Air-conditioner Refrigerants and Their Environmental Impact

The main Properties required of refrigerants are stability, adequate pressure, and efficiency.

• Stability
Air-conditioners and refrigerators have an expected lifetime of 10 years or more, so the refrigerants used must work stably for at least 10 years. This means that refrigerants must be chemically stable. Refrigerants cannot be used if they undergo chemical reaction over the years and significantly change in performance.

• Adequate Pressure
For air-conditioners to give superior performance, their refrigerants must have adequate pressure.
If the vapor (condensation) pressure is too high, the amount of heat generated when the refrigerant liquefies is too little, so the COP*drops.
Likewise, if the vapor pressure is too low, a greater volume flow is needed. This means a bigger pressure loss due to flow speed, resulting in the need for larger pipes or a decrease in COP.

*COP is the energy consumption efficiency. COP=cooling (heating) capacity (kW) divided by rated power consumption,

• Efficiency
Air-conditioners don’t just contribute to global warming directly due to refrigerant emissions; they also contribute indirectly by consuming energy to operate, as well as when they are manufactured and disposed of. Compared to the direct effects from the refrigerants of air-conditioners and refrigerators, the indirect effects from their operation are usually much larger.

In order to truly reduce the total global warming impacts of air-conditioners, it’s crucial to reduce the global warming effects overall.
If we create measures that deal with the global warming impacts of refrigerants alone, or with the impacts of consumed energy alone, this may increase the total global warming effect. Therefore, refrigerants must have high efficiency. It’s possible to make up for poor refrigerant efficiency by raising efficiency through larger components on the air-conditioner. But making larger components will consume more energy during manufacture and disposal, thus offsetting any gains.

The table below shows the characteristics of the main candidate refrigerants for air-conditioning. You can see that using HFCs will help avoid ozone layer depletion.
However, HFCs have a relatively high global warming potential (GWP), while natural refrigerants generally have a GWP close to zero.

Ammonia
Ammonia does not contribute to global warming, and it is a superb refrigerant. However, because it is toxic and slightly combustible, it must be carefully controlled. Since we believe ammonia is suitable for use in places like factories, where it can be strictly controlled, we use it in large-scale air-conditioning equipment.
To use ammonia for general air-conditioning, much of the cost will be used for safety equipment. As well, because copper material cannot be used, there will be less money available to spend on performance. As a result, we believe that indirect global warming impact will increase.

Propane
Propane has equivalent performance to R22, and isobutane, a related substance, is used as a refrigerant in refrigerators. Propane is highly combustible and thus susceptible to explosion. To use as an air-conditioner refrigerant, the volume of propane must be dramatically reduced to ensure that it is safe. (Air-conditioners use about 10 times as much refrigerant as refrigerators. Ten times the refrigerant volume increases the danger of explosion by 1,000 to 10,000 times.) As well, the pipe work for air-conditioners must be done on-site. Currently, there is not sufficient technology to guarantee safety in such cases, a problem that must be solved if we are to achieve practical application.

Carbon dioxide (CO₂)
CO₂ is not toxic or flammable and thus poses no additional safety problems to HFCs. However, because it has a low COP, air-conditioners using it require more electricity, Thus, there are doubts whether it will lessen the total global warming impact. In addition , it has significantly higher operation pressure than conventional refrigerants. But because it has similar performance as conventional refrigerants for applications like water heaters, Daikin uses CO₂ as a refrigerant for heat pump water heaters.

HFC32
A type of HFC, HFC32 has the potential to significantly reduced global warming: it has a global warming potential approximately one-third of HFC410A, and HFC407C, and it is more efficient. It can also be used in a relatively short time. However, even though HFC32 is not classified as a flammable gas under general high-pressure gas safety laws, it is slightly combustible. That is why we are currently developing technologies to ensure its safe use and assessing the risk. International standards for the safe use of propane, HFC32, and other flammable refrigerants are currently under consideration.

Although these future refrigerants may make splendid contributions to the reduction of global warming, there are a number of obstacles, such as safety, to overcome, so it will not be easy to use these refrigerants widely in the near future.
In the meantime, raising the energy efficiency of air conditioners is a safe and immediate way to reduce global warming. As well, the conventional refrigerants with a high global warming potential will not contribute to global warming if they are not released into the atmosphere.

Currently, HFC410A and 407C, used as substitute refrigerants, have similar global warming impact and efficiency to conventionally used HCFC22. The use of these will eliminate ozone layer depletion inpact. As well, we believe that for the time being the best measures we can take against global warming are to recover refrigerants and make products more energy efficient.
Of course, we are also continuing to research and develop the use of natural refrigerants like ammonia and carbon dioxide (CO₂) for their potential applications.