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Currently used legacy refrigerants for air conditioning and refrigeration applications such as R-410A, R-404A and R-134a have high global warming potentials (GWP). Due to this, these refrigerants have become targets for phase-down as part of global carbon emission reduction initiatives (Kigali amendment to the Montreal Protocol, EU F-Gas Regulation, etc.). Refrigerant alternatives for existing systems to be used in aftermarket applications are required to be nonflammable. Similar performance in efficiency and capacity while providing a reduction in GWP are required. Refrigerant manufacturers have developed options that attempt to fulfill these needs. However, the reduction in GWP often leads to blends that impose a gliding temperature profile in the heat exchangers besides other factors that need to be considered for drop-in situations like operating pressures, compressor discharge temperatures or material compatibility, among others. This paper evaluates the agreement between different refrigerants and the requirements for existing legacy refrigerants in air conditioning and refrigeration applications. A focus on temperature glide and inherent performance impact is evaluated and related to possible considerations for use. Refrigerant options with similar performance and operating characteristics for R-410A, R-404A and R-134a are identified with R-466A, R-448A/R-449A/R-407H and R-513A/R-456A, respectively. A close evaluation of material compatibility and detailed system modeling beyond this screening evaluation are needed to confirm viability for the specific application. [ABSTRACT FROM AUTHOR]

CO2 refrigeration has been a strong candidate for ultra-low global warming refrigeration. However efficiency of a transcritical CO2 refrigeration cycle suffers in hotter ambient due to the excessive amount of flash gas produced that needs to be re-compressed back to high gas cooler pressure. Exergetic analysis of such a cycle indicates that a large amount of exergy is destroyed through entropy production during the throttling across a Joule-Thompson valve. To solve this problem, this paper presents new CO2 refrigeration architectures using a novel rotary Trans-Critical Pressure Exchanger (TCPX) to achieve high cycle efficiencies. TCPX reduces compression work required by the cycle using a direct fluid-tofluid pressure exchange between high-pressure supercritical CO2 and low-pressure gaseous CO2, that takes place within its rotary ducts, thus allowing for an efficient pressure recovery. A TCPX placed between the gas cooler and receiver / evaporator serves simultaneously as a compressor and as an isentropic expansion device all within a single rotary device. It utilizes acoustic compression waves generated in a multi-ducted high-speed rotor to compress the low-pressure CO2 without requiring external mechanical energy input and simultaneously expands high-pressure supercritical CO2 to produce a two-phase, cold fluid stream ready for heat absorption. Various refrigeration architectures integrated with this TCPX are designed and the energy savings provided by TCPX are evaluated. [ABSTRACT FROM AUTHOR]

The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) announced an industry-wide cooperative research program to evaluate alternative refrigerants that have low global warming potential (GWP). This paper presents testing results for the performance of an air conditioner and a heat pump using three low GWP refrigerants (R32, D2Y-60 and L-41A) and R410A. The results show R32 and L-41A are good replacement candidates for R-410A. The paper also presents thermophysical property differences the four refrigerants. The paper also presents the cycle modeling which was used to investigate soft-optimization for D2Y60. [ABSTRACT FROM AUTHOR]

Refrigerants are the life-blood of vapor compression systems that are widely used in Heating, Ventilation, Air-Conditioning, and Refrigeration (HVAC&R) applications. The HVAC&R community is currently transitioning from mainstream refrigerants that have high Global Warming Potential (GWP) to alternative lower-GWP refrigerants. During this transition, it is important to account for the life cycle climate performance of alternative refrigerants since their performance will be different than that of higher-GWP refrigerants. This requires the evaluation of the system performance with the new refrigerants. Unfortunately, it is extremely difficult to predict the realistic performance of new alternative refrigerants without experimental validation. One of the main challenges in this regard is modeling the compressor performance with high fidelity due to the complex interaction of operating parameters, geometry, boundary conditions, and fluid properties. High fidelity compressor models are computationally expensive and require significant pre-processing to evaluate the performance of alternative refrigerants. This paper presents a new approach to modeling compressor performance when alternative refrigerants are used. The new modeling concept relies on using existing compressor performance to create an approximate model that captures the dependence of compressor performance on key operating parameters and fluid properties. The model can be built using a myriad of approximation techniques. This paper focuses on Kriging-based techniques to develop higher fidelity approximate scroll compressor models. Baseline and at least one alternative refrigerant performance data are used to build the model. The model accuracy was evaluated by comparing the model results with compressor performance data using other refrigerants. Preliminary results show that the approximate model can predict the compressor mass flow rate and power within ±5%. [ABSTRACT FROM AUTHOR]

In response to environmental concerns raised by the use of refrigerants with high Global Warming Potential (GWP), the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) has launched an industry-wide cooperative research program, referred to as the Low-GWP Alternative Refrigerants Evaluation Program (AREP), to identify and evaluate promising alternative refrigerants for major product categories. This paper reports one of the Oak Ridge National Laboratory (ORNL) contributions to AREP. It compares performance of alternative refrigerants to that of R-410A and R-404A for heat pump and medium temperature applications, respectively. The alternatives reported in this paper are: R-32, DR-5, and L-41a for R-410A and ARM-31a, D2Y-65, L-40, and a mixture of R-32 and R-134a for R-404A. All performance comparison tests were conducted using scroll compressors of ~1.85 tons (6.5 kW) cooling capacity. Tests were conducted over a range of combinations of saturation suction and saturation discharge temperatures for both compressors. The tests showed that, in general, energy efficiency ratio (EER) and cooling capacity of R-410A alternative refrigerants were slightly lower than that of the baseline refrigerant with a moderate increases in discharge temperature. On the other hand, R-404A alternative refrigerants showed relative performance dependence on saturation suction and saturation discharge temperatures and larger increases in discharge temperature than for the R-410A alternatives. This paper summarizes the relative performance of all alternative refrigerants compared to their respective baseline. [ABSTRACT FROM AUTHOR]

In building space conditioning vapor compression cycles provide cooling. The working fluid is often a refrigerant that has good thermal and transport properties and high volumetric capacity for AC applications, but it might have unfavorable effects on the environment in case of leakage. Energy conservation and environmental concerns are the core reasons for the tremendous growth of high performance and environmentally friendly heat transfer fluids. This paper presents data of the thermal performance of four Low Global Warming Potential (LGWP) refrigerants, that is, refrigerant R32 (GWP ~ 675), R1234yf (GWP ~ 4) and two new developmental refrigerants that have GWPs of about 300 and 500. The fluids investigated in this work replaced refrigerant R410A (GWP ~ 2088) in a ducted split system for residential air conditioning applications. The COPs, cooling capacities, refrigerants thermodynamic cycles characteristics are discussed in details in this paper and for a broad range of ambient temperatures; especially for extreme high temperature conditions of 110° and 115°F (43° and 46°C). Refrigerant R1234yf had an intriguing behavior when compared to R410A. This refrigerant had slightly lower COP at mild ambient temperatures but higher COPs at high ambient conditions. However, by adopting the same system, R1234yf provided only about 54% of the nominal capacity of the AC unit. R32 had a higher capacity and similar COPs as that of R410A but its discharge temperatures and pressures were significantly higher. The two novel developmental refrigerants yielded good COPs and cooling capacities with similar cycle pressures and compressor discharge temperatures. The charge of DR-4 in the system had to be carefully adjusted for the tests at high temperature ambient conditions. With minor adjustments of the expansion valve of the unit, the refrigeration cycles with the two new developmental refrigerants were optimally controlled and further improvements of the capacity and COPs were achieved. [ABSTRACT FROM AUTHOR]

The Kigali amendment to the Montreal Protocol will require the phase out of R410A used in air conditioning systems in developed countries by the late 2020s. The HVAC&R industry will therefore need to begin using R410A replacements by the mid 2020s. Alternatives for R410A with lower global warming potentials (GWP) have been studied extensively over the past few years with limited success in finding an optimal replacement. A number of near design-compatible candidates (close match in capacity, efficiency, and other factors) have been proposed and evaluated, including R32, R452B, R454B, HPR2A, ARM-71a, and R447B. These fluids are all classified as “2L” flammable. This paper reports the characteristics and performance of a new and innovative R410A alternative in two air conditioning platforms. System performance measurements with this new refrigerant are presented for a 100 RT air-cooled packaged water chiller along with R410A as baseline, as well as R32 and R452B. The chiller comprised scroll compressors, a brazed plate evaporator, and microchannel condenser. Also, system performance results with the new refrigerant are presented for a 3 RT residential split system along with R410A as baseline. The new refrigerant was designed to be compatible with existing R-410A equipment, requiring minimal modifications to equipment for air conditioning and heat pump applications. [ABSTRACT FROM AUTHOR]

Today's air conditioning product and applications designers, as a result of climate change contribution concerns for high direct global warming potential (GWP) refrigerants, are being asked to consider lower GWP refrigerants which have potential for decreased chemical stability. Chlorofluorocarbons (CFCs) and hydrofluorocarbons (HCFCs) were developed after years of research and field experiences, while they presented some chemical stability concerns with materials, they still offered good product reliability. Hydrofluorocarbons (HFCs) that later replaced the CFCs and HCFCs were generally found to be more chemically stable with materials. In recent years, the HVACR industry has been actively investigating new lower GWP refrigerants, many of which are new molecules with little knowledge available on their chemical reactivity in HVACR systems. In this paper, we will summarize the current accelerated test methodologies, for example the application of Arrhenius relationship to ASHRAE 97 sealed glass tube methodology, to qualify a new refrigerant for use. The authors will propose methodologies for extrapolating small scale highly accelerated laboratory results to real life HVACR operational conditions using climate zone data for both water cooled and air cooled equipment. Examples will be given using this methodology to show the relevance of the technique for various refrigerants and HVACR applications. [ABSTRACT FROM AUTHOR]

Flammable refrigerants are becoming more widely used in industrial, commercial (stationary and mobile), and residential applications as alternatives to conventional hydrofluorocarbon refrigerants. In addition to having low global warming potential and ozone depletion levels, HVAC&R systems utilizing these alternative refrigerants have demonstrated improved performance and energy efficiencies. However, despite these advantages, flammable refrigerants pose an increased fire risk over conventional non-flammable refrigerants in the end-use. In this paper, the thermodynamic cycle pressures, temperatures, and efficiencies of several common flammable and non-flammable refrigerants are compared. Typical hazard scenarios for light commercial and residential applications are illustrated with event trees, hazard thresholds are discussed, and some precautions are given. Lessons learned through case studies and conducted research projects are also presented and concluded with recommendations when working with flammable refrigerants. [ABSTRACT FROM AUTHOR]

Today designers, as a result of climate change concerns, are being asked to consider new lower Global Warming Potential (GWP) unsaturated hydrofluorocarbon (HFO) refrigerants and blends of hydrofluorocarbon (HFC) with HFO refrigerants, some of which are slightly flammable under certain conditions, as well as the less than desirable natural refrigerants. In the lower GWP refrigerant future, the world will adopt refrigerants with less than optimal properties in some applications. A single refrigerant, such as R-22 or R-410A that addresses a large area of market demands for a safe, high efficiency refrigerant with lowest cost products may not be available. In general, product designs may have to compromise on efficiency, safety and reliability which could lead to increased product costs for consumers and may result market fragmentation by refrigerant type to enable this future. In some instances, new HFO refrigerants will be able to maintain society's demands for efficiency, safety and reliability while balancing the need for lower direct GWP impact. In other instances, acceptance of significant product and application design compromises, such as the use of flammable refrigerants, will be required or more costly solutions will need to be considered because of safety, efficiency, capacity or reliability constraints. Natural refrigerants will gain more attention and expanded use when efficiency, safety and reliability can be delivered at a reasonable cost to consumers. Some natural refrigerants being considered and adopted today will be phased out because of ever increasing efficiency needs. This paper will review the various low GWP refrigerant options being proposed and weigh the compromises they present for their future adoption. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of tests run on a small (~4.5 RT) air-cooled water chiller in which lower GWP refrigerants were "dropped in". The first set of tests evaluated R32 and refrigerant blends with capacities and pressures similar to R410A. Following a change of compressor and TXV, a second set of tests evaluated refrigerant blends with capacities and pressures more similar to R22. The refrigerants tested covered a range of operating pressures, global warming potentials, and flammability ratings. In general, the experimental results agreed reasonably well with the predictions of a simple thermodynamic model with some refrigerants showing a positive deviation in capacity and COP from the model prediction and others showing a negative deviation. In particular, refrigerant blends with large glide did not perform well in the tested equipment. Several "near drop-in" candidates exist for R410A with GWPs of 400-500. All are "mildly flammable" (class 2L), as is R32 (GWP = 675). R22-like blends can have GWPs as low as 200-300, although these are also class 2L. On the other hand, R22-like blends can be made that are non-flammable (class 1). However, they have relatively higher GWPs of 1300-1600. In conclusion, lower GWP options to R410A and R22 are possible. Trade-offs between specific capacity, efficiency, GWP, and flammability will need to be made. These trade-offs may result in the need for changes to existing equipment designs. [ABSTRACT FROM AUTHOR]

Refrigeration systems using carbon dioxide (CO2) as a refrigerant, either in subcritical or transcritical cycles, or as secondary coolant systems, have recently received considerable attention due to carbon dioxide's low Global Warming Potential (GWP). This paper presents a comparative analysis of various CO2 transcritical refrigeration systems to optimize the operating parameters of these systems. In addition, the performance of selected CO2-based refrigeration systems is compared to the baseline R-404A multiplex direct expansion system using bin analyses in sixteen cities from eight climate zones of the United States. The operating parameters considered in this study include ambient temperature, suction line heat exchanger (SLHX) effectiveness and evaporator superheat. [ABSTRACT FROM AUTHOR]

The new refrigerant HFO-1234yf is being evaluated for use as a replacement for R-134a in many cooling applications. It has been proposed to use HFO-1234yf for many AC and refrigeration applications, but we show that it is not a direct replacement for higher performance refrigerants like R-410A for heating and cooling. New refrigerant compositions have been developed and are being evaluated for use in air conditioning and heat pump applications in order to reduce emissions of carbon dioxide and higher GWP gases that can contribute to global climate change. Some of these new compositions are marginally flammable, and are expected be classified by ASHRAE and ISO as "2L" refrigerants based on low burning velocity and low heats of combustion. This paper presents measured cooling and heating performance results for some of the new candidate refrigerants, and environmental impacts are modeled based on those measured results.. Some of the trade offs impacting environmental impact of the developmental refrigerants, including GWP value and energy efficiency performance will be discussed. It is shown the lower GWP fluids do not necessarily give the best environmental performance. [ABSTRACT FROM AUTHOR]

In this paper a comparative study of different configurations of refrigeration systems is presented. The main focus of the study is the comparison of energy efficiency and TEWI. The study was done by means of simulation software. According to the study a suitable system configuration with natural refrigerants not only reduces the direct global warming impact, but also improves energy efficiency. The study indicates that in comparison to two independent R404A systems for supermarket applications, an NH3/CO2 cascade system will always have superior performance, while a CO2 booster system provides best efficiency in moderate and cold climates. A R290/CO2 cascade has similar performance to the reference system (heat reclaimed not considered). Even though real system data are scarce, available studies confirm the theoretical simulations. [ABSTRACT FROM AUTHOR]