Pumps are used to circulate the flow and to provide a sufficient pressure increase to overcome pressure losses in the system. Pumping BCs usually contain the following components & parameters:

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The BC itself has two parameters:

Minimal pump head percentage: The minimal pump head that will be used. When a lower pump head is needed, the pump shuts off. By default, this value is set to 10%.

Change speed: The rate at which the pump can change its head during operation. By default, this value is set at 60 s/m.

The pump component has the following parameters:

Operation mode: The modus in which the pump will operate. At the moment, the Optimiser supports three types of operation:

• Constant speed: The most traditional way of operation. By keeping the pump’s rotation speed constant, its pump curve is fixed. This implies that, when the system pressure drop decreases during partial load operation, the resulting pressure head created by the pump must be throttled away. This way, constant speed pumps operate very inefficiently during partial load conditions. In general, most old pumps are constant speed pumps.

• Constant head: By altering the pump’s rotation speed through a control, the pump curve can be altered. During partial load, this mode will reduce the pump’s rotation speed in such a way that the design pump head is kept constant. In fact, the pump head is kept constant until the flow rate level of the pump has reached its maximal power. Further increasing the system flow rate then decreases the pump head.

• Proportional head: By altering the pump’s rotation speed, the pump curve can be altered. During partial load, this mode will decrease the pump’s rotation speed in such a way that the design pump head is decreased proportionally with the required flow rate.

Note that it’s also possible to control the pump with an external signal. When doing this, ensure that the pump is set in constant speed operation mode. Applying a control signal between 0 and 1 will then modulate the pump between its minimal and maximal speed. This way, the original pump curve will shift between a minimal and maximal pump head curve while keeping its original shape.

Ensure that, if you have a pump in a constant flow, the operation mode is set at constant speed. Pumps in a variable flow situation need to be set according to their pump operation mode: on constant speed with an external signal for the variable speed drive, on constant head or proportional head. The operation mode will affect the final pump energy consumption. An example is given further below.

Pump head: The necessary pump head during the operating point in full load. This value can be manually filled in & locked by the user or can be calculated by the Optimiser during the ‘Optimise components’ step.

The pump head is calculated by combining all pressure losses within the path of the most resistance. In the small example below, this path is indicated by the blue dots (which can be shown in the model by hovering over the pump). The total calculated pressure loss is 34 785 Pa (1 667.5 Pa + 33 117.5 Pa), using the formula below.

Note that, when hovering over the pump, the user can get more insight on how the pressure loss is divided over the components. In general, the pressure losses over the piping system should be within the range of 10% - 20% of the total pressure loss.

• H = Pump head (m)

• p = Total pressure loss (N/m² = Pa)

• ρ = Density (965 kg/m³ @75°C)

• g = Gravity (9.81 N/kg)

Pump curve: A curve mapping the pump head to the volume flow rate. This curve can be filled in manually (which is advised whenever the type of pump & its pump characteristic is known), or can be calculated by the Optimiser during the ‘Optimise components’ step.

When the curve is calculated, the Optimiser uses the (calculated) pump head value as its duty point (indicated by the blue dot in the pump curves above). The pump curve is then further shaped in function of the chosen operation mode. For constant speed operation, the pump curve will be approximated by a parabolic line. For constant head, the pump head from the duty point is kept constant at lower volume flow rates. For proportional head, the pump head decreases from its calculated head in the duty point until half this value at zero flow.

Parameter validation

When the pump head is locked at 2 m instead of the calculated 3,68 m, the pump curve will be fitted on the blue dot point (2 m, 7,84 m³/h). The selected pump is in this particular case too small and will influence the actual flow. The red line in the graph below shows the pressure loss curve, the red dot 1 is the needed duty point at (3,68 m and 7,84 m³/h), but the actual duty point (red dot 2) is (2,4 m and 6,91 m³/h). In case the pump is selected incorrectly the software will show this as an error. The actual flow will also be shown on the label.       

Efficiency: A curve mapping the pump efficiency to the volume flow rate. This curve can be filled in manually (which is advised whenever the type of pump & its pump characteristic is known), or can be calculated by the Optimiser during the ‘Optimise components’ step.

When being calculated, the Optimiser imposes a default efficiency curve shape. It will take the duty point as the point of highest efficiency. By default, the efficiency in this point is set to 53.7%.

The pump efficiency will reduce as a function of the system flow, this is shown in the plot below. The pump electricity consumption is calculated in time during the simulation taken into account; the differential pressure, flow, and pump efficiency.   

• P_e = Power (W)

• Δp = Differential pressure (Pa)

• Q = Flow (kg/s)

• η_pomp = Efficiency (%)

Maximum efficiency: This is an optional parameter. By filling in the maximum efficiency, the Optimiser will recalculate its default efficiency curve such that the duty point has an efficiency equal to this value. When the nominal efficiency is known, but not the actual efficiency curve of the pump, leaving the pump efficiency curve open and filling in the nominal efficiency here is a good first approximation.

Pump lift: The maximal percentage of its lift that the pump can use during simulation. By default, this value is set at 100%.

The non-return valve component has only one parameter:

KV value: The KV value expresses the amount of flow for a pressure drop of 1 bar. By default, this value is set at 1 000 000. In general, the value is not changed during conceptual optimisation.

Types of pump BCs

At the moment, the Optimiser has five different pump BCs.

Supply pump

This BC is mostly used on collectors and risers. The pump is mounted on the supply pipe.

Boiler pump

This BC is mostly used on production units (boilers, heat pumps, cogeneration). The pump is mounted on the return pipe.

Study case: impact of operation mode on electricity consumption 

In this example, the 4 pump operation modes (internal and external) are simulated during January and compared based on electricity consumption. This case is a variable flow installation with a constant supply temperature.

In partial load, as shown in the plots below the pump head will follow the pump curve as a function of the flow in the installation (the blue dot is the design duty point and the red dots are the pump head according to the flow). In the case of the external pump control, the pump speed will be adjusted according to the input signal that comes from the PI control, the minimum pump speed is respected by filling in a minimum modulation percentage (the pump speed is reduced so the most open valve (±60%) will go to 95% open position).

There is a big difference in electricity consumption between the 4 pump operation modes respectively 56,7 kWh, 36,2 kWh, 20,9 kWh, and 14,2 kWh within the same installation. Depending on the used concept the electricity consumption will differ.