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| Fig. 1: Traditional Air Conditioning Methods Source: Wikimedia Commons) |
Without thinking about the potential risks to the environment, millions of individuals and establishments use air conditioning units to improve thermal comfort and indoor air quality. It has even been proven to increase productivity. Arguably, air-conditioning has become a center piece of American culture, and is seemingly a luxury that Americans cannot function without. [1] According to the International Energy Agency, in 2016, around 10% of the world's energy use went to power air conditioning. [1] The rate is set to triple by 2050, with AC consuming as much electricity as is used in China. Additionally, in the U.S., air conditioners use about 5% of all of the electricity produced. [2] Although, AC produces large amounts of CO2, it also releases potent greenhouse gases in the form of hydrofluorocarbons (HFCs). Cooling chemicals in previous generations were even more detrimental, worsening the ozone hole over Antarctica. [3] The Montreal Protocol in the late 80's phased out the use of chemicals like halons and chlorofluorocarbons (CFCs). As a result, HFCs were introduced.
Hydrofluorocarbon (HFC) is an organic compound composed of hydrogen, fluorine, and carbon, produced synthetically. HFCs are normally nonflammable, chemically stable, and non-reactive. They are projected to increase substantially due to the growing demand for refrigeration, air-conditioning, and insulting foam products from developing countries that don't have regulations of HFC emissions. Although HFCs are less damaging, they still play an active role in global warming as the fastest growing greenhouse gas. [3] HFCs are sometimes called high-GWP (global warming potential) gases, because, for a given amount of mass, they trap more heat than CO2 (the GWP depends on the type of HFC). If your air conditioner is working properly, it won't release HFCs into the atmosphere. Unfortunately, HFCs are released during the manufacturing process, and could easily be when there is a leak, or when you throw away a unit.
From projected stats, Global HFC emissions significantly exceeded previous estimates after 2025. Studies show that developing countries will have 800% more emissions than developed countries in 2050. [3] Additionally, in 2050 if there is no adaptation of a CO2 stabilization target, CO2 concentrations will reach 500 ppm, and emissions will be 40-60 GtCO2 per year. These numbers show the large contribution of HFC emissions to future climate forcing in the coming decades. When HFCs are released into the atmosphere, the compound decomposes relatively quickly; the atmospheric lifetime for HFC-134a is about 14 years, compared to CFCs that could stay in the atmosphere for 100 years. HFCs' breakdown process takes place in troposphere, the lowest portion of the atmosphere. In the troposphere, they are split by reactions with hydroxyl radicals. In addition, the carbon-fluorine bonds in HFCs are successful at not only trapping solar radiation, but also at redirecting the radiant energy toward Earth's surface. This process, called radiative forcing, plays a role in global warming. Because of the detriment of environment due to air conditioning systems releasing HFCs and other harmful gases, in 2016, countries agreed that HFCs would be phased out over the next 15-20 years. [3]
A new low-cost roof-top sized array that could provide efficient cooling for homes while using little electricity was introduced. This system is built from highly reflective material from glass and polymers, and made out of a cooling meta-material engineered film that is not found in nature. [3] It deflects away almost all incoming light from the Sun, causing temperatures to drop quickly. The material, which is slightly thicker than aluminum foil, is material made out of glass microspheres in a polymer film, with a thin silver coating. In tests, this roof-top has kept water 10°C cooler than the air when exposed to some of the warmest temperatures. [3] The material's main use is to cool thermoelectric power generating plants. [3] Scientists has recently improved the system making it small enough to fit roof-tops, allowing these panels placed on the roofs satisfying its cooling requirements. It also could be strategically manufactured on rolls, making it easier to apply on residential homes.
This innovative roof top is a part of the global initiative to phase out gases that are making global warming worse. Richer economies, like the European Union and the US, will start to limit their use of HFCs within a few years; their goal is to cut at least 10% by 2019. [3] Other developing countries, like China and countries in Latin America, announced that they'll stop their use of HFCs from 2024. Despite this drive, those countries, like China or India, with constant hot and humid weather will be very difficult to convince. Not only are large air conditioning units cheaper than these meta-materials, it is hard to implement into a building. From '93 to '05, energy efficiency improved by about 30%, but household energy consumption for air conditioning doubled. [2] The individuals in the U.S. and in countries that are perpetually warm will continue to use traditional forms of air conditioning in retail and office buildings, like room systems, for quite some time (see Fig. 1). Studies show that there will be a global cap on the use of HFCs along with a global adoption of technologies required to meet national regulations. [3] Although it will be difficult to implement, enforcers are hoping for HFC radiative forcing to decline before 2050. [3] This innovative roof top used in Colorado is just a start; however, there will be other alternatives to spread this movement.
© Melissa Lord. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] S. Robbins, "Keeping Things Cool: Air-Conditioning in the Modern World," OAH Magazine of History 18, No. 1, 42 (October 2003).
[2] L. A. Horta Nogueira, "Package of Measures to Promote Efficient Air Conditioning," World Energy Council, June 2013.
[3] G. J. M. Velders et al., "The Large Contribution of Projected HFC Emissions to Future Climate Forcing," Proc. Natl. Acad. Sci. (USA) 106, 10949 (2009).
