Europe has the ambition to utilize district heating (DH) as the backbone of the energy transition because it can store energy from unstable renewable energy sources like wind and sun, which is necessary for reducing the CO2-emissions by 40% in 2030.
But to do so, the temperatures in DH grids must be lowered without letting people freeze. This article tells you how the municipalities of Gentofte and Gladsaxe in Denmark did it by zoning the grid!
By Carsten Østergård Pedersen, Head of District Energy, Business Development
The municipalities of Gentofte and Gladsaxe in Denmark have a fast-growing district heating network. Situated north of Copenhagen, the municipalities have a mix of commercial buildings, multi-storage residential buildings, and single-family homes.
During cold winters, all supply temperatures were 110°C for meeting the heat demand for every customer. But single-family houses do not need that high temperature so lowering the supply temperature in parts of the distribution network seemed like a good idea.
Comfort for everybody
“We wanted to turn down the temperature to save energy without affecting negatively on the comfort for those living in critical points of the distribution network. So, we made some experiments in collaboration with installers and consultants.
But we did not find the ideal solution” says Magnus Justesen, Technical Manager, at Gentofte and Gladsaxe District Heating Co. (GGF). “What we needed was a pre-fabricated turnkey solution meeting our demands for temperature reduction, simple installation, and operation.”
For saving energy and utilizing of surplus heat and green energy in the DH network, flow temperatures must go down. But lowering the temperatures, without any customer freezing, requires a special technique.
The solution was Grundfos iGRID. It lowers the supply temperature locally in specific zones of the grid. To do so a local mixing loop pumps water from the return pipe into the local supply pipe.
By monitoring the critical parts of the network with pit measure points, the mixing loop can adjust temperature and pressure to meet the exact consumer need in real-time. This reduces heat losses and improves comfort.
Lowering the supply temperature in parts of the district heating grid saves energy and makes it easier to utilize green energy.
27% heat loss reduction
The first zoning solution was developed in cooperation between Grundfos and GGF for a zone supplying 300 large villas consuming 9,000 MWh/year.
From 2018 to 2019 supply temperature in the zone was lowered from 90 to 67°C during winter and from 72 to 62°C during summer.
By working with selected house owners optimizing their return temperatures, GGF expects to lower supply and return temperatures in the zone even further, leading to a 27% heat loss reduction in 2020 compared to 2018.
Low temperature – high gain
Based on Euroheat & Power country statistics 2017, the energy in the European DH networks is approximately 415 TWh. Assuming temperatures in half of the grid in zones with a current heat loss of 20%, could be lowered by 20°C, this would lead to a potential heat loss reduction of more than 15 TWh and a reduction in carbon emissions of 3.700.000 tons.
The average heat consumption is 12 MWh per EU household: This leads to free heating for 1,3 million households, only through temperature optimization!
* The zone is continuously adding new houses, as it is an area converting from natural gas to district heating.
Benefitting the pipe lifetime and the green energy transition
Lowering the supply temperature brings additional benefits. According to Magnus Justesen, it reduces the risk of pipe damage and leakage and it paves the way for utilizing wind and solar energy as well as surplus heat from industries to the DH network.
“We are very satisfied with the solution and the energy savings it offers, and we will install similar solutions in other residential areas in the future,” says Magnus Justesen.
iGRID is an end-to-end solution reducing heat losses in district heating zones through real-time temperature optimisation. The next versions include heat pumps (HP) for the low-temperature zones enabling surplus energy connected to the DH locally. HP can increase capacity and lower carbon emissions too.