Why a pumping station?
The buildings connected to the thalassothermy network are at all times in one of the following situations:
- the building is heated by taking heat from the water of the network to put it in the air of the building;
- the building is cooled, taking heat from the air inside the building to put it into the water of the network;
- the building is left as is, and the water temperature is unchanged at the substation level.
Idealy the whole system is well-balanced: the quantity of heat injected by some buildings in the water loop is equal to the quantity extracted by others from the water loop. Of course this is almost never the case, and there must be some way to keep the water loop temperature in the normal operating range, not too hot, not to cold, but tempered.
It's the sea water role at the pumping station level, which naturally contains the energy to, depending on the case, heat up or cool down the water of the loop hence heat up or cool down the buildings.
The video below briefly explain the pumping station operation.
Influence of the pumping station on the sea
Pumped sea water volume
The pumped sea water volume has almost no importance: absolutely all the sea water pumped is sent back to the sea a few minutes after having cooled or heated the fresh water of the network. But it is important to minimise the energy used to pump that water in order to optimise the costs, that is why three cascading pumps are used close to their best efficiency
Sea water temperature modification
The used sea water volume is low and the modification of its temperature has a negligible impact on the sea: the sea temperature variation is less than 1°C 5 meters away from the release point of the pumping station according a four year long study from Dalkia. But this could have detrimental effects on the close environment if the temperature difference between the pumped and released water was too high. Regulations require that the temperature of the released water must be under 30°C. Is that the case for our pumping station? Summer is the period when the released water is the hotter, because the sea water is used to cool down the fresh water of the network heated up by refreshing the buildings. The curve below shows the temperature of the released sea water on a six month period containing a summer: we can see that the regulations are observed.