Worst-point control

District heating network, part 7: configure worst-point control for optimal pump regulation

Overview ▶ 0:07

District heating network for configuring worst-point control — Installing a controlled pump with worst-point control for more efficient pump regulation

This tutorial demonstrates how to install a more efficient pump control. In the previous tutorials, a pump with a constant pressure increase was used. Here, a controlled pump is used instead, which regulates on a worst point.

Installing a controlled pump ▶ 0:40

Replacing the constant pump with a controlled pump in the system editor — Replacement: remove the constant-head pump and insert a controlled pump

Open the energy plant and remove the current pump (with constant head, delta-p-c).
Insert a pump with controlled head and reconnect it.

Controller settings ▶ 1:08

Worst-point control with 0.6 bar pressure difference and selection of all network points — Controller settings: worst-point control on 0.6 bar pressure difference with all network points

In the settings of the controlled pump:

Select worst-point control as the controller.
Set the pressure difference that is to be maintained at the worst point slightly higher than the maximum pressure loss of the transfer stations. With a maximum transfer-station pressure loss of 0.5 bar, 0.6 bar is chosen, for example, to always guarantee a positive pressure difference across every transfer station.
Under Worst point, select the points to be considered. In the simplest case: all points in the network — the simulation then automatically determines the point with the lowest pressure difference at every time step.

Important: A worst point must always be selected, otherwise the system is flagged as invalid.

Steady-state calculation and pump sizing ▶ 2:27

Steady-state calculation and pump sizing for the controlled pump — Steady-state calculation with unchanged pressure loss and re-sizing of the controlled pump

Calculate the network in steady state — the pressure loss (e.g. 1.6 bar at a 15 Kelvin spread) has not changed.
Under Results > Pump sizing, re-size the pump. Since a controlled pump is now installed, a matching manufacturer data set must be assigned.
Select a suitable pump from the list and assign it.

Setting the worst point from steady-state results ▶ 3:12

Targeted selection of the worst point from the steady-state results — Alternative: set a specific worst point from the steady-state calculation results

As an alternative to the automatic worst point, a specific worst point can also be set from the steady-state results.

Simulation and results ▶ 3:46

Simulation over 14 days with worst-point control — Simulation with worst-point control: results after 14 days of simulation time

After starting the simulation (e.g. over 14 days), the results show:

Checking the temperature difference ▶ 4:00

Temperature difference mostly at 15 K with small overshoots — Temperature difference: 15 K is largely maintained — small overshoots due to slower control

With the simple transfer stations, it is important to check the temperature difference. The desired 15 Kelvin is largely maintained — small overshoots are attributable to the somewhat slower pump control and are usually uncritical.

Pump diagram ▶ 4:36

Pump diagram with quadratic curve due to worst-point control — Pump diagram: quadratic curve due to worst-point control instead of constant pressure increase

The pump diagram shows the difference from constant pressure increase: with worst-point control, the head follows a quadratic curve. The control follows the system curve, which results in significantly higher efficiency and, above all, a lower electricity demand of the pump.

Head profile ▶ 5:15

Variable head: the pump adapts to demand — lower electricity demand compared to constant head

The head profile makes the difference clear: instead of a constant 1.6 bar, the pump moves with the network demand and settles lower when less heat is needed. In the evaluation, this shows up as a lower electricity demand.