chilled pump

Introduction to Chilled Pumps

Chilled water pumps (CHWPs) are essential components in building cooling systems, responsible for circulating chilled water through a loop that facilitates heat transfer from the user side to the source side. These pumps consume a significant amount of energy within building energy systems, making their optimal control and operation a critical area of research and development.

Operation and Challenges of Chilled Water Pumps

The operation of CHWPs can be adjusted through two controllable variables: pump on/off status and pump working frequency. In standard engineering practices, pump working frequency is typically controlled by local PID controllers to maintain the chilled water grid pressure at a preset point. The running number of pumps is often set according to the chiller operation or passively adjusted to prevent pump frequency from exceeding safe limits.

However, passive control of pump running numbers often falls short of energy-saving objectives. Previous studies have focused on pump speed/frequency control, neglecting the potential energy savings from active optimization of pump running numbers. Moreover, existing studies have drawbacks such as complex workflows, dependence on accurate system performance models, and high requirements for monitoring and sensors.

Optimization of Chilled Water Pump Running Number

To address these challenges, a new approach has been proposed that simplifies the optimization of CHWP running numbers based on similarity/affinity laws and pump performance curves. This method requires minimal preconditions and offers a simple workflow, making it feasible for engineering practices. It has been implemented in a real cooling system in a battery factory, yielding promising results.

The proposed method involves several steps:

Deduction of grid resistance using monitored header pipe flow rate and pressure difference.
Determination of needed header pipe flow rate based on grid pressure difference set point and deduced grid resistance.
Distribution of the needed flow rate among the running pumps to calculate single pump flow rate.
Calculation of targeted pump head considering pressure drop between the pressure meter and pump inlet/outlet.
Estimation of targeted pump frequency using similarity/affinity laws and known nominal/reference pump head curve coefficients.
Energy-Saving Potential and Validation

The results from the implementation of this method suggest that it is accurate enough for optimal control, with flow rate estimation errors less than 2% and frequency estimation errors less than 1 Hz. The energy-saving effect is significant, with a 20% reduction in pump energy consumption compared to previous control logic. Importantly, the water grid operation condition is well maintained, with only a 1.4% change in grid pressure difference and a 2.6% change in flow rate.

Conclusion

The active optimization of chilled water pump running numbers presents a viable solution for energy conservation in building cooling systems. By simplifying the control process and leveraging existing pump performance curves, this method offers a practical approach to reducing energy consumption without sacrificing cooling supply. The validation through engineering practice confirms its effectiveness, making it a promising strategy for enhancing the energy efficiency of building cooling systems.