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R134a and various mixtures of R22/R134a as an alternative to R22 in vapour compression heat pumps
Abstract
The performance of an air to water vapor compression heat pump has been investigated experimentally. The main purpose of this study was to investigate the possibilities of using R134a as a working fluid to replace R22 for vapor compression heat pumps. Pure R22, pure R134a and some binary mixtures of R22/R134a were considered as working fluids. The performance of the system was characterized by mixture ratio, COP and evaporator air inlet temperature. Comparisons are made between the pure refrigerants and refrigerant mixtures on the basis of the COP. Experimental results show that the mixture ratio affects the COP significantly, and the COP could be improved by using pure R134a or an appropriate mixture of R134a/R22 instead of pure R22. The maximum COP occurred at a mixture ratio of around 50/50% R134a/R22. For a mass percentage of 50% of R134a, the COP was enhanced by about average 25%.
... In the twentieth century chlorofluorocarbons (CFCs) such as R12 was widely used in air-conditioning system applications, and was recognised as an excellent heat transfer medium. This is due to the superior thermo-physical properties such as non-flammability, non-toxicity, high thermal conductivity, and chemical stability [7]. However, the chlorine atoms in CFCs have a major impact on ozone depletion. ...
... However, the chlorine atoms in CFCs have a major impact on ozone depletion. Karagoz, Yilmaz [7] indicated that chlorine atoms liberated from CFCs act as catalysts in ozone depleting reactions [7]. Strong UV light breaks apart the CFC molecule and releases chlorine atoms. ...
... However, the chlorine atoms in CFCs have a major impact on ozone depletion. Karagoz, Yilmaz [7] indicated that chlorine atoms liberated from CFCs act as catalysts in ozone depleting reactions [7]. Strong UV light breaks apart the CFC molecule and releases chlorine atoms. ...
In recent years, conservation of energy has become a challenging issue in air-conditioning applications. In order to overcome this issue, many researchers have recommended the use of a Parallel Flow Condenser and a low Global Warming Potential and Ozone Depletion Potential refrigerant, such as R32, in air conditioning systems. However, PFC faces the critical challenge of flow maldistribution in the tubes. This literature review mainly examines the refrigerant maldistribution problem which has been investigated by previous researchers. It was found that many of the researchers did not properly analyse the influence of flow maldistribution profiles on the performance degradation of heat exchangers. In order to have a comprehensive analysis of tube-side maldistribution in Parallel Flow microchannel heat exchangers, it is recommended that the influence of the higher statistical moments of the probability density function of the flow maldistribution profiles on performance degradation be quantified. Additionally, R32 maldistribution should be analysed and compared with R410A, which is the current commonly used refrigerant in air conditioning units. Moreover, in order to have a realistic simulation of the effect of refrigerant flow maldistribution profiles on performance degradation of heat exchangers, the effect of superheat and sub-cooling must be analysed.
... In the twentieth century chlorofluorocarbons (CFCs) such as R12 was widely used in air-conditioning system applications, and was recognised as an excellent heat transfer medium. This is due to the superior thermo-physical properties such as non-flammability, non-toxicity, high thermal conductivity, and chemical stability [7]. However, the chlorine atoms in CFCs have a major impact on ozone depletion. ...
... However, the chlorine atoms in CFCs have a major impact on ozone depletion. Karagoz, Yilmaz [7] indicated that chlorine atoms liberated from CFCs act as catalysts in ozone depleting reactions [7]. Strong UV light breaks apart the CFC molecule and releases chlorine atoms. ...
... However, the chlorine atoms in CFCs have a major impact on ozone depletion. Karagoz, Yilmaz [7] indicated that chlorine atoms liberated from CFCs act as catalysts in ozone depleting reactions [7]. Strong UV light breaks apart the CFC molecule and releases chlorine atoms. ...
... R448A provided 9 to 20% energy savings for supermarket refrigeration systems [14]. Detailed studies on energy and exergy analysis of cooling systems using alternative refrigerants can be found in the literature [15][16][17][18][19][20][21][22][23][24]. Park et al. performances of two pure hydrocarbons and seven mixtures composed of propylene, propane, HFC152a, and dimethylether were measured to substitute for HCFC22 in residential air-conditioners and heat pumps [15]. ...
... Joudi and Al-Amir investigated performance of residential air conditioning systems using R22 and alternatives R290, R407C, R410A [21]. Karagoz et al. investigated the possibilities of using R134a as a working fluid to replace R22 for vapor compression heat pumps [22]. Chen carried out performance and environmental characteristics of R410A and R22 residential air conditioners [23]. ...
... This is attributed to the additional degrees of freedom during blend design, facilitating a targeted fine-tuning of blend properties within environmental/safety constraints and technical requirements. The use of refrigerant blends is not uncommon, as seen with the release of R410A with the phase-out of chlorodifluoromethane (R22) and dichlorodifluoromethane (R12) [24,25]. Similarly, synthetic medium-GWP blends (i.e., GWP ≈ 500-750) exploiting low-GWP HFOs and non-flammable HFCs [26] such as R513A and R450A, have been proposed as mid-term replacements for R134a (GWP = 1300), given their high technical performance [27,28]. ...
... Direct hot water production uses 4% of all the electricity used, according to a study conducted in China [42]. Comparing the heat pump performance of the several operating refrigerants, it was found that R134a provides the most practical replacement for R22, specifically for low-temperature situations [43]. It is evident that solar-assisted heat pump (SAHP) systems surpass conventional processes when compared to the coherence of conventional heat pumps or conventional solar air heaters [44]. ...
This paper describes the working principle of hybrid heat pump system which is used for the applications of water heating in the domestic purpose along with flow rate optimization of the condenser cum storage tank. The performance analysis of experimental heat pump water system of heating to minimize domestic energy consumption was also reported. Serpentine tube arrangement in the flat plate collector has been used for this study to collect solar energy to reduce the compressor work. The objective of this paper is to optimize the use of hot water and hot water output to maintain a constant temperature in the condenser cum storage tank of water for the hot water supply during nighttime. The current study performs flow optimization depending on an experimental examination for a water heater with a solar aided heat pump. Results clearly show the best system's performance as comparing with electric geyser. Experimental results also depicted that the system performance and COP are high in the sunrise time.KeywordsRefrigerantHot waterSolar water heating system
... This is attributed to the additional degrees of freedom during blend design, facilitating a targeted fine-tuning of blend properties within environmental/safety constraints and technical requirements. The use of refrigerant blends is not uncommon, as seen with the release of R410A with the phase-out of chlorodifluoromethane (R22) and dichlorodifluoromethane (R12) [24,25]. Similarly, synthetic medium-GWP blends (i.e., GWP ≈ 500-750) exploiting low-GWP HFOs and non-flammable HFCs [26] such as R513A and R450A, have been proposed as mid-term replacements for R134a (GWP = 1300), given their high technical performance [27,28]. ...
... Residential air conditioning R22 [11][12][13][14][15][16][17][18] (retrofitting R22 are R134a (GWP-1300), R407C (GWP-1624), R407A ...
Low global warming potential (GWP) refrigerants for the next-generation air conditioning systems have been investigated with target domestic applications. High-GWP refrigerants are mostly used in climate control applications such as heating, ventilation and air conditioning (HVAC) and refrigeration systems. The majority of refrigerants are responsible for significant environmental issues such as ozone layer depletion and global warming. The Montreal Protocol and the Kyoto Protocol have been implemented to address such issues. In the meantime, authorities in many countries have taken the initiative to phase out the usage of environmentally harmful refrigerants in vapor compression refrigeration systems. Following the global warming mitigation scheme by many signatory countries, research interest has been focused on finding alternative refrigerants with low or ultra-low GWP. This study considered the research trend and development of low-GWP refrigerants while examining system performance, safety issues, and the equivalent environmental impact as the critical assessment parameters. Here, the focus is primarily set on the potential of refrigerant blends (HFCs + HFOs) where the GWP value of 300 is set as the threshold value. Targeted for domestic heat pump systems, the performance of such systems using various refrigerant blends is collated and discussed. Many blends offer innovative drop-in replacements for R410A-conforming F-gas regulations. The technical difficulties and realistic remedies for the existing refrigerants are also discussed
... A minichannel fi nned heat exchanger was used as an evaporator in a study to evaluate thermal performance, heat transfer rate, and the refrigerant distribution in the manifold (Arteconi et al., 2014). Refrigerants replacing with the low ODP and GWP gases and also using their mixtures in a system have been investigated for different mass fractions and refrigerant types (Comakli et al., 2009;Karagoz et al., 2004). A dual-mode heat pump coupled with cold and hot thermal storages was suggested as a smart high-effi ciency grid (Liu et al., 2017). ...
H eat pumps are seen as a highly efficient promising technology for space heating and cooling. Their efficiency has been
widely studied for different types of heat pumps operating with various energy sources including air, ground, and water.
However, different components of the heat pump need to be closely investigated to improve the performance of the system.
This study surveys the effects of compressor cooling fan, to evaluate how a heat pump system behaves at different fan
speeds. Refrigerant R134a has been used as a circulating fluid in the system. The results obtained from detailed experiments
are analyzed to optimize the performance of the entire system using a compressor cooling fan, considering COP, P–h diagrams, efficiency, and thermodynamic properties. It is concluded that cooling the compressor has a remarkable effect on the
thermodynamic state of refrigerant which leads to a positive influence not only on the compressor efficiency but also on the
entire heat pump unit.
... Most of the previous research focused on alternative refrigerants to R22 at low and medium condensing temperatures. Karagoz et al. [3] studied the possibilities of using R134a and some binary mixtures of R22/R134a as alternative refrigerants to R22 for a vapor compression heat pumps. The experimental results showed that the mixture ratio affects the COP, and the COP could be improved by using pure R134a or an appropriate mixture ratio of around 50/ 50% R134a/R22. ...
... Binary and ternary refrigerant mixtures have been widely analyzed to optimize system efficiency in cooling device like refrigerator and freezer [20,43,44] , and air conditioning units like heat pumps [22,28] . ...
Heat pumps and refrigerators are two systems with different usage, but same working principles. Generally, HPs work in steady state condition and specific thermodynamic cycle, but refrigerator or freezer apparatus have variable cycle and work in the unsteady condition.
In this study, two different data sources are gathered to analyze thermodynamic differences between two mentioned systems. Initially, an existing heat pump unit is analyzed in different working conditions with different refrigerants and then the unit is converted to a refrigeration device to compare their thermodynamic conditions and treatments.
Thermodynamic laws, COP value and efficiency, compressor power consumption, optimum charge amount, and flow rate of secondary fluid are main parameters which are considered to compare heat pump and refrigerator performances by using several refrigerants including R134a, R407c, R22, and R404a.
In the case of freezer mode, entropy reduction in compressor and COPL drop to very low values are other substantial issues discussed in this research. It was also revealed that, optimal charge amount of the freezer is 15-25% lower than that of the system when works in HP mode. Experiments showed that, in some cases COP of the heat pump was even more than 100 times greater than that of the freezer.
... 49 The COP of 1.93 is comparable to systems with similar operating conditions using R-134a. 50 A relaxed solution to the mixture design problems shows a COP value of 1.97. Thus, the discrete group variables are made continuous to obtain a theoretical best solution. ...
An integrated optimization-based framework for product and process design is proposed. The framework uses a set of methods and tools to obtain the optimal product-process design solution given a set of economic and environmental sustainability targets. The methods and tools required are property prediction through group contributions, unless supported with a database, computer-aided molecular and mixture/blend design for generation of novel as well as existing products and mathematical programming for formulating and solving multi-scale integrated process-product design problems. The application of the framework is demonstrated through three case studies: (i) refrigeration cycle unit for R134a replacement, (ii) a mixed working fluid design problem for R134a replacement, and (iii) pure solvent design for water-acetic acid LLE extraction. Through the application of the framework it is demonstrated that all solutions satisfy product, process, economic and environmental targets simultaneously. The solution is obtained through a direct deterministic mathematical optimization strategy. The framework proposed in this work is generic and can be applied to a wide range of problems where an integrated solution to process-product design is beneficial.
... ?? 1 ?? HCFCs?HFCs ???? ODP ??????????????????? GWP ??? ???? " ???? " ???????????????? S. Karagoz [15]?????????????? R134a ?? R22 ?????????R134a ? COP ?? R22 ?? ? ...
首先讲述了温室效应和臭氧空洞的形势严峻性，然后从环保、安全、热力性能等方面介绍了R22替代制冷剂的研究现状，并通过对比总结了常见的几种替代制冷剂的特点。依据适应当前国情的需要，总结了国内外学者对提高自然制冷剂安全性研究并进行了综述。本文对R290和R1270加入HFO制冷剂(充当阻燃剂)展开分析和展望，以期盼可以有效的解决制冷剂替代这一热门问题。 With the increasing greenhouse effect and ozone depletion, the author introduces the research status of R22 alternative refrigerants from the aspects of environmental protection, safety, and thermodynamic properties. We make a conclusion about some alternative refrigerants. In order to meet the need of national conditions at present, the domestic and foreign scholars have made a summary of the research on improving the safety of natural refrigerants. In this paper, we discuss about the issue that the HFO refrigerants (as a flame retardant) are mixed into R290 or R1270 re-frigerant to look forward to solve the refrigerant alternative.
... Also, focus has been on how to improve energy efficiency, heat pump performance and reduce primary energy consumption [5]. The proposed replacements for the CFCs are pure hydrochlorofluorocabons (HCFCs), hydrofluorocarbons (HFCs), natural refrigerants (NRs) and zeotropic and azeotropic mixtures of environmentally benign refrigerants [6]. Alternatives for R22 -which has been extensively used as residential heat pump and air-conditioning systems for more than five decades are R134a, R404a, R407c, R410a,b, R508 etc. [1,7,8]. ...
An experimental study of convective condensation heat transfer of R134a was conducted in an inclined smooth copper tube of inner diameter of 8.38 mm. The test condenser had a straight copper tube section with an effective length of 1.488 m and was cooled by water circulated in the surrounding annulus in a counter-flow arrangement. The rate of heat transfer was maintained at an average of 250 W throughout the experiment while the vapour qualities ranged between 0.1 and 0.9, mass flux between 200 kg/m 2 s and 400 kg/m 2 s for inclination angles varied between-90 o (vertical downward) and +90 o (vertical upward) covering the whole range of inclination at saturation temperature of 50 o C. The results show that the inclination angles and vapour qualities strongly influence the coefficient of heat transfer and an optimum inclination angle was found to be between-15 o and-30 o (downward flow). The developed correlation gave an average and mean deviations of 0.81% and 9.91% respectively for horizontal flow and, 9.86% and 21.21% respectively for vertical downward flow.
... Also, focus has been on how to improve energy efficiency, heat pump performance and reduce primary energy consumption (Churi and Achenie 1997). The proposed replacements for the CFCs are pure hydrochlorofluorocabons (HCFCs), hydrofluorocarbons (HFCs), natural refrigerants (NRs), and zeotropic and azeotropic mixtures of environmentally benign refrigerants (Karagoz et al. 2004). Alternatives for R22-which has been extensively used as residential heat pump and air-conditioning systems for more than five decades are R134a, R404a, R407c, R410a,b, R508, etc. (Cavallini 1996;Jung, Song, and Park 2000;Li, Guo, and Wang 2002). ...
An experimental study of convective condensation heat transfer of R134a was conducted in an inclined smooth copper tube of inner diameter of 8.38 mm. The mean vapour quality ranged between 0.1 and 0.9, mass flux between 200 kg/m2s and 400 kg/m2s, inclination angle between -90o (vertical downward) and +90o (vertical upward) at saturation temperature of 50oC. The results show that inclination angle and mean vapour quality strongly influence the coefficient of heat transfer. The developed correlation gave an average and mean deviations of -3.44% and 9.22% respectively for horizontal flow and, 5.25% and 19.41% respectively for vertical downward flow.
... Most of the previous research focused on alternative refrigerants to R22 at low and medium condensing temperatures. Karagoz et al. [3] studied the possibilities of using R134a and some binary mixtures of R22/R134a as alternative refrigerants to R22 for a vapor compression heat pumps. The experimental results showed that the mixture ratio affects the COP, and the COP could be improved by using pure R134a or an appropriate mixture ratio of around 50/ 50% R134a/R22. ...
... As such, they have the ability to decrease the irreversibility associated with heat transfer over a finite temperature difference across the working fluid and the thermal heat source or heat sink reservoir. Zeotropic mixtures as working fluids have been investigated for heat pumps [6][7][8] and vapor compression cycles [8][9][10]. The use of zeotropic mixtures as working fluids for the ORC has gained interest recently. ...
The thermodynamic performance of non-superheated subcritical Organic Rankine Cycles (ORCs) with zeotropic mixtures as working fluids is examined based on a second law analysis. In a previous study, a mixture selection method based on a first law analysis was proposed. However, to assess the perfor-mance potential of zeotropic mixtures as working fluids the irreversibility distributions under different mixtures compositions are calculated. The zeotropic mixtures under study are: R245fa–pentane, R245fa–R365mfc, isopentane–isohexane, isopentane–cyclohexane, isopentane–isohexane, isobutane– isopentane and pentane–hexane. The second law efficiency, defined as the ratio of shaft power output and input heat carrier exergy, is used as optimization criterion. The results show that the evaporator accounts for the highest exergy loss. Still, the best performance is achieved when the condenser heat pro-files are matched. An increase in second law efficiency in the range of 7.1% and 14.2% is obtained com-pared to pure working fluids. For a heat source of 150 °C, the second law efficiency of the pure fluids is in the range of 26.7% and 29.1%. The second law efficiency in function of the heat carrier temperature between 120 °C and 160 °C shows an almost linear behavior for all investigated mixtures. Furthermore, between optimized ORCs with zeotropic mixtures as working fluid the difference in second law efficiency varies less than 3 percentage points.
... It has been proposed various substitutes to R22: R134a, R404A, R407C, R410A, R410B, R508, etc. (see Table 1). Among these alternatives, three directions seem to be gaining most favorable support depending on application and system design: the use of a look-alike zeotropic mixture such as 407C; the use of higher pressure, nearly azeotropic mixtures R410A or R410B; and the use of the lower pressure refrigerant R134a [2]. ...
In this study, refrigerants R22 and R404A five of their binary mixtures which contain about 0%, 25%, 50%, 75% and 100% mass fractions of R404A were tested. It is investigated experimentally the effects of gas mixture rate, evaporator air inlet temperature (from 24 to 32 °C), evaporator air mass flow rate (from 0.58 to 0.74 kg/s), condenser air inlet temperature (from 22 to 34 °C) and condenser air mass flow rate (from 0.57 to 0.73 kg/s) on the coefficient of performance (COP) and exergetic efficiency values of vapor compression heat-pump systems. To determine the effect of the chosen parameters on the system and optimum working conditions, an experimental design method suggested by Genichi Taguchi was used. In this study, it was observed that the most effective parameters are found to be the condenser air inlet temperature for COP and exergetic efficiency.
This paper deals with the condensation heat transfer characteristic of propane (R290) inside a 4-mm-inner-diameter (ID) horizontal smooth tube. Three-dimensional Computational Fluid Dynamics (CFD) simulations were performed based on the volume of fluid (VOF) multiphase flow model and shear stress transport (SST) k-ω turbulence model together with a dedicated user-defined function (UDF) compiled for the phase change model. The flow pattern and velocity field distribution were derived, and the condensation heat transfer coefficient (HTC) versus mass flux, saturation temperature, and heat transfer temperature difference were analyzed in detail. The results demonstrate that the area-weighted average condensation HTC of the wall takes on an average increase rate of 33.69% as the mass flux increases from 180 to 360 kg/(m2 s), and an average decrease rate of 19.83% with the increasing saturation temperature. Besides, the local condensation HTC swells more than twice as the temperature difference increases from 5 to 20 K. Compared with the saturation temperature, the mass flux and heat transfer temperature difference have a more remarkable effect on the condensation flow pattern and velocity field distribution. Under the specific conditions, the flow condensation of R290 inside the tube can be successively transformed from annular flow, annular wavy flow, half annular flow to plug flow, and the annular flow region can be enlarged with increasing mass flux. Comparing the simulated results with those of the experiment, it can be concluded that the numerical model adopted in this paper has good accuracy and the relative deviation is within ± 20%.
In traditional industrial applications and MEE/MSF desalination system, steam production is usually the technical basis for heating, processing or fresh water accumulating. However, steam boilers are environment unfriendly thus being prohibited of usage in urban areas. High temperature heat pump (HTHP) integrated with flash tank is promising substation of boiler to be employing in steam producing. The large amount of industrial waste heat could also be recovered in this way. In this article, theoretical model is proposed to predict and investigate the capacity and efficiency of a steam production HTHP system using industrial waste heat, while a testbed is also built to validate the simulated results and to evaluate performance of the system. The influence of the operating conditions on the heating capacity, compressor efficiency and steam prices are also illustrated. The results show that the COP increase from 3.06 to 10.95 with the increase in evaporating condition and decrease in steam pressure significantly. The specific price of steam is 189 to 88 RMB/t at 200 kPa steam pressure, and 126 to 49 RMB/t at 110 kPa.
La predicción del coeficiente de ebullición forzada en líquidos está sujeta a grandes errores debido a la dificultad para especificar las características de los patrones de nucleación y circulación del fluido en este proceso. Sin embargo, el coeficiente de ebullición forzada forma parte del cálculo del coeficiente global de transferencia de calor en un evaporador y el error en su cálculo se puede propagar en la simulación del evaporador. Por tanto, es importante reducir los errores en el cálculo de este parámetro con el objetivo de optimizar el diseño y simulación de comportamiento de evaporadores, usados tanto en aplicaciones de refrigeración como aire acondicionado. El objetivo de esta investigación es realizar una comparativa de las correlaciones de Chen, Shah, Gungor y Winterton, Kandlikar, Liu y Winterton, y Panek para la obtención del coeficiente de ebullición forzada para el refrigerante R134a circulando por el interior de un intercambiador carcasa-tubos. Las mediciones son realizadas sobre una típica instalación de compresión de vapor comercial en un rango variado de condiciones de operación.
Natural refrigerant ammonia R-717 and synthetic azeotropic refrigerant R-507 (a blend containing 50% R-143a and 5% R-125 by weight) are used in a wide range of refrigeration systems especially in low temperature applications. R-717 and R-507 are ozone friendly refrigerants, which have no Ozone Depletion Potential (ODP). Global Warming Potential (GWP) of R-717 and R-507 is equal to zero and 3300 respectively. The high amount of R-507 GWP demonstrates its negative effect on the earth’s climate change. In this study, a refrigerated warehouse located in Cincinnati, Ohio was modeled and the total energy demand and Coefficient of Performance (COP) was evaluated by eQUEST using two scenarios. The R-717 and R-507 were used as refrigerant in the first and second scenarios, respectively. The results showed that using R-717 in the refrigeration system leads to a 15% energy saving and a higher COP compared to R-507 in all working conditions. The only exception is that at an evaporating temperature below −35°C which COP values of both refrigerants are approximately equal.
Energy efficiency is an essential component of water heating considerations in the overall efforts to achieve national energy saving goals. Although heat pump water heaters have been around for over three decades, this technology has only matured in recent years, in part because of improved systems and infrastructure as well as emerging energy conservation standards on water heating. The goal of this study is to provide a comprehensive and in-depth review of heat pump water heater research on system energy efficiency and performance topics. The study focuses on laboratory and field (in-situ) experiments and measurements, modeling of energy use and efficiency, technological modifications or upgrades, and control operation strategies; with emphasis on the Coefficient of Performance (COP), reliability, and energy savings. The review shows that while most of current heat pump water heater systems operate in the COP range of 1.8-2.5, there are some potential technological updates that could augment the current systems and increase COP to a range of 2.8-5.5. Issues that could dampen the adoption of these technologies are discussed. The review identified key areas for future studies that are still lacking in support of various changes suggested for increasing heat pump water heaters efficiency and performance.
In our society, there is an ever increasing need for electricity. However, today most of the electricity is generated by burning fossil fuels in a thermal power plant. A proposed alternative is to make use of low temperature heat from renewable sources (geothermal and solar) or waste heat (excess heat that is dumped into the atmosphere) in an organic Rankine cycle (ORC) to generate electricity. The purpose of the presented work is to support further adoption of ORC technology. To achieve this, two main challenges need to be resolved. First, sound criteria should be devised to compare and size ORCs and secondly the performance of the ORC should be increased further. From literature it is clear that novel ORC architectures have the opportunity to increase the performance of the basic subcritical ORC. However these studies are not cross comparable. As such, a new screening approach is created which rigorously compares and quantifies the potential of three different ORC architectures. Secondly, the sizing and the financial appraisal of the ORC is tackled by introducing a multi-objective optimization which combines financial and thermodynamic criteria in the optimization objectives. Finally, experimentally validated part-load models of the ORC were developed. These part-load models are crucial to predict the actual power output of time varying heat sources like waste heat streams. In addition, the models permit to investigate the concept of retrofitting existing subcritical ORCs to work under the more optimal working regime of partial evaporation.
An industrial heat pump can upgrade heat from a low temperature level to a high temperature level with the aid of an external energy source. It has received considerable attention as an efficient means of waste energy recovery in the recent years in China. This paper summarizes the research work done and advances in the application of industrial heat pump systems in China, including advances in refrigerants, multistage system, double-effect absorption system, compression–absorption system, solar assisted system, and chemical heat pump system. Industrial heat pumps used in three industrial fields (drying of wastewater sludge, crude oil heating in oil field, and process heating in printing and dyeing) are discussed in detail. Three basic problems in designing an engineering heat pump system, i.e., selection of the type of heat pump and determination of its capacity, energetic and exergetic analyses of the heat pump, and estimation of investment payback time are discussed in the above three industries, respectively. Further research needs in China on industrial heat pumps are proposed, which may also be beneficial to the international community.
Although the world is aware of the hiking level of global warming, still numerous conventional air-conditioners are being put up for application in buildings adding contribution to global warming. To resolve this issue, the combined heating and cooling cycle is proposed by providing an additional heat rejecter next to compressor in a traditional vapor compression refrigeration cycle. Design and analysis for the proposed cycle is done with R134a as working fluid. The optimum operating conditions are predicted, delivering maximum COP of 3.36 at 3 bar at mass flow rate of 1 kg/s. Approximately, 31 kW of process heat has been gained with 45.5 tons of refrigeration. This work infers that with small amendment in traditional refrigeration cycle results in an increased efficiency and converts from only cooling to cooling cogeneration plant.
In this study, a compressor, driven by external heat, was used in the vapor compression refrigeration system instead of an electrically driven compressor and the performance of this compressor was determined. R-134a, an ozone-friendly refrigerant, was used in the system. In the first test, the designed and constructed compressor was driven by electricity. In the second test, the heat energy and electricity were applied to the compressor at the same time. The results showed that COP of the system, in the first test, varied in between 2.77 and 3.49, COP of the system, in the second test, varied in between 2.11 and 2.02. In addition, in the tests which were carried out by applying heat energy, it was observed that the speed of the compressor increased by 4.5 % and the electricity consumption decreased 8.5 %.
The goal of this work is to determine the optimum set of parameters by using the Taguchi method in vapour compression heat pump systems. The experimental apparatus consist of an air-to-liquid vapor compression heat pump, a water cooled condenser, a forced air evaporator, an electrical air and water heaters, and various measuring elements and other auxiliary equipments. Refrigerants R22, R407C, and five of their binary mixtures which contain about 0%, 25%, 50%, 75%, and 100% mass fractions of R407C were tested. To determine the effect of the chosen parameters on the system and optimum working conditions, an experimental design method suggested by Genichi Taguchi was used. The most effective parameters are found to be the condenser water mass flow rate for the coefficient of performance and to be condenser water inlet temperature for the exergetic efficiency.
R22 being a HCFC is to be phased out soon as per the Montreal protocol. This paper presents the experimental performance study of an air-conditioner retrofitted with M20 (a refrigerant mixture of R407C, R600a and R290 in the mass fraction 80:10.96:9.04 respectively). M20 is considered as a substitute for R22 in window air-conditioners with mineral oil as the compressor lubricant. Previously, the performance of the same mixture has been reported with 19% extra condenser length as compared to that in the R22 system. In this study, experiments were conducted in a 5.25 kW window airconditioner to assess the potential of M20 as a retrofit refrigerant without making any system alteration other than changing the capillary. The system performance study was carried out with R22 and later with the M20 charge in a psychrometric test facility as per BIS and ASHRAE standards. Experimental results showed that with the M20, the system had 4.18% to 7.47% lower cooling capacity with respect to that of R22. The COP for the M20 refrigerant was lower, in the range of 0.58% to 7.78% than that of R22. Hence, M20 can be used as a drop- in-substitute for R22 in window air-conditioners but with a marginal reduction in cooling capacity.
This study presents a comparative performance analysis of a direct expansion geothermal evaporator using R410A, R407C and R22 as refrigerants. The main goal is to predict the best refrigerant capable of serving as a substitute for R22. A validated geothermal evaporator model developed by our research team was used. The simulation results show that for low refrigerant flow rate, the R410A DX evaporator shows better performance than that of R22, but from the pressure drop observed and superheating recorded with the former, it can be concluded that R407C is the best fluid to replace R22 in the DX GHP. That notwithstanding, to minimize pressure drop, especially for high refrigerant flow rates, R410A would be a better choice for the design of new DX systems.
An analytical investigation on the performance of adsorption–compression hybrid refrigeration systems with two different cycle configurations, cascade type and subcool type has been performed. In the former type, a cascade condenser is used which works as a condenser for mechanical compression cycle and evaporator for adsorption cycle. In the latter type, an evaporative subcooler is used which subcool the fluid of mechanical compression cycle. The refrigerants examined for the mechanical compression cycle are R134a, R152a, R1234yf and R1234ze whereas ethanol is the refrigerant for the adsorption cycle. The main feature of the proposed system is the capability to significantly reduce work input for the mechanical compressor which results up to 30% energy saving potential depending on the selection of refrigerant and system configuration. Based on the thermodynamic properties and laws the study analyzed the effect of the major design parameters such as evaporation temperature, compressor discharge pressure and desorption temperature on the system performances.
An analytical investigation on the performance of adsorption–compression hybrid refrigeration systems with two different cycle configurations, cascade type and subcool type has been performed. In the former type, a cascade condenser is used which works as a condenser for mechanical compression cycle and evaporator for adsorption cycle. In the latter type, an evaporative subcooler is used which subcool the fluid of mechanical compression cycle. The refrigerants examined for the mechanical compression cycle are R134a, R152a, R1234yf and R1234ze whereas ethanol is the refrigerant for the adsorption cycle. The main feature of the proposed system is the capability to significantly reduce work input for the mechanical compressor which results up to 30% energy saving potential depending on the selection of refrigerant and system configuration. Based on the thermodynamic properties and laws the study analyzed the effect of the major design parameters such as evaporation temperature, compressor discharge pressure and desorption temperature on the system performances.
This study highlights theoretical energetic and exergetic performance evaluation results of Bethe-Zeldovich-Thompson (BZT) fluids in geothermal heat pumps. In this study, hexafluoroethane (R116), octafluoropropane (R218), and octafluorocyclobutane (RC318) were selected as possible alternative replacements to the traditional refrigerants in geothermal heat pumps. According to the calculations, coefficient of performance of 101 kW geothermal heat pumps (COPHP) changes with range between 3.84, 3.08, and 2.92 for octafluorocyclobutane (RC318), hexafluoroethane (R116), and octafluoropropane (R218), respectively. Moreover, R116 shows the maximum exergy efficiency 68% among the selected BZT fluids.
In the vapour compression plants possible leaks can vary the composition of a zeotropic refrigerant mixture. The main aim of this paper is to verify experimentally if the plant performances are restored with a proper recharge, when leaks are imposed. As for the R407C mixture the percentage of the less volatile component (R134a) increases, while the percentage of the more volatile components (R32 and R125) decreases when leaks occur. The experimental tests have been realized determining refrigerant leaks from the liquid receiver placed at the condenser outlet and measuring the properties in steady state condition. The recharge is realized in different ways: with R407C, with R134a and R410A or with R32 R125 and R134a. The different solutions are then compared from the economical point of view, in terms of COP, refrigeration power and air temperature at the evaporator outlet, adopting an iteration method. This method determines the real composition of a zeotropic mixture working in a compression plant, when only the temperature and pressure values at the expansion valve inlet and outlet are known.
This paper presents the cooling performance of several CO2/propane mixtures measured in air-conditioning test rig at several conditions. The discharge pressure of CO2/propane mixtures is reduced with increasing mole fraction of propane and their reduced values coincide approximately with the circulation concentrations of propane. Since propane is the refrigerant having a higher refrigerating effect and a much lower vapor density than CO2, adding propane to CO2 improves the system efficiency and reduces the cooling capacity. The temperature glide effect of CO2/propane mixtures on the cooling performance was analyzed based on the experimental data. To utilize the temperature glide effect successfully, a sufficient heat exchange area is required, and the temperature gradient of refrigerant must be similar to that of secondary heat transfer fluid. It is better the temperature change of refrigerant can prevent pinching with that of the secondary heat transfer fluid.
HFCs are the leading options for replacing R22 in air conditioning applications due to the Montreal Protocol. Among the HFCs, one of the more promising refrigerants is R407C, a zeotropic refrigerant mixture with a glide temperature difference of roughly 6°C. However, R407C could not be used as a drop-in substitute since HFCs are immiscible with conventional mineral oils and POE is used as a lubricant. But POE is highly hygroscopic in nature and will cause adverse effects in the system. Previous research reported that M20 (80% R407C and 20% HC blend by weight) could be a viable substitute without changing the mineral oil. But, in that study, the condenser tube length was increased by 19% to limit the discharge pressure within the acceptable limits of an existing R22 compressor. In the present study a test is conducted to assess the performance of M20 as a drop-in substitute for R22 in a window air conditioner, without increasing condenser length but with the capillary length alone changed. The indoor and outdoor air temperatures were varied in accordance with BIS 1391 (1992) standard and the test was carried out in a psychrometric test facility. Experimental results showed that M20 refrigerant had 4.18% to 7.47% lower cooling capacity compared to the R22 system. Hence M20 can be used as a drop-in substitute for R22 in a window air-conditioner but with marginal reduction in cooling capacity.
A high-temperature electrically operated heat pump water heater is evaluated in terms of the viability of employing capacity control using zeotropic refrigerant mixtures. The system coefficient of performance (COP) is improved by introducing capacity control, which offers continuous modulation by varying heat pump capacity to match the load. This is accomplished by using a zeotropic refrigerant mixture and changing the composition (x) of the circulating mixture. The zeotrope R-22/R-142b is selected due to the requirements for a high condensing temperature and a wide capacity range. A comparison is made of the energy-saving potential of the R-22/R-142b mixture in a capacity-controlled heat pump, relative to an R-22 heat pump. Computer simulations show that the capacity-controlled heat pump, operating between compositions of 100% R-22 and 70% R-22, shows a 29.6% improvement in energy conversion when compared with a conventional R-22 heat pump water heater. An advanced heat pump water heater is proposed, which would exploit the advantages of using a zeotropic mixture.
The problem of R22 phase-out in a vapour compression plant is analysed. A comparison is performed between R22 and R407C. Attention is paid to the global evaluation of the environmental impact in terms of greenhouse effect. The analysis has been performed on the basis of the experimental results obtained from a vapour compression pilot plant. The contribution to the greenhouse effect has been taken into account by evaluating the TEWI values (Total Equivalent Warming Impact) corresponding to different experimental conditions.
The glide-matching study presented in Part 1 was a laboratory investigation which demonstrated the evaporator performance in detail. However, since it was not possible to instrument the condenser sufficiently, some computer simulation work was conducted using a semi-theoretical model cycle-11, which has been under continual development at NIST for the past five years. As in the experimental effort, R22, R142b, R22/142b, R23/22/142b and R23/142b working fluids were investigated, but the simulation work did not include heat pump operation with liquid-line/evaporator heat exchange. By utilizing the model to quantify entropy generation at various state points within the cycle, it was possible to locate the likelihood of temperature profile pinch points in both the condenser and evaporator. This information clarified the impact of non-linearities on the system performance.RésuméL'étude sur les correspondances de glissement présentée dans la première partie et effectuée en laboratoire décrivait en détail les performances d'un évaporateur. Cependant, étant donné qu'il n'était pas possible d'équiper le condenseur de façon suffisante, on a entrepris de simuler la même expérience sur ordinateur à l'aide d'un modèle semi-théorique CYCLE-11 que NIST développe depuis cinq ans. Comme pour l'expérience en laboratoire, on a étudié les fluides actifs R22, R142b, R22/142b, R23/22/142b et R23/142b mais pas l'exploitation d'une pompe à chaleur avec échange thermique entre conduites de liquide et évaporateur. L'utilisation de ce modèle pour quantifier l'entropie à différents points d'état du cycle a permis de mettre en évidence la vraisemblance des profils de température pour le condenseur et l'évaporateur. Ces données ont clarifié l'impact de la non-linéarité sur la performance du système.
Three methods for comparing cycle Performance of working fluids. pure as well as non-azeotropic mixtures. are investigated for two applications and for two mixture pairs, HCFC22-CFC114 and HCFC22-HCFC142b, and their pure components. The methods differ in the way of calculating the heat exchange processes. They assume, respectively. equal minimum approach temperatures, equal mean temperature differences and equal heat transfer areas. Changes of coefficient of performance (COP) with composition arc explained for all methods. It is shown that transport properties must be taken into account when making rigorous comparisons between working fluids. To predict the relations between fluids with high accuracy, one must use the method with equal heat transfer areas. By the method with equal mean temperature differences, the COP can be estimated with the same accuracy for mixtures as for pure fluids, and can be used for rough estimations of the COP level with different fluids. The method of equal minimum approach temperatures should be avoided for non-azeotropic mixtures.
An experimental, water-to-water, breadboard heat pump (that is one designed to be easily reconfigured) was constructed for comparison of pure R22 to the refrigerant mixtures R22/R114 and R13/R12. Three evaporator configurations were extensively studied. In all cases the best mixture outperformed R22. The best efficiency with R22/R114 was 32% higher and with R13/R12 was 16% higher than the best efficiency measured with R22. Other observations were, first, that mixtures can take advantage of heat exchangers efficiency that, in a gliding temperature application, a pure refrigerant is incapable of utilizing. Secondly, that heat exchange between the condensed and evaporating refrigerant is beneficial to some mixed refrigerants. Finally, mixtures exhibit nonlinearity of enthalpy versus temperature in the two phase region which has significant impact on both heat exchanger and cycle design. 12 figs.
The solar-assisted heat pump system in question has 72.5 sq m of fluid-heating solar collector with an organic heat transfer fluid as the working fluid. The storage system is 34,091 l capacity uninsulated steel tank buried in a quartz sand envelope. Water is used as the storage medium in the tank and the volume of the water in the tank can be changed for specific research efforts. The system operates in the following modes: direct utilization of stored thermal energy to heat the house and preheat domestic water, air-to-air heat pump for heating the house when storage is depleted, fluid-to-air heat pump operation using a storage system as both a heat source and a heat sink, electric resistance heaters used to add heat to storage during off-peak hours on electric network, and electric resistance heaters in house air stream used to heat house and supplement air-to-air heat pump capacity.
In Swedish district heating systems several large (25 MW) turbo-compressor driven heat pumps using R22 are installed. The only commercially available alternative is R134a, but its use could decrease the heating capacity by 35%. In this paper a method for finding the best working fluid for a specific heat pump plant is presented, and applied to a district heating plant. First, a screening is made among almost 2000 mixtures, using criteria such as condenser pressure, Mach number and temperature glide. Simulations of the plant are then made to investigate the change in heating capacity and COP when using a mixture instead of R134a. The results show that there are mixtures that can offer a substantially higher heating capacity than R134a, but there is a decrease in COP. The importance of considering the limiting parameters of the heat pump, such as maximum volume flow to each compressor stage and minimum evaporator pressure, is shown.
The phasing out of fully halogenated halocarbons becomes effective at the end of 1995 by international agreement. Under the same ozone depletion issue, the companion fluids HCFCs are suffering a similar fate, as they are considered controlled substances with a virtual phase-out by 2020, and more drastic reductions may be proposed in the near future. Some international action might also be agreed upon on refrigerants with regard to the threatened environmental emergency of anthropogenic global warming. Therefore, in choosing replacement fluids primary concern must be given to minimising the total warming impact, which, for most applications, calls for improved energy efficiency. During recent years, industry has scrutinised and proposed a number of new synthesised products as immediate drop-in or long-term replacements for fluids harmful to the environment. Together with some single-component new generation refrigerants, quite a few two-component, three-component or even four-component mixtures, both with zeotropic and azeotropic behaviour, are being considered. The main issues associated with the use of the new generation refrigerants are discussed, such as behaviour with oil; flammability; efficient use of temperature glides, fractionation and heat-transfer degradation with zeotropic mixtures. The full environmentally friendly option of resorting to natural fluids is also considered by examining some recent innovative applications as refrigerants of some hydrocarbons, ammonia, carbon dioxide, water and air.
A refrigeration test facility was constructed to examine the performance of potential alternatives to R22. For the purpose of this paper, the performance of R407c (a zeotropic mixture of R134a, R125 and R32 in a 52% 25% 23% composition by mass) was compared to that of R22. It was found that the performance of R407c approached that of R22 at higher evaporator temperatures, but reductions in evaporator capacity and COPc were found with decreasing evaporator temperature. The effects on evaporator performance of a 32 cSt polyol ester compressor lubricating oil were also noted. It was seen that while R22 and this oil responded in typical fashion for a soluble refrigerant-oil pair (reduced capacity, increased evaporator pressure drop and fall-off in capacity at low superheats), R407c displayed a two-stage performance decline occurring over a greater range of superheat. The combined effect of differential solubility of the individual components of the mixture in conjunction with a more gradual solubility effect due to the presence of a temperature glide in the evaporator lead to a minor change in composition of the circulating refrigerant mixture resulting in a drop in evaporator capacity and COPc.
The use of liquid-phase mixtures is common in a number of industrial applications. Mixtures have certain advantages over individual components, and these have been exploited advantageously. For the case of refrigerants, a number of azeotropic mixtures are used in practise. The use of non-azeotropic refrigerant mixtures, however, is not as common. This paper looks at the design of refrigerant mixtures for a refrigeration cycle consisting of two evaporators operating at two different temperatures. Such a cycle has been proposed for use in, for example, a commercial refrigerator having a separate freezer section.Compared to the single evaporator cycle operating at the freezer temperature and circulating the cold air from the freezer to the rest of the refrigerator, the double-evaporator cycle can give higher efficiencies since cooling is not done at a lower temperature than what is required. Also, the use of nonazeotropic mixtures has a number of advantages over single component refrigerants and azeotropic mixtures. A mathematical programming approach developed earlier is applied to the double-evaporator cycle to obtain refrigerant mixtures that maximize cooling.
Refrigerant mixtures may be used to solve the ozone layer depletion problem as they offer the optimum combination of favorable technical performance with environmentally acceptable behavior. This work reports the thermodynamic properties and characteristics of the binary mixtures R-32/R-134a in compositions 20–80%, 30–70%, 40–60% by mass and of the ternary mixture R-407c: 23 wt% R-32 + 25 wt% R-125 + 52 wt% R-134a. A computer code has been developed for the phase equilibrium relationship of the binary mixtures using related activity and fugacity coefficients. Our results are in good agreement with existing experimental data. For the ternary blend, we present enthalpy and entropy correlations, diagrams illustrating the real gas behavior by means of k-type isentropic change exponents (k=cp/cV, kp,V, kT,V, kp,T) and figures for the refrigerating systems efficiency expressed by coefficient of performance values.
This book was written to provide chemical engineers with information needed to assess various types of heat pumps in different industrial applications. The authors assume the reader is familiar with chemical engineering unit operations. Includes literature, an appendix with temperature entropy diagrams, a cited author index, and a subject index.
A comprehensive investigation is carried out, on a systematic and consistent basis, to explore a range of advanced heat pump cycle concepts using nonazeotropic refrigerants for COP enhancement and capacity modulation along with the trade-offs associated with refrigerant mixture selection. The objectives of the study were to: identify candidate nonazeotropic mixtures and advanced heat pump cycle concepts with emphasis on their potential for single-speed capacity modulation with mixture composition control; assess the effect of conjunction with nonazeotropic mixture cycles; evaluate the cycles analytically and recommend the most promising cycles and mixtures for further development; and provide recommendations relating to the needs for additional refrigerant property data, experimental studies of basic heat transfer phenomena with mixed refrigerants, development of system components, and/or more detailed modeling of specific components. 18 refs., 7 figs., 3 tabs.
This investigation compared the performance of R22 to the performance of propane (R290) and zeotropic mixtures of HFC's and hydrocarbons in a water-to-water heat pump. Baseline testing began with R22 and proceeded to R290, R32/290, R32/152a, and R290/600a. The use of brazed plate heat exchangers arranged in counterflow for both heating and cooling allowed glide matching using the zeotropic refrigerant mixtures. The performance of the system was characterized by air-side capacity, air-side Coefficient of Performance (COP), compressor RPM, and refrigerant conditions.
The thermodynamic differences in behaviour between non-azeotropic mixtures and pure fluids in two-stage cycles are theoretically investigated for two applications and over the whole composition range of three mixture pairs, HCFC22HFFC152a, HCFC22HCFC142b and HCFC22CFC114. Twe two most common types of two-stage plant are covered:those working with a flash vessel at an intermediate pressure, and those in which an economizer heat exchanger is used. The coefficient of performance (COP) and the capacity of the two types with different working aluids are compared with each otheras well as with the performances of a one-stage cycle. It is found that the COP and the capacity of a non-azeotropiic mixture increase more than those of a pure fluid upon changing from a one-stage cycle to a two-stage cycle with economizer heat exchanger. In the search for the 'best' working fluid, pure or a mixture, for a given application, the optimal choice depends on which type of cycle one intends to use.
In this paper, energy efficiency results are presented for a new HFC ternary blend proposed as a substitute for CFC 502 and HCFC 22. The blend is composed of R-23/R-32/R-125. Performance evaluation test results were obtained after an experimental heat pump set up with a 3 kW rotary compressor. The refrigerants tested in this study under different conditions were HCFC-22, as a reference base refrigerant and R-410a (HFC-32/HFC-125), R-407c (HFC-32/HFC-125/HFC-134a), as well as quaternary mixture; HFC-32/HFC-125/HFC-143a/HFC-134a. The experimental data showed that our proposed HFC ternary blend R-23/R-32/R-125 has superior performance compared to other proposed HFC alternatives such as R-410a and R-407c, under the same conditions. Pressure ratios and head pressures were compatible with new compressors to be used in new systems. Furthermore, experimental results demonstrated that the ternary blend R-23/R-32/R-125 is the best performing replacement for R-22 in heat pump applications and low temperature equipment. Experiments also showed that the heat pump system using R-23/R-32/R-125 was stable and experienced reasonable head pressures. © 1997 John Wiley & Sons, Ltd.
Today many factors affect the fluids that are being selected for use in domestic and commercial heat pumps. These include environmental issues, system cost and efficiency and several papers have been written to promote and discredit hydrofluorocarbon against natural (hydrocarbon) fluids as the best replacement for R22. This paper attempts to resolve this issue in terms of the environment, energy efficiency and system costs for small domestic and commercial heat pumps. Copyright © 2001 John Wiley & Sons, Ltd.
Power saving can be achieved in air conditioning/heat pump systems by using a refrigerant mixture whose temperature glide in the condenser and evaporator approximately matches the temperature intervals through which air is heated and cooled. The challenges are in the choice of mixture, the designs of the condenser and evaporator, and the control system. Solutions to all these problems are advanced and these are tested in a laboratory rig running on an R22/R142b mixture. A range of results is presented showing power savings as high as 25% compared with a conventional R22 system. This experience is incorporated in a computer model by which the performance of a similar system running on a wide range of environmentally acceptable mixtures is tested. Predictions are reported for a range of mixtures, from binary to quaternary, showing how units can be designed with a 25% power saving for an additional first cost of the same order.
The aim of the present study is to suggest two new fluids as alternatives of R12 in a vapour compression cycle. These fluids are the methyl trifluoromethyl ether (E143a) and the hexafluorocyclopropane (C216), which belong to halogenated derivatives of dimethyl ether and cyclopropane, respectively. The two suggested fluids have low degree of toxicity and a quite short atmospheric life. They also have suitable boiling points and a relatively simple molecular structure.A method of estimation of the thermodynamic properties of E143a and C216 is presented. The theoretical performance of the new fluids are evaluated and compared to those of the R12.
A water-to-water high temperature heat pump was studied experimentally. The performance of the system was characterized by refrigerant compositions, compressor RPM and water temperature change. For the experimental conditions of the inlet water temperature of evaporator of 40 °C and the inlet and outlet water temperatures of the condenser of 70 and 80 °C, respectively, the experiment shows that the coefficient of performance is maximum when the molar component of R22 is about 75%. It is shown that the maximum pressure of the system is under 2.5 MPa after taking R22/R141b as working fluids, even though the highest cooling water temperatures is about 80 °C.
The results of the simulations for a conventional heat pump, a conventional solar air heater and two serial solar-assisted heat pump (SAHP) systems are presented in this paper. The thermodynamic properties of R22, R404a and R134a are given in the form of correlations with correlation factors higher than 0.99. The performance characteristics of the heat pump are investigated using these working refrigerants, for wide ranges of evaporator temperature (0–45°C), condenser temperature (50–70°C) and air mass flow rates (1000–2000 kg/h). The comparison of the heat pump performance for the considered working refrigerants proved that R134a is the most promised alternative to R22 for low-temperature applications. This is confirmed by more than a 23% increase in the coefficient of performance for R134a over R404a. The operating conditions and the performance of both the conventional solar air heater and SAHP systems have been evaluated over 1 year using the meteorological data of Cairo (latitude of 30°N). Comparison between the performance of the SAHP systems, conventional heat pump or conventional solar air heater, shows that the SAHP systems provide better characteristics over the conventional systems. The SAHP system in which heated air flows from the collector to the evaporator, then through the condenser, is preferable. This system using R134a gives an increase of more than 50% in the coefficient of performance of the heat pump and an average saving in the collector area of about 25% during high radiation months (April–October) and 50% during low radiation months (November-March). Moreover, the economic analysis demonstrates that this system grants the lowest annual total cost among the considered systems.
This paper presents an experimental study on the performance of hydrocarbon refrigerants, namely propane and a liquefied petroleum gas (LPG) mix as suitable replacements for the widely used refrigerant HCFC22 in refrigeration and heat pump applications. A cylinder of commercially available LPG from New Zealand market was obtained for this study. The composition of the specific LPG mix (by mass fraction) was propane (HC290)-98.95%, ethane (HC170)-1.007%, iso-butane (HC600a)-0.0397% and other constituents in small proportions. Experiments were carried out in a laboratory heat pump test facility with maximum condenser capacity of approximately 15 kW. Condensing temperatures were held constant at 35, 45 and 55 degrees C, while evaporating temperatures were varied over a wide range from -15 to +15 degrees C. All tests were carried out at constant degree of superheat (about 1 K) and subcooling (about 8 K). All appropriate precautions were observed against any leaks or fire. The analysis revealed that the hydrocarbon refrigerants performed better than HCFC22 bur with a small loss of condenser capacity. The mass flow rate and compressor discharge temperature were found to be significantly lower than HCFC22. The performance of the specific LPG mix tested was found to be better than HC290 at higher condensing temperatures but poorer at a lower condensing temperature. No adverse effects were found with the LPG mix despite the presence of little moisture (less than 0.01%) in its composition. The study reveals that LPG of the tested composition (i.e. predominantly a mixture of propane, ethane and iso-butane) can be an excellent refrigerant in heat pump/refrigeration applications.
Performance of a heat pump system using hydrocarbon refrigerants has been investigated experimentally. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane isobutane and propane/butane are considered as working fluids in a heat pump system. The heat pump system consists of compressor, condenser, evaporator, and expansion device with auxiliary facilities such as evacuating and charging unit, the secondary heat transfer fluid circulation unit, and several measurement units. Performance of each refrigerant is compared at several compressor speeds and temperature levels of the secondary heat transfer fluid. Coefficient of performance (COP) and cooling/heating capacity of hydrocarbon refrigerants are presented. Experimental results show that some hydrocarbon refrigerants are comparable to R22. Condensation and evaporation heat transfer coefficients of selected refrigerants are obtained from overall conductance measurements for subsections of heat exchangers, and compared with those of R22. It is found that heat transfer is degraded for hydrocarbon refrigerant mixtures due to composition variation with phase change. Empirical correlations to estimate heat transfer coefficients for pure and mixed hydrocarbons are developed, and they show good agreement with experimental data. Some hydrocarbon refrigerants have better performance characteristics than R22.
Multi-stage heat pumps composed of a condenser, evaporator, compressor, suction line heat exchanger, and low and/or high stage economizers are studied by computer simulation. Their thermodynamic performance and design options are examined for various working fluids. In the simulation, HCFC22/HCFC142b and HFC134a are studied as an interim and long term alternatives for CFCI2 while HFC32/HFC134a and HFC125/HFC134a are studied as long term alternatives for HCFC22. The results indicate that the three-stage super heat pump with appropriate mixtures is up to 27.3% more energy efficient than the conventional single-stage system with pure fluids. While many factors contribute to the performance increase of a super heat pump, the most important factor is found to be the temperature matching between the secondary heat transfer fluid and refrigerant mixture, which is followed by the use of a low stage economizer and suction line heat exchanger. The contribution resulting from the use of a high stage economizer, however, is not significant. With the suction line heat exchanger, the system efficiency increases more with the fluids of larger molar liquid specific heats. From the view point of volumetric capacity and energy efficiency, a 40%HCFC22/60%HCFC142b mixture is proposed as an interim alternative for CFC12 while a 25%HFC32/ 75%HFC134a mixture is proposed as a long term alternative for HCFC22.
In this study, 14 refrigerant mixtures composed of R32, R125, R134a, R152a, R290 (propane) and R1270 (propylene) were tested in a breadboard heat pump in an attempt to substitute HCFC22 used in residential air-conditioners. The heat pump was of 3.5 kW capacity with water as the heat transfer fluid (HTF) in the evaporator and condenser that are in a counter current flow configuration. All tests were conducted with the HTF temperatures fixed to those found in the ARI test A condition. Test results show that ternary mixtures composed of R32, R125, and R134a have a 4-5% higher coefficient of performance (COP) and capacity than HCFC22. On the other hand, ternary mixtures containing R125, R134a and R152a have both lower COPs and capacities than HCFC22. R32/R134a binary mixtures show a 7% increase in COP with the similar capacity to that of HCFC22 while R290/R134a azeotrope shows a 3-4% increases in both COP and capacity. The compressor discharge temperatures of the mixtures tested are much lower than those of HCFC22, indicating that these mixtures would offer better system reliability and longer life time than HCFC22. Finally, test results with a suction line heat exchanger (SLHX) indicate that SLHX must be used with special care in air-conditioners since its effect is fluid dependent.
Worldwide reactions to the debates on global warming and ozone depletion have led to social responses and legislative measures which have serious implications for refrigeration and associated industries. This paper discusses the problems to be faced, and the ways in which the industry can contribute to meeting the wider global objectives. The discussion considers the choice and availability of working fluids, the increased complexity of using fluid mixtures, and the risk of losing the simplicity in design and construction which was possible with CFC single fluids. Education and training are presented as issues because of the changes in technology.RésuméLes réactions mondiales aux débats sur le réchauffement planétaire et l'appauvrissement de l'ozone stratosphérique ont engendré des réponses sociales et des mesures législatives qui ont des implications sérieuses pour l'industrie du froid et les industries associées. Cette communication expose les problèmes que cela engendre et les moyens par lesquels l'industrie peut contribuer à atteindre les objectifs globaux. La discussion met l'accent sur le choix et la disponibilité des fluides actifs, la complexité croissante de l'utilisation des mélanges de fluides, et le risque de perdre la simplicité en termes de conception et et construction qui étaient possibles lorsqu'on utilisait des CFC seuls. L'éducation et la formation sont présentées comme problématiques dans le contexte des changements technologiques.
The results of the simulations for a conventional heat pump, a
conventional solar air heater and two serial solar-assisted heat pump
(SAHP) systems are presented in this paper. The thermodynamic properties
of R22, R404a and R134a are given in the form of correlations with
correlation factors higher than 0.99. The performance characteristics of
the heat pump are investigated using these working refrigerants, for
wide ranges of evaporator temperature (0-45°C), condenser
temperature (50-70°C) and air mass flow rates (500-2000 kg/hr). The
comparison of the heat pump performance for the considered working
refrigerants proved that R134a is the most promised alternative to R22
for low temperature applications. This is confirmed by a 22% increase in
the coefficient of performance for R134a over R404a. The operating
conditions and the performance of both the conventional solar air heater
and SAHP systems have been evaluated round the year using the
meteorological data of Cairo (latitude of 30°N). Comparison between
performance of the SAHP systems, conventional heat pumps or conventional
solar air heaters, shows that the SAHP systems provide better
characteristics over these conventional systems. Moreover, the SAHP
system in which heated air flows from the collector to the evaporator,
and then through the condenser, is preferable. This system using R134a
gives an increase of more than 50% in the coefficient of performance of
the heat pump and a saving of 21% in the collector area
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