The alternative to this solution would be that the customers who need process steam would have to produce the steam themselves – and possibly the production of steam would be based on fossil fuels. Thus, the overall efficiency of the overall energy supply system would possibly decrease at the same time as the environmental impact would increase. Need for clarification of the term “generations”. As confusion has thus arisen around the term "generations" and the "generations" are mixed up with the years in which the generations were introduced, IEA DHC - the hub for international DHC research - has found it necessary to prepare a concise definition of the district heating network generations, which can be downloaded here:
IHowever, it has also given some people the impression that 2GDH is always considered better than 1GDH, that 3GDH is always better than 2GDH, and that all DHS should undergo a development phase to move to the ‘next level’. This is a misunderstanding, and it is important to recognise that there are some vital services that require higher temperatures, such that even 1GDH based on steam can be an optimal starting point for the green transition.
The following two examples illustrate this fact:
Example 1 In Manhattan, New York, the DHS is based on steam. With the very high heat demand density currently present there, a conversion to district heating with a flow temperature of below 100 ° C would require the establishment of a network of pre-insulated district heating pipes with much larger dimen - sions than the system in place to cover the current heat demand. However, this would not be feasible since there is simply not enough space for such large pre-insulated pipes in the “crowded” underground. Therefore, the most sensible goal would likely be to run a 1GDH as effectively as possible and to change the heat source to a carbon neutral one, such as switching from fossil fuel boilers to heat of deep geothermal origin. This would create a carbon neutral and future-proof solution, even though the 1GDH in Figure 1 can be interpreted as belonging to 1890-1930. Example 2 A DHS system has a large customer base that uses steam for process purposes. In such a situation, parts of the system must be based on steam, but this does not prevent partial areas from converting from steam to hot water if it is technically possible. Thus, the total DHS will consist of both 1GDH, 3GDH, and possibly 4GDH.
https://www.iea-dhc.org/iea-dhc-network-generations
Conclusion As is evident from Figure 1, the production side of district heat- ing can be complex. Therefore, the focus in the IEA DHC's defi- nition of the generations is solely on the characteristics of the district heating network (DHN) - i.e., temperature level:
• 1st generation DHNs use steam.
• 2nd generation DHNs use liquid water above 100°C.
• 3rd generation DHNs provide heat between 100°C and 70°C.
• 4th generation DHNs provide heat below 70°C.
As mentioned before decreasing DHN temperatures often provides several benefits. Therefore, a generations terminolo- gy based on network temperatures and fluid characteristics makes sense down to 70°C. Below 70°C additional measures
20 HOTCOOL no.5 2024
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