Technologies

Market leading technologies coupled with the highest quality services

High-Efficiency Centrifugal Chiller Model RTBA using Low-GWP Refrigerant R1224yd (Z)

Shunsuke AMANO,
Doctor of Engineering, EBARA Refrigeration Equipment & Systems Co., Ltd.

Refrigeration and air-conditioning equipment are essential for modern life. HFC refrigerants used in such equipment are already subject to production regulations all around the world to reduce global warming. Therefore, it is necessary to replace HFC refrigerants with low Global Warming Potential (GWP) refrigerants. EBARA Refrigeration Equipment & Systems developed a new centrifugal chiller model RTBA and released it in April 2018. This model uses R1224yd (Z) (AMOLEA® 1224yd), a low GWP refrigerant for centrifugal chillers, which ensures the same level of both safety and security as conventional refrigerants and complies with all the essential needs for refrigerants. Since the model RTBA not only uses a low GWP refrigerant but is also highly efficient and reliable, it is an ideal product for customers seeking a safe, reliable, and easy-to-use chiller that reduces the environmental impact. In addition, we are developing a retrofit service to allow the use of R1224yd (Z) refrigerant in previously delivered centrifugal chillers by replacing some parts.

Keywords: Centrifugal chiller, Model RTBA, Low GWP refrigerant, HFO, R1224yd (Z), Non-flammable, Toxicity, Kigari amendment, Retrofit

1. Introduction

Reducing global warming is a common goal for all mankind. For the first time in history, the Paris Agreement was adopted to reduce worldwide greenhouse gas emissions such as CO2. In this connection, it is imperative to use low GWP refrigerants to replace the conventional refrigerants in refrigeration and air-conditioning equipment, which are indispensable for our modern urban livelihoods. The refrigerants are used inside a closed housing structure of the equipment. Since hydrofluorocarbons (HFCs) conventionally used as refrigerants have a very high GWP, they can have an impact on global warming in the event of leakage1). For that reason, the new activities for reducing HFCs are being put into effect in Japan and all around the world, and there are increasing demands from customers for conventional refrigerants to be replaced with low GWP refrigerants. To meet such demands, EBARA Refrigeration Equipment & Systems has developed the new centrifugal chiller model RTBA and released it in April 2018. This model uses R1224yd (Z) refrigerant (AMOLEA® 1224yd), which can comply with the new HFC refrigerant regulations that have been established in Japan. This paper covers the following topics: (1) the conditions of the newly established HFC refrigerant regulations as the background that led to the development of our new refrigerant centrifugal chiller, (2) alternative refrigerant candidates, and (3) features of the newly adopted refrigerant and the new centrifugal chiller model RTBA using low GWP refrigerant R1224yd (Z). Finally, the paper describes retrofitting technologies.

2. Background of newly established HFC refrigerant regulations

Up until now, the refrigerants used in centrifugal chillers have been replaced several times. Highly toxic and flammable substances were used as refrigerants for chillers manufactured prior to the invention of chlorofluorocarbons (CFCs) since there were no other suitable substances. Following the development of the first non-flammable and low toxic chlorofluorocarbon halomethane CFC-12 in the 1920, we can use a safe and reliable substance as refrigerant.
 In the 1970s, however, it was posited that CFCs destroy the ozone layer in the stratosphere. As a result, the 1987 Montreal Protocol was enacted as a step toward the abolishment of designated CFCs by 1996 along with a gradual phase-out of substitute hydrochlorofluorocarbons (HCFCs). Accordingly, HFCs that do not destroy ozone layer were developed in order to replace HCFCs. In Japan, companies first replaced CFC refrigerants with HCFC refrigerants and then later on with HFC refrigerants in consideration of the environment, ahead of other countries, earlier than the regulation timetable set up in the Montreal Protocol.
 HFC refrigerants do not destroy the ozone layer, and are non-flammable and low toxic, which make HFC safe and reliable. But GWP of HFC is high. Therefore, a new movement was started for implementing legal regulations on HFCs. In 2006, the EU F-gas Regulation was established first and then the proposal to phase down HFCs under the Montreal Protocol on substances that deplete the ozone layer was issued through the leadership of the U.S. These new endeavors led to the amendment of the “Law Concerning the Recovery and Destruction of Fluorocarbons” to the “Act on Rational Use and Proper Management of Fluorocarbons” (commonly known as “Fluorocarbon Emission Control Law”) and came into effect from April 2015, in Japan. As for the global scene, the Parties to the Montreal Protocol reached an agreement at their 28th Meeting of the Parties (MOP28) in October 2016 in Kigali, Rwanda to phase down HFCs (Kigali Amendment)2). To be more specific, as shown in Figure 1, it was decided that the developed countries should gradually reduce their production and consumption of HFCs (on a CO2 equivalent basis) by 10% by 2019, by 40% by 2024, and then by 70% by 2029, and eventually by 85% by 2036. The developing countries, on the other hand, would have to reduce HFCs production and consumption with a time delay of approximately 10 to 13 years. As a whole, all parties are required to reduce HFCs over a period of 30 years. This transition mechanism is similar to that of the past efforts toward reducing HCFCs. In consequence of the Kigali Amendment, the regulations of the Fluorocarbon Emission Control Law in Japan have been gradually strengthened further3). In December 2017, the government announced proposals to add a centrifugal chiller to designated product category, which demands that equipment manufacturers replace existing refrigerants with lower GWP refrigerants, then centrifugal chiller manufacturers must regulate GWP values to 100 or less from 2025 onwards4). The proposals were finally notified to all concerned in January 2019.

19-04f1_E.jpg
Fig. 1 Global hydrofluorocarbon (HFC) regulation (Kigali Amendment)

 Because of the events mentioned above, a movement for newly regulating conventional HFC refrigerants has become a reality here and now, on a global scale including Japan, and there is an increasing demand from customers to replace the conventional refrigerants with low-GWP refrigerants.

3. Low GWP refrigerant candidates

The properties of refrigerants change inevitably in order to achieve low-GWP levels. Although substances called natural refrigerants have a very low GWP, they have downsides too. For example, hydrocarbons are highly flammable, whereas ammonia is both highly flammable and toxic. To find a way around these hurdles, hydrofluoroolefins (HFOs) with a carbon–carbon double bond has been developed recently as another candidate for a low-GWP refrigerant. HFOs decompose when exposed to ultraviolet rays and thus has a short atmospheric lifetime and a low GWP. As an inherent trade-off for reducing GWP, however, substances tends to become flammable because the stability of molecules is reduced in order to increase the speed of decomposition. Although different types of low GWP refrigerants have been developed for various refrigeration and air-conditioning equipment5), 6), we can summarize that non-flammability is not necessarily-achieved property in the effort to achieve low GWP.
 Table 1 is a summary of HFOs and HFO-based refrigerants that can serve as candidates of low-GWP refrigerants suitable for centrifugal chillers. This table lists up GWP, atmospheric lifetime, standard boiling points, molecular weight, class of flammablity and toxicity, Refrigerant Concentration Limit (RCL), Occupational Exposure Limits (OEL), and cooling capacity per suction volume of a compressor (hereinafter referred to as “volumetric capacity”; relative value to existing refrigerants). R1234yf and R1234ze (E) refrigerants, which can be used as substitutes for the R134a refrigerant (GWP: 1 430), have a very low GWP of less than 1 but is slightly flammable (also written as “mildly flammable”). The R513A refrigerant is a non-flammable azeotropic mixed refrigerant, but has a high GWP of 573. There is a research analysis which concludes that it is very difficult to achieve both non-flammability and low GWP in the range of saturation pressure higher than that of R134a7). On the other hand, a non-flammable R1336mzz (Z) refrigerant is available as a substitute for R123 (GWP: 77), but it has a low volumetric capacity. The azeotropic mixed refrigerant, R514A, is non-flammable and has a volumetric capacity close to that of the R123 refrigerant, but it is classified as higher toxicity. R1233zd (E) and R1224yd (Z) refrigerants are available as substitutes for R245fa (GWP: 1 030). They have a low GWP of less than 1 and they are also non-flammable and classified as lower toxicity. In particular, the R1224yd (Z) refrigerant has high stability as a substance that is equivalent to existing HFC refrigerants8).

19-04t1.jpg

4. Features of newly adopted refrigerant

We attempted to formulate a hypothesis about the desirable properties of refrigerants of customers who use centrifugal chillers with regard to refrigerants from a global warming prevention standpoint. Understandably, the answers to this question differ from one customer to another, but the following properties can be generally estimated.
●Low GWP: Reduces the environmental impact and complies with environmental regulations.
●Low toxicity: Assures high safety even if the refrigerant leaks.
●Nonflammability: Assure no risks of fire and toxic emissions.
●Single substance: Enables refilling of refrigerant even if the refrigerant leaks.
●High stability: Assures no change in performance and does not cause problems such as corrosion after long use.
●High efficiency: Provides high cycle efficiency and indirectly contributes to a lower environmental impact through reduction of electricity consumption.
 After due consideration of both the development status of low GWP refrigerants described above and the essential needs for the abovementioned refrigerants, EBARA Refrigeration Equipment & Systems has adopted R1224yd (Z) (AMOLEA® 1224yd) as a new low GWP refrigerant for centrifugal chillers.
 The R1224yd (Z) refrigerant complies with all the desirable properties mentioned above and also has the following advantages.
●R1224yd (Z) is exempted from the Fluorocarbon Emission Control Law.
●R1224yd (Z) is also used for other purposes (such as a foaming agent) that are produced in large volumes.
●R1224yd (Z) is easy-to-handle and has low pressure.
●R1224yd (Z) has the same-level of High Coefficient of Performance (COP) and cooling capacity as existing refrigerants.

5. Features of the new centrifugal chiller model RTBA

The centrifugal chiller model RTBA (Figures 2 and 3) is a core product of EBARA Refrigeration Equipment & Systems. We have developed the chiller model RTBA based on the technologies used in the centrifugal chiller model RTBF, which has a long-proven track record and high reliability. The features of the centrifugal chiller model RTBA are listed below.

19-04f2_E.jpg
Fig. 2 Centrifugal chiller model RTBA
19-04f3_E.jpg
Fig. 3 Features of centrifugal chiller model RTBA

●Use of a newly developed environmentally-friendly, safe and reliable R1224yd (Z) refrigerant
 This chiller uses a refrigerant that has an extremely low GWP of less than 1. It is not only non-flammable, but also is low toxic and highly stable. Furthermore, this chiller is exempted from the Fluorocarbon Emission Control Law.
● High Coefficient of Performance (COP)
 This chiller has a high efficiency of COP 6.4 at the top in series.
●High-efficiency two-stage compressor
 The compressor of this chiller inherits the basic structure of the two-stage compressor of centrifugal chiller model RTBF, and offers both high reliability and high efficiency because it has been optimally designed for using with a new refrigerant.
●High-performance heat exchanger
 The heat exchanger of this chiller uses high-performance heat transfer tubes.
●Wide range of product lineup
 The products of this series cover sufficiently wide range of cooling capacity from 220 refrigeration tons to 1 250 refrigeration tons (Tables 2 and 3).
●Provided with various specifications
 Centrifugal chillers often have to be provided with various specifications in order to cope with customer-specific applications. The centrifugal chiller model RTBA inherits the flexibility of being able to incorporate various specifications like its predecessor model RTBF. To be more specific, the chiller model RTBA can be provided with specifications that make it easier to use; for example that are modifiable, chilled water temperature difference, nozzle direction, and multiplexing of various filters. This series also offers a model equipped with a variable-speed drive(VSD), which is becoming a standard specification. Furthermore, model RTBA provides an optional explosion-proof model and a model with a modular structure, which may be of particular importance when the system is delivered to a place that has no adequate passageways to transport the chiller.

19-04t2.jpg
19-04t3.jpg

 The centrifugal chiller model RTBA uses a new low GWP, non-flammable, and low toxic refrigerant and is also very user-friendly for customers in the same way as its predecessor. In other words, model RTBA has no downsides caused by the use of a low GWP refrigerant and is an easy-to-use centrifugal chiller for all customers. Therefore, this chiller is an optimal product for customers who wish to reduce the environmental impact and want a safe and reliable refrigerant.

6. Technologies used for applying a new refrigerant to a centrifugal chiller

The basic technologies for applying a new refrigerant to a centrifugal chiller include confirming the durability of materials to be used with the new refrigerant, particularly, insulation material and sealing material (elastomer) and selecting refrigerant oil compatible with the new refrigerant. We have thoroughly studied these basic technologies and successfully achieved higher reliability to use the new refrigerant.
 We conducted durability tests for various materials against the new refrigerant, and changed materials which were needed to be changed more suitable materials.
 There are various requirements for the lubricant used in a chiller. In addition to the appropriate viscosity, it must have various characteristics to maintain liquidity at low temperatures and to be properly dissolved with the refrigerant in the temperature range of chiller operation. It is known that the solubility of HFO-based refrigerants to synthetic oil used for HFC refrigerant is higher than that of HFC refrigerants. Since R1224yd (Z) refrigerant dissolves with both synthetic oil and mineral oil, we carried out extensive studies with the cooperation of a lubricant manufacturer and selected the refrigerant oil with optimal properties for the R1224yd (Z) refrigerant.
 After developing the basic technologies, we meticulously verified the performance, functions, and reliability of model RTBA. For example, the graph that indicates the Coefficient of Performance (COP) (cooling efficiency) of model RTBA is shown in Figure 4. Although model RTBA inherits the basic structure of model RTBF, the internal structure of model RTBA has been designed optimally in order to use the new refrigerant so that model RTBA achieves a COP equivalent to the predecessor model RTBF.

19-04f4_E.jpg
Fig. 4 Performance of centrifugal chiller model RTBA (1)

 We also verified the Integrated Part Load Value (IPLV), which indicates the efficiency of the chiller including partial load. Figure 5 shows the graph that compares IPLVs of a fixed-speed chiller and variablespeed chiller in relative values where IPLVs of the existing refrigerants of both chillers are 100%. IPLVs of model RTBA in the fixed-speed chiller and variable-speed chiller were 107% and 100%, respectively. In other words, both the fixed-speed chiller and variable-speed chillers achieve an IPLV equal to or higher than chillers using the existing refrigerant.

19-04f5_E.jpg
Fig. 5 Performance of centrifugal chiller model RTBA (2)

7. Development of retrofitting technologies

It is desirable to replace refrigerants with lower GWP refrigerants as early as possible in order to reduce effective global warming impact. In the current situation, however, other refrigerants, which are not designated for chillers by its chiller manufacturers, are not applicable. Therefore, introducing new models using low-GWP refrigerants at a faster pace will be more effective in reducing the environmental impact. On the other hand, the centrifugal chiller is a machine with an extremely long product life. In that case, even if a new centrifugal chiller using a low-GWP refrigerant is released in the market, some customers using centrifugal chillers may not need to install a new chiller for another 10 or 20 years.
 The newly adopted R1224yd (Z) refrigerant has physical property such as saturation pressure that are very close to those of the existing R245fa refrigerant. Therefore, we have developed a retrofitting service that enables using the R1224yd (Z) refrigerant in existing centrifugal chillers installed in field.To be more specific, when customers request us retrofitting of their chillers that use the R245fa refrigerant, we can retrofit the chiller to use the low-GWP R1224yd (Z) refrigerant by replacing some minor parts of the chiller during our periodical maintenance using the technologies we developed. Since the R1224yd (Z) refrigerant is non-flammable and has low toxicity, customers can maintain the same safety and reliability as before and at the same time they can reduce the impact of refrigerant to the environment at an earlier time. Therefore, even though it could take decades before an existing centrifugal chiller needs to be replaced because of its long product life, customers can reduce the environmental impact in practice and more effectively with our retrofitting service.

8. Conclusion

There is an urgent need to replace HFC refrigerants used in refrigeration and air-conditioning equipment (that are indispensable to our modern lifestyles) with low-GWP refrigerants in order to prevent global warming, and regulations to gradually phase down HFCs are taking place on a global scale. We have adopted the new low-GWP R1224yd (Z) refrigerant for centrifugal chillers because it achieves low GWP and ensures the same level of both safety and security as conventional refrigerants and complies with all the essential requirements for refrigerants. Consequently, we have developed the centrifugal chiller model RTBA and released it in the market in April 2018.
 This product received the Jury’s Special Award at the 21st Annual Ozone layer Protection and Global Warming Prevention Award sponsored by Nikkan Kogyo Shimbun9). We believe that we received this award as a recognition of our efforts at developing technologies of a centrifugal chiller that uses a new low-GWP refrigerant that provides safety and reliability as well as ease of use for all customers.
 We have been receiving a great number of inquiries for the highly safe, reliable, user-friendly, and environmentally-friendly centrifugal chiller model RTBA and have already received orders for 10 units that have been shipped. The model RTBA was developed based on the technologies of model RTBF, which has a long track record. We plan to carry out further development for wider use of the model and meet the various needs of our customers.

* AMOLEA is a trademark of AGC Inc.

References

1) Guus J. M. Velders et al. The large contribution of projected HFC emissions to future climate forcing
https://www.epa.gov/sites/production/files/documents/velders_pnas.pdf
2) Report on MOP28 and investigation policies in the future (Ministry of Economy, Trade and Industry)
http://www.meti.go.jp/shingikai/sankoshin/seizo_sangyo/kagaku_busshitsu/flon_taisaku/pdf/009_05_00.pdf
3) Basic items of new regulations on alternative fluorocarbons based on the Kigali Amendment (Ministry of the Environment)
https://www.env.go.jp/press/y0615-05/mat02.pdf
4) About the settings of target GWP and target year of the designated products (draft)
December 18, 2017, (Ministry of Economy, Trade and Industry)
http://www.meti.go.jp/shingikai/sankoshin/seizo_sangyo/kagaku_busshitsu/flon_taisaku/pdf/012_04_00.pdf
5) Building equipment and plumbing, Volume 55, No. 9 (2017 August Issue), PP.35-39
6) BE Building equipment, Volume 68, No. 11 (2017 November Issue), PP.57-62
7) Mark O. McLinden et al., Hitting the Bounds of Chemistry: Limits and Tradeoffs for Low-GWP Refrigerants, The 24th IIR International Congress of Refrigeration ICR2015 Yokohama
8) AMOLEA 1224 yd technical document
http://www.agc-chemicals.com/jp/ja/products/detail/index.html?pCode=JP-JA-G016
9) 21st Annual Ozone layer Protection and Global Warming Prevention Award sponsored by the Nikkan Kogyo Shimbun
https://biz.nikkan.co.jp/sanken/ozon/number21.html