Low-GWP Refrigerants; Options and Issues

Piotr A. Domanski*(a), Riccardo Brignoli(a),

J. Steven Brown(b), Andrei F. Kazakov(c), Mark O. McLinden(c)

(a)National Institute of Standards and Technology, 100 Bureau Dr., Gaithersburg, MD 20854, USA 

(b)The Catholic University of America, 620 Michigan Ave, NE, Washington, DC 20064, USA 

(c)National Institute of Standards and Technology, 325 Broadway, Boulder CO, USA 

*Corresponding author, Tel: 1-301-975-5877; Fax: 1-301-975-8973

E-mail: piotr.domanski@nist.gov 

ABSTRACT

This research explored the possibilities for refrigerants having low global warming potential (GWP) with a particular focus on medium- and high-pressure applications. The search for suitable refrigerants relied on screening of a comprehensive database using filters of environmental acceptance, chemical stability in the system, low toxicity, coefficient of performance (COP), volumetric capacity (Qvol), and flammability. Among different screening steps, the performance potential (COP and Qvol) of the candidate fluids was assessed using a simulation model that included both thermodynamic and transport properties, and heat exchangers with optimized refrigerant circuitry. The need for this detailed methodology was demonstrated for systems relying on forced-convection evaporation and condensation. The study showed that the low-GWP refrigerant options are very limited, particularly for fluids with volumetric capacities similar to those of R-410A and R-404A. The identified fluids with good COP and low toxicity are at least mildly flammable. Accepting the thermodynamic argument that viable refrigerants are restricted to small molecules, it is out contention that the screened database contained all suitable candidates and our screening process yielded a list of the ‘best’ low-GWP fluids. Refrigerant blends allow for tradeoffs between COP, volumetric capacity, flammability, and GWP. The probability of finding ‘ideal’, better-performing low-GWP fluids is minimal. The limited refrigerant options and environmental concerns make it imperative to use refrigerants judiciously, which includes refrigerant selection for each application with consideration for environmental and safety risks; use of high-efficiency, leak-free equipment; and implementation of the best practices for refrigerant handling, equipment commissioning, servicing, and decommissioning.