How Does a Rooftop Packaged Unit Work?

Today Rooftop Packaged Unit is among the most common HVAC systems for commercial buildings. They are cost-effective, pre-engineered, and adaptable for many applications. Learn more about how a rooftop unit works to keep your building cool in the summer and warm in the winter.

The term “rooftop unit” is synonymous with “packaged unit” because packaged units are most often installed on the roof. However, they can also be slab-mounted on the ground.

How Does a Rooftop Unit Work?

In a typical rooftop unit, the compressor is located at one end of the cabinet and condenser coils are wrapped around or in close proximity to it. Cool, low - pressure refrigerant arrives at the compressor as a gas. It compresses into a hot, high - pressure gas as it flows into the condenser coil, where it gives off its heat. The metal fins on the coil act as a heat sync and the condenser fan blows the exhaust up and away from the building.

Warm return air travels through the ductwork into the rooftop unit, and fresh air enters as well for ventilation purposes. Air filters are positioned over the return air duct and fresh air intake to trap contaminants and prevent them from landing on the sensitive cooling equipment.

Returning to the refrigerant cycle, the now - cooled liquid refrigerant passes through the evaporator coil. The pressure drops, and as the liquid evaporates, it converts back into a gas. As warm air from inside the building passes over the evaporator coil, the refrigerant extracts heat from the air, making it ice - cold when the evaporator fan blows it back into the building.

Upon leaving the evaporator coil, the refrigerant is warm, having absorbed heat from the return air. It circulates back to the compressor to give off its heat, and the cycle begins all over again. This process repeats continuously until the temperature in your building reaches the thermostat setting.

Rooftop units that also provide heating often contain a gas heat exchanger downstream from the evaporator fan. In heating mode, return air is discharged into the heater and blows over gas - fired coils. A fan then sends newly heated supply air back into the building.