It also incorporates a real time perturb and observe procedure to locate on-line the optimum high-pressure that minimizes the compressor power consumption. The paper presents the experimental evaluation of the control strategy, verifying the stable operation of the algorithm and the energy optimization of the plant. KEYWORDS

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“…In this second solution the surplus of the gaseous component is conveyed to the liquid-gas separator by means of the differential valve, while the liquid is carried into a second electronic expansion valve (EEV) based on a PWM control (Pulse Width Modulation). The last solution leads to a higher COP in double expansion than in a single (traditional) one [8,11,14,15,22,27]. Moreover, it is widely recognized that the optimal working condition of electronic expansion valves is achieved when only the liquid phase enters the valve: avoiding flash gas at the inlet of the valve, not only is the best working efficiency guaranteed due to a correct and homogeneous lamination, but also an increase in the service life.…”

Section: Basic Experimental Co2 Plantmentioning

confidence: 99%

“…CO2 has a critical temperature of only 31 °C, which determine some limitations in terms of energy efficiency in those areas of the world characterized by temperatures close to or above this value. [8][9][10]. The subcritical refrigeration cycle (Figure 1a) is comparable to that of other fluids; it is widely used as a low temperature one in cascade plants, while the primary one generally works with ammonia or R134a [11][12][13][14][15][16].…”

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confidence: 99%

CO2 Employment as Refrigerant Fluid with a Low Environmental Impact. Experimental Tests on Arugula and Design Criteria for a Test Bench

et al. 2015

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Abstract:In order to define design criteria for CO2 refrigeration systems to be used for agricultural products and foodstuff storage, a variable geometrical system was realized, with the goal of meeting a wide range of environmental and process conditions, such as producing low environmental impact and maintaining the highest Coefficient of Performance (COP), at the same time. This test-bench, at semi-industrial scale, was designed as a result of experimental tests carried out on Arugula. The storage tests showed that all samples stored in cold rooms with R.H. control showed a slight increase of weight but also small rot zones in all the boxes due to an excessive accumulation of water condensation; thus, the system may not have achieved conditions that RH requires in a given range, without reaching saturation condition. At the same time, the use of CO2 must be adequately tested along its thermodynamic cycle, during steady state and/or transient conditions, imposing OPEN ACCESSSustainability 2015, 7 3735 variable working conditions that can simulate plant starting phase or some striking conservation process, like those that characterize sausages. The designed plant will allow studying these specific performances and evaluate COP variation, according to environmental and plant operating conditions.

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Energetic evaluation of a CO2 refrigeration plant working in supercritical and subcritical conditions

Cited by 24 publications

References 13 publications

Experimental evaluation of a CO2 transcritical refrigeration plant with dedicated mechanical subcooling

Experimental evaluation of a CO2 transcritical refrigeration plant with dedicated mechanical subcooling

A new approach to optimize the energy efficiency of CO2 transcritical refrigeration plants

CO2 Employment as Refrigerant Fluid with a Low Environmental Impact. Experimental Tests on Arugula and Design Criteria for a Test Bench

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