At Brande, fresh air will be used to heat living rooms

The energy system in Denmark is changing. Work is underway to convert the energy system to a fossil-free and renewable energy production system by 2050, and at least 90% of the energy used by the district heating system must be in the form of energy other than coal, oil and gas by 2030.

If energy is to be based on sources other than direct sunlight and wind, then large heat pumps will be required. This will make it possible to exploit the energy from waste water, groundwater, fresh air and geothermal heat.

Large heat pumps can also recover surplus heat from industry, refrigeration plants and energy plants. They are typically linked to the district heating network, which thus ensures that the energy is distributed to the rest of society. Small heat pumps are typically installed in homes for individual heating.

Heat pump at Brande
District heating utillity Brande Fjernvarme A.m.b.a. has invested DKK 75 million in a heat pump plant, where a high-pressure and low-pressure heat pump generates a district heating output of 8 MW. The heat pump is powered by a gas engine, and the energy is obtained primarily from the outdoor air and secondarily from the gas engine’s surplus heat. The heat pump is prepared for electric operation in order for the plant to be supplemented by two electric motors, and thus the heat pump can be powered directly by wind turbine power if it is profitable. The heat pump uses ammonia as a coolant and works at a temperature range of -30 °C to 120 °C and with an overpressure of up to 32 bar.

As an adviser to the contractor Victor-DST, Artelia has been responsible for the detaileddesign of the heat pump’s mechanical and piping systems as well as the steel structures in the heat pump building and the evaporation yard.

The project has been a mechanical and construction project, where work has been carried out consistent with 3D design and visualisation in 3D Plant, Tekla and Navisworks. This has created a digital layout for the entire project.

In addition, Artelia has dimensioned the district heating and ammonia pipes, optimised the load and flexibility of the  pipe systems and the location of supports using the program AutoPIPE, and prepared isometrics and other drawing documentation with 3D Plant.

For the steel structures, the static calculations have been performed in the program ROBOT, and the working drawings have been generated using Tekla.

The technology behind heat pumps
The heat pump operates based on the same basic technical principle as a refrigeration plant: A coolant is evaporated while absorbing energy from a medium that is cooled down, and the coolant is subsequently condensed while emitting energy to a medium that is heated up.

When large heat pumps use air as a source of heat, it will typically be fresh air that is cooled down, and energy from this process will be transferred to the district heating water when the coolant is condensed.

Air as a source of energy has low energy density compared to other possible sources of energy. For example, 5,000 times more m3 of air than m3 of ground water must flow through a heat pump to achieve the same heat pump effect. The transfer of energy from air therefore requires a significantly greater heat transfer area and thus a larger plant. Air as a source of energy, however, has the great advantage that it is readily accessible and available in unlimited quantities.