Most hydronic systems in buildings are variable flow systems where the pump adapts its performance to the pressure needed. As you may know, variable speed pumps can be operated in different control modes.

The pump's energy consumption will depend on the control mode that you choose.

Let’s look at 3 differential pressure control modes and their matching curves to see which one is the most energy-efficient.

We have the constant pressure mode, the proportional differential pressure mode with a “linear” control curve, and the proportional differential pressure mode with a “quadratic” curve that adapts to the real pressure needed in the system. With the “quadratic” curve setting there is no need to install pressure sensors far away from the pump.

Here, the pump is designed to automatically adjust its speed based on the pressure needed in the system, regardless of the flow. The pump simply calculates the pressure demand, which is proportional to the square of the flow rate, and adjusts its performance accordingly. The result is an optimised pump curve that makes differential pressure sensors redundant.

Let’s quickly look at the control modes mentioned as they are used for different types of systems. The constant differential pressure mode is used in variable flow systems, where the pressure requirement is the same regardless of flow. This is the case in underfloor heating systems, UFH, or open systems with a dynamic pressure loss share that is insignificant.

Proportional pressure control modes are used in variable flow systems, where there is a correlation between flow and pressure requirement. This is the case in circulating HVAC systems. Both the linear and the quadratic pressure settings may be used here.

However, the proportional pressure control mode with a quadratic curve setting is the most energy efficient ……as it adapts to the real pressure requirement, even without the use of remote pressure sensors. The savings are at least 15%.