All or nothing. That’s what the typical, single-stage compressors found in many rooftop units (RTUs) deliver. The problem is that cooling systems are usually designed for worst-case scenarios, meaning their capacities are oversized for normal, day-to-day operation when something less than “worst case” is required. And that results in constant, on/off cycling as the system attempts to cool the space, while simultaneously failing to run long enough for proper dehumidification. In short, the system is running inefficiently, and occupants aren’t comfortable.

The Benefits of Multi-stage and Variable-Speed Compressors

In rooftop units, the compressor draws more power than any other component in the entire system, which is why improving compressor performance is critical. One way to increase efficiency is through multi-stage compressor technology. By offering two or more stages in a single compressor, multi-stage compressors like those found in Johnson Controls Pro and Series 20 Ultra-high Efficiency (UHE) Commercial Rooftop Units can match the requirements of individual spaces more closely and reduce the overall compressor power draw. Going even further, these units offer optional variable-air volume (VAV) control logic that uses a variable-frequency drive and pressure transducer to maintain constant static pressure in the supply duct and meet ASHRAE 90.1-2019 and 2018 IECC requirements.

Using an inverter motor, a variable-speed drive (VSD) compressor can provide an even wider range of capacities to match the cooling and load requirements while enabling better dehumidification and minimizing power use across the entire operating range. .

System Optimization Makes the Most of the Variable-Speed Compressors

Rooftop units from Johnson Controls benefit from total system optimization that leverages technologies including variable-speed compressors, IntelliSpeed™ discrete fan control (DFC), ECM condenser fan motors and variable-air volume (VAV) control logic to offer improved comfort cooling and class-leading standard efficiency levels. In fact, the benefits of technologies like variable-speed compressors can raise efficiency levels to as much as 21 IEER in some models, providing a notable improvement in energy efficiency over the life of the unit while providing a lower total cost of ownership.

Building owners are faced with ongoing increases in energy costs, and ever-changing sustainability goals. With technologies like variable-speed compressors and VAV systems married to Smart Equipment controls and service-optimized designs, Johnson Controls rooftop units are making it easier than ever for owners and specifiers to meet the challenge. To learn more about how Johnson Controls 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.