The September Gustav Lorentzen 2014 Conference served once again as a meeting place for key HVAC&R stakeholders, industry leaders, organisations and academics to present latest research on natural refrigerants. hydrocarbons.21 highlights two presentations by Daniel Colbourne from Re-phridge centred on safety requirements and flammability risk assessment when employing hydrocarbon refrigerants.
Numerical model to assist in the risk assessment when using flammable refrigerants
The design and construction of air-conditioning and refrigeration appliances are key factors that minimise risk of hydrocarbon (HC) refrigerant flammability.
Through the paper titled “Characterisation of a leak of flammable refrigerant within equipment enclosures” by D. Colbourne and K.O. Suen, the authors presented a numerical model to describe the behavior of HC refrigerant concentrations within different types of enclosures, including ducting, refrigerated cabinets and equipment housing, in which refrigerant leaks can occur. The model aims to assist in the risk assessment of the use of flammable refrigerants by providing reliable and accurate data of the average developed concentrations and flammable quantities of HC within those disclosures.
Results show that the size of the leak (rate), the geometry and the configuration of the enclosure, as well as the use of airflow can have a major impact on the size and duration of flammable mixtures and flammability risk. Therefore, taking into account the effect of these characteristics, refrigerant flammability risk can be minimised.
Comparative risk assessment of hydrocarbon refrigerant in a refrigerator and split air conditioner
In the paper “Comparative risk assessment of hydrocarbon refrigerant in a refrigerator and split air conditioner” by D. Colbourne, the comparative frequency and severity of ignition of domestic refrigerators (DR) using HC-600a (iso-butane) and split air conditioners (SACs) using HC-290 (propane) is examined by quantitative risk assessment methods.
The study concludes that the frequency of ignition of the SACs is much lower than domestic refrigerators DR. The results indicate that in the event of deflagration, SAC are more conducive for dispersion of leaked refrigerant with less potential for confinement. The author uses quantitative risk assessment in probabilistic safety analysis to come to this conclusion by systematically evaluating and quantifying the factors that might lead to ignition and unwanted consequences.
Conclusion of the study: SAC reveals lower risk than DR
In the result of the study, an extrapolation of the situation suggests that the risk of SACs is much lower than for DRs. The comparative study concluded the following:
The design and construction of air-conditioning and refrigeration appliances are key factors that minimise risk of hydrocarbon (HC) refrigerant flammability.
Through the paper titled “Characterisation of a leak of flammable refrigerant within equipment enclosures” by D. Colbourne and K.O. Suen, the authors presented a numerical model to describe the behavior of HC refrigerant concentrations within different types of enclosures, including ducting, refrigerated cabinets and equipment housing, in which refrigerant leaks can occur. The model aims to assist in the risk assessment of the use of flammable refrigerants by providing reliable and accurate data of the average developed concentrations and flammable quantities of HC within those disclosures.
Results show that the size of the leak (rate), the geometry and the configuration of the enclosure, as well as the use of airflow can have a major impact on the size and duration of flammable mixtures and flammability risk. Therefore, taking into account the effect of these characteristics, refrigerant flammability risk can be minimised.
Comparative risk assessment of hydrocarbon refrigerant in a refrigerator and split air conditioner
In the paper “Comparative risk assessment of hydrocarbon refrigerant in a refrigerator and split air conditioner” by D. Colbourne, the comparative frequency and severity of ignition of domestic refrigerators (DR) using HC-600a (iso-butane) and split air conditioners (SACs) using HC-290 (propane) is examined by quantitative risk assessment methods.
The study concludes that the frequency of ignition of the SACs is much lower than domestic refrigerators DR. The results indicate that in the event of deflagration, SAC are more conducive for dispersion of leaked refrigerant with less potential for confinement. The author uses quantitative risk assessment in probabilistic safety analysis to come to this conclusion by systematically evaluating and quantifying the factors that might lead to ignition and unwanted consequences.
Conclusion of the study: SAC reveals lower risk than DR
In the result of the study, an extrapolation of the situation suggests that the risk of SACs is much lower than for DRs. The comparative study concluded the following:
- The overall ignition frequency of SAC is about one-hundredth of the DR
- The overall risk of overpressure and the risk of thermal intensity for the SAC was around 100 times lower than the DR
- The calculated ignition frequency of both appliances is extremely low, being less than one ignition event per million DRs over a 10-year period or one event per 100 million SACs in 10 years, with the frequency of secondary fire is about 10 times lower than the ignition frequency
- The risk for enclosures should be very low, but it is notably higher for the DR cabinet because of the inability of the refrigerant to drain from it
- The reasons for lower ignition frequency risk of SACs are because of the use of a fan that helps to disperse the leaked refrigerant, and due to the fact that a high level release can easily disperse to below the flammable limits through the adoption of certain measures.
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By Pilar Aleu
Oct 17, 2014, 11:16
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