Be careful in reducing your mainline/submain diameters…

When designing a system, it can be tempting to reduce mainline and submain costs by using smaller diameter piping. Although you will save money upfront, our experience has shown this can lead to significantly increased energy bills.

Pressure is lost as it passes through piping due to friction loss. Once you exceed 2.5 meters (8 feet) per second for the mainlines, significant pressure loss is incurred, resulting in increased pumping costs to achieve the required pressure. High velocities in mainlines can also increase the likelihood of water hammer.

We would generally recommend keeping to a maximum of 1.5–2.5 meters (5–8 feet) per second for the mainline and 2.5–3.5 meters (8–11 feet) per second across the submains, dependent on the situation.

The difference in cost is not to be underestimated. We have modeled that a poorly designed system with incorrect mainlines and submains can equate to a 50% increase in pumping costs compared to a correctly designed system.

In different regions, there are also specific standards of maximum and minimum velocity that must be followed.

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