Have you ever wondered about how air conditioners keep you cool, furnaces keep you warm or heat pumps do both? Here is a basic rundown of how each of these systems work.
How Your Central Air Conditioner Works
Everyone knows that central air conditioning systems make it cooler in your home, but few understand how they work. The process usually involves two pieces of equipment, one outside and one inside of your home. This split-system is the most common in homes throughout the Charlotte area.
Key Air Conditioning Components
Air Conditioners have three main components:
- Condenser Coil
- Evaporator Coil
In a split system, the compressor and condenser coil are located in the outdoor unit (what most of us think of as the air conditioner). The evaporator coil is commonly in a metal box attached to the top of the furnace unit. Most people would mistake this as part of the furnace, but it is actually an important part of your central AC system. It might also be located in a separate air-handling unit if your home uses radiator heating, rather than a forced air furnace.
How the A/C Keeps You Cool
When the temperature in your home rises, your thermostat automatically kicks your air conditioning system on. Warm air from the house is sucked through the air return vents and into the air handler, where it blows across the evaporator coil. The cold refrigerant in the evaporator absorbs the heat from the air and turns into vapor inside the copper tubing. This process cools the air in the air handler and the cooler air is then pushed through your ducts back into the living areas in your home.
Meanwhile, the refrigerant is pumped to the outdoor unit, where the compressor pressurizes it and moves it through the outside condenser coil. This process releases the heat outdoors with the help of a large fan. After moving through the condenser, the refrigerant is expanded so it can be returned to the evaporator as a cold, low-pressure liquid. This cycle repeats until the air in your home drops in temperature enough that your thermostat turns off the system.
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How a Gas Furnace Works
Gas furnaces have the simple job of keeping your house warm when it is cold outside. In Rock Hill, South Carolina and the surrounding areas, gas heating is common. Natural gas pipelines are available throughout much of the Charlotte metro area, so gas heat is generally a very affordable and efficient way to heat your home. But just how does the natural gas from the pipeline end up as warm air coming out of your vents on a cold winter day? The entire process of how a furnace works is actually fairly simple.
Parts of a Furnace
Furnaces don’t have a lot of moving parts, but they are still fairly complex appliances. The main parts of a furnace are the draft inducer fan, the ignition system and burner, the heat exchanger and the furnace blower.
Ignition System and Burner
The ignition system includes the gas line to the furnace. When it gets too cold in the house, the thermostat sends a signal to the furnace starting the ignition system. The gas line to the furnace opens and the igniter lights the gas that begins flowing through the burner. The burner is simply a set of tubes where the gas is ignited and burns.
The next step for the furnace is to heat the air that will then be pushed out of your duct system. The heat exchanger is an important part of the furnace, as this is where the heat generated by the burner makes the air hot. The furnace blower pulls cooler air in through the air return ducts in your home (and air filters) and pushes out the hot air from the heat exchanger so that it travels through your ductwork and out into each room. The draft inducer fan creates airflow that sends waste gases like carbon monoxide up into the flue pipe and out of your home, keeping you safe.
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How a Heat Pump Works
Heat pumps came about as a way to reduce the amount of HVAC equipment needed in a house. They are capable of both heating and cooling the air in your home. Or, more accurately moving the hot air into or out of your home, depending on where you need it.
In most homes with available natural gas lines, the cold nighttime temperatures during Carolina winters make it more efficient to use a natural gas furnace and air conditioning unit. However, in areas where natural gas pipelines are not accessible, heat pumps with a backup heating source can be much more efficient than heating with propane.
Parts of a Heat Pump
Heat Pumps are pretty much reversible air conditioners. Just like a split-system air conditioner, a heat pump has an indoor and outdoor unit. The outdoor unit in a heat pump contains the compressor and an outdoor coil, as well as a reversing valve. The indoor unit or air handler, contains the indoor coil and a supplemental heating system (usually an electrical resistance heater).
A tubing system connects the outdoor unit and the indoor unit. The refrigerant absorbs heat at one of the coils and transfers it to the coils in the other unit. In summer mode, the refrigerant absorbs heat from the indoor air and transfers it to the outdoor unit, where a fan helps blow it outside. This process is the same as with an air conditioner.
When it gets cold, the heat pump changes over to heating mode. Even when it is cold outside, the outdoor air contains some energy that can be used to create heat. The outdoor coils gather and transfer this heat to the refrigerant and it is pumped indoors to the indoor coil, which releases the heat into the air blowing through your ducts.
When temperatures drop below freezing, the heat pump can’t extract enough heat from the outside air to keep the house warm. That is when the backup heat system in the indoor unit kicks in. The backup heater is often electrical resistance heating, but propane is also common. Cold temperatures will also force the heat pump to run a defrost cycle, which reduces the efficiency of the system, but keeps the outdoor coils from icing up and shutting down the heat pump. Somewhere around 15 degrees, the heat pump will shut down completely and only the backup heating system will be used to heat the house.
Types of Heat Pumps
The explanation above refers to traditional full-sized heat pumps. Other types of heat pumps are also available. Ductless mini-splits can be configured as cooling units only or as heat pumps. Ground source or water source heat pumps (more well known as geothermal heat pumps) use a different process, but similar theory to heat and cool your home using the energy stored underground or underwater.