NREL ORC Working Fluid Selection Matrix (v3.2) – Excel Tool with GWP, T_crit, and Safety Class Filters

The NREL ORC Working Fluid Selection Matrix (v3.2) builds upon earlier versions to incorporate updated refrigerant data from authoritative sources such as NIST Chemistry WebBook, ASHRAE Standard 34 (2022), and IPCC AR6 GWP values (100-yr horizon). Its core functionality revolves around a curated database of ~150 organic compounds—including hydrocarbons, siloxanes, fluorocarbons, and ethers—each characterized by over 30 standardized parameters: molecular weight, normal boiling point, latent heat of vaporization, liquid density, viscosity, thermal conductivity, and environmental metrics (ODP, GWP, atmospheric lifetime). Users apply dynamic filters (e.g., GWP < 10, T_crit between 150–300°C, safety class A1 or A2L) to narrow candidates based on site-specific constraints—such as resource temperature (e.g., 90–150°C medium-enthalpy geothermal brines), turbine inlet pressure limits, or regulatory phaseout timelines (e.g., EU F-Gas Regulation). The matrix also includes calculated secondary indicators like critical reduced temperature (T_red = T_evap / T_crit), which correlates strongly with ORC thermal efficiency, and provides guidance on compatibility with common construction materials (e.g., stainless steel, elastomers) to mitigate degradation risks. Beyond screening, the tool facilitates trade-off analysis—e.g., balancing high efficiency (favored by low T_crit fluids) against environmental impact (penalized by high GWP) or safety (constrained by toxicity/flammability)—making it integral to early-stage techno-economic and life-cycle assessments of binary geothermal systems.