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Central Heating and Air System Operation

A central heating and air system is complex and if you haven’t been trained to work on them, its likely you’ll have questions about their operation in your home. Most residential systems are split systems where the individual components are segregated to the indoor units and outdoor units.

How Does a Furnace Work?

Obviously you know the furnace in your home is responsible for burning a source of fuel to heat your home or business. HVAC questions are more centered around how it does this exactly. Most furnaces are what we call air to air furnaces, where they heats the air it circulates around your home and indoor spaces. Furnaces typically burn natural gas, oil, or propane to accomplish this. Air Handler units are part of a heat pump system which we’ll discuss later. These units use electric strip heat to heat the air it is circulating around your house to warm it. 

When you turn your thermostat to heat mode and set it to the desired temperature, a sequence of operations take place at the furnace. First the draft inducer motor is energized to create a draft in the heat exchanger that draws the combustion gases out and up a flue pipe venting outside the house. Second, a systems intermittent pilot light or electronic ignition is energized to ignite the burner. Once a flame is proven by the flame sensor, a temperature probe signals the blower motor to come on. As air is pulled from the return air ducts in your house across the heat exchanger, it is warmed and distributed throughout your home by ducts to supply registers. The system will remain on until the temperature set point at the thermostat is satisfied. The sequence of operations for the furnace is controlled by the main printed circuit board housed in the blower sections. Its also worth mentioning that the blower used for the heating cycle is the same used in cooling mode too.  Furnace control boards typically have a LED light that will flash error codes that can lead to the source of a problem. Sometimes these can be misleading though, and the best course of action at this point is to call your local HVAC service professional to diagnose the problem. 

Electric Air Handlers can either be stand alone or used in conjunction with a heat pump system. Like furnaces, this is where the blower for air distribution in your home or business is housed. Instead of a fossil fuel being burned though, the air handler uses electric heating elements controlled by the thermostat. In heat pump systems these electric resistance coils are used to “boost” the temperature and output of the heat pump system. When temperatures outside drop below 30 degrees or colder, heat pumps tend to operate less efficiently and so the heat strips will then be activated by the heat pump. Such operations are usually done automatically. Houses that use heat strips solely for a source of heat often have higher electric bills. 

How Does an Air Conditioner Work?

Many homeowners have questions about the air conditioning process and how their A/C unit works. There are typically four basic components that make up the air conditioning system. these are as follows: the compressor, condenser coil, evaporator coil, and metering device. The compressor and condenser coil are housed in a single outdoor unit technicians often refer to as the “condenser.” The evaporator coil and metering device are house inside, attached to the furnace and duct system. The compressor pumps the freon in vapor form to the condenser coil, where it is condensed to liquid form before traveling inside to the evaporator section. At the evaporator section the metering devices only allows a certain amount of refrigerant into the evaporator. Thereby changing the freon from liquid form to vapor/liquid and greatly reducing the pressure. This also causes the temperature of the freon to drop substantially. So when air is pulled across the evaporator coil, the heat from it is transferred to the freon causing it to “boil” back off to a vapor. The vapor moves back to the condenser unit outside where the process starts all over again. This process of air conditioning is the removal of heat from the inside of your house to the outdoors via the medium of the refrigerant. This is a constant loop and the process is repeated until the desired temperature is reached inside the home or business. 

How Does a Heat Pump Work?

 Finally, we get to talk about heat pumps and how they work. A Heat pump is a different kind of air conditioning condenser that has additional components and controls that create questions on how they operate. Using the compressor heat pumps offer both heating and cooling by moving heat from one ares to another. During the heating season, heat pumps extract heat from the outside (if we get real sciency with the definition of heat, then yes, technically there is still heat outside) and condense it using the medium of freon. Heat pumps are equipped with a reversing valve that pumps the high pressure, high temperature freon inside first to the evaporator coil. As air from the blower moves across it, it heats the air going into your home. Essentially in heating mode, your evaporator becomes your condenser, and your condenser becomes your evaporator, and the flow of freon is “reversed.” Simple right? In cooling mode, the flow of refrigerant is identical to the air conditioning process described in the previous paragraph. 

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The 4 Different Types of Heating & Air Conditioning Systems

The 4 Different Types of Heating

& Air Conditioning Systems

For most people, the systems that provide central heating and air for our homes remain mysterious and complicated. The reality is the basics of heating & air conditioning/HVAC are fairly easy to understand. Buckle up and get ready to expand your HVAC knowledge!

HVAC or, Heating, Ventilation and Air Conditioning systems come in all different sizes and applications for your home or business. The whole purpose is to provide a comfortable indoor environment.

The Four Types of Heating and Air Conditioning Systems

  • Heating and Air Conditioning Split Systems
  • Heat Pump Systems
  • Ductless or Mini-Split Systems
  • Packaged Heating and Air Conditioning Systems

Heating and Air Conditioning Split Systems

It is called a split system because the components are split up into the outdoor and indoor units connected via a copper line set. On the outside is the air conditioning condenser. This house the compressor, condenser fan, condenser coil and electrical components that control its operation. The indoor units house the evaporator coil, and the blower. Usually a furnace is usually connected to this type of system. On the other hand, it might be housed in a single unit called the air handler which consists of a coil, blower, and electrical controls.

These are the most common residential type of system. They are usually the most efficient and cheapest to install for residential applications.

HVAC split systems will commonly have:

  • An outdoor unit that houses the condenser coil, compressor, fan, and electrical components
  • Refrigerant that circulates to and from the outdoor to the indoor units via a copper line set.
  • An evaporator coil connected to a furnace or fan coil
  • A blower that circulates air throughout the house and across the evaporator coil to supply air ducts.
  • A single thermostat that controls the operation, or perhaps several in a zone system.
  • Air ducts that carry air across the evaporator coil and out to supply air ducts in the house.
  • Optional accessories for indoor air quality like Humidifiers, Air Scrubbers, or UV lamps.

Heat Pump Systems

Heat Pumps are heating and cooling systems that use the power of the compressor and circulation of refrigerant to heat or cool your home. In short they are air conditioning units that work in reverse. However, they are not appropriate for all climates. For example, the colder the average outdoor temperature is the less efficiently they work. Typically they require the installation of auxiliary heat strips.

In addition, they might also be installed in conjunction with a furnace, this system type is known as dual fuel system. This usually requires different controls to ensure your system operates most efficiently. On all but the coldest nights a heat pump takes heat from the outdoor, and condenses it in the refrigerant to bring it into your home.

With Heat Pump or Dual Fuel system you will have the following:

  • A heat pump condenser that heats and cools using refrigerant
  • a furnace plus the evaporator coil for conversion of the refrigerant and circulation of air
  • Ductwork to move the air to and from the indoor furnace and coil in your house.
  • A thermostat to control the system and maintain consistent temperature in your home
  • Optional accessories for indoor air quality, or surge protection

Ductless or Mini- Split Heat Pump systems

A ductless unit has just that, no indoor ducts to move air. Installed in the zones that they heat or cool, ductless units require very little space. They are great for applications where installation of air ducts is hard or would disturb existing architecture. You can even connect as many as six indoor units to a single outdoor unit. Ductless systems are extremely efficient and operate very quietly.

They will typically have the following:

  • Single outdoor heat pump condensing unit connected to the indoor units via a copper line set and control wire.
  • Made up of a compact design for both indoor and outdoor units
  • They utilize smaller copper line sets requiring and control wire carrying voltage and communication wire to indoor units.
  • The indoor units don’t require a power source at their individual locations.

Packaged Heating & Air Conditioning Systems

A package unit is exactly what it sounds like. It contains all the components that make up a HVAC unit in a single package. Commonly installed in commercial applications, usually on roof tops of buildings.

Sometimes they are used in residential applications, installed on the roof or close to the foundation. They come in all different system configurations, from gas/electric, to heat pump with auxiliary heat.

Packaged HVAC systems include:

  • The air conditioning portion or heat pump together with the evaporator and fan coil in one unit.
  • Also thermostat/control interface for complete control of the system
  • Optional accessories that provide better air quality for employees or inhabitants of a home.

Now you know more about each type of HVAC system and you are equipped with a greater understanding of each kind of system.

As always the primary goal for each heating & air conditioning system is to provide year round comfort in your home or business. With a good working knowledge of each type and an understanding of your specific needs you will be better equipped to select a system that works best for you.

Don’t underestimate the value of a quality HVAC installation by a reputable HVAC company. A quality installation will always ensure that you get the kind of system performance and longevity that you expect.

And to make sure that your investment in your home comfort system remains efficient and reliable for years to come, remember to schedule regular annual maintenance for your heating and cooling system.