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This is the 37th issue of our heatbeat Research Newsletter, in which we provide updates on recently published research on district heating, district cooling, and district heating and cooling systems. In this issue, we look at opportunities for improvement on the secondary side in the district heating network. In this regard, an article entitled "A study on how efficient measures for secondary district heating system performance can be encouraged by motivational tariffs" was recently published.
District heating networks can very quickly decarbonize city districts or entire cities, particularly through their transformation to renewable energies, such as large-scale heat pumps. An important prerequisite here is the efficient operation of the heating network, which depends on a variety of factors. Some factors, such as the pipe network, the network pumps, the heat exchangers or generator units, can be controlled and optimized by the district heating network operator. Other factors, however, such as efficient operation of the customer sides downstream of the substations, are often beyond the control of the network operator. In this context, an efficient secondary side contributes to a reduction in return temperature or at least to compliance with the required temperature limits and thus, through lower heat losses and more efficient use of central generation, increases the overall efficiency of the network. The measures that can be used to improve the secondary side and the influence that the district heating system operator can have in this regard are discussed in the recently published article "A study on how efficient measures for secondary district heating system performance can be encouraged by motivational tariffs" by Lygnerud et al.
Here, the article tries to answer the central question: "Which measures should be promoted to increase the performance of the secondary grid?". For this purpose, in a first step, the research team developed a pricing model that takes into account the possibility that the utility can motivate customers to run the secondary more efficiently through this pricing model. Currently existing pricing models with such a motivating component are used as a guide. Thus, a total of four common methods are explained in the article:
The markets from which these four methods were summarized are primarily the established district heating markets from Sweden and Denmark. At this point, it should be noted that in Germany this form of tariffs are not so widespread, which means that the potential in this country has not yet been fully exploited.
For the final evaluation, the authors derive their own tariff composition, which consists of a fixed tariff component (basic price or capacity price), a variable tariff component (consumption in MWh) and an incentive component (credit for efficient operation). This is then examined with various measures to increase efficiency on the secondary side.
Various options are available for increasing efficiency on the secondary side. We briefly summarize the options presented in the article and their impact below.
Essentially, the article examines the effects on the primary-side return temperature of four measures. A more efficient circulation with and without return admixture on the secondary side, the use of low-temperature radiators with 55 °C / 45 °C, the use of a domestic hot water storage tank with and without bypass, and the use of a second, parallel heat exchanger for domestic hot water supply.
The results show that a reduction in the return temperature of 3.2 Kelvin can already be achieved by using variable volume flow control on the secondary side. It is also interesting to note that the costly conversion to a second heat exchanger for the pure provision of domestic hot water only proves to be very useful from a combination of 3 measures onwards, in which case a temperature reduction of 15.2 Kelvin is possible. In this case, the measure is combined with low-temperature radiators and variable volume flow control.
In addition, the payback periods of the measures presented are determined. This is calculated under the assumption that the savings achieved by the return temperature are passed on directly to the customer. Thus, depending on the heat production costs, payback periods of 1 - 9 years can be achieved depending on the combination of measures.
In summary, the article shows measures on the customer side in the heating network which lead to a reduction in the return temperature and thus to an increase in efficiency in the entire heating network. Incentives can be created for the customer to implement these measures if such measures are appropriately remunerated by means of a variable credit. The article also points out that certain measures, such as the use of a second heat exchanger for the pure provision of domestic hot water, can only be implemented in consultation with and with the help of the network operator. For this reason, it is recommended that a stronger relationship should be established between the energy supplier/network operator and the customer at the same time. Only in this way is it possible to implement joint solutions for a more efficient and sustainable energy supply.
The full text of the article can be found here: https://doi.org/10.1186/s13705-023-00417-0. As always, we recommend reading the full-length article.
The next issue of our newsletter will be published on December 6, 2023. Until then, feel free to follow us on LinkedIn where we share smaller use cases and information.