District Heating Systems are a closed loop network of insulated pipes laid around a city which are used to supply heated water (usually close to boiling point) to council buildings, civic centres and communal housing. The heated water is normally supplied from an Energy Centre which uses gas or biomass fuel to heat the water before it enters the supply pipe network.
The heated water from the supply pipework enters the various city buildings and heat is then transferred to the building pipework via heat exchangers. The cooled water is returned to the Energy Centre via a network of return pipes which run in parallel to the supply pipes.
HAL have modelled many district heating systems to optimise the piping design, confirm pump selection, calculate the range of system pressure and temperature losses, determine the maximum surge pressures and pipe loads which can occur due to operation of pumps / valves and to optimise the control system. This will include an assessment of the pump control system. The key objectives of a hydraulic study are to ensure the control system and operation:
- Meet the heat transfer obligations
- Maintain a continuous supply of flow to the users
- Maximise efficiency
- Minimise any controller instabilities
The model will normally be calibrated for various different operating conditions, including accounting for thermal effects. The model will include all equipment and instrumentation which can affect the system dynamics and thermodynamics. We will determine the system pressure and temperature losses and to provide hydraulic and temperature grade lines throughout the system for the full range of operating conditions (winter, summer and mid-point demands). We will identify the most hydraulically remote user in terms of supply pressures and temperatures and the model can predict and generate results consistent with real-time operation.
We can also demonstrate the rate at which the system cools following an upset event (power failure to pumps) and also re-heats following re-start of the pumps. We will determine the time taken to drain the system in the event of maintenance being required and to advise on the required location of drain points and air valves.