Viability of commercial liquefied petroleum gas as drop-in refrigerant in air conditioning systems

Abstract

This study focuses on the use of commercial grade liquefied petroleum gas (LPG) namely, propane and butane to replace chlorodifluoromethane (HCFC-22) or commercially known as R-22. Malaysia being a signatory to the Montreal Protocol has committed to phaseout the use of HCFC and subsequently introduced hydrofluorocarbons (HFC) refrigerants as replacements. HFC is a global warming gas and is also subjected to phasedown in the future. A replacement refrigerant using hydrocarbons such as, propane and butane were available in the market where most of them were imported. It was the objective of this study to find out the suitability, efficiency and the safety of LPG, which are widely available in Malaysia to be used as replacement as refrigerant, for R-22. The scope of research included conducting the cooling capacities and energy efficiency tests with variations of outdoor temperatures using R-290 & HC 22a (both were refrigerant grade propane), variations of LPG compositions based on mass percentage and R-22. Tests were conducted in psychometric chamber to compare the cooling capacities and energy efficiencies of R-22, refrigerant grade propane and LPG using the ISO 5151 standard as a reference. To study the safety aspects, in the use of LPG as refrigerant, computational fluid dynamics (CFD) simulations using the ‘fire dynamics simulator version 6” software was used to generate propane leak scenarios of an indoor unit of the 1.0 horsepower split air conditioner in an enclosed room. In cooling capacities tests, by comparing, commercial propane was comparable to R-22, losing out only by 10 % of the capacity as compared to R-22. A 20 % propane and 80 % butane LPG blend meanwhile was the highest in energy efficiency ratio (EER) ratings but losing out by 40 % cooling capacities. In simulation studies, leak hole with a diameter of above 2.40 mm posted hazards of forming combustible mixture when propane was leaking from the indoor unit. The leak holes diameters of 0.08 mm, 0.76 mm, 1.50 mm and 1.90 mm posted no hazards in forming the combustible gas mixture when entire content of refrigerant was leaked into the room. Areas inside and surrounding the cover of the air conditioner’s indoor unit were susceptible to fire upon reaching the lower flammability limit of propane due to the leak of refrigerant from the air conditioner. This study also established that, commercial propane could be used as a “drop-in” to replace refrigerant R-22 without significant loss in refrigerant capacities and could achieve better EER ratings than R-22. A combustible leak detection system installed, capable of detecting propane leakage from the cover of the indoor unit of split unit air conditioner could enhance safety when utilizing commercial propane as a refrigerant.