The use of carbon dioxide (CO2) as refrigerant is driven by the need to phase down the traditional synthetic refrigerant so as to mitigate the warming climate. In this study, the thermal performance ...of a two-stage compression transcritical CO2 refrigeration system with R290 mechanical subcooling unit is conducted. The goal is to obtain the maximum coefficient of performance (COP) of five different mechanical subcooling systems under the optimal subcooling temperature and compressor discharge pressure. The two-throttling and two-stage compression high-pressure mechanical subcooling system is found to have a higher COP. When the evaporation temperature is −30 °C, the COP of the two-throttling and two-stage compression high-pressure mechanical subcooling system is improved by 76.74%. The COP of the two-throttling and two-stage compression high-pressure mechanical subcooling system is 1.52 at an ambient temperature of 40 °C, which is 21.87% higher than that of the two-throttling and two-stage compression low-pressure mechanical subcooling system. The power consumption ratio of one-throttling and two-stage compression low-pressure mechanical subcooling system is significantly higher than that of other systems. From a comprehensive analysis of the proposed four systems, the two-throttling and two-stage compression high-pressure mechanical subcooling system has the best performance over all other systems.
•Two-stage compression transcritical CO2 refrigeration systems with R290 mechanical subcooling are analyzed.•Two-throttling, two-stage high-pressure mechanical subcooling is most advantageous.•Two-stage compression transcritical CO2 cycle with R290 mechanical subcooling unit is suitable for warm and hot regions.
District cooling plants are predominantly based on vapor compression refrigeration cycles with detrimental environmental impacts due to fossil-based electricity. Vapor absorption refrigeration cycles ...promise operating improvements and emission reductions in vapor compression-absorption refrigeration system configurations. However, the use of conventional vapor absorption refrigeration working fluids and the limited studies of systems with capacities that are relevant to district cooling plants, prohibit their scaling-up. This work compares the thermodynamic, environmental, and economic performance of seven configurations of the vapor compression refrigeration cycle with a double-effect vapor absorption refrigeration cycle that employs either the conventional ammonia/water or the novel acetaldehyde-N,N-dimethylformamide working fluid. These three cycles are compared with the cascade and parallel vapor compression-absorption refrigeration system configurations, with ammonia/water or acetaldehyde-N,N-dimethylformamide in the vapor absorption refrigeration. The coefficient of performance of the vapor compression refrigeration unit in the cascade configurations is 252% higher than the stand-alone vapor compression refrigeration configuration. The stand-alone vapor absorption refrigeration coefficient of performance with the novel fluid acetaldehyde-N,N-dimethylformamide is 9.1% higher than that of the vapor absorption refrigeration with ammonia/water. The cost per ton of cooling and the total equivalent warming potential of the cascade vapor compression-absorption refrigeration system with acetaldehyde-N,N-dimethylformamide are 65% and 67.8% lower than those of the stand-alone vapor compression refrigeration. The electrical energy utilization factor is 30.5% lower for the acetaldehyde-N,N-dimethylformamide fluid compared to ammonia/water, in the cascade configuration.
•VCR-VAR cycles are promising for district cooling plants.•Comparative assessment of Cascade and Parallel VCR-double effect VAR systems.•Utilization of real district cooling plant and novel working fluid in VAR.•Coefficient of performance of the VCR in the VCR-VAR is increased by 252%.•Costs and emissions in VCR-VAR are reduced by up to 67.8%.
In this study, a solar single/double-effect switching LiBr-Hsub.2O absorption refrigeration system was investigated to make full use of solar energy and give full play to the advantages of solar ...refrigeration systems. A corresponding thermodynamic dynamic mathematical model was developed. The operation characteristics of the system operating continuously for one week were analyzed. In order to highlight the advantages of the solar single/double-effect switching absorption refrigeration system, it was compared with other forms of solar refrigeration systems and compression refrigeration systems. The practical application potential of the single/double-effect switching LiBr-Hsub.2O absorption refrigeration system was evaluated from the perspective of economy and environmental effect. The results showed that the system could achieve the switching operation between single-effect mode and double-effect mode under weather conditions of high solar radiation intensity, and the daily cooling efficiency on such days was relatively high. After an auxiliary heater was added, the primary energy savings of the solar single/double-effect switching LiBr-Hsub.2O absorption refrigeration system were 25-52%, depending on the area of the collector and the volume of the storage tank. The solar fraction of the system was about 71.99% for continuous operation during the whole refrigeration season. However, the initial investment cost of the system equipment accounted for 89.66% of the total cost. Compared with the traditional compression refrigeration system, the initial investment cost of the solar single/double-effect switching LiBr-Hsub.2O absorption refrigeration system was higher, but it had a better environmental protection effect.
•A novel solid state magnetic refrigeration system is proposed.•The system is based on a new cascade micro-unit regeneration cycle.•The design concept and operation mechanism are described in ...detail.•A quasi 2-D simulation model is developed for the system.•The system shows good potential for practical application.
Magnetic refrigeration (MR) is regarded as an alternative solution for vapor-compression refrigeration system to eliminate the usage of hydrofluorocarbons (HFCs). However, better solutions and breakthroughs are urgently needed to promote the commercialization process of MR. In this paper, a novel solid state MR system is proposed based on a new cascade micro-unit regeneration (MUR) cycle, in which heat can be regenerated at the correct time and in the reasonable space through the special cycle design. The heat regeneration in such system is one-way solid-to-solid heat conduction with a small temperature difference, thus avoiding the heat transfer loss that exists in conventional active magnetic regenerators. The cycle design concept and operation mechanism are described in detail. A quasi-two-dimensional numerical simulation model is developed for the proposed system to investigate optimal geometric parameters, operating characteristics and system performance. Using gadolinium as the magnetocaloric material and an applied magnetic field of 1.5 T, a maximum no-load temperature span of 50.9 K and a maximum COP of 4.2 are achieved by a 72-lattice configuration. Moreover, the optimal rotating speed range is determined for maximizing the specific cooling power (SCP) under different configurations and operating conditions. The obtained maximum SCP range is from 2.6 W kg−1 to 105.8 W kg−1. The results reveal good potential for practical application.
As an emerging solid‐state refrigeration technology with zero‐emission and high energy conversion efficiency, there is a compelling need for ferroelectric materials with giant electrocaloric effects ...(ECEs) at room temperature suitable for refrigeration applications. The complex perovskite antiferroelectric (AFE), PbMg0.5W0.5O3, containing non‐equivalent B‐site ions with a symmetric giant positive and negative ECE near room temperature is presented. At the Curie temperature of 36 °C, the first‐order AFE–paraelectric phase transition gives rise to a large enthalpy change of 3.92 J g−1, more than four times that of BaTiO3. This leads to a significant ECE under the influence of an electric field. The direct electrocaloric characterization shows that the adiabatic temperature change, ΔT, exhibits symmetric peaks with a giant positive maximum of 1.79 K (ΔS = 1.68 J kg−1 K−1) at 36 °C and a negative maximum of −2.02 K (ΔS = −1.93 J kg−1 K−1) at 34 °C. The ultrahigh magnitude of ΔT near room temperature makes PbMg0.5W0.5O3 a superior electrocaloric material far beyond traditional PbZrO3‐based AFEs. The coexistence of symmetric giant positive and negative ΔT to further improve cooling efficiency is expected. In addition, the good reversibility and negligible leakage current should pave the way for practical applications.
In ordered PbB′0.5B″0.5O3 perovskite oxide ceramic‐PbMg0.5W0.5O3, a first‐order antiferroelectric–paraelectric phase transition occurs near room temperature (36 °C), with a large enthalpy change of 3.92 J g−1. The resultant symmetric giant positive (ΔT = 1.79 K, ΔS = 1.68 J kg−1 K−1) and negative electrocaloric effect (ΔT = −2.02 K, ΔS = −1.93 J kg−1 K−1) favors solid‐state ferroelectric refrigeration application.
Dans le souci d'améliorer les pratiques actuelles, ¡I devient essentiel de mettre en lumiére le seul organisme reconnu par RECYC-QUÉBEC qui assure le recyclage responsable des appareils ménagers de ...refrigeration et de climatisation partout au Québec: GoRecycle. Ainsi, le programme de GoRecycle offre aux citoyennes et citoyens la seule solution responsable et légale pour le recyclage de ces appareils; ¡I permet de valoriser 95 % des matiéres, en plus de récupérer les halocarbures et les matiéres dangereuses. II éta it urgent de recruter une equipe motivée pour relever ľimmense défi qui se présentait, dans lequel M. Foisy Lapointe a Hait endosser le role de directeur général, et ce, en pleine pandemie et penurie de main-ďoeuvre, et ne pouvant s'appuyer sur aucune notoriété existante. Ľéquipe compte désormais huit personnes convaincues que les entreprises et le secteur public peuvent trava il ler ensemble pour lutter contre les changements climatiques et la gestión des déchets. Aujourd'hui, ce sent plus de 170 membres de l'industrie qui financent le programme et participent activement â la recherche de solutions pour augmenter le volume d'appareils collectés. Grace â la collaboration des vilies et municipalités ainsi que des détaillants, ľorganisme a mis sur pied plus de 450 points de collecte au Québec, dont prés de 300 écocentres et 90 banniéres de détaillants offrant un service de collecte et de recyclage â ľachat d'un appareil neuf. II est crucial pour GoRecycle que le Reglement seit applique afin d'éliminer ľimportant marché parallele provoqué par les recycleurs de métauxqui achétent les appareils refrigerants sans en assurer le traitement conforme. Visitez le gorecycle.com pour connaître toutes les solutions de réemploi, de reparation et de recyclage des appareils ménagers. * «Ainsi, le programme de GoRecycle offre aux citoyennes et citoyens la seule solution responsable et légale pour le recyclage de ces appareils; II permet de valoriser 95 % des matiéres, en plus de récupérer les nalocarbures et les matiéres dangereuses.»
•Exergoeconomica analysis of an efficient geothermal multigeneration system.•Simultaneous production of power, cooling, and hydrogen vial an innovative integration.•Comparison between absorption and ...ejector refrigeration cycles in same conditions.•Energy and exergy efficiencies are 22.28% and 21.37% for whole system, respectively.•The unit cost of multigeneration system is found as 29.29 $/GJ.
The novel multi-generation system is developed to produce power, cooling, and hydrogen. The present work is suggested to employ the geothermal energy to start a Kalina cycle and then with regard to the high temperature of the saturated liquid leaving the Kalina cycle separator, the absorption refrigeration system is employed for providing cooling as a subsystem. Also, an electrolyzer and the power production capacity of the cycle have been utilized to produce hydrogen. The proposed system is evaluated thermodynamically and exergoeconomically, and a parametric study was performed for the following parameters: geothermal heat source temperature (THS,in), the temperature difference in vapor generator 1 (ΔTPP,vg1), the pressure of vapor generator 1 (Pvg1), condenser temperature (Tcon), evaporator temperature (Teva) and ammonia concentration (YB). The governing equations are coded in the EES software. In the base case, the results display that the proposed system is capable of producing 258.6 kW of cooling, and in this case, the thermal and exergy efficiencies and the unit cost of multigeneration are 22.28%, 21.37% and 29.29 $/GJ, respectively. Also, increasing the evaporator temperature does not have a significant effect on power production capacity. Moreover, condenser 1 has the most exergy destruction rate of 65.03 kW.
A novel combined cooling and power (CCP) system utilizing liquefied natural gas (LNG) cryogenic energy and low-temperature waste heat was presented. The proposed system consists of two subsystems, ...absorption refrigeration/power cycle (ARP) subsystem and LNG refrigeration/power cycle (LRP) subsystem. The Rankine cycle and absorption refrigeration cycle were connected in series to form the ARP and they showed mutual enhancement in the integration. The operating performance of the system was calculated and analyzed. And the effects of generator pressure and circulation ratio on the performance were analyzed. Furthermore, a typical application case, in which the proposed system is integrated into the gas-steam combined cycle system as an LNG pre-processing and power enhancement unit, had been studied. The results showed that the net power generation efficiency, comprehensive energy utilization ratio, and exergy efficiency of the proposed CCP system reached 32.70%, 81.63%, and 35.14%, respectively. The feasibility and performance of the integrated system with combined cycle gas turbine were proved. And suggestions for the parameter design were presented.
•A cogeneration system is proposed to utilize LNG cryogenic energy and waste heat.•Rankine cycle and absorption refrigeration cycle are combined in series.•Net power generation efficiency and exergy efficiency reach 32.70% and 35.14%.•Suggestions for system design are presented.•The integration with combined cycle gas turbine greatly improves performance.
•A novel trascritical CO2 trigeneration system driven by low-grade heat resource is presented.•System performance is investigated from the thermoeconomic viewpoint.•The effects of key operating ...parameters on system performance are identified.•Multi-objective optimization for the system in different operation modes is carried out.
This work focuses on designing a self-sufficient trigeneration system for low-grade heat resource applications. For this purpose, a novel transcritical CO2 combined cooling, heating, and power (CCHP) system is proposed, which integrates a Rankine power cycle and an ejector refrigeration cycle (ERC). To evaluate the feasibility of the proposed system, the mathematical model of the combined cycle is built and validated. The effects of seven key parameters on system performance are investigated from the thermoeconomic viewpoint. Furthermore, multi-objective optimization is performed for the system when it generates both cooling and power or simultaneously produces heating and power. The results show that when using low-grade heat resource, the proposed plant not only has desirable net power output under all considered conditions, but also achieves adjustable output for cooling and heating in a broad range. The exergy efficiency of the proposed system and the coefficient of performance (COP) of ERC under base case conditions are respectively improved by 13.3% and 167.7% compared to the reference cycle. Under optimal conditions, the total useful energy and exergy efficiency of the system respectively are 127.3 kW and 22.7% for the combined cooling and power (CCP) mode, while corresponding values are 126.2 kW and 43.6% for the combined heating and power (CHP) mode, respectively. The cost per unit of exergy products for the system in the CCP mode is 3.4 times more than that in the CHP mode.
