Rooftop Unit

What Is a Rooftop Unit?

A rooftop unit (RTU) is a self-contained heating, ventilation, and air conditioning (HVAC) system that’s typically installed on the roof of a building but can also be installed on the ground. Rooftop units are common solutions for commercial buildings and are sometimes used in residential settings. They are designed to provide conditioned air to the interior of the building by connecting directly to the building’s ductwork.

How Does a Rooftop Unit Work?

Rooftop units work by drawing in air, conditioning it (heating, cooling, and filtering), and then distributing it through ductwork into the building. Here’s a step-by-step breakdown of the process:

1. Air intake: The unit recirculates air from inside the building, takes air from outside the building, or mixes outside and inside air.
2. Filtering: The air passes through filters that remove pollen, dust, and other particles.
3. Conditioning: The air is either heated or cooled. It can be heated by passing over electric elements, a gas burner, hydronic heat, or a heat pump. Cooling happens when the air passes over an evaporator coil containing refrigerant, which absorbs heat from the air.
4. Air Distribution: Once heated or cooled, a blower fan pushes the air through the ductwork throughout the building.
5. Exhaust: To balance air pressure, some units exhaust stale air from the building.
6. Thermostat or Zone Sensor: The system is controlled by a thermostat, which may stand alone or as part of a bigger building controls system.
7. VAV boxes: Rooftop unit systems can also include a variable air volume (VAV) box, depending on whether the system is single-zone VAV or multiple-zone VAV.

What is a Packaged Rooftop Unit?

A packaged RTU in HVAC contains all its components, including the compressor, condenser, evaporator coil, and blower fan, in one compact box. This “packaged” design simplifies installation and maintenance.

What Are the Advantages and Disadvantages of a Rooftop Unit?

Advantages of a Rooftop Unit

• Space savings: Installing an RTU on a roof means freeing up valuable space inside or on the grounds.
• Simplified installation and maintenance: Having all the components in one package means no additional refrigerant lines are required. Everything being in a single location makes it easier for technicians to access and service the system without disrupting the building’s occupants.
• Improved air quality: Units that pull in fresh outside air and use advanced filtration systems can improve the building’s indoor air quality.
• Security: Rooftop placement can deter theft and vandalism.
• Adaptability and scalability: Multiple units can be installed for larger buildings or zoned climate control.
• Reduced noise: Noise levels inside the building are reduced when HVAC components are located on the roof.
• Energy efficiency: Many RTUs are designed with energy-saving features, like variable speed compressors, fans and economizers, which use outside air for cooling when the temperature is right for it.

Disadvantages of a Rooftop Unit

• Accessibility issues: Maintenance and repairs can be challenging or dangerous during bad weather. Installation costs may be higher, too, since special equipment is required to place the unit on the roof.
• Out of sight, out of mind: Regular maintenance is crucial for the life of RTUs, and because they are on the roof, there’s a risk that they will be neglected.
• Weight restrictions: The building structure must be able to support the weight of the rooftop unit.
• Aesthetic concerns: If the unit is visible from nearby buildings, it may be considered an eyesore, depending on the neighborhood.

How do you weigh the pros and cons of rooftop units to know whether they are the solution for your building? Talk to a local Trane expert to evaluate your unique situation.

Resources for Rooftop Units

• Video: Meeting New Industry Standards with Rooftop Systems and Intelligent Controls
• Video: Helicopter Lift for 37 20T Voyagers™
• Case study: Trane Provides a Turnkey Solution for Salem Community Schools
• Case study: ARRIS Group, Inc.

For more information on whether rooftop units could be the right solution for your building, contact your local Trane office.