Simulate a passive network & check the hydraulics

Cold district heating, part 3: dynamic simulation of a passive network and verification of the hydraulics

Overview ▶ 0:11

Passive cold district heating network with decentralized circulation pumps — Starting point: passive cold district heating network with decentralized circulation pumps for hydraulic simulation

This third tutorial demonstrates how the hydraulic simulation of a passive cold district heating network works. It examines how the pressure losses affect pump control and whether the decentralized circulation pumps are sufficient to run the network.

Checking the decentralized heat pumps ▶ 0:30

System editor with decentralized heat pump and controlled circulation pump — Hydraulic configuration of the decentralized heat pump with controlled circulation pump (3 K spread)

The hydraulic configuration of the decentralized heat pump consists of:

Circulation pump: A controlled pump that regulates to a temperature difference of 3 Kelvin.
Heat pump: Passively produces a pressure loss of 0.1 bar.

The volume flow and heating power of the heat pump are automatically set from the stored building data. The associated volume flow is calculated via the 3 Kelvin spread.

Running the simulation ▶ 1:52

Simulation settings with 7 days of simulation time — Starting the hydraulic simulation with 7 days of simulation time to verify the circulation pumps

Click Start simulation.
For the first hydraulic check, a short simulation time of 7 days is sufficient.
The goal is to check whether the circulation pumps are sufficient to circulate the network.

Evaluating the results ▶ 2:19

Simulation results with volume flow, pressure loss, and COP of the heat pumps — Results: volume flow, pressure loss, and COP of the heat pumps at the consumers

After the simulation, the following quantities are shown in results mode:

Volume flow and pressure loss at the consumers
COP of the heat pumps (varies depending on supply temperature and domestic hot-water operation)
Temperature difference: Should meet the configured 3 Kelvin

Checking pump operating points ▶ 3:04

Pump diagram with operating points along the quadratic curve — Pump diagram: operating points move along a quadratic curve due to the spread-based control

In the Pump diagrams tab, the pump operating points are shown. Because the pumps regulate on a temperature spread, the operating points move along a quadratic curve (not at constant head). The pumps should operate within their operating range.

Testing the effect of higher pressure losses ▶ 3:46

System editor with increased manifold pressure loss of 0.25 bar — Increasing the manifold pressure loss in the probe field to 0.25 bar to test its impact

To evaluate the effect of higher pressure losses, the manifold pressure loss in the probe field can be increased, for example:

Open the system editor via Databases > Systems.
Edit the probe field and set the manifold pressure loss to, say, 0.25 bar.
Run the simulation again.

Evaluating the impact ▶ 4:28

Results with exceeded temperature difference due to pressure losses that are too high — Impact of increased pressure losses: temperature difference is exceeded, pumps reach their limits

With increased pressure losses, the following is observed:

The temperature difference is slightly exceeded (above 3 Kelvin) because the pumps reach their limits.
The operating points move at most along the pump curve.
A lower mass flow than required results, which manifests as a higher temperature difference.

This effect demonstrates the correct feedback of the installed pump on the network in the dynamic simulation. For a passive network, it is important to carefully match the pump capacity to the network pressure losses.