Optimising network pressure-management
Learn how to optimise network pressure management with pressure-boosting and pressure-reducing measures, enabling you to achieve a preselected minimum constant pressure to satisfy consumers.
In this module you will hear about how to control pressures within a water distribution network to ensure the preselected minimum constant pressure is achieved to satisfy consumers.
Maintaining an optimised pressure throughout the entire city distribution network is not possible from one pressure source or one main pumping station, and higher-than or lower-than water pressure will always be found in water distribution networks.
Let’s begin by looking at the characteristics of the pipe network. The network can be at different ground levels, with different pipe sizes and feeding larger or smaller number of consumers, close and far from the main pumping station.
Imagine a city-wide network. Without pressure boosting, the water pressure will inevitably decrease as the water travels through pipes, leaving the people on the end of the network and at higher elevations with little or no pressure in the taps.
To avoid leaving some people at these critical points with little or no pressure, the pressure at the main pumping station will need increasing.
But increasing the pressure at the main pumping station to satisfy the critical points in the network also increases the entire network pressure, providing most of the city with unnecessary excess pressure.
However, this can be mitigated by dividing the distribution pipe network into zones. This means that some zones can then have their own booster set, while some other zones can have pressure-reducing valves (PRVs).
In Module 2 we describe a zoned network using District Metering Areas (DMAs). Pressure zoning will allow the main pumping station and most of the network to operate at a much lower pressure.
Typically, there is a huge demand for water in the morning, but once everyone has gone to work, the demand falls significantly until people return. The booster pump with variable speed will automatically adjust to changes in the pattern to keep energy consumption as low as possible.
So how do you make the booster set do that? Well, you simply define a pressure set point at the pumping station. The pump will then operate to maintain the same pressure at all times – but will, during periods of reduced water consumption, such as during the day or at night, reduce the speed to save energy. At very low flow demands the pump can stop altogether to use no energy at all.
The common pressure boosting solutions include booster pumps with variable speed operating to achieve a fixed constant pressure setpoint at the discharge of the booster pumps. Likewise, PRVs operate to maintain a fixed constant pressure at the outlet or downstream side of the valve.
The pressure setting at the pumping station or at the PRVs is based on peak flow demands, so at that peak flow moment the pressure at the critical points in the network is sufficient for consumer satisfaction.
A more efficient way to operate is using a proportional pressure control system. A proportional-pressure control system sets the pressure at the booster pump according to the flow demand, so that the pressure setpoint will be highest at peak flow demands and lower as the flow demand decreases.
Grundfos has taken network pressure control one step further. We call this system Demand Driven Distribution. We have developed a solution that automatically and daily adjusts the proportional-pressure control curve to satisfy the minimum pressure at the critical points in the network.
Let’s recap what we have presented in this module:
- Why more than one pressure source or pumping station is needed for an optimal city network pressure management
- How dividing a city water distribution network into pressure zones is an effective way to control and lower pressure in the network
- How pressure-boosting and PRVs are used to regulate pressure in the network with varying demand flows
- How booster pumps with proportional-pressure control provide a more efficient pressure control in the network