Existing Refrigeration System Research Articles

Exergy assessment of a multistage multi-evaporator vapor compression refrigeration system using eighteen refrigerants

The use of lower global warming potential refrigerants as an alternative to hydrochlorofluorocarbons and hydrofluorocarbons from an environmental perspective is the need of an hour. The feasibility and possibility of alternative refrigerants in the existing refrigeration system can be recognized using exergy assessment. This will lead to improving the thermal performance of the refrigeration systems. In this paper, exergy assessment of a multistage multi-evaporator vapor compression refrigeration system is performed using the Simulink model. A total of eighteen refrigerants are considered for the analysis from the environmental perspective, safety considerations, etc. The evaporator-1, evaporator-2, and condenser temperatures are varied from 0 °C to 15 °C, −15 °C to −5 °C, and 25 °C to 33 °C respectively. The highest exergy destruction among all the components is found for both the compressors, followed by the condenser, evaporators, expansion devices, and internal heat exchanger. Refrigerants R141b, R123, R245ca, R245fa, and R152a showed better thermal performance than hydrofluoroolefins refrigerants, but have high GWP values. R1234ze(E), and R1234yf are environmentally friendly and achieved similar performance to conventional refrigerants.

Drop-in and retrofit refrigerants as replacement possibilities of R134a in domestic/commercial refrigeration and automobile air conditioner applications

According to the EU F-gas Regulation, the phase-out of the high global warming potential (GWP) refrigerants (with higher than 150 GWP value) had been established. The most currently existing household and commercial refrigerators and automobile air conditioners applications based on single-stage vapour compression systems operate with R134a as working fluid. The present paper aims, to review and evaluate the performance of a set of eco-friendly alternatives refrigerants to replace R134a, without change or with minor modifications in refrigeration equipment. The theoretical and experimental studies performed in this field of research were reviewed for this objective. These alternative refrigerants are some of HFCs, HFOs and HCs and their mixtures, which are expected to be an excellent candidates in many refrigeration applications. There are Many replacement possibilities had been proposed viz. drop-in replacement, retrofit refrigerant, and new systems. The results exhibited that the most suitable refrigerants as R134a drop-in substitutes are R1234yf, R152a, R450A, and R513A. The pure R1234ze and its mixtures are not suitable drop-in replacements of R134a but can be a good alternative to R134a only in new refrigeration systems. In terms of hydrocarbon refrigerants R290, R600, and R600a could replace R134a with some modifications to existing refrigeration systems to overcome the flammability issue. We should be using certain HFC and HC mixtures with the lowest TEWI index.

Modelling and cooling power control of a TES-backed-up vapour-compression refrigeration system

This work addresses the modelling, power control, and optimization of a thermal energy storage (TES) system combined with a vapour-compression refrigeration facility based on phase change materials (PCM). Given a novel design of a PCM-based TES tank and its interconnection with an existing refrigeration system, the joint dynamic modelling is first studied, exploring the different time scales that coexist at the interconnected system. Diverse operating modes are defined, according to the intended use of the TES tank as a cold-energy buffer to decouple cooling demand and production, whereas the static characteristic and power limits are calculated and show the high coupling between the main cooling powers involved (TES charging/discharging power, and direct power production at the evaporator). In this light, a decoupling control strategy is proposed, where the low-level controllers are simply PI regulators and the refrigerant/secondary mass flows are considered as virtual manipulated variables, applying a feedforward-based cascade strategy. The control performance is evaluated through a thorough simulation that includes all operating modes, where the reference tracking is shown to be fast and reliable enough to address high-level scheduling strategies, where the references on the main cooling powers are intended to be imposed considering economic and efficiency criteria.

Modelling of a real CO2 booster installation and evaluation of control strategies for heat recovery applications in supermarkets

This paper compares and quantifies the energy, environmental and economic benefits of various control strategies recovering heat from a CO2 booster system in a supermarket for space heating with the purpose of understanding its potential for displacing natural gas fuelled boilers. A theoretical steady-state model that simulates the behaviour of the CO2 system is developed and validated against field measurements obtained from an existing refrigeration system in a food-retail building located in the United Kingdom. Five heat recovery strategies are analysed by modifying the mass flow and pressure level in the condenser. The model shows that a reduction of 48% in natural-gas consumption is feasible by the installation of a de-superheater and without applying any advanced operating strategy. However, the CO2 system can fully supply the entire space-heating requirements by adopting alternative control strategies, albeit by penalising the coefficient of performance (COP) of the compressor. Results show that the best energy strategy can reduce total consumption by 32%, while the best economic strategy can reduce costs by 6%. Findings from this work suggest that heat recovery systems can bring substantial benefits to improve the overall efficiency of energy-intensive buildings; nevertheless trade-offs need to be carefully considered and analysed on a site by site basis before embarking on such initiatives.

Analysis of a closed-loop water-cooled refrigeration system in the food retail industry: A UK case study

Abstract Refrigeration in supermarkets accounts between 30% and 60% of total electricity demand in UK stores. The aim of this study is to conduct a pre-feasibility analysis of whether the use of a water-cooled configuration rejecting heat to the soil can improve the overall cooling performance of commercial refrigeration systems against air-cooled designs. In this work, a model simulating the operation of an existing refrigeration system is presented and validated against field data measurements taken from a supermarket. The examined system is used as a baseline and then modified to evaluate the impact of installing a water-cooled gas cooler. Results indicate that the use of water-cooled gas coolers has the potential to reduce electrical consumption of refrigeration systems by up to a factor of 5 when external temperatures are high. Overall, annual operation indicates the water-cooled alternative uses 3% less electricity than the air-cooled approach. A hybrid system is also considered consisting of coupled air-cooled and water-cooled units operating in parallel, for which an energy reduction of 6% is obtained compared against the baseline system. An economic evaluation of these systems shows promising results with a payback period of about 5 years for systems installed in new stores, although retrofits are costlier.

Theoretical and experimental investigation of a novel high temperature heat pump system for recovering heat from refrigeration system

Ammonia has been widely employed as the working media in industrial refrigeration systems including cold chain or pharmaceuticals industry. The condensers of such system are releasing large amount of heat especially in large capacity applications. On the other hand, heating supply at the temperature of 80°C or even higher is also greatly demanded in related processing systems. High temperature heat pumps, which are capable of recovering heat from condensers of refrigeration systems, could be much more highly efficient compared to boilers or electric heaters. Conventional heat pumps employ heat exchangers on existing refrigeration system condenser, but have much drawback and less efficiency in practical applications. In this paper, a novel system employing higher temperature ammonia twin screw compressors is introduced and analyzed for recovering heat and supplying hot water. A new semi-empirical model is specially developed for high pressure twin screw compressors. Both theoretical and experimental investigations are conducted on such system, while validation of simulation accuracy and efficiency analysis of such system is also given.

Development of Waste Heat Fired Activated Carbon Ammonia Adsorption Chiller

Adsorption systems are promising alternative to the existing refrigeration systems in the wake of alarming energy crisis and potential danger due to the use of ozone depleting refrigerants. Sorption systems use thermal energy as its power source and solid adsorbent beds to adsorb and desorb a refrigerant to obtain the desired cooling effect. Solar energy, engine exhaust and low grade waste heat could be used to drive the sorption compressors. The use of non-ozone depleting refrigerant makes these systems environmentally benign. Adsorption refrigeration systems can meet the cooling requirement across a wide range of temperatures. These systems have minimal moving parts and hence they are free of noise, vibration and related problems. This paper will present the description, operation and simulated system characteristics for a 1000W adsorption chiller. The adsorption system performance factors such as coefficient of performance (COP), specific cooling power (SCP), and cycle time were predicted. Parameters such as the generation and adsorption temperature, condenser and evaporator temperature were varied to analyze the influence of the varied operating conditions. A two bed 1000 W capacity adsorption water chiller to chill water from 12 to 7 C was considered for the simulation. COP of the simulated system ranged between 0.3 to 0.4 and SCP from 90 to 180 W/kg AC respectively. The maximum value of cycle time obtained was 25 minutes when the generation outlet temperature was 180 oC.

Process optimization of freeze desalination of brine using HybridICETM pilot plant

Freeze desalination of synthetic brines prepared from sodium chloride was investigated. Brine solutions of levels between 2.3% to 10% sodium chloride were used as feed to the plant operated in a batch and continuous mode. The effects of pump, gear motor speed, and differential temperatures on ice formation and purity were investigated. The HybridICE process produced ice of quality levels between 80–96% purity. It was observed that the pump speed was directly proportional to the effluent flow rate coming out of the heat exchangers. Generally, it was observed that the quality of product ice was higher at low to medium flow rates of feed. The gear motor speed variation was inversely proportional to effluent flow rate from the heat exchangers. The HybridICE was found to be a viable desalination technology in terms of quality of water produced, energy consumption, and its easiness to be incorporated into existing refrigeration systems.

Condensing Heat Recovery of Existing Large-Scale Refrigeration System

Existing refrigeration systems generally put the high temperature and pressure of refrigerant vapor into the atmosphere or cooling water through the condenser to reach the purpose of condensing refrigerant. But this will lead to the environment “thermal pollution”, and a waste of energy. This paper describes a plan of modification of the existing refrigeration system, through the waste heat recovery unit can be recovered the condensing heat effectively and product hot water in 50~ 60 to provide bathing. This system also can improve the refrigeration system operating conditions and the efficiency of generating units to achieve the purpose of energy saving.

Alternative Drop-in Refrigerant to R22 for Refrigerating System of Refrigerated Warehouse

e tested to use several compositions of a four-component-mixture R32/125/134a/600 as erant for replacing R22 in refrigeration system of refrigerated warehouses. R32, R125, 34a are hydrofluorocarbons and R600 is normal butane. The refrigeration system d for R22 can be used without any change or with very minor change. By using iate composition of the four-component refrigerant, existing refrigeration system can best performance because the adjusted properties of the refrigerant can somewhat sate for the individual hardware problems. Practical operation test was done by using a ation system of nominal cooling capacity of 30.2 kW with a 22 kW two-stage ssor which equipped for an 858 m refrigerated warehouse maintaining at −30 °C. The e condition and the coefficient of performance of R32/125/134a/600 are similar to R22 theoretical viewpoint. The power consumption of R32/125/134a/600 was small enough o be worse than that of R22, which was confirmed from the actual test results.

THERMODYNAMIC EVALUATION OF A TWO STAGES COMPRESSION REFRIGERATION SYSTEM INTEGRATED TO AN ABSORPTION SYSTEM

This work is based on the principles of administration, with technical and economic data from a frigorific fishing industry, at analyzing the convenience of integrating to the existing refrigeration system (by vapor compression) a refrigeration system by absorption. By comparing the existing system, and this one integrated with absorption, it was applied a thermodynamic evaluation for a mean frigorific output of 33.43 kW. The profitable result obtained from this evaluation indicated the feasibility of the integrated refrigeration system, with an operation time of up to 25.64 %, less than the existing refrigeration system, enabling a lower amount of time for investment return than five years. In the evaluation, they were compared the energetic model, associating energy and the operation cost. The highest profitability of integrated system shows, for the system applied in the industry, that by applying such system it contributes to lower the operations costs, with further results of increased in the product offer, and competitiveness in marketing frigorific items.

Efficiencies of transcritical CO 2 cycles with and without an expansion turbine : Rendement de cycles transcritiques au CO 2 avec et sans turbine d'expansion

With the discovery that fluorocarbons may have a profoundly detrimental effect on the earth's atmosphere, it has become necessary to find a suitable replacement for a fluorocarbon-based refrigeration cycle. Such a replacement must perform comparably to current refrigerants, be economically feasible, and significantly reduce the possibility of a negative environmental impact compared with current refrigerants. A review of the literature on the first vapor compression refrigeration cycles indicate that carbon dioxide was used as the working fluid prior to and after the turn of the century. Moreover, recent literature has suggested that carbon dioxide will work for certain air conditioning applications. Initial investigation of the heat transfer properties of carbon dioxide and subsequent modeling of a transcritical carbon dioxide vapor compression cycle suggest potential performance comparable to that of existing refrigeration systems. This paper will present a detailed literature review of carbon dioxide's role in refrigeration cycles and what has been investigated so far to find a suitable application for carbon dioxide as a refrigerant. In addition, two thermodynamic models for transcritical carbon dioxide cycles with and without an expansion turbine have been developed. Both models contain an internal suction-to-supercritical line heat exchange. The efficiencies of the transcritical carbon dioxide cycles will be compared with the ones of conventional HCFC-22 cycles. A second law analysis on both carbon dioxide and HCFC-22 cycles will be included.

Cyclic simulation of a model describing heat transfer from a ground-coupled water source heat pump, considering transient effects on both soil and water sides

A dynamic model has been developed to simulate transient response of a heat transfer loop coupling the heat rejection of the Freon side of a heat pump to the soil as a heat sink. The model simulates thermal storage effects in both the soil and the water side. The closed water loop side is also simulated using convective transport and conduction effects from the water to the soil. This paper presents how the model works, using a sample of real experimental data from an existing refrigeration system as the input or forcing function for the model. The simulation is repeated for 18 cycles using the same daily input on the condenser heat rejection side to observe when the effect of the initial conditions subsides and when the simulation reaches a cyclic steady state. The model shows the temperature distribution in the water along the length of the loop. It can also monitor the average soil temperature for the whole solution domain. With the advent of affordable computing power, the model should be useful for design purposes, after adequate testing. The model can be used in choosing the optimum length for a water loop according to the type of soil and heat transfer demand patterns imposed on that part of the heat pump which is coupled to the ground and some a priori design criteria.