Seminar 2 Thermodynamic Analysis for Low-GWP Refrigerants. Possibilities and Tradeoffs for Low-GWP Refrigerants

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1 Seminar 2 Thermodynamic Analysis for Low-GWP Refrigerants Possibilities and Tradeoffs for Low-GWP Refrigerants Mark O. McLinden National Institute of Standards and Technology Boulder, Colorado ASHRAE Winter Conference New York City January 19, 2014

Thermodynamic Analysis of Low-GWP Refrigerants Seminar 2 Learning Objectives Explain the tradeoff between the COP and volumetric capacity of the vapor compression cycle Describe the refrigerant

2 Thermodynamic Analysis of Low-GWP Refrigerants Seminar 2 Learning Objectives Explain the tradeoff between the COP and volumetric capacity of the vapor compression cycle Describe the refrigerant thermodynamic parameter with the dominant influence on the COP and volumetric capacity Describe under what operating conditions the vapor compression cycle theoretically approaches the Carnot cycle COP Describe desirable characteristics of refrigerants Provide screening process of candidate fluids to serve as a refrigerant Explain search results for an ideal refrigerant ASHRAE is a Registered Provider with The American Ins9tute of Architects Con9nuing Educa9on Systems. Credit earned on comple9on of this program will be reported to ASHRAE Records for AIA members. Cer9ficates of Comple9on for non- AIA members are available on request. This program is registered with the AIA/ASHRAE for con:nuing professional educa:on. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construc:on or any method or manner of handling, using, distribu:ng, or dealing in any material or product. Ques:ons related to specific materials, methods, and services will be addressed at the conclusion of this presenta:on.

3 Acknowledgements Co-authors: Andrei Kazakov, NIST, Boulder, CO J. Steven Brown, The Catholic University of America Washington, DC Piotr Domanski, NIST, Gaithersburg, MD Sponsorship: U.S. Department of Energy Office of Energy Efficiency and Renewable Energy A. Bouza, B. Habibzadeh, Project Managers

4 Outline/Motivation Industry needs low-gwp refrigerants What are the thermodynamic limits to performance? what are optimum thermodynamic parameters? how do current fluids compare? What molecules might be good refrigerants? è Can We Do Better? ç

5 What s the Problem? Opportunity? HFC refrigerants are shortlived climate pollutants (SLCP) (along with methane, black carbon [soot], and tropospheric ozone) GWP impact is short lived Ê understated by usual 100-year time horizon Control of SLCPs offer faster impact on global temperature increase Temperature Increase ( C) opportunity to impact warming by 2050 Business as usual Control CO 2 only Control SLCPs only Control both CO 2 and SLCPs Figure adapted from Hu, et al., Nature Climate Change (2013)

6 Cycle Analysis & Optimum Thermodynamic Parameters

7 Cycle Analysis What do the results mean? Mass basis versus molar basis Ê properties vary less on a molar basis

8 Cycle Analysis What do the results mean? Efficiency versus critical temperature Ê higher T crit moves cycle away from pinched top of 2-phase dome

9 Cycle Analysis What do the results mean? Efficiency versus critical pressure Ê higher p crit moves cycle away from critical point (similar to effect of higher critical temperature)

10 Cycle Analysis What do the results mean? Efficiency versus vapor heat capacity Ê optimum value of C po : too small è high superheat losses too large è high expansion losses

11 Properties From Molecular Structure

warming potential (GWP)* Ê atmospheric life

12 What Properties are Important? Safety Ê toxicity (acute and chronic) Ê flammability* Environmental Ê ozone depletion potential (ODP) Ê green house warming potential (GWP)* Ê atmospheric life (impacts ODP & GWP)* Materials Ê compatibility with metals, seals, etc. Ê lubricant Ê stability (hydrolysis, polymerization, etc.) Performance Ê thermodynamic properties** Ê transport properties* **focus of this project *secondary objective

NIH) Listing of 100 000 000 chemical compounds Select: Ê

13 Fluid Screening Fluids from PubChem database (U.S. NIH) Listing of chemical compounds Select: Ê 15 or fewer atoms in molecule Ê only C, H, N, O, S, F, Cl, Br [Midgley, 1937] 56,203 compounds 1,234 compounds virtual screening

14 Estimation of GWP GWP itself not amenable to direct estimation Ê insufficient learning set (only ~100 fluids) But, GWP is related to: I-R absorption spectrum & atmospheric lifetime Approach Optimize 3-D structure of each molecule minimize energy by quantum mech. methods Compute I-R absorption spectrum Ê + atmospheric absorption è radiative efficiency atmospheric window + I-R absorption spectrum Atm. lifetime est. by reaction w/ hydroxyl radical Ê established group-contribution methods Lifetime + radiative efficiency è GWP Resulting GWP sufficient for screening ò radiative efficiency Figures adapted from Pinnock, JGR (1995)

15 Estimation of GWP RMS deviation: factor of 3 (adequate for screening)

16 Estimated GWP for 56,000 Compounds GWP not sufficient filter (93.5 % have GWP < 200)

17 Estimation of Flammability RMS deviation: factor of 1.24

18 Fluid Screening

19 Filters Applied Remaining Starting list: 56,203 compounds Fluid Count GWP 100 < 200 Ê estimation method of Kazakov, et al. (2012) 52,265 Toxicity screen Ê markers/groups compiled by Lagorce, et al. (2008) 30,135 Flammability: LFL > 0.1 kg/m 3 Ê estimation method of Kazakov, et al. (2012) 20,277 Critical temperature: 300 K < T crit < 550 K Ê estimation method of Kazakov, et al. (2010) 1728 Stability: screen out problematic groups (e.g., peroxides, 3-member rings, see paper) 1234

20 Fluid Screening Results Halogenated alkanes; e.g., HFCs

21 Fluid Screening Results Halogenated alkenes (a.k.a. olefins); e.g. HFOs

22 Fluid Screening Results Oxygen-containing; e.g., halogenated ethers & alcohols ether [ O ] alcohol [ OH]

23 Fluid Screening Results Fluids containing N or S; e.g., amines, thiols, thioethers amine [central N] thiol [ SH] thioether [ S ]

Fluid Screening Results 62 Fluids passed all filters + 300 K T crit 400 K 1

nated alkane (HFC-152a) 39 nated olefins [e.g.

1 HBFO (Br-containing) Ê 7 2-carbon; 20 3-carbon; 10 4-carbon; 2 5-carbon 11 nated

24 Fluid Screening Results 62 Fluids passed all filters K T crit 400 K 1 halogenated alkane (HFC-152a) 39 halogenated olefins [e.g., R1234yf, R1234ze(E)] Ê 23 HFOs; 8 FOs (fully fluorinated) 7 HCFOs (Cl-containing); 1 HBFO (Br-containing) Ê 7 2-carbon; 20 3-carbon; 10 4-carbon; 2 5-carbon 11 halogenated ethers Ê all contain a C C double bond Ê 2 cyclic ethers 4 halogenated amines Ê (+ ammonia, T crit = 405 K) 3 sulfur-containing compounds Ê 2 thioethers;1 thiol 3 halogenated alkynes (C C triple bond) CO 2

25 Tradeoffs

26 Tradeoffs Thermodynamic Reality Cycle analysis: Ê high p crit, low C p 0 optimal for ideal cycle Ê higher values of C p 0 optimal for cycle with LL/SL HX Estimate p crit, C p 0 for candidate fluids High p crit, low C p 0 sparsely populated by real fluids Ê LL/SL HX better matches fluids that are available

27 Tradeoffs Cycle Efficiency Simulate fluids: Ê simple cycle Ê LL/SL HX (with optimized ε) Ê economizer Screen fluids based on: COP/COP Pareto (at same Q vol ) (otherwise, results skewed towards fluids with high T crit) Many fluids benefit from LL/SL HX or economizer (some a little, others a lot) Cooling (40 C/10 C) cycle with optimized LL/SL HX

Tradeoffs Practical Considerations [focus on HFOs limited data for other classes of fluids] Toxicity

g., R1216] to listed in Chemical Weapons Convention [PFIB: CF 2 =C( CF 3 ) 2 ] Ê =CF 2 group appears

(perhaps as a component in blends) Flammability Screening included moderately-flammable fluids (few

28 Tradeoffs Practical Considerations [focus on HFOs limited data for other classes of fluids] Toxicity HFOs/FOs range from: ASHRAE class A [R1234yf, R1234ze(E)] to moderate toxicity [e.g., R1225ye(E)] to highly toxic [e.g., R1216] to listed in Chemical Weapons Convention [PFIB: CF 2 =C( CF 3 ) 2 ] Ê =CF 2 group appears to be problematic?wider use of moderately toxic fluids? (perhaps as a component in blends) Flammability Screening included moderately-flammable fluids (few candidates are non-flammable) Ê safety codes examining wider use of 2L fluids Ê hydrocarbons widely used in small-charge systems

Tradeoffs Practical Considerations Stability Low-GWP almost synonymous with lower stability [exceptions are HC, CO 2, NH 3 ] HFOs have potential to polymerize Ê ranging from very unlikely to polymer

29 Tradeoffs Practical Considerations Stability Low-GWP almost synonymous with lower stability [exceptions are HC, CO 2, NH 3 ] HFOs have potential to polymerize Ê ranging from very unlikely to polymer precursor Ê polymerization inhibitors are available Ozone Depletion Potential (ODP) Some candidates contain Cl or Br Ê ODP will be very small if atmospheric lifetime is short [R1233zd(E), ODP < , approved by U.S. EPA] Cost More complex molecules will be more costly Ê?instead, implement safety measures to allow use of flammable refrigerants? $

30 So What are the Choices (1)? HFCs Ê familiar; many in ASHRAE class A1; high GWP HCs (hydrocarbons) Ê flammable, ASHRAE class A3 NH 3 (ammonia) Ê excellent thermodynamics Ê ASHRAE B2L CO 2 (carbon dioxide) Ê ASHRAE A1 Ê high operating pressures, supercritical cycle HFOs (hydrofluoroolefins) & related compounds Ê new, not fully characterized Ê some now being commercialized Ê others known in other applications (e.g., polymers) New fluids Ê???

31 So What are the Choices (2)? HFOs: Ê R1234yf, R1234ze(E): slightly flammable Ê R1234ye(E): limited data Ê R1225ye(Z), R1225ye(E): chronic toxicity Ê R1243zf: limited data, flammable Ê R1132(E), R1132(Z): unknown risks HCFOs (chlorine-containing) Ê some possibilities if non-flammable essential Fluorinated ethers Ê 2 possibilities Fluorinated alkyne (C C triple bond) Ê 1 possibility Nitrogen or sulfur containing: Ê long shots

So What are the Choices (3)? Blends Use blends to: Ê adjust properties Ê azeotropes might give higher Q vol than pures Ê allow use of additional components (flammable or moderately toxic?

32 So What are the Choices (3)? Blends Use blends to: Ê adjust properties Ê azeotropes might give higher Q vol than pures Ê allow use of additional components (flammable or moderately toxic?) HFO + HFC: Ê proposed and currently under test HFO + HFO: Ê might allow use of R1225 isomers? Blends with hydrocarbons: Ê likely to be flammable if HC > 5 % Blends with CO 2 : Ê adjust properties (raise pressure & Q vol )

33 Conclusions Majority of compounds screened have low GWP Thermo analysis: better fluids at least allowed 62 fluids identified with: Ê GWP Ê LFL 0.1 kg/m [~ASHRAE Class 1 or 2] Ê no obviously toxic or unstable groups [but some of the 62 are known to be toxic] Ê 300 K T crit 400 K Poor correspondence between optimum thermo parameters and real-fluids Ê at least for the simple vapor compression cycle Ê fit the cycle to the fluid Exhaustive search Ê there is no magic fluid

34 References Kazakov, A.; McLinden, M. O.; Frenkel, M. (2012). Computational design of new refrigerant fluids based on environmental, safety, and thermodynamic characteristics. Ind. Eng. Chem. Res. 51, McLinden, M. O.; Domanski, P. A.; Kazakov, A.; Heo, J.; Brown, J. S. (2012). Possibilities, limits, and tradeoffs for refrigerants in the vapor compression cycle, 2012 ASHRAE/NIST Refrigerants Conference, Gaithersburg, MD, ASHRAE, Inc. Domanski, P. A.; Brown, J. S.; Heo, J.; Wojtusiak, J.; McLinden, M. O. (2013) A thermodynamic analysis of refrigerants: Performance limits of the vapor compression cycle, International Journal of Refrigeration (in press), doi/ /j.ijrefrig McLinden, M. O.; Kazakov, A. F.; Brown, J. S.; Domanski, P. A. (2013). A thermodynamic analysis of refrigerants: Possibilities and tradeoffs for Low-GWP refrigerants. Int. J. Refrigeration (in press), doi/ / j.ijrefrig

35 Questions? Mark McLinden

Transition to Low-GWP Refrigerants: Options and Tradeoffs

Transition to Low-GWP Refrigerants: Options and Tradeoffs Piotr A. Domanski Leader, HVAC&R Equipment Performance Group Engineering Laboratory National Institute of Standards and Technology Gaithersburg,