Document RJK2vr1VGDOE5RpbBgYzGDRRv
July, 2023
Best practice examples for refrigeration and heat pumps with natural refrigerants
-Annex to the REACH statement of Refolution Industrieklte GmbH-
Published on: 25.07.2023
Refolution Industrieklte GmbH, Karpatenstrae 26 ,76227 Karlsruhe Geschftsfhrer: Thomas Frank, Handelsregister Mannheim: HRB 733782 USt-ID: DE324935121
Best practice examples for refrigeration and heat pumps with natural refrigerants
July, 2023
List of content
1. Introduction ........................................................................................... 1 2. Mobile air conditioning (MAC) and transport refrigeration ........... 3 3. Refrigeration.......................................................................................... 5
3.1 Low temperature refrigeration.......................................................................... 5 3.2 Refrigerated centrifuges ................................................................................... 6
4. Industrial heat pumps........................................................................... 6 5. Conclusion.............................................................................................. 7 6. Literature ............................................................................................... 8
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1. Introduction
Considering the proposed restrictions for PFAS the ECHA thoroughly discussed the availability of solutions with alternative refrigerants in Annex E to the Annex XV restriction report. It is recognized that a lot of applications with natural refrigerants already exist on the market, as can be seen for example in the EIA's cooling product list [1]. There are, however, some sceptical positions concerning for example transport refrigeration and cooling below -50 C that we would like to comment on, as we have practical experience from our work as engineering bureau. We would also like to provide additional examples for products using natural refrigerants that were not mentioned yet.
Figure 1 shows the vapour pressure curves of the commonly used natural refrigerants in the temperature range between -120 C and 200 C. Considering the usual operating pressure range between 1 bar(a) and 30 bar(a)1, the diagram shows that there is a suitable natural substance with a vapour-liquid phase change across the entire temperature range from ultra-low temperature (ULT) applications at -120 C to ultra-high temperature heat pumps at 200 C. All those substances can be used as a refrigerant in vapour compression cycles, which includes heat pumps. This means that from a purely physical point of view there is no need for alternative substances.
To reach temperatures below -50 C cascade systems with multiple vapour compression cycles operating with different refrigerants or mixed refrigerant cycles (MRC) are usually required. A different technology, especially suitable for ULT refrigeration, is gas cycle refrigeration based on the Joule cycle, using for example air (R729) as refrigerant.
We strongly believe that fulfilling all refrigeration demands with natural refrigerants is not only possible, but also efficient and economical. A good example to illustrate how such a development is possible are domestic refrigerators.
1 Notable exceptions for this pressure range are trans-critical CO2-cycles, which typically have a high pressure of more than 80 bar.
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Figure 1: Vapour pressure curves of the most important natural refrigerants
The first domestic electric refrigerators were developed in the early 20th century and used toxic substances like ammonia, methyl chloride and sulfur dioxide as refrigerants. Due to the safety hazard in case of leakage a new group of non-toxic and non-flammable chemicals called Freons (chlorofluorocarbons, CFCs) were introduced in the 1930s, R12 being the most widely used [2]. Those however turned out to deplete the ozone layer, which lead to their phase out regulated by the Montreal Protocol in 1987. The Montral Protocol was eventually amended to include hydrochlorofluorocarbons (HCFCs), which also damage the ozone layer and have a high global warming potential (GWP). As replacement for the ozone depleting refrigerants, hydrofluorocarbons (HFCs) like R134a were developed. Due to their high GWP they are currently being phased out as well [3, 4].
The German manufacturer Foron was the first to develop a refrigerator without CFCs and HFCs in 1992, using a mixture of hydrocarbons called "Dortmunder Mischung" and later isobutane (R600a) as refrigerant [5]. After market introduction, the technology was quickly adopted by other manufacturers, as the refrigerants were cheaper and the
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refrigerators were about 10 % more efficient than those with R134a. Foron eventually went bankrupt, but their environmentally friendly technology still became the international standard with a market share of ca. 75 % in 2018 [6]. Considering the phase out of R134a and the push for higher efficiencies incentivized by increasingly strict energy labels (e.g., EU label for refrigeration appliances [7]), this percentage is expected to approach 100 % in the coming years.
There are several takeaways from this example. For one thing, the fact that most people today have refrigerators with R600a in their home shows that the fear of flammable refrigerants is largely exaggerated if safety standards are met. For another, regulations can help promote innovation and ultimately lead to more sustainable and efficient solutions.
Other examples where natural refrigerants are already state of the art are commercial refrigeration (e.g. supermarkets) with R744 or R290, industrial refrigeration with R717 and heat pumps with R744 or R290. Systems with R290 are usually installed outside or in machine rooms due to safety reasons and operate with secondary loops. There are, however, no safety requirements if the refrigerant charge is kept lower than 150 g. In their LC150 project Fraunhofer ISE developed a heat pump prototype with 146 g R290 and a heating capacity of 11,4 kW, proving that R290 is also suitable for domestic heat pumps installed indoors [8].
2. Mobile air conditioning (MAC) and transport refrigeration
Mobile Air Conditioning (MAC) systems with CO2 as refrigerant are already commercially available for personal vehicles (e.g. VW ID.4) as well as buses (e.g. Konvekta). They are especially suitable for electric vehicles where they can be operated in heat pump mode, saving energy for heating and increasing the effective range of the vehicle [9].
While MACs with hydrocarbons are not commercially available yet, it has been shown in various studies that retrofitting R134a units with mixtures of R290 and R600/R600a such as R436B leads to higher cooling capacities and higher COPs with less charge
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required [10-12]. Conversely, R1234yf was shown to be less efficient than R134a [13- 15]. There are already drop in solutions with hydrocarbons available for example in Australia [16]. The portion of vehicles with small MAC systems retrofitted with hydrocarbons in Australia was estimated to be 4,2 % in 2016, which amounts to approximately 743 000 vehicles, proving the technical feasibility [17]. Considering the comparably high leakage rates of MACs and the implications for the environment if all vehicles currently using R134a and R1234yf are operated for many more years, requiring several refills in that time, the retrofit of those systems should be made a priority. Achieving this on a large scale requires support of manufacturers and political legislation. According to MaclaineCross and Leonardi [18] it is generally safe to operate MACs with hydrocarbons. There are several ways to further increase safety. Obrist Engineering, for example, developed a Thermal Event Suppression System (TESS) for the engine compartment, which consists of a bottle that releases a fire suppressing aerosol when activated by a crash sensor or by heat [19]. Another approach are secondary loop systems, which enable the separation of refrigerant cycle and passenger compartment [20]. Given that retrofits have been proven to work and that hydrocarbons have superior physical properties, there should be no issue to also design new, optimized MAC systems that are safe and outperform the current state of the art. There are already promising developments in this direction like the thermal management system for electric vehicles by the German manufacturer ZF that uses R290 as refrigerant in a hermetically sealed unit [21].
Regarding transport refrigeration Annex E to the Annex XV restriction report lists safety, variable operating conditions, and transport over long distances as main challenges for natural refrigerants. There are, however, already solutions available like for example the electric refrigeration systems by ECOOLTEC, using R1270 (Propylene) as refrigerant. The systems are reported to require 60 to 80 % less energy and produce up to 98 % less emissions than conventional diesel-powered refrigeration systems [22]. Due to the fully hermetic construction and special design, the formation of a flammable atmosphere in case of refrigerant leakage is impossible.
For special transport cooling requirements, we developed a ULT trailer in cooperation with Gebr. Thomaidis GmbH capable of realising temperatures between -40 C
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and -110 C [23]. The main storage room is cooled by highly efficient air cycle refrigeration machines by Mirai Intex and has an air lock to reduce air exchange during loading and unloading. Air as refrigerant poses no risk to humans or the environment, as it is nontoxic, non-flammable and the operating pressures don't exceed 1 bar(g). Because of the actively cooled machine room operation is possible even during extreme outside temperatures, making the trailer suitable for long distance transport with variable climate conditions.
3. Refrigeration
3.1 Low temperature refrigeration
In Annex E to the Annex XV restriction report it is stated that low temperature refrigeration below -50 C in large capacities is expected to still depend on fluorinated gases in 10 years. We object to this statement.
An example of natural refrigerants already being used on very large scales is the liquefaction of natural gas using mixed refrigerant cycles (MRC) with mixtures of hydrocarbons ranging from C1 to C5 and nitrogen as refrigerants. The two most commonly used methods are the propane mixed refrigerant (C3MR) cycle and the double mixed refrigerant (DMR) cycle, using a multi-stage propane cycle and an MRC respectively to pre-cool the natural gas and the main MRC [24]. By using mixtures instead of pure refrigerants, the temperatures in the heat exchangers can closer match the temperatures of the natural gas, increasing efficiency. Moreover, MRC require less compressors and other components and they are easier to control and maintenance than equivalent pure refrigerant cascades.
Another important use for low temperature refrigeration is pharmaceutical production (e.g. freeze drying) as well as transport and storage of medical or biochemical products. We have developed solutions for the entire supply chain, using air cycle refrigeration, including the aforementioned ULT trailers, mobile storage containers and stationary storage rooms of different sizes as well as cryo-condensation and freeze drying plants [25]. For small scale storage freezers that use R290/R170 cascades (e.g. VIP ECO series by
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PHCbi for -86 C) or MRC (e.g. CRYO series by Arctiko for -150 C) are commercially available solutions.
3.2 Refrigerated centrifuges
In Annex E to the Annex XV restriction report a 12-year derogation for refrigerated centrifuges is proposed in consideration of a rotor failure. The hazard emerging with the use of natural refrigerants, which are flammable (hydrocarbons) or have high pressures (R744), is rated highly. However, small centrifuges with R290 are already commercially available (e.g. Eppendorf Centrifuge 5427 R [26]), showing that the industry is willing and able to adapt. Larger refrigerated centrifuges that require more than 150 g refrigerant charge could easily be cooled with secondary loop systems, where the refrigerant cycle is spatially separated from the rotor.
4. Industrial heat pumps
Industrial heat pumps are a vital technology for the shift towards renewable energy, as they allow the usage of waste heat, drastically reducing the primary energy demand for heating. Current state-of-the-art commercial heat pumps are suitable for temperatures up to about 100 C [27]. High temperature and ultra-high temperature heat pumps for temperatures > 200 C that can be used, e.g., for steam production are currently being researched and tested.
As always, the refrigerant strongly depends on the temperature range. Up to about 150 C hydrocarbons (R290, R600, R601), CO2, ammonia and water are viable natural refrigerants. A heat pump with a very high heating capacity of 50 MW and temperatures up to 150 C is currently being built by MAN Energy Solutions for the Danish city Esbjerg. It uses CO2 as refrigerant, sea water as heat source and power from wind turbines, making it an exceptional example for sustainability [28].
Beyond 150 C most heat pumps use water as refrigerant, which has a very high critical temperature of 374 C among other advantageous properties like high latent heat. Notable compressor manufacturers for water vapour are Spilling and Piller with maximum heating
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capacities of 15 MW and 70 MW and maximum supply temperatures of 280 C and 212 C respectively [27].
5. Conclusion
The purpose of this document was to give a short overview of the current state of the art of refrigeration with natural refrigerants, focusing on the aspects and applications that were not or only insufficiently mentioned in Annex E to the Annex XV restriction report. To our knowledge there is no refrigeration application currently using PFAS that can't be adapted to work with natural refrigerants instead. The industry is already prepared to fully switch to natural refrigerants, waiting only on new legislations to shift consumer demand and the past has shown that manufacturers are quick to adapt. Therefore, we recommend not to make unnecessary derogations for the use of PFAS in new refrigeration applications.
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6. Literature
1. Environmental Investigation Agency (2021) Pathway to Net-Zero: Cooling Product List. https://eia-international.org/report/pathway-to-net-zero-cooling-product-list/. Accessed 6 July 2023.
2. Energy Saver 101 History Timeline: Refrigeration and Refrigerators. https://www.energy.gov/energysaver/energy-saver-101-history-timeline-refrigeration-and-refrigerators. Accessed 4 July 2023.
3. Ozonaction (2018) About Montreal Protocol. https://www.unep.org/ozonaction/who-we-are/about-montreal-protocol. Accessed 4 July 2023.
4. Umweltbundesamt (2023) EU-Verordnung ber fluorierte Treibhausgase. https://www.umweltbundesamt.de/themen/klima-energie/fluorierte-treibhausgasefckw/rechtliche-regelungen/eu-verordnung-ueber-fluorierte-treibhausgase#aktuelles. Accessed 5 July 2023.
5. Historische Klte- und Klimatechnik e. V. (HKK) Unternehmensgeschichte Dkk Scharfenstein. Accessed 4 July 2023.
6. Joachim Wille (2019) Die kaltgestellte Revolution. https://www.fr.de/panorama/kaltgestellte-revolution-10981615.html. Accessed 4 July 2023.
7. (2019) Commission Delegated Regulation (EU) 2019/2016.
8. Fraunhofer-Institut fr Solare Energiesysteme ISE (2023) Klimafreundliches Heizen: Fraunhofer ISE entwickelt Propan-Kltekreis fr Wrmepumpen - Fraunhofer ISE. https://www.ise.fraunhofer.de/de/presse-und-medien/presseinformationen/2023/klimafreundliches-heizen-fraunhofer-ise-entwickelt-propan-kaeltekreisfuer-waermepumpen.html. Accessed 20 July 2023.
9. Koegelenberg I (2022) Volkswagen Gains Efficiency with CO2 Heat Pump in Electric SUV. https://r744.com/volkswagen-cites-efficiency-gains-from-co2-heat-pumpin-first-electric-suv-coupe/. Accessed 7 July 2023.
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10. Kandhaswamy K, Periasamy S, Mayilsamy S, Thangavel S (2017) Experimental investigations on automobile air conditioners working with R134a and R290/R600a as an alternative. Therm sci 21(suppl. 2), 515-522. 10.2298/TSCI17S2515K.
11. Wongwises S, Kamboon A, Orachon B (2006) Experimental investigation of hydrocarbon mixtures to replace HFC-134a in an automotive air conditioning system. Energy Conversion and Management 47(11-12), 1644-1659. 10.1016/j.enconman.2005.04.013.
12. Hsieh H-K, Teng T-P (2022) Retrofit assessment of automobile air conditioners using hydrocarbon refrigerants. Applied Thermal Engineering 214, 118781. 10.1016/j.applthermaleng.2022.118781.
13. Mota-Babiloni A, Navarro-Esbr J, Barragn , Mols F, Peris B (2014) Drop-in energy performance evaluation of R1234yf and R1234ze(E) in a vapor compression system as R134a replacements. Applied Thermal Engineering 71(1), 259-265. 10.1016/j.applthermaleng.2014.06.056.
14. Sieres J, Santos JM (2018) Experimental analysis of R1234yf as a drop-in replacement for R134a in a small power refrigerating system. International Journal of Refrigeration 91, 230-238. 10.1016/j.ijrefrig.2018.05.019.
15. Qi Z (2015) Performance improvement potentials of R1234yf mobile air conditioning system. International Journal of Refrigeration 58, 35-40. 10.1016/j.ijrefrig.2015.03.019.
16. https://hychill.com.au/en/products/minus-30. https://hychill.com.au/en/products/minus-30. Accessed 7 July 2023.
17. (2023) Cold Hard Facts 3 - Review of the Refrigeration and Air Conditioning Industry in Australia - DCCEEW. https://www.dcceew.gov.au/environment/protection/ozone/publications/cold-hard-facts-3. Accessed 7 July 2023.
18. Maclaine-Cross IL, Leonardi E (1995) Hydrocarbon refrigerant risk in car air-conditioners. International CFC and Halon alternatives conference.
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19. College of Climate Change (2013) New technology allows safe use of high-efficient HC in MAC - College of Climate Change. https://collegeofclimatechange.com.au/new-technology-allows-safe-use-high-efficient-hc-mac/. Accessed 7 July 2023.
20. Li G, Eisele M, Lee H, Hwang Y, Radermacher R (2014) Experimental investigation of energy and exergy performance of secondary loop automotive air-conditioning systems using low-GWP (global warming potential) refrigerants. Energy 68, 819- 831. 10.1016/j.energy.2014.01.018.
21. Haroldsen JO (2023) German Concept Electric Vehicle Features Propane Heat Pump. Hydrocarbons21, 12 July 2023. https://hydrocarbons21.com/german-conceptelectric-vehicle-features-propane-heat-pump/. Accessed 20 July 2023.
22. (2023) ECOOLTEC at ITT Hub. https://refindustry.com/news/news-events/ecooltec-at-itt-hub/. Accessed 10 July 2023.
23. Refolution (2023) CryoCargo110 mobile storage solution | Refolution. https://www.refolution.de/en/products-und-services/products/cryocargo110-mobilestorage-solution/. Accessed 10 July 2023.
24. Wu X, Wang Z, Dong M, Dong L, Ge Q (2022) A Critical Analysis of Natural Gas Liquefaction Technology. Fluid Dynamics & Materials Processing 18(1), 145-158. 10.32604/fdmp.2022.018227.
25. Refolution (2023) Products | Refolution. https://www.refolution.de/en/products-undservices/products/. Accessed 10 July 2023.
26. (2023) Eppendorf stellt erste Mikrozentrifuge mit Kohlenwasserstoffkhlung vor Eppendorf Deutschland. https://www.eppendorf.com/de-de/company-careers/newsmedia/newsroom/eppendorf-introduces-first-microcentrifuge-with-hydrocarbon-cooling/. Accessed 10 July 2023.
27. Arpagaus C (2023) Hochtemperatur-Wrmepumpen fr industrielle Anwendungen. Karlsruhe.
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28. (2023) Dnisches Esbjerg setzt auf Growrmepumpe | en:former. https://www.enformer.com/daenisches-esbjerg-setzt-auf-waermepumpen/. Accessed 20 July 2023.
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