Cooling the house with heat from the sewage water is becoming a reality in this new housing estate

2023-06-28 06:59:00

The Waterfront construction site near the center of Harderwijk looks like a dry sand plain. ‘Here we are building 100 percent emission-free on the sustainable Waterfront district’ is written on a sign. Close to the largest business park in Gelderland, more than a thousand homes are being built in this phase in the new Waterfront district.

The first hundred homes are ready. “The new residents cool their well-insulated house on these hot days with the energy that we recover from the sewage treatment plant you see there,” says alderman Martijn Pijnenburg (D66).

The treated sewage water that the Vallei en Veluwe water board discharges has recently been interrupted on its way to Lake Veluwe. The still slightly warm water is pumped to a heat exchanger in a sea container. There, the sewage heat is transferred to water from a heat network.

“It is a low-temperature heat network of about 13 degrees. This can now be used for cooling via a heat pump in the new homes, and for warm water in the underfloor heating in the winter,” explains project leader Machiel Karels.

More low temperature sources

The advantage of such a low-temperature network is that in the future all kinds of low-temperature sources can be connected to supply heat or cold. That starts with energy from the surface water of Lake Veluwe, water from the port. But sewage pipes of the houses can also become damaged. Because all together, the shower water produces a lot of waste heat.

The municipality of Harderwijk thinks that by 2050 the city can be completely ‘off the gas’ in this way. To start with, the municipality will connect the new Waterfront building, but in time the adjacent Zeebuurt may also follow, after a thorough insulation. “To set a good example, we will also connect the town hall to this heating network after the summer holidays,” says alderman Pijnenburg.

If the demand and supply of heat and cold are large enough, the municipality can store hot and cold water in the ground per season. “In the winter, stored hot water provides homes and offices with heat, the cold water provides cooling in the summer,” says Karels. The heat and cold are stored in the bottom as in a well-insulated thermos.

Energy stays nearby

This is how small ‘district heating plants’ keep the energy nearby, is the idea. “In the subsoil we can also store a surplus of summer solar energy as warm water for use in the winter. In this way we relieve the grid”, Karels explains the involvement of regional grid operator Alliander.

The Harderwijk project is one of the first in the Netherlands to work with low-temperature energy from purified (waste) water. The water boards believe that more attention should be paid to such forms of what is called aquathermal energy.

“We want to make a maximum contribution to sustainable forms of energy, because we are most affected by climate change,” says Sander Mager, director of the Union of Water Boards. “We are affected by both drought and flooding, as well as rising sea levels and salinisation and subsidence.”

‘The closer to an urban area, the greater the opportunities’

The water boards want to examine all more than three hundred wastewater treatment plants for possibilities such as in Harderwijk. “The closer to an urban area, the greater the opportunities,” says Mager. There are then fewer energy losses, the costs of the heat network are lower and modular construction is possible. “You can lay a pipeline to the smallest new housing estate and then expand it later to other parts of the city.”

Together with the Amsterdam water board Amstel Gooi en Vecht, Mager is investigating the possibilities of generating energy from the large body of water in the Sloterplas in Amsterdam. This could be used to cool and heat 30,000 households.

“We think that 200,000 homes in Amsterdam can use the energy from surface water or wastewater,” says Mager. A three-year pilot project will start in September. “Energy cooperatives of residents appear to be very motivated to use this local energy source,” says Mager.

New mix

After years of privatization and scaling up, is the Netherlands reinventing the old municipal energy company (GEB)? “In any case, a new mix of sources will emerge, such as large-scale private offshore wind farms and highly local heat networks in public hands,” thinks Mager.

Of course there are also risks and teething problems with these new forms of highly decentralized heat supply, acknowledges alderman Pijnenburg in addition to the brand new heat pipeline in Harderwijk. “But we have to stick our necks out, otherwise nothing will ever happen.”