HVAC systems are designed to maintain interior spaces at comfortable temperatures during extreme heat and cold weather events. Since extreme weather events are rare, HVAC systems typically operate well under their maximum capacity. Most HVAC systems are driven by electric motors. An electric motor that spends the majority of its operational life running below maximum output is an ideal candidate for Variable Speed Drives.
HVAC control systems utilize various techniques to provide temperature control with primary systems that are generating excess heating or cooling. On/off control, which remains popular activates the system when a temperature reaches a certain level and then shuts off once the temperature is increased/decreased a couple of degrees. Choking or throttling is also a common technique to control temperature. In a forced air system, variable position dampers are used to change the amount of air that is allowed into a zone to maintain the temperature of that zone. The dampers create inefficiencies in the system that cause the fan motor to run at a higher horsepower. It has been shown that the use of a variable speed drive on a fan system used for cooling often results in significant power savings compared to a fan running at full speed.
The control of compressors and pumps with adjustable speed drives also provide significant power savings opportunities. The system demand on pumps and compressors are usually well below their maximum capacity. Driving those devices at lower speeds will provide adequate output with lower power consumption.