Conversion of existing DH to low temperature operation and extension of new areas of buildings

The Hypothesis of this project was that it is possible to convert the existing district heating grid from high temperature to low temperature. This means reducing supply/return temperatures to 50/25 in areas with low energy demand buildings and extend DH grids to areas where the existing buildings will be energy renovated over the next decades or newly built-areas with low energy demand buildings. By lowering district heating operating temperature, it is possible to utilize low-grade energy sources and renewables to provide heating. This is fundamental in the Danish objective of being 100% fossil fuel free by 2050.

Finding the optimal supply temperature in existing DH system has a key role in the implementation of low-temperature district heating. Reducing supply temperature will results in a heat loss reduction in the distribution network. It may however also result in an increase in pump power demand in the network.

The study aimed to develop a new model for applying low temperature DH concept for existing DH network by evaluating several factors simultaneously. The model was developed to find the optimal supply temperature in existing network, considering pipe network heat loss, bypass heat loss, pump power demand and return temperature all together.

Furthermore the new configuration for bypass system was evaluated in order to reduce the heat loss and inefficiencies caused by bypass in existing DH networks. The developed model was applied in district heating network in Harlev, Aarhus, to find out the optimal supply temperature for an existing system.

The main outcomes of this project were related to:
• Optimal supply temperature in existing DH network
• Proposing new configuration for bypass application in district heating system to reduce losses.
• Recommending and applying possible modification in existing DH networks (Case study area) in line with the possible modification in existing buildings which results in reduction in supply and return temperature in DH networks.
• Recommendation for reduced return temperature (EUDP project- March 2014)


Related articles

Conversion of existing DH systems to low temperature operations and extentions of new area of buildings
Presentation by Soma Mohammadi on the 4DH Ph.d. Fellow seminar, March 6th 2012, Aalborg University.










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