Constant-Speed Constant-Volume Pump and Motor
Understand how the constant-speed constant-volume pump and motor works. Explore component overviews, measurements, and additional resources.
Overview
A constant-speed, constant-volume (CSCV) pump and motor operates at a single speed to circulate liquid (e.g., water, water, and glycol solution) through a piping network where the flow rate through the pump does not vary more than 5%. Centrifugal pumps are the most common type of pumps used.
Types of Constant-Speed Constant-Volume Pumps
Explore the types of CSCV pumps used in various plants and system configurations. CSCV 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:
Service Water Pump
Pumps water into a steam boiler.
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 Motor True RMS
Directly measure the three-phase power of the pump motor using a compatible metering device.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure pump motor true RMS power with a handheld meter while the motor is running.
Borrow Equipment and Download Calculator
Reserve loggers, download the calculator, and enter your measured data.
This tool kit includes:
CSCV Pump Motor Energy (kW) Calculator
Provides estimated annual electricity consumption of a constant speed pump, using motor True RMS power data.
For more details about the methodology behind this calculator, see Pump Motor Energy Consumption.
Download CalculatordownloadMeasure Motor True RMS and Runtime
Take multiple spot measurement of true RMS power and long-term hourly measurements of the operational schedule of the pump motor. The spot measurements of true RMS power will be averaged and the average value will be used to determine annual energy consumption. True RMS Power is measured at the mainfeed of the panelboard using a handheld power meter. A motor on/off logger is used to measure the hourly motor runtime.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure pump motor true RMS power with a handheld meter while the motor is running.
Use this technique to measure hourly pump motor runtime.
Borrow Equipment and Download Calculator
Reserve loggers, download the calculator, and enter your measured data.
This tool kit includes:
CSCV Pump Motor Energy (Runtime) Calculator
Provides estimated annual electricity consumption of a constant speed pump, using motor runtime data
For more details about the methodology behind this calculator, see Pump Motor Energy Consumption.
Download CalculatordownloadMeasurement Locations
Measure Electrical Current and Spot Measurements
Take hourly measurements of the electrical current supplied to the pump motor. This data will provide insight on the hours of operations of the pump. Take measurements of voltage and power factor with a handheld power meter that can measure the three-phase power.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure true RMS power, current, voltage and power factor of pump motors.
Use this technique to measure hourly motor current draw of pump motors.
Borrow Equipment and Download Calculator
Reserve loggers, download the calculator, and enter your measured data.
CSCV Pump Motor Energy (Current) Calculator
Provides estimated annual electricity consumption of a constant-speed, constant-volume pump using electrical current and spot measurement data.
For more details about the methodology behind this calculator, see Pump Motor Energy Consumption.
Download CalculatordownloadMeasurement Locations
Assess 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 involves measuring the differential pressure across the pump and using the manufacturer’s pump curve to infer the flow rate.
Direct Measurement of Water Flow Rate
An ultrasonic flow meter can be installed on the piping to directly measure the pump flow.
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.
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.
Proxy Measurement of Water Flow Rate
CSCV pump flow rate measurement relies on having access to the specific pump curve for the pump, which is a function of the specific pump model, impeller diameter, and horsepower of the pump motor. If this data can be accessed, measuring the pressure differential across the pump over time can provide confirmation that the pump is providing a constant flow and a detailed average pressure that the pump is exerting on the liquid. By converting the pressure to the feet of head, the average pump flow can be interpolated off the pump curve.
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.
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.
Further Reading
Evans , P. (2017, Sept 26). How a Chiller, Cooling Tower and Air Handling Unit work together. Retrieved from The Engineering Mindset.com: https://theengineeringmindset.com/chiller-cooling-tower-air-handling-unit-work-together/
Evans, P. (2023, Jan 6). How Do Centrifugal Pumps Work. Retrieved from The Engineering Mindset.com: https://theengineeringmindset.com/how-do-centrifugal-pumps-work/