Variable Speed Compressors: Save Energy While Increasing Comfort

In rooftop units (RTUs), the secret to reducing energy use while making spaces more comfortable for occupants lies in a technology YORK® pioneered for commercial applications over 40 years ago: the variable-speed drive (VSD) compressor. The compressors found in RTUs typically represent the largest, single electrical load in the entire system. That’s why making them run more efficiently is key to overall system performance. 

Overcoming Single-Stage Challenges

Cooling systems are typically designed for worst-case scenarios, meaning their capacities are oversized for typical, day-to-day operation. Unfortunately, since most comfort cooling systems still use single-stage compressors, the system is operating at a single speed for every condition — and cycling on and off as it attempts to cool a space without overcooling it (but not remaining on long enough for adequate dehumidification).

To combat this cycling effect, multi-stage compressor technology was introduced. By offering two or more capacity ranges, compressors like those found in YORK® 6.5- to 12.5-ton Sun™ Pro and 15- to 23-ton Large Sunline™ rooftop units equipped with Ultratech™ technology can match the requirements of the individual space more closely and reduce the overall compressor power draw. Optional variable-air volume (VAV) technology helps maintain constant static pressure in the supply duct to further improve efficiency.

The Variable-Speed Advantage

Since a system’s total performance is limited by the number of discrete compressor stages, the ideal compressor would be one that could vary its capacity based on the specific cooling load requirements. In fact, that’s just what variable-speed compressors deliver. Using an inverter motor, the variable-speed drive can provide a wide range of capacities to match the compressor more closely to the load while enabling better dehumidification and minimizing power use across the entire operating range.

By leveraging technologies, including variable-speed compressors, energy recovery wheels (ERWs), IntelliSpeed™ discrete fan control (DFC) and variable-air volume (VAV) control logic, commercial rooftop units from YORK® offer improved comfort cooling and class-leading standard-efficiency levels. In fact, the benefits of technologies like variable-speed compressors raise the integrated energy efficiency ratio (IEER) rating to the point where most costs are offset by the notable improvement in energy efficiency over the life of the unit.

The impact of variable-speed compressors, VAV systems and other intelligent technologies like Smart Equipment controls are bringing about a transformation in RTU design. To learn more about how YORK® rooftop units are benefitting from these and other class-leading innovations, download your free copy of the complete Variable-Air Volume (VAV) Application Guide for Rooftop Units.