Variable-Speed Variable-Volume Fan and Motor
Understand how the variable-speed variable-volume fan and motor works. Explore component overviews, measurements, and additional resources.
Overview
A variable speed fan and motor uses a power-driven rotating impeller to circulate air. Air flow rates fluctuate as required by the plant and system it serves. Outdoor air temperature (OAT) is an indirect variable driving fan speed (since heating and cooling loads are affected by OAT). Axial and centrifugal fans with a variable speed drive are the most common type of variable speed fans used in buildings.
Types of Variable-Speed Variable-Volume Fans
Explore the types of VSVV fans used in various plants and system configurations. VSVV fans can go by many names depending on the plant and system the are in. Some of the most common types are:
Condenser Fan
Pulls outdoor air through the condenser coils to reject heat from the indoor space. The controlling variable is outdoor air temperature.
Found in the following plants and systems:
Cooling Tower Fan
Pulls or pushes large volumes of outside air through a cooling tower to facilitate evaporation. The controlling variable is Wet-bulb temperature
Found in the following plants and systems:
AHU Supply Fan
Pushes conditioned air into the building’s indoor spaces. The controlling variables can be motor schedule and/or Outdoor air temperature.
Found in the following plants and systems:
AHU Return Fan
Pulls stale air out of conditioned spaces and push it through the return ductwork. The controlling variables can be motor schedule and/or Outdoor air temperature.
Found in the following plants and systems:
Burner Fan
Pulls fresh oxygen into the combustion chamber for the gas burners and safely pushes exhaust gases and carbon monoxide to the outside. The controlling variables can be motor schedule and/or Outdoor air temperature.
Found in the following plants and systems:
- Hot-Water Heating Plant
- Steam Plant
- Domestic Hot Water Plant
How do I…
Quantify Electricity Usage (kWh) of AHU, Chiller Condenser and Boiler Burner Fans
Select a strategy depending on what can be measured:
Measure Hourly True RMS Electricity and OAT
The measurement strategy for a variable-speed fan and its motor involves measuring power draw of the fan motor at various known speeds and the associated controlling variable (OAT, Wet-bulb temperature). The calculator included with this measurement strategy works even if only one fan is measured.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure the hourly three-phase power of the fan motor.
Use this technique to measure outdoor air temperature.
Borrow Equipment and Download Calculator
Reserve loggers, download the calculator, and enter your measured data.
This tool kit includes:
VSVV Fan Motor Energy (kW) Calculator
Provides estimated annual electricity consumption of a fan that operates at variable-speed, variable-volume using kW and OAT data.
For more details about the methodology behind this calculator, see Fan Motor Energy Consumption.
Download CalculatordownloadMeasurement Locations
Quantify Electricity Usage (kWh) of Cooling Tower (CT) Fans
Select a strategy depending on what can be measured:
Measure True RMS, OAT and Outdoor Air Relative Humidity
The measurement strategy for a variable-speed CT fan and its motor involves measuring power draw of the fan motor at various known speeds and the associated controlling variable (OAT, Wet-bulb temperature).
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure the hourly three-phase power of the fan motor.
Use this technique to measure outdoor air temperature.
Use this technique to measure outdoor air relative humidity.
Borrow Equipment and Download Calculator
Reserve loggers, download the calculator, and enter your measured data.
This tool kit includes:
VSVV Cooling Tower Fan Motor Energy (kW) Calculator
Provides estimated annual electricity consumption of a cooling tower fan that operates at variable-speed, variable-volume using power, OAT and outdoor relative humidity data.
For more details about the methodology behind this calculator, see Cooling Tower Fan Energy Consumption.
Download CalculatordownloadMeasurement Locations
Further Reading
Boyd, BK.; McMordie Stoughton, KL.; Lewis, T. (2017). “Cooling Tower (Evaporative Cooling System) Measurement and Verification Protocol.” Golden, CO: National Renewable Energy Laboratory. https://www.nrel.gov/docs/fy18osti/70219.pdf.
Crowther, H.; Furlong, J. (2004). “Optimizing Chillers and Towers.” ASHRAE Journal, Vol. 46, No. 7; pp. 34-40.
Morrison, F. (2014). “Saving Energy with Cooling Towers.” ASHRAE Journal, Vol. 56, No. 2; pp. 34-40.
Tom, S. (July 2017). “CHILLED WATER SYSTEM OPTIMIZER.” Cat. No. 11-808-616-01. Farmington, Connecticut: Carrier Corporation.