How A Rooftop HVAC Unit Works

Person using remote control to control rooftop HVAC unit

Ever wondered how a rooftop HVAC unit works? Well, what is a rooftop HVAC unit in the first place?

Rooftop HVAC units or RTUs are normally stationed on the roof of small commercial buildings to provide heating and air conditioning to certain defined locations of a building. They come as a package and since it comes readily assembled from the factory, they can be easily installed to building ductwork (where air travels through).

What Are Rooftop HVAC Units Used For?

RTUs are used to heat and cool residential and commercial buildings.

Compared to an indoor system, RTUs are weather-proof and robust. This enables them to prevent debris, rain, snow and tiny animals from getting in - but only air passed through it.

RTUs are also common because they consume less space and demand less maintenance. Since they are mostly placed on rooftops, the possibility of theft or someone tampering with them is low. It's for these reasons that most commercial buildings such as offices, hospitals and schools take advantage of Rooftop HVAC systems.

How Does A Rooftop HVAC Unit Work?

It's worth noting that while RTUs are slightly different from indoor HVAC systems, the main function is the same: They heat and cool our premises during those hot and cold days.

While some RTUs heat and cool only, others can do both.

How RTUs heat

A HVAC rooftop unit heats air by first connecting to either an electrical heating element, a heat pump or a gas burner. Other RTUs, though less common, create heat via a gas heat exchanger such as a furnace.

How RTUs cool

If the RTU is cooling only, then it would have one coil together with a refrigeration unit and here's what happens:

  • Heat goes through the evaporator coil when it comes out from the refrigerant.
  • As the pressure lowers, the refrigerant turns liquid.
  • While still in its liquid form and spreading via the could, the refrigerant sucks up heat from the building's warm air.
  • Once the heat from the air is sucked up by the refrigerant, cooler air is passed via the ductwork by the evaporator fan to the rooms within the building.
  • At this point, the refrigerant is heated and changes to gas form. While in this state, it goes back to the compressor to let out and deplete the heat.
  • This process keeps on happening until the building's surrounding temperature aligns with those set by the thermostat and other controls.