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).
| Plant | System | Component |
|---|---|---|
| Air-cooled chilled water plant | Chilled water loop | Primary chilled water pump |
| Water-cooled chilled water plant | Condenser water loop | Condenser water pump |
| Water-cooled chilled water plant | Chilled water loop | Primary chilled water pump |
| Water-cooled chilled water plant | Chilled water loop | Secondary chilled water pump |
| Water-cooled chilled water plant | Waterside economizer | Waterside economizer pump (if present) |
| Hot water plant | Hot water boiler | Makeup water pump |
| Hot water plant | Hot water loop | Building loop pump |
| Steam plant | Steam boiler | Makeup water pump |
| Steam plant | Feedwater tank | Feedwater pump |
| Service water plant | Service hot water loop |
|
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.
| Component Quantification | Values to be Quantified | Measurement |
|---|---|---|
| Electricity usage of a CSCV pump 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.
| Equipment | Description | Measurement (Units) |
|---|---|---|
|
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) |
|
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.
Further Reading
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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/
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Evans, P. (2023, Jan 6). How Do Centrifugal Pumps Work. Retrieved from The Engineering Mindset.com: https://theengineeringmindset.com/how-do-centrifugal-pumps-work/
