Annual simulation & heat gains of the network

Cold district heating, part 4: perform the annual simulation and analyze the thermal gains of the network

Overview ▶ 0:10

Cold district heating network ready for annual simulation — Starting point for the annual simulation to determine the heat gains of the pipe network

This tutorial demonstrates how to run an annual simulation to determine the heat gains of the pipe network. This is an essential aspect in the planning of cold district heating networks.

Checking the heat source ▶ 0:28

Probe field model with hydraulic and thermal parameters — Probe field as heat source with hydraulic losses and heat-exchange configuration

In the baseline example, a probe field is used as the heat source. The probe field model considers:

Hydraulic losses: Pressure losses of all parallel probes
Heat exchange: A fixed time series for the probe temperature

Adjusting the probe temperature

If you simulate a cold district heating network with a probe field, you can import the probe temperature from your probe sizing software. Switch to user-defined temperature and select a corresponding TSV file.

Ground boundary conditions for the pipe network ▶ 1:36

Ground boundary conditions with soil type, burial depth, and moisture content — Configuration of the ground boundary conditions: soil type, burial depth, pipe spacing, and moisture content

Under Heat exchange via the pipes, the ground boundary conditions can be configured:

Set the soil type
Define the burial depth and pipe spacing
Enter the moisture content of the ground
Account for ice formation — recommended for simulations with a probe field or collector field in order to capture the full ground heat gains

Alternatively, a fixed temperature can also be prescribed to run a simplified simulation. For a detailed evaluation of the heat gains, the detailed ground model is recommended.

Starting the simulation ▶ 3:15

Simulation settings with 2 years of simulation duration — Simulation settings: at least 2 years of duration so the ground can settle during the first year

For the annual simulation, the following settings are recommended:

Simulation duration: At least 2 years, so the ground can settle during the first year. The evaluation then refers to the second year (last 8760 hours).
Disable fixed time step: With decentralized pumps, the option “Calculate the system only at fixed time steps” can be disabled. This often results in a faster and more stable simulation.

Evaluating the results ▶ 4:38

Annual simulation results with source heat flow from the energy plant — Evaluation of the annual simulation: source heat flow from the ground into the probes

Energy plant (probe field)

One important output is the source heat flow — the heat flow from the ground into the probes. It can be exported as a CSV file and used for a separate probe simulation.

Iterative workflow ▶ 5:27

Iterative workflow between network and probe simulation — Iterative workflow: export source heat flow, feed into probe simulation, and re-import the temperature

The recommended workflow for network simulation with a probe field:

Simulate the network with an assumed probe temperature
Export the source heat flow from VICUS Districts
Apply the heat flow in the probe simulation
Import the resulting temperature back into VICUS Districts
Iterate this procedure 2-3 times to obtain reliable values for the heat gains

Heat gains of the network ▶ 6:18

Display of the heat gains of the network as negative heat losses — Heat gains of the network: negative values show the heat flow from the ground into the network

The heat gains of the network are displayed as “heat loss”. Negative values represent heat gains (heat flows from the ground into the network).

Additional results ▶ 6:37

Heating power, COP, and operating points of the heat pumps — Additional results: heating power, COP of the heat pumps, and operating points of the pumps

Heating power of the heat pumps and temperature difference
COP of the heat pumps: Often higher in winter (heating operation) and lower in summer (domestic hot-water operation only)
Operating points of the pumps

Summary ▶ 7:27

Summary with seasonal performance factor, heat gains, and energy demand — Summary: supplied heat, seasonal performance factor (approx. 4.2), and heat gains in MWh and percent

The summary shows at a glance:

Total supplied heat
Heat extracted by the heat pumps
Electrical energy demand of the heat pumps and circulation pumps
Seasonal performance factor (e.g. approx. 4.2)
Heat gains in absolute terms (MWh) and relative terms (percent)

The evaluation always refers to the last 8760 hours (one year).

External Post Processing ▶ 8:34

External Post Processing with diagrams and temperature field in the ground — External Post Processing: detailed evaluation with diagrams and visualization of the temperature field in the ground

For more in-depth analyses, External Post Processing is available (it must be selected during the VICUS Districts installation). With it you can:

Evaluate all simulation quantities individually
Generate diagrams
Visualize the temperature field in the ground around the pipes