CORDIS - EU research results

Cool ways of using low grade Heat Sources from Cooling and Surplus Heat for heating of Energy Efficient Buildings with new Low Temperature District Heating (LTDH) Solutions.

Periodic Reporting for period 3 - COOL DH (Cool ways of using low grade Heat Sources from Cooling and Surplus Heat for heating of Energy Efficient Buildings with new Low Temperature District Heating (LTDH) Solutions.)

Reporting period: 2020-10-01 to 2022-09-30

COOL DH project has innovated, demonstrated, evaluated, and disseminated technological solutions needed to exploit and use sources of low-grade surplus heat for heating of energy efficient buildings via Low Temperature District Heating (LTDH). The project shows how the transition of District Heating (DH) systems towards LTDH can make these more resource and energy efficient.
COOL DH includes several full-scale demonstrations in Lund (Sweden) and Høje Taastrup (Denmark). They cover new LTDH developments, a stepwise transition of existing DH systems towards LTDH and energy retrofitting of building installations. The consortium consisted of utilities, municipalities of 2 demo cities, leading DH energy specialists, consultants and industrial manufacturers.
Key objectives:
- Innovation, design and build cooling and heat recovery process systems, enabling heat recovery to a local LTDH grid. The heat recovery systems are mainly driven by renewables.
- Design and build a LTDH grid with non-conventional pipe materials. Testing of new pipe components introduced by COOL DH.
- Innovation and design suitable heating systems and controls inside buildings that combine LTDH with photovoltaic power(PV) produced on the buildings.
- Development of viable business models and new pricing systems, which ensure a good (low) return temperature and provide the building companies with maximum flexibility regarding the choice of heating systems.
- Demonstrating a full system with all needed components suitable also for ultra-low DH temperatures incl. demo of systems for heating of DHW without risk of legionella.
COOL DH organised the innovation process and developed new innovative solutions that will be demonstrated on-site.

The demo works have all been achieved. Continuous monitoring started in 2022; data was collected to evaluate/ validate the pros and cons of the various solutions investigated:
Demand side solutions:
- Avoiding risks of legionella: The research found that only in countries which use the exception of the 3-litre-rule in small systems, decentralized substations that heat water to 45-50oC can be used together with uLTDH. Otherwise, central DHW preparation / temperature topping to 50-55oC (60oC) is required. Or electrochemical water treatment can be added to avoid bacteria growth.
- Local integration of renewables at the buildings: Of the many solutions identified, air-to-water or PVT heat pumps may be a good alternative to supplement DH at the consumer. Split flow solutions with heat recovery from the ventilation system are a promising in multi-family houses. However, a deeper analysis of each technology is required for each specific project, where the entire installation requirements and energy consumption can be assessed precisely.
- Substation solutions: Substations with heat exchangers designed for LTDH operation (gives better cooling of DH water) and includes better insulation and controls
- System solutions for multifam./tertiary buildings: Analysis showed that substations in the individual flats do not increase energy eff. in multifam. buildings. They tend to lead to higher investment and operational cost compared to a trad. solution with only one substation.
Distribution side:
- Design concepts for optimisation of LTDH distribution systems: Optimising network design (pipe insulation, pipe technology/sizing, network length optimisations) showed that significant reductions in heat loss can be achieve.
- Pipe components for LTDH distribution systems: New PE-RT pipes up to dia. 116 mm single pipes 16 m lengths or in rolls and for connection by mirror welding were demonstrated. PE-RT twin pipes up to dia. 65 mm for press fittings. Pipes are suitable for LTDH PN 13 bars. Fittings for electro-welding are yet to be approved according to standards for LTDH use.
- Internal distribution in buildings: DH pipes twin and single for internal mains is an energy efficient solution, but it requires firegaskets when passing fire partitions. With DH substations in the flats only 3 supply pipes are needed vs normally 5 pipes. This reduces heat losses from pipes.
- Metering concepts. Remote on-line metering is suited for diagnostics to find consumers with operational faults and for return temperature optimisation,- important for the overall system optimisation
Supply side:
- Cascade couplings for optimal use of low-temperature sources: When producing district heating based on low temperature heat sources of 7-23oC, the highest overall COPh is achieved when similar heat pumps are used in cascade coupling and are working under similar conditions. R717 (Ammonia) resulted in the highest COPh of refrigerants investigated. Integration of additional renewables. Use of an intelligent shunt at the connection points for the LTDH system provides an ideal location for integration of low temperature heat sources / renewables available, in stead of adding renewable energy to the supply line at higher temperature.
The following additional key activities were performed:
- A big heat storage of 70.000 m³ (30 MW, 3300 MWh) in Høje Taastrup was investigated during the project, approved and completed early 2021, with an investment of 10 million €. It is planned for 26 cycles per year.
- A business plan for LTDH was implemented for Lund with a new LTDH tariff. A business model for co-production of LTDH and district cooling with use of PV for Høje Taastrup was implemented.
- The legislative framework for LTDH was studied for Denmark and Sweden incl. the changes in legislation since the start of the project. Early findings of the project were presented at a high-level decision-maker seminar at COWI with a.o. the Danish Minister of Climate, Energy and Supply and the Mayor of Lund.
COOL DH developed new DH pipes offering new characteristics: use of PE-RT plastic material instead of PEX and steel; improved insulation material; integrated oxygen and vapour barrier; weldable coupling methods; leak detection system; higher flexibility; and larger dimension than normal PEX.
The implemented impacts are as follows:
- Installation of a 1.3 MW heat pump at CITY2 shopping mall in Høje Taastrup with potential many full load hours able to provide 4.03 GWh/y LTDH and 2.97 GWh/y district cooling. Primary energy savings: 4.2 GWh/y.
- Installation of 2x350 m of recovery pipes along a main distribution pipe that connects CITY2 to the renovated DH network in Østerby in Høje Taastrup. The 6kW heat pump can supply up to 80.6 MWh to the LTDH network. Primary energy savings: 38.4 MWh/y. In this way the main line becomes a "zero loss" pipe
- Installation of a prosumer heat pump (1.9 MW heating and 1.5 MW cooling capacity) at a Bank in Høje Taastrup in 2020, with around 6500 yearly full load hours, providing 12.5 GWh/y in LTDH plus 11.7 GWh/y of cooling. Primary energy savings: 17.4 GWh/y.
- In Lund the share of renewable energy in the DH network has increased from 98% to 99%; in Høje-Taastrup from 51% to 90% for the served area in Østerby.
- The heat losses in DH systems are usually more than 17%, in the actual case in Østerby it was more than 35%. Network optimisation and simulations indicated reduced loss to about 13% in Østerby (monitored to about 16%) and less in Brunnshög district in Lund when fully constructed. This project reduce heat cost be about 20% for tenants in Østerby.
- There are more than 800 DH utilities in Sweden and Denmark alone with areas that could be converted to LTDH.
The new LTDH pipes in Østerby area in Høje Taastrup.png
The Xplorion building in Lund where several LTDH solutions are tested.png
1.34 MW PV driven heat pump at CITY2.png
Principle of the new multilayer PE-RT pipes.png