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Topical article: From Waste Heat to Cheese
Data centres are known for producing excess heat. The new centre in Appenzell, Switzerland is no exception: in full operation it could provide the district heating network with approximately 1.5 MW excess heat. But the benefits don’t end there. Thanks to the installation of a high-temperature heat pump, the excess heat will also be used as process heat in a neighbouring cheese factory.
 
The heat from the heat pump is first temporarily stored in a stratified storage tank in the cheese factory. The processes in the cheese production are then supplied with heat from this storage tank when needed. The lower heat levels of the storage tank are used for space and hot water heating. In total, the arrangement will save the cheese factory 1500 MWh of natural gas use annually. This can be compared to the total energy demand of 1800 MWh/year.
 
The installed heat pump is equipped with a highly efficient and compact semi-hermetic two-stage screw compressor. It also has an economizer cycle with vapour injection into the compressor. This is an efficient solution for high temperature lifts, as part of the condensate flow is expanded to a medium pressure level. Solid shell-and-tube heat exchangers are used as evaporator and condenser. The refrigerant is R1234ze(E), which has the fairly low global warming potential GWP100 of 6.
 
Due to the economizer cycle, the heating capacity is higher when the temperature lift is higher. At 100 °C on the heating side, the heating capacity is up to 520 kW. The COP is higher when operating at lower temperatures and is reduced when in part load operation (as an effect of slide valve control).
 
The data centre is the most energy efficient in Switzerland. Photo-voltaics are installed, generating an amount of electricity corresponding to the energy requirements for 50 households. And the sophisticated cooling system makes use of adiabatic processes, generating approximately 1.5 MW excess heat at 20 °C. All in all, this means that only 15% additional energy is needed for cooling and heat exchange.
 
The new cheese factory building is currently under construction and the data centre is underutilised to supply enough waste heat to its new neighbours. The start-up of the high temperature heat pump and waste heat integration from the data centre is planned for the end of 2020 and beginning of 2021. When in operation, this case study will show how large amounts of heat can be exchanged across industries in the small Swiss village of Gais. Hopefully such synergies for heating and cooling will also be recognised at other locations in order to further decarbonise the Swiss industry.
 
Cordin Arpagaus, Switzerland
 
The text has been shortened by the HPC team

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Read the full text in the HPT Magazine