Low GWP Chiller Refrigerants: Weighing the Tradeoffs

Transcription

1 (GWP: Global Warming Potential) Low GWP Chiller Refrigerants: Weighing the Tradeoffs ASHRAE/UNEP: Road to Climate Friendly Chillers Cairo, Egypt October 1st, 2010 Kostas Kontomaris, Ph.D. DuPont Fluorochemicals R&D CFCs HCFCs HFCs HFOs

2 2 Centrifugal water chillers Condenser High Pressure Refrigerant Gas Electricity Expansion Valve Evaporator Water Chilled Water To Building Centrifugal Compressor Low Pressure Refrigerant Gas Number of centrifugal chillers in Operation around the world: Over 130,000 Total refrigerant bank: ca. 60,000 tonnes Previous centrifugal chiller refrigerants and transitions CFC-11 HCFC-123 CFC-12 HFC-134a Ozone Depleting High GWP Need more environmentally sustainable replacements for HCFC-123 & HFC-134a

3 HFO-1234yf and : Basic Properties (HFO: Hydro-Fluoro-Olefin) Marginally Flammable Non-flammable 3 Property Chemical Formula Safety Class (ASHRAE Std 34) ODP GWP , ca. 600 T cr [ o C] T b [ o C] Chiller Glide [ o C] CFC-12 CCl 2 F 2 A N/A HFC-134a CH 2 F-CF 3 A N/A HFO- 1234yf CF 3 CF=CH 2 A2L N/A Azeotrope A1 (expected) Negligible (ODP: Ozone Depletion Potential)

4 4 HFO-1234yf and : Vapor Pressure HFC- 134a HFO- 1234yf HFC- 134a HFC- 134a CFC- 12 HFO- 1234yf CFC- 12 HFC-134a Pressure [kpa] Compression Ratio CFC-12 HFO-1234yf T evap =4.4 o C Chiller Operation Temp [oc] T cond = 37.8 o C

5 5 HFO-1234yf and : P-h Diagram Approximates HFC-134a Closely CFC-12 Pressure [kpa] 1000 HFC-134a HFO-1234yf Enthalpy [kj/kg]

6 6 Predicted Efficiency. Capacity Trade-Offs T eva = 4.4 [ o C]; T cond = 37.8 [ o C]; T subc = 0 [ o C]; T superh = 0 [ o C]; P=0 [Pa] COP Relative to HFC-134a HFC-1234yf CFC-12 HFC-134a Attractive COP-Capacity Trade-off Vol Vol Cooling Capacity Realtive Relative to to HFC-134a (COP: Coefficient Of Performance)

7 Centrifugal Compressor Operation Tip Speed Diameter Tip Speed Diameter HFC- 134a HFC- 134a CFC HFO- 1234yf HFC- 134a HFO- 1234yf CFC Ω = Ω ˆ h comp υ CFC-12 HFO-1234yf Θ Θ HFC-134a = Q& υ D 2 7

8 HFO-1234yf: Thermal Stability 8 Neat HFO-1234yf Neat HFC-134a After o C Sealed glass tube testing procedure based on ASHRAE-ANSI STD 97 HFO-1234yf HFC-134a No Detectable Fluoride nor Acid Generation Similarly for

9 HFO-1234yf and : Compatibility with POE Lubricants, Plastics and Elastomers (POE: Polyol Ester) 9 HFO-1234yf/POE and /POE blends: Miscible over range of chiller conditions Stable with metals at 175 o C for 2 weeks HFO-1234yf and with Polymers and Elastomers: Degree of interaction comparable to HFC-134a

10 A Low GWP HCFC-123 Replacement: DR-2 HCFC-123 cannot be used in new equipment in EU today and the US in 2020 HCFC-123 production already scheduled for phase-out by 2030 Normal Boiling Point [ºC] Critical Temperature [ºC] Critical Pressure [MPa] OEL [ppmv] LFL [vol ] ODP Atmospheric life time [yrs] HCFC None DR To be determined None (24 days) 10 GWP 100 YR ITH Glide 77 None <10 None Based on evaluations to date: Favorable Toxicity Profile Adequate Thermal Stability and Compatibility with Chiller Materials

11 DR-2 Vapor Pressure. HCFC P evap [kpa] P cond [kpa] Compr Ratio DR-2 HCFC-123 () DR-2 Temp [ o C]

12 DR-2 P-h Diagram. HCFC HCFC-123 Pressure [kpa] HFO- 1336mzzZ DR Enthalpy [kj/kg] Use to predict cycle performance (next)

13 DR-2 Cycle Performance. HCFC-123 T eva = 4.4 [ o C]; T cond = 37.8 [ o C]; T subc = 0 [ o C]; T superh = 0 [ o C]; P=0 [Pa] 13 HCFC-123 DR-2 DR-2 HCFC-123 () Cooling Duty kj/s 3,517 3,517 Heat of Compression-Isentropic kj/kg Net Refrigeration kj/kg COP Isentropic Vapor Density at Compr Inlet Kg/m Volumetric Cooling Capacity kj/m Vol Flow Rate at Compr Suction m 3 /s Impeller Tip Speed m/s Impeller Diameter m Large tonnage centrifugal chillers using DR-2 could be designed with energy efficiency comparable to HCFC-123

14 Summary I: Low GWP Chiller Refrigerants 14 C O P _ is HFC-123 DR-2 HFC-134a The case for DR-2 Low-P Mid-P COP DR-2 DR DR-2 HFO- 1234yf HFO-1234yf ,000 1,500 2,000 2,500 3,000 Vol Cool Cap [kj/m3] Higher energy efficiency Lower vapor pressure (containment; no pressure rated vessels) Favorable safety and environmental properties

15 Summary II: HFC-134a Replacements 15 Two promising low GWP candidates to replace HFC-134a in centrifugal chillers: HFO-1234yf and Low Toxicity; Attractive Environmental Properties Thermal Stability Compatibility with POE Lubricants, Plastics and Elastomers Performance close to HFC-134a; No glide Energy Efficiency Cooling Capacity HFC-134a Retrofit FLAMMABILITY GWP 100 HFO-1234yf 2L 4 Higher Higher Easier Nonflammable <600 Preferred Refrigerant?

16 Outlook: Need for Regulatory Flexibility 16 Refrigerant with lower GWP may not lead to lower environmental impact: Contributions to Chiller Total Equivalent Warming Impact (TEWI): Energy Consumption>>Refrigerant Emissions TEWI TEWI HFO-1234yf?? KEY: Flexible climate protection regulations Acceptance of optimum refrigerants