How Does an HVAC System Work?

Heating, ventilation and air conditioning (HVAC) systems provide climate control for indoor spaces through a sophisticated system of heating and cooling. Present in most residential and commercial structures, these systems exist to improve the quality and circulation of air inside a building. HVAC systems can work in a variety of ways and do much more than just heat and cool the air. These systems can control air humidity and air quality as well as continuously circulate air into and out of the building.

HVAC versus Air Conditioning 

So, what is the difference between HVAC and air conditioning? Air conditioning is exclusively involved with cooling the air. Although air conditioning is an integral and necessary part of an HVAC system, cooling is not the whole story. In fact, air conditioning is only one part of the system, which also includes a furnace, a network of ducts, thermostats, fans and filters. Working together, the various parts of the HVAC system become a whole package that includes heating, cooling, humidifying, dehumidifying, circulating and filtering. For a better understanding of the various parts of the system and how they function, continue reading below. 

The Furnace’s Role in Providing Heat

The “H” in HVAC is for heating, and heating is accomplished through the use of a furnace. Although there are other types of furnaces used for heating, like electric heaters and radiators, the furnaces in HVAC systems are generally forced hot air furnaces, meaning that heated air is blown into each zone through a network of ducts.

Heating occurs when colder air is pulled into the system and is passed over a burner. Burners are fueled by oil or gas, and true to their name, they are burning when they are active. Air passes over the burning gas and is then forced into the building’s interior through the use of a fan. Furnaces are generally located inside of a building, either in a basement, attic or dedicated utility closet. 

Using Air Conditioning to Cool the Air

The “AC” in HVAC refers to air conditioning. Air conditioning units are located outside of the building since they produce heat as they work. Air conditioning technology is probably one of the most complex parts of the HVAC system, as it relies on a series of chemical reactions to keep the air continuously cool.

First invented in 1925, air conditioning units rely on the use of a chemical refrigerant, which must have specific properties including a boiling point that is lower than the desired temperature. The refrigerant will pass through a series of components as follows:

  • The Compressor — The compressor pulls the refrigerant from the evaporator coil, where it has converted to a gaseous form. The compressor’s job is to pressurize the refrigerant, which also increases its temperature.
  • The Condenser Coil — The heated gas moves from the compressor into the condenser coil, which cools the refrigerant by allowing the heat to radiate into the air as it travels through the network of coils. Cooling is aided by the use of a fan that blows over the coils. During this process, the refrigerant reverts to liquid form.
  • The Evaporator Coil — The evaporator coil absorbs the heat from the air, thereby cooling it. Air from an air return vent is blown over the coils, cooled and then returned to the building through the vents.

Ductwork Delivers the Air

Built into walls, ceilings and floors, a network of ducts are responsible for delivering heated and cooled air from the air conditioning unit and furnace to the zone in need of heating or cooling. The ductwork also returns air to the air conditioner and furnace, and circulates the air by venting and pulling it to and from outside, depending on the type of system.

The ductwork may seem like a simple construction, but it must be precisely designed to work efficiently. The fans used to propel air through the system must be strategically placed and carefully calibrated to provide the exact right amount of force.

The Thermostat Controls the System

The thermostat is the brains of the HVAC System. At its simplest, a thermostat measures the air temperature and tells the system to heat or cool the room. At its most complicated, thermostats can control the heat and humidity in various zones throughout the building, and be connected remotely by computers or smartphones. 

HVAC Maintenance

It is essential to remember that an HVAC system is a precisely calibrated network of equipment, which can suffer significantly from the breakdown of any part of the system. HVAC systems need to undergo regular maintenance in order to continue working safely and efficiently. But properly maintaining an HVAC system is more than just changing filters. HVAC systems should also be regularly inspected for cracks, leaks, freezes or clogs. Periodic service can help reduce costly repairs and system failures, keeping the system running at peak efficiency all year long.