New positions for an internal heat exchanger in a CO2 supercritical refrigeration plant. Experimental analysis and energetic evaluation

Applied Thermal Engineering

Sanz-Kock

Cabello

et al. 2015

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We present the experimental evaluation of an internal heat exchanger or suction-line/liquid-line heat exchanger in a CO2 subcritical refrigeration plant with gas-cooler. The plant, driven by a 1.5kW CO2 semi hermetic compressor, uses brazed plate heat exchangers as condenser, evaporator and internal heat exchanger, an air finned tube gas-cooler and an electronic expansion valves. The evaluation (77 steadystates) covers evaporating temperatures from -40 to -25 ºC and condensing temperatures from -15 to 0 ºC, always at the nominal speed of the compressor. Here, the effect of the internal heat exchanger on the main energy parameters is analysed, i.e., cooling capacity, COP and heat rejection at gas-cooler and condenser. Also, the effect of the internal heat exchanger in a cascade cycle is analysed theoretically. It has been concluded that the internal heat exchanger does not improve the performance of the subcritical cycle, but it could improve the energy performance if it is used inside a cascade refrigeration system. KEYWORDS

Section: Introductionmentioning

confidence: 93%

Experimental evaluation of an internal heat exchanger in a CO2 subcritical refrigeration cycle with gas-cooler

Applied Thermal Engineering

Sanz-Kock

Cabello

et al. 2015

Self Cite

“…Aprea & Maiorino (2008) and Sánchez et al (2014a) studied the improvements by using the internal heat exchangers (IHX) in single-stage plants and Cavallini et al (2007) in two-stage systems. The experimental measurements demonstrated that the IHX can improve the COP up to a maximum of 10 %.…”

Section: Introductionmentioning

confidence: 99%

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

International Journal of Refrigeration

Nebot‐Andrés

Sánchez

et al. 2016

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130

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

“…The IHX allows obtaining this increase in suction temperature providing at the same time a small subcooling of the liquid CO2 at the exit of the condenser. This element has been widely analysed for plants working with HFC refrigerants [7][8][9] and for plants working with CO2 in transcritical conditions [10,11]. In general, its use is beneficial if the refrigerant has high heat capacity.…”

Section: Introductionmentioning

confidence: 99%

Effects caused by the internal heat exchanger at the low temperature cycle in a cascade refrigeration plant

Applied Thermal Engineering

Sanz-Kock

Sánchez

et al. 2016

Self Cite

This work analyses and quantifies the effects caused by the use of an internal heat exchanger (IHX) at the CO2 subcritical cycle in an HFC134a/CO2 cascade refrigeration plant that incorporates a gas-cooler at the exit of the low temperature compressor. Previous theoretical and experimental studies showed that the IHX reduces the refrigeration capacity and COP of the subcritical cycle, however, it has been seen that it also lowers the heat to be rejected at the condenser. This reduction, when the cycle is a part of a cascade system, allows reducing the heat load of the high temperature cycle, modifying the working conditions of the cascade plant. The modifications result in an increment of the overall coefficient of performance of the cascade system. The analysis here presented is based on the evaluation of an experimental HFC134a/CO2 refrigeration plant, which has been analysed with and without internal heat exchanger in an evaporating temperature range from -40 to -30 ºC and in a condensing one from 30 to 50 ºC. The plant incorporates a gas-cooler at the exit of the CO2 compressor. The experimental results confirm that the IHX slightly reduces the cooling capacity but it can increment the overall COP up to 3.7 %.