How does my HVAC system work?
According to the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, heating and cooling account for about 43 percent of the energy use in a typical U.S. home, making it the largest energy expense for most homes.
So, it's likely a good idea to know a little about how various HVAC systems work.
WHAT KIND OF SYSTEM?
There are several basic energy sources for home:
Air conditioners can range from small family window units to central air conditioning, sometimes with two or more units for large homes. Large office buildings may have 10 or more condenser units on their roofs.
An air conditioner works by removing warm air from your house and cycling it back as cooler air. The blower that's also often used for the furnace pushes the cool air throughout the house until the air reaches the desired temperature on your thermostat.
A central air conditioner is either a split-system unit or a packaged unit.
In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners, this indoor cabinet also contains a furnace or the indoor part of a heat pump. The air conditioner's evaporator coil is installed in the cabinet or main supply duct of this furnace or heat pump. If your home already has a furnace but no air conditioner, a split-system is the most economical central air conditioner to install.
In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner also is used in small commercial buildings. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors.
AIR GOES ROUND AND ROUND
Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers.
Here's how it works:
Throughout the second half of the 20th century, nearly all air conditioners used chlorofluorocarbons (CFCs) as their refrigerant, but because these chemicals are damaging to Earth's ozone layer, CFC production stopped in the United States in 1995. Nearly all air conditioning systems now employ halogenated chlorofluorocarbons (HCFCs) as a refrigerant, but these are also being gradually phased out, with most production and importing stopped by 2020 and all production and importing stopped by 2030.Production and importing of today's main refrigerant for home air conditioners, HCFC-22 (also called R-22), will begin to be phased out in 2010 and will stop entirely by 2020. However, HCFC-22 is expected to be available for many years as it is recovered from old systems that are taken out of service. As these refrigerants are phased out, ozone-safe hydrofluorocarbons (HFCs) are expected to dominate the market, as well as alternative refrigerants..
HOW TO TELL IF YOU'RE BUYING AN EFFICIENT DEVICE?
For furnaces, the acronym AFUE (annual fuel utilization efficiency) rates how efficiently the unit delivers warm air into the house. A furnace with a 78 percent AFUE rating, the minimum by federal standards, means that 78 percent of the heat the furnace creates gets into your home and the other 22 percent goes up the flue. High-efficiency furnaces can deliver as much as 96 percent. SEER is the acronym for cooling units. The seasonal energy efficiency ratio (SEER) is similar in that the higher number indicates better cooling efficiency. Federal law dictates that new central air-conditioning systems need a SEER of at least 13.
WHAT ELSE DO AIR CONDITIONERS DO?
Air conditioners help clean your home's air as well. Most indoor units have filters that catch dust, pollen, mold spores and other allergens as well as smoke and everyday dirt found in the air. Some advanced filters can help if allergens interrupt sleep. Most air conditioners also function as dehumidifiers. They take excess water from the air and use it to help cool the unit before getting rid of the water through a hose to the outside.
WHAT IF MY FURNACE OR AIR CONDITIONER BREAKS DOWN?
You can do basic maintenance, such as changing a filter monthly, but a pro may be needed if the device just won't work. Do know how to turn off the main system, such as the shutoff valve for gas furnaces and water heaters. Electric systems should have a switch or a circuit breaker or fuse. Fuel oil tanks also have shutoff valves. A good way to keep your equipment running is to have an HVAC professional check your furnace in the fall and air conditioning in early spring.
Source: U.S. Department of Energy
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