Variable-Speed Variable-Volume Pump and Motor
Understand how the variable-speed variable-volume pump and motor works. Explore component overviews, measurements, and additional resources.
Overview
A variable-speed, variable-volume (VSVV) pump and motor circulate liquid (e.g., water or water and glycol solution) through a piping network where the flow rate fluctuates as required by the plant and systems they serve. Outdoor air temperature (OAT) is the independent variable that drives the pump speed since heating and cooling loads are generally affected by OAT.
The pump motor is equipped with a variable frequency drive (VFD) which may be integrated in the pump and motor package or installed separately. Centrifugal pumps are the most common type of pumps used in buildings.
Types of Variable-Speed Variable-Volume Pumps
Explore the types of VSVV pumps used in various plants and system configurations. VSVV pumps can go by many names depending on the plant and system the are in. Some of the most common types are:
Primary Chilled Water Pump
Circulates chilled water through the chiller’s evaporator.
Found in the following plants and systems:
Secondary Chilled Water Pump
Distributes chilled water from the central plant (where it is cooled) to the building’s terminal loads.
Found in the following plants and systems:
Condenser Water Pump
Circulates water between a chiller’s condenser and a cooling tower.
Found in the following plants and systems:
Waterside Economizer Pump
Circulates cool water through a heat exchanger.
Found in the following plants and systems:
Makeup Water Pump
Supplies fluid to a system to replace losses caused by leaks, evaporation, or blowdown.
Found in the following plants and systems:
Feedwater Pump
Pumps water into a steam boiler.
Found in the following plants and systems:
Building Loop Pump
Pushes hot water through the line and uses the cold-water pipe as a return.
Found in the following plants and systems:
Recirculation Pump
Keeps hot water continuously moving through the plumbing network.
Found in the following plants and systems:
- Service Hot Water Plant
- Service Hot Water Loop
How do I…
Quantify Electricity Usage (kWh)
Select a strategy depending on what can be measured:
Measure Hourly True RMS and OAT
Directly measure the three-phase power of the pump motor using a compatible metering device. Also measure the hourly outdoor air temperature using a weatherproof data logger.
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 pump 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 Pump Motor Energy (kW) Calculator
Provides estimated annual electricity consumption of a variable-speed, variable-volume pump using power and OAT measurement data.
For more details about the methodology behind this calculator, see Pump Motor Energy Consumption.
Download CalculatordownloadMeasurement Locations
Measure Motor Speed from BAS and Electrical Spot Measurements
Take multiple spot measurements of the three-phase power of the pump motor using a power meter. Use the average value of the measurements with the hourly motor speed data from the BMS to estimate the full year electricity consumption of the pump motor. Use hourly measurements of OAT to establish correlation with pump operation.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to take multiple spot measurements of true RMS power draw of the pump motor.
Use this technique to measure outdoor air temperature.
Motor Speed data from the BAS
If the BAS can trend the pump motor speed, download it and resample to hourly intervals.
Borrow Equipment and Download Calculator
Reserve a kit, download the calculator, and enter your measured data.
This tool kit includes:
VSVV Pump Motor Energy (Speed) Calculator
Provides estimated annual electricity consumption of variable-speed, variable-volume pump using electrical spot measurements speed and OAT data.
For more details about the methodology behind this calculator, see Pump Motor Energy Consumption.
Download CalculatordownloadAssess Component Performance
To determine if the pump is performing as intended, the pump flow rate should be quantified. Two strategies exist, one involves a direct measurement of water flow rate with an ultrasonic flow meter, and the other strategy involves measuring the differential pressure across the pump and use the manufacturer’s pump curve to infer the flow rate.
The measurement of the VSVV pump flow rate relies on having access to the specific pump curve for the pump, which is a function of the specific pump model, the impeller diameter, and the horsepower of the pump motor. If this data can be accessed, short-term measurements of the pressure differential across the pump at several known speeds can be converted to feet of head, which then can be converted to flow rate using the pump curve. From this information a mathematical relationship can be developed between the pump motor speed and flow rate. Collect hourly average motor speed and associated OAT to develop a relationship between flow rate and OAT.
Direct Measurement of Water Flow RateWeather Dependent Operation.
Weather Dependent Operation.
Install an ultrasonic flow meter directly onto the pipe to measure hourly flow rate.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure pump flow rate in GPM.
Use this technique to measure outdoor air temperature.
Motor Speed data from the BAS
If the BAS can trend the pump motor speed, download it and resample to hourly intervals.
Borrow Equipment
Reserve loggers, sensors and meters to perform the measurements.
Device that uses high-frequency sound waves to measure the velocity of a fluid and calculate its volumetric flow rate.
Data logger that measures and records temperature and relative humidity in outdoor environments.
Proxy Measurement of Water Flow RateWeather Dependent Operation.
Weather Dependent Operation.
Install pressure transducers on the piping system to measure the hourly pressure differential across the pump. Use this data with the manufacturer’s pump curve to infer the hourly water flow rate across the pump.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to take water pressure measurements to infer the water flow rate.
Use this technique to measure outdoor air temperature.
Motor Speed data from the BAS
If the BAS can trend the pump motor speed, download it and resample to hourly intervals.
Borrow Equipment
Reserve loggers, sensors and meters to perform the measurements.
Device that converts mechanical pressure from gases or liquids into a proportional electrical signal.
Data logger that measures and records temperature and relative humidity in outdoor environments.
Direct Measurement of Water Flow RateNon-Weather Dependent Operation.
Non-Weather Dependent Operation.
Install an ultrasonic flow meter directly onto the pipe to measure hourly flow rate.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure pump flow rate in GPM.
Use this technique to measure the hourly amperage of the pump motor and determine the operating schedule of the pump.
Borrow Equipment
Reserve loggers, sensors and meters to perform the measurements.
Device that uses high-frequency sound waves to measure the velocity of a fluid and calculate its volumetric flow rate.
Device that supports up to four external sensors allowing you to measure temperature, current, voltage, air flow, pressure and more.
Sensors that converts high AC current into a proportional electrical signal.
Proxy Measurement of Water Flow RateNon-Weather Dependent Operation.
Non-Weather Dependent Operation.
Install pressure transducers on the piping system to measure the hourly pressure differential across the pump. Use this data with the manufacturer’s pump curve to infer the hourly water flow rate across the pump.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure the inlet and outlet pressure of the pump.
Use this technique to measure the hourly amperage of the pump motor and determine the operating schedule of the pump.
Borrow Equipment
Reserve loggers, sensors and meters to perform the measurements.
Device that converts mechanical pressure from gases or liquids into a proportional electrical signal.
Device that supports up to four external sensors allowing you to measure temperature, current, voltage, air flow, pressure and more.
Sensors that converts high AC current into a proportional electrical signal.
Further Reading
Chaurette, J. (2003). In PUMP SYSTEM ANALYSIS AND CENTRIFUGAL PUMP SIZING (5th ed.). Retrieved November 2019, from https://www.pumpfundamentals.com/download/book/chapter4.pdf
Satterfield, Z. (2010). Fundamentals of Hydraulics: Pressure. Tech Brief, 9(4), pp. 1-4. Retrieved November 21, 2019 , from https://www.nesc.wvu.edu/files/d/5c5a9fd1-0f8b-48c5-9063-b55d12651b91/fund-of-hydr-pressure.pdf
Taylor, S. T. (2002, February). Primary-only vs. primary-secondary variable flow systems. ASHRAE Journal, 25-29.
Tane. (2002). Variable-Primary-Flow Systems Revisited. Trane Engineers Newsletter, 31(4). Retrieved November 2019, from https://www.trane.com/content/dam/Trane/Commercial/global/products-systems/education-training/engineers-newsletters/waterside-design/adm_apn005_en.pdf