Constant-speed, Constant-volume Pump and MotorComponent

General 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.

Table 1 shows the plant and system configurations that may contain a CSCV pump and motor that operate based on a regular schedule (e.g., same time of day, same days of week).

Evaluation of Energy Consumption

The primary energy source for a CSCV pump is the electricity used to run the pump motor. Table 2 provides a summary of measurements needed to quantify the annual energy consumption and operating characteristics of the CSCV pump and motor.

Measurement Strategy

The measurement strategy for a CSCV pump and motor is to do a one-time measurement of the power draw and long-term measurements of the operational schedule of the motor. The approach assumes that the power draw stays constant throughout the measurement period. Because the motor runs at constant-speed and is under a constant load, it is either operating at full power (when on) or it is drawing no power (when off). A motor on/off data logger is used to record the operating schedule. The true RMS power is measured at the main feed to the constant-speed motor. Measurement locations are generically represented in Figure 1.

Measurement Equipment

Table 3 provides the equipment required to carry out the measurements of this component.

Table 3. Measurement equipment.

Equipment	Description	Measurement (Units)
Onset HOBO Motor On/Off Data Logger (UX90-004)	Records when a motor is on and off, as well as runtime. Requires HOBOware software and a USB connection cable for programming and downloading data files.	Motor Runtime (minutes)
Fluke 345 Power Quality Clamp Meter	Multi-purpose electrical measurement tool used to take true RMS power readings over a short period of time.	True RMS Power (kW)

Calculation Methodology

Click the button below to go to the calculators for this component.

Pump Motor Energy ConsumptionCalculation

The equations and calculators in this page estimate the annual energy consumption of variable-speed and constant-speed pump motors.

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/