Reading the Load Profile on the System Curve

Learn how to interpret load profiles for typical pump applications.

Understanding the load profile for your application is an essential part of pump selection. However, the load profile is not actually an aspect of the pump curve, but of the system curve. This is due to pumps with a constant duty point will soon become outdated.

In this module, we will look at how the reduction of break tanks and control valves, and the popularisation of variable speed drives, would mean that most of the pump applications would have variable demand.

The water consumption pattern of a system depends on the application. For example, in a residential building there are peak hours of hot and cold-water consumption in the morning when everyone is taking a shower and low demand hours in the night when everyone is sleeping.

Another example is the water consumption pattern in a commercial building’s air-conditioning system which depends on the thermal load inside the building. This is affected by other factors such as the amount of people at a given time; the climate; building insulation; building orientation against solar radiation; building lighting; and, equipment and chiller selection.

If we look at a zoned irrigation system, we see that the water consumption pattern depends on the: crop type; irrigation system type; precipitation levels; ambient temperature; and; evaporation and humidity.

Our final example is an industrial production site, where the water consumption pattern could be totally unpredictable and tied to: production levels; number of shifts per day; and, specific machine water demand.

The load profile for any these examples can be determined by estimating how many hours per day the system will demand a specific water flow. Once we have the load profile, we can go to to select our pump. If this information is not available, the product sizing tool at can provide a non-specific load profile for many applications.

The most important thing to consider when selecting a pump for variable flow is that the peak flow does not occur most of the time, so it is imperative to select pumps which offer the best efficiency with lower frequent flows. This is counterintuitive, as we have the tendency to select a pump with the best efficiency at the peak flow, which will lead to an application that uses much more energy than needed.

You are now ready to use your new knowledge on load profiles to make better pump selections.

Course overview

Modules: 3
Completion time
Completion time: 15 minutes
Difficulty level
Difficulty level: Basic