R744 System Research Articles

A comparative study on the performance of a R22 window air conditioner retrofitted with R407C/R290/R600a refrigerant mixture

SYNOPSIS 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.

Performance comparison of air source heat pump with R407C and R22 under frosting and defrosting

The dynamic performance characteristics of the air source heat pump (ASHP) with refrigerants R22 and R407C during frosting and defrosting are studied. The results show that both refrigerant systems have similar performance characteristics, except that the performance of the R407C system deteriorated faster than that of the R22 system under frosting, and the performance of the R407C system attains its steady state faster than that of the R22 system after defrosting. R407C refrigerant can be used in either existing systems or in new systems that were originally designed for R22.

Experimental validation of a prototype ejector designed to reduce throttling losses encountered in transcritical R744 system operation

This study presents experimental results obtained from a transcritical R744 system using a refrigerant ejector. The results were compared to that of a conventional system with an expansion valve. For the test conditions considered, the cooling capacity and COP simultaneously improved by up to 8% and 7%, respectively. Experiments were analyzed to quantitatively assess the effects on system performance as a result of changes in basic ejector dimensions such as motive nozzle and diffuser sizing. Small angles of 5° yielded best results for the static pressure recovery of the high-speed two-phase flow entering the diffuser. Experiments confirmed that like in a conventional transcritical R744 system with expansion valve, the high-side pressure control integrated into the ejector could be used to maximize the system performance. Numerical simulation results helped identifying this basic trend. Due to difficulties in the ejector throat pressure measurements, a more practical performance metric was introduced in order to quantify overall ejector efficiencies. According to this definition, the prototype ejector was able to recover up to 14.5% of the throttling losses.

Effects of refrigerant charge amount on the performance of a transcritical CO 2 heat pump

A typical transcritical CO 2 system shows lower performance than conventional air conditioners in cooling mode operation. In addition, the CO 2 system shows a large variation of the performance according to refrigerant charge whereas the conventional systems do not show large variation. In this study, the performance of the CO 2 heat pump was measured and analyzed by varying the refrigerant charge amount at standard cooling condition. In addition, the performance sensitivity of the CO 2 system as a function of refrigerant charge was compared to those for the R22, R410A, and R407C systems. The cooling COP of the CO 2 system was reduced more significantly at undercharged conditions than at overcharged conditions as the deviation from the optimal charge increased. The expansion loss was the dominant factor affecting system performance at undercharged conditions, while the gascooler loss became the major parameter at overcharged conditions. Among the systems investigated and compared in this study, the CO 2 system showed the most reduction in performance at undercharged conditions.

Air conditioning with R744 refrigerant

The environment-friendly A/C system by Behr being introduced in 2003 is more powerful than a conventional system. However, the requirements have changed: Instead of a higher cooling performance, the same performance of a R744 system is expected in comparison to a state-of-the-art system with R134a, with minimal additional costs. The second generation R744 system fulfils these requirements.

Flash gas bypass for improving the performance of transcritical R744 systems that use microchannel evaporators

The performance of transcritical R744 systems with direct expansion (DX) can be significantly improved by implementing a Flash Gas Bypass (FGB). The idea behind the concept is to bypass refrigerant vapor, created during the isenthalpic expansion process, around the evaporator. By feeding the evaporator with liquid refrigerant, pressure drop is reduced and refrigerant distribution is improved. With R744 as the working fluid, increased refrigerant-side heat transfer coefficients are expected as well. In addition, the FGB concept proves to be beneficial in terms of system design, in particular for combined air-conditioning and heat pumping applications. An experimental comparison to a conventional DX-system reveals that FGB increases the cooling capacity and COP at the same time by up to 9 and 7%, respectively. Even larger improvements are possible in case a variable speed compressor is utilized to match the performance of the conventional DX-system. A simulation model helps to separate the individual improvement mechanisms. It was found that the reduction of refrigerant-side pressure drop is the dominant improvement mechanism of FGB.

Experimental determination of the critical locus for the difluoromethane (R32) and propane (R290) system

Vapor–liquid coexistence curves in the critical region for binary difluoromethane (R32) + propane (R290) mixtures have been measured by visual observation of the meniscus disappearance. Twelve and 15 data of saturated vapor and liquid densities for 70 mass% R32 and 90 mass% R32, respectively, have been obtained in the temperature range of 316 K<T<345 K and in the density range of 109 kg/ m 3 <ρ<717 kg/m 3 . The uncertainties of the temperature, density, and composition measurements are estimated to be within 10 mK, 0.3–1.1 kg/m 3, and 0.03%, respectively. On the basis of the present results of the vapor–liquid coexistence curve, the critical temperature and the critical density for the R32 + R290 system have been determined considering the meniscus disappearance level as well as the intensity of the critical opalescence. The critical pressure of the mixtures were estimated based on the measured critical temperature and the REFPROP database.

Influence of the expansion device on the performance of a heat pump using R407C under a range of charging conditions

The objective of this study is to investigate the effects of the expansion device on the performance of a water-to-water heat pump using R407C, which has been considered as one of the alternative refrigerants to replace R22 with “soft-optimization”, at various charging conditions. The heat pump applying the expansion devices of a capillary tube and an EEV was tested by varying refrigerant charge amount from −20% to +20% of full charge and changing water temperature entering the condenser from 30 °C to 42 °C, while maintaining water temperature entering the evaporator at 25 °C. The R22 capillary tube system is utilized as a baseline unit for the performance comparison with the R407C system. The performance of the capillary tube system is more sensitive to off-design charge than that of the EEV system. As the refrigerant charge deviates from the full charge, the R407C EEV system shows a much lower degradation of capacity and COP as compared to the R22 and R407C capillary tube systems due to an optimum control of superheat by electronically adjusting the EEV opening. In addition, the R407C EEV system shows more a stable compressor discharge temperature at off-design charge than the R407C capillary tube system.

Mutual solubility and VLLE correlation for the R32 + R290 system

Following our recent study on vapour–liquid-equilibrium (VLE) of the difluoromethane (R32) + propane (R290) system, that covered the temperature range between 248.13 and 294.91 K, the present study focused on the behaviour of the liquid phase down to 215 K. The immiscibility of the liquid phase was observed at temperatures below 230 K and the mutual solubility was ascertained by the visual observation of the cloud point with a new apparatus. The experimental results were used to develop a method for deriving vapour–liquid–liquid-equilibrium (VLLE) parameters using an equation of state. The azeotropic pressures found from VLE at temperatures above UCST and the heteroazeotropic pressures derived from VLLE formed a common trend well represented by the Antoine equation. A common trend was exhibited also by the azeotropic compositions found from the VLE data above UCST and those found from the VLLE data correlation. Both regularities observed may be considered as an internal consistency of two independent experiments within the estimated uncertainty.

Experimental results of transcritical CO 2 heat pump for residential application

This paper describes experiments comparing a commercially available R410A heat pump and prototype R744 (carbon dioxide) system in heating mode. The R744 system utilizes aluminum microchannel heat exchangers and a prototype semi-hermetic compressor. System performance is compared for two configurations: first, when the R744 compressor speed is set to match the baseline system’s heating capacity at 8.2 °C outdoors and 21.1 °C indoors; and second, when the air conditioning capacity is matched at 35 °C outdoors and 26.5 °C indoors. The R744 system operates with a slightly lower heating COP, but its higher capacity at lower outdoor temperatures reduces the need for less efficient supplementary heating capacity.

Measurements of PVTx and Saturation Properties for the Binary 1,1,1,2-Tetrafluoroethane + Propane System

Natural refrigerants such as hydrocarbons (HCs) are considered as promising long-term alternatives in some of the restricted applications for refrigeration systems, since they have zero ozone depletion potential (ODP) values and negligible global warming potential (GWP) values. One of the crucial disadvantages of HCs, however, is flammability. For the purpose of solving this important issue, we have decided to study the thermodynamic properties of binary mixtures of HCs blended with nonflammable HFC refrigerants. The present paper, therefore, aims to measure a set of reliable PVTx property data for the binary 1,1,1,2-tetrafluoroethane (R-134a) + propane (R-290) mixtures in two-phase and gas-phase regions. The experimental PVTx properties of the binary R-134a + R-290 system have been measured at four different compositions by a constant-volume method coupled with expansion procedures in an extensive range of temperatures from 312 K to 400 K, at pressures up to 6.1 MPa, and for densities up to 196 kg·m-3, r...

98/04204 Emission performance improvement at Hasselby power station in Sweden

All the R22 substitutes from the US EPA list together with some popular alternative refrigerants were studied. From the ODP and GWP criteria, only seven substitute refrigerants (R134a, R407C, R437A, R744, R1234yf and R290) were accepted. The environmental impact, compatibility with existing R22 systems and system performance of each refrigerant were compared. The system performances were studied in systems without and with internal heat exchangers. It was found that R744 is the most environmentally friendly refrigerant. R290 and R407C are the most suitable to retrofit existing systems. R290 and R134a have superior system performances as compared to other alternative refrigerants.

97/03156 Air conditioning technology—shell and tube evaporators

In recent years a new refrigerant, R422D, has been introduced as substitute of R22 for refrigeration systems. This new fluid is an easy-to-use, non-ozone-depleting HFC refrigerant and, differently from its predecessor (R407C), it is compatible with mineral oil. However, R422D has a very high GWP, and it tends to worsen the efficiency of retrofitted R22 systems. Consequently, even if R422D respects the limits of Montreal Protocol, its global environmental impact could be high. In this paper, we report an experimental analysis in terms of TEWI aimed to identify the global environmental impact of R22 systems retrofitted with R422D. For this purpose, we considered a direct expansion refrigerator for commercial applications and we investigated energy consumption with the temperature of the cold reservoir set to −5, 0, 5, 10 °C. The experimental investigation confirmed that the system, when retrofitted with R422D, leads to an increase of TEWI. Therefore an optimization analysis aimed to eco-friendly scenarios was performed.

Clathrate Phase Equilibria for the Water + Deuterium Oxide + Carbon Dioxide and Water + Deuterium Oxide + Chlorodifluoromethane (R22) Systems

Clathrate phase equilibria for two ternary water + deuterium oxide + carbon dioxide and water + deuterium oxide + chlorodifluoromethane (R22) systems were measured at several different mass % of water and deuterium oxide mixtures. Equilibrium dissociation pressures of these two ternary systems at the three-phase (clathrate−liquid−vapor) boundaries range (1.43 to 4.86) MPa and (0.141 to 0.886) MPa, respectively. The temperature range occupied by the three-phase boundary of the water + deuterium oxide + R22 system is a little larger than that of the water + deuterium oxide + carbon dioxide system. The dissociation pressures at the quadruple points were found to steadily increase with deuterium oxide composition.

Wide-boiling refrigerant mixtures for energy saving

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.

Development of absorption refrigeration units for cold storage of agricultural products

To meet the requirements of continuous refrigeration installations, powered by low-grade heat sources, e.g. waste heat, flat-plate solar collectors or solar ponds, and providing cooling or refrigeration at subzero (°C) temperatures, rational selection of suitable refrigerant-absorbent pairs is necessary. It is demonstrated that the use of R22 and suitable organic solvent systems is desirable in absorption refrigeration installations. Since no data were available on the vapour-liquid equilibria of these combinations, they were measured over a broad range of pressures, temperatures and concentrations. A rational selection of the optimal combinations was made using results obtained from a computerized simulation model giving the performance characteristics of a specific refrigeration system operating with selected refrigerant-absorbent combinations. An efficient thermodynamic cycle has been constructed for the chosen refrigerant-absorbent pairs. Within the region of feasible operation of the cycle, optimal operating conditions are determined. In selecting these conditions it is also necessary to take into account the heat transferred in the heat exchangers of the unit and the operating stability. On the basis of the research performed a 15 ton refrigeration prototype unit for the storage of agricultural products has been constructed and is in the final stages of being run in. It operates at a coil temperature of −3°C and maintains the storage chamber at 5°C. Hot water is supplied at 95–98°C, and cooling water is provided at 26°C.

Measurements of the vapor-liquid coexistence curve for the binary R12 + R22 system in the critical region

Measurements of the vapor-liquid coexistence curve for the binary R12 + R22 system in the critical region

Thermodynamic design data for optimum performance of multi-stage refrigeration-heat pump systems operating on R12, R22, and R717

A multi-stage refrigeration-heat pump system to produce both cooling and heating for industrial applications is an interesting possibility. Such refrigeration-heat pump systems operating on working fluids R12, R22 and R717 have been optimized numerically. Optimum inter-stage temperatures, coefficients of performance, compression ratios, heating and cooling effects and refrigerant mass handled by high pressure compressor have been presented in tabular form for condensing temperatures of 20, 40 and 60°C, and evaporating temperatures of from 5 to −45°C in 5°C increments. Several graphs have been prepared to illustrate the feasible operating range for R12, R22 and R717 multi-stage refrigeration-heat pump systems. The design data presented can be used for the preliminary optimum design of multi-stage refrigeration-heat pump systems operating on R12, R22 and R717.

Measurements of the PVTx Properties of Binary Refrigerant R12+R22 System : 2nd Report, PVTx State-Surface and Composition Dependence of the Thermodynamic Properties

二成分系混合冷媒R12+R22系について,等容法と等温膨張操作を組合せた測定原理にもとづいて測定したPVTx性質の実測値情報より,露点および沸点曲線を解析し,温度300～420K,圧力9MPa,密度900kg/m3までのPVTx状態曲面を表示するBWR状態式とその係数の混合則を作成した.さらに,作成した状態式および混合則からR12+R22系の種々の熱力学的性質を解析的に求め,その組成依存性を明らかにした.

Measurements of the PVT&lt;SUB&gt;x&lt;/SUB&gt; Properties of the Binary Refrigerant R12+R22 System : 1st Report, A Mixture of 80 wt%R12+20wt%R22

Measurements of the PVT&lt;SUB&gt;x&lt;/SUB&gt; Properties of the Binary Refrigerant R12+R22 System : 1st Report, A Mixture of 80 wt%R12+20wt%R22