In 2013, industrial company Grundfos and Bjerringbro District Heating company inaugurated a joint system to exploit heat for district heating, extracted from the cooling compressors used for cooling production machinery in the factory. Operation of compressors is very energy demanding and expensive, and a lot of surplus heat has to be cooled off to the atmosphere by means of cooling towers.
The thermal storage system
The new plant is based on three elements: Exploitation of surplus heat from the cooling machines, indirect storage of heat in an underground aquifer and use of a heat pump to raise the temperature of the stored energy. The surplus heat is used in the local district heating system.
During summer months there is no need for heat from Grundfos, and therefore the entire condenser heat from the cooling compressors is sent in a pipeline to the storage, where the heat is put “on stock” in the aquifer about 750 meters away. In autumn, when the district heating system requires heat from the storage, 80-85 % 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 will raise the temperature by means of a heat pump. In winter, the district heating company gets the surplus heat from the storage and directly from the compressors.
Sizeable cost and emission savings
From the start, it was clear that the current capacity was unable to cover the complete cooling requirement for Grundfos. 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. On top, 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 % of the power consumption used up until now in the cooling towers, and the district heating company will be able to cut the gas consumption in its combined heat and power (CHP) plant. In total, USD 6 million has been invested by the partners, who have split the costs 50/50, and USD 0.5 million will be saved in energy costs annually.
This corresponds to a payback time of 12-13 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 energy conservation and sustainability, this result is acceptable for the company.
Author: Anders Nielsen, Application Manager, Grundfos