Medium Temperature Refrigeration Research Articles

Solubility, miscibility and compatibility studies of low GWP non-flammable refrigerants and lubricants for refrigeration and air conditioning applications

Majority of currently used refrigeration and air conditioning systems utilize high GWP refrigerants such as R410A, R404A and R134a. These systems have large leak rates which leads to significant amount of release of HFC's to the environment. The growing environmental concerns are driving stringent regulations to phase out these high GWP refrigerants and move towards adoption of lower GWP refrigerants. This transition would require understanding of interaction between low GWP refrigerants and lubricating oil as well as the material compatibility with commonly used thermoplastics and elastomers. In this article, nonflammable low GWP refrigerants, R515B and R471A are introduced as the potential replacements for R410A, R404A and R134a in an air-conditioning and medium temperature refrigeration applications. Solubility and miscibility of R515B and R471A with polyol ester-based oil (POE32) is experimentally investigated over a temperature range of −20 °C to 120 °C and −30 °C to 75 °C, respectively. Further this article also presents the compatibility results of R515B and R471A (POE32) with thermoplastics and elastomers used in refrigeration and air-conditioning systems.

Defrosting frequency optimization in a cooling system: Minimization of energy consumption vs reduction of the number of on/off cycles per hour. Definition of a methodology and assessment of commercial methods based on experiments

This paper presents the definition of a new method to obtain the optimum defrosting start time for a medium temperature refrigeration system with hot-gas bypass defrosting technique. A series of experiments is performed for a monoblock prototype placed in a cold room with controlled temperature (from −4 °C to +2 °C) and relative humidity (from 70% to 90%), whereas the ambient temperature is set to 25 °C and monitored in a calorimetric chamber. Specific tests are carried out by leaving the machine in operating mode up to the complete blockage of the evaporator, measuring the corresponding defrosting phase period and frost accumulated mass. A new method for data reduction of experimental data is presented to calculate the average energy consumption of the whole cycle (on–off operation and defrosting). With these results from experiments, firstly, the average energy consumption is used as one of the decisional parameters together with the number of hourly on–off cycles of a multi-criteria optimization under constrained heating load versus cooling capacity ratio. Secondly, an assessment of the results achievable with commercial defrosting method is carried out. The new method for data reduction could be used to collect performance maps under lab conditions and then use it as multi-criteria decisional basis for a control system. The commercial methods monitoring air-evaporator temperature difference or pressure drop across the evaporator do not allow to keep the heating load versus cooling capacity below a desired threshold value under all operating conditions. Conversely, a control system based on a defined maximum allowable heating load versus cooling capacity ratio permits to control the temperature of the cabinet.

Study on the Performance of Scroll Compressor Applied for Medium Temperature Refrigeration System

Recent research shows great interest in increasing energy efficiency of a refrigeration system and finding appropriate configurations to optimize its performance. One of the main component in the refrigeration system is compressor. Therefore, the compressor plays an important role in a refrigeration system for energy performance optimization. The study is aimed to experimentally investigate temperature and energy performance of a scroll compressor applied for medium temperature refrigeration systems. Tests were conducted in a water cooled medium temperature refrigeration system. Temperature performance evaluation of the compressor referred to the IEEE Standard 112, while energy efficiency of the compressor was calculated from the energy performance of the refrigeration system. The results clearly show that evaporating temperature together with degree of superheat at suction line of the compressor can significantly affect temperature performance of the scroll compressor. Results of the study have also shown significant improvement on the compressor energy efficiency accounted for 10.4% when the evaporating temperature increases from -8.3 °C to -2.4 °C.

The Data Mining Technique Using RapidMiner Software for New Zeotropic Refrigerant

This research presents the development of environmentally-friendly and energy efficient refrigerant for medium temperature refrigeration systems that new azeotropic refrigerant mixture of hydrofluorocarbons and hydrocarbon that can retrofit in the refrigeration system using R404A. The medium back pressure refrigeration testing standard that follow CAN/ANSI/AHRI540 standard air-conditioning, heating, and refrigeration institute (AHRI) and The properties of refrigerants and refrigeration simulation system that used national institute of standards and technology (NIST) reference fluid thermodynamic and transport properties database (REFPROP) software and NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties (CYCLE_D-HX) software. The methodology uses decision tree function in datamining by rapid minor software that first of KDnuggets annual software poll that showed new azeotropic refrigerant mixture had cooling capacity, refrigerant effect, GWP and boiling point were lower than R404A but work and pressure for medium temperature refrigeration system of azeotropic refrigerant mixture were higher than R404A. The artificial intelligence (AI) by data mining technic can predictive environmentally-friendly and energy efficient refrigerant for medium temperature refrigeration. The result of refrigerant mixed by R134A, R32, R125 and R1270 and is consistent with the evolution of fourth-generation refrigerants that contain a mixture of HFCs and HCs which are required to produce a low-GWP, zero-ozone-depletion-potential (ODP), high-capacity, low-operating-pressure, and nontoxic refrigerant.

Improving Energy Efficiency in the Supermarket by Retrofitting Low E Glass Doors for Open Refrigerated

This research presents the improving energy efficiency by retrofitting doors for open refrigerated in central Thailand supermarkets that open in the daytime (06.00 am - 6:00 pm) and close in night-time (00.00 am – 6:00 am). The Materials and Methods were open refrigerated 15 cabinet and retrofitting doors for open refrigerated that 41 frames, 82 doors in medium temperature refrigeration system and measure power consumption kW, kWh by power meter data logger for analysis and summarize. The power consumption saving average per 7 days for retrofitting doors was 576 kWh/day, 39.67% that daytime 418 kWh/day, 41.93%, and night-time 116 kWh/day, 33.24%. Besides, the energy of day time more than night time because 1) The time of opening store is longer than closing store 2) In the night time, the refrigerated will close by plastic curtain 3) The request cooling load of day time is longer than day time 4) The sale area/ambient temperature of night time more than day time but the humidity was contrasted. Before retrofitting doors, the maximum and minimum of power consumption was 83.25 kw/hour and 44.73 kw/hour, respectively. Also, the power consumption swing at 38.52 kw/hour, 46.72%, and the maximum and minimum of power consumption after retrofitting doors was 33.15 kw/hour and 30.19 kw/hour, respectively. The power consumption swing at 2.96 kw/hour, 8.93%. In addition, the power consumption swing will after be retrofitting doors will less than before retrofitting doors by 1) The average cooling load will be the same as bolt conditions 2) The request cooling load of doors refrigerated will less than by product load, the swing of sale area temperature and humidity, customer behavior that effect power condition will have the low running operation. This research's investment was 21,694 €, while the payback period of this research was 14 months. Besides, within 1.1 years, that energy saving was 16,020 kWh/Month or 1,542 €/Month, 16,020 kWh/month or 192,220 kWh/Year or 18,503 €/Year.

Development of Environmentally - Friendly and Energy Efficient Refrigerant for Medium Temperature Refrigeration Systems

Development of Environmentally - Friendly and Energy Efficient Refrigerant for Medium Temperature Refrigeration Systems

A thermo-economic analysis of a combined cooling system for air conditioning and low to medium temperature refrigeration

This work investigates an integrated dual temperature system for combined air conditioning and low to medium temperature refrigeration applications (−40 °C to −10 °C). The system combines a steam driven parallel flow triple effect H2O–LiBr absorption cooling cycle with a CO2 refrigeration cycle. In this integrated system, the generated cooling effect by the H2O–LiBr absorption cycle is utilized in two different evaporators connected in series: the first evaporator as a heat sink or condenser for the CO2 refrigeration cycle, and the second evaporator as a regular evaporator for the absorption cycle. The system performance was evaluated from thermodynamic and economic viewpoints, and also detailed parametric studies were conducted. The integration of cycles assisted to significantly decrease the power requirements and annual operating cost of the CO2 refrigeration cycle as well as to increase its coefficient of performance. On the other hand, integration required a larger size absorption cooling cycle with a higher steam requirement, leading to an increase of the total capital cost and annual operating cost as well as a decrease of coefficient of performance of the absorption cycle. The economic analysis showed that integration causes a significant reduction in the annual operating cost and the unit production cost compared to the separate construction of both cycles. For the specified design and operating conditions, the annual operating cost and unit production cost of the integrated system reduced between 35.5% and 48.5% as well as between 23.4% and 34.5%, respectively.

The role of vegetable oil in water based phase change materials for medium temperature refrigeration

This research aims to investigate development of water based phase change materials (PCM) for cold thermal energy storage (CTES). Mixtures of water with small amount vegetable oil addition were chosen as candidates of the PCM that were considered to be suitable for medium temperature refrigeration application with temperature range of products between −1 °C and +5 °C. The PCM candidates were tested experimentally through DSC and T-history method. The results showed that esters of vegetable oils played very important role on the solubility of the vegetable oil in water. The esters made the investigated vegetable oil (soya oil or corn oil) mix well in water solutions and they worked as nucleating agents that could lower freezing point and reduce super-cooling of the water. It was found that addition of vegetable oils by 5% to 10% in water solution could decrease the freezing temperature from 0 °C down to respectively −3.5 °C to −6.5 °C and could also minimize degree of super-cooling of the PCM candidates.

Comparative analysis of energy improvements in single transcritical cycle in refrigeration mode

One solution to increase the energy performance in transcritical cycles in refrigeration mode is the coupling of elements to the cycle. Thus, this paper presents the analysis of configurations for achieving an increase in the performance, and in order to achieve it, it is proposed to include an internal heat exchanger, an ejector and a turbine. Both the ejector and the turbine have been considered as a solution for the irreversibilities that are produced in the expansion stage during the cooling cycle. A comparison among the three proposals is carried out, and the adequate operational conditions to which it is recommended to use one or other configuration are analyzed. The results show that the use of the ejector is recommended for output temperatures above 27 °C in the gas cooler. By doing this, an increase in the coefficient of the energy performance was achieved, which is superior to the one obtained when an intermediate heat exchanger is used. Finally, the increase in the COP as a function of the evaporation technology in each cycle is higher in the analyzed proposals, in which the increase reached is 35.85% when using an ejector, 24.21% when using a turbine, and 25.74% when using the internal exchanger. All of the configurations have been simulated under conditions of medium temperature refrigeration.

Retrofitting of R404a commercial refrigeration systems using R410a and R407f refrigerants

This paper presents an experimental analysis about the retrofitting of two commercial stationary refrigeration systems marketed by an Italian leading company. Such systems operate both at medium temperature (MT), i.e. [−5; 10]°C, and low temperature (LT), i.e. [−25; −15]°C, and they are originally designed to work with hydrofluorocarbon (HFC) R404a, known as a high global warming potential (GWP) fluid (GWP = 3922). The goal is to investigate the performances of HFC R410a (GWP = 2088) and R407f (GWP = 1825), chosen as effective alternatives to HFC R404a. Such fluids are compatible with the refrigeration systems, non-flammable and easy-available. Furthermore, they meet the European Union (EU) restrictions in force in the next future, so that they are suitable to start the transition toward efficient and eco-friendly refrigeration systems. The experimental campaign shows the feasibility of adopting R407f and R410a for the MT refrigeration system and R407f fluid for the system operating at LT.

Analysis on energy saving potential of integrated supermarket HVAC and refrigeration systems using multiple subcoolers

The paper presents a model-based analysis on the energy saving potential of supermarket HVAC (heating, ventilating, and air-conditioning) and refrigeration systems using multiple subcoolers among the high-temperature HVAC system, the medium-temperature refrigeration system, and the low-temperature refrigeration system. The principle of energy reduction is to have the higher COP (coefficient of performance) system generate more cooling capacity to increase the cooling capacity or reduce the power consumption of the lower COP system. The subcooler could be placed between the medium-temperature and low-temperature systems, between the high-temperature and medium-temperature systems, and between the high-temperature and low-temperature systems. All integration scenarios of adding one, two and three subcoolers have been investigated. The energy saving potential varies with the load ratio between high-, medium- and low-temperature systems, COP of three systems, and the “on-off” duty time of HVAC system. The optimal sequence of adding subcoolers is also proposed.

Heat Exchanger Design for CO2 Cycle with a Linear Compressor

Hermetic linear compressors already have been developed for subcritical cycles, especially for small-capacity refrigeration systems, which have a refrigeration capacity less than 500 W and have demonstrated better performance potential than conventional compressors. In this paper, the performance potential of a transcritical carbon dioxide (CO2) cycle with a linear compressor is explored for medium-temperature refrigeration systems, which have a return air temperature range from −2°C to 6°C, through CO2 cycle simulation using compressor efficiencies measured. In addition, the design of the heat exchanger for such systems was practiced. The simulated results of the transcritical CO2 cycle performance showed that the cooling capacity was 235 W at 40.5°C ambient temperature and the coefficient of performance was 1.31 at 32.2°C ambient temperature. The heat exchangers were then designed using a verified heat exchanger design software. As a target application, a 200 liter effective volume refrigerator cabinet was selected, and its refrigeration load was evaluated by using load calculation software. When the CO2 linear compressor with suitably designed heat exchangers was applied to the selected refrigeration cabinet operating at medium temperature refrigeration conditions, the simulated results showed that the designed CO2 system based on a linear compressor could provide sufficient refrigeration capacity.

An evaluation of options for replacing HCFC-22 in medium temperature refrigeration systems

Due to the ongoing global phase-out of R-22, which is still the most widely used refrigerant around the world, there is a need to replace this refrigerant in many different applications. This paper focuses on a thorough evaluation of the R-22 replacement options for medium-temperature refrigeration applications. It includes a thermodynamic analysis, comparison of heat transfer and pressure drop characteristics, system performance comparisons using a validated detailed system model, safety issues, and determination of the environmental impact of refrigerant selection. Three potential alternatives to the R-22 were studied: two HFCs (404A and R-410A) and one HC (R-290). An HFC refrigerant, R-410A, is shown to be an efficient and environmentally acceptable option to replace R-22 in medium temperature applications.

Frost formation and defrost control parameters for open multideck refrigerated food display cabinets

In order to achieve the required air and product temperatures in refrigerated food display cabinets, the evaporator coils, which are normally located in the base of the cabinets, operate at temperatures below the freezing point of water. The air which is circulated over the evaporator coil is cooled below its dew point and water vapour present in the air condenses and eventually freezes on the coil surface. With continuous operation of the coil, frost will accumulate on the coil surface leading to a decrease both in the air flowrate and in the overall heat transfer coefficient. In order to maintain satisfactory performance, evaporator coils are defrosted periodically. Although different defrost control strategies can be employed, for simplicity and cost considerations, defrosting in supermarket refrigeration systems is usually controlled by a pre-set time cycle. It is widely acknowledged, however, that time-based defrost may cause a number of unnecessary defrost cycles and this reduces the energy efficiency of the refrigeration systems as well as the accuracy of temperature control of the cabinets. Implementing defrost only when it is needed or on ‘demand’ should reduce the number of defrost cycles and lead to savings in energy and improved product quality. This paper reports on field and experimental investigations on the processes of frosting and defrosting of medium-temperature display cabinet evaporator coils. The results show that for medium-temperature refrigeration applications where the environment temperature is kept reasonably constant, the store humidity is the primary parameter influencing the rate of frost formation. Using relative humidity as a control parameter the defrost frequency can be reduced considerably without affecting cabinet performance and product integrity. Alongside the effect of relative humidity, the paper also considers the effects of other performance parameters on the processes of frosting and defrosting such as cooling time and length of previous defrost cycle, and discusses ways in which some of these parameters may be used to implement defrost on demand.