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District energy

District heating

Surplus heat

Turning surplus heat into warm homes

Optimum co-operation: How to use groundwater as a source for cooling and heat recovery.
1 April 2020

Partnership between industry and district heating company generates substantial savings for the partners and benefits the environment. Using thermal storage to eliminate energy waste in an existing district heating system brings us closer to zero impact buildings.

In 2013, the industrial company Grundfos and the local GUES utility company inaugurated a joint system to exploit heat extracted from the cooling compressors in the factories for district heating. Operation of compressors requires a lot of energy and is thus expensive. Furthermore, a large amount of surplus heat has to be emitted into the atmosphere by means of cooling towers. Or at least that is how it used to be.

The thermal storage system

The new system is based on three elements: using surplus heat from the cooling machines, indirect storage of heat in an underground aquifer and use of  heat pump to raise the temperature of the stored energy. The surplus heat is used in the local district heating system.

During the summer months, Grundfos doesn’t require heat, and therefore all the condenser heat from the cooling compressors are transferred to the storage aquifer, where the heat is put “on stock”. In autumn, when the district heating system requires heat, 80-85 per cent of the heat stored during summer is still available. In order to increase the temperature to the level needed in the district heating network, Bjerringbro District Heating increases the temperature by using a heat pump. In winter, the district heating company gets the surplus heat from the storage and directly from the compressors.

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Sizeable cost and emission savings

From the start, it was evident that the  current system capacity was unable to cover the complete cooling requirement for Grundfos’ production.  However, after only a few years in operation, it is now clear that the economy in this system is sufficiently attractive to be extended further. This also helps Grundfos achieve its overall goal of reducing carbon emissions by reducing power consumption from conventional chillers.

Grundfos will save up to 90 per cent of the power consumption used up until now in the cooling towers, and the district heating company will be able to cut gas consumption in its combined heat and power plant (CHP). In total, USD 6 million has been invested by the partners, who have split the costs 50/50, and EUR 457,000 will be saved in energy costs annually. The saved costs on water are in addition to this amount. This corresponds to a payback time of 8-10 years, which is fine for a district heating company, but a little long for an industrial company. However, at the same time, 3,700 tonnes of CO2 are saved annually, and in light of Grundfos’ policies related to energyconservation and sustainability, this result is acceptable for the company.

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