HVAC 101

Many homeowners looking to install HVAC, especially those in older homes, have some apprehension based on not understanding exactly what a central system entails.  

An air conditioner does make rooms cooler, but instead of cooling the air, it is actually just removing the heat from the air in a house.  It moves the heat from inside the house to the outside as systems are comprised of both indoor and outdoor components.  A closed loop of copper tubing contains a refrigerant, known as Freon, that is constantly circulated from the inside of the house to the outside and back.  The outdoor component of an air-conditioning system, the condenser/compressor unit, is visible outside the home and is usually set on a concrete pad where it can receive ample shade.  Units produce a fair amount of noise and give off a large amount of heat. 

Inside the house is a matrix of ductwork connected to a plenum, which is a large air distribution box.  From the plenum, one system of ducts delivers cooled air to the rooms through vents on the floors, walls, or ceilings.  The return is a second duct system that pulls warm air from the rooms and connected to the plenum is an air handler with a fan and an evaporator inside. 

All of these components work in tandem as pressurized liquid refrigerant enters the house inside the loop of copper tubing and is carried to the evaporator.  The evaporator then sprays the refrigerant through a nozzle causing its temperature to drop as it evaporates inside the tubing and turns to a gas.  At the same time, warm air from the return passes over the evaporator, causing the heat in the air to be absorbed by the gaseous and cooled refrigerant.  Then, the cooled air is pushed through the air handler, into the distribution box, out through the delivery duct and through the vents into each room. 

The refrigerant is then pumped outside the house into the condenser unit.  The compressor further pressurizes the gaseous refrigerant, which raises its temperature.  The high-pressure, high-temperature refrigerant gas enters the condensing coil and is cooled to a liquid state by a fan blowing outside air across the condensing coil.  The fan blowing across the coil releases the heat into the atmosphere and cools the refrigerant, turning it back to a liquid before it re-enters the house, and the whole process continues.  Forced-air heating systems use the same ducts as the A/C, but the air is heated by a furnace. 

Having some basic knowledge about how traditional heating and cooling systems work will help those involved in making the decisions to install central HVAC.