Heat pump and heat recovery from the wastewater network in Lisses (France)

October 2020

Agence pour l’Environnement et la Maîtrise de l’Energie (ADEME)

Why take action ?

The Grand Paris Sud Seine-Essonne-Sénart urban community comprises 23 local authorities across two departments (Essonne and Seine-et-Marne) and has a population of over 350,000. As part of its remit, it sought to install a system using local renewable energy to heat the water in the Long Rayage swimming pool, located in Lisses. This sports facility includes, in particular, a 25-metre pool and a paddling pool.

After careful consideration, the local authority opted for an innovative system that recovers heat from wastewater in its sewerage network. Initial studies were launched in 2014, with work carried out in 2017, leading to the system being commissioned in November 2017.

The stakes are high: primary energy consumption in public buildings, particularly sports facilities, represents a significant cost, both in environmental terms (greenhouse gas emissions) and economic terms (running costs). In Lisses, for example, the swimming pool’s electricity consumption was 260 MWh in 2015, whilst its gas consumption stood at 1,447 MWh.

However, heat from wastewater can be recovered and utilised to contribute to heating and/or domestic hot water production via heat pumps. This is a form of geothermal energy that uses heat from wastewater, rather than from groundwater or the ground.

In partnership with the Essonne Departmental Council, the ADEME Regional Directorate for Île-de-France supported this investment in Lisses by awarding a grant to the Grand Paris Sud Seine-Essonne-Sénart Urban Community, as part of the ‘Heat Pumps’ call for projects.

Application

The process for recovering energy from wastewater comprises three main components :

• a heat exchanger located on the wastewater network, which recovers the heat ;

• a primary circuit connecting the heat exchanger to the heat pump, with a heat transfer fluid and a circulation pump ;

• a heat pump, installed in the building, which transfers energy from the water at a low temperature to a higher temperature (35°C to 55°C).

In Lisses, the works involved :

• installing a wastewater bypass system on the existing network, as well as the heat exchange system and the pipework connecting the heat extraction point to the heat release point in the heat pump room;

• demolishing the old building to construct a new building housing the heat pump, a new air handling unit (AHU) and associated equipment;

• installing the hydraulic distribution systems between the various production units (heat pump, circulation pumps, peripheral equipment, connection to the existing heating network).

The installation has a total capacity of 600 kW for the gas boilers (providing backup) and 80 kW for the heat pump. Between 2015 (the reference year) and 2018 (the first year of operation of the new system), electricity consumption rose from 260 MWh to 349 MWh, whilst gas consumption fell from 1,447 MWh to 661 MWh.

The waste water heat recovery system now covers 95 per cent of the pools’ heating requirements and 53 per cent of the total energy needs of the facilities.

Testimonial : The Long Rayage swimming pool was built in the 1970s, at a time when fossil fuels were virtually the only technically and economically viable solution for heating the building and the pools. The heating system needed renovating, and it became clear that we had to replace as much of the gas as possible with a local renewable energy source. Geothermal energy using the wastewater network is not very widespread in the Île-de-France region, and we are confident that our project will serve as an example for other local authorities.

Focus

After one year of operation, the results fell short of the performance levels guaranteed to the urban community by the operator. To meet its contractual commitments, the operator was able to optimise the installation via the centralised technical management system.

Reproducibility factors

Heat from wastewater can be recovered from treated water at the outlet of a wastewater treatment plant or from raw water in the sewers, upstream of the treatment plants. The system’s performance depends mainly on the flow rate and temperature of the wastewater.

ADEME, particularly through its regional offices, can support project leaders involved in heat recovery projects by providing them with technical and methodological support and, subject to certain conditions, financial support.

Sources

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