1、Steve Kujak is the director-next generation refrigerant research for Ingersoll Rand, La Crosse, WI. Kenneth Schultz, PhD, is a engineer- next generation refrigerant research for Ingersoll Rand, La Crosse, WI. Julie Majurin is chemist- next generation refrigerant for Ingersoll Rand, La Crosse, WI. Co
2、mprehensive Assessment of Centrifugal Chillers Using Next Generation Refrigerant R1233zd(E) Steve Kujak Kenneth Schultz, PHD Julie Majurin Member ASHRAE Member ASHRAE Member ASHRAE ABSTRACT A new olefin refrigerant, R1233zd(E), has been identified for use in HVAC chillers. R1233zd(E) is being consid
3、ered for a number of applications including use as, but not limited to, a solvent, a foam blowing agent, a refrigerant in large centrifugal chillers, and a refrigerant in heat recovery equipment. R1233zd(E) provides specific environmental and safety features of interest including very short atmosphe
4、ric life (26 days), no impact to stratospheric ozone, ultra-low Global Warming Potential (GWP of 1), no measured secondary adverse environmental impacts (such as increases in ground level ozone or trifluoroacetic acid (TFA), low toxicity, and non-flammability. This paper will provide an overall asse
5、ssment of applying this new olefin refrigerant in centrifugal water cooled chillers. System performance characteristics will be compared to a number of refrigerants including R134a, R1234ze(E), R245fa, and R123. LCCP emission profiles will be compared. Reliability indicators, such as material compat
6、ibility and chemical stability, will be provided INTRODUCTION New regulatory policies and regulations to restrict and lower the direct GWP impact of F-gases have recently been proposed and adopted by some countries. These regulations have spurred both the technology development of alternative lower
7、GWP F-gas chemistries and renewed consideration of so-called “natural” refrigerants, such as water (R718), ammonia (R717), carbon dioxide (R744), and hydrocarbons. A new olefin refrigerant, R1233zd(E) or trans-1-chloro-3,3,3-trifluoro-1-propene, is under consideration as a refrigerant which meets th
8、ese new regulatory requirements. R1233zd(E) is a single component refrigerant that ASHRAE Standard 34 has listed as Class A1 (lower toxicity/non-flammable). This makes R1233zd(E) compatible with existing application standards and building codes and therefore allows its immediate use. As shown in Fig
9、ure 1 and Figure 2, R1233zd(E) does not possess the thermodynamic and physical properties to directly replace existing HCFC or HFC refrigerants currently used in HVACR equipment, like R123 or R245fa. The operating pressures of R1233zd(E) are 30% to 45% higher than R123 for a given temperature. R1233
10、zd(E) produces 39% more capacity than R123 for a given compressor volumetric displacement when operating at 44F (6.7C) evaporator saturation temperature and 100F (37.8C) condenser saturation temperature. The thermodynamic efficiency of R1233zd(E) falls short of R123 by less than 1% at these conditio
11、ns. Use of R1233zd(E) represents a new design centerline and therefore requires new equipment designs for optimal performance. R1233zd(E)s higher operating pressures require equipment designs to meet ASME or other pressure vessel codes. A newly designed centrifugal chiller, using R1233zd(E) has been
12、 developed and is being offered in the market place as a future low GWP replacement option for R123, R245fa and R134a centrifugal chiller applications. Figure 1 Pressure-enthalpy comparison for R1233zd(E), R245fa, and R123 Figure 2 Temperature-entropy comparison for R1233zd(E), R245fa, and R123 ASSE
13、SSMENT OF R1233ZD(E) IN CENTRIFUGAL CHILLER PRODUCTS Environmental and Safety Environmental: An assessment of the environmental impact is needed prior to widespread use of any new chemical or a specific class of chemicals. A number of environmental factors need to be considered, such as climate chan
14、ge, tropospheric ozone formation, formation of noxious environmental degradation products, and stratospheric ozone loss. The unifying chemical feature in olefin (unsaturated) HFCs or olefin HCFCs is the presence of a carbon-carbon double bond that limits atmospheric lifetime as compared to saturated
15、 compounds. As a result, the ability of these molecules to contribute to photochemical ozone creation potential (POCP), direct GWP, and ozone depletion potential (ODP) is severely limited in nature. These olefins have short atmospheric lifetimes, measured in days to weeks, which results in negligibl
16、e POCPs, GWPs, and ODPs. A recently published article (Wallington et al., 2014) summarizes the atmospheric chemistry and features of a range of short-chain haloolefins, including R1233zd(E), compared to a wide range of currently used refrigerants. R1233zd(E) is documented to have an atmospheric life
17、time of 26 days, a GWP of 1, a POCP of 3.9, no significant reports of environmental breakdown products of concern, and an ODP near zero. In comparison, saturated HFCs have GWPs of 858 for R245fa, 1300 for R134a, and 79 for R123. Photochemical ozone creation potential is defined as the additional ozo
18、ne formed in a multi-day modelling relative to adding the same mass of ethene to simulate the impact on local ozone air quality. The POCP scale is relative to a reference substance, ethene, with a POCP defined as 100. Haloolefins have POCPs which are larger than halocarbons but much smaller than tho
19、se of alkenes. Haloolefins have POCPs which lie between methane (0.6) and ethane (12.3) which both oxidize sufficiently slowly so as not to contribute to local air quality issues and are exempt from air quality regulations. R1233zd(E)s POCP of 3.9 indicates that it should not contribute to local air
20、 quality issues and as such the US EPA has ruled that R1233zd(E) is not a local area quality target pollutant. Another potential source of environmental concern for haloolefins is the potential for TFA formation. TFA formation has been studied extensively and the World Meteorological Organization co
21、ncluded in 2011 that TFA from degradation of HCFCs and HFCs will not result in environmental concentrations capable of significant ecosystem damage. The same is applicable and documented for haloolefins. In the case of R1233zd(E), chlorine-substituted oxidization products are expected, HCOCl, and no
22、 TFA formation is expected to be produced in the environment. HCOCl is expected to be incorporated in rain, cloud, and fog water, followed by hydrolysis and removal by wet deposition within days, followed by hydrolysis to produce formic acid. Formic acid is a pervasive component of the environment a
23、nd is of no concern. Sulbaek Andersen et al. (2012) proposed an alternate atmospheric fate mechanism, but the proposed route did not show a high likelihood of TFA as a possible degradation product. Chlorine- and bromine-containing haloolefins could potentially contribute to stratospheric ozone, alth
24、ough it is negligible in most cases because of the haloolefins short atmospheric lifetimes which are measured in days, rather than years as in the case of saturated halocarbons. Patten and Wuebbles (2010) concluded that at the concentrations likely to be emitted by R1233zd(E), which has an ODP of 0.
25、00034, it will not affect stratospheric ozone. Wallington et al. (2014) also concluded that haloolefins have ODPs that are zero or near zero and so will not impact stratospheric ozone. Safety: R1233zd(E) has been recently classified by ASHRAE 34 as a Class A1 (lower toxicity and non-flammable) refri
26、gerant, which is the same classification as R134a. This makes R1233zd(E) compatible with existing application standards and building codes and therefore allows its immediate use. ASHRAE Standard 15 allows Class A R1233zd(E) to be used with fewer restrictions in regards to mandatory mechanical equipm
27、ent room requirements compared with R123 and R245fa that have a B1 (higher toxicity/non-flammable) classification, and will allow the refrigerant to be used in direct expansion heat exchangers in an occupied space if warranted. The refrigerant concentration limit for R1233zd(E) is 16,000 parts per m
28、illion by volume and the occupational exposure limit is 800 parts per million as documented in ASHRAE 34. There has been some confusion about the flammability of R1233zd(E). Two of the new proposed olefins, medium pressure R1234yf and R1234ze(E), are flammable according to the test methods and so ar
29、e classified by ASHRAE 34 as Class 2L. However, the new low pressure olefins R1233zd(E) and R1336mzz(Z) are non-flammable and so are listed as Class 1. System Performance Manufacturer has tested several centrifugal chillers using R1233zd(E) and this chiller performance test data was used to calibrat
30、e the thermodynamic analysis presented in this section. A simple thermodynamic model was created and used to compare the efficiency of various refrigerants as presented in Figure 3. The modelling compared R134a, R1234ze(E), R245fa, R1233zd(E), and R123 utilizing a 2000 ton (7034 kw) single stage cen
31、trifugal compressor vapor compression cycle. The lift conditions were 41 F (5 C) evaporator and 99 F (37 C) condenser operation with a typical system design of 81% compressor efficiency, 96.5% motor efficiency and 2% mechanical losses. This comparison did not include the addition of economizer or su
32、bcooling cycle improvements. As shown, R134a and R1234ze(E) have similar levels of COP (Coefficient of Performance commonly used by the industry to state performance) while R123 and R1233zd(E) have similar but better COP than R134a or R1234ze(E). The spread in efficiency is approximately 7% from low
33、 to high. Using R1233zd(E) as a R123 replacement results in a small efficiency penalty due to its thermodynamic properties, but R1233zd(E) still offers the highest efficiency of the next generation refrigerants being considered today. A second thermodynamic analysis was conducted to explore the impa
34、ct of heat exchanger performance on overall chiller performance. Figure 4 shows the impact on energy efficiency, kw per ton (kw/ton), as a function of the total heat exchanger approach temperature (sum of evaporator and condenser approach temperatures) for given leaving chilled water temperature and
35、 entering condenser cooling water temperature. Today, both R134a and R123 centrifugal chillers can meet the minimum efficiency requirements in ASHRAE Standard 90.1. However, the total heat exchanger approach temperature needs to be almost 3 F (1.6 C) smaller for an R134a chiller to achieve the same
36、efficiency as an R123 chiller. R1233zd(E) requires only about 0.45F (0.25 C) smaller total approach temperature to achieve the same efficiency as R123. Refrigerant-side heat transfer coefficients have been measured for both the evaporator and condenser with R123, R245fa, and R1233zd(E) in a single t
37、ube heat transfer test rig as shown in Figure 5 and Figure 6, respectively. In a typical chiller application, a heat flux of 5 kBtu/ft2 (20 kW/m2) is representative of a high efficiency bundle and is used here as the point of comparison. R245fa and R123 had roughly the same evaporator performance, b
38、ut R1233zd(E) showed 60% better performance than R123 and R245fa. This finding was a pleasant surprise because most next generation R134a refrigerants evaluated by Trane in the AHRI AREP program showed equal or reduced performance (Schultz, 2014). The condenser performance difference between the thr
39、ee refrigerants was less dramatic. Still, R1233zd(E) and R245fa condenser performance were 23% and 8% higher than R123 at 5 kBtu/ft2 (20 kW/m2) heat flux. R1233zd(E)s better evaporator (primarily) and condenser (secondarily) performance allows for it to overcome the reduced thermodynamic difference
40、with R123 and provides similar total heat exchanger approach temperatures as compared to R123. Figure 3 Comparison of efficiency for various refrigerants Figure 4 Specific power consumption (COP) as a function of total heat exchanger approach temperature for various refrigerants Figure 5 Evaporator
41、heat transfer performance comparison for various refrigerants Figure 6 Condenser heat transfer performance comparison for various refrigerants Life Cycle Climate Performance (LCCP) Life Cycle Climate Performance (LCCP) is a methodology to assess the total GWP impacts of both direct and indirect emis
42、sions, expressed as an equivalent mass of carbon dioxide (kg CO2,eq), over the lifetime of a particular refrigerant, piece of equipment, or system. LCCP is expressed as a summation of all relevant sources of direct and indirect emissions. The calculations can be very simple, looking at only one or a
43、 few contributing factors, or they can be very complete, even detailing the type and rate of leaks associated with specific types of connecting hose or piping technology. In general, there are three major factors that contribute to the greenhouse gas emissions of a chiller system: 1) the energy cons
44、umption of the system, 2) the GWP of the refrigerant, and 3) the refrigerant leakage potential. Some would interpret the GWP of the refrigerant and the leak rate to be directly related, but the authors would suggest these are independent variables and either be controlled to improve the LCCP impact
45、of a specific product or application. A certain level of granularity is necessary to determine the indirect contributions due to energy consumption since the refrigerant efficiency, in combination with the refrigeration or air-conditioning cycle chosen, the method and location the chiller is operate
46、d in, will act to impact the results. The energy efficiency of chillers used for air conditioning has been regulated for over 20 years in the United States. Chillers must now meet minimum efficiency standards per ASHRAE 90.1. In the case of large water-cooled centrifugal chillers, both R134a and R12
47、3 are used successfully to meet ever increasing energy efficiency requirements. In this study, two 550 ton (1935 kw) chillers with 0.60 kw/ton (5.86 COP) were used to obtain the amount of electrical energy consumed by an office building in four climatic zones over 20 years of life expectancy. Fixing
48、 the energy efficiency, application and location determines the amount of indirect emissions from the chillers, all being the same. Comparison of various refrigerants then becomes a simple examination of the respective direct emission profiles. The methodology used for calculating the indirect contr
49、ibutions from energy efficiency can be found in Kujak et al. (2014). Indirect emissions from the energy consumption for this LCCP simulation in Houston, Texas, USA, were determined to be 41,568 lbs (18,856 kg) CO2,eq per ton of cooling. Leakage rates of 0.5%, 1% and 5% were used in this study because these are typical for medium pressure R134a (5% or less) and low pressure R123 (0.5% or less) chillers. Leakage rates for chillers using R1233zd(E) were determined to be similar to R123 chillers in laboratory testing. This low leak rate result was expected as R1233zd(E) is a low
