Energy Efficiency and Heat Pumps ConsortiumCopyright © 2020 Center for Environmental Energy Engineering
IEA Annex 54 Update –Low-GWP Refrigerants in Residential AC
June 2020
Tao Cao, Yunho Hwang
Center for Environmental Energy EngineeringDepartment of Mechanical Engineering
University of MarylandCollege Park, MD 20742-3035
Energy Efficiency and Heat Pumps ConsortiumCopyright © 2020 Center for Environmental Energy Engineering
Background• Low GWP refrigerants are coming for residential AC systems.• Yet, there hasn’t been a consensus on the winning candidate.• What’s the latest R&D and regulation efforts in bringing low
GWP alternatives to residential AC?
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• AC leads the power consumptions in residential sectors.
Fig. source: [1]
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Recent Reviews• Comprehensive reviews focusing on residential AC alternatives are needed.
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Author Focus Highlights
Dalkilic and Wongwises (2010) [2]Theoretical analysis R12, R22 and R134a replacement with
mixtures from (R134a, R152a, R32, R290, R1270, R600 and R600a)
R290/R600a (40/60) best alternative for R12; R290/R1270 (20/80) best alternative for R22
Benhadid-Dib and Benzaoui (2012) [3] Briefing on refrigerant phasing history up to 2015. Cover the basics of most refrigerants, and overview of regulation efforts
Wang et al. (2012) [4]Alternative refrigerants for air conditioners, heat pumps,
chillers, water heaters, ice makers and refrigeration equipment
AHRI led, industrial-wide cooperative program lasts years, covers dozens candidates
Bolaji and Huan et al. (2013) [5] Natural refrigerants: R717, HCs, R718, R744 Reviewed potential application of major natural refrigerants, including oil compatibility
McLinden et al. (2014) [6] 62 candidates with critical temperatures within 300 to 400 K Thermodynamic analysis indicate no ideal fluid
Sarbu (2014) [7] Candidates for air conditioning, heat pump and commercial refrigeration applications Describes refrigerants selection based on properties
Mota-Babiloni et al. (2015) [8]Commercial refrigeration working fluids R404A, R507A and their substitutes: HC, Natural (CO2, NH3), HFC, HFO/HFC
mixture
No universal solution: propane for low charge; low-GWP HFC or HFC/HFO mixture as drop-in or retrofit; CO2 for
transcritical
Pham and Monnier (2016) [9] R410A interim replacements (R32 and other A2L HFO blends) and long term replacements (natural, HCs)
Dedicated overview for R410A, different paths towards long term ultra-low-GWP
Domanski et al. (2017) [10] R410A and R404A candidates review Comprehensive database search based on modeling and cycle analysis
Mota-Babiloni et al. (2017) [11] Focused on recent low-GWP investigations because of F-gas Regulation for applications of all sizes
Unique perspective looking into policy driven advancements in low-GWP research and commercialization
Harby (2017) [12] Hydrocarbon as replacements in refrigeration, AC and automobile AC Comprehensive review of latest HC research efforts
Abas et al. (2018) [13] Major natural and synthetic refrigerants A parametric quantification based model for natural refrigerant selection and optimization
Ciconkov (2018) [14] Historic overview of refrigerants transition up to now and future envisions, focusing on natural refrigerants and HFOs
Proposed direct phase-in of natural refrigerants instead of step by step phase down
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R&D Progress – A1
• R744, GWP: 1• Pros: environmentally benign and stable• Cons: need major system redesigns to improve performance and reliability (high pressure)• R&D Gaps: mostly focused on applications other than residential
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• R466A (49% R32, 11.5% R125, 39.5% R13I1), GWP: 730• Pros: non-flammable, similar properties of R410A• Cons: supply and cost associated with iodine in R13I1• R&D Gaps: need more performance and reliability studies
Energy Efficiency and Heat Pumps ConsortiumCopyright © 2020 Center for Environmental Energy Engineering
R&D Progress – A2L• R32, GWP 675• Performance: close to R410A (lower discharge T limits)• Pros: low GWP, pure fluid, validated success in ductless units• Cons: flammability, interim replacements• R&D Gaps: safety study (for unitary systems)
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• A2L mixtures, GWP: ~200 to ~700)• Representatives: R452B (67% R32 + 26% R1234yf + 7% R125); R454B (68.9% R32 and 31.1% 1234yf);
R446A (29% R32 + 3% R600 + 68% R1234ze); R447A (68% R32 + 3.5% R125 + 28.5% R1234ze(E))…
• Performance: on par with R410A with variations• Pros: lower GWP than R32• Cons: flammability, interim replacements, not validated in the market• R&D Gaps: need to find convincing advantages over R32 and R466A
Operating Envelop R32 vs. R410A [15]
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R&D Progress – A3
• A3, GWP < 100• Representatives: R290, R161• Performance: slightly lower than R410A but can be improved with system redesigns• Pros: ultra-low GWP (ultimate replacements)• Cons: flammability, costs with associated product redesigns• R&D Gaps: ways to handle flammability without sacrificing performance and cost
• Safety precautions• Secondary loop• Novel designs (On-going efforts)
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Comparison
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• R466A, R32, R452B / R454B and R290 remain the top replacements of R410A for now, considering balances among the GWP, performances and property similarities.
Fig. source: [16]
Energy Efficiency and Heat Pumps ConsortiumCopyright © 2020 Center for Environmental Energy Engineering
Regulation Progress – USA• Refrigerants
• ASHRAE Standard 34: refrigerant classification• EPA SNAP: identify acceptable substitutes (environmental aspect)
• System• ASHRAE 15: refrigerant system safety (subcommittee 15.2 for residential application)• UL IEC: safety of household appliances
• Building & Local Codes
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Code Adoption Process
Fig. source: [17]
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Novel Unitary System Design• Propose a novel design, enabling safe flammable refrigerant usage while ensuring
performance advantages over R410A• The APF can be increased by up to 45% as compared to the existing design based on simulations.• Refrigerant charge can be reduced by 54%.
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System Schematic
COP Comparison vs. Ambient Temperature (Top);Performance Comparison in Different Climates (Bottom)
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2nd Year Work – Component Optimization
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• Objective:• A comprehensive review of latest R&D progress on component
optimizations using low-GWP refrigerants in residential AC• Performance, charge and cost comparisons of various novel HX
designs aiming for low GWP refrigerants in residential AC• Expected outcome:
• An report covering latest R&D progress, clarifying research trends of component optimizations for residential AC refrigerant replacements (On-going, 30+ review completed)
• A quantitative comparison of various novel HX designs. Guidelines on future high performance, low charge HX designs for residential AC
Energy Efficiency and Heat Pumps ConsortiumCopyright © 2020 Center for Environmental Energy Engineering
Conclusions• We have completed a review of recent R&D and regulation
progress on low GWP refrigerants for residential AC.• R466A is the most promising non-flammable immediate
replacements, though more performance and reliability studies are necessary.
• R32 remains in strong position over other A2L mixtures with proven market success, other than unitary systems.
• The ultra-low-GWP replacements are still an open question.• Existing efforts to promote interim refrigerants mostly focus
on product safety re-designs.
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Thanks!
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Energy Efficiency and Heat Pumps ConsortiumCopyright © 2020 Center for Environmental Energy Engineering
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