On a hot summer day, there are few appliances more useful than the window air conditioner. These miracles of engineering move heat from inside your home to the outside, cooling the air inside to make it more comfortable. These devices pump heat from one side to another, shifting the heat to the outside and circulating wonderful cool air inside. And they do this in a remarkably small space, without having to knock holes in the wall. So, how do these miracles of cool work? Fundamentally, a window AC unit is a pump, one that shifts heat instead of water. It does this by using a chemical that turns from a liquid into a gas with a relatively small shift in pressure. Called a phase transition, this process is at the heart of how window AC units work: by repeatedly pressurizing and then releasing this chemical, the window AC unit moves energy from one side to the other. Combine this with a fan that circulates the air through the unit, and you get air conditioning. At the core of a window AC unit is a loop of pipe, usually copper, with a pump on one side and a small expansion valve on the other.

This loop has two radiators on it: one on the outside and one on the inside, which have fans behind them to push the air over them.On most modern units, this loop is filled with a coolant called R-410A, which is a mixture of two chemicals: difluoromethane (CH2F2) and pentafluoroethane (CHF2CF3). This coolant is used because if you compress it, it becomes a liquid. If you then release this pressure, it evaporates to become a gas, and the difference in pressure needed to go between the two states is fairly small. These two states are the mechanism that moves the heat from inside your house to outside. When the pump is active (which you can usually hear; it's the low-frequency rumble from a working AC), it's compressing the coolant so it becomes a liquid. This liquid passes through the outside radiator, where it sheds heat into the outside air. When it reaches the expansion valve, only a small amount is let through, so the pressure on the other side is much lower. This makes the coolant evaporate, which cools it down.

From there, it passes through the inside radiator, and the air passing over this is cooled. The coolant absorbs the energy (the heat) from the air inside the room, cooling it. air handling units sizingThe coolant then moves into the pump, where it is compressed again and pushed into the outside half of the loop, and the process repeats. my window ac unit freezes upThe whole process is controlled by a computer that measures the temperature of the air being sucked into the unit and turns the pump on and off as required. prices for commercial air conditioning unitsBecause the coolant takes time to pass through the expansion valve, the pump doesn't run all the time when the unit is cooling: when the pressure on the hot, outside part of the loop reaches a certain level, the controller turns the pump off until the pressure falls.

As the coolant passes through the pressure valve, it evaporates and cools in the inside radiator, and you feel the cool air. That's why you don't feel an immediate rush of cool air when you turn on a window AC unit: the pump has to build up the pressure before the cooling can begin. The cooling power of windows AC units is measured in British Thermal Units (BTU). This is a measure of how much energy (in the form of heat) the device can shift from one side to the other. Specifically, one BTU is the amount of energy it takes to heat (or cool) one pound of water by one degree Fahrenheit. The higher this number, the more energy (heat) the unit can move, and the larger the area it can cool.Most window AC units range from 2,000 to 25,000 BTU. However, most units over 15,000 BTU will require a dedicated 230V power line, like those used by electric dryers. This process of repeatedly compressing the mix uses a lot of energy, which is why window AC units are notorious power hogs, especially when the pump first starts.

That's why the lights sometimes flicker when a window AC unit turns on: The device is sucking down a lot of juice to get the pump started compressing the mix and beginning the cycle. But let's be honest -- that wonderful rush of cool, clean air on a hot day is worth the electricity bill. So, on a hot, sunny day, give thanks to the science of thermodynamics, the invention of the refrigeration cycle and the complex engineering that keeps you cool.Written Double pane window glasses are used in some cars.1)Over-Weight: 2)Condensation: not for de-frosting3)Ineffectiveness & expenses:Email to a friend Check out this article Air Scare. Claim: Automobile components emit dangerous levels of cancer-causing benzene fumes. Example: [Collected via e-mail, May 2009] Do not turn on A/C immediately as soon as you enter the car! Please open the windows after you enter your car and do not turn ON the air-conditioning immediately. According to a research done, the car dashboard, sofa, air freshener emits Benzene, a Cancer causing toxin (carcinogen- take note of the heated plastic Smell in your car).

In addition to causing cancer, it poisons your bones, causes anemia, and reduces white blood cells. Prolonged exposure will cause Leukemia, increasing the risk of cancer. May also cause miscarriage. Acceptable Benzene level indoors is 50 mg per sq. ft.. A car parked indoors with the windows closed will contain 400-800 mg of Benzene. If parked outdoors under the sun at a temperature above 60 degrees F, the Benzene level goes up to 2000-4000 mg, 40 times the acceptable level ... and the people inside the car will inevitably inhale an excess amount of the toxins. It is recommended that you open the windows and door to give time for the interior to air out before you enter. Benzene is a toxin that affects your kidney and liver, and is very difficult for your body to expel this toxic stuff. Origin:This item about the dangers of benzene supposedly emitted by automobile components has been widely misunderstood. Many readers have come away from the article with the impression that it warns drivers not to use their cars' air conditioning because the A/C system itself is producing benzene, but what the article actually cautions against is the practice of turning on the air conditioning immediately upon entering an automobile.

Motorists should instead, it says, roll down their windows in order to allow accumulated benzene fumes (allegedly emitted by other components, such as dashboards and upholstery) to vent from the car first before re-closing the windows and turning on the A/C. How much truth is there to this warning? Evidence suggests an association between exposure to benzene and an excess risk of leukemia, as noted by the American Cancer Society (ACS): A considerable number of human studies provide evidence linking benzene and cancer. Initially, increased risks of leukemia, chiefly AML, were reported among workers with high levels of benzene exposure in the chemical, shoemaking, and oil refining industries. More recently, studies have focused on workers with relatively lower exposure. The human data are supported by animal studies. There is sufficient evidence for the carcinogenicity of benzene in experimental animals. Key animal studies support the finding of an excess risk of leukemia in humans from exposure to benzene by inhalation and ingestion.

The details of these studies have been reviewed and found to support the association between benzene and cancer. But do automobiles really produce potentially cancer-causing levels of benzene? No studies have yet documented that claim to be true. A 2001 study of commuter exposure (in both cars and buses) in Korean urban areas found some relationship between automobile use and exposure to benzene, but its observations differed from the warning quoted above in some significant areas: The study found that traveling by automobile increased exposure to a number of deleterious compounds, including benzene, but the primary factor in this regard was the fuel used by the vehicles, not internal components such as dashboards. The study found that benzene levels were higher in older cars than newer cars, which suggests that the primary factor in automobile benzene levels was not associated with the "new car smell" emitted by components such as dashboards and upholstery. The study found that exposure levels were significantly higher during the winter months, which suggests that automobile air conditioning use is not a major factor in benzene exposure.

The Korean study itself did not establish a connection between commuter exposure to benzene and the onset of cancer. A 2007 German study on "Toxicity of Parked Motor Vehicle Indoor Air" which specifically tested the health effects of emissions from one new and one three-year-old vehicle exposed to "parked in sunshine" conditions found "no apparent health hazard of parked motor vehicle indoor air": Buters and his colleagues first collected molecules from the air inside a new car and a three-year-old vehicle of the same brand placed under 14,000 watts of light, where temperatures reached up to 150 degrees Fahrenheit. They next exposed these compounds to human, mouse and hamster cells grown in lab dishes. These are commonly used to test toxicity. New car smell does not appear to be toxic, the scientists found. Air from the new car did cause a slight aggravation of the immune response that could affect people with allergies, but the same was not seen with the older vehicle.

(The German study also found the total amount of volatile organic compounds in a new car to be one-tenth the level claimed in the e-mail for benzene alone.) The ACS similarly noted of this e-mail that: We found no published studies that confirm the claims of this e-mail. Benzene levels that exceed recommendations for chronic workplace exposure have been observed in some moving cars, but these levels seem unlikely in properly maintained cars. The e-mail did get one thing right, though: Upon returning to a closed car on warm days, you should open the windows for a minute or so rather than immediately turning on the air conditioning. The reason has nothing to do with benzene levels, however; rather, it's because when a car is parked in the sun with its windows rolled up, that condition can create a greenhouse effect which causes the interior of the vehicle to warm up to a temperature considerably higher than that of the outside air. Opening the windows for a few moments allows for the exchange of hot air from inside the vehicle with cooler air outside, speeding up the process of cooling off the car more than air conditioning alone would.