High Global Warming Potential Refrigerants Research Articles

Mitigation of safety and environmental challenges posed by refrigerants

The abatement of safety and environmental burden associated with low and ultra-low Global Warming Potential (GWP) refrigerants is a critical undertaking. As the industry shifts towards more environmentally friendly alternatives, mitigating the potential risks and ensuring safety standards becomes paramount. The adoption of mildly and highly flammable refrigerants contributes significantly to minimizing the greenhouse gas impact on the environment, aligning with global climate and sustainability goals. However, it is essential to address safety concerns and potential environmental implications associated with the end use of these refrigerants.A method to mitigate the safety risk in a flammable refrigerant based heating, ventilation, air-conditioning, and refrigeration (HVACR) system is the primary focus of this paper. Advent of A2L and A3 refrigerants as replacements to high GWP refrigerants requires careful handling of leak episodes to lower or eliminate the risk associated with creating flammable mixtures capable of fire/explosion hazard. Solid materials tailored to target the molecule of interest (i.e., refrigerant.) by engineering the microporous structure as well as chemically functionalizing the surface to attract and hold on to the chemical compound being removed from the gas stream was realized. Quantitative analysis reveals the adsorbent's effectiveness in reducing leak potential in the range of 40 %–100 % for various refrigerants. Strategic placement and active leak management with negative pressure offer promising avenues for capturing leaked refrigerants, enhancing overall safety.

Energy, environmental and economic analysis of low GWP refrigerant heat pumps for simultaneous heating and cooling applications

Industries such as hotels, pharmaceuticals, dairy and food and beverage units require heating and cooling for their functional requirements. These industries mostly use fossil fuel-fired boilers for heating (hot water at 60 to 90 °C) and vapor compression refrigeration systems for cooling (−30 to 5 °C), which results in higher primary energy consumption and CO2 emissions. Heat pumps (HPs) are a sustainable option for meeting the simultaneous heating and cooling demands. However, HPs use synthetic refrigerants with high global warming potential (GWP). Therefore, this research aims to evaluate the potential of low and medium-temperature HPs using low GWP refrigerants such as R744, R290, R600a, R161, R1234yf, R1234ze(E) and R1233zd(E). The best refrigerant for the HPs is proposed based on energy efficiency, environmental impact and economic feasibility as critical factors, compared with the conventional high GWP refrigerant (R134a). The occurrence of pinch points across the gas cooler/condenser is evaluated in the analysis. Life cycle climate performance (LCCP) is assessed to study the environmental impact. Also, the operating costs of these HPs are estimated and compared with the conventional systems used in the industry. Results show that R744 HP is an energy-efficient and clean solution for simultaneous heating and cooling applications, primarily at higher temperature lift (lower Tw,i and higher Tw,o) conditions.

Exergy Analysis of Tita nium Dioxide (TiO2) Suspended with R290/R600 as a Substitute for R134a

Synthetic refrigerants are being phased out gradually in accordance with international environmental protection protocols because of global warming and ozone layer depletion. Adopting R290/R600 refrigerant, an environmentally friendly refrigerant, to replace R134a, a high global warming potential refrigerant, provides one of the solutions. In this study, exergy analysis of R134a and TiO2 suspended with lubricant and R290/R600 with a composition of 60% R290 and 40% R600 (60:40) was investigated in vapour compression system (VCRS) using R290/ R600 in TiO2 nanomixture lubricant and compared with R134a and R290/ R600 in pure lubricant. At the inlets and outlets, the main components of the VCRS are connected to temperature and pressure sensors to measure the inlet and outlet temperatures and pressures. The results obtained were used to analyses the exergy losses at various VCRS components (compressor, condenser, evaporator, expansion valve) were investigated to determine the refrigerator’s total exergy destruction (E·xdest.Total) and efficiency (ηex). The E·xdest.Total of R290/R600 in pure lubricant and R290/R600 TiO2 nanomixture lubricant was reduced by 26.9% and 42.3%, respectively, and system ηex increased by 27.7% and 38.9% respectively when compared to R134a in the system. Hence, TiO2 suspended with R290/R600 is potential a substitute for R134a.

Fire-Extinguishing Dibromomethane Mixtures with Fluorinated Alkanes for Fire and Explosion Protection of Oil and Gas Industry Facilities

The high fire hazard level is specific to the oil and gas industry due to the circulation of large volumes of flammable gases and liquids. To ensure fire protection at the oil and gas industry facilities, automated gaseous fire extinguishing is widely used. The main fire-extinguishing agents in automated gaseous fire-extinguishing systems are refrigerants HFC 23, 125, 227еа, FC 318c, and fluorinated ketone FK 5-1-12. Upon the adoption of the international agreements on combating global warming, most fluorinated gaseous fire-extinguishing agents currently used for fire extinguishing fell under restrictions. The article indicates the importance of refrigerants HFC 23, 125, 227еа, and FC 318c, whose production volume must be reduced by 85 % by 2036 to ensure the required level of fire and explosion protection of oil and gas industry facilities. A method to reduce the volumes of used fluorinated alkanes by producing highly efficient fire-extinguishing mixtures, one of the components of which is an agent of high global warming potential (GWP) and the other is a chemical compound with a short atmospheric lifetime, has been proposed. Dibromomethane, which fully meets the latest environmental requirements, is to be considered a short-lived component. Based on the well-known kinetic data, the rates of elementary chemical reactions generated in the flame of the methane-oxygen mixture when contacting with refrigerants HFC 23, 227еа, and dibromomethane, have been calculated and compared. The efficiency of using dibromomethane to increase the fire-extinguishing efficiency of refrigerants HFC 23 and 227еа has been substantiated. An experimental determination of the minimum fire-extinguishing efficiency of the generated mixed compositions is conducted to confirm the correctness of theoretical calculations. The obtained mixed gaseous fire-extinguishing agents enable the reduction of the volume of high global warming potential refrigerants by 1.5–2 times. It has been also demonstrated that the obtained mixed compositions have no toxic impact on a human.

Control of CO2 evaporation in an integrated photovoltaic module: experiments and modelling

The use of environmentally friendly refrigerants and the improvement of the system performance are two main topics in the research on heat pump technology. Given the recent limitations imposed on the usage of high global warming potential refrigerants, there is a growing demand in the market for the adoption of natural refrigerants, like CO2. Nevertheless, CO2 heat pumps operate under transcritical conditions, which can adversely affect its efficiency. Therefore, incorporating a solar heat source into a CO2 heat pump can offer a solution to mitigate low system performance issues. In the present study, a photovoltaic module integrated with the evaporator of a CO2 heat pump is experimentally studied. The PV-T evaporator exploits solar radiation to both generate electricity in the PV cells and ensure the evaporation of CO2 in the collector’s tubes. Simultaneously, the PV conversion efficiency is improved by the cooling effect of the evaporation. The present evaporator works in dry expansion mode, thus the refrigerant flow after the expansion device is sent to the solar collectors, where it evaporates before returning to the compressor. When using a PV-T evaporator, it is necessary to prevent superheating in the evaporator to keep a uniform and efficient cooling of the PV cells. The current heat pump design prevents the occurrence of superheated vapor at the PV-T evaporator’s outlet. Beside the experimental activity a dynamic numerical model of the system has been developed and validated.

Recent progress in pool boiling heat transfer of low GWP refrigerants with the effect of POE lubricant oil

The recent research on pool boiling heat transfer of low global warming potential (GWP) refrigerants under the effect of polyolester (POE) lubricating oils are summarized in this article. Recently, several low GWP refrigerants have been developed as alternatives to the high GWP refrigerants such as hydrofluorocarbons (HFCs). However, it is crucial to comprehend how lubricating oil affects the performance of low GWP refrigerants in terms of compatibility and pool boiling heat transfer (commonly seen in flooded evaporators). The overview suggests that the low GWP refrigerants are compatible with POE oil. Whereas, its heat transfer performance depends on the mass concentration of oil present in the refrigerant. In addition, the pool boiling performance of the low GWP refrigerant is also affected by other factors such as evaporator pressure, saturation temperature, heat flux, and thermophysical properties of refrigerant and oil mixture. The analysis of available heat transfer coefficients (HTCs) for refrigerant-oil mixture shows that the heat transfer performances of the enhanced surfaces are very sensitive in the presence of oil; whereas, it is less severe on a smooth surface. On smooth surfaces, a refrigerant-oil mixture (3% mass concentration) could augment the HTCs as compared to the pure refrigerants subject to evaporator pressure/saturation temperature. In contrast, the simulation studies show that the oil additives always deteriorate the HTCs compared to the pure refrigerant.

Heat loads analysis and creation of a uniform model for commercial refrigeration equipment calculation

The global commercial refrigeration equipment market size was valued at USD 33.53 billion in 2020. It is expected to expand at a compound annual growth rate (CAGR) of 4.2 % from 2021 to 2028. Furthermore, factors such as regulatory pressures, shift to lower Global Warming Potential (GWP) refrigerants, technological breakthroughs, and the ability to cater to the ever-changing consumer behaviors are also anticipated to create promising growth opportunities for the market. Environmental issues related to high GWP refrigerants, including global warming and ozone depletion, are compelling commercial refrigeration equipment manufacturers to seek alternatives. The rising demand for advancements in technologies that can help reduce hazardous gas emissions has led to the market participants increasingly equipping their products with modern and magnetic refrigeration systems. Apart from this, these systems improve the energy efficiency of refrigeration equipment, bringing down the cost of operation.
 The analysis of the structure and heat loads of the commercial freezer with monitoring of temperature distribution on the body of heat-insulating fences and in the internal volume during operation of the system is carried out. The heat loads on the body depending on the structure of the freezer are substantiated on the example of the M400S commercial freezer model. The obtained results allow to significantly reduce the time of selection and calculation of the dimensions of a given model range of equipment for product storage, by developing a standard calculation taking into account the climatic class in which the equipment will be used, and taking into account experimental data obtained during the experiment

Exergetic performance analysis of low GWP refrigerants as an alternative to R410A in split air conditioner

In the present analysis, five alternative refrigerants namely R32, R447A, R447B, R452B, and R454B have been analysed based on exergy to find an alternative of high global warming potential refrigerant R410A, in a split air conditioner. Evaporator temperature is considered as 4.5 °C whereas condenser temperature is taken from 40 °C to 60 °C in the interval of 4 °C. Different performance parameters have been calculated like total exergy destruction (TED), exergy destruction ratio (EDR), exergy efficiency, along with the coefficient of performance (COP) and efficiency defect. The result shows that R447A is found to be the potential alternative to replace R410A in the air conditioner as it has 9.24% higher COP and 15.38% less destruction of exergy along with 9.3% higher exergy efficiency compared to R410A at a condenser temperature of 60 °C. TED and EDR, are found to be minimum with the R447A system among all the considered refrigerants.

Energy efficiency implementation and Greenhouse gas (GHG) reduction by replacing air conditioners by hot water absorption chiller

Climate change impacts are burning issues now-a-days all over the world. GHG emissions are mostly due to fossil fuel burning and inefficient energy use. Energy inefficiencies occurred by use of conventional energy technologies. The textile industries are one of the major manufacturing sectors in Bangladesh and energy consumption is quite high for energy production in this sector. Due to high energy demand, most of the textile industries use non-renewable energy source like natural gas, diesel and furnace oil for energy production. This high energy demand increases high consumption of fossil fuels & accelerating emission of GHGs. So, for future sustainability, energy efficiency is must to reduce GHGs and lowering the quantity of natural gas use for energy production. Moreover, purchased electricity consumption from national grid is also increasing every year. This report shows energy efficiency incorporation by using low energy consuming technologies for HVAC systems where co-generation is used i.e. using generator exhausts or hot cooling water (as a source of heat) for making cool water and use it for air cooling which will reduce dependency on air conditioners enhancing GHGs emission reduction. This will reduce the quantity of high Global warming potential refrigerants (R-22, R-134a and R407c) used in air conditioners. No extra heat source will be required in my process design & reuse the hot water as heat source for air cooling cycle. Financial feasibility also has done which will ensure economic profitability in parallel to Energy savings & GHG reduction. This study reveals that it is possible to reduce natural gas & refrigerant’s consumption which is responsible for GHG emissions.

Performance simulation of HFC-161 as an alternative refrigerant to HCFC-22 for room air conditioner

According to recent Kigali amendment in 2016, ODS (ozone depleting substances) and high GWP (global warming potential) refrigerants must be phased out. There is need to find an alternative refrigerant for air conditioning applications. This article presents the performance comparison for selected low GWP refrigerants commonly used by different air conditioner manufacturers. A baseline test was conducted on a 5.2 kW air conditioner originally designed for HCFC-22 in psychrometric lab as per Indian standard IS 1391 part 1. Simulation tool was tuned and validated against the experimental results within ± 5% accuracy. Parametric analysis was done using IMST-ART tool for the best suitable configuration of compressor capacity, capillary tube, heat exchangers etc. for maximum energy efficiency. Simulation study concluded that the HFC-161 is an energy efficient and climate friendly alternative since it has zero ODP (ozone depletion potential) and ultra-low GWP of 12 except its flammability issue. European standard EN 378, specifies the limit of about 15 g/m3 for charging HFC-161 in the AC system. For HFC-161, the highest cooling capacity of 5.3 kW is achieved in case 4. The HFC-161 gave 27.2% higher EER compared to HCFC-22 system due to 26.47% lowered power consumption. Discharge temperature of HFC-161 is also lowered in the range of 70 °C to 82 °C compared to selected refrigerants. The required charge for HFC-161 was only 55% of HCFC-22.

Thermodynamic Analysis of Split Air Conditioner Using Energy and Exergy Viewpoint with Low GWP Refrigerants Alternative to R410A

In this paper, a comparative thermodynamic analysis on energy and exergy viewpoint is done on different low global warming potential (GWP) refrigerants to find the possible alternative of high GWP refrigerant R410A. R410A is used nowadays in air conditioning systems due to its ozone-friendly characteristic as zero ozone depletion potential (ODP=0) but it has high GWP (GWP=1924) that leads to global warming. Now a day’s global warming is considered to be one of the critical aspects when environmental protection is taken into consideration and researchers from every corner of the globe are working to find refrigerants that not only have zero ODP but it has low GWP too. In this analysis, four prospect refrigerants namely R32, R447A, R447B, and R452B have been studied to find their suitability to replace R410A on different performance criteria as the coefficient of performance (COP), power consumption, exergy efficiency, and exergy destruction. Thermodynamic properties of the studied refrigerants have been taken from the Genetron Properties 1.4 software. The result indicates that all the studied refrigerants have better performance characteristics compared to R410A but R447A has maximum COP and exergy efficiency along with the least total exergy destruction that makes it a possible alternate of R410A.

Modelling the barriers to low global warming potential refrigerants adoption in developing countries: A case of Indian refrigeration industry

Conventional synthetic refrigerants are responsible for ozone depletion and have high global warming potential (GWP). Thus, countries across the globe are progressively phasing out such refrigerants by 2050 under the Kigali amendment. While the developed countries in Europe are the pioneers in promoting the use of low GWP refrigerants, the developing countries are still lagging. This is happening despite these countries being a signatory to the Kigali amendment. However, it is contextual to mention here that the refrigeration industry in developing countries, such as India, faces several barriers to the adoption of low GWP refrigerants. The phasing out of high GWP refrigerants will be considerably delayed if these issues remain unresolved, and there is inadequate research on such barriers to the adoption. With an aim to investigate the precincts of limited adoption, this study identifies 18 barriers through an extensive literature survey. It also contributes to the literature by proposing two more factors responsible for the limited adoption of low GWP refrigerants in the Indian context. Interpretive structural modelling (ISM) methodology is used to elucidate the hierarchical relationship among these barriers. Lack of government incentives emerges as the most compelling factor limiting the adoption of low GWP refrigerants. The research also suggests a four-pronged strategy to promote the adoption of low GWP refrigerants in India.

Applications of refrigerant R1234yf in heating, air conditioning and refrigeration systems: A decade of researches

Abstract HFC refrigerants as R134a, R404A, R407C and R410A are commonly used in heating, air conditioning and refrigeration (HACR) systems since Kyoto protocol. However, they are phased-out due to their high global warming potential (GWP). There are various options to replace high GWP refrigerants, among all hydrofluorolefin (HFO) fluids, such as R1234yf, represents an excellent alternative. With GWP

Theoretical energy performance assessment and environmental impact of various new ozone-friendly refrigerants used in residential air conditioners

This study focuses on energy performance investigation and environmental impact analysis of various new ecofriendly refrigerant blends as alternatives to high global warming potential refrigerant R22 theoretically. In this study, 23 refrigerants were considered at various composition. The present work considered the practical vapour compression refrigeration cycle for the performance assessment of various R22 alternatives. Essential studies such as toxicity, flammability, and total equivalent warming index of various novel refrigerants were also conducted in this study. Results obtained from practical vapour compression refrigeration cycle revealed that the energy efficiency ratio of refrigerants such as R1270 (2.860) and RB03 (R290/R152a of 60/40 in mass %) (2.854) was closer to the energy efficiency ratio of R22 (2.940). Volumetric refrigeration capacity (VRC) of R1270 (3293 kJ/m3) was similar to that of R22 (3297 kJ/m3) whereas VRC of RB03 (2908 kJ/m3) was almost similar to that of R407C (2925 kJ/m3) which was an alternative to R22. Compressor discharge temperature of RB03 was 15.78 ℃ lower when compared to R22. Flammability study revealed that all the new refrigerant blends (RB01 to RB04) were classified into weakly flammable (A2) and flammable (A3) category refrigerants whereas toxicity study revealed that all the investigated refrigerants were classified into non-toxic group (A). Refrigerant blend RB03 was less flammable compared to R1270. Total equivalent warming index analysis revealed that the environmental impact of R422A was 27.88% higher than R22 whereas RB03 has 4.97% lower environmental impact compared to R22. Overall, performance of refrigerant blend RB03 was better compared to 23 investigated refrigerants and it was very nearer to the performance of R22 and hence, it could be considered as an ecofriendly alternative to replace high global warming potential refrigerant R22 used in air conditioners.

Theoretical thermodynamic performance assessment of various environment-friendly novel refrigerants used in refrigeration systems

The present investigation focuses on theoretical performance of various new environment-friendly refrigerant mixtures as substitutes to high global warming potential refrigerant R22. In this investigation, 34 refrigerants were considered at various composition. In this work, both complex vapor compression cycle (actual cycle) and standard vapor compression cycle (ideal cycle) was considered for the performance assessment of refrigerants. Vital studies such as flammability, toxicity, and environmental impact of various novel refrigerants were also carried out in this study. Results obtained from actual cycle showed that the coefficient of performance of refrigerant mixture RM40 (R1270/R134a 90/10 in mass %) (2.728) was the greatest among 34 investigated alternatives and it was closer to the coefficient of performance of R22 (2.770). Compressor discharge temperature of RM40 was 13.36 ℃ lower when compared with R22. Volumetric refrigeration capacity of RM40 (3335 kJ/m3) was slightly higher than that of R22 (3297 kJ/m3). Power spent per ton of refrigeration of RM40 (1.288 kW/TR) was marginally higher than that of R22 (1.269 kW/TR). Global warming potential (GWP100) of RM40 (133) was very low compared to the GWP100 of R22 (1760). Total equivalent warming index (environmental impact) of RM40 was 5.61% lower than R22. However, performance results obtained from standard cycle for various investigated refrigerants were better than actual cycle, since various losses occur were neglected in the standard cycle. Overall, thermodynamic performance of refrigerant mixture RM40 (R1270/R134a 90/10 in mass %) obtained from both actual and standard cycle was the highest among 34 investigated refrigerants and it was very closer to the performance of R22 and hence, it could be considered as an environment-friendly alternative to replace high GWP refrigerant R22 used in refrigeration systems.

Energetic and Exergetic Analysis of Low Global Warming Potential Refrigerants as Substitutes for R410A in Ground Source Heat Pumps

In the European Union (EU), buildings are responsible for about 40% of the total final energy consumption, and 36% of the European global CO2 emissions. The European Commission released directives to push for the enhancement of the buildings energy performance and identified, beside the retrofit of the current building stock, Heating, Ventilation, and Air Conditioning (HVAC) systems as the other main way to increase renewable energy sharing and overall building energy efficiency. For this purpose, Ground Source Heat Pumps (GSHPs) represent one of the most interesting technologies to provide energy for heating, cooling, and domestic water production in residential applications, ensuring a significant reduction (e.g., up to 44% compared with air-source heat pumps) of energy consumption and the corresponding emissions. At present, GSHPs mainly employ the refrigerant R410A as the working fluid, which has a Global Warming Potential (GWP) of 2087. However, following the EU Regulation No. 517/2014 on fluorinated greenhouse gases, this high GWP refrigerant will have to be substituted for residential applications in the next years. Thus, to increase the sustainability of GSHPs, it is necessary to identify short time alternative fluids with lower GWP, before finding medium-long term solutions characterized by very low GWP. This is one of the tasks of the UE project "Most Easy, Efficient, and Low-Cost Geothermal Systems for Retrofitting Civil and Historical Buildings" (acronym GEO4CIVHIC). Here, a thorough thermodynamic analysis, based on both energy and exergy analysis, will be presented to perform a comparison between different fluids as substitutes for R410A, considered as the benchmark for GSHP applications. These fluids have been selected considering their lower flammability with respect to hydrocarbons (mainly R290), that is one of the main concerns for the companies. A parametric analysis has been performed, for a reversible GSHP cycle, at various heat source and sink conditions, with the aim to identify the fluid giving the best energetic performance and to evaluate the distribution of the irreversibilities along the cycle. Considering all these factors, R454B turned out to be the most suitable fluid to use in a ground source heat pump, working at given conditions. Special attention has been paid to the compression phase and the heat transfer in evaporator and condenser.

Cooling mechanism of a solar assisted air conditioner: An investigation based on pressure–enthalpy chart

This paper reports a theoretical study of a conventional vapor compression air conditioner combined with a solar energy source. This system comprises two parts: the cooling mechanism and the solar heat source to operate it. Only the cooling machine part will be considered here, in which the refrigerant temperature leaving the immersed coil inside the storage tank can be calculated directly from the pressure–enthalpy diagram of the operating refrigerant. The investigation has been made using a new low global warming potential refrigerant that belongs to HFO family as an alternative to two high global warming potential refrigerants that belong to HFC family. These are R-1234ze(E) as an alternative to R-134a and R-410A. Comparisons between the classical vapor compression air conditioner and the solar assisted air conditioner and also between the selected refrigerants are investigated. The effects of the refrigerant temperature leaving the storage tank on the main performance parameters such as the coefficient of performance, the gain based on compression work, and the required condenser surface area are discussed.

Experimental evaluation and field trial of low global warming potential R404A replacements for commercial refrigeration

R404A refrigerant is widely used for various refrigeration applications ranging from centralized refrigeration systems for supermarkets to transport refrigeration for truck/trailer. Various environmental regulations have been proposed in the United States and Europe that phase out the use of high global warming potential refrigerants like R404A (global warming potential = 3943) in these applications. This article presents an evaluation of two low global warming potential R404A replacements: A nonflammable refrigerant R448A with global warming potential of 1273 and a mildly flammable refrigerant R455A with global warming potential of 146. Tests carried out with a commercially available R404A self-contained freezer showed that the compressor run time of R448A and R455A are similar to R404A due to similar capacity. The 24-h energy consumption of the compressor is 9% lower for R448A and 6% lower for R455A compared to R404A. Tests were also performed with R448A in a commercially available walk-in freezer/cooler. R448A matches the capacity with 4 to 8% higher efficiency compared to R404A. This indicates that R448A and R455A can reduce both the direct and indirect emissions significantly in these systems. Finally, this study presents the performance results conversion of an actual supermarket refrigeration system from R404A to R448A, which resulted in energy savings from about 9 to 20% depending on outdoor ambient temperature.

(Invited) Beyond Vapor Compression Technologies

The Building Technologies Office (BTO) of the U.S. Department of Energy (DOE) seeks to accelerate the development of the next generation of heating, ventilation, and air-conditioning (HVAC) technologies, including both electric- and natural-gas-driven solutions. HVAC is the largest energy end-use for U.S. buildings, consuming approximately 37.3% (~15 Quads) of total energy.[1] Vapor compression based systems have effectively and efficiently served the HVAC needs for residential and commercial buildings for close to 100 years. Vapor compression technologies are currently the dominant HVAC technology due to their scalability, relatively compact size, high reliability, and other attributes. However, the refrigerants used in these systems have detrimental global effects on the environment when released into the atmosphere. The scientific community has responded to such environmental threats by several proposals to phase down refrigerants with large global warming potential (GWP). What is needed is a paradigm shift in HVAC technologies, moving beyond today’s refrigerants and toward a future based (at least in part) on non-vapor-compression HVAC technologies with the ultimate goal to eliminate high GWP refrigerants all together. This new paradigm is the ultimate environmental solution (zero GWP cooling fluids), provides energy savings for consumers, and will enable manufactures to avoid the challenge of future refrigerant change out cycles. A primary objective is to focus on an end-state with no refrigerants required, while enabling U.S. manufacturers to innovate in ways that will enhance their competitiveness over the longer term. What comes after vapor compression technology? U.S. Department of Energy has recently completed a report on the Energy Savings Potential and RD&D Opportunities for Non-Vapor-Compression HVAC Technologies to help frame the state of these next generation technologies. Possible candidate technologies include, but are not limited to: sorption technologies, alternative thermodynamic cycles, solid state technologies, membrane technologies, electrochemical cycles , and mechanical technologies. BTO currently has several projects that use electrochemical cycles in its HVAC, Water Heating and Appliance R&D portfolio. [1] http://buildingsdatabook.eren.doe.gov/

Two-phase pressure drop and condensation heat transfer of R32/R1234ze(E) non-azeotropic mixtures inside a single microchannel

Much attention has been paid in the recent years to the possible use of fluorinated propene isomers for the substitution of high global warming potential refrigerants. Among the fluorinated propene isomers, R1234ze(E) may be a substitute of R134a for refrigeration applications. R1234ze(E) has a global warming potential lower than 1 (considering a period time of 100 years), and it is receiving some attention also as a component of low global warming potential mixtures. In this article, a mixture of R1234ze(E) and R32 has been investigated at two different mass compositions (23/77% and 46/54% by mass) with regard to the performance at the condenser. The local heat transfer coefficients during condensation in a single microchannel with 0.96 mm diameter are measured and analyzed. The frictional two-phase pressure drop in the same channel is also investigated. The present tests are carried out on the experimental apparatus available at the Two-Phase Heat Transfer Lab of the University of Padova. The new experimental data are compared to those of pure R1234ze(E) and R32. This allows the heat transfer penalization due to the mass transfer resistance occurring during condensation of these zeotropic mixtures to be analyzed and suitable predicting models to be assessed. The knowledge of heat transfer coefficient and pressure drop allows evaluation of the overall performance of these mixtures when used in condensers.