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4 definitions by AutoHVACNut

Central air conditioning, commonly referred to as central air (U.S.) or air-con (UK), is an air conditioning system that uses ducts to distribute cooled and/or dehumidified air to more than one room, or uses pipes to distribute chilled water to heat exchangers in more than one room, and which is not plugged into a standard electrical outlet.
With a typical split system, the condenser and compressor are located in an outdoor unit; the evaporator is mounted in the air handler unit. With a package system, all components are located in a single outdoor unit that may be located on the ground or roof.

Central air conditioning performs like a regular air conditioner but has several added benefits:

When the air handling unit turns on, room air is drawn in from various parts of the building through return-air ducts. This air is pulled through a filter where airborne particles such as dust and lint are removed. Sophisticated filters may remove microscopic pollutants as well. The filtered air is routed to air supply ductwork that carries it back to rooms. Whenever the air conditioner is running, this cycle repeats continually.
Because the condenser unit (with its fan and the compressor) is located outside the home, it offers a lower level of indoor noise than a free-standing air conditioning unit.
Most new homes being built in the United States today have central air.

It must be ninety degrees outside, can you turn on the central air?
by AutoHVACnut February 08, 2012
See Heat Pump and Defrost Cycle. A winter phenomenon produced by a heat pump, for which conditions have to be just right. If you actually catch a heat pump giving a steam show and have a video camera handy, it makes for one hell of a YouTube video.

Many heat pumps have interval defrost and will have a defrost cycle every 30, 60, or 90 minutes whether they need to or not, even if they are NOT frozen or iced over. The ones with more modern demand defrost will oly defrost on an as-needed basis, basically when there is ice/frost buildup on the coils. The best conditions for a steam show are when it is below 40 degrees, and a heat pump will freeze up much faster when it is wet, rainy, or snowy. However, a heat pump is capable of producing a good steam show on a nice, sunny day with no precipitation. The best steam shows typically occur below 37 degrees regardless of weather conditions.

How much steam a heat pump produces depends on the outside temperature, how much ice/frost/snow has built up on the outdoor coils, and the heat pump itself. To someone not familiar with a heat pump, a steam show can be misleading, and calls to the fire department in the winter by people claiming their heat pump is on fire are not out of the ordinary. Some stubborn customers also wind up spending hundreds of dollars on unnecessary service calls only to find out their heat pump is doing exactly what it is supposed to do.
The heat pump at the elderly couple's new condo produced such a big steam show that they thought the unit was on fire, shut it off, and called the HVAC company, only to find out that their heat pump was doing exactly what it was supposed to.

An HVAC tech once told me the story of a customer who observed a steam show and thought their heat pump was on fire, and paid over a hundred dollars for a guy to come out only to tell them it had been defrosting.
by AutoHVACNut February 08, 2012
See Heat Pump. Also called "defrosting" and "going into a defrost."

When it gets below about 45 degrees, a heat pump running in HEAT mode may develop ice or frost on the coils. There are exceptions to the rule, however, as I have seen heat pumps defrost when it is abve 45 degrees and even in the 50s! If it gets frozen enough, it may have to defrost. A defrost cycle is initiated by the the reversing valve switching the flow of Freon and putting the unit in COOL mode. However, unlike when the unit is running in COOL mode on a hot day, the fan blades in outdoor unit are not spinning, and the system typically has its electric, gas, or oil backup heat running to prevent the heat pump from effectively air-conditioning the house while it is defrosting. Sometimes, depending on a number of factors, a steam or fog may appear above the heat pump (see Steam Show). A defrost cycle can last anywhere from less than a minute to ten minutes or more depending on a number of factors, including outdoor temperature, ice/frost buildup on the outdoor coils, whether or not it is raining or snowing, and what temperature the thermostat is set at.
The first time I saw a defrost cycle at my new house, I thought my heat pump wa broken and about to explode!

My heat pump is located right outside the master bedroom window, and it woke me up this morning when it went into defrost.

I was playing with my dog in the backyard on a chilly winter day, when my heat pump went into defrost and scared her so much that she started barking at it.
by AutoHVACNut February 08, 2012
See central air.

A heat pump is just like a central air-conditioner when running in COOL mode. However, during the winter months or when it is cold outside, a heat pump has a component called a reversing valve that allows it to reverse the flow of refrigerant. Instead of removing the heat and humidity from the structure and subsequently cooling it as a result, a heat pump extracts ambient heat from the outside air and moves it into the structure. There is heat in the air right down to absolute zero. However, once it gets below freezing, even the newest, most efficient, top-of-the-line heat pumps tend to struggle in terms of heating performance without some sort of backup heat.

In areas where it is almost always warm, like many parts of Florida, a heat pump with no backup heat (gas, oil, electric) is just fine. However, the farther North you go, the more likely you are to need backup heat. Electric strip heat is little more than oversized toaster coils with a fan that blows over them to circulate the heat through the building's ductwork. This will work anywhere in the country, but the farther North you go, the more expensive it is going to be to run it. In parts of the country with really cold winter climates, a heat pump matched up with a gas or oil furnace, or even a hot water boiler, is a very efficient choice, possibly even more efficient than a straight-cool central air-conditioner matched up with a furnace. This is called a hybrid or dual-fuel system.
Those new tract homes in Florida have those efficient heat pumps instead of regular electric heat.

My friend's house in the Pennsylvania has a heat pump, and it sucks at heating when it gets below forty degrees!

My new house has a heat pump and a gas furnace for maximum efficiency
by AutoHVACnut February 08, 2012