Significant Energy Savings are available for many AC Motor applications, simply by the addition of a Variable Frequency Inverter Drive. For example, a 50% Saving is available for only a 20% reduction in speed for Fans and Centrifugal Pumps. This is because power consumed follows the cube of speed. Greater savings are available for greater speed reductions.
Examples are:-
1) A single fan and ducting provides ventilation or extract for a number of machines. In this case machines not in use are arranged to close individual dampers in the ductwork and the fan speed reduced via a Fan/Pump rated Inverter Drive. Most Inverter drives have provision for pre-set speeds via multiple digital inputs to simply this application.
2) Commercial buildings that are not fully occupied can reduce ventilation fan speeds to suit the density of occupation, weather conditions, outside temperature, fresh air requirements and the time of day or night. There are a number of specialist Contractors who provide this service.
3) Cooling Tower fans are speed controlled by Inverter Drives to maintain the cooling water temperature. This is a simple application for a suitable temperature controller with a 4-20mA modulating output.
4) Pumps are speed controlled by Inverter Drives to suit a constant pressure. This is in place of a by-pass flowing for pressure relief. A suitable pressure sensor is required as feedback to the built-in control loop resident in most Inverter drives.
5) Refrigeration Compressors both large and small are speed controlled by Inverter Drives to a control loop of temperature. A suitable temperature controller with a 4-20mA modulating output is required. In the case of large compressors, the use of variable speed significantly reduces maintenance costs by extending the safe operating period. Many modern small air conditioning packages already include a variable frequency Inverter Drive for the fan in the compressor to maximise energy saving.
6) A Conveyer feeding material into a single large power load can be speed controlled to optimise the process load on the large main motor. Energy reductions are available by operating the main motor at full load, maximising production efficiency and reducing production time. A Current measurement device is required in the supply line to the large main motor as feedback to a load control loop modulating the small Inverter Drive controlling the conveyer motor speed.
7) Kitchen fans in hotels and restaurants benefit from variable speed control of their extract fans to suit the cycle of activity. Energy is saved directly by reducing the fan speed, but also by reducing the heated or conditioned air otherwise lost from the kitchen and restaurant.
8) Agricultural drying fans are speed controlled to suit the bulk or density of material being dried.
9) Agricultural pumps are speed controlled to suit the flow and pressure required for irrigation systems.
10) Large Greenhouse ventilation schemes and pumps are often speed controlled to suit the distribution of heated air and water to the various growing areas.