How Does a HVAC Work?

High Pressure Side

An air-conditioning unit consists of two sides, a high pressure and a low pressure side. The high pressure side of the HVAC system begins with the compressor. When the refrigerant (the special gas used inside the air-conditioning system) enters the compressor it is spun rapidly until it is highly pressurized. This highly pressurized gas, which is very hot as a result of being pressurized, then exits the compressor and flows through a tube to the condenser. The condenser uses a large fan to blow air over tubes containing the high pressure gas, cooling the gas, which transforms it into a liquid state. In some systems, the high pressure liquid will then enter a dryer to be purified, but most home systems send the liquid refrigerant through a tube directly into the evaporator.

Low Pressure Side

The high pressure liquid will enter the evaporator, which begins with a metering device. The metering device, which is a section of tubing that tapers into a small opening, allows only a small amount of high pressure refrigerant to enter into the low pressure section of the system, causing it to drop rapidly in pressure and vaporize. This rapid drop in pressure also causes a rapid drop in temperature, and this now extremely cold refrigerant gas travels through a number of tubes and then back into the compressor. The air-conditioning system uses a large fan to pull in air from inside the building and then runs that air over the cold tubing of the evaporator, rapidly cooling it and sending it back into the building via the air vents. It is this cold air which cools the inside of the building.

The Heater

The heating system of a building utilizes part of the central air-conditioning system in order to function. With a standard heating system, a gas burner is lit and powered in order to create a heat source. This heat source then uses the fan from the air-conditioner, the one that was used to run air over the evaporator, to run air over the gas burner. This air then exits the air-conditioning vents into the building, and is used to heat the building to the desired temperature. As with the air-conditioning system, the air used to run over the burner is also taken from inside the building. This recirculation allows for the building to keep a constant temperature with a minimal amount of energy.

References

• Consumer Energy Center
• Energy Quest