New design concepts for optimisation of LTDH distribution systems

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Emanuele Zilio

In this report you will learn about the design process of a low-temperature district heating network, highlighting the design factors that lead to reduction of heat losses in the distribution pipes. To demonstrate the technology, two real-scale demonstration projects are described in Høje-Taastrup, Denmark and in Lund, Sweden. Emanuele Zilio, engineer at COWI A/S, gave a short interview to summarize the report.

What is the main purpose of the report?

The purpose of this report is to explain the design process that can lead to the reduction of the heat losses in a district heating system as well as to present the main factors that affect the heat losses. In particular, the factors considered are; improved pipe insulation, use of twin pipes, reduced pipe size, reduced pipe length and the distribution principle in between the buildings.

In the report we are looking at two demonstration sites of low-temperature district heating networks in Høje-Taastrup, Denmark and in Lund, Sweden. In Høje-Taastrup a part of an existing district heating network will be replaced with a low-temperature network that will use surplus heat from a shopping mall. The existing buildings connected to the existing network will be upgraded to be ready for the low-temperature supply.

In Lund, the completely new area Brunnshög with research facilities, offices and residential buildings etc. is being built. A new low-temperature district heating network is constructed and will utilise the surplus heat from the world’s strongest synchrotron microscope (MAX IV) located in the area.

What are the main findings in your study?

The design phase of a DH-system defines the technical aspects of the network, and has a high influence on the heat losses. Here are the main findings to consider when designing for an optimized LTDH-distribution system:

Pipe insulations: The pipes insulation level can affect the performance of the network greatly. Heat loss from double pipes with the highest level of insulation can be around 50% lower than a single pipe with the lowest insulation level (based on catalogues data).

Reduced pipe size and use of double pipes: A smaller diameter can reduce heat losses. However, smaller diameters lead to higher pressure gradients in the pipes and an increase of pumping requirements. The first phase of the optimisation of Østerby’s district heating network showed a reduction of heat losses by 45% thanks to a hydraulic optimisation and the implementation of double pipes with the highest insulation instead of low insulated single pipes.

Reduced pipe length and distribution between the buildings: The optimisation of the network’s length is another important factor that can reduce heat losses, for example by reducing the length of the service pipes. The optimisation of the network’s length in Østerby district led to a reduction of 1 km of service pipes, out of 3.7 km, and a reduction of heat losses by about 23%. The percentage of heat losses in relation to the total supplied energy was about 10.8%, which was the aim of the optimisation process.

Regarding the network in Brunnshög area, the optimisation process was applied from the early design stage. In the district, it is expected to reach 3.5% of heat loss in relation to the total supply energy, once all the consumers will be connected to the network.

LTDH network design optimisation factors

LTDH network design optimisation factors

The table below summarises the important dos and don’ts characteristics of a LTDH-system, which can lead to an optimised network and reduce heat losses.

Characteristics of a LTDH-system - dos and dontsd

Table: Dos and dont’s of a LTDH-system

What happens now?

The work in Høje-Taastrup and in Lund continues. As for this report, we hope it will be used by DH-companies who are about to renovate an existing DH-network, or to design a new one. In addition, consultant companies can use this report as guideline for DH networks design.

More information

Click here to read the report

If you are interested in reading other papers and reports from COOL DH click here: reports and documents.