Prde University Prde e-pbs nternational Refrigeration and Air Conditioning Conference School of Mechanical Engineering 2 R32 As a Soltion for Energy Conservation and Low Emission R. Yajima Daikin ndstries K. Kita Daikin ndstries S. Taira Daikin ndstries N. Domyo Daikin ndstries Follow this and additional works at: http://docs.lib.prde.ed/iracc Yajima, R.; Kita, K.; Taira, S.; and Domyo, N., "R32 As a Soltion for Energy Conservation and Low Emission" (2). nternational Refrigeration and Air Conditioning Conference. Paper 59. http://docs.lib.prde.ed/iracc/59 This docment has been made available throgh Prde e-pbs, a service of the Prde University Libraries. Please contact epbs@prde.ed for additional information. Complete proceedings may be acqired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at https://engineering.prde.ed/ Herrick/Events/orderlit.html
R32 AS A SOLUTON FOR ENERGY CONSERVATON AND LOW EMSSON Ryzabro Yajima Koiti Kita Sigehar Taira Nobo Domyo Daikin ndstries, Ltd. Kanaoka 134, Sakai, Osaka, Japan E-Mail ryzabro.yajima@daikin.co.jp koichi.kita@daikin.co.jp shigehar. taira@daikin.co.jp nobo.domyo@daikin.co.jp TEL +81-722-5-9 FAX +81-722-59-9283 ABSTRACT We selected the low GWP refrigerant R32, as a promising refrigerant candidate in the air conditioning field, which has a potential of economically satisfying the reqirements for safety and environmental protection. We investigated its performance and TEW of a 16kW prototype with a variable speed compressor driven by a motor controlled by DC inverter. The test analysis shows that the COP of R32 is higher than that of R41A not only nder the rated capacity bt even nder the capacity redced by compressor speed control. The analysis also shows that its heating COP at a low ambient temperatre and its cooling COP nder the overload condition are sperior and the refrigerant charge can be redced by adoption of smaller diameter heat transfer tbes for heat exchangers. As a reslt, if a R32 system is operated dring the specified seasonal period in Tokyo area, its TEW drops by 18% in comparison with that of R41A and direct impact portion in case of R32 decreases to 7% of the total impact. Since the international standard for safe se of flammable refrigerants is crrently nder drafting, its speriority in performance and low impact on warming may enhance the ftre refrigerant change. NTRODUCTON For protection of ozone layer, in Japan, since early 1997 the air conditioning eqipment with HFC refrigerant has been lanched into the market and the whole air conditioning indstry is on the move to complete the refrigerant change of its major prodcts by the end of 23. n November 1997, for prevention of global warming the Kyoto Conference agreed to establish a target for emission control of greenhose gas in the advanced contries and the restriction also applies to the emission of HFC refrigerants. Tab:Sl P:ropezt:jes ofrefl::i;jemnts 1--1!111 -.,,. d (canpamd wi:h R22) *1) Tl ODP*Zl GWP. 31.*C.) Capacq*4l *4) Flmlm- D:is.Temp! 1 COP Pmss. amlqr ci: R11=1 C2=1 (Yo] (Yo] pal [degc l R32 Low P:zopane Low 97 82 1.:71 54 R41A Nan LOw 234 91 14 3D6 69 R22 Nan Low OD55 19 1 1 194 69 *l)by ASHRAE Standald *2)zane Depl!t:bn Potent::Bl. *3)G bba1w ann :i1g Potent::Bl, PC C 98.;LOOyeaxs *4'fre/Tc/SC /SH=S/5/3/ [degc] *S'frbenno P:mpm:ties by NET REFPROP V6 Eighth nternational Refrigeration Conference at 47 Prde University, West Lafayette, N, USA- Jly 25-28, 2
Up to now, R47C and R41A are selected within the framework of selecting the candidates among the nonflammable refrigerants of which safety is already verified. On the other hand, some reports are pblished from the past regarding the speriority of slightly flammable R32 in energy efficiency1> 2 ) and its risk assessment 3 >. However, R32 is crrently exclded from the candidates, since the consenss abot the reslts of safety assessment is not yet achieved. However, recently R32 is reviewed from the viewpoint of its low GWP and high energy efficiency and some reports are pblished regarding assessment reslts of TEW of the air conditioning eqipment by making comparison with other refrigerants 4 > 5 > 6 ) and the performance when mixed with hydrocarbon 7 >. n general, the higher the non-flammability of a refrigerant is, the larger its GWP and the lower its energy efficiency. Therefore, from the viewpoint of global warming prevention it is desirable to clarify the range of safe application of slightly flammable refrigerants instead of adhering to nonflammability and open a gateway to its adoption within this range. The range of charge amont for safe se of flammable refrigerants is crrently being discssed at the meetings related to the international standard sch as EC and SO and the drafting of the standard is to be completed in the near ftre. When the standard is established, the move toward the practical se of slightly flammable refrigerant will be made. From the above mentioned reasons, we selected the low GWP refrigerant R32 as an alternative refrigerant candidate which has a potential of economically satisfying the reqirements of safety and environmental protection in the air conditioning eqipment indstry. To clarify it, we tested and analyzed its performance and TEW of a 16kW prototype with a compressor driven by DC inverter controlled motor. REFRGERANT PROPERTES Table 1 shows the characteristics of R32, R41A and propane. As for the featres of R32, its GWP is low, high system COP can be expected and it is possible to redce the amont of refrigerant charge becase of its low-pressre drop. The tasks to be taken on are slight flammability and high discharge temperatre. GWP and Flammability Fig.l shows the relation between GWP and the combstion heat per nit weight of each refrigerant. There are many indexes to indicate combstibility sch as the lower flammable limit, the difference between pper and lower flammable limit, the combstion speed and the minimm ignition energy. n this figre the combstion heat per nit weight which is adopted by ASHRAE is sed. 16 -r 2-3 - -----------------------,---------------- 14- Non- LowerFlml:mabl! ----H:\herFlmlmabl! ------1 Flmlmabl! 1 116 12 4HL.-- -+------ 1 1 L---------+---------r---------t 12 D 1 -P=-----,----------.---------.-------- Samt;y c lass:ifi::athns ano 1 4 acco:tdilg tn ASHRAE 34 aooo----.--r-------. 1 ------;---------;,------ 1 GWP lpcc '98..OO:yeam 6 11--s-_7_A--133_a -------+-------+-------l Dt.2'i 4jJl y 4 D 2 _ :'Ho1c ----.L 1 --------+----:Pmpane(29) -M,thane!SO> Btane(6) Ethane(17) 123""" Op la,.,.m:monil!17 j l!lobtane(6da) mnl!ne_,sl-27 j._. 1 1 2 3 4 Com bst.dn Heat 5 J/kg] F:tJJ. GWP and Flammab:il:ii:;Y ofrefi:\leiants Eighth nternational Refrigeration Conference at Prde University, West Lafayette, N, USA- Jly 25-28,2 48
Thogh this index does not always indicate the combstibility of ammonia in nitrogen compond, it well indicates the combstibility of florine-based compond and hydrocarbon. Classification of nonflammable, slightly flammable and highly flammable is in accordance with that of ASHRAE. What can be roghly said from this figre are, 1) The lower the GWP of refrigerant, the higher the combstibility. Since hydrocarbon sch as propane does not contain florine, its GWP is low. However, since the performance and the cost mst be sacrificed for its safe se, its application to the air conditioning eqipment is not practical. On the other hand, if a refrigerant verified as non-flammable is sed, thogh there is no risk of fire accident, global warming impact of the refrigerant emitted into the atmosphere withot being recovered cannot be redced. 2) R32 is near the bondary between non-flammable and slightly flammable Among the slightly flammable refrigerants, R32 exists near the range of non-flammable. Therefore, there is a great potential of sing R32 safely by restriction or redction of refrigerant amont to be charged into the air conditioning eqipment. n addition, since the GWP can be redced to approximately 1/3 in comparison with R41A, the global warming impact of refrigerant can be redced to a great extent. From the above 1) and 2), we selected R32 as the refrigerant, which can decrease the global warming impact withot sacrificing the performance and the cost. Test Unit RESULTS Table 2 shows the specification of prototype. Using the latest R22 model with DC inverter as a mother nit, the compressor, heat exchanger and motorized expansion valve are modified for R32 application. The heat exchanger adopts grooved tbes of 6.35mm in diameter for the otdoor nit and 6mm for the indoor nit. The test of this prototype was condcted with both R32 and R41A for comparison of their performance. Table2 Spec.ofP:rototype R32 and R41A Systems Base Unit: Model Sper nver\:er(r22) Type Split: Capacity Cooling 6 14kW,Heat:ing 6 l8kw Compressor Type High Pressre Side Scroll (Optimm Cylinder Volme for R32) Motor Direct: Crrent: Drived Lbricant: Ether Oil (VG68) ndoor Pipe Dia. 6mm Heat: Pipe Type Grooved Exchanger Path Pattern Cont:er(Cooling) Otdoor Pipe Dia. 6.35mm Heat: Pipe Type Grooved Exchanger Path Pattern Cont:er(Cooling) Expansion Type Electric Drived Exp. Valve Device (Optimm Needle Dia.) Connecting Dia. Gas 3/4inch, Liqid 2.5/Sinch Pipe Length. 5m Reslts and Discssions Eighth nternational Refrigeration Conference at 49 Prde University, West Lafayette, N, USA- Jly 25-28,2
By adoption of smaller diameter tbes for heat exchangers, with R32 the refrigerant charge amont can be redced to 57% of that of R22 mother nit and with R41A to 62%. As for the heat exchanger performance, both the condensing and cooling heat-exchanging capacity increase and the COP Eighth nternational Refrigeration Conference at 41 Prde University, West Lafayette, N, USA- Jly 25-28, 2
::: L<ll..., rl..., ll ll 7kW 14kW Capacity ::: L<ll..., rl..., ll ll +1 +2 14kW Capacity Condensation Heat Transfer -Evaporation Heat Transfer Pressre Drop -Theoretical L..----1 COP Fig. 2 Standard(Cooling) Fig. 4 Overload (Cooling) ::: ::: L<ll.-{... p;. rl. ll ll L<ll......, rl. ll ll +1 +1 SkW 16kW Capacity Fig. 3 Standard (Heating) tj CD 'U 15. CD :::1..., ll CD 1 E-t CD tj ll,q 11.1 rl e:l 7kW 14kW 14kW Standard 15.2kW Capacity Fig. 5 Low otlet Temp. (Heating, -iii.ggc) BkW 16kW 15. 2kW Overload Standarow Otlet Temp. Cooling Mode Heating Mode Fig. 6 Discharged Gas Temperatre Eighth nternational Refrigeration Conference at 411 Prde University, West Lafayette, N, USA- Jly 25-28,2
improves by adoption of smaller diameter tbes. On the other hand, the evaporator capacity drops with R41A de to increase of refrigerant pressre loss cased by adoption of smaller diameter tbes. Since we condcted the test with the small diameter heat exchanger having the same nmber of paths, the pressre drop of R41A was nreasonably large. We, however, considered that the heat exchanger temperatre drop de to pressre drop of each refrigerant mst be eqivalent. Therefore, we compensated the COP of R41A so that it may be fairly jdged. ts vales were compensated from +4 to +6%. The following data show the measred vales with compensation added. Fig. 2 and 3 show the comparison of COP when the capacity is changed by inverter control. The factors for improvement of performance with R32 obtained by the test data analysis are shown in these figres. The bars on the right show the performance nder the rated capacity and those on the left show the performance nder the capacity redced to 112 by rotation speed control. Under the rated capacity, de to improvement in theoretical COP and heat transfer of evaporation and condensation and redction in pressre loss, the COP improves by 1% nder cooling operation and 7% nder heating operation in comparison with those of R41A. Usally the operation nder the capacity redced to 112 occrs more freqently in the field than that nder the rated capacity. Therefore, the COP vale nder this condition has a significant meaning when we discss abot the efficiency dring the specified seasonal period of the air conditioning eqipment with inverter control. Under the capacity redced to 112, the COP improves by 7% nder cooling and 5% nder heating. Since the test nit is a split type, the sction side pressre loss nder cooling is larger than that nder heating. Therefore, the R32 system that has small pressre loss is more favorable nder cooling. f the capacity is redced to 112, as the pressre loss is by natre small, the effect of redction in pressre loss cannot be taken into accont. However, de to improvement in heat transfer effect and theoretical COP, the COP mentioned above is obtained. According to some reports 8 ), the evaporation heat transfer coefficient of R32 is more favorable than that of R41A particlarly in the low mass flx range. When the capacity is redced to112, as the mass flx is in this low range, the speriority in heat transfer coefficient of R32 on refrigerant side brings benefits to COP. n addition, it is necessary to evalate the COP nder the cooling overload condition, becase depending on the installation the ambient temperatre may rise higher than the otdoor temperatre. Fig.4 shows the COP ratio of R32 to R41A nder the cooling overload condition in Japan (ambient temperatre 43). The COP ratio nder the rated capacity is 11% (Fig.2) and that nder the overload condition is 111% (Fig.4). Therefore, even nder the overload condition, the COP of R32 exceeds that of R41A. f the ambient temperatre frther rises, the theoretical COP ratio also increases, which means that if the eqipment is sed beyond the overload condition still R32 is sperior to R41A. Thogh the temperatre scarcely goes below in Japan except for the northern areas, we investigated the low ambient temperatre of -1 for global application. Fig.5 shows the com.larison at -1 ambient temperatre. The effect of redction in refrigerant pressre loss ( + 1.3 +4.1 [Fig.3, Fig.S]) is large in comparison with that nder the rated standard heating condition and the COP ratio is 11% (Fig.5). Therefore, even nder this condition R32 is sperior to R41A. Fig.6 shows the discharge temperatre nder each condition. Under the cooling and heating standard conditions and the cooling overload conditions, the discharge temperatre is 8 to 17deg higher than that of R41A. And nder the heating low ambient condition whose evaporating temperatre is low, it is 33 higher. Refrigerants sch as ammonia and R32 of which latent heat is large and performance is highly efficient have a tendency of discharge temperatre getting high. Therefore, the know-how for applying the material technology and the control technology becomes important. Global Warming mpacts n order to evalate TEW of air conditioners with inverter control, we estimated the annal power consmption sing the data shown in Fig. 2 - Fig. 5. t is assmed that the air conditioner is installed in a store in Tokyo. Fig.7 shows the specified seasonal performance factor calclated CSPF, HSPF and APF. For propane application, in order to prevent the refrigerant leak into the room, indirect expansion systems mst be sed instead of direct expansion system. f an indirect system is sed, de to Eighth nternational Refrigeration Conference at Prde University, West Lafayette, N, USA- Jly 25-28,2 412
the beat exchange between the heat medim, COP drops 2% compared with a direct system. Fig.8 shows comparison of TEW of packaged air conditioners with those refrigerants. Recovery rate is assmed to be 5% in all refrigerants. We can redce TEW by 18% in comparison with R41A. The direct warming impact decreases down to 7% of TEW in case of R32. The drop in efficiency by adoption of indirect expansion system diminishes the merit of propane. Conseqently, TEW of propane is almost eqivalent to the vale of R41A. From the viewpoint of seasonal performance and TEW, R32 can be considered as the most promising candidate. R41A [J Propane. s:: R32.j.l 25 : Direct - D ndirect 2 19. 19.3 rl r---..j.l. 111 :::... - k 3-15.5 15-1.1 1.-1 r-1..t: H '"" 111 t: E-t s:: r-1 ll.j.l 111 111 s:: G) til ll 111 ll til 1 5 - r- 1-1- r- 15.3 14.4,.. - - - 1- CSPF HSPF APF R41A R32 Fig. 7 Seasonal Performance Propane (Chiller Fig. 8 Seasonal TEW Evalati FUTURE PROSPECTS An example of refrigerant change in the history of air conditioning indstry is the change from R12 to R22. This change took place not becase of the restriction to the refrigerant bt the change took place, advanced and spread throghot the market becase of the driving force generated by the inherent performance difference of the refrigerant itself. Since restrictions are 1 9 something that greatly depends on the politics and pblic opinion on the global environmental isses of the times, they cannot become a definite standard. However, since the inherent difference of refrigerants is something that does not change over the times, it can become a standard when we consider the ftre refrigerants. Fig.9 shows the transition of refrigerant for the air conditioning eqipment. The ratio of COP improvement obtained when the refrigerant was changed from R12 to R22 is + 7% if we estimate it from the theoretical COP and the pressre loss. f we consider the COP improvement 6 5 %Valle shows the gailofcop., q\lq -js" iv", qqq, Jl {V " ""***"" '''" ' ilf t ", <i'o qi'q (/ Cc=5 JilC/SH=3/degC Jremp.Dmp 1 :h Base Urrl:. :G 3 5 deg BeatE:HchangerPm:lbnnance :is co itn c F:b'.9 1 2 3 4 H:tJh PmSSUJ:B ll!olpa.] T:ransi::bns ofrefi:::belan,ts Eighth nternational Refrigeration Conference at Prde University, West Lafayette, N, USA- Jly 25-28,2 413
ratio as the driving force for promoting the refrigerant change, from the past history we can make a hypothesis that if the COP improvement ratio is 7% or more, the change of refrigerant will be promoted. f we estimate the COP improvement ratio between R32 and R41A, it is +7% even if we don't take into accont the difference in heat exchanger performance of these refrigerants. Therefore, jdging from the above hypothesis, it is not too mch to say that there is a possibility of ftre refrigerant change. n addition, the energy saving effect obtained from the refrigerant change will definitely contribte to improvement of COP, miniatrization of eqipment and improvement in profitability. The standard for se of flammable refrigerants are crrently being discssed at the ECSO joint working grop meeting and most probably the pper limit of refrigerant charge will be stiplated for secrity of safety. Committee members inclding those from Japan are working hard for preparation of the standard and it is said that discssion among the members on the draft of the standard has been finalized. As mentioned before, R32 is a slightly flammable refrigerant among the flammable refrigerants. Therefore, the pper limit of refrigerant charge amont is likely to be specified within the practically applicable range. There is no impeccable refrigerant, which satisfies all the reqirements for inflammability, low GWP and high-energy efficient performance. Technology and society need to spplement its shortcomings. t is a desirable thing that the above international standard is crrently being discssed to probe the range for safe se of slightly flammable refrigerant and establish the rle for practical application. t is tre that the consenss of safety to R32 is growing and that is something we hope for. Since R32 has a potential to economically satisfy the reqirements of safety and environmental protection simltaneosly, R32 is likely to become the major refrigerant for the ftre air conditioning eqipment. REFERENCES 1) R. Yajima et al., 1994, "The Performance Evalation of HFC Alternative Refrigerants for HCFC- 22", R Joint meeting, CFCs The Day After, Padova 2) K. Frhama et al., 1994, "Performance Evalation of Residential Air Conditioner with HFC32/125 Mixtre, The nternational Symposim HCFC Alternative Refrigerants, Kobe 3). Kataoka et al., 1996, "Flammability Evalation of HFC-32 and HFC-32/134a nder Practical Operating Condition, nternational Refrigeration Conference, Prde 4) K. Koiti et al., 1998, "Performance Evalation of low GWP HFC Refrigerants", The nternational Symposim HCFC Alternative Refrigerants, Kobe 5) K. Frhama et al., 1999, "Alternative refrigerants in Air-Conditioners for residential and Commercial Use", 6th lea Heat Pmp Conference 6) G. Nagai, 1999, "Global Warming and Evalation oftew", Annal Meeting of JSME, Tokyo 7) Y. Yji et al., 1999, "Residential Use Air Conditioner for Advanced COP:Acceptability of HFC32/Hydrocarbon Mixtres", 6th lea Heat Pmp Conference 8) H. Fjino et al., 1999,"Heat Transfer Performance in Horizontal Tbe of HFC-32", JSRAE Meeting Eighth nternational Refrigeration Conference at Prde University, West Lafayette, N, USA- Jly 25-28, 2 414