Larry D. Burns

Computational fluid dynamics modeling of flammable refrigerant leaks inside machine rooms: Evaluation of ventilation mitigation requirements

Computational fluid dynamics simulations were undertaken to quantify ventilation dilution requirements needed for mitigating flammability risks during leaks of flammable refrigerants from large chillers inside machine rooms. Machine rooms ranging in size from 376 to 2256 m3 were modeled using computational fluid dynamics to simulate major leaks from a 2640 kW (750TR) chiller. As is required by existing safety standards, a refrigerant sensor was incorporated to trigger and activate an alarm or emergency level ventilation system to dilute the room with fresh air. A range of refrigerant leak rates and different alarm-triggered ventilation rates were evaluated to understand dilution requirements to prevent significant flammable mass accumulation. To verify the computational fluid dynamics findings, verification testing was also conducted in a 574 m3 machine room setup using carbon dioxide as a surrogate refrigerant. When matching volumetric leak rates, computational fluid dynamics results were comparable with verification testing data. These results will be discussed in light of current machine room ventilation standards and used to establish a relationship for the alarm ventilation rate needed for mitigating risks for major refrigerant leaks inside machine rooms.

CFD Modeling of Flammable Refrigerant Leaks inside Machine Rooms- Emergency Ventilation Rate for Different Size Chillers

Computational fluid dynamics (CFD) simulations, verified against test data, were undertaken to quantify ventilation dilution requirements needed for mitigating flammability risks during leaks of mildly flammable refrigerants from different size chillers inside machine rooms in an extension of our prior work for very large chillers. For this study, a 376 m3 machine room configuration was modeled using CFD to simulate significant refrigerant leaks from a chiller with different refrigerant charge levels. Three different mildly flammable refrigerants with various leak rates and various air ventilation rates were evaluated to understand dilution requirements to prevent significant refrigerant flammable mass accumulation. These results are discussed in light of previously published machine room ventilation requirements for mitigating sustained leaks from large chillers, and used to establish a generalized relationship for the emergency ventilation rate needed for mitigating risks for significant refrigerant leaks inside machine rooms for the full range of chiller charge levels incorporating any mildly flammable refrigerant with A2L safety group classification.