Cold heating network running

08.04.2025

Source: E & M powernews

The energy supplier Rhenag has connected the first buildings to a project with cold local heating and ice storage.

In a new development area in Rommerskirchen-Widdeshoven, a district is to be supplied with climate-neutral heating and cooling via a cold local heating network. In cooperation with the municipality, Cologne-based Rhenag presented the innovative district concept in 2021. The first buildings have now been connected to the supply.

"The cold heating network, which is filled with a glycol-water mixture as a carrier fluid, is up and running," the company has now announced. The first buildings on the approximately 15,000 square meter site of a former nursery have been connected. The energy source is a so-called ice storage tank.

The first customer to connect was an existing natural daycare center, which has now built an extension. Several detached houses are also currently being built, one of which is already standing and is already drawing heat from the network. Some plots are still for sale.

600 tons less CO2

The prerequisites for cold local heating are buildings with a high level of energy efficiency, i.e. with a low demand for heating. According to Rhenag, the use of this technology makes particular sense if the building is not only to be heated but also cooled, for example to air-condition detached houses in summer.

"The CO2 savings over 20 years amount to around 600 tons compared to conventional heat supply," says Tim Winterscheidt, Head of Energy Services at Rhenag Energie. In addition, the costs for the residents remain predictable and are not dependent on market prices. For the connection to the cold heating network, they pay a fixed price for the operation and maintenance of the system, but not for the heat that is taken from the network.

The technology is not new, but has so far only been established as a pilot project in a few places in Germany, Rhenag continues. However, the development in Rommerskirchen was complex. This was due to the fact that it was not possible to plan how many and which properties would be connected and when. "In future, we would use the ice storage tank in districts where the development can be planned right from the start," says Winterscheidt.

Cistern with 275 cubic meters

The heat supply via an ice storage tank works on the principle of cold local heating: the floor, into which the four-metre-deep storage tank with a diameter of nine meters is sunk, supplies the heat in winter that was stored in summer from the surroundings or from cooling the buildings.

The cistern in Rommerskirchen holds 275 cubic meters of water. Heat is extracted from this via a heat exchanger. The carrier fluid is brought to a comfortable temperature directly in the residential units using heat pumps with low electricity consumption.

The heat extraction gradually turns the water in the storage tank into ice. When the water turns to ice, further energy is released. By way of comparison, freezing ten cubic meters of water generates the same amount of energy as burning around 100 liters of heating oil.

In summer, the principle works in reverse: the condensation water from the ice that thaws over the summer, which is a free "waste product" in winter, is fed into the houses, where it keeps them pleasantly cool - without the need to operate a heat pump. At the end of the summer, the cistern again acts as an intermediate storage tank and the water is recharged with surplus heat from the solar thermal systems. The cycle starts all over again.

Author: Stefan Sagmeister