1、Steve Kujak is the director-next generation refrigerant research for Ingersoll Rand, La Crosse, WI. Kenneth Schultz, PhD, is an engineer- next generation refrigerant research for Ingersoll Rand, La Crosse, WI. Optimizing the Flammability and Performance of Next Generation Low GWP R410A Replacements
2、Steve Kujak Kenneth Schultz, PhD Member ASHRAE Member ASHRAE ABSTRACT Lower global warming potential (GWP) refrigerant replacements for R410A have been extensively studied over the past few years with limited success in finding an optimal replacement. Refrigerant candidates offered to date have been
3、 a trade-off of GWP to performance, but so far candidates have not been offered that trade GWP to flammability while preserving or improving performance of R410A to allow for quick and orderly transition to lower GWP refrigerants. These refrigerants have been either pure R32 or blends of R32 with va
4、rious new olefin refrigerants, like R1234yf and R1234ze(E), along with other traditional hydrofluorocarbons. Pure R32 has good performance, but would require significant hardware redesign to accommodate fluid properties differences, the GWP is one of the highest (GWP=675), as well as being one of th
5、e more flammable refrigerants (burning velocity 6.7 cm/sec). Performance modelling, unit performance testing, and flammability studies were conducted to guide the best refrigerant design to optimize GWP to flammability for blends of R32, R1234yf and R125. This study determined that in fact flammabil
6、ity can be minimized while allowing for a R410A “design compatible” refrigerant that improves on the performance of R410A while balancing GWP. INTRODUCTION Growing concerns about the global warming impact of refrigerants used in HVAC R32 runs 1% to 2% higher than R410A. DR-55 exhibits a small temper
7、ature glide, ranging from 1.6 F (0.9 C) at 40 F (40 C) to a maximum of 2.3 F (1.3 C) at 77 F (25 C). Figure 5. GWP (AR5) and burning velocity relationships for R32/R125/R1234yf blends. Figure 6. Lines of constant capacity relative to R410A for R32/R125/R1234yf blends. Figure 7. Pressure-enthalpy dia
8、gram for R410A, DR-55, and R32 at the A Test condition Figure 8. Temperature-entropy diagram for R410A, DR-55, and R32 at the A Test condition Table 2. Critical Properties of Refrigerants R410A DR-55 R32 Critical temperature (F/C) 160.4 / 71.3 175.4 / 79.7 172.6 / 78.1 Critical pressure (psia/MPa) 7
9、11 / 4.90 803 / 5.53 839 / 5.78 The critical temperature and pressure of R410A, DR-55 and R32 are listed in Table 2. DR-55s critical temperature is much higher than R410A and slightly higher than R32. This provides extended high ambient temperature operating range relative to R410A. The Ph and Ts do
10、mes are wider for DR-55 than R410A because of DR-55s higher R32 content. This reduces the refrigerant mass flow rate needed to achieve a given capacity, potentially reducing pressure drops through heat exchangers. Although DR-55 has an elevated compressor discharge temperature relative to R410A, it
11、is substantially lower than with R32. System Performance Testing of DR-55 4 Ton Residential Split HP Unit DR-55 was evaluated in the original equipment manufacturers laboratories in a 5 ton (17.6 kW), 19 SEER residential split HP unit with variable speed compressor and fans. Unit performance was det
12、ermined in accordance with AHRI Standard 210/240 (AHRI-210/240, 2008). Performance at a number of extended high ambient and low ambient temperatures was determined as well. The unit contains an EXV for cooling and a TXV for heat pump operation. The DR-55 refrigerant charge was determined to be 10% l
13、ess than R410A to achieve the same condenser exist subcooling of 15 F (8 C) at the “A” rating condition. The TXV was not adjusted for the heating tests. Table 3 below gives a summary of the test points and conditions. As noted above, the thermodynamic capacity of the DR-55 is slightly less than R410
14、A by 2% to 3%. Here, all tests were run at equal capacity by increasing compressor speed slightly. Figure 9 shows the relative EER of DR-55 to R410A at all test points. The EER is higher for DR-55 during cooling operation and slightly lower during heating operation as compared to R410A. SEER is used
15、 as the efficiency performance rating factor for residential products. The nominal catalogue SEER for this product is 19.0 with R410A and was determined in this testing to be 19.18. The SEER with DR-55 was determined as 19.65 based on two trials or about a 2.5% increase in efficiency. This increase
16、comes in part from the favourable thermodynamic characteristics of DR-55 noted above. In addition, the refrigerant mass flow rate is lower for the DR-55, leading to lower pressure drop losses in the coils and a higher evaporator exit saturation temperature. DR-55 has been designed to have a marginal
17、ly higher compressor discharge temperature than R410A, but significantly lower than with R32. Unexpectedly, the compressor discharge temperatures with DR-55 were lower than with R410A for most test points; see Figure 10. After review of the test setup, this was likely due to improper instrumentation
18、 positioning. The conclusion from the testing is that DR-55 is a “design compatible” refrigerant for this R410A product and offers increased efficiency over R410A while balancing both capacity and compressor discharge temperature. Table 3. Summary of 4 Ton Residential Split Test Points & Conditions.
19、 Mode Outdoor Temp F (C) Compressor Speed Mode Outdoor Temp F (C) Compressor Speed Cooling 120 (49) High Heating 62 (17) Low Cooling 95 (35) High Heating 47 (8) High Cooling 87 (31) Int. Heating 47 (8) Nom Cooling 82 (28) High Heating 47 (8) Low Cooling 82 (28) Low Heating 35 (2) High Cooling 67 (19
20、) Low Heating 35 (2) Int. Heating 17 (-8) High 15 Ton Packaged Rooftop AC Unit DR-55 was tested at third party laboratory in an experimental high performance 13 ton (45.7 kW) R410A packaged rooftop air conditioning unit. Unit performance was determined in accordance with AHRI Standard 210/240 (AHRI-
21、210/240, 2008) practices. No adjustments were made to the unit other than the refrigerant charge. DR-55 charge was found to be 10% less than R410A to achieve the same condenser subcooling. Figures 11, 12 and 13 show the performance characteristics of DR-55 at a number of extended high ambient condit
22、ions. DR-55 high ambient performance was far superior to R410A in this unit configuration. These large increases in both EER (12% to 27%) and capacity (5% to 18%) are partially the result of DR-55 having a higher critical temperature and preferential thermodynamic properties to R410A which allowed i
23、t to achieve both higher efficiency and higher capacity than R410A. DR-55s lower mass flow rate also helped with allowing for better efficiency and capacity as a result of lower heat exchanger pressure drop. In this case, compressor discharge temperatures with DR-55 were increased over R410A, but by
24、 only small amounts (10F, 5C) that are compatible with todays R410A compressor designs. Again, the conclusion from the testing is that DR-55 is a “design compatible” refrigerant for this R410A product with the additional benefit of offering increased efficiency and capacity over R410A at very high a
25、mbient temperatures while balancing compressor discharge temperatures. 4 Ton Packaged Rooftop HP Unit A 4-ton (14.9 kW), 13 SEER packaged rooftop heat pump unit has also been tested with R410A as baseline and with DR-55 in the original equipment manufacturers laboratory. As above, tests were run acc
26、ording to AHRI Standard 210/240 (AHRI-210/240, 2008). A total of five tests with each refrigerant were run at the “A” rating condition (95F/35C ambient) to determine repeatability. The ratios of the average net air-side capacity, latent capacity, and EER or COP are shown in Figure 13. The variation
27、in net capacity was 1.5%, latent capacity was 5%, and EER/COP was 1.5%. The unit with DR-55 produced essentially the same net capacity and latent capacity as with R410A while the efficiency was about 4% higher. DR-55 and R410A show essentially the same indoor coil surface temperatures at the beginni
28、ng of each tube circuit (eight total) while the leaving circuit saturation temperature with DR-55 is about 1.5 F (0.8 C) higher than with R410A. This higher evaporator leaving saturation temperature boosts both capacity (higher suction density) and efficiency (lower pressure difference). Figure 9. T
29、rends in DR-55 EER relative to R410A. Figure 10. Trends in DR-55 compressor discharge temperature relative to R410A. Figure 11. Trends in DR-55 capacity and EER relative to R410A Figure 12. Trends in DR-55 compressor discharge temperatures (CDT) relative to R410A Figure 13. Ratio of net air-side cap
30、acity (CAP*), latent capacity (LAT*), and EER or COP (EER*) at the “A” condition. Figure 14. Ratio of net air-side capacity (CAP*) and EER or COP (EER*) as a function of ambient outdoor temperature. Figure 15. Difference between DR-55 and R410A compressor discharge temperatures. The ratios of DR-55
31、to R410A capacity and EER (COP) as a function of ambient outdoor temperature are shown in Figure 14. There is a slight upward trend in capacity and efficiency with DR-55 as ambient temperature increases. Figure 15 shows the difference between DR-55s compressor discharge temperature (CDT) relative to
32、 R410A. DR-55 produces a higher compressor discharge temperature by only 5F to 15F (3C to 8C). Again, it can be concluded that DR-55 is a “design compatible” refrigerant for this R410A product. Further analysis of this data will be presented in future publications. CONCLUSIONS Considerations of safe
33、ty related to the flammability of low GWP alternative refrigerants are hindering selection of replacements for R410A. No non-flammable (Class 1) candidates have been found or offered to date. Debate continues around the criteria to classify refrigerant flammability and ability to apply those refrige
34、rants safely. It is clear that safety increases as flammability decreases. This paper offers a candidate refrigerant blend labelled DR-55 67% R32 / 7% R125 / 26% R1234yf that has performance characteristics superior both to R410A (efficiency) and superior to R32 (better match to capacity of existing
35、 designs and significantly lower compressor discharge temperatures) with flammability characteristics much lower than R32 while holding GWP to 675. These optimized characteristics of DR-55 offer a potential path forward to enable an orderly transition to low GWP for our industry. REFERENCES AHRI. 20
36、12. AHRI Low-GWP Alternative Refrigerants Evaluation Program, see http:/www.ahrinet.org/ahri+low_gwp+alternative+refrigerants+evaluation+program.aspx. AHRI-210/240. 2008. ANSI/AHRI Standard 210/240 with Addenda 1 and 2, 2008, Standard for Performance Rating of Unitary Air-Conditioning & Air-Source H
37、eat Pump Equipment, AHRI, Arlington VA USA. Available here: http:/ahrinet.org/App_Content/ahri/files/standards%20pdfs/ANSI%20standards%20pdfs/ANSI.AHRI%20Standard%20210.240%20with%20Addenda%201%20and%202.pdf. ASHRAE-34. 2013. ANSI/ASHRAE Standard 34-2013. Designation and Safety Classification of Ref
38、rigerants, ASHRAE, Atlanta, GA 30329. See: http:/ ASTM E681. 2009. E681 09 Standard Test Method for Concentration Limits of Flammability of Chemicals (Vapors and Gases). ASTM International, West Conshohocken, PA. Available here: http:/www.astm.org/Standards/E681.htm. Goetzler W, Burgos J. 2012. Stud
39、y of Input Parameters for Risk Assessment of 2L Flammable Refrigerants in Residential Air Conditioning and Commercial Refrigeration Applications, ASHRAE Research Project Report RP-1580. Available here: http:/ Metghalchi H. 2013. Developing Alternative Approaches to Predicting the Laminar Burning Spe
40、ed of Refrigerants Using the Minimum Ignition Energy, ASHRAE Research Project Report 1584-RP, Available here: http:/ ISO 817. 2014. ISO 817:2014 Refrigerants Designation and Safety Classification, International Standards Organization, Geneva, Switzerland. Available here: http:/www.iso.org/iso/catalo
41、gue_detail.htm?csnumber=52433. Lemmon EW, Huber ML, McLinden MO. 2013. NIST Standard Reference Database 23: Reference Fluid Thermodynamic and Transport Properties-REFPROP, Version 9.1, National Institute of Standards and Technology, Standard Reference Data Program, Gaithersburg. See: http:/www.nist.
42、gov/srd/nist23.cfm. Minor B. 2012. Intercompany communication from Chemourst to Ingersoll Rand. Schultz K, Kujak S. 2012. System Drop-in Test of R-410A Alternative Fluids (ARM-32a, ARM-70a, DR-5, HPR1D, L-41a, L-41b, and R-32) in a 5-RT Air-Cooled Water Chiller (Cooling Mode), Test Report #1 of the
43、AHRI Low GWP AREP. The report is accessible here: http:/www.ahrinet.org/ahri+low_gwp+alternative+refrigerants+evaluation+program.aspx. Schultz K, Kujak S. 2013. System Drop-in Test of R-22 Alternative Fluids (ARM-32a, DR-7, L-20, LTR4X, LTR6A, and D52Y) in a 5-RT Air-Cooled Water Chiller (Cooling Mo
44、de), Test Report #6 of the AHRI Low GWP AREP. The report is accessible here: http:/www.ahrinet.org/ahri+low_gwp+alternative+refrigerants+evaluation+program.aspx. Schultz K. 2014. Performance of R410A and R22 Alternative Lower GWP Refrigerants in a Small (5 RT) Water Chiller, presented at the ASHRAE Winter Conference, 19-22 Jan 2014, New York City, Conference Paper NY-14-C066. http:/
