Propane air conditioners: improving leakage safety
The latest research and developments in leakage safety of R290 air conditioners are presented in several articles recently published in the IJR.
According to a September 2022 report by UNEP’s the Technology and Economic Assessment Panel, nearly half of the total production of split room air conditioners worldwide in 2021 contained HFCs, either R410A (GWP 2100) or R32 (GWP 704). Enterprises around the world continue to evaluate and develop products with various HFC/HFO blends and lower GWP alternatives. 
India has shown leadership in the marketing of R290 (propane) in split type room air conditioners, after a national manufacturer introduced R290 to the local market since 2012, combined with a network of trained installers.  Further conversion of production lines to R290 in China, Southeast Asia and South America is underway but market introduction is limited (except for small and portable units). 
Although R290 has excellent thermodynamic properties, it has the disadvantage of being a class A3 refrigerant, i.e. highly flammable, which presents a risk in the event of a leak.
To minimise explosive risk after leakage, research had previously focused on reducing the amount of R290 charge. Indeed, one of the easiest and most efficient methods of increasing safety is to reduce the total system charge or releasable charge.  According to the recently updated IEC 60335-2-40 (2022) standard, the releasable charge should not result in a concentration above 50% of lower flammability limit (LFL) for safe use.  The 7th edition of the IEC 60335-2-40 standard allows for higher charges when additional mitigation factors are used. For instance, using safety shut-off valves allows to keep the refrigerant charge mostly in the outdoor section of a split system, thus limiting the releasable charge inside. Only the flammable refrigerant charge that will leak into the occupied space is considered to cause a significant hazard. 
Ventilation is another a typical safety feature to decrease the concentration of flammable refrigerant in case of a leak.  According to Colbourne and Suen, airflow of an indoor unit can be used to dilute a refrigerant leak, enabling substantially greater charge quantities to be used.  In an article published in IIR’s International Journal of Refrigeration, Guoqiang et al. proposed a novel integral-type AC with heat recovery using R290.  The prototype was built based on a split AC with a rated cooling capacity of 3500 W. The authors experimentally studied the influences of operation mode, diameter of leakage hole and supply air wind speed on leakage safety. 
In another article, Ning et al. studied the critical releasable charges under which a fire may occur at different installation heights of indoor units.  A refrigerant pump-down method was proposed to remove the R290 from the indoor unit by the compressor to bring it below the critical releasable charge under off-mode. 
 TEAP September 2022. Decision XXVIII/2 TEAP Working Group Report – Information on alternatives to HFCs (volume 5). https://ozone.unep.org/science/assessment/teap
 May 2021 TEAP Report, Decision XXXI/7: Continued provision of information on energy-efficient and low-global-warming-potential technologies https://ozone.unep.org/system/files/documents/TEAP-EETF-report-may2021.pdf
 Ning, Q., He, G., Fan, M., Xiong, J., & Li, X. (2022). Flammable refrigerant leakage hazards control for split-type household air conditioners. International Journal of Refrigeration, 144, 188-201. https://iifiir.org/en/fridoc/flammable-refrigerant-leakage-hazards-control-for-split-type-household-146297
 Guoqiang, W., Guoyuan, M., Shuxue, X., Xiaoya, J., Shuailing, L., & Yuexuan, G. (2022). Experimental study of leakage safety of a novel integral-type air conditioner using R290. International Journal of Refrigeration, 144, 296-304. https://iifiir.org/en/fridoc/experimental-study-of-leakage-safety-of-a-novel-integral-type-air-146230
 Colbourne, D., Suen, K.O., 2022. Airflow to disperse refrigerant leaks from hydrocarbon refrigeration systems. Int. J. Refrig. 137, 220–229. https://iifiir.org/en/fridoc/airflow-to-disperse-refrigerant-leaks-from-hydrocarbon-refrigeration-145166