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LOW valued energy sources UPgrading for buildings and industry uses

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Cool ways of using low-grade energy from sewage and industrial wastewater

Lukewarm wastewater discharged by industries and higher-temperature effluent from underground sewer networks are excellent energy sources for space heating and cooling and countless industrial processes. An EU-funded project demonstrated technologies that capture the heat wastewater retains.

Climate Change and Environment
Industrial Technologies
Energy

Heating and cooling in buildings and industry accounts for half of the EU’s energy consumption. According to 2018 figures from Eurostat, 75 % of heating and cooling is still generated from fossil fuels. Gathering 13 partners from 7 European countries, the EU-funded LOWUP project has demonstrated innovative technologies that capture and re-use low-grade energy. Waste heat is an untapped resource that offers a step forward towards reducing significantly CO2 emissions and primary energy consumption.

Flushing valuable heat out of sewers

As surprising as it may seem, beneath our feet is a hidden source of energy that has remained virtually unnoticed: domestic sewage. According to studies conducted in Germany and Switzerland, 3 % of all buildings could be supplied with heat (or cold) by harnessing heat from wastewater. “Sewage systems contain wastewater whose temperatures vary between 10 °C and 25 °C. This temperature permits economical operation of heat pumps for the heating (or cooling) of tertiary buildings such as hospitals, hotels, swimming pools and malls,” notes Rafael Socorro, project coordinator. Compared to other traditional energy sources for heat pumps (groundwater, geothermal heat, outdoor air), wastewater from residential drainage systems offers an ideal basis for heat recovery as it exhibits higher temperatures. The challenge is to combine a high-performance heat exchanger (which extracts heat from sewage) with a heat pump. The innovative HEAT-LowUP solution demonstrated in a university in Spain relies on a hybrid heat exchanger developed by project partner Wasenco. The system recovers around 20–30 % heat from the wastewater going down the drain to heat water which is used in the kitchen and for laundry. It does so by consuming virtually no electricity thanks to a passive solution implemented.

Recovering heat from industrial wastewater

In a pulp and paper company in Portugal, the project demonstrated HP-LowUP – a solution that recovers heat from lukewarm wastewater produced by industrial processes. Waste heat is converted into a higher-temperature stream that can be re-used to increase the efficiency of the production line. Key to the success has been a rotating heat exchanger developed by project partner Pozzi Leopoldo Srl. “This type of heat exchanger is specifically designed to work with dirty effluents containing mechanical particulate without losing efficiency. By holding a constant rotation of the exchanging surfaces (the discs), it can keep itself clean, thus requiring little-to-no maintenance,” explains Socorro. “Normally, heat exchangers tend to clog or foul when processing dirty fluids. These effects can impair the efficiency of wastewater energy recovery installations to a high degree. In the worst case, they can decrease the heat transmission performance of the heat exchanger by a factor of 2.5” adds Socorro. LOWUP is still running. The focus will now be on conducting market studies and exploitation strategies to evaluate the benefits and maximise the impact of the demonstrated technologies. Beyond CO2 and primary energy savings, results generated by LOWUP may open new opportunities for the heating and cooling industry, create new jobs and reduce Europe’s dependency on imported energy.

Keywords

LOWUP, wastewater, heat exchanger, sewage, heating and cooling, heat pump, waste heat, low-grade energy, pulp and paper

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