Air conditioning and air-cooling technology
Air conditioning and air-cooling technology encompasses methods and systems designed to regulate indoor air temperature and comfort. Historically, various cultures developed techniques such as circulating cool water or using fans to create breezes, but these methods often had limitations, especially in humid conditions. The modern air conditioning system, largely based on principles first proposed by Willis Carrier in 1902, operates similarly to electric refrigerators by using specific fluids that change states from liquid to gas to absorb heat, effectively cooling the air.
Initially, older systems employed hazardous refrigerants like ammonia or propane; however, the introduction of chlorofluorocarbons (CFCs) in the late 1920s marked a significant advancement due to their non-toxic and stable properties. Unfortunately, CFCs were later found to deplete the ozone layer and contribute to global warming, prompting international efforts like the Montreal Protocol to reduce their usage. Today, energy efficiency is a critical focus, as air conditioning represents a substantial portion of electricity consumption in warmer climates. The Seasonal Energy Efficiency Ratio (SEER) is a key metric used to evaluate the efficiency of air conditioning units, with higher SEER ratings indicating better energy performance. As technology progresses, newer refrigerants are being developed to minimize environmental impact, though they often require system modifications.
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Air conditioning and air-cooling technology
Definition: Intentional modification of indoor air temperature, humidity, or other characteristics for the purpose of comfort, health, or protection of items sensitive to temperature or humidity
Air conditioning benefits humankind in many ways, but it also has some negative environmental impacts. The refrigerants long used in air conditioners have proven to have adverse effects on ozone in the earth’s stratosphere, and the use of air conditioning accounts for a high percentage of energy consumption, particularly in regions with warm climates.
Since ancient times, human beings have tried to make the air inside buildings more comfortable. The Romans circulated cool water through buildings. Other cultures created fans or encouraged breezes to blow across pools of evaporating water to cool buildings. Cooling by evaporation of water, however, can lower temperatures only by a few degrees and is not effective when the air is humid.
Most modern air conditioners are similar to that first proposed by Willis Carrier in 1902. Air conditioners work in much the same way as do electric refrigerators. Both kinds of devices make use of the thermodynamics of fluids. A fluid with a boiling point somewhat below room temperature is selected, and a compressor is used to compress the fluid. Under sufficiently high pressure, the fluid liquefies. This process produces heat, so, in a part of the system outside the area to be cooled, fans blow air over tubes containing the warm liquid to cool it. The liquid is then circulated into the part of the system within the area to be cooled, where it passes through tubes in which the pressure drops, allowing the fluid to evaporate. The evaporating fluid then cools to a temperature near its boiling point. A fan blows air over the cold tubes, cooling the air. Many early air conditioners used fluids such as ammonia, methyl chloride, or even propane. The problem with these materials is that they are health hazards, explosion or fire hazards, or both.
In 1928, Thomas Midgley Jr., developed chlorofluorocarbons (CFCs), a family of related chemicals that were nontoxic and nonexplosive and that had boiling temperatures and other properties making them suitable for use in air conditioners and refrigerators. It was unknown at the time that these nontoxic CFCs, when released into the atmosphere, break down ozone in the earth’s stratosphere. Because ozone in the stratosphere blocks ultraviolet light from the sun, maintenance of the ozone layer is important to life on earth. Without the ozone layer, the earth’s surface would receive a lethal dosage of ultraviolet light. Some damage has already been done to stratospheric ozone by CFCs released from leaking air-conditioning systems. In addition to depleting stratospheric ozone, CFCs are greenhouse gases, which means that they contribute to global warming.
The international agreement known as the Montreal Protocol calls for the gradual reduction of the production of CFCs and other chemicals known to harm the ozone layer, and since the adoption of the protocol in 1987 the use of these substances has been greatly reduced around the world. Some non-CFC refrigerants have been developed that are less damaging to the environment; however, these newer refrigerants have slightly different properties and cannot simply be substituted for CFCs in older air-conditioning systems without modifications to the systems, some of which can be expensive.
In regions with warm climates, air conditioning accounts for the largest use of electricity in buildings. With electricity becoming increasingly expensive, many manufacturers of air conditioners emphasize energy efficiency in their marketing. The standard reference for air-conditioner energy efficiency is the seasonal energy-efficiency ratio (SEER), which is the thermal energy removed (measured in British thermal units) divided by the energy used (measured in watt-hours). The larger the SEER, the more energy-efficient the air conditioner.
Bibliography
Achermann, Marsha E. Cool Comfort: America’s Romance with Air-Conditioning. Washington, D.C.: Smithsonian Institution Press, 2002.
Kwong, Qi Jie, Nor Mariah Adam, and B. B. Sahari. “Thermal Comfort Assessment and Potential for Energy Efficiency Enhancement in Modern Tropical Buildings: A Review.” Energy & Buildings 68 (2014): 547–557. Academic Search Complete. Web. 14 Jan. 2015.
Miller, Rex, and Mark R. Miller. Air Conditioning and Refrigeration. New York: McGraw-Hill, 2006.
Sivak, Michael. “Will AC Put a chill on the Global Energy Supply?” Amer. Scientist. 101.5 (2013): 330–333. Academic Search Complete. Web. 14 Jan. 2015.
Todorovic, Marija S., and Jeong Tai Kim. “In Search for Sustainable Globally Cost-Effective Energy Efficient Building Solar System—Heat Recovery Assisted Building Integrated PV Powered Heat Pump for Air-Conditioning, Water Heating and Water Saving.” Energy & Buildings 85 (2014): 346–355. Academic Search Complete. Web. 14 Jan. 2015.