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Harnessing available heat to provide swimming pools with clean air and water at the right temperature

The challenge Dalkia Solution Key figures Client benefits Témoignage client Dalkia contact

An innovative heat-recovery system

Swimming pools are among the most energy-intensive public facilities. The Neptunia leisure centre in Loos-Haubourdin in northern France is no exception. It needs to strike the right balance in providing pool users with water at the right temperature and clean air that is not too humid, all at a reasonable cost to the local authority. All of which makes water and air management crucial in terms of health, cost and the environment. Which is why Dalkia, which operates more than 500 aquatic centres in France, was drawn to an innovation created by a French startup: the Terrao® heat exchanger.


The solution? Feed the air into the water!

Terraotherm's simple solution has revolutionised the heat-exchanger concept by creating direct contact between air and water. The air in swimming pools is at a temperature of around 30°C and is filled with moisture, which evaporates from the pool. For comfort and health reasons, this ambient air has to be extracted, since its moisture content promotes the development of chloramines, which can irritate eyes and airways. The extracted air is then replaced with clean air. At the Neptunia swimming pool, the ambient air is recycled by an innovative heat exchanger that filters and transfers the thermal energy in the air to the water in the pool. As a result, the air is not only dehumidified, purified and cooled but is also used to heat the water.

How it works ? 

The Terrao® heat exchanger ensures direct contact between the extracted air and the pool water, enabling an almost perfect transfer of calories between the two fluids to achieve complete efficiency, well above that of conventional plate-based heat exchangers. As a result : All thermal energy from the air is immediately transferred to the water, and vice versa; the vapour condenses and mixes into the water; the filtered and cooled air is channelled into the ventilation system; the recovered thermal energy is reused to heat the pool water. The different settings (water outlet temperature, air outlet temperature and humidity) are controlled by adjusting the inflow rate of the two fluids.


tonnes of CO2 prevented per year

4 000

cubic metres of air recycled before emissions


MWh of energy saved each year, cutting consumption by 28%

What are the benefits?

The Terrao® heat exchanger is used for heating and climate/moisture control to enable extremely energy-efficient, low-carbon air treatment solutions. Environmental benefits 35 tonnes of COprevented per year,  4,000 cubic metres of air recycled before emissions, effective control over chloramine and moisture content. Economic benefits 660 MWh of energy saved each year, cutting consumption by 28%.




The engineer had an idea that was simple but difficult to model. Previous exchanger concepts have involved passing the water through the air. However, he looked at things the other way around and designed what you might call an industrial hookah. The majority of the energy used to heat a pool evaporates. Terrao®allows us to recover and recycle that energy again and again. The air dehumidification system opens up opportunities wherever there is a need to maintain specific humidity levels, such as in museums, data centres, archive/storage facilities, and so on.




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