packaged rooftop unit, or RTU, is a type of HVAC system that contains all the components needed to provide conditioned air in one concise unit.

Packaged rooftop units are commonly found in light and large commercial applications. They are very popular with retail and industrial properties.

A packaged rooftop unit is usually a large metal box containing the following components:

  • Expansion device
  • Evaporator
  • Compressor
  • Air-cooled condenser

Packaged rooftop units typically connect directly to a ductwork system that distributes the conditioned air through the space and returns it to the packaged rooftop unit.

An RTU controlled by a thermostat blows and receives conditioned air directly through the ductwork 

Here is a look into a basic packaged rooftop unit:

Window air conditioners are basically just small rooftop units! 

First, the air returns from the space, passing back to the packaged rooftop unit. Outdoor air is sometimes also brought into the unit and mixed with the return air in order to produce fresher air flowing back to the space. From here the air moves through a rack of filters, continuing on to the cooling coil that chills the air by running it over the cold refrigerant. The refrigerant is cooled with a standard refrigeration cycle. The air will then flow through both the blower, leaving it conditioned and ready to be delivered to the space. Some units have small heating elements near the blowers to further adjust the humidity of the air. In packaged rooftop units, there is typically a clear and insulated divide in the unit between the evaporator coils that cool the return air and the condenser coils and compressor rejecting heat to the atmosphere.

A basic thermostat typically controls packaged rooftop units. However, they can be a part of a more complex control system depending on the application.

There are also some specialized applications for packaged rooftop units. For instance, there may be a unit on a building that conditions 100% outdoor air. This means that all the air running through the unit is coming from outside and the unit uses no return air from the space. These packaged rooftop units are typically called 100% dedicated outdoor air units, or makeup air units, and require increased insulation, additional parts, and potentially more energy to accomplish their design criteria.

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