The project utilises sewage thermal energy, also known as riothermia or aquathermy. Sewage water is a stable and reliable heat source, with a temperature of about 18°C in the summer and 12°C in the winter. A submersible pump installed in the centre of the buffer tank at the sewage pumping station to draw up the dirty but warm water which is then pushed through a 100 metre pipe installed beneath the surface of the ground. This runs from the pumping station to the sports facility and back.
Two other pipes are wrapped around this ‘dirty water’ pipe. One of these pipes carries coolant (glycol) with the other carrying clean water that will be heated during the flow within the pipe. These pipes run into the sports complex, while the dirty water pipe runs back to the buffer tank at the pumping station.
Once inside the sports complex, the coolant and water pipes connect with a heat pump that heats the water to 28 degrees, after which it flows directly into the swimming pool. The pipe with the coolant also flows to a heat pump to help heat the building and sports facility via a heat exchanger. There are a total of five heat pumps installed, with the fifth heat pump being used to heat the water to over 70 degrees to avoid legionella, given that the piped water has a lower temperature than the gas used to heat other such facilities.
To prevent heat loss in winter, the heat will be stored in the ground at a depth of 200 metres, utilising two wells, one for storing heat in the summer and retrieving it in the winter and the other for returning cooled water to the ground. This is aquifer thermal energy storage (ATES), which is already being used to heat and cool the city hall in The Hague.
The Blinkerd has also implemented other sustainability technology, with all the lights being replaced by LED lighting and the windows fitted with HR++ glass.
“For ventilation, we have equipment that extracts heat from the air blown outside” said Wesley Verschoof, Manager of Sportcentrum De Blinkerd. “We can use it to warm up the cold air coming from outside. Additionally, we cover the pools with blankets when the pool is closed. The less heat loss, the less energy is needed.”
The Municipality in The Hague is aiming to make all swimming pools in the city sustainable. The project is a new experiment for Hoogheemraadschap Delfland, the organisation that manages the sewage, which will carefully evaluate the system. If other projects are planned in the future, it is not likely they will utilise the same sewage pumping station as extracting too much warmth from the buffer tank may cause other challenges for the organic digestion of the system.
“Within the City of The Hague we have different initiatives for energy transition” added Patrick Wagemans, project leader at the Municipality of The Hague. “But the Blinkerd is the first swimming pool in The Hague that moved away from natural gas. Globally there are only a few swimming pools heated by this type of heat source. The technique is quite new and not applicable in every situation. The building and the location are very important. We're lucky to have a large sewage pumping station just 50 metres away for wastewater and a large field between it.”
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