Low-GWP refrigerants

We, the editors of this special issue on low-global warming potential (GWP) unsaturated halocarbon refrigerants, are pleased to present 16 articles with authors hailing from six countries. The special issue has been more than 1.5 years in the making and is the extension of and outcome from a long-standing collaboration among the editors spanning three continents and some 8 years. The authors represent industry (six authors), government (six authors), and academia (34 authors).

We have specifically elected to focus this special issue on unsaturated halocarbon refrigerants to the exclusion of other low-GWP refrigerants, e.g., air, ammonia, carbon dioxide, hydrocarbons, and water, inter alia, primarily (1) because of the relatively recent, large amount of research and development regarding unsaturated halocarbon refrigerants, and (2) because there are other avenues (e.g., Gustav Lorentzen Natural Working Fluid Conferences; its 12th edition took place in August 2016) for publishing articles related to low-GWP natural refrigerants. Regardless, the editors of this special issue believe a future low-GWP special issue focused on natural refrigerants would be an important and worthy undertaking.

Perhaps the primary impetus for the recent worldwide focus on low-GWP refrigerants is the Kyoto Protocol (1997) and ensuing legislation, primarily centered in Europe. In particular, in 2002, the European Union (EU) formerly adopted the Kyoto Protocol and followed this action with the adoption of the so-called F-Gas Regulations (2006) and the Mobile Directive (2006). More recently, the EU has repealed the 2006 F-Gas Regulations and passed more stringent F-Gas Regulations (2014). While the EU legislative initiatives are not the only ones in the world, the Mobile Directive led to enormous development efforts and monies being spent on developing low-GWP halocarbon refrigerants for automotive vehicle applications, with R1234yf (2,3,3,3-tetrafluoroprop-1-ene) having emerged as the “preferred solution” for meeting the directive. As a result of these automotive-focused development efforts and other legislative, regulatory, and taxing initiatives around the world, a number of other low-GWP unsaturated halocarbon refrigerants have been, and are being, investigated.

While the definition of “low-GWP” is a qualitative one, is non-exact, and periodically changes based on historical circumstances, UNEP (2014) recently classified working fluids based on their 100-year time horizon GWP values relative to CO₂. The UNEP taxonomy is provided in Table 1.

Table 1 UNEP (2014) taxonomy of GWP values.

Range	Classification
GWP < 30	Ultra-low or negligible
30 < GWP < 100	Very low
100 < GWP < 300	Low
300 < GWP < 1000	Medium
1000 < GWP < 3000	High
3000 < GWP < 10,000	Very high
GWP > 10,000	Ultra-high

The articles contained herein consider several unsaturated, “ultra-low GWP” halocarbon refrigerants, both in their pure form and as components in blends, as well as more traditional HFC refrigerants, e.g., R-32, R-134a, and R-410A. The unsaturated halocarbons include R-1123, R-1234yf, R-1234ze(E), R-1234ze(Z), and R-1243zf. Of the 16 articles, five deal with blends, six with single-component refrigerants, and three with both single-component refrigerants and blends. Three of the articles regard equation of state modeling. Three report experimental boiling heat transfer measurements. Five document experimental assessment studies at the systems level. One is a low-GWP refrigerant heat transfer review. One deals with oil/refrigerant miscibility. Finally, one regards the measurements of properties.

While the 16 articles reported in this special issue represent a wide-range of topics and authorship, in a certain sense we have just “scratched the surface.” There is a large amount of on-going work throughout the world which could potentially fill many more volumes and we look forward to the publication of these studies both in this journal and elsewhere.

We hope you enjoy this issue and learn a lot from it! We also welcome your comments and feedback, and hope you will consider publishing your future low-GWP related work in Science and Technology for the Built Environment (STBE).