Fourth Generation District Heating Networks
Fourth Generation District Heating Networks are designed to work at lower temperatures and enable a more cost effective transition away from burning fossil fuels toward heat supplied from local renewable and secondary heat sources, such as from waste heat or heat transfer from groundwater.
The objectives of 4G district heating networks include:
- Cost effective retrofit of existing buildings, including buildings that are not currently on networks, so that they can be connected into scalable heat networks
- Reducing the operating temperature of heat networks to allow the installation of less expensive distribution circuits between buildings, without the need for expensive insulation to restrict heat losses to the ground and allowing for absorbing heat from low grade waste heat sources
- more efficient heat emitter systems within buildings to accommodate lower operating temperatures
- lower carbon emissions to combat climate change
- lower emissions of nitrous oxides and particulates to improve urban air quality
Generations of District Heating Networks
The first generation of district heating from the 1880s was based on heat distribution by steam.
The second generation from the 1930s was based on pressurised hot water with temperatures above 100°C.
The third generation from the 1970s was also based on hot water, but with temperatures below 100°C and usually incorporate prefabricated parts in construction. Many suffered from poor temperature control systems.
The fourth generation from the 2020s is expected to be based on a much lower temperature water distribution to limit installation costs and heat losses to the ground, together with a much higher contribution from renewable energy and waste heat in order to limit carbon emissions and reduce air pollution.
A 4GDH network is coupled with higher insulation standards for buildings to restrict the amount of heat needed and looks forward to the electrification of heat by using heat transfer instead of combustion to provide the heat and to integrate with smart electric networks to balance the demands on the electric grid by using the thermal mass of buildings to store heat, and to restrict demand for electricity when there is supply pressure on the grid.
The trend in District Heating is towards lower distribution temperatures
The clear trend for district heating systems is to move to lower distribution temperatures.
The logical conclusion is to move toward distributing water circuits at near ambient ground temperature and to use heat pumps in each building to extract heat from the network if the building needs heating – and to reject heat to the network when a building needs cooling.
This allows for provision of heating and cooling in city centres without emitting any CO2, and without contributing to urban air pollution.
It also allows for the collection and reuse of waste heat at any temperature above ambient ground temperature.
Heat Sharing Networks
All the objectives of fourth generation district heating systems can be achieved by using Heat Sharing Networks that use low temperature water circuits between buildings. Each building has a heat pump to extract the heat that it needs from the network.
This arrangement allows for further benefits in terms of cooling, because any building that needs cooling can use its heat pump to reject heat to the communal circuit.