To identify and experimentally demonstrate the performance and flammability behavior of binary and ternary non-flammable refrigerant blends with global warming potential (GWP) less than that of HFC-134a and zero ozone depletion potential (ODP) that can potentially replace HFC-134a in air-conditioning (AC) equipment. The selection criteria include: ODP, GWP, coefficient of performance (COP), volumetric capacity (Qvol), flammability, and toxicity.

This project will follow the limited-scope project (WP-2740) with experimental verification of its findings. The limited-scope project identified 22 binary and ternary refrigerant blends as possible non-flammable replacements for HFC-134a with significantly lower GWPs, using analytical and simulation methods. Notwithstanding using a state-of-the-art refrigerant property prediction program, an advanced thermodynamic cycle simulation model, and a novel method for estimating flammability, the limited-scope results are associated with significant uncertainness, which necessitate experimental validation of the identified refrigerant replacement options.

The ultimate outcome of the core project will be performance data of HFC-134a and three best low-GWP refrigerant blends in a military environmental control unit (ECU). The test data will be taken in the National Institute of Standards and Technology (NIST) environmental chambers on a ECU using an expansion device and refrigerant charge individually optimized for each fluid. This laboratory-measured performance will be further extended via simulations to determine the performance of each refrigerant in an ECU with an optimized compressor, evaporator and condenser, thus indicating the performance potential in a completely optimized system. NIST will perform these simulations with a validated first-principles-based simulation model utilizing evolutionary-computation algorithms for heat exchanger optimization.

Four separate experimental tasks will precede the ECU tests to enable proper selection of the three best blends based on their cycle performance and acceptable flammability behavior (i.e., confirmation of non-flammability), and to ensure accurate test data reduction and ECU modeling. These tasks will entail preliminary performance validation via testing in the NIST mini-breadboard heat pump, flammability testing by two different test methods, measurements of blend properties and development of a blend equation of state, and measurements of blend evaporative forced-convention heat-transfer performance. Throughout the duration of the project the research team will follow the most recent developments regarding low-GWP fluids and will consider novel promising replacement fluids if such fluids become available.

This project will identify the best options for the transition to low-GWP HFC-134a replacement blends based on experimentally-validated understanding of their performance potential and flammability behavior. The developed knowledge will contribute to the competitiveness of U.S. industry. Most importantly, the results of this project will provide the military with a technical base for an informed decision moving forward regarding replacement of HFC-134a.