Enjoying AC in Your Home? Thank Mr. CarrierPublished on: March 28, 2013
All over the world, people depend on air conditioning to stay cool no matter how hot the summer weather becomes. Air conditioning systems are available in a huge range of styles and options, from traditional split-level units to compact ductless systems and from budget-friendly basic models to advanced systems with pinpoint control equipment. Although air conditioners have been improved greatly since their inception in the early twentieth century, the basic cooling cycle has remained a constant throughout their history.
Origins of Air Conditioning
Since intense summer heat has posed a threat throughout human history, it is only natural that people have been working on ways to cool their homes for thousands of years. The ancient Egyptians, for instance, would hang damp reeds in their windows; as hot air entered the home, water would evaporate off the reeds and remove heat from the air. Though primitive, this early system used the same basic heat transfer principle that keeps modern homes cool; the reeds also improved indoor air quality by releasing extra moisture into the air. Other ancient civilizations, such as the Romans and the Persians, likewise developed ways to stay cool in the face of the summer heat.
More immediate forerunners of the modern air conditioner emerged in the nineteenth century as inventors experimented with ways to transfer heat for a variety of applications. In 1820, Michael Faraday found a way to chill air by compressing and liquefying ammonia, the same process that many early air conditioners used. Two decades later, Dr. John Gorrie used a compressor-based ice maker to cool his hospital in Florida. He envisioned using the same technology to cool other buildings and even entire cities in time, but after his death in 1855, the idea faded into the background for nearly half a century. Still, the HVAC industry considers Dr. Gorrie to be one of the fathers of modern refrigeration and air conditioning.
The first truly modern air conditioner was invented by Willis Carrier, who designed the system in 1902. Carrier’s original air conditioner was intended to perform four simple tasks: control temperature, maintain acceptable humidity, direct ventilation and make the air cleaner. Carrier officially patented the first spray-type air conditioner in 1906 and designed an automatic control system later that year. He went on to found the Carrier Corporation, which is still one of the world’s leading manufacturers of heating and cooling equipment.
The Cooling Cycle
Since Carrier’s innovation more than a century ago, every modern air conditioning system has incorporated the same basic cooling cycle. Air conditioners take advantage of a basic property of matter: When a liquid evaporates to become a gas, it absorbs heat. Likewise, when a gas condenses to become a liquid, it releases heat. A chemical that goes through these phase changes over and over again can, in time, transfer substantial amounts of heat from one place to another.
Modern air conditioners use refrigerant chemicals, which have special properties enabling them to change phase at fairly low temperatures, to carry out this heat transfer. At the evaporator coil, liquid refrigerant absorbs heat from inside the home and becomes a gas. The unit then transfers the gaseous refrigerant from the evaporator to the condenser coil, where a special pump called a compressor forces it to become liquid by applying intense pressure. As it condenses, the refrigerant releases its stored heat outside the home. The air conditioner then pumps the liquid refrigerant back to the evaporator coil to repeat the process.
One of the greatest advantages of this cooling cycle is that the machine consumes nothing other than electricity to keep it running. Although refrigerant plays a key role in the heat transfer, the phase changes themselves are efficient; that is, no refrigerant is lost as it goes from liquid to gas and back to liquid.
Development of Refrigerant
Early air conditioners used refrigerant chemicals that were quite toxic, such as ammonia or highly flammable, such as propane. Although these chemicals worked reasonably well as refrigerants, they could lead to fatal accidents in the event of a leak. In 1928, chemist Thomas Midgley, Jr., invented Freon, the first non-flammable and non-toxic refrigerant chemicals.
The term Freon refers to a collection of chlorofluorocarbons (CFC), hydrochlorofluorocarbons (HCFC) and hydrofluorocarbons (HFC) that can be used as refrigerants. Individual chemicals in this group are given numbers based on their molecular composition, such as R-11, R-12 or R-22. For decades, R-22 refrigerant was the blend used in the majority of home and commercial air conditioners, while most automotive air conditioners used R-12.
Recent concerns about the environmental impact of CFCs have led the industry to develop cleaner alternatives to R-22 refrigerant. Today, the most common is R-410A, which Carrier uses under the brand name Puron. Over the course of several decades, the HVAC industry has phased out the older R-22 refrigerant; since 2010, manufacturers have been banned from using the chemical in new machines. However, small quantities of R-22 are still manufactured to service existing HVAC systems.
Variations and Specialized Systems
Heat pumps are special heating and cooling devices that use the same cycle as traditional air conditioners to transfer heat in either direction. During the summer, a standard heat pump works just like an air conditioner, collecting heat from inside the home and transferring it outside to lower the indoor temperature. In the heating season, the cycle effectively reverses, as the evaporator coil collects heat from outside the home and the condenser coil releases it inside. Because they combine heating and cooling functionality in a single system, heat pumps are relatively compact, and they run quite efficiently in areas with fairly mild climates. However, they do tend to require a good deal of maintenance because they run all year long.
Another fairly recent development in the HVAC industry is the ductless air conditioner, which circulates cool air throughout the home with no need for extensive ductwork. Ductless systems are quite compact and generally sit high up on a wall, making them excellent choices for small homes where there is little available space. They also run quietly and efficiently and require limited maintenance once they are installed.
Air Conditioning Control Equipment
For nearly as long as air conditioning systems have existed, engineers have been working to find ways to better control them. The basic thermostat actually predates the air conditioner itself by two full decades, having been invented by Warren S. Johnson in 1883. Since then, the thermostat has been refined greatly, to the point where modern digital devices don’t need any moving parts at all. They use special resistor components called thermistors to detect temperature changes, then switch associated air conditioners and heat pumps on and off as needed.
Modern programmable thermostats can be pre-set to turn air conditioners on and off at various times throughout the day. Many homeowners, for instance, set their thermostats to cool the home a few minutes before they get home from work and enjoy the comfortable temperature as soon as they arrive. Some thermostats also allow for zoned control, which means the user can set different rooms throughout the house to maintain different temperatures. A few HVAC systems can even be manipulated remotely by on-the-go homeowners.
Service and Maintenance
Although air conditioners have come a long way since their invention in 1903, they are still somewhat prone to mechanical issues. With a little preventative maintenance, however, they can keep running at a high level of energy efficiency for many years to come. At the beginning of the cooling season and periodically thereafter, look at the refrigerant gauge to confirm that the refrigerant is still at an appropriate level and check the wires coming into the machine for any corrosion or rust. These routine checks can catch small issues before they become big, expensive problems.
Over time, any air conditioner’s air filter will become clogged with dust and debris, which can reduce operating efficiency and lead to maintenance issues such as freezing. Reusable filters should be removed and cleaned on a monthly basis; remember to let the filter air dry completely before putting it back in the unit. Before replacing a disposable filter, check with a local factory authorized dealer to get a replacement designed to fit the right make and model of air conditioner.
To really make the most of modern air conditioning, consider having your home HVAC systems professionally serviced on an annual basis. A trained and certified technician can spot many emerging issues and correct them easily before they lead to expensive failures. Any service visit also includes small calibration adjustments that will maximize energy efficiency and minimize the risk of future failures. Thus, an annual service agreement saves you money in the short term by cutting your utility bills and in the long term by heading off future repair costs. Keep your air conditioners properly maintained, and you will be able to enjoy the comfort first envisioned by Willis Carrier for years to come. Our network of expert dealers at AC Southeast® is available to address all HVAC questions and concerns. Just call one of our local dealers in your area for information on air conditioning systems, maintenance and repairs.