Packaged Rooftop Air Conditioners

The majority of US commercial floor space is cooled by self-contained, packaged air-conditioning and heat pump units, most of which sit on rooftops (Figure 1). These rooftop units (RTUs), also called unitary air conditioners or simply “packaged units,” are mass-produced machines that include cooling equipment, air-handling fans, and sometimes gas or electric heating equipment. RTUs are available in sizes ranging from 1 ton to more than 100 tons of air-conditioning capacity (1 ton of cooling capacity will remove 12,000 Btu of heat per hour).

Figure 1: Up on the roof
Rooftop units are the workhorses of commercial air conditioning and are used widely in industrial facilities as well.

The compressor is the main power consumer in an RTU, accounting for about 80 percent of the peak power; the supply fan and condenser fan equally consume the remaining 20 percent (Figure 2). However, because supply fans are used to provide ventilation and deliver outside air to maintain indoor-air quality even when the compressor is not in use, the compressor’s annual energy usage typically accounts for only about 55 percent of total energy use, while fans account for the remaining 45 percent.

Figure 2: Anatomy of a rooftop unit
The rooftop unit shown contains electric cooling and gas heating components.
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