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.
