Adjusting a high-efficiency pump correctly
A high-efficiency pump only saves energy if the control mode is suited to the system and the Characteristic curve is set correctly. Proportional pressure, constant pressure or constant speed – this article explains which operating mode is suitable for which heating, air-conditioning or domestic hot water circuit, how to select the appropriate setting, and how to identify a pump that has been set too high.
It is the type of control system that matters, not the efficiency class
A controlled circulation pump continuously adjusts its speed to match the heat demand. The control mode determines how it does this. It is the parameter that has the greatest influence on electricity consumption – and the only one that can still be adjusted after installation without altering the hydraulic system.
Biral circulation pumps for heating, air conditioning and domestic hot water offer the same three basic control modes: proportional pressure (pp), constant pressure (cp) and constant speed (cs). With the ModulA T2, each of the three modes can be finely adjusted in ten steps; with the PrimAX RED T2, this can be done in four steps via the control panel. With the VivarA, you select the control mode at the touch of a button; the setpoint is displayed on LED panels.
Proportional pressure (pp) – also known in the industry as Δp-v
With proportional pressure control, the set flow head decreases as the flow rate increases. When the thermostatic valves close, the Pump reduces the pressure. This is suitable for systems in which a large proportion of the pressure loss occurs in the distribution network: traditional two-pipe radiator heating systems with long runs.
Constant pressure (cp) – also known in the industry as Δp-c
With constant pressure, the pump maintains the set head across the entire flow rate range. This is the right choice when the pressure loss occurs mainly close to the pump and the pipework is short – for example, in underfloor heating systems and single-pipe radiator heating systems.
Constant speed (cs)
In constant-speed mode, the pump operates at a fixed speed, regardless of the differential pressure in the system. This is appropriate wherever the flow rate is required to remain constant: in boiler circuits, in storage tank charging systems and in drinking water networks.
The cost of an incorrectly set characteristic curve
If the setting is too high, this means that the Pump is delivering more head to the system than the installation requires. There are almost always three consequences.
Higher power consumption: The pump operates continuously above the required operating point without causing any room to become warmer.
Flow noise: Excess pressure can be heard at thermostatic valves and manifolds, particularly during part-load operation.
Unstable control: The valves are working against an excessively high differential pressure and are losing their effectiveness.
If the setting is too low, this is first noticeable at the furthest radiator: the radiator at the end of the circuit no longer gets warm, whilst the rooms near the boiler are heated. The correction is the same in both cases – adjust the setting up or down by one notch, and then check the operating point.
Check the setting rather than guess at it
The PrimAX RED T2 shows the air flow rate and power consumption directly on the display. With the ModulA T2 and VivarA models, the Bluetooth interface and the Biral ONE app also give you access to a live dashboard displaying current operating data, a guided commissioning process, and warning and alarm messages. Operating logs can be viewed and sent from the app – handy for documenting a setting change following the change of heating season.
Quick assignment
Control method by system type
This classification applies to the Biral PrimAX, ModulA and VivarA series. The decisive factor is always where in the circuit the pressure drop occurs.
Two-pipe radiator heating system
Proportional pressure (pp). The pressure loss occurs largely in the long runs – the required delivery head may decrease as the flow rate decreases.
Underfloor heating
Constant pressure (cp). Short pipework and a pressure drop that occurs mainly close to the Pump.
Single-pipe radiator heating system
Constant pressure (cp). The flow rate in the loop remains largely constant; the differential pressure is to be maintained.
Boiler circuit
Constant speed (cs). The circuit requires a constant flow rate, regardless of the distribution network.
Battery charging circuit
Constant speed (cs). Charging takes place at a defined flow rate; pressure control offers no advantage in this case.
Hot water circulation
Constant speed (cs), with the bronze design of Module A BLUE. It is certified for domestic hot water systems; the maximum fluid temperature is +85 °C, although operation at temperatures below +65 °C is recommended to prevent limescale build-up.
Air-conditioning and chilled water circuit
Select the GREEN design; the control mode depends on the distribution network. The ModulA GREEN is designed for air-conditioning systems, cooling systems and geothermal heat pumps.
Conclusion
The control method is determined by the hydraulics, not by habit: proportional pressure where there is pressure loss in the system; constant pressure for short runs; and constant speed wherever the flow rate is to remain constant. Set the stage deliberately during commissioning, check the operating point on the display or in the Biral ONE app, and make adjustments after the first heating period. Where the situation is unclear, Biral’s advisory service will review it with you.
Frequently Asked Questions
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