Which gas is suitable for AC ?

 The suitability of a gas for air conditioning (AC) depends on various factors, including its thermodynamic properties, safety, environmental impact, efficiency, and cost. Historically, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) were commonly used as refrigerants, but their use has been phased out due to their detrimental effects on the ozone layer and contribution to global warming.

Currently, the most suitable gases for AC systems are those with low environmental impact, high energy efficiency, and safety. Some of the commonly used refrigerants in modern AC systems include:

1. Hydrofluorocarbons (HFCs): HFCs were introduced as alternatives to CFCs and HCFCs because they do not deplete the ozone layer. However, many HFCs have high global warming potential (GWP), contributing significantly to climate change. Therefore, while they are still widely used, there's a global effort to phase out high-GWP HFCs and replace them with more environmentally friendly alternatives.

2. Hydrocarbons: Hydrocarbons such as propane (R-290) and isobutane (R-600a) are natural refrigerants with very low GWP. They are highly energy-efficient and have excellent thermodynamic properties. However, they are flammable, which requires careful handling and proper safety measures in AC systems.

3. Hydrofluoroolefins (HFOs): HFOs are a new generation of refrigerants designed to have low GWP while maintaining high energy efficiency. They are being increasingly used in new AC systems as they offer a balance between environmental impact and performance.

4. Ammonia (NH3): Ammonia is an efficient refrigerant with zero ozone depletion potential and very low GWP. It has been used for many years in industrial refrigeration but is less common in household AC systems due to its toxicity and flammability risks.

5. Carbon dioxide (CO2 or R-744): Carbon dioxide is a natural refrigerant with zero ozone depletion potential and a low GWP. It's gaining popularity in commercial refrigeration and some AC applications due to its environmentally friendly properties, although it requires higher operating pressures compared to other refrigerants.

The choice of refrigerant depends on various factors, including regulatory requirements, safety considerations, system design, and application requirements. As environmental concerns become more prominent, there's a growing trend towards using refrigerants with lower GWP and environmental impact in AC systems.