A study on the performance of a portable single-duct propane air conditioner and ways of reducing the amount of refrigerant

A study on the performance of a portable single-duct propane air conditioner and ways of reducing the amount of refrigerant

The use of environmentally-friendly refrigerants is important for keeping the environment free from ozone-depleting substances and helping minimize global warming threats. Propane (R290) is one of the environmentally-friendly refrigerants. It is a flammable hydrocarbon gas without ozone depletion potential and its contribution to global warming is negligible. Many countries have developed a safety standard to regulate products that use flammable refrigerants.

There are many types of air conditioners to meet the increased demand for cooling, and one of these is the portable air conditioner. Portable air conditioners are designed to be moved wherever the system is needed and are compact system so all components are constructed in a single package located inside the conditioned room. There are two types of portable air conditioners: single-duct and double-ducts. A single-duct system utilizes the conditioned room air to absorb the condenser’s heat and releases the heat to the outside of the room through the duct. A double-duct portable air conditioner has an extra duct to bring outside air to the condenser instead of utilizing air within the conditioned room. This study focuses on single-duct portable air conditioners.

This study was conducted with two aims in mind. First, to compare the performance of a single-duct portable air conditioner with the non-portable air conditioner. Second, to investigate ways of reducing the amount of refrigerant within a single-duct portable air conditioner. It is important to minimize the refrigerant within the air conditioner to increase safety due to the flammability of the refrigerant.

From the assessment of the effects of refrigerant charge and room temperature on the performance of a selected portable air conditioner, it was found that there are more similarities than differences between the two systems. Similar to non-portable air conditioners, an increase in room temperature increases: refrigerant temperature at the inlet of all main parts of the system, refrigerant mass flow rate, work done by the compressor, and maximum pressure. In other words, an increase in room temperature decreases the level of sub-cooling and coefficient of performance (COP). The main differences in the effect of increased room temperature are: a decrease in maximum refrigerant velocity of the portable air conditioner at the overcharge condition and a slight increase in the cooling capacity of the portable air conditioner. Similar to non-portable air conditioners, an increase in refrigerant charge increases: the refrigerant density at the outlet of the compressor, the level of sub-cooling, refrigerant mass flow rate, and work done by of the compressor. The main differences in the effect of an increase in refrigerant charge between portable and non-portable air conditioners are: an insignificant change in refrigerant temperature at the evaporator inlet for the portable air conditioner, and a decrease in refrigerant temperature at the evaporator inlet for non-portable air conditioners; a continuous increase in cooling capacity and COP for the portable air conditioner, and both cooling capacity and COP reach their maximum for non-portable air conditioners.

This study found a few ways to decrease the refrigerant charge in the system: using a capillary tube with a smaller diameter, reducing the coil diameter of the capillary tube, reducing evaporator pressure, and increasing condenser pressure. In this research it was also discovered that, integrating the capillary tube and liquid line and replacing them with a single capillary tube, decreases the refrigerant charge.

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