Converting constant-volume package rooftop units to variable-volume operations can have a significant impact on energy consumption. Since their creation, package rooftop units (RTUs) have been designed to operate at either zero or 100 percent.
An RTU is defined as an air handler that is designed for outdoor use, typically on roofs. The science of these units has remained basically unchanged since the invention of electromechanical cooling by Willis Carrier back in 1902. Although the idea isn’t much different than having forced air blow over coils to condition the indoor air while removing humidity, the design of the air handler has changed over time. Most of the units now include steel framing, insulated panels and filters, heating/cooling elements, a mixing chamber, and a supply fan. Almost all units incorporate fresh air to combat sick building syndrome, and high carbon dioxide levels indoors. This is typically accomplished using a basic damper or an economizer controlled with air sensors.