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The experience of the Optimized Return Flow

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Optimization of the return temperatures of district heating plants and a new tariff system

Why is it import to optimize the return temperature of the water flow between heating systems and the district heating plants?

The optimization of the return temperature not only signifies an advantage for the district heating plant operators but also brings advantages for the heat customer.

Indeed, the greatest energy loss in a district heating plant arises in the heat net. The higher the net temperature (meaning the temperature of the water flowing through the net), the higher the heat loss. The reason for this is that the greater the temperature difference between the heat net and the temperature of the surrounding soil, the greater the heat loss.

The problem arises because the soil temperature surrounding the heat net cannot be influenced. This means that all district heating operators need to focus on keeping the temperature in the heat net as low as possible. On the other hand, the forward temperature for most customers in their own heating system must not fall below 80 ° C, because the heating systems are designed in this way.

This is the reason why keeping a low temperature of return is the best way to minimize the losses on both sides.

What options are there to achieve a lower return temperature?

In order to reduce the return temperature in an existing heat net, it is necessary to include the heat customers. This is especially important for large heat customers like schools, hotels and other industrial buildings etc.. Many heat customers have a very low temperature spread due to poorly maintained or not optimized in-house heating distribution. It often happens that the water from the district heating plant enters the house at 85 ° C and is fed back into the district heating network at 70 ° C, meaning that hardly no temperature is given away from the thermostats to the rooms. In these cases, the energy is used very badly and therefore inefficiently. The result is that much more water has to be pumped through the heating system than necessary and there are more net losses. Consequently, investments need to be increased to compensate the increasing pump effort and higher line losses due to higher return temperatures for the heat customers.

Hydraulic balancing helps!

Hydraulic balancing of installed radiators can slow down the rate of dilution by increasing the residence time of the water in the rooms to be heated. Through this action every room is efficiently and equally heated and reduces the pump performance and the energy available in the water can be used more efficiently.

Usually, the technician that installs the heating systems, manually sets every single radiator – as this can take quite some time, very few technician do set the radiators correctly. This is why every single household, building, firm, hotel etc. needs to undertake this action individually.

New tariff systems

To incentivize heat customers to invest in optimizing their own plant, innovative tariff systems could be introduced so that those who have optimized their plant to achieve a low return temperature will receive a more favorable heat tariff. A win-win situation for heat customers and district heating operators.