Quick Review: What are Rooftop HVAC Units or RTUs?
Rooftop units, or RTUs, are an example of a packaged HVAC unit for smaller commercial buildings. “Packaged” means they’re a self-contained all-in-one air HVAC unit. The entire system comes entirely assembled from the factory, and easily installs and connects to building ductwork. These simple and adaptable units provide heating and air conditioning to a defined area of a building.
Do Rooftop Units Heat and Cool?
Yes. Some cool only, some heat only, and some do both.
Where are RTUs Used?
As the name says, on rooftops of generally flat-roof buildings under 10 stories. Because of their location, housings are robust and made to be weather-resistant against environmental factors like sun, wind, rain, frost, etc. All major components like the evaporator coil, fan, condenser and compressor are inside the housing.
In some cases, they are mounted on slabs on the ground. In this case, they’re more likely to be called “packaged units.” If rooftop access is difficult or dangerous, it’s often easier to place RTUs next to the building. This makes maintenance and repairs easier but may provide more access for rodents and other pests.
Types of Rooftop HVAC Units
Fresh Air RTUs
These RTUs only invite in 100 percent fresh air for conditioning, and in some cases, heating. An external exhaust fan removes return air to keep air pressure balanced.
These RTUs recirculate air compared to exclusively using fresh air. This is common during winter weather when the outside air temperature is much lower than the indoor air. This method reduces the heating load in the winter and saves energy for heating.
In order to prevent a buildup of carbon dioxide and other gasses, recirculating RTUs also use fresh air with the recirculated air. Some recirculating units have the option of cycles using only fresh air.
Heat Wheel RTUs
A more recent innovation, the heat wheel acts as a rotating heat exchanger. It pulls in air, it passes through a filter before passing through the heat wheel. The wheel also absorbs heat from air leaving through the return ducts and adds it to the incoming air. This helps saves energy and utilities by reducing the need to heat the new air.
How Commercial HVAC Rooftop Units Work
Here’s an illustration of how commercial HVAC rooftop units (RTUs) work in this video:
While each RTU type operates a little differently, the basic functions are the same.
How an RTU Removes Heat
- Following the installation of a rooftop HVAC unit, cool, low-pressure refrigerant gas moves into the compressor.
- There, it compresses and becomes highly-pressurized and hot as it passes into the condenser coil.
- Then, metal fins take in the heat and push exhaust away from the building using the condenser fan.
How an RTU Cools Air
If the RTUs only cool, it commonly uses a single coil with a refrigeration unit. In most cases,
- Once the heat leaves the refrigerant, it passes through the evaporator coil.
- The refrigerant returns to its liquid state as the pressure drops.
- Circulating through the coils, the refrigerant absorbs heat from the building’s warm air.
- After the refrigerant extracts the heat from the air, the evaporator fan pushes the cooler air through the ductwork to the building’s rooms.
- The refrigerant, now heated and returned to its gaseous state, circulates back to the compressor to release and exhaust the heat.
- This cycle repeats until the building’s ambient temperature reaches the setting requested by the thermostat and other building controls.
How an RTU Heats Air
Generally, to heat air RTUs connect to a heat pump, an electrical heating element or a gas burner. Most rooftop HVAC units function as a heat pump by transferring heat from the indoor or outdoor air. Some RTUs generate heat using a gas heat exchanger, much like a furnace. These are less common in our climate but they exist.
Why Use a Commercial HVAC Rooftop Unit?
Many building owners, facility managers, and property managers prefer RTUs because they:
- come completely packaged as a single unit
- save valuable floor space
- run quietly, improving the experience for occupants
- reduce installation costs
- are easily maintained because of their compact location
Older models are often inefficient and easily waste $900 to $3,700 per unit each year. Knowing around 60 percent of U.S. commercial floor space receives its heating and cooling this way, that’s a lot of wasted energy and dollars.
Make sure you maintain your RTU to get the most efficiency from it. If it frequently needs repairs or your utility bills continue to grow, consult with a commercial HVAC expert like Estes Commercial for an estimate on a new RTU.
How to Maintain Rooftop HVAC Units
Like any other HVAC equipment, RTUs have filters. For the best performance and air quality, change the filters regularly according to manufacturer recommendations. For the most return on your investment, plan, and budget for preventive maintenance. The easiest way to do this is to have a service plan.
Estes Commercial, who has helped Atlanta with heating and cooling needs for more than 70 years, customizes service plans for commercial HVAC clients. A plan just for you makes sure you’re getting what you need at the best cost and at regular intervals.
For Rooftop HVAC Unit Estimates, Service, Repair or Installations, Call Estes Commercial
Estes Commercial helps greater Atlanta businesses and organizations protect their operations and equipment, preventing power outages from disrupting business as usual.
Contact us today to learn more about rooftop HVAC units for your school, daycare, place of worship, retail property or healthcare facility.