In commercial HVAC systems, two popular systems are rooftop systems and Variable Refrigerant Flow (VRF) systems. Both can heat, cool and control air quality in air-conditioned spaces. They have their unique advantages and disadvantages, making them suitable for different applications and preferences. Understanding the key differences between these systems can help in making an informed decision that aligns with specific building specifications, application needs and customer/facility owner targets.

We aim to provide a comprehensive comparison of these two systems, grouped by relevant themes, to highlight their distinct characteristics and help you make an informed decision based on your specific needs and priorities.

System Configuration
• Rooftop systems:
They typically contain: a packaged rooftop

A packaged rooftop unit is a type of HVAC system commonly used in commercial buildings. It is called "packaged" because all the components needed for temperature control, humidity control and air quality control are contained within one single unit installed outside the building.
Its functions of heating, cooling and supply of fresh air (thanks to a CO2 sensor) to maintain indoor air quality are managed with one single unit controller.
Rooftops systems can operate in free-cooling mode, bringing significant savings by using the cooler air from outside.

• Multi-split, also known as VRF (Variable Refrigerant Flow) systems:
They typically contain: indoor unit in false ceiling, outdoor unit on façade wall, fresh air handling unit, refrigerant pipes in the occupied space.
Multi-split indoor and outdoor units must be paired with a separate primary (fresh) air unit. A CO2 sensor on the fresh air unit monitors CO2 levels and determines if fresh air is needed based on air quality.
VRF cannot operate in free cooling and cannot benefit from the higher efficiency and savings that free cooling can offer.

Installation
The installation of a rooftop is plug and play as it is connected to the duct system of the occupied space, either directly or via a roofcurb. The plug and play nature of roofops makes installation and commissioning easier and faster.
No refrigerant pipes are needed inside the building which simplifies and standardizes the fulfillment of safety norms.

In comparison, VRF systems, with their multiple components, require more time to install and require a final verification step to check for leakages.

The pipes that contain the refrigerant cross the occupied rooms and therefore they are subject to restrictions and have limitations.

The cost for medium and small installations is often higher as they are more complex and require more labour for installation, start-up, verifications and adjustments.

Refrigerant, Environmental Impact and Safety
We know that it’s always better to use the least amount of refrigerant possible. Less refrigerant means less cost, less environmental impact, less risk, and better for sustainability targets.
And since rooftop systems contain less refrigerant compared to VRF systems, rooftop units are preferred from a refrigerant charge perspective.

Another point to consider is that in rooftop systems, the refrigerant is contained within the packaged rooftop and the circuit is factory sealed. This design feature enhances safety by minimizing the risk of leaks, and in any case a refrigerant leak detector is installed as per standard.
We shouldn’t neglect the fact that refrigerant piping of VRF systems runs into the occupied room, posing a danger to occupants if there is a leak.

Reliability and Maintenance
Rooftop units from reputable manufacturers ensure long-term availability of spare parts, allowing for efficient maintenance and repairs without the worry of parts becoming obsolete.
They usually have a longer lifespan because they come ready to install and are factory-checked. From a sustainability perspective, rooftop systems are well-rated.

VRF systems, as they are composed of units installed in serial configuration, may be fully stopped if one of the many units breaks down.
Multi-split systems are often considered disposable due to rapid technological obsolescence. In a relatively short time, spare parts become unavailable, and you cannot replace an indoor unit without also replacing the outdoor unit, and vice versa. Consequently, you must refurbish the entire system.
Overall, the serial installation, rapid obsolescence of parts, and the need for comprehensive system refurbishments make VRF systems a less convenient and less sustainable option.

Cost
While VRF equipment may appear to be a more economical choice at first glance, the added complexity and labour requirements can make it a more expensive option for smaller and medium-sized projects.

Performance and efficiency
A rooftop’s efficiency can be significantly boosted by introducing a free-cooling module. In consequence, the savings in energy drastically lowers operating costs of the system.
As previously stated, multi-split systems cannot operate in free-cooling mode and unfortunately cannot claim the energy savings that free-cooling offers.
One very important component driving high energy efficiency for systems is the system controller.

Trane rooftop units are often paired with Trane’s Tracer™ Concierge system, an affordable and advanced management solution that allows for the control of multiple rooftop units at one site. Tracer™ Concierge features a user-friendly, full-color touch screen display with intuitive navigation, offering building managers quick status updates, easy setpoint adjustments, and straightforward problem diagnostics. This system enhances productivity by simplifying the management process.

VRF systems can have a controller in charge of a series of units, but its role is limited to basic on-off and scheduling functions and it does not optimize efficiency or take into account fresh air and free cooling.

In conclusion, rooftop systems offer non-negligible advantages in terms of simplicity, ease of installation and use, energy efficiency and sustainability.

Learn more about Trane Rooftop systems