•Multi-stage cycles and parallel compression are included in two-stage cascades.•Forty different combinations of cycles are simulated.•Low global-warming potential natural refrigerants R-290 and ...R-170 are considered.•The influence of each cycle on the whole configuration is analyzed.•–80 °C refrigeration coefficient of performance is increased.
In response to the COVID-19 pandemic, some vaccines have been developed requiring ultralow-temperature refrigeration, and the number of these freezers has been increased worldwide. Ultralow-temperature refrigeration operates with a significant temperature lift and, hence, a massive decrease in energy performance. Therefore, cascade cycles based on two vapor compression single-stage cycles are traditionally used for these temperatures. This paper proposes the combination of six different cycles (single-stage with and without internal heat exchanger, vapor injection, liquid injection, and parallel compression with and without economizer) in two-stage cascades to analyze the operational and energy performance in ultralow-temperature freezers. All this leads to 42 different configurations in which the intermediate cascade temperature is optimized to maximize the coefficient of performance. Ultra-low global warming potential natural refrigerants such as R-290 (propane) and R-170 (ethane) for the cascade high- and low-temperature stage have been considered. From the thermodynamic analysis, it can be concluded that liquid and vapor injection cascade configurations are the most energy-efficient. More specifically, those containing a vapor injection in the low-temperature stage (0.89 coefficient of performance, 40 % higher than traditional configurations). Then, using an internal heat exchanger for such low temperatures is unnecessary in terms of energy performance. The optimum intermediate cascade temperature varies significantly among cycles, from −37 °C to 2 °C, substantially impacting energy performance. Parallel compression configuration improves energy performance over single-stage cycles, but not as much as multi-stage (between 20 % and 30 % lower coefficient of performance). For most of low-temperature cycles, the high-temperature stage can be based on a single-stage cycle while keeping the maximum coefficient of performance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZAGLJ, ZRSKP
In this paper, a review of the research state of art of the solar sorption (absorption and adsorption) refrigeration technologies is presented. After an introduction of basic principles, the ...development history and recent progress in solar sorption refrigeration technologies are reported. The application areas of these technologies are categorized by cooling temperature demand. It shows that solar-powered sorption refrigeration technologies are attractive alternatives that not only can serve the needs for air-conditioning, refrigeration, ice making and congelation purposes, but also can meet demand for energy conservation and environment protection. However, a lot of research work still needs to be done for large-scale applications in industry and for the replacement of conventional refrigeration machines.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•The performance is not optimal in maintaining soil initial temperature balance.•The performance of solar assisted ground source heat pump system can reach 4.95.•The performance of whole system can ...reach 3.49 at the heating season.•Solar space heating can improve the performance of whole system by nearly 25.8%.
The operational performance of a hybrid solar ground source heat pump (HSGSHP) system built at the Hebei University of Technology and composed of a ground source heat pump (GSHP) system and a solar-assisted ground source heat pump (SAGSHP) system is investigated in this work. For the GSHP system, the coefficient of performance (COP) of heat pump unit and system of the GSHP system varies from 4.59 to 5.07 and 3.87 to 4.28, respectively, in the cooling seasons from 2012 to 2016. During the heating season, the COP of heat pump unit and system of the GSHP system varies from 4.59 to 5.07 and 3.87 to 4.28, respectively. The annual COP of heat pump unit and system of the GSHP system increases from 3.19 to 4.18 and 3.03 to 3.63, respectively. For the SAGSHP system, solar space heating can improve performance by nearly 79.0%. For the HSGSHP system, increasing the proportion of the heat supply of the SAGSHP system within a certain range can effectively improve the COP of the HSGSHP system in the heating season. The results show that solar space heating can improve the performance of the HSGSHP system by nearly 25.8%.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A novel solar water heating system with inserted heat pipe and PCM is fabricated.•Different working modes can realize the seasonal maximum utilization of solar energy.•The system performance ...analysis is based on the study of a whole year measurements.•PCM can overcome the immediate influence of solar radiation fluctuation on system.•The system with PCM can increase efficiency and shorten the time to heat water.
In this paper, a novel solar water heating system (SWHS), capable of reducing the impact of solar radiation intensity fluctuations, has been fabricated by using phase change materials (PCM) for thermal energy storage and inserted oscillating heat pipe (OHP) for performance improvement. Different working modes can be selected according to the solar radiation intensity in different seasons and different climate conditions. A test rig has also been made for the performance measurement of the system. The full-year measurement in all kinds of environmental conditions has been carried out for a couple of consecutive years, in Nanjing city of China. The system performances, such as collecting efficiency (CE), average collecting efficiency (ACE), coefficient of performance (COP) and exit water temperature (EWT), have been measured and compared between the systems with and without PCM. Under similar operation conditions, the system with PCM is illustrated to have much better performances. In daytime, CE fluctuation with PCM is over 30% less than that without PCM. At summer night, EWT with PCM can keep over 50 °C, while EWT without PCM has an obvious decrease. At winter night, COP with PCM is over 3.0 that can make EWT reach to 50 °C in a much shorter time than that without PCM. The system presented is proved to be effective and useful in the application of solar energy.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The auto-cascade refrigeration cycle (ACRC) is suitable for low temperature refrigeration fields. From the perspective of fractionation purification matching expansion work recovery, a fractionated ...auto-cascade refrigeration cycle coupled with the two-phase ejector (FACRC-TPE) using environmentally-friendly R1150/R600a is proposed in this paper. In the novel cycle, the two-phase ejector is substituted for the throttle valve at the liquid stream passage from the separator bottom to recover expansion work and cut down the energy consumption, while the fractionation heat exchanger is applied for purification of low boiling point component in the vapor stream from the separator top to boost the cycle exergy efficiency and achieve a refrigeration temperature below −80 °C. The energetic and exergetic analysis methods are used to evaluate and compare the performances of the three cycles, and comparisons of superiority and irreversibility of FACRC-TPE are also made with the unfractionated auto-cascade refrigeration cycle with the two-phase ejector (UACRC-TPE) and the fractionated auto-cascade refrigeration cycle (FACRC). The results show that the cooperative application of the fractionation heat exchanger coupled with the two-phase ejector not only significantly boosts COP of FACRC-TPE and obtains lower refrigeration temperature, but also cuts down the total exergy loss of FACRC-TPE. With R1150 mass fraction varying in the range of 0.29–0.48, the average COP of FACRC-TPE is 10.57% higher than that of UACRC-TPE, and is 15.18% higher than that of FACRC, whereas FACRC-TPE has a lower evaporator inlet temperature of −100.48 °C to −87.96 °C, as compared with UACRC-TPE. In addition, FACRC-TPE obtains the highest exergy efficiency of 32.23%, while the UACRC-TPE exergy efficiency of 26.99% is slightly higher than the FACRC exergy efficiency of 25.19%.
•A fractionated auto-cascade refrigeration coupled with two-phase ejector is proposed.•Concept of fractionation process matching expansion work recovery is used.•Thermodynamic performances of the three cycles are evaluated and compared.•COP of the proposed cycle is higher than that of other two cycles respectively.•The proposed cycle obtains the highest exergy efficiency among the three cycles.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A novel phase change material-assisted earth-air heat exchanger is proposed.•The new heat exchanger reduces PCM usage but achieves better cooling performance.•The heat storage performance of the PCM ...unit in the new heat exchanger is improved.•New heat exchanger’s cooling capacity is 70.75% higher than the conventional one.•New heat exchanger’s COP is increased by 49.02% compared to the conventional one.
Studies confirmed that phase change material (PCM) can improve the cooling potential of an earth-air heat exchanger (EAHE). However, the poor utilization of the PCM unit’s latent heat storage (LHS) capacity and insufficient understanding of energy efficiency hinder its applications in EAHE. To solve these problems, this study made a structural improvement to the PCM unit and proposed a centrally located hollow cylindrical PCM-assisted EAHE (CHCPCM-EAHE). Then, numerical simulations were conducted on this CHCPCM-EAHE through a 3-D model built on the ANSYS FLUENT, and its cooling performance in Chongqing (China) summer was comparatively studied. The results found that the LHS performance of the PCM unit in this CHCPCM-EAHE was improved despite the significant reduction in material volume. Compared to the PCM unit in the previous PCM-assisted EAHE, the maximum liquid fraction and average charged latent heat in all charge–discharge cycles of the PCM unit in this CHCPCM-EAHE were increased by 56.82 % and 10.46 %∼56.43 %, respectively. The results also found that the CHCPCM-EAHE performed better in cooling potential and coefficient of performance (COP). Compared to the conventional EAHE and previous PCM-assisted EAHE, its average cooling capacity increased by 60.12 %∼70.75 % and 4.05 %∼10.96 %, and average COP increased by 47.22 %∼49.02 % and 6.88 %∼8.18 %, respectively.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The component-based double-stage auto-cascade refrigeration cycle is proposed.•There is the optimum R170 mass fraction to obtain the highest COP of this cycle.•Concept of grade compression is used ...to boost the performance of the new cycle.•Theenergysavingperformanceoftheproposedcycleisproventobeexcellent.
It is difficult for the conventional single-stage compression auto-cascade refrigeration cycle to achieve higher refrigeration efficiency and lower refrigeration temperature, because the stream rich in high boiling point component from the phase separator bottom undergoes a single-stage compression process of high pressure lift ratio. Based on the concept of the evaporating temperature of the high/low boiling point component matching the grade compression of two streams from the phase separator, a component-baseddouble-stagecompressionauto-cascaderefrigeration (CDACR)cycle using R170/R600a is proposed in this paper. In the novel cycle, one dedicated compressor with two suction ports is used as the substitute for a conventional compressor with the sole suction port to realize grade compression process of the component of the refrigerant mixtures, and the stream enriched with high boiling point component from the separator bottom is sucked into the high-pressure suction port and undergoes the low-pressure-lift-ratio compression process, while the stream rich in low boiling point component from the separator top is sucked into the low-pressure suction port and executes the high-pressure-lift-ratio compression process, so as to cut down the compressor power consumption and obtain a lower refrigeration temperature. The mathematical model of the proposed cycle is developed to evaluate the thermodynamic performance of the system and comparisons with the conventional single-stage compression auto-cascade refrigeration (SCACR) cycle are also discussed. The results indicate that application of the component-based grade compression to the conventional auto-cascade refrigeration cycle dramatically improves the performance of the CDACR cycle, and there is optimum composition ratio of refrigerant mixtures for the CDACR cycle to obtain the highest coefficient of performance (COP). It is also shown that the performance of the CDACR cycle is significantly better than that of the SCACR cycle. As compared with those of the SCACR cycle, the compressor power consumption of the CDACR cycle decreases by 44.83%-53.17%, and its COP increases by 0.34–0.43, as the evaporating temperature at the evaporator outlet ranges from −60°C to −40°C. In addition, at the condenser outlet temperature in the range of 26°C- 40°C, the compressor power consumption for the proposed cycle is 37.74%-47.03% lower than that for the SCACR cycle, while COP of the CDACR cycle is 0.29–0.42 higher than that of the SCACR cycle.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZAGLJ, ZRSKP
The use of an air conditioning system requires large amounts of electrical energy to carry out repeated vapor compression cycles. The use of an evaporative cooling system in this research is by ...spraying condensate water on the condenser, which is one solution to absorb condenser heat. Another thing that can be done is to reset the fan speed on the condenser to cool it. Resetting the fan speed on the condenser can also help improve AC performance and reduce electrical energy use. The test was carried out by modifying the 1 Pk R-410a AC split condenser by installing 6 nozzles, 2 rows of 3 columns and a DC pump to spray water on the condenser. The independent variables of this research are spraying position and fan speed. The result obtained from the research is an increase in COP by 35% and a reduction in electrical power usage by 15% by using additional water spray with a nozzle behind the condenser both when blowing the full blower and when the blower blowing speed is reduced by 75%. The use of evaporative systems in air conditioning technology is a promising solution to achieve sustainable and efficient cooling solutions.
In recent years, due to the use of renewable energy such as geothermal and capability of reduction of energy consumption and greenhouse gas emissions by ground source heat pumps, these heat pump ...cycles have attracted considerable attention as a green energy system. The variations in temperature of soil play an important role in efficiency of ground source heat pump cycles which is determined by some effective parameters such as ambient temperature, soil type and depth. Besides, in cold regions where the ground is covered by snow and ice at least part of the year, the factors like the temperature and thickness of snow and ice layer are also effective on soil temperature. Therefore, this paper investigates the effects of variations of soil temperature on performance of ground source heat pump at different soil depths of 20 cm, 50 cm and 100 cm which are covered by 0 cm–50 cm of ice and 0 cm–40 cm of snow where the temperature of air ranges from −40 °C to 0 °C. The study is divided into two parts including the heat transfer analysis in soil covered with snow and ice using computational fluid dynamics and thermo-economic-environmental analysis of a proposed cascade ground source heat pump system. The proposed cascade heat pump cycle is operated using R41-R161 refrigerant pair as low global warming potential and zero ozone depletion potential working fluids. The continuity, Brinkman momentum and energy equations are firstly employed as governing equations for computational analysis to obtain the soil temperature profile. Then, the energy-exergy-economic-environmental analysis is performed to optimize the performance of the cascade ground source heat pump system based on the soil temperature profiles obtained from the previous step using Pareto-based multi-objective optimization method. Optimization results show that there is an optimal operating point for the proposed cascade ground source heat pump system where the maximum coefficient of performance of 3.2, maximum exergy efficiency of 64% and minimum total cost rate of 10300 $/year are obtained. Finally, the optimal soil depth and evaporator temperature are determined for different snow and ice thicknesses at different weather conditions.
Display omitted
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Due to the environmental concerns, refrigerants with low global warming potential (GWP) are good alternatives to use in the most refrigeration system. In this paper, an ...energy-exergoeconomic-environmental model is presented for a cascade refrigeration system (CRS) at high and low temperature cycles operating with six pairs of refrigerants with low GWP including R41-R161, R41-R1234yf, R41-R1234ze, R744-R161, R744-R1234yf, R744-R1234ze. The optimal performance of the system is studied under the effects of temperature variations in condenser, evaporator and cascade heat exchanger. To do this, the coefficient of performance (COP), exergy efficiency and total cost rate are optimized for each pair of refrigerants to evaluate the optimal operational conditions of CRS using Pareto front curve. Results show that the maximum COP of 2.09 and maximum exergy efficiency of 35.32% are obtained at condenser temperature of 40 °C and evaporator temperature of − 30 °C. In addition, the minimum total rate cost is equal to 13587 $/year when the condenser temperature is 40 °C and evaporator temperature is 32.5 °C. Finally, it is concluded that R41-R161 and R41-R1234ze are optimal refrigerant pairs with the highest COP/exergy efficiency and lowest total cost rate.
Display omitted
•The performance of a cascade refrigeration system is optimized energy-exergoeconomic-environmentally.•Variations in temperature of condenser, evaporator and cascade heat exchanger is studied.•The optimal operational conditions of different refrigerant pairs are investigated.•The optimal refrigerant pairs are introduced using pareto front curve.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
