On this page you learn everything about LowEx networks: What are LowEx heat networks? What is the difference to cold district heating networks? Where are LowEx networks planned?

Definition: What are LowEx networks?

LowEx networks are a special form of low-temperature networks that are operated at a lower temperature level than conventional heating networks. A rigid definition for LowEx networks does not yet exist. The term "LowEx network" stands for Low-Exergy network. This means that the heat network provides energy or heat at a low exergy level. In general, temperatures below 50 °C can be applied to LowEx networks. Sometimes the term LowEx network is also used synonymously with "cold local heat" (5GDHC network) or "anergy network". At the same time, conventional low-temperature networks (4th generation heating networks) are also referred to as LowEx networks. Due to the high potential for confusion and the non-existing definition, the term LowEx network should be avoided and either low-temperature network (4th generation heat network) or cold local heat network (5th generation district heating and cooling network) should be used. Typical features of LowEx heat networks are heat recovery (i.e., the use of waste heat), use of ambient heat or heat sources with low temperature levels (and thus low exergy content), low-temperature heating systems in buildings (underfloor heating), and high-temperature cooling systems for room air conditioning. Often, the decentralized feeding of waste heat into the grid is used as a characteristic for LowEx grids. The term Low-Exergy expresses that the supplied heat contains only a low part of exergy and a high part of anergy, i.e. the heat is close to the ambient temperature.

Difference between LowEx network and 5GDHC networks

As explained in the previous section, no general definition of the term "LowEx network" exists. In some cases, a LowEx network refers to a typical 5GDHC networks or anergy network. 5GDHC and anergy networks refer to the same supply concept and are defined by the low heat network temperatures, which are not sufficient to supply heat directly to buildings (decentralized water-to-water heat pumps are necessary in each building). Further explanations can also be found in the glossary on 5GDHC networks.

In the nPro tool, both, LowEx networks and 5GDHC networks can be planned and simulated.

Projects in implementation

A well-known heating network advertised as a "LowEx network" is the planned 5GDHC network on the former airport site in Berlin Tegel (TXL), Germany. The site will be home to the so-called Urban Tech Republic, a modern research and industrial park, and the Schumacher District. More than 5,000 new residential units will be built in the Schumacher District. The area will be supplied with heating and cooling via one of the longest 5GDHC networks, which is being implemented by the energy company E.ON and the Berlin public utility company Berliner Stadtwerke. A variety of different heat sources are integrated, from geothermal energy and waste heat to waste water heat. The network is operated at 20 °C in summer and 40 °C in winter. Heat demands can be met by decentralized heat pumps in the buildings. Cooling requirements are met by chillers that feed the waste heat into the LowEx network. The distribution network will have a length of over 10 km, making it the longest 5GDHC network in Germany at the time of its construction.

Research projects

Some German research projects have specifically addressed the notion of LowEx network and investigated different supply concepts. The LowEx-Bestand and LowExTra projects are briefly presented below.

Research project: LowEx-Bestand (existing buildings)

The short title "LowEx-Bestand" stands for "LowEx concepts for the heat supply of refurbished multifamily existing buildings" and investigated heat supply solutions for the use of heat pumps, heat transfer stations as well as ventilation systems in refurbished multifamily buildings. The aim of the project was to research and technologically develop LowEx concepts for existing buildings. The main focus was on improving the economic efficiency and operating quality with the aim of speeding up market introduction.

Research project: LowExTra (heat networks)

The research project "LowExTra" investigated novel heating network concepts similar to the well-known 5GDHC networks. The networks were designated as low-exergy networks, which is the origin of the project acronym. In particular, bidirectional heat networks were investigated, i.e. cold networks that provide not only heat but also cold and do not have a fixed supply and return pipe, but only a warm and cold pipe (multi-pipe or two-pipe system). The prosumer idea plays a prominent role in these networks, since cold consumers also represent heat producers. The supply concept investigated in LowExTra is nowadays also referred to as 5th generation heating and cooling networks, in which a bidirectional energy flow takes place (heat and cold supply).

Pipe systems for LowEx heat networks: Steel or plastic?

The lower the network temperatures, the more plastic pipes and, in the case of 5GDHC, also uninsulated plastic pipes make sense. Conventional heating networks (3rd generation heating networks) are operated at high pressures and temperatures (around 100 °C) and are therefore only built with steel pipes. Modern low-temperature networks (4th generation heat networks), on the other hand, often manage with pre-insulated flexible plastic pipes. The laying and material of these pipes are much less expensive and much easier to handle during installation. In addition, uninsulated pipelines are often used in 5GDHC networks, as listed in the overview of 5GDHC networks. These are uninsulated polyethylene (PE) pipes that even allow heat gains when the grid temperatures are below the ground temperature.