Sizing of pressure exchanger systems

Discover how to specify and size pressure exchanger systems for reverse osmosis with Grundfos' online tools.

Reverse osmosis has traditionally been a costly way to convert seawater to potable water…. …as the high-pressure pump needed to overcome the osmotic pressure consumes large amounts of energy. 

With a pressure exchanger, excess pressure from the brine can be transferred to the feed side and thus decrease this energy consumption dramatically. As well as the high-pressure pump, you need a pressure exchanger, booster pump and various pressure, flow and temperature sensors. 

It can be a daunting task to specify such a system, but it’s easy when you do it online at Click the dotted icon to open the quick links, and select “Grundfos Product Center”. 

Now we’re ready to begin. We’ll do this sizing by “Application”… …and then select “Industrial water treatment” as the application area… Next, choose “Desalination” as the application, and automatically, “Reverse osmosis” appears as the installation type. Proceed by clicking the arrow to the right. 

We can now insert our parameters. Let’s start with the pre-feed pressure… …which we’ll set to 3 bars. Then, set the peak feed pressure… …to 65 bars. 

You’ll now get a suggestion for average feed pressure based on your prior inputs. We’ll leave that as it is, at 62 bars. Now, set the permeate flow… …to 50 cubic meters per hour, and the recovery percentage… …to 35.

Let’s leave the density at 1,030 kilos per cubic meter, as this is typical for seawater. For the evaluation criteria, let’s go with “Price + energy costs” – but it is also possible to evaluate solely based on “System price” or “Energy cost”. In fact, this is all that’s needed to do the sizing… …but before seeing the result, let’s briefly look at the optional parameters, where you can make further customisations. The first is “Your requirements”, where you can specify safety margins, number of pumps or motor type.

Next is “Sensors”. Here you can specify particular material requirements and also deselect one or more sensors. Under “Operational conditions” you can select frequency, voltage, and temperature. You can also set the annual operating time to match that of your application. This will result in a more precise estimate of the energy consumption. At “Life cycle cost” you can enter data from an existing pump for comparison.

And finally, we have “Hit list settings”, where you can limit results to certain product numbers for both the pumps and the pressure exchanger… And specify parameters such as energy price, number of hits, the calculation period and much more.

Now let’s head back and see the results by clicking the green button. We now see 10 results, sorted by life-cycle costs. Let’s click on the topmost result, which has the lowest life-cycle cost. Here we get an overview of all the components in the bundled package such as the high-pressure pump, booster pump, pressure exchanger and the various sensors. These are included in a system drawing with an overview of all system parameters. You are also provided with options for further information… And the possibility to see performance curves for the various pumps. 

When you’re finished, you can export a PDF with your selections by clicking the blue button. In the pop-up, specify which items are to be included, such as pumps, pressure exchanger, sensors, system drawings and so on, and then click the blue button at the bottom. The generated PDF is a great way to share your selection with colleagues… …or with subcontractors.

Now let’s sum up the many other benefits of sizing your pressure exchanger system at Save time on the selection process; One supplier for most of the major system components; A full system package which is correctly sized and fully optimised; Insight into energy consumption; and a system illustration with an overview of all system parameters.

Course overview

Modules: 4
Completion time
Completion time: 20 minutes
Difficulty level
Difficulty level: Advanced