The variety of local heating networks: a comparison of cold local heating networks, low-ex networks and warm networks
In this blog post, we explain
what a heating network is,
what the what the differences are between local and district heating, define
cold local heating networks,
low-ex-networks and
warm local heating networks and give an outlook on the
future of heating systems.
What are heating networks?
Heating networks are used to distribute heat via a transfer medium such as water or brine. This takes place via flow and return pipes, which transport the heat energy and provide heating and hot water in the buildings.
The cooled fluid is transported back via the return pipe, where it is reheated and fed back into the circuit.
Traditional hot networks usually use fossil fuels such as gas or oil as an energy source. However, in order to become more environmentally friendly, more and more heating networks are relying on alternative, sustainable heat sources such as anergy from water or the earth, solar thermal energy or industrial waste heat, which would otherwise be lost unutilised.
Difference between local heating networks and district heating
While district heating networks often supply thousands of buildings, local heating networks tend to be found in smaller districts and neighbourhoods and to supply municipalities or industrial estates. However, there is no clear distinction or numerical limit for one type of network or the other. The same technical differentiation criteria apply as for local heating networks.
Interesting for the promotion of networks in Germany: If 2 to 16 buildings are supplied with heat and hot water from one network, this is referred to as a building network (the GEG applies). If there are more than 16 buildings (or 100 residential units), then it is a heating network, subsidised according to BEW.
1. Cold local heating networks
Efficient 5th generation local heat supply
Cold local heating networks are characterised by a local heat supply with comparatively low investment costs. They enable the provision of source heat without major losses over short distances. In contrast to traditional local heating networks, in which the water is heated to high temperatures, a cold local heating network uses the lower temperature of the source directly. This is usually in the range of -5-25°C. Sources can be the ground, water, air, solar thermal heat and exhaust air.
Water or brine is usually used as the heat transfer medium in the cold network. Once in the building, the brine is fed through a heat exchanger and brought to a usable temperature level by the decentralised heat pump. As each building requires its own heat pump, a cold local heating network is referred to as a decentralised energy solution. A direct heat supply via the grid is not possible with this type of grid, as the grid temperature is too low. However, by reversing the heat pump operation, the cool grid temperature can also be used to cool the buildings in summer - without additional air conditioning systems. This can be done in summer and winter operation or often simultaneously or in parallel.
Pros:
- Low investment costs: As cold local heating networks use low temperatures, the PVC pipes do not need to be insulated - the network expansion is more cost-effective.
- Local heat supply without large heat losses: Due to the lower temperatures, there are hardly any heat losses during transport in the heat network - on the contrary, sometimes the ground through which the network runs is even warmer than the source and therefore even gives off heat to the network itself.
- Flexibility of heat sources: Cold local heating networks can be effectively fed and coupled with various renewable heat sources such as aqua and geothermal energy or waste heat. In this way, the most suitable source can be utilised depending on availability and regional conditions.
- Flexibility in the provision of heat: supplying buildings with heating and cooling via a thermal network.
- Operation of the heat pump with solar power from the roof for lower electricity costs!
- Balancing heating and cooling requirements within buildings and between buildings in a neighbourhood.
- "Exergetic refinement at the consumer to the temperature level required by the individual building energy system. In other words, the grid temperature does not have to be set so high that the building with the highest flow temperature in the heating system is also supplied (existing buildings with an old heating system and flow temperatures above 70 °C). Instead, the heat is raised individually for each building by the decentralised heat pumps to the temperature level required in the respective building." www.mwirtz.com/5gdhc_de.html
When using cold local heating networks, however, there are also some
Challenges:
- One of the main questions is the correct dimensioning of the heating network and its sources: Is the basic demand taken into account or also a rarely occurring peak load (which makes the network much more expensive)? Can a heating rod, fossil fuels or a CHP unit be used as an alternative for peak loads?
- Hydraulic control is challenging due to the small temperature differences in the flow and return. Larger volume flows are required for the system to work smoothly, which in turn requires larger pipe diameters.
- In addition, each connected household requires its own heat pump, with the associated costs, space, maintenance and repair requirements.
Nevertheless, studies and practical experience show that cold local heating networks have great potential to cover heating requirements efficiently and sustainably.
Applications:
- Housing estates and neighbourhoods in new developments or mixed-use areas
- Urban neighbourhoods
- Commercial areas with short distances between buildings
2. Low-ex-networks
The mid-warm with central heat pump
Low-ex networks (low-exergy networks) lie between cold and hot networks in terms of temperature. They work at a low temperature level with operating temperatures between 35-55 °C. The network heat can therefore be used directly for heating and - with very efficient transfer - for hot water without the need for a heat pump in the household (term "exergy": directly usable heat). The name means that the network heat is provided at a relatively low exergy level (you can find out more about anergy and exergy here). Regenerative sources such as solar thermal energy, aquathermal energy, geothermal energy or waste heat from industrial processes are used as sources. The required heat is generated centrally and then channelled into the building at the "right" temperature via the network. The pipes must therefore be well insulated in order to reduce heat losses in the distribution network.
Exception: The mains temperature is very low - 40 °C, for example. This is sufficient for (underfloor) heating. For hot water (legionella issue), a booster heat pump is then also required in the household or, for example, in nurseries or care homes.
It is not possible to cool the buildings via the Low-Ex grid as the temperatures in the grid are too high.
Caution: As there is no strict definition of Low-Ex, the term is sometimes used as a synonym for energy networks! In this case, the above description no longer applies. To avoid confusion, it is best to speak of low-temperature networks.
3. Warm networks
The classic local heating supply
Warm networks are the oldest and currently still the most widespread local heating networks.
They transport hot water (at temperatures of 60-90 °C) from a central production plant, the heating plant, via insulated pipes and house transfer stations to the individual households. Depending on location and availability, the sources for hot networks can be fossil fuels, biomass or renewable energies such as solar energy or (deep) geothermal energy. The aim is to make these grids CO2-free in the near future via transformation plans and therefore more environmentally friendly, less lossy and more efficient.
Some pros and cons of warm nets are:
- Warm grids have been a proven technology for many years, so the cost/benefit factors are easy to assess.
- However, the high water temperatures lead to heat losses, both during transport and especially in summer, when little heat is taken.
- They are largely fuelled by fossil fuels and therefore cause high emissions of greenhouse gases. They must therefore be transformed and decarbonised by 2045.
- Warm grids from 100 % renewable energies: When heating via a centralised heat pump, the grid temperature should be as low as possible (approx. 60°C). It is also possible to generate heat from biogas and biomass through combustion.
Overall, hot grids offer a proven solution for local heating supply if they are stored from renewable sources such as deep geothermal energy or industrial process waste heat. Fossil sources such as natural gas, oil or coal, on the other hand, are no longer fit for purpose - they will soon have to be replaced due to legal requirements. Newer technologies such as combined heat and power (CHP) help to reduce these disadvantages.
The future of heating supply
Local and district heating currently accounts for around 14 per cent of final energy consumption in German households, with around 23 per cent of this coming from renewable energies and waste heat. However, the majority, around 77 per cent, is still generated using natural gas, coal and waste as "fuel". In future, the operators of heating networks will have to completely replace the proportion of fossil fuels with alternative energy sources.
Through careful planning and taking into account the local potential and consumers, a local heating project can guarantee a reliable and cost-effective heat supply for the connected users. At the same time, it offers local authorities the opportunity for local development and value creation and makes a concrete contribution to the energy transition and climate protection.
Note: We have omitted the old steam networks - 1st generation heating networks - despite their widespread use, as they have high energy losses and are no longer being built.
At goodmen energy, we help you switch to renewable sources with feasibility studies that determine the potential for utilising renewable energies as multi-sources for local heating systems as well as energy-saving potential and requirements. We will find the most economical or environmentally friendly solution, whether it's a new grid installation or a transformation - contact us.