In commercial and industrial facilities, rooftop units (RTUs) are usually turned off or greatly curtailed during unoccupied periods, for example, overnight and/or on weekends. Unfortunately, too little attention is given to the schedule RTUs are programmed for restart. If the desired setpoint is reached too early, energy is wasted, while reaching it too late adversely affects occupant comfort. Optimizing RTU start times means programming each RTU so as to reach its desired space temperature setpoint at the intended time. However, many facility managers fail to appreciate the energy and cost savings benefits of optimizing their HVAC startup schedule and simply program RTU start times to ensure they start early enough to guarantee the setpoints are reached before start of business.
Rooftop HVAC units are almost always one of the biggest energy consuming devices for any commercial and industrial (C&I) buildings. In fact, C&I buildings consume more than a third of the energy used in first-world countries, and HVAC units account for almost half of this energy. They are also one of the largest contributors to greenhouse gas emissions.
The fact is that rooftop units – or RTUs – hold enormous potential for dramatic reductions in both energy costs and carbon emissions. This potential has gone largely unrealized, however, because RTUs have long been one of the least intelligent of a building’s energy-consuming devices. Yes, there are smart thermostats and building management systems that definitely help, but only to a point because even with these energy efficiency tools in place, RTUs function in isolation, cycling on and off with no knowledge of how and when other units are operating. As a result, RTUs have remained largely untapped as an opportunity for smarter energy management and the accompanying energy savings.